Note: Descriptions are shown in the official language in which they were submitted.
10518Z7
MINING AND PROCESSING METHODS AND APPARATUS
Our invention relates, in one aspect, to novel,
improved techniques for separating coal from the foreign
material with which it is found in nature and elsewhere.
- Raw or as mined coal commonly contains foreign matter
in amounts as high as 20 to 60 percent by weight. Even though
the cost of doing so can become relatively high ($1.50 to $4.00
per ton for a product selling at up to $60 per ton), coal is
in almost all cases cleaned to rid it of the foreign material
prior to use because of: environmental factors, economic
considerations such as the cost of hauling unusable material
over extended distances, and limitations on the amount of
foreign materials which can be tolerated in the process in which
the coal is to be used.
Many techniques for cleaning coal have heretofore
been proposed; and a number of these are in current commercial
use including air separation, jigging, froth flotation, cyclon-
ing, and shaking on Deister tables.
There are disadvantages to each of the foregoing
techniques for cleaning coal. One common to all of them is t~at
only a narrow size consist can be handled; that is, the coal to
be processed must consist of particles in a relatively narrow
size range. This may require that the coal be separated into
two or more fractions before it is cleaned, adding to the cost
of cleaning the coal.
Another disadvantage of currently employed cleaning
techniques such as jigging and shaking on Deister tables is
that they are often inefficient. Such techniques take
10518Z7
advantage of the relative behavior of coal and foreign material
in a moving stream of water, and many coals have specific
gravities which make dynamic separation inefficient. Many of
the coal particles will act like and settle into the bed of
foreign material rather than migrating to a separate strata.
Also, hydraulic separation techniques require large
quantities of water. This is an important disadvantage,
especially in arid regions or where environmental requirements
demand that the plant water circuit be completely closed; i.e.,
that there be no water effluent.
Cyclones are used to only a small extent because of
the expense and poor product yield.
Froth flotation is another coal separation technique
that has from time-to-time been touted. However, froth
flotation requires a degree of sophistication in precondition-
ing and flotation chemistry that is in most cases not available
in the field and the size consists that can be handled are
limited. Accordingly, while efficient when properly carried
out, froth flotation is not used to any significant extent.
Another type of coal cleaning process which has been
proposed is gravity or sink-float separation. This process
takes advantage of the differences in specific gravity between
coal (typically 1.25 to 1.55) and the foreign material associat-
ed therewith (typically 1.8 to 6.0) to separate the coal.
The coal and foreign matter are introduced into a
body of a parting liquid having a specific gravity intermediate
that of the coal and the foreign material. By virtue of
Archimede's principle, the coal rises to the top of the
parting liquid; and the foreign matter or gangue sinks to the
bottom. The two layers of material, respectively termed
"floats" and "sinks", are recovered separately from the
parting liquid.
1~518Z7
Gravity separation using a moving aqueous slurry of
magnetite as the parting liquid is in widespread use today.
Like other currently employed techniques, gravity
separation as now practiced has significant disadvantages.
One is that the coal must b~ in the form of relatively large
particles (typically 10 inches to 1/4 inch). Otherwise, the
separating velocities of the coal relative to induced or
random velocities in the separating vessel will be so small
that coal particles will report to the sinks and particles of
foreign material will report to the floats.
The requirement that the coal have a minimum particle
~ize on the order of 1/4 inch also means that, in many cases,
considerable amounts of pyrites may be left in the product coal.
In some coals large quantities of pyrites exist in particle
sizes as small as -200 mesh (this and all sieve sizes referred
to hereinafter are of the U. S. Standard series). Therefore,
-if the coal is only reduced to a 1/4 inch particle size prior
to gravity separation, large quantities of pyritic sulfur will
remain with the product coal.
Another important disadvantage of gravity separation
as currently practiced is that fine coal particles or clays,
if not completely removed from the plus 1/4 inch coal prior to
separation, can foul the bath. This increases the viscosity
of the bath, resulting in poor separation efficiency and
magnetite recovery.
The coal product of the magnetite-water separator
must be mechanically or thermally dried or both. Because water
has a relatively high boiling point and a high latent heat of
vaporization, the cost of drying the coal can be considerable.
Other gravity separation techniques for cleaning coal
are described in U. S. Patents Nos. 994,950 issued June 13,
.
.
- 3 -
105~8Z7
1911, to DuPont; 2,150,899 issued March 21, 1939, to Alexander
et al; 2,150,917 issued March 21, 1939, to Foulke et al;
2,208,758 issued July 23, 1940, to Foulke et al; 2,842,319
issued July 8, 1956, to Reerink et al; 3,026,252 issued
March 20, 1962, to Muschenborn et al; 3,098,035 issued
July 16, 1963, to Aplan; 3,261,559 issued July 19, 1966, to
Yavorsky et al; and 3,348,675 issued October 24, 1967, to Tveter.
The gravity separation techniques disclosed in these patents
differ from that just discussed primarily in the parting liquids
the patentees propose.
Our novel process for cleaning coal is, like those
described in the just-cited patents, of the gravity separation
type. However, a far superior parting liquid is employed; and,
as a result, our process enjoys a number of advantages not
possessed by the patented processes.
In particular, we employ as a parting liquid a fluoro-
chloro derivative of methane or ethane (hereinafter referred to
as a "fluorochlorocarbon") or 1,2-difluoroethane.
At least 24 derivatives fitting the foregoing
description have been reported in the literature. Of these,
16 are of no interest because their boiling points are so low
that the cleaning process would have to be refrigerated, which
is obviously impractical, or so high that the cost of recovering
them from the clean coal and rejects would be prohibitive.
In fact compounds in the latter category would be inferior to
water-based parting liquids even though they are much more
expensive.
The fluorochlorocarbons which we consider suitable
because of their boiling points (ca. 40-150F) and other physical
characteristics (low viscosity and surface tension and useful
1~51827
specific gravity) and thcir ch~mical inertncss toward coal and
other materials under the process conditions we employ are:
l-Chloro-2,2,2-trifluoroethane
1,1-Dichloro-2,2,2-trifluoroethane
Dichlorofluoromethane
l-Chloro-2-fluoroethane
1,1,2-Trichloro-1,2,2-trifluoroethane
1,1-Dlchloro-1,2,2,2-tetrafluoroethane
Trichlorofluoromethane
Of the listed compounds, all but the last three are
at the present time too expensive to be practical from an
economic viewpoint. And, of the latter, trichlorofluoromethane
is preferred because of its optimum physical properties, its
chemical activity, and its low cost.
Also, this compound has an almost ideal boiling point
and an extremely low latent heat of vaporization (87 BTU/lb
as opposed to 1000 BTU/lb for water). Accordingly, the compound
can be recovered from solids with which it is associated by
evaporation with only a modest expenditure of energy.
A principal advantage of our novel process for clean-
ing coal is effectiveness.
The efficiency of a coal cleaning operation is
generally ascertained by a washability study which, in principle,
identifies how closely the operation comes to processing the
coal to a theoretical level of cleanness. While there is no
industry wide standard for performing washability studies, the
procedures all have much in common. The coal to be rated is
sampled, graded into different fractions by size consist, and
subjected to gravity separation in a mixture of hydrocarbons
_ 5 _
.
~OS1827
and halogenated hydrocarbons or in an aqueous salt solution for
an extended period of time. Characteristic's such as yield and
moisture, heat value, ash, and sulfur content are then ascer-
tained and reported.
With our novel process, we are consistently able to
obtain higher yields and lower ash, sulfur, and moisture
contents than are indicated to be theoretically possible by
many washability study procedures. This s important from both
the economic and ecological viewpoints.
Parting liquids which resemble ours to the extent
that they are halogenated hydrocarbons have heretofore been
disclosed in the Tveter patent identified above. According
to the patentee these parting liquids are suitable for beneficiat-
ing coal.
All of the compounds listed in the Tveter patent
contain iodine or bromine or both; as a consequence, they have
a number of disadvantages.
One is that their boiling points are too high for
the compounds to be of any practical value in the processing of
coal. A substantial amount of the parting liquid is chemically
adsorbed on the particles of the coal and the gangue in any
separation process. Economics dictate that this parting liquid
be efficiently recovered and that the recovery be effected at
low cost.
In our opinion the only practical way to recover the
parting liquid at the present time is to do so in vapor form.
The energy required to recover high boiling point compounds by
this technique makes their use economically impractical.
In fact one paper flatly states that direct evaporation is
"not applicable" to liquids with high boiling points (Tippin
et al, Heavy Liquid Recovery Systems in Mineral Beneficiation,
10518'~7
SME TRANSACTIONS, March 1968, pp. 15-21).
Even assuming that they would be effective, other
techniques for recovering a halogenated hydrocarbon parting
liquid such as washing-the floats and sinks with water and then
recovering the parting liquid from the wash water (see Baniel
et al, Concentration of Silicate Minerals by Tetrabromoethane
~TBE), SME TRANSACTIONS, June 1963, pp. 146-154) would likewise
be economical~y impractical, especially in circumstances where
the customer's specification requires that substantial amounts
of the wash water subsequently be removed from the coal. The
same would be true of the even more complicated parting liquid
recovery scheme using solvents described in Patching,
Developments in Heavy-Liquid Systems for Mineral Processing,
MINE & QUARRY ENGINEERING, April 1964, pp. 158-166.
The problems of recovering a parting liquid as disclosed
in Tveter are compounded when the solids, like coal, have
microcracks, a large volume of pores, and other defects into
which the parting liquid can be absorbed. Recovery of such
liquid can easily become economically impractical.
Another disadvantage of most of the Tveter compounds
is that their specific gravities are too hlgh for them to be of
much value for coal beneficiation. Bituminous coals have
specific gravities in the range of 1.25-1.55 as indicated above,
and parting liquids having specific gravities above 1.70 are of
little importance as the amount of gangue which reports to the
floats with the coal becomes too high. All of the compounds
listed by Tveter have specific gravities above 1.70.
Furthermore, a number of the listed compounds are
little more than laboratory curiosities; they are not commercial-
~05~8'~
ly available at all. Others, which can be purchased fromsuppliers of rare chemicals in small amounts, are too expensive
to be of any value. For example, the price quoted for Tveter's
1,1-dibromo-2,2-difluoroethane is $431 per pound.
Finally the Tveter list includes compounds which are
anesthetics (1,2-dibromo-tetrafluoroethane, for example) ahd
narcotics (such as trichloroethylene) and others which have a
relative high level of mammalian toxicity such as carbon
tetrachloride.
Halogenated hydrocarbon liquids for coal beneficiation
are also discussed in Foulke et al patent 2,150,917. Their
halogenated hydrocarbons include many with the disadvantages
discussed above and, to some extent, elaborated upon in
O'Connell, Properties of Heavy Liquids, SME TRANSACTIONS, June
1963, pp. 126-132, which also lists still other halogenated
hydrocarbons heretofore proposed as parting liquids.
The Foulke et al list also includes compounds such
as trichloroethylene and tetrachloroethane which chemically
react with coal (carbon tetrachloride is also in this category).
Such parting liquids are not useful because the parting liquid
and the coal both become contaminated.
Contamination of the parting liquid makes the process
economically im~ractical because of the cost of purifying it
and because of the loss of the parting liquid. A commercial
scale operation cycles at least several hundred tons per hour
of the parting fluid, and loss of even a small proportion of the
liquid is accordingly economically significant.
Also, as discussed in the above-cited O'Connell paper,
a related disadvantage of many of the heretofore proposed
halogenated hydrocarbons is that they adversely react with
common construction materials such as mild steel, rubber and
10518;~7
other gasket materials, etc. as well as lubricants or decompose
into compounds which will so react, especially if moisture is
present. Both 1,2-difluoroethane and the fluorochlorocarbons
we employ are much less inclined to react with such materials,
whether or not moisture is present, which is of self-evident
importance.
Coals contaminated with halogen ions are also
undesirable. In the case of steaming coals this can cause
boiler corrosion. Contaminated coking coals can undesirably
alter the chemistry of the reactions in which they are typically
employed.
Another advantage of the present invention is that
it can be employed in circumstances where the water content of
the coal is high. For example, one application where our
invention is particularly advantageous is in the cleaning of
slurry pond coals. Such coals, drip dried and supplied to the
beneficiation apparatus, may have a moisture content as high
as 15 percent.
In contrast coal beneficiation processes employing
halogenated hydrocarbon parting liquids such as those disclosed
in Tveter cannot be employed if the moisture content of the
coal exceeds two percent according to the patentee. This makes
such processes of little commercial value because only a few
coals and anthracites have mined moisture contents this low.
Anthracites in toto account for less than one percent of the
annual coal production in this country.
Tveter does not stand alone in emphasizing that the
presence of water is highly deleterious in application
involving the use of halogenated parting liquids. The same point
is made in the above-cited Patching article.
g
,
1~
10518Z7
Still ~nother advan~ e of our inventioll is tha~ e
specific gravity of the novel fluorochlorocarbons we emp]oy
and l,2-difluoroethane can be readily adjusted to make the
specific gravity of the parting liquid optimum for cleaning a
particular coal.
For example, the nominal 1.5 specific gravity of
trichlorofluoromethane can be varied within a range of approxi-
mately 1.55-1.4 by modest variations of the gravity separation
bath temperature and pressure.
Lower specific gravities can be obtained by mixing
a diluent such as a light petroleum fraction with the l,2-di-
fluoroethane or fluorochlorocarbon because of the inertness
which such compounds display toward the organic materials in
coal and toward the parting liquid and because the parting
liquid is miscible in the light petroleum fraction. The same
technique can also be employed to maintain the specific gravity
of the parting liquid constant or to vary it in a controlled
manner under changing ambient conditions.
Petroleum ether (a mixture of pentane and hexane)
can be employed in an amount sufficiently small that the vapors
from the parting liquid are nonexplosive and non-flammable to
reduce the specific gravity of the parting liquid to as low as
1.3 at ambient temperature and pressure. Other liquids can be
employed instead of petroleum fractions. Pentane, for example,
has the properties which makes it useful for this purpose -- a
low boiling point and a low heat of vaporization.
The use of hydrocarbon diluents to adjust the specific
gravity of a parting liquid has heretofore been suggested in U.S.
patents Nos. 2,165,607 issued July 11, 1939, to Blow and
3,322,271 issued May 30, 1967, to Edwards. However, the diluents
described in these patents -- benzene (boiling point 80 plus
C.) and petroleum fractions with boiling points in the
-- 10 --
1051827
70-100C. range -- boil at too high a temperature for them to
be usable in our coal cleaning processes which require that the
diluent boil at a temperature as nearly as possible the same
as that of the fluorochlorocarbon or 1,2-difluoroethane.
For this reason even the next higher homolog of
pentane with its boiling point of 68C. is undesirable. And if
we employ a petroleum ether, we preferably employ one having
a boiling point toward the lower end of the range which such
petroleum fractions have (40-60C.).
In general the lowest specific gravities that would
be useful for our purposes are 1.40 to 1.30. Specific gravities
in this range can be obtained by mixing with CC13F, for example,
from 7.7 to 16.4 weight percent of a petroleum ether based
on the total weight of the parting liquid.
Another advantage of the novel parting liquids we
employ is that they have viscosities which are low even in
comparison to other liquids heretofore used as parting liquids
in gravity separation processes as shown by the following
table:
Table 1
Parting Liquid Viscosity (Centipoises at 20C.)
Carbon tetrachloride .969
Tetrachloroethane 1.844
Methylene bromide 1.09
Water 1.00
Tetrabromoethane 12.0
Bromoform (CHBr3) 2.152
-325 Mesh Magnetite 6-40 (average 12.0)
and water (1.6 specific
gravity - production bath
survey)
Trichlorofluoromethane 0.4
-- 11 --
10518Z7
Low viscosity is important because the velocity at
which the particles move through the parting liquid and,
therefore, the speed at which beneficiation proceeds is inversely
proportional to the viscosity of the parting liquid -- as the
vi6cosity of the parting liquid is lowered, the speed of the
separation process increases.
In our process separation is completed in 1.0 to 5.0
minutes depending upon the size consist of the coal and
refuse even when the top size is less than 100 mesh. In
contrast separation in the carbon tetraçhloride, bromoform,
and ethylene dibromide typically used in standard washability
studies may require 2 to 24 hours.
Other advantages of low viscosity parting liquids
are discussed in U. S. Patent No. 3,098,035 issued July 16,
1963, to Aplan.
Our novel parting liquids are also superior to others
heretofore proposed and employed because they have lower surface
tensions. For the liquids listed above, the surface tensions
are:
Table 2
Parting Liquid Surface Tension (dyne/cm)
Carbon Tetrachloride 27
Tetrachloroethane 36
Methylene Bromide 40
Water 75
Bromoform 41.5
-325 Mesh magnetite 75
and water
Trichlorofluoromethane 18
Surface tension is important because wetting ability
is a function of low surface tension. If the coal is not
completely wetted by the parting liquid, air will be trapped on
105~827
both the coal and gangue particles, making them tend toward a
common density. As a consequence, separation becomes more
difficult and less efficient.
The problem is particularly acute for particle sizes
of one millimeter or less. Yet the presence of such particles
may not be avoidable as in the recovery of coal from slurry
ponds, for example.
The novel parting liquids we employ have surface
tensions so low that the free surfaces of even very small
particles, including micro cracks, are essentially instantaneous-
ly wetted. This is one reason that we are able to attain
separation efficiencies which often exceed those predicted by
theoretical washability curves.
Another advantage of our invention is that there is
no need to separate the raw coal into large and small particle
consists as is necessary in presently employed coal cleaning
processes. Lumps of 5-6 inches and larger in diameter can
easily be handled as can those 325 mesh and smaller although
separation times are longer (up to several minutes) for these
smaller particles.
In general, therefore, the only restrictions on
particle size are those imposed by the material handling
equipment available and by the size to which the raw coal must
be reduced to liberate the impurities necessary to meet product
specifications.
Also, essentially all of the parting liquid can be
recovered. This not only makes the process viable from the
economics viewpoint but has a decidedly favorable environmental
impact. No contaminated water or other ecologically detrimental
chemicals are discharged from the process.
'
- 1~
105~8Z7
Other advantages of the novel parting liquids we
employ are that they are non-flammable, odor free, and non-toxic.
Yet another advantage of our process is that, as far
as we can observe, there is no tendency for slimes to form even
in circumstances where significant amounts of clays are present.
This is important because the control of slimes in other gravity
separation processes is a pressing problem as evidenced by the
discussions of the problem in the above-identified Aplan patent
and in U. S. Patent No. 2,136,074 issued November 8, 1938, to
Crawford et al.
Nor have we seen any evidence of flocculation
and/or rafting. That flocculation can be a problem in other
gravity separation processes is apparent from Tveter and
U. S. Patent No. 3,308,946 lssued March 14, 1967, to Mitzmager
et al.
The only reference known to us which suggests that a
fluorochlorocarbon be used as a parting liquid is U. S.
Patent No. 3,322,271 issued May 30, 1967, to Edwards. This
patent avers that 1,1,2-trichloro-1,2,2-trifluoroethane can
be used as a parting liquid to separate tea stalks from tea
leaves although there is nothing in the patent such as a work-
ing example which shows that this can actually be done.
Even more important the teachings of Edwards would
lead one to believe that this compound would not be useful for
gravity separation of coal. The patentee suggests that
1,1,2-trichloro-1,2,2-trifluoroethane and the other liquids
listed in the patent (trichloroethylene, perchloroethylene,
and carbon tetrachloride) are all equivalents as parting liquids.
However, all of these other liquids are known to dissolve and
chemically react with coal which is highly undesirable for the
reasons discussed above. As it is associated in the Edwards
- 13a -
~ 0518Z7
patent only with liquids which are not suitable for coal
beneficiation, one would not expect 1,1,2-trichloro-1,2,2-
trifluoroethane to be useful for that purpose.
A fortiori, there is nothing in Edwards which would
even xemotely suggest that l,1,2-trichloro-1,2,2-trifluoroethane
would have the unexpected advantages in cleaning coal which we
have found it does. There is nothing in the patent to indicate
that this compound would effect the removal of organic sulfur
from coal, that it would cause water associated with coals of
high water contents to report to the sinks or rejects, or
that the liquid could be recovered from the coal in almost
quantitative proportions with only very modest expenditures of
energy.
There is also an allegation that "fluorine substituted
... alkyl compounds" can be used as parting liquids in U.S.
Patents Nos. 3,802,632 issued April 9, 1974, and 3,746,265
issued July 17, 1973, both to Dancy. However, no specific
compounds are named; and, as discussed above, only a handful
of the many compounds meeting this description are suitable
for our purposes.
Although not essential, we prefer to prewet or
condition the coal to be cleaned with a mixture of a fluoro-
chlorocarbon or 1,2-difluoroethane and an ionic surface active
agent prior to introducing it into the gravity separation bath.
This conditioning with the combination of ionic surface active
agent and fluorinated hydrocarbon has unexpectedly been found
to cause significant proportions of the surface water which
would be expected to remain with the coal to instead report to
the sinks.
The removal of water to the sinks is particularly
important in the processing of coals of higher water content
G as the redistribution of the water in the system can simplify,
and even eliminate, subsequent dewatering of the coal.
- 14 -
10518'~
More specificall~, coar~e product coal typically has
a moisture content of 4-7 pereent while that of fine product
eoal can range from 10-30 plus percent. Moisture contents in
the latter range and the upper end of the first-mentioned
range both reduce the efficiency with which the coal can be
burned and generate handling problems. For example, entire
earloads of coal of such moisture content can freeze into a
single lump in freezing temperatures, making it tremendously
difficult to unload and handle the coal.
Larger sizes of coal are conventionally dewatered on
shaker screens or eonical screens. Smaller size eonsists are
eustomarily dewatered in a basket type eentrifuge and still
smaller partieles in solid bowl centrifuges. Alternatively,
eoal ean be thermally dewatered; that is, heated to a temperature
high enough to evaporate part or all of the moisture. Fluidized
bed dryers are eustomarily employed for this purpose.
By redueing the need for dewatering by the teehniques
just deseribed our novel eoal eleaning process generates
eorresponding savings in eapital investment for equipment, in
operating eosts, and in expenditures of energy.
Another advantage of eonditioning the coal to be
cleaned with our novel eombination of 1,2-difluoroethane or a
fluoroehlorocarbon and a surfaee aetive agent is that this
results in a greater reduetion in the sulfur eontent of eoal
than ean be obtained by other proeesses for whieh data on
reduetions in sulfur content have been reported. Maximum
removal of sulfur is important because the sulfur contents of
eoals found in the United States range as high as seven to ten
percent while, preferably, coking coals contain no more than
1.3 percent sulfur, and government standards proposed for the
late 1970's would limit many steaming coals to a sulfur content
in the range of 0.5 pereent.
'~,
- 15 -
1051827
Three types of sulfur can be present in coal. These
are:
(a) Pyritic sulfur -- FeS2, density 4.9 g/cm3;
~ b) Sulfate sulfur -- usually calcium sulfate result-
ing from the reaction of water and pyrites to form sulfuric
acid and the subsequent reaction of the acid with calcium
carbonate associated with the coal; and
(c) Organic sulfur -- sulfur bound with carbon atoms
in the coal matrix into molecules of organic character. Dis-
crete compounds have not as yet been positively identified,
but organic sulfide and sulfone linkages appear to be present.
In chemical analyses of coal, total, pyritic, and sulfate sulfur
are measured; and the difference between the latter two and
total sulfur is reported as organic sulfur.
Pyritic sulfur particles as small as 0.01 inch in
diameter are common. As discussed above, even particles of
this minute size can be efficiently removed by our novel
process when they are released from the coal because the
excellent wetting properties of the parting liquids we employ
make it feasible to use a size consist of this magnitude in
the beneficiation process. In contrast, conventional
hydrobeneficiation becomes inefficient to an increasing and
dramatic degree as particle sizes decrease below 0.2 inch in
diameter and becomes totally inoperable at particle sizes lower
than 0.02 inch in diameter. Therefore, hydrobenefication
techniques are inherently incapable of removing as much of
the pyritic sulfur which may be present in a particular raw
coal as our process.
We have also found that, surprisingly, a reduction
in organic sulfur can be obtained by our novel process. This
has been ascertained by evaporating used parting liquid to
- 16 -
1(~5~8Z7
dryness and making an infrared analysis of the residue. There
is evidence that some organic sulfur also reports to the sinks
(gangue) in our process.
Hydrobeneficiation, in contrast, does not alter the
organic sulfur concentration of the raw coal under any condi-
tions.
In fact, to our ~nowledge, the only heretofore
available techniques for removing organic sulfur from coal are
pyrolytic. Such techniques are not usable in cleaning coal
generally because of the energy expended in heating large
tonnages of coal to the requisite temperature and because of
the alteration in the chemical composition and the structure
of the coal which results.
We have also found that the use of surface active
agents in our novel process increases the quality of the
separation when wet coal -- that is, coal with a moisture
content as high as 25 percent -- is being cleaned. This
is entirely unexpected because of the insistence by Tveter
that halogenated hydrocarbon/surfactant mixtures cannot be
used to clean coal with a moisture content of more than two
percent; that is, that they are only useful in cleaning dry
coal.
Water affects other gravity separation type coal
cleaning processes because it forms on the coal particles
a thin film to which small particles of more dense foreign
material can adhere. This creates "agglomerates" which may
have a specific gravity greater than the parting liquid,
causing them to report to the sinks (gangue) rather than the
floats (product coal) if the coal particles are small. Condi-
tioning the coal as described above apparently makes our novel
- 17 -
-
1051827
parting liquids capable of rupturiny these thin films, thus
preventing the formation of agglomerates.
This phenomenom is particularly apparent in the
reclaiming of coal from slurry ponds. When cleaned in accord
with the technique just described, even ultra-fine clay
particles are separated from the coal.
Also, there is evidence that part of the pyritic
sulfur present in some coals is bonded to the coal particles
by forces (probably electrostatic and less likely thin film)
which can be neutralized by those combinations of parting
fluids and additive described above. We are in any event able
to obtain reductions in pyritic sulfur content which indicate
that pyrite particles smaller than those liberated by fine
grinding are being separated from the raw coal.
Among the surface active agents we have successfully
employed are the following:
- 18 -
105~8Z7 o o
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- 19 -
.~
-- 1051827
Anionic surface active agents are preferred as are
those which are a single compound rather than a blend. Blends
tend to be less effective on a unit weight basis, apparently
because they tend to emulsify the water on the coal rather than
removing it to the sinks.
Small amounts of the surface active agent are lost,
probably with the water removed to the rejects. However, the
cost of lost material is not expected to exceed $.30 per ton
of coal; it will in general be substantially less.
The amount of surface active agent used will depend
upon the particular additive which is selected and the size
consist and moisture content of the coal, but will typically
range from six pounds per ton for ultrafine coals with high
moisture contents down to 0.03-0.05 pounds per ton for coarser
coals of lower moisture content.
Agitation of the coal in the conditioning step has
also been found to be advantageous. This can be accomplished
by mechanical folding of the liquid, coal mixture.
We can also employ No. 4 or No. 6 fuel oil or certain
alkyl amines as surface active agents instead of the composi-
tions just described. Mixtures employing these compositions
produce essentially the same results as those using composi-
tions more conventionally thought of as surface active agents
though less effectively.
No. 4 and No. 6 fuel oils are both employed in an
amount ranging from 0.5 to 6 pounds per ton of coal.
Alkyl amines can be employed in amounts ranging
from 0.05 to 0.5 pounds per ton of coal. Examples of
satisfactory amines are: diethylamine, ethylene diamine, and
monoethyl amine.
- 20 -
i~h '
10518'~7
The use of surfactants in gravity separation
processes has heretofore been discussed in Blow,Tveter, Aplan,
and Foulke et al 2,208,758, and in U.S. Patent No. 2,899,392
issued August 11, 1959, to Schranz. The Blow and Schranz
patents, however, are not concerned with the cleaning of coal;
and there is nothing in either patent which would leave one to
believe that surfactants could be used to advantage in coal
cleaning processes. Foulke et al chose surfactants which
would fix the water film on the material being recovered rather
than freeing it from the material for removal to the sinks.
This class of surfactants has completely different properties
than those we employ and, moreover, properties we consider
undesirable.
The parting liquids with which Aplan is concerned
are aqueous suspensions of solid particles. The patent
discloses nothing regarding parting liquids which are
combinations of 1,2-difluoroethane or liquid fluorochloro-
carbons and surface active agents and their advantages.
Much the same is true of Tveter. The parting
liquids disclosed in that patent are not fluorochlorocarbons.
The latter have a number of advantages over the Tveter parting
liquids as discussed above; and moreover, there is nothing
in the patent which would lead anyone to believe that any
advantage would accrue from combining surface active agents
with such parting liquids, let alone that this would increase
the sulfur or fine particle removing capabilities of such
eompounds.
Furthermore, Tveter is coneerned in his use of
sufaetants only with inhibiting floe formation. This would
not lead one to use a surfaee aetive agent in the manner
and for the purposes we do.
- 21 -
" .~
~0518Z7
Furthermore, the foregoing patents are for the most
part concerned with the use of surface active agents for slime
control and to stabilize heavy medium suspensions of solids
and not with the removal of water from the product to the
rejects in a gravity separation process.
Nor is the surface active agent employed in a
conditioning step as it is in our process. It is instead added
to the parting liquid in the gravity separation bath. Our
technique has the advantage that amount, exposure, and time
factors can be optimized independent of the separation stage.
In another aspect our invention resides in the
provision of novel improved techniques for moving coal and
other solids from place-to-place and, more particularly, to
the use of 1,2-difluoroethane and fluorochlorocarbons as
described above for this purpose.
Coal is commonly transported in the form of an
aqueous slurry because this is the product of the coal
beneficiation process.
We have now discovered that these advantages can be
retained and additional advantages obtained by employing a
1,2-difluoroethane or fluorochlorocarbon carrier.
Specifically, because these compounds have lower
viscosities than water, slurries in which they are used as the
carrier liquid can be pumped with less power than water-based
slurries with the same solids content. Or, viewed otherwise,
the solids content of the slurry can be increased for a given
power output. From both points-of-view the significant factor
is that the cost per unit weight of moving the coal or other
solids is lower.
- 22 -
,; i,,.
- 1051~Z7
In addition, because the liquids we employ are
chemically inert in most circumstances, the corrosion problems
attendant upon the use of water in circumstances where soluble
minerals are present are avoided. Furthermore, our carrier
liquids do not cause the flocculation problems which water may.
Also, as when they are used in our novel
beneficiation process, their lower latent heat of vaporizati~n
and lower boiling points permit the liquids we employ to be
removed at the terminal point with less energy and therefore
at a lower cost than water.
Even at that, however, we find it necessary to add
heat to the slurry to recover the carrier liquid. Also, a
vacuum or gas purge is required as, otherwise, so much carrier
liquid will remain in the pores of the coal particles as to
make the process impractical.
The precise temperature to which materials are
heated to remove a carrier liquid associated therewith in our
novel process for transporting coal and in the other novel
processes described herein which employ a carrier liquid
removal step will vary from application-to-application and
will depend upon a number of factors. Among these are the
boiling point of the carrier, the removal rate required to
maintain equilibrium in the system, etc. In a typical
application using trichlorofluoromethane, however, a drying
or liquid removal temperature of 100F (25F above the boiling
point of the liquid) will be employed.
In addition, because of the physical characteristics
of the carrier liquids we employ, coal particles do not tend
to pack in the carrier liquid to the extent they do in water.
Accordingly, even after it has remained static for an extended
- 23 -
1051827 - ? 4-
period, flow can be initiated almost instantaneously in a
slurry formed according to the present invention.
Numerous patents disclose techni~ues for transporting
aqueous slurries of coal. Among these are Nos. 449,102 issued
March 31, 1891, to Andrews; 2,128,913 issued September 6,
1938, to Burk; 2,346,151 issued April 11, 1944, to Burk et
al; 2,686,085 issued August 10, 1954, to Odell; 2,791,471
issued May 7~ 1957, to Clancey et al; 2,791,472 issued May
7, 1957j to Barthauer et al; 2,920,923 issued January 12,
1960, to Wasp et al; 3,012,826 issued December 12, 1961,
to Puff et al; 3,019,059 issued January 30, 1962, to McMurtie;
3,073,652 issued January 15, 1963, to Reichl; and 3,524,682
issued August 18, 1970, to Booth.
Other carrier liquids have been proposed. These,
typically, are liquid petroleum fractions used alone or with
water, etc. Exemplary of processes employing such carrier
liquids are those disclosed in patents Nos. 1,390,230 issued
September 6, 1921, to Bates; 2,610,900 issued September 6, 1952,
to Cross; 3,129,164 issued April 14, 1964, to Cameron;
3,190,701 issued June 22, 1965, to Berkowitz et al; 3,206,256
issued September 14, 1965, to Scott; 3,377,107 issued April
9, 1968, to Hodgson et al; and 3,359,040 issued December 19,
i967, to Every et al.
The use of a heavy liquid as a carrier for coal ls
suggested in U. S. Patent 2,937,049 issued May 17, 1960, to
Osawa. However, in the Osawa technique the carrier liquid
is employed to float the coal to the top of a vertical shaft
and is therefore of limited applicability. Furthermore, the
heavy liquids proposed by this patentee (aqueous dispersions
of silt plus pulverized pyrite, hematite, limonite,
magnetite, ferrosilicon, or galena) would be unsuitable for
pipeline transport because they are highly abrasive if for
no other reason.
~0518Z7
Wasp (U.S. Patents Nos. 3,637,263 issued January
25, 1972, and 3,719,397 issued March 6, 1973) does suggest
that aqueous coal slurries containing magnetite, magnesite,
barites, hematite, etc. can be used for the pipeline
transportation of coal. However, we consider this technique
inferior because of the abrasion problem discussed above. Also,
the recovery of the carrier at the terminus, the drying of
the coal, and the return of the carrier liquid is a much more
complex and expensive procedure than we find necessary.
There is one patent of which we are aware that
suggests using a fluorochlorocarbon as the carrier for a coal
slurry. This patent is No. 3,180,691 issued April 27, 1965,
to Wunsch et al.
However, one of the fluorochlorocarbons which
Wunsch et al propose to use (dichlorodifluoromethane) boils
at -30C. Accordingly, the pressure in the pipeline must be
kept at 77 psig simply to keep the fluorochlorocarbon liquid
at room temperature (72F.) and at 106 plus psig to keep the
carrier liquid at the easily reached summertime temperature
of 95F. We consider this undesirable because of the energy
required, the problem of sealing the line against leakage
engendered by the large pressure differential, and the
difficulty there would be in effecting movement of the solids
if any significant amount of the carrier were lost.
Wunsch et al also suggest that trichlorofluoro-
methane can be used as the carrier liquid in their coal
transport process. We disagree because, in their process,
the carrier liquid is removed from the solids by evaporation
at ambient temperature and pressure which means that the
latent heat of vaporization must be supplied by the solids
and from the ambient surroundings.
- 25 -
10518Z~
As a practical matter, the bulk of the heat must
come from the latter source. For example, if the solids were
to supply all of the sensible heat required to evaporate tri-
chlorofluoromethane from a slurry composed of equal parts by
weight of carrier and solids, the solids would have to decrease
283F. in temperature, an obvious impossibility as the tempera-
ture of the solids may not be much above ambient temperature
when the slurry reaches the terminus.
Trichlorofluoromethane vaporizes at ca. 75F. at
atmospheric pressure. As a coal transport process has to be
capable of operating on a twenty-four hour basis to be of any
practical value and as the temperature differential between
the ambient surroundings and the boiling point of the carrier
liquid must be significant for evaporation of the liquid to
proceed at an appreciable rate, the Wunsch et al process
using trichlorofluoromethane as the carrier liquid would be
operable only where the round-the-clock ambient temperature
at the terminus exceeds 75F. by a significant margin. As
such conditions exist only in controlled environments and
in a few tropical locations (see, for example, Handbook of
Fundamentals, American Society of Heating, Refrigerating, and
Air Conditioning Engineers, 345 East 47th Street, New York,
N. Y., 1972, pp. 667-688), the process in question has little
if any practical value.
In contrast, our novel process for transporting
coal is essentially independent of the ambient temperature
at the terminus. It can be used in Arctic and tropical
conditions and in any conditions ranging therebetween.
Another disadvantage of the Wunsch et al process if
trichlorofluoromethane or a comparable carrier liquid is employ-
ed is that recovery of the carrier by evaporation under ambient
- 26 -
10518Z7
conditions, alone, will leave a large pxoportion of the
carrier liquid in the pores of the solids. In the case
of a typical eoal this would be on the order of six pounds
of carrier per ton of coal. As trichlorofluoromethane current-
ly sells for $0.30 per pound, the cost of unrecovered carrier
liquid would be $1.80 per ton of coal transported. This
would make the process economically impractical.
In eontrast, our novel use of a purge at the terminus
results in the reeovery of essentially all the carrier liquid
from the slurry. Because of this and other factors, our
novel process is highly viable from the economic viewpoint. For
example, we ean typieally reduee the earrier content of the
coal to on the order of 20 pereent by drip drying, a teehnique
not diselosed in Wunseh et al. Drip drying ean reduce the
energy required to remove the earrier liquid by as much as 60
pereent or more depending upon the partieular applieation of
our invention.
It is sometimes advantageous to incorporate additives
into eoal to modify its properties. For example, recent
studies have shown that the addition of quieklime (chiefly
ealeium oxide) or ealeined dolomite (ehiefly caleium-magnesium
oxide) to eoal brings about a signifieant reduetion in the
sulfur eontent of the eombustion produets generated when the
eoal is burned.
In still another aspect our invention involves a
novel teehnique by which a virtually unlimited variety of
additives ean be easily, economically, and uniformly dispersed
in eoal.
Briefly, we dissolve or disperse the additive or
additives in a fluorochlorocarbon as described above or 1,2-di-
fluoroethane; immerse the coal in or spray or drench it with
the earrier, additive composition, or otherwise effect contact
between the coal and
10518Z7
the composition; and then remove the carrier, leaving the
additive absorbed in and/or adsorbed on the free surfaces of
the coal particles.
In processes also involving a coal cleaning step the
additive can in some cases be dispersed in the parting liquid
bath in the gravity separator or in the parting liquid mixed
with uncleaned coal in a conditioning step. Alternatively, the
additive can ~e distributed in a unit downstream from the
gravity separator.
Our novel technique for incorporating additives is
highly effective because the low viscosity and-surface tension
of the fluorochlorocarbon or 1,2-difluoroethane carriers permit
them to penetrate and transport the additives into even the
smallest pores and micro cracks in the coal particles.
Another advantage of our novel dispersing process,
attributable to the physical properties of the carrier liquid,
is that the carrier can be easily, inexpensively, and essential-
ly completely recovered after the dispersion of the additive
has been completed.
Also, the process can be carried out at ambient
temperature and at atmospheric pressure. Because of this and
the lack of toxicity and corrosiveness possessed by our carrier
liquids, exotic and expensive equipment is not required.
Yet another advantage of our novel technique, in a
multi-step operation, is that the coal need not be freed of the
parting liquid employed in the cleaning step before the additive
is dispersed. This is because both the carrier and parting
liquids may be 1,2-difluoroethane or the same, or compatible,
fluorochlorocarbons, making removal of the parting liquid un-
necessary.
Yet another advantage of our novel method of
~.~
- 28 -
1~518Z~
dispersing additives is that no water is introduced into the
system. This is important, as an example, in the addition of
quicklime to coal to reduce sulfur emissions. The reaction
CaO + H20 ~ Ca(OH)2
is highly exothermic and, also, reduces the availability of
one of the reactants needed for the subsequent sulfur removal
reaction. By avoiding the introduction of water into the
product our novel process insures that the reactant is avail-
able in its more reactive form to the maximum extent.
Other exemplary applications where our novel technique
for dispersing additives can be employed to advantage are the
dustproofing and waterproofing of coal and the addition of
a binder as a preliminary to low-temperature briquetting.
The addition of a dustproofing agent is particularly
important. In transporting coal of smaller size consists by
rail 1-10 percent of the coal is not uncommonly lost between
the preparation plant and the point-of-use. By dustproofing
coal in accord with our invention, this loss can be substantial-
ly reduced.
One exemplary technique for dustproofing coal in
accord with the present invention involves the distribution of
fuel or residual oil on the coal to coalesce the finer particles
into agglomerates. Amounts in the range of 0.05 to 0.5 percent
based on the weight of the coal will typically be employed,
depending upon the size consist of the coal.
The dustproofing agent is first dispersed in the
fluorochlorocarbon or 1,2-difluoroethane carrier in an amount
ranging from 0.1 to 5 weight percent based on the weight of
the carrier. The coal is immersed in the composition and the
carrier removed by evaporating it.
~ -29-
10518Z7
The removal of the carrier leaves the oil residuc
on the coal surface. This causes agglomeration, substantially
reducing the proportion of dust-size particles present.
The application of our novel process for dispersing
additives to the waterproofing of coal is also important.
As indicated above, as mined coals may have moisture
contents as high as 20-33 percent. If these coals are shipped
with a moisture content of this magnitude, almost one-third of
the freight charges paid by the shipper are for transporting
water. To compound the problem, coals with water contents of
the high magnitudes in question are typically young Western
coals and must be shipped relatively long distances to the
point-of-consumption.
However, it has not heretofore been practical to
remove the water from the coal before shipping it. Readsorption
of water often occurs so rapidly, especially if the coal is
exposed to precipitation, that spontaneous combustion occurs
because of the build-up in temperature due to the heat of
adsorption. Entire carloads of coal have been destroyed in
this manner.
In accord with our invention the coal is dried and
the free interior and exterior surfaces coated with a water-
proofing agent such as a crude oil or other heavy bitumen by
immersing the dried coal in or otherwise intimately contacting
it with a dispersion of the waterproofing agent in 1,2-difluoro-
ethane one of the fluorochlorocarbons listed above. The carrier
liquid is then removed, leaving a thin film of the waterproofing
agent on the exterior surfaces of the coal and on those inner
surfaces which are accessible to liquids. This keeps water
from readsorbing onto the surfaces accessible to it, and
spontaneous combustion cannot occur.
- 30 -
10518Z~7
Further benefits are that oxidation and slaking of
the coal are effectively inhibited by the coating of waterproof-
ing agent as is the freezing together of the coal under low
ambient temperature conditions. All of the foregoing benefits
are of course realized in the storing of coal as well as in
transporting it.
Processes for treating coal to keep the particles
from freezing together are known. One such process is des-
cribed in U.S. Patent No. 3,794,472 issued February 26, 1974, to
Macaluso et al. However, in the Macaluso process, the coal is
sprayed with substantial quantities of water (up to 68 percent
of the coating composition). This water would be absorbed by
the coal to a large extent. Therefore, even if the coal
particles were thereafter surrounded with films which would
entrap surface water and keep it from freezing the particles
together, the other problems appurtenant to the presence of
absorbed water, such as spontaneous combustion, would not be
solved as they are by our novel waterproofing technique which
not only does not add water to the coal but prevents the coal
from reabsorbing water.
The making of briquettes, mentioned above, is
another important application of our additive dispersing
process.
In briquetting coal, small particles treated with a
binder such as No. 6 fuel oil by use of the technique just des-
cribed are compacted in a mold at room temperature and under
moderate pressure (2000 to 5000 psi depending upon the binder,
size consist, and moisture content). The resulting briquettes
are stable, even under relatively high impacts, and the process
is economical.
U.S. Patent No. 3,027,306 issued March 27, 1962, to
Muschenborn et al discloses a process for making briquettes
31
1051~3~Z7
which, like ours, involves a gra~ity separation st~p and th~
use of a binder. However, Munschenborn et al use carbon
tetrachloride or a magnetite suspension as the parting liquid.
These have major disadvantages, discussed above, and further-
more, would not be useful as a carrier for the binder as our
novel parting liquids are. In addition, Munschenborn et al
find it necessary to coke the coal before cleaning it, a step
we need not employ.
Additives can be dispersed on solids other than coal
by the process just described. For example, this process can
be used to dedust sinks generated in a coal cleaning operation,
ash generated in burning steaming coal, etc. Still other solids
can be treated by our process as will be readily apparent to
those skilled in the relevant arts.
Rejects can be treated in the gravity separator,
in a conditioning step, or in a separate unit after they are
removed from the gravity separator. In applications which do
not involve a cleaning operation the solids are necessarily
treated in a unit provided especially for this purpose.
As indicated above, a virtually unlimited range of
materials can be dispersed by our process. One restriction on
the additive is that it be soluble or otherwise uniformly
dispersable in the carrier liquid. A second limitation in
some cases is that the additive not react chemically with the
carrier liquid.
In yet another aspect our invention resides in the
provision of a novel, integrated process for handling coal
from the mine face to a consumption point or other terminus in
which the beneficiation and slurry transport techniques described
above are employed.
- 32 -
10518Z7
Mininy machines of th~ hydraulic or continuous type
may be employed in our novel system. The mined coal is crush~d
and transported away from the mine face in a slurry with one
1,2-difluoroethane or of the liquid fluorochlorocarbons identi-
fied above rather than by the conventional belt, shuttle car,
or other mechanical arrangement. The fluorochlorocarbon or 1,2-
difluoroethane and additive system is also employed for dust
supression at the mine face as such compounds are more effective
than water for this purpose. In addition, the fluorochloro-
carbon or 1,2-difluoroethane, perhaps with an appropriate addi-
tive such as No. 6 fuel oil and/or one or more alkyl amines,
can reduce cutter wear and energy requirements.
The coal slurry can be pumped to a primary cleaning
plant, typically located in the mine itself. Here, an initial
gravity separation of the foreign matter and raw coal is made
as described above.
The gangue separated from the coal is stripped of
parting liquid, optionally treated with a dust suppressant,
and conveyed to a mined-out area of the mine.
The floats from the initial separation step, slurried
in the parting liquid, are pumped to a final treating plant,
typically located aboveground at the mine mouth. There the
coal is ground to a size which will release the maximum amount
of foreign material and subjected to a second gravity separation,
again using a fluorochlorocarbon or 1,2-difluoroethane parting
liquid in accord with the principles of the present invention.
Sinks from this step are stripped of parting liquid
conveyed to a disposal area. They may first be treated to inhi-
bit the generation of acidic ground water and/or other
ecologically undesirable phenomena.
Floats (or, product coal) from the final cleaning
step, again slurried with the parting liquid, may be pumped
- 33 -
10518Z7
to the point of consumption, typjcally a power gene~ting plant,
and stored. Prior to use they are stripped o~ the parting/carrier
liquid and, if necessary, ground to a smaller size consist.
Liquid stripped from the coal in the final preparation
step can be employed to slurry ash from the power plant furnace
bottoms and fly ash precipitators and convey it back to the
final cleaning plant. Here, the ash is stripped of the carrier,
treated as required, and conveyed to the refuse area with the
gangue separa~ed in the final cleaning step. The liquid is
recycled, typically to the raw coal slurry pump and to the
mine face.
~ he advantages of using lt2-difluoroethane a fluoro-
chlorocarbon as a dust suppressant at the mine face were dis-
cussed above. Because of these and the other advantages of our
novel materials such as lack of corrosiveness, toxicity, and
flammability, explosion hazards are reduced and safety otherwise
promoted by our novel system.
Explosion hazards are also reduced because the system
is essentially closed beginning at the mine face. Accordingly,
methane and other combustible gases ~i.e., firedamp) can be
captured and removed from the mine face as well as from
the coal during beneficiation, transportation, and storage
to a point where they can be safely disposed of or recovered
if the concentration warrants.
Another potential advantage of the novel coal mining
and handling system just described is that only a small fraction
of the gangue is removed from the mine. This materially reduces
the material handling capacity and energy required and, also,
the aboveground disposal problems.
A related advantage is that the disposal of refuse
from the powex generating plant or other consumer of the
product coal is simplified.
... /, .
- 34 -
~0518Z7
Also, if quicklime is mixed with the coal to suppress
sulfur emissions as described above, the refuse from the
generating plant will tend toward a basic pH. The presence of
this refuse in the refuse pile with pyrites and other acid
forming rejects from the cleaning operations will tend to
neutralize any acids formed by water contacting the refuse pile,
thus reducing the ecological hazards which such refuse piles
commonly present.
~ Other related advantages of our invention are that
the conveyor system in the mine occupies less room and can
more conveniently be relocated and extended than conventional
conveyor systems.
A further significant advantage is that the coal is
protected against oxidation from the time it is mined until
it is consumed. This gives it potentially better combustion
characteristics than conventionally handled coal and, also,
minimizes the losses in heating value which can occur through
oxidation.
Furthermore, the area required for coal storage at
the point of consumption is considerably reduced as is the fire
hazard; and there is no need for compaction or dust suppression.
In addition all the underground and surface activities,
including material handling and transportation, are independent
of weather and climate.
Other advantages of our novel, integrated, coal hand-
ling and processing technique, attributable to the nature
of the parting, carrier liquids we employ, were described above
in conjunction with the coal cleaning and transporting aspects
of the invention.
Another important advantage of our novel system is
that the advantages at one stage carry over to other stages.
- 35 -
105~827
For example, because the use of a fluorochlorocarbon or 1,2-
difluoroetharle in con-~eying Lhe product c~al ~rom the final
cleaning station to th~ po;nt o~ consumption inhibits oxidation,
the coal may be ground for the cleaning step to a size consist
which will optimize the separation of pyrites and other foreign
material from the coal without regard to the increase in
surface area and the accompanying potential for chemical
reaction which results.
It will be appreciated by those conversant in the
relevant arts that our novel coal handling and processing system
is not limited in application to operations where the coal is
to be burned at the mouth of the mine. The coal recovered from
the final cleaning plant can instead be transported elsewhere
in slurry with the parting liquid or, after the latter is
stripped from the coal, by conventional modes of transport.
Also, it will be readily apparent to those to whom
this is addressed that, with easily visualized modifications, the
novel integrated system just described can be used in associa-
tion with open pit as well as deep mines.
Yet another important advantage is that the system
can, to a large extent, operate automatically and unattended.
In yet another aspect our invention resides in certain
novel techniques for recovering from coal and refuse the
fluorochlorocarbons or 1,2-difluoroethane employed as carriers
and as parting liquids. The fluorochlorocarbon or 1,2-difluoro-
ethane may be stripped from the coal or refuse by a vacuum
purge or simple evaporationO It is then compressed, condensed,
purged of noncondensible gases, and recycled.
Alternatively, the hydrocarbon is stripped from the
coal or refuse by evaporation and an air purge. The gas
vapor mixture is compressed and condensed, converting the
fluorochlorocarbon or 1,2-difluoroethane to a liquid and
leaving the air as a gas. Additional fluorochlorocarbon or
'~
- 36 -
1051~327
1,2-difluoroethane can be recov~red by compressing and re-
frigerating the noncondensibles, and the purge air can
be recycled.
As air purge is also employed in a third recovery
techni~ue. The air and fluorochlorocarbon or 1,2-difluoroethane
mixture is compressed and/or condensed and the noncondensible
vapor stream contacted with a fuel oil or any other liquid
capable of selectively absorbing the hydrocarbon. The noncon-
densible gases are recycled or rejected, and the fluid is heated
to vapori2e and release the fluorochlorocarbon or 1,2-difluoro-
ethane. The latter is compressed and condensed, the absorption
fluid is cooled to restore its absorption capabilities, and the
sensible heat is recovered.
Advantages of these novel techniques for recovering
the parting, carrier liquids are that they are economical and
efficient. Also, the equipment in which the recovery is effected
can be readily integrated with the apparatus in which the other
of the process steps described herein are carried out.
Vacuum and air purges are, as such, known as is the
use of an "oil" to separate one gas from another by selective
absorption as shown by the following U.S. Patents: 2,429,751
issued October 28, 1947, to Gohr et al; 3,392,455 issued July
16, 1968, to Kingsbaker et al; 3,439,432 issued April 22, 1969,
to Bellinger et al; 2,497,421 issued February 14, 1950, to
Shiras; 2,614,658 issued October 21, 1952, to Maher et al;
2,652,129 issued September 15, 1953, to Benedict; 2,710,663
issued June 14, 1955, to Wilson; 2,870,868 issued January 27,
1959, to Eastman et al; 2,961,065 issued ~ovember 22, 1960,
to Helm et al; and 3,208,199 issued September 28, 1965, to
Pruiss.
However, none of these patents disclose a method for
recovering fluorochlorocarbons or 1,2-difluoroethane or techniques
which, even if they could somehow be adapted to this use, would
- 37 -
~ 10518Z7
have the advantages ours give. The same is true of the hereto-
fore proposed techniques for recovering organic fluorine compounds
described in the following U.S. Patents: 2,508,221 issued
May 16, 1950, to Calfee et al; 3,013,631 issued December 19,
1961, to Johnson; 3,197,941 issued August 3, 1963, to Colton
et al; 3,236,030 issued February 22, 1966, to Von Tress; 3,581,466
issued June 1, 1971, to Rudolph et al; 3,617,209 issued
November 2, 1971, to Massonne et al; and 3,680,289 issued
August 1, 1972, to Rudolph et al.
Yet another suggestion that halogenated hydrocarbons
such as acetylene bromide can be recovered by selective
absorption is found in an unpublished article by Tveter and
O'Connell entitled Heavy Liquids for Mineral Beneficiation.
However, our technique for recovering fluorochlorocarbon and
1,2-difluoroethane parting liquids differs in an advantageous
manner in that we are able to recover from the absorbing
medium significant amounts of the sensible heat added to
the medium to release the parting liquid from it.
The novel recovery techniques described above are
of course of general applicability. That is, they can be
used to recover fluorochlorocarbons and 1,2-difluoroethane
from other solids besides coal, rejects from a coal cleaning
operation, and ash generated by burning coal.
The invention is directed to a method of processing
coal in which the coal is beneficiated to separate it from
foreign matter mixed therewith by introducing the coal into a
body of a parting liquid which is or contains a halogenated
hydrocarbon and has a specific gravity intermediate that of
the coal and foreign material so that the coal will rise
toward the top of the body of liquid and the foreign material
Ll~
-
~ 10$1~27
`~ill sink toward the bottom the~ebf, any halogentated hydro-
carbon present in the par~ing liquid in the beneficiation
step being 1,2-difluoroethane or a fluorochloro derivative
of methane or ethane selected from the group consisting of
l-chloro-2~2~2-trifluoroethane~ dichloro-2,2,2-trifluoro-
ethane, dichlorofluoromethane, l chloro-2-fluoroethane, 1,1,2-
trichloro-1,2,2-trifluoroethane, 1,1-dichloro-1,2,2,2-tetra-
fluoroethane, and trichlorofluoromethane.
This invention also relates to the method as described
above in which, in the beneficiation of the coal, parting
liquid is evaporated from the body of parting liquid to thereby
alter the specific gravity of the parting liquid. The method
as described above can also include,in the beneficiation of
the coal, the provision that the specific gravity of the parting
liquid be regulated by var~ing the apparent temperature of the
coal to be cleaned before the coal is introduced into the body
~ of par~ing liquid. In the~beneficiation step, the apparent
temperature of the coal to be cleaned can be varied by forming
a slurry of the coal and parting liquid, heating the slurry,
and thereafter transferring the slurry to the body of parting
liquid. The method as described initially can ïnclude the
step of preconditioning the coal which is to be cleaned by
adding to the coal before it is introduced into the boay of
parting liquid a mixture of a fluorochloro derivative as aforesaid
- or 1,2-difluoroethane and a surface active agent. From B.03
to six pounds of surface active agent per ton of coal can be
added to the coal in the preconditioning of the coal. The
surface active agent added to the coal in the preconditioning
of the coal may be an ionic surfactant. The surface active agent
added to the coal in the preconditioning of the coal can be an
~ ~ - 38a -
10518Z7
ester or salt of a sulfosuccinic a_id. The surface active agent
added to the coal in the preconditioning of the coal can also
be a lower alkyl or alkylene amine. The surface active agent
added to the coal in the preconditioning of the coal may be
a No. 4 or No. 6 fuel oil.
In the method described for the preconditioning of the
coal to be cleaned, the coal and the mixture of fluorochloro
derivative of 1,2-difluoroethane and surface active agent may
be agitated. The speciflc gravity of the body of parting
liquid can be controlled by mixing a diluent which may be a
petroleum fraction or a liquid alkane with the fluorochloro
derivative or 1,2-difluoroethane and coal in the preconditioning
of the coal to be cleaned in an amount sufficient to reduce
the specific gravity of the parting liquid to not less than
about 1.30. The diluent mixed with the coal in the preconditioning
of said coal may be a petroleum ether. The diluent mixed with
the coal in the preconditioning of said coal may be pentane.
The method can include the steps of recovering parting liquid
from the separated coal and the foreign material and resolving
the recovered liquid into its constituents to thereby furnish
parting liquid and diluent which can be employed to regulate
the specific gra*ity of the body of parting liquid.
In the method described the only halogentated hydrocarbon
present in the body of parting liquid in which the coal is
cleaned can be trichlorofluoromethane. The coal to be cleaned
may be a bituminous coal. The coal to be cleaned may be the
product of a hydrobeneficiation process. The coal to be cleaned
may be from the refuse of a coal cleaning process.
The invention is also directed to a method as described
originally in which the coal and associated foreign material are
Ll
38b -
G
-~ 1051827
r~uced to particles which are predominantl~ less than 200 mesh
in diameter prior to introducing the coal and foreign material
into the body of parting liquid so that essentially all pyrite
'present will separate:.from the coal in the body of parting
liquid. The foreign material to be separated from the coal in
the beneficiation of the coal may include water or organic sulfur
or both water and organic sulfur.
The method originally described may include the step
of incarporating in the clean coal or the foreign material or
in both the coal and the foreign material an additive capable
of altering the physical and/or chemical characteristics of the
material into which it is incorporated. The additive may be
incorporated into the coal and/or foreign material by dispersing
it in the body of parting liquid in which the coal is
beneficiated. The additive may be a dustproofing agent. The
dus~proofing agent may be a petroleum fraction.
, The material into.which the additive is to be incorporated
can be composed of coal particles and the additive can be.a water-
proofing agent. The waterproofing atent may be fuel oil. The material
into which the additive is to be incorporated may be composed of
coal~particles, the additive can-contain calcium or magnesium
- oxide, or both, and the additive ~.a.n, be added to the coal in an
amount effective to reduce the content o~ sulfur in gaseous
combustion products generated by the subsequent burning of the
coal. The material to be processed can be composed of coal
particles and the additive can be a binder by which the coal
particles can be agglomerated into briquettes and the like. The
method can include the step of compacting the material to which the
binder has been added under a pressure ranging from'2000 to
5000 psi.
Related and also i,mportant but more specific objects
~f the invention reside in the provision of methods for
beneficiating coal:
- 38c -
-
10518Z7
(1) which are efficient an~ economical;
(2) which employ parting liquids that can be essential-
ly completely recovered at a modest cost;
(3) which employ parting liquids with specific
gravities in a range that make the liquids capable of effecting
a sharp separation between the coal and associated foreign
matter;
(4) which employ parting liquids that are available
in large quantities at modest cost;
~ 5) which employ non-corrosive, non-toxic, and non-
flammable parting liquids that are chemically inert with
respect to coal under the process conditions we employ;
(6) which can be carried out at ambient pressure and
temperature or under conditions which vary only modestly from
ambient;
(7) which employ parting liquids that will not leave
corrosive or other unwanted residues on the product coal;
(8) which are efficient even when the moisture content
of the coal to be processed is high;
(9) which are capable of efficiently recovering coal
from slurry ponds, gob piles, and the like at modest cost;
(10) in which the separation of the coal from the
foreign material proceeds rapidly;
(11) which are highly effective in separating sulfur
from coal;
(12) which, in conjunction with the preceding object,
are capable of separating organic as well as pyritic and sulfate
sulfur;
(131 which do not have the slime and flocculation
problems common to many gravity separation processes;
- 39 -
1~18Z7
(14~ in which the specific gravity of the p~r~ing
liquid can be r.eadlly adjusted and, equally easily, be kept
constant or varied in a controlled mann~r under chan~in-J
pressure and temperature conditions;
tl5~ which are effective to separate coal of large
size consists and of very small particle size;
tl6) which do not generate ecologically undesirable
wastes.
Another important and primary object of our invention
resides in the provision of novel, improved methods for trans-
- porting coal and other solids from place-to-place.
: Related and important but more specific objects of
the invention reside in the provision of solids transporting
techniques:
(17) which are efficient and economical and in which
the solids are transported in slurry form;
(18) which, in conjunction with the preceding object,
permit substantially all of the carrier liquid to be recovered
from the solids at the terminus with only modest expenditures
of energy;
tl9) in which, in conjunction with the preceding object,
a non-corrosive, non-toxic, and non-flammable fluorochloro
derivative of a lower alkyl which has a low viscosity, which is
easily recovered, and which is chemically inert relative to the
solids under process conditions or 1,2-difluoroethane is employed
as the carrier liquid;
(20) which have the advantage that the carrier liquids
do not cause flocculation problems;
(21) which employ a carrier liquid that permits the
solids-to-liquid ratio of the slurry to be increased above con-
ventional levels without an increase in the power required to
move the slurry;
(22) which minimize the tendency of the particles
- 40 -
1051827
to pack and therefore permit flow to be initiated virtually
at once even after the slurry has been static for an extended
period of time.
Still another primary object of the present invention
resides in the provision of novel, improved techniques for
associating additives with coal and other solids to ~.odify the
characteristics of the solid material.
Related and more specific but also important objects
reside in the provision of techniques;
(23) which can be used to distribute any of a variety
of additives uniformly and economically;
(24) which can be employed to advantage to dedust and
waterproof coal;
(25) which can be employed to in~imately distribute
compositions such as quicklime among coal and thereby reduce
the sulfur pollutants generated when the coal is burned;
(26) which are capable of introducing additives into
even fine pores and micro cracks in the solids being treated;
(27) in which the additive is associated with the
solids by dispersing it in 1,2-difluoroethane or a liquid,
fluorochloro derivative of methane or ethane; spraying the
resulting composition on the solids or submerging the solids in
or drenching them with the composition; and removing the liquid
carrier;
(28) in which, in conjunction with the preceding
object, the carrier liquid is one which is non-corrosive, non-
flammable, non-toxic, chemically inert with respect to the
additive and the solids, and readily recovered from the solids;
(29) which can be carried out under ambient or other
mild conditions and without expensive and exotic process equip-
ment;
(30) which can employ as carrier liquids those used
- in accord with the principles of the present invention in the
- 41
-
10518Z7
beneficiation and transportatiOrl of coal, theFeby si~p]i~ying
and reducing the cost of multi-step processing of coal;
(31) which avoid the introduction of water into the
product, thereby avoiding the deleterious effects which water
can have.
t32~ which can be employed to associate a binder with
coal so that the coal can subsequently and economically be
agglomerated into structurally stable briquettes and the like.
An associated, primary object of our invention resides
in the provision of novel, improved methods for economically
making briquettes from particulate coal in which a binder is
associated with the coal by dispersing it thereon in a 1,2-di-
fluoroethane of liquid fluorochlorocarbon carrier and in which
the carrier is then removed and the particles compacted into the
desired shape.
A further important and primary object of our
invention resides in the provision of novel, improved, integrated
methods for processing raw coal and for conveying it from a
mine face to a location where the product coal is to be burned,
processed, shipped, or otherwise used.
Related and more specific but nevertheless important
objects of the invention reside in the provision of such coal
handling and processing techniques;
(33) which optimize the recovery of raw coal and its
conversion into a product of maximum usefulness as well as the
movement of the raw coal to a point-of-use or other terminus;
t34) which are capable of producing higher yields
than can be gained by present commercial techniques;
(35) in which the handling and processing steps
are so related as to maximize the efficiency of the process;
- 42 -
10518Z7
(3~) which reduce the manpower required to mine and
process coal and the attendant pxoblems and expense;
(37~ which, to a substantial extent, insulate the
mining, processing, and transportation of coal from the effects
of inclement weather and adverse climates;
(38) which reduce the handling of foreign material
associated with the coal;
(39) in which the coal can be protected against
oxidation until it reaches the point of consumption;
~ 40) which can also be employed to efficiently dispose
of the refuse generated in the consumption of the coal;
t41) which promote safety and productivity and extend
the useful service life of equipment;
t42) which can be utilized to reduce the sulfur
generated in the combustion of coal;
(43) which can be used to generate refuse piles with
less potential for ecological damage than is currently the case;
(44) which employ conveyor apparatus that is less bulky
and more easily relocated than that of conventional character.
Yet another primary object of our invention resides
in the provision of novel, improved techniques for recovering the
fluorochlorocarbons and 1,2-difluoroethane employed in our novel
cleaning, transporting, additive incorporating, and briquetting
process and in our novel, integrated process for handling and
processing coal from the mine face to the point-of-use or other
terminus.
Important, related, and more specific objects of the
invention reside in the provision of processes in accord with
the preceding object:
- (45) by which essentially quantitative amount of the
fluorochlorocarbons and 1,2-difluoroethane can be recovered at an
economic cost;
- 43 -
105~8Z7
(4~) which can readily be integrated with the process
in which the 1,2-difluoroethane or fluorochlorocarbon is employed.
Still another important and primary object of the
invention resides in the provision of novel, improved appara-
tuses in and by which the various processes discussed above can
be carried out.
Other Lmportant objects and features and additional
advantages of our invention will be apparent to those knowledge-
able in the relevant arts from the foregoing and from the
appended claims and working examples and from the detailed
description and discussion which follows taken in conjunction
with the accompanying drawing, in which:
Figure 1 is a schematic illustration of apparatus for
beneficiating or cleaning coal in accord with the principles of
the present invention and for recovering from the coal and the
foreign material separated therefrom 1,2-difluoroethane or a
fluorochlorocarbon employed as a parting liquid in the bene-
ficiation process;
Figure 2 is a schematic illustration of one type of
apparatus for controlling and adjusting the specific gravity
of the parting liquid employed in the beneficiation apparatus
of Figure l;
Figure 3 is a schematic illustration of a second form
of apparatus for controlling and adjusting the specific gravity
of the parting liquid;
Figure 4 is a view similar to Figure 1 of coal
beneficiation apparatus in accord with the principles of our
invention whic~ is designed for the conservation of heat energy;
Figure 5 is a view similar to Figure 4 of a second form
of coal beneficiation apparatus designed for the conservation of
heat energy;
- 44 -
10518Z7
Figures 6 and 7 are schematic illustrations of alter-
nate systems for recovering 1,2-difluoroethane and fluorochloro-
carbons; these systems can be used to recover 1,2-difluoroethane
and fluorochlorocarbons used as parting liquids in beneficiation
processes, as carrier liquids, etc. in other application of our
invention, and for various purposes in other processes;
Figure 8 is a schematic illustration of an integrated
system in accord with the principles of the present invention
for handling and processing raw coal;
Figure ~, which appears on the same sheet as Figure 6,
is a schematic illustration of a final eleaning plant employed
in the integrated system of Figure 8;
Figure 10, which appears on the same sheet as Figures
4 and 5, is a schematic illustration of apparatus for associating
additives with coal in accord with the prineiples of the present
invention; and
Figure 11, which appears on the same sheet as Figure 7,
is a sehematie illustration of a pilot seale plant for benefi-
eiating eoal in accord with the principles of the present
invention.
Referring now to the drawings, Figure 1 sehematieally
depiets a plant or system 20 for eleaning coal whieh is eonstrue-
ted in aeeord with the principles of the present invention. The
major eomponents of system 20 inelude à eonditioning tank or
eonditioner 22 whieh ean be omitted in those applieations where
eonditioning is not required. The run-of-mine or other raw
eoal to be eleaned is transferred from a storage faeility to the
eonditioning tank as by serew eonveyor 24. The plant also in-
eludes: a separator 26 of bath, drum, trough, eyclone or other
eonstruction in which gangue or ash is separated from the
eoal by a gravity or centrifugal separation (or sink-float)
proeess; dryers 28 and 30 for reeovering the parting liquid
- 45 -
- - 1051827
from the clean coal (or floats) and the rejects (or sinks);
and a system identified generally by reference character 32
for recovering parting liquid in vapor form from conditioning
tank 22, separator 26, and dryers 28 and 30; condensing the
vapor to a liquid, and returning the liquid to storage tank 34.
Also incorporated in the system are a storage facility 36 from
which a surface active agent can be introduced into the media
supply line to tank 22 by pump 38 and a heating system 40 for
adjusting the effective temperature of the coal in the condi-
tioning tank before it is transferred to separator 26.
The conveyor 24 for feeding the raw coal into theconditioning unit can be of the screw or auger type. As shown
in Figure l, it will typically be positioned with a gap between
the discharge end and the surface of the liquid in the condi-
tioner. This keeps vaporized liquid in the conditioner,
necessarily under some pressure, from blowing out through the
conveyor when warm coal is introduced into the conditioner.
Trichlorofluoromethane or another of the fluorochloro-
carbon parting liquids we can use or 1,2-difluoroethane is
pumped at a controlled rate by pump 41 to the discharge side of
pump 38 where it is premixed with the surface active agent (if
employed) to insure subsequent homogeneous distribution of the
latter.
The parting liquid or mixture of this constituent
and surface active agent then flows to conditioning tank 22
where the liquid phase and coal introduced by conveyor 24 are
blended into a uniform mixture by agitator 42. The latter also
generates the turbulence necessary to insure sufficient surface
and thermal exposure of the raw coal to the conditioning
material or materials.
- 46 -
.. .
- 10518Z7
At the same time, heating system 40 may be utilized
to add to the mixture such heat as may be necessary to control
the temperature, and therefore the specific gravity, of the
parting liquid in separator 26. Heating system 40 includes
a tube type or other circulating liquid heat exchanger 44 in the
bottom of conditioning tank 22 and a pump 46 for circulating
steam or hot water from a boiler 48 to and through heat
exchanger 44 and back to the boiler.
~ Only modest quantities of heat will, at most, need
to be added to the coal being cleaned. This is because it is
not necessary to heat larger particles or lumps o~ coal through-
out. It is only required that their surface temperature be
approximately that of the parting liquid in separator 26 during
the short period of time the coal remains in the separator.
It is also significant that "hot" coal, for example
that in the summertime, can be cooled in tank 22 without using
additional energy to keep the temperature of the bath in
separator 26 from rising if trichlorofluoromethane or a comparable
fluorochlorocarbon is employed as the parting liquid. Because
this compound has a boiling point only slightly above room
temperature, such coal will cause the parting liquid introduced
into tank 22 by pump 41 to evaporate. The latent heat of
vaporization is supplied by the coal, and the temperature of the
coal and other components of the mixture in tank 22 is accord-
ingly reduced as the parting liquid vaporizes.
The mixture formed in conditioning tank 22 is trans-
ferred to separator 26 as by a screw type conveyor 50. The
coal in the mixture floats to the top of the body or bath 52
of parting liquid in the separator while the ash or rejects
sink to the bottom.
1051827
The coal is skimmed from the surface of sink-float
bath 52 as by an auger conveyor 54, preferably equipped with
folding flights. This skimmer discharges the coal into the
lower, feed end of an upwardly inclined conveyor 55. The
conveyor transfers the coal to floats dryer 28. As the coal
moves upwardly through transfer conveyor 55, the bulk of the
parting liquid drains from it and flows by gravity back into
separator 26.
Reiects are removed from the bottom of separator 26
as by a folding flight, auger conveyor 56 and discharged into
the lower, feed end of a second, upwardly inclined, transfer
conveyor 58 in which the parting liquid drains from the rejects
into separator 26. From conveyor 58, the rejects are discharged
into sinks dryer 30.
Dryers 28 and 30 will typically be ~f the indirect,
conductive type. Examples of such dryers which are suitable
are the rotary, steam tube, and Hollow Flite*types. Steam or
hot water is supplied to the dryers to vaporize the parting
liquid associated with the floats and sinks from boiler 48 by
pump 46 through supply conduit system 59. After circulating
through the dryers, the heat exchange medium returns to the
boiler through fluid conduit system 60.
For the sake of clarity, sinks dryer 30 is shown at
a lower elevation than floats dryer 28 in Figure 1. In actual
practice it is located at approximately the same level as dryer
28 so liquid can drain back into separator 26 which it could
not do if the dryer were located at the illustrated level.
The dry coal and dry rejects are discharged from
dryers 28 and 30 to material handling systems indicated general-
ly by arrows 61 and 62 in Figure 1. The rejects are trans~erred
,. , - .
*Trade mark
- 48 -
J- . ~
1051827
to a gob pile and the clean coal to the point-of-use or to a
coking or other coal treating operation.
Vaporized parting liquid generated in dryers 28 and
30 is combined with that from conditioning tank 22 and separator
26 in a line 63 leading to the inlet side of a compressor 64.
As the vapor from conditioning tank 22 may carry a significant
amount of entrained fines, this vapor is first preferably scrub-
bed with parting liquid in a conventional scrubber 66.
. After flowing from the compressor through a valve 67
employed to maintain pressure in the system, the vaporized
parting liquid is circulated through a condenser 68 which may
be of the conventional shell and tube type. Cooling liquid
ttypically water) at a temperature on the order of 85F. is
circulated from the lower end of a conventional cooling tower
72 through the condenser by pump 74 to condense the parting
liquid.
After exiting from the condenser, the water, now at a
temperature on the order of 95F., returns to and is sprayed
into the upper end of the cooling tower through no~zles 76.
As the water flows down through the cooling tower, it is
contacted by an upwardly moving stream of air generated by
cooling tower fan 78. This reduces its temperature to the level
at which it is circulated to condenser 68.
Condensed parting liquid flows through an expansion
valve or orifice 80 to reduce its pressure to atmospheric and
then to the parting liquid storage facility or tank 34.
Noncondensible gases and any parting liquid which
may not have condensed proceed from condenser 68 to a purge
unit 82. This may be a scrubber or other absorption type
device or a mechanically refrigerated unit, for example. The
remaining parting liquid is condensed in this unit and returned
to storage tank 34.
- 49 -
10518Z7
Noncondensible gases flow through a conduit system
identified generally by reference character 84 to the floats
and sinks dryers 28 and 30. The gases are circulated through
these dryers in countercurrent relationship to the solid
material to strip parting liquid vapors from the solid material.
In cleaning some coals, significant amounts of
middlings may be generated. To expedite the separation of this
material, pump 86 can be employed. This pump circulates the
middlings and parting liquid in which they are entrained from a
zone in bath 52 intermediate those to which the floats and sinks
report to a cyclone, centrifuge, or other polishing device 88.
Here, the solids are separated from the parting liquid and dis-
charged from the separator as indicated by arrow 90. Depending
upon the proximate analysis of these solids, they are conveyed
to either the floats dryer 28 for clean coal or the sinks dryer
30 for rejects. The parting liquid is pumped to either condi-
tioning tank 22 as shown by solid line 92 or to gravity
separation tank 26 as shown by dotted arrow 94.
As will be apparent to the reader, variations can
be made in the illustrated equipment. Obvious changes are
necessary if the conditioning tank 22 is not employed. Other
types of conveyors may be used. The conditioner tank and
agitator may be replaced with a pug mill, jacketed screw
conveyor, or other blender, etc. Centrifuges can be employed
instead of or in addition to drip drying as in conveyors
55 and 58 to remove parting liquid (ca. 97 percent) from
the solids as can static and vibrating screens, etc. And
shelf-type and other kinds of dryers can be used instead
of those discussed above. Still other alternatives will
readily suggest themselves to those skilled in the relevant
arts.
In addition to those discussed above, a system as
- 50 -
1~51827
just described has the advantage that losses of the parting
liquid constituents are acceptable. In a typical operation,
losses would not exceed 0.25 pounds of liquid per ton of coal
cleaned.
As indicated above and discussed in more detail
hereinafter, it may in some instances be advantageous to adjust
the specific gravity of the parting liquid to increase the
amount of ash separated from the coal even though this may
result in some coal reporting to the sinks and thereby lowering
the yield.
The manner in which this is done in the case of the
preferred parting liquid, trichlorofluoromethane, is exemplary.
Trichlorofluoromethane has a nominal specific gravity of 1.5
which can readily be varied over a range of approximately 1.4-
1.55 by increasing the temperature under an above-atmospheric
pressure to reduce the specific gravity or decreasing the
temperature to increase the specific gravity. One typical
system for adjusting the specific gravity of the parting liquid
by these techniques is shown in Figure 2 and identified by
reference character 100.
This system differs from that shown in Figure 1 in
that a thermal conditioner or holding tank 102 is interposed
between conditioner 104 and separator 106, which can be
isolated from the floats and sinks dryers (not shown) by valves
108 and 110.
A coil 112 through which a heat transfer fluid such
as hot water, steam, etc. can be circulated is housed in thermal
conditioner tank 102. The conditioner tank is connected to the
suction side of a compressor 114.
In operation, the slurry of coal and parting liquid
formed in conditioner 104 is transferred to thermal conditioner
102 by pump 116. Here, the specific gravity of the parting
105~827
liquid can be raised by employing compressor 114 to flash
liquid in the conclitioner into vapor, extracting heat from and
increasing the specific gravity of the remaining liquid.
Alternatively, the specific gravity of the parting liquid can
be lowered by adding heat to the liquid with heater 112. This
can typically be accomplished in not more than 10 minutes.
The practical limits within which the specific gravity
of the parting liquid can be decreased and increased will vary
depending upon the parting liquid. The limits will be compar-
able to those mentioned a~ove for trichlorofluoromethane.
The flow of heat transfer fluid and therefore the
amount of heat added to the coal and parting liquid can be
controlled manually. Or, as shown, the flow can be regulated
by a conventional thermostatic valve 118 having a senser 120
in the thermal conditioning tank.
Similarly, evacuation of parting liquid vapor from
thermal conditioner 102 to decrease the specific gravity
of the parting liquid can also be controlled manually or
automatically. In the latter mode control is exercised by
a valve 122 with a temperature responsive senser 124 in the
thermal conditoner tank.
If reduced pressure is employed to alter the specific
gravity of the parting liquid, valves 108 and 110 will be kept
closed until the separation step is completed. This, together
with the seal afforded by pump 116, isolates the thermal
conditioner and gravity separator from the ambient atmosphere,
insuring that the pressure on the parting liquid and its
specific gravity remain constant.
We pointed out above that larger changes in the spe-
cific gravity of the parting liquid can readily be made by di-
luting the fluorochlorocarbon or 1,2-difluoroethane with a light
petroleum fraction or a liquid hydrocarbon. A coal cleaning
- 52 -
10518Z7
system in which the specific gravity of the parting liquid can
be altered in this fashion is illustrated in Figure 3 and
identified by reference character 130.
System 130 is comparable to system 20 in that it
includes a conditioner tank 132; a separator 134; floats and
sinks dryers 136 and 138; a condenser 140 to which recovered
vapors are pumped by compressor 141; a purge unit 142 for re-
covering parting liquid from the dryers, purging it of noncon-
densibles, and condensing it; and a fluorochlorocarbon storage
tank 144 which may be used to contain 1,2-difluoroethane. System
130 also includes a storage tank 146 for the liquid diluent
employed to lower the specific gravity of the fluorochlorocarbon
or 1,2-difluoroethane and a storage tank 148 for the parting
liquid - typically a mixture of trichlorofluoromethane and
petroleum ether.
The operation of this system is generally the same
as that shown in Figure 1. The recovered, condensed parting
liquid, however, can be returned from condenser 140 to the
parting liquid storage tank 148 and/or stripped of nonconden-
sibles in purge unit 142 and circulated to a conventionalfractionation tower 149.
Parting liquid is transferred from tank 148 to
conditioning tank 132 by pump 150 as necessary to maintain
the level of parting liquid in gravity separation tank 134
constant. This level can be automatically maintained by
a modulating valve 152 in the parting liquid supply line 154.
The operation of this valve is regulated by a conventional
level controller 156 having a senser (not shown) in tank 134.
The parting liquid returned to fractionation tower
149 is first passed through an evaporator 157 to insure that
it is in the gas phase. The gases are then separated in the
~ - 53 -
.
1051827
fractionation tower into 1,2-difluoroethane or fluorochloro-
carbon and diluent constituents which, after condensing,
return to tanks 144 and ~
- 53a -
., ,
1051827
146, respectively. Liquid3 are fed from these tanks into
parting liquid suppl~ line 154 as necessary to keep the dcnsity
of the parting liquid constant. Control over this operation is
afforded by modulating valves-158 and 160 in supply lines 162
and 164. The operation of the valves is regulated by a conven-
tional density controller 165 with a senser (not shown) in
gravity separation tank 134.
If the supply of liquids in tanks 144 and 146 runs low,
valve 166 is opened. Liquid is then pumped from tank 148 to
evaporator 157 and fractionation tower 149 to replenish the
supply. Conversely, if the levels in the fluorochlorocarhon
and diluent tanks become too high, valve 167 can be closed and
the 1,2-difluoroethane or fluorochlorocarbon, diluent mixture
returned directly to storage facility 148 from purge unit 142
through line 168.
A third valve, 169, reduces the pressure on the liquid
returned to storage tank 148 through line 170a from that in the
condenser (the discharge pressure of compressor 141) to that in
the storage tank. Line 170b is used to return vapors generated
by the expansion of liquid in valve 169 to the inlet side of
compressor 141.
A typical parting liquid specific gravity that the
system just described might be employed to maintain is 1.3.
This can be generated at ambient temperature and pressure by
mixing 22.2 weight percent petroleum ether with 77.8 percent
trichlorofluoromethane.
As the seasons change, the temperature of the incoming
coal may vary. The variations in the specific gravity of
the parting liquid which this will tend to cause are automatical-
ly compensated for in the system shown in Figure 3. Density
controller 165 will vary the proportions of trichlorofluoromethane
and diluent to offset any tendency of specific gravity to
vary.
- 54 -
`
1~51827
As discussed above, coal cleaning plants in accord
with the principles of the present invention may also be
constructed in a manner which will permit siqnificant amounts
of heat generated in the course of cleaning the coal to be
recovered. One arrangement for accomplishing this goal is shown
in Figure 4 and identified by reference character 171. In this
system, vaporized parting liquid is pumped to a condenser 172 as
described above by compressor 173. Here, it gives up heat to
a cooling liquid circulated through the condenser, increasing
the temperature of the latter and condensing the parting liquid.
The heated cooling water is discharged from condenser
172 at a temperature typically in the range of 95 to 120F.,
which is well above the vaporization temperature of our pre-
ferred trichlorofluoromethane. The heated water is circulated
by pump 174 through conduit system 176 to floats and sinks
dryers 178 and 180 and then through conduit system 182 back to
the condenser, thereby supplying heat required to operate the
dryers. This further reduces the already modest cost of clean-
ing coal in accord with the principles of the present invention.
In some applications, the water discharged from
condenser 172 may contain more heat than is needed for the
operation of dryers 178 and 180. A three-way modulating valve
184 controlled by a thermostat 186 is therefore preferably
interposed between pump 174 and dryers 178 and 180. This
valve automatically diverts water as necessary to cooling
tower 188 where its temperature is reduced. The cool water is
piped through conduit 190 and mixed with the water recirculated
to condenser 172 from the dryers.
Alternatively, or in addition, the excess hot water
can simply be discharged from the system into a sewer, etc.
- 55 -
10518;27
as shown by line 192 and replaced by cooler makeup water a~
shown by arrow 194.
Figure 5 illustrates a heat conservation arrangement
200 which differs from system 171 in that the vaporized parting
liquid recovered from the floats and sinks dryers, gravity
æeparation tank, and conditioning tank (the conditioning tank
and separator are not shown) is employed to operate the dryers.
In system 200, a thermostatically controlled, three-
way valve 202 is interposed between compressor 204 and condenser
206. Vapor recovered from the system components mentioned in
the preceding paragraph flows from this valve to floats and
sinks dryers 208 and 210 through conduits 212 and 214 to
operate the dryers. Vapor in excess of that required to operate
the dryers is automatically diverted to condenser 206 where it
is processed as described above.
Parting liquid condensed in the dryers returns to the
storage facility through conduits identified generally by
reference character 216. Noncondensibles and vapor flow through
conduits identified collectively by reference character 218 to
condenser 206 where the parting liquid is condensed and returned
to storage. Noncondensibles and any remaining uncondensed parting
liquid flow to a purge unit (not shown) such as that identified
by reference character 82 in Figure 1. Here, additional part-
ing liquid is recovered and returned to storage. Noncondensi-
bles are recirculated to the dryers 208 and 210 as a stripping
gas or rejected from the system.
The system just described has the virtue of reducing
the capacity of condenser 206 with a concomitant decrease in
capital investment and in the cost of operating the coal
cleaning plant.
- 56 -
10518Z7
As shown in the drawing, plants 171 and 200 are both
preferably equipped with a second, independent heat source such
as the boiler 48 and circulation system 59, 60 illustrated in
Figure 1. This system is used during start-up of the plant when
required and, if necessary, to augment the heat supplied to the
floats and sinks dryers 178 and 180 or 208 and 210 by the heated
fluid in piant 171 or the vaporized parting`liquid in plant 200.
One system for drying the coal and the rejects and
recovering the vaporized parting liquid associated with the solids
is illustrated in Figure 1 and was described above. A second
system for accomplishing these objectives is illustrated in
Figure 6 and identified by reference character 220.
In this system the drip dried but vapor saturated coal
or refuse is fed into one end of a purge tube or vessel 222
through which it is conveyed as with auger type conveyor 224.
As the material moves through purge tube 222, the vaporized
parting liquid is stripped from it by gases introduced at the
discharge end of the purge tube. These gases are circulated
through the purge tube in countercurrent relationship to the
movement of the solids by compressor 226 and exit from the feed
end of the purge tube.
Entrained solids are removed from the vapor laden
gases exiting from the purge tube by a filter 228. The pressure
on the mixture is then increased by compressor 226 to a level
at which the parting liquid can be economically condensed; and
the mixture is circulated to condenser 230, which may be of the
i character described above. The parting liquid vapor is condens-
ed and the liquid returned to storage.
Heat rejected from the condenser may be recovered
as discussed above in conjunction with the systems 171 and 200
shown in Figures 4 and 5.
- 57 -
1051827
The noncondensible gases rejected from the condenser
are recirculated to purge tube 222 for use as a stripping gas.
As shown in Figure 6, they may first, however, be compressed
to a higher pressure and circulated through a second condenser
to recover additional parting liquid (the secondary compressor
and condenser are identified collectively by reference character
232).
In addition, or optionally, outside air can be intro-
duced into the discharge end of purge tube 222 to strip vapors
from the solids therein as indicated by arrow 234.
Other vapor recovered from the coal cleaning plant
can also be stripped of noncondensibles recovered in system 220.
The gases are introduced into the parting liquid recovery system
at the location indicated by arrow 236.
The components of a parting liquid recovery system
of the character just described do not necessarily have to be as
shown in Figure 6. For example, a belt conveyor could be sub-
stituted for the illustrated screw conveyor. A vertical purge
tube could be employed and the conveyor eliminated, the solids
travelling down the purge tube by gravity. Still other modifi-
cations will suggest themselves to those conversant with the
relevant arts.
In yet another variation of the illustrated system,
the gases and vapors are evacuated by drawing a vacuum in the
purge tube. The parting liquid is then recovered and the
noncondensible gases utilized as discussed above or rejected to
the ambient surroundings as they also can be in the illustrated
system.
While the system for recovering the parting liquid
described in the preceding paragraph is somewhat complicated
- 58 -
~0518'~7
and cumb~rso~e because of the locks, etc. needed to maintdirl a
subatmospheric pressure in the purge vessel, it is also eff;cient.
For example, a typical coal contains 42.76 percent by volume
voids. At 75F., this coal contains 6.28 pounds of trichloro-
fluoromethane per ton. By reducing the pressure on the dried
coal to 29 inches of Hg below atmospheric and recovering the
gases generated in doing so, all but 0.24 pounds per ton of the
parting liquid can be recovered.
We have also discovered that the natural affinity
which 1,2-difluoroethane and the fluorochlorocarbons we employ
possess for oils can be taken advantage of in recovering vapor-
ized parting liquid. The vapor is contacted with oil, which
absorbs the vaporized parting liquid but not the noncondensibles,
which can be used as a stripping gas or rejected. The oil is
then heated to release the parting liquid which is condensed
and recycled. This approach is both more effective and more
economical than the previously described mechanical compression
and condensation when the ratio of noncondensible gases to part-
ing liquid vapor is high.
An exemplary system for recovering parting liquid by
the technique just discussed is illustrated in Figure 7 and
identified by reference character 240.
In this system, the vaporized parting liquid is strip-
ped from the coal or refuse in purge tube 242, compressed, and
pumped into the lower end of vertical tower 244 by compressor
246. Number 2 fuel oil or other absorbent liquid is sprayed
into the upper end of tower 244 through nozzles 248 and travels
downwardly through the tower in countercurrent relationship to
the upwardly flowing gases. The absorption medium scrubs or
strips the parting liquid vapors from the noncondensible gases,
the vapor rich oil collecting in a sump 250 at the bottom of
., . . ~
- 59 -
518Z7
tower 244. Noncondensible gases pass through a separator 251,
which removes entrained liquid and vapors; exit from the upper
end of the tower; and recirculate to purge tube 242.
The parting liquid is recovered by pumping the
1,2-difluoroethane or fluorochlorocarbon rich oil from sump 250
through a heater or heat exchanger 252 with pump 254. The
parting liquid vapor released from the oil in heater 252 is
condensed as described previously (the condenser is not shown)
and recirculated to the coal cleaning process or returned to
storage.
The stripped absorption medium is cooled in a heat
exchanger 256 to increase its absorption capacity and recircu-
lated through tower 244.
The heaters or heat exchangers 252 and 256 may be
of the shell and tube type although it is not essential that
this particular kind of device be used.
As shown in Figure 7, oil pumped from sump 250 may
be diverted into line 258 and sprayed into tower 244 through
nozzles 260. This increases the concentration of parting liquid
in the oil collecting in sump 250, reducing the thermal loads
on heat exchangers 252 and 256.
System 240 is also designed to recover parting liquid
vapors from mixtures collected from other components of the coal
cleaning plant such as the conditioner, gravity separator, and
dryers. Gases and vapors from these components are circulated
through a filter 262, compressed, and circulated to a condenser
264 by a compressor 266. The parting liquid is condensed in
condenser 264 and recirculated or returned to storage. The
noncondensible gases rejected from the condenser are combined
with those recovered from purge unit 242 on the discharge side
of compressor 246 and thereby recirculated to tower 244 to
recover additional parting liquid.
-60-
~05~8Z7
As shown in Figure 7, an economizer 268 can be inter-
posed between pump 254 and heater 252. Pump 269 circulates
water or other heat exchange liquid from cooler 256 through the
economizer. Sensible heat extracted from the oil in cooler 256
by the heat exchange liquid is given up to the parting liquid
rich oil flowing to heater 252, thereby conserving energy by
reducing the load on the heater.
Also, compressor 246 may be eliminated; and the gases
from purge tube 242 may be delivered through duct 270 to the
inlet of filter 262.
In some applications a combination of the systems 220
and 240 just discussed can be used to optimize the recovery of
the parting liquid. Mechanical compression and condensation
are employed to recover the parting liquid from the vapor rich
gases, and the parting liquid is recovered from the leaner gases
by the absorption technique.
It is also to be understood that the purge tubes
employed in the systems of Figures 6 and 7 can be used as dryers
in the systems described above and hereinafter. Or, what is
referred to in the description of such systems as a dryer may
constitute one or more purge tubes and other drying equipment
arranged in the order deemed most suitable for a particular
application.
As discussed briefly above, coal cleaning apparatus
of the character described in conjunction with Figures 1-7 can
be integrated into a novel system for handling and processing
coal in which the parting liquid is also employed to convey
the coal and ash generated in its combustion. One integrated
coal handling system of this character is illustrated in Figure
8 and identified by reference character 271.
- 61 -
10518Z7
In this sys~em, coal is s~parat~d from mine face 272
as by a continuous miner or auger 274 such as a Badger Manu-
facturing Company Coal Badger or a Salem Tool Company MC MUL-T,
for example. From the miner the coal and gangue flows to an
optional crusher 276, where the mined coal is reduced to a typi-
cal top size of in the range of 1.5 inches, and then to a slurry
pump 278, where it is mixed with 1,2-difluoroethane or one of the
fluorochlorocarbons descri~ed above. As shown in Figure 8, the
miner, crusher, and slurry pump can conveniently be mounted on
a single chasis 280.
The liquid content of the foregoing and other slurries
formed in accord with the principles of the present invention
will vary from application-to-application. This phase will,
however, constitute from 40 to 99 weight percent based on the
total weight of the slurry~
Slurry pump 278 transfers the coal and 1,2-difluoro-
ethane or fluorochlorocarbon mixture to a primary cleaning
station 282 of the character described above in conjunction with
Figures 1-6 and preferably located in the mine. The dried re-
jects from the cleaning operation, typically first coated with
a dust suppressant, are conveyed to and dumped in a mined-out
area of the mine as indicated by arrow 284.
The floats generated in the primary cleaning station
~coal plus foreign material not removed in the primary cleaning
step) and parting liquid from the primary cleaning station form
a slurry which is pumped by slurry pump 286 to a final cleaning
plant 288 located on the surface.
The initial unit 290 of the final cleaning station,
shown in Figure 9, will typically include a second crusher for
reducing the solids in the slurry to the size consist specified
by the consumer or to a size which will free additional
- 62 -
105182~
pyrites and/or other foreiyn material. Unit 29~ will in general
also include a conditioning tank such as that shown in Figure 1
so that additives and parting liquid can be blended with the
.
slurry, the temperature of the coal adjusted, etc.
From this unit, the slurry is transferred as by screw
conveyor 292 to a gravity separator 294 also as described above.
The sinks from the gravity separator are transferred to a
dryer 296 where the 1,2-difluoroethane or fluorochlorocarbon
parting and carrier liquid is separated by adding heat to the
slurry to evaporate the liquid and by purging the 1,2-difluoro-
ethane or solids to recover the fluorochlorocarbon from the
pores of the solids. Also, as discussed above, the sinks may
first be drip dried to reduce the energy required to remove
the fluorochlorocarbon or 1,2-difluoroethane by evaporation.
Suitable equipment for these functions is that discussed above
and illustrated in Figures 1, 6, and 7, for example.
The dried rejects, first optionally coated to inhibit
oxidation and the generation of acidic ground water, are convey-
ed to a gob pile or other disposal area. The vaporized parting
liquid recovered from dryer 296, together with that from unit
290 and gravity separation tank 294, flows to compressor 298.
Compressor 298 pumps the vapor to a unit 300 typically consist-
ing of a condenser and purge unit as discussed above.
The noncondensibles are separated from the parting
liquid vapor in unit 300. As in the embodiments of the inven-
tion discussed above, they can be recirculated and used as a
stripping gas in sinks dryer 296. Alternatively, or in
addition, they can first be processed through an absorber or
other conventional device 301 to separate and recover
commercially valuable products such as methane removed from
the mine face, etc.
.~
- 63 -
1051827
The condensed parting liquid is circulated through
conduits identified generally by reference characters 302, 304,
and 306 to slurry pump 278 and to mine face 272. The latter
liquid alone, or with such additives as may be desired, is
sprayed onto the mine face as through nozzles 308. This
suppresses dust generated at the mine face, reducing the
explosion hazard. The liquid also reduces cutter wear and the
power needed to operate continuous miner 274.
In a typical application the clean coal from gravity
separator 294 is pumped in slurry with the parting liquid to
a storage tank 310 by slurry pump 312. The slurry is typically
stored at ambient temperature and pressure.
On demand, the slurry is withdrawn from storage tank
310 and transferred to a final preparation station 313. This
station includes a floats dryer and a parting liquid recovery
unit as described above for recovering the fluorochlorocarbon
--- or 1,2-difluoroethane carrier liquid used in the transport of the
coal and for recirculating the noncondensibles to the dryer
and/or recovering certain of the gases. Also, the final
preparation unit may include one or more units for further
treating the coal. For example, quicklime or calcined dolomite
can be blended with the coal at this station to, as discussed
above, decrease the sulfur content of the combustion products
generated when the coal is burned.
The amount of quicklime or dolomite added to the coal
will of course depend upon a number of factors including the
sulfur content of the coal, the conditions under which it is
burned, etc.
In a typical application 90 pounds per ton of 200m
x 0 calcined dolomite is intimately dispersed on Pittsburgh
- 64 -
,.. .
~ , ~,
~0518Z7
coal using trichlorofluoromethane as the carrier. The efficiency
of the reaction between the calcium and magnesium oxides and
the sulfur in the coal during the subsequent burning of the coal
is ca. 80 percent. This reduces the sulfur content of the
combustion gases from the three percent level of untreated coal
to a level of 0.6 percent. The latter level is well within
Environmental Protection Agency limits.
The reduction in sulfur content is also well below
that which can be achieved by adding the same materials to coal
in the conventional manner; viz., dry mixing. This technique
is capable of only imperfectly distributing the additive, making
the efficiency of the subsequent oxide, sulfur reaction much
lower than it is when the additive is distributed by our novel
process.
Our novel process for reducing combustion gas sulfur
content is also superior to more conventional techniques for
accomplishing the same goal such as scrubbing the combustion
products. Treating the coal in the exemplary application describ-
ed above by our process costs ca. $1.13 per ton. To accomplish
similar results by scrubbing would cost $3-4 per ton of coal
burned.
Referring again to Figure 8, in the exemplary illustrat-
ed system the coal is transferred from final preparation station
313 to a boiler 314 typically equipped with a precipitator 316
to recover fly ash generated in the combustion of the coal.
The ash generated in boiler 314 and in precipitator
316, respectively, is quenched in units 318 and 320 to reduce
its temperature to on the order of 100F. Liquid recovered
in final preparatlon unit 313 is circulated to the discharge
sides of the quench units by pump 322 and mixed with the ash
to form a slurry. This slurry is pun~ped to the sinks (ash)
i
1051~27
dryer and purge unit 296 of final cleaning plant 28~ through
a conduit system indicated generally by reference character
324. The ash can accordingly be dried and disposed ol with the
re~ects from the final cleaning process.
One important advantage of the novel system 271 just
described is that as much as 10 to 30 percent of the- mined
solids may not have to be conveyed to the surface, resulting in
a significant cost savings. Also, because the rejects from the
final cleaning station typically constitute only 12 to 50
percent of the mined material, the aboveground cost of disposing
of rejects can also be lowered.
Furthermore, the system is highly versatile. As
discussed previously, it can with only readily made modifications
be used to furnish the feed for a coal gasification plant,
coking operation, etc. Also, final cleaning plant 288, storage
tank 310, and final preparation plant 313 are sources o~ clean
coal for shipment to other locations. That is, the user need
not be located at the mine as in the illustrated system.
In addition, as previously mentioned, the system
can c~ntain and collect gases such as methane released during
mining of the coal. It can similarly accommodate gases generated
or released during cleaning, transportation, or storage of
the coal and/or handling of the ash.
As discussed above, one aspect of our invention has
to do with the blending of additives with coal and other solids.
Many mechanical arrangements can be employed for this purpose.
In general all that is required is an agitator in a vessel to
which the solids, the additive, and the 1,2-difluoroethane or
fluorochlorocarbon liquid carrier can be supplied or a con-
ventional screw conveyor, rotary mixer, pug mill, etc.
In this rudimentary system the solids, additives, and- 66 -
10518Z7carrier are mix~d until the additiv~ is unifor~ly d;sp~rse~.
The carrier is then evaporated into the ambient surrour,dings,
a step which can be accelerated by supplying heat to the vessel.
Figure 10 depicts a more sophisticated system 330.
This system provides for recovery of the 1,2-difluoroethane or
fluorochlorocarbon and can be readily incorporated into coal
cleaning plants as described above and integrated systems as
shown in Figures 8 and 9.
In system 330 distribution of the additive is accom-
plished in a unit 332 which, as described above, may be an agi-
tator equipped vessel, screw conveyor, etc. If system 330 is
associated with a coal cleaning plant or integrated system, the
floats dryer can be bypassed and the drip dried floats transfer-
red directly from the gravity separation operation to unit 332
as indicated by arrow 334. The 1,2-difluoroethane or fluoro-
chlorocarbon carrier and additive are added directly to the unit
as indicated by arrows 336 and 338. Alternatively, as shown by
arrow 340, the additive and liquid can be premixed and then
supplied to unit 332 as indicated by arrow 336.
The blended product is transferred as indicated by
arrow 342 to a dryer of the character discussed above to remove
the carrier liquid. This liquid is then recovered by any of the
techniques described herein and recirculated, and the nonconden-
sibles stripped from the carrier are rejected or recirculated
to the dryer.
The additive can also be added to the conditioning
tank or even the gravity separator in those applications of our
invention involving a coal cleaning step. Dust suppressants,
oxidation inhibitors, and other additives can conveniently be
added to the clean coal and/or the rejects by this technique.
Referring again to the drawing, we have described
hereinafter a variety of tests successfully conducted on a pilot
- 67 -
lOS18Z7
plant scale. Tlle plant irl whicl~ se t~sts were sn~de is ~ho~n
diagr~mmatically in FLCJUre 11 and identified by reference
character 350.
The pilot plant includes a storage tank 352 for the
parting liquid. The tank can be connected to the inlet side of
pump 354 by opening valves 356 and 358. With valves 359 and
360 also open and valve 362 closed, pump 35~ pumps the liquid
through a filter 364 into a 24 inch diameter by 6 foot 7Ong
gravity separation vessel 366 until the vessel is filled to the
level indicated by reference character 368. A valve 369 is
opened while tank 366 is filled to equalize the pressure in
storage tank 352 with that elsewhere in the system so that a
vacuum will not be drawn in the tank.
After tank 366 is filled, valves 358, 359, and 360 are
closed; and valve 362 is opened. This valve drains a second,
similarly oriented and dimensioned vessel 370 in which clean
coal is first drip dried and then dried with a heated gas.
If the coal is conditioned prior to the separation
step, 1,2-difluoroethane or fluorochlorocarbon parting liquid
or the liquid plus a surface active agent and any other addi-
tives are mixed with the coal by hand in a drum. The coal,
conditioned or not, is p-aced in a hopper 371 and transferred
through a valve 372 into a hand-cranked screw conveyor 374. The
screw conveyor discharges the coal into the bath 376 of parting
liquid.
As the separation of the coal and rejects proceeds,
the floats are skimmed from the body 376 of parting llquid and
transferred to drying vessel 370 by a motor driven screw
conveyor 380.
Valves 362, 382, 383, and 356 are open, and pump 354
is energized as this occurs. The parting liquid draining from
., ,~ . .
, ~'.
.. . . .
- 68 -
~051827
vessel 370 is acc~rd ngly pumped tllrough -filter 38~ ~ck i lltO
storage tank 352. ~t the end o~ the separation st~p thg drain
valve 360 from g~avit~ separation vessel 366 is also opened
and the liquid in it drained and pumped through filter 364 to
storage tank 3S2.
The solids in tan~s 366 (sinks~ and 370 (floats) are
trapped on 140 mesh screens 385 and 386 in the bottoms of tanks
366 and 370, respectively. Filters 364 and 384 trap three micron
and larger particles which pass through the screens.
Valves 387 and 388 are open throughout the coal
separation process. Saturated parting liquid vapor flows through
these valves to a shell and tube condenser 390 and is condensed,
using water as a cooling liquid. The condensed liquid is pumped
to storage tank 352 through valves 392 and 356 by pump 354.
After the parting liquid has drained from tanks
366 and 370, a Roots blower 394 is energized; and hot water
tca. 140F) is circulated through the shell side of a shell
and tube type heat exchanser 396. Parting liquid vapor is
first circulated through the tube side of heat exchanger
396 by the blower to superheat it and then through filters
364 and 384 and through the solids in tanks 366 and 370 to
dry the solids trapped on screens 385 and 386 and on the
filters.
Noncondensibles and any vapor which is not condensed
in condenser 390 are compressed by a diaphragm compressor 398
and pumped to a pipeline condenser 400. Here, the remaining par-
ting liquid is condensed. The noncondensibles are rejected to
the surrounding environment through a valve 402 provided to main-
tain pressure in the system. The condensate flows through a float
- 69 -
10518Z7
valve 404, provided for the same purpose, and is returned to
storage tank 352.
After the solids have been dried the bottoms of tanks
or vessels 366 and 370 are opened and screens 385 and 386
removed, discharging the coal and rejects into separate
receptacles (not shown). Filters 384 and 364 are removed. The
coal trapped on filter 384 is combined with the coal from drip
dry tank 370, and the rejects trapped on filter 364 are combined
with those from gravity separation vessel 366. The solids are
weighed and subjected to proximate analyses, etc. in accord with
the test procedures set forth below.
Pilot plant 350 also demonstrates that coal can be
readily transported in a slurry as discussed above. The coal is
moved in this manner from separator 366 to drip dry tank 370.
The examples which follow describe representative
tests which illustrate various facets of our novel coal cleaning
and other processes.
For the sake of convenience the bulk of these tests
were made on a bench scale basis.
In the bench tests a raw coal sample is quartered
as prescribed by ASTM Standard No. D2013-72 into two or more
kilogram lots. One lot is employed to characterize the raw
coal as to size consist and bulk water content and for a
complete proximate analysis which furnishes a standard for
comparison.
The samples are stored in airtight containers until
tested.
At the time of the bench test, the coal is, in some
cases, first mixed with the parting liquid or the latter plus
- 70 -
; :~
105~8~7 ;
a surface active agent for 2-30 seconds to form a slurry contain-
ing 5~-80 percent solids.
Separation is effected in one liter of the selected
parting liquid in a six-inch diameter container at room tempera-
ture t65-72oF.). The coal is transferred to the container in
batches of 25-50 grams and briefly stirred.
The clean coal and the rejects are recovered separate-
ly from the parting liquid which is then filtered to recover any
middlings which may be present (the "middlings" are those
fragments which do not report to the sinks or the floats usually
because they are very small in size and of almost the same
specific gravity as the parting liquid).
The three phases are separately air dried. A material
balance is made, and proximate analyses are made of the coal or
the coal and the middlings.
If the water content of the coal is desired, that
phase is not dried. It is instead placed in a flask and heated
at a temperature of 30C. until the parting liquid is completely
evaporated. The sample is then weighed, heated at 100C. in a
vacuum oven until the free water evaporates, and reweighed.
The difference is the weight of the water content.
Variations in the basis bench test procedure just
described will be discussed in the examples in which they
are introduced.
To more nearly duplicate a commercial operation,
tests are also run in the pilot plant 350 described above.
Samples of up to about 1,000 pounds are employed; and the
cleaning rate is six-eight tons per hour.
Any surface active agents which are to be employed
are first mixed with the parting Iiquid. The coal is then
- 71 -
- 1051827
added on an approximately equal weight basis, forming a stiff,
moist mixture. This mixture is batched into the pilot plant
feed hopper 371 described above.
Dried coal recovered from the pilot plant is quartered
in accord with ASTM Standard D2013-72, providing samples for
proximate and other analyses.
The tables which are included in the examples are
for the most part self-explanatory. However, the significance
of two entries may not be readily apparent. These are "BTU
Yield" and "percent reduction per million BTU's".
BTU Yield is determined by the formula:
BTU/lb of clean coal x Weight Yield in percent
BTU/lb of run-of-mine coal
BTU Yield shows what percent of a run-of-mine coal's heating
value can be sold at the analysis constituted by the figures
in a given column in the tables which follow.
Taken with the figures indicative of reduction in
sulfur and ash content and the amount of coal reporting to the
sinks,BTU Yield is indicative of the effectiveness of the coal
cleaning process.
If the BTU Yield is low, the other figures will
show whether this is attributable to the removal of pyritic
sulfur and/or dissolved organic material to the refuse
(desirable) or whether the coal is being misplaced to the rejects
(undesirable).
Conversely, if the BTU Yield is high, the sulfur
and ash reduction figures will show whether this is
attributable to the lack of pyrites and/or dissolved organic
material in the rejects or to the efficiency of the operation
in separating foreign matter from the raw coal.
- 72 -
.
10S18;~7
In both cases the BTV Yield is valuable because it
is a direct indicator of the per BTU cost of mining and recover-
ing the coa~. Coupled with sulfur and ash reduction, it is also
indicative of the cost of handling refuse from the combustion
process and of maintaining the sulfur level in the combustion
products at an acceptable level.
.
Percent reduction per million BTUs can be calculated
~or ash and for total, pyritic, and organic sulfur. The figure
` is calculated by the formula:
1 _ Y lbs/106 BTU in clean coal I x 100
z lbs/106 BTU in raw coal
where y is pounds of ash, sulfur, etc. in the clean coal
and z is the same for the raw or uncleaned coal. Percent
- reduction /106 BTU is a significant value because it relates
ash and sulfur content to product BTU; and BTUs or fixed
..
carbon, not-pounds, are what is of value to the customer.
In the results reported in the examples all percent-
ages are by weight unless otherwise indicated. All qua~titative
res~lts are reported on a moisture-free basis.
20~ Complete proximate analyses are not made in all cases,
and this is reflected in the data tabulated in the examples.
Such analyses are expensive and time consuming; and it is not
necessary to make a complete analysis of the coal from each
and every run because reduction in ash content, standing alone,
is a good measure of the efficiency of a coal cleaning process.
- 73 -
- ~OSl~Z7 -
Example I
To demonstrate the effectiveness of our novel process
in its most basic sr elementary form, a bench scale test as
described above was run at a specific gravity of 1.50 on Upper
Freeport coal having a size consist of 3/8 inch x 0 and a
moisture content of 6.5 percent (nominal). The size distribu-
tion of the particles in the sample was as follows:
+ 3/8 inch7.5 percent
3j8 x 5m27.7 percent
5m x lOm21.7 percent
lOm x 30m29.9 percent
30m x 60m10.8 percent
60m x lOOm1.6 percent
- lOOm 1 percent
Trichlorofluoromethane (CC13F) without additives
was used as the parting liquid.
The ash content of the coal was reduced from 35.37
to 13.10 percent in the test, showing that a major part of the
foreign matter had been separated from the coal. More ash could
have been removed by reducing the size of the larger particles.
They were sufficiently large that all of the ash had not been
liberated from the coal itself.
The test is also significant in that the coal which
was used had a moisture content much higher than that which
is acceptable if the coal is to be cleaned by processes such
as described in the Tveter patent identified above.
1~518Z7
Example II
To demonstrate that fluorochlorocarbon parting liquids
other than trichlorofluoromethane can be used, the test describ-
ed in Example I was repeated, using CClF2CClF2 (dichlorotetra-
fluoroethane) as the parting liquid.
In this test the ash content of the product coal was
13.0 percent which is virtually indistinguishable from the
result obtained in the test described in Example I. The weight
yield was a slightly lower 56.6 percent.
The test shows that trichlorofluoromethane is not the
only one of the listed fluorochlorocarbons which can be used
in the gravity separation of the coal from foreign material.
Example III
A test as described in Example I was made to demonstrate
the advantages of adding a surface active agent to the parting
liquid. The results are compared to those obtained by Warner
Laboratories, Inc., Cresson, Pa. in a standard washability
study of the coal in Table 4 below.
The coal was that from the Upper Freeport seam (see
Examples I and II). The parting liquid was trichlorofluoro-
methane, and about two pounds of surface active agent per ton
of coal was employed. The particular surface active agent
selected for the test was Pace Perk. As discussed above this
is an ionic surface active agent which consists pximarily of
salts of dodecylbenzenesulfonic acid. The surface active
agent was mixed with the parting liquid before the coal was
added.
- 75 -
1051~Z7
Table 4
Run-of-mine Washability Present
Coal Study Invention
Volatile Matter % 28.42 34.77
Fixed Carbon % 46.03 59.55
Ash - % 25.55 8.9 5.68
lbs/m BTU 23.5 3.98
% Red'n/m BTU 83
Total Sulfur % 1.46 0.95 0.52
lbs/m BTU 1.34 0.36
% Red'n/m BTU 72.8
Pyritic Sulfur % 1.09 0.16
lbs/m BTU 1.00 0.11
~ Rea'n/m BTU 88.8
Organic Sulfur % 0.35 0.32
lbs/m BTU 0.32 0.22
% Red'n/m BTU 30
BTU/lb 10,891 14,262
BTU/lb (MAF) 14,629 15,121
Weight Yield % 64.9 68.5
BTU Yield % 89.7
Specific Gravity* 1.55 1.51
Moisture (input) 7.1 7.1
Coke Button** 7 8.5
Recovered Coal 2.18
Moisture
m BTU = 106 BTU
Red'n = reduction
MAF = moisture and ash free basis
*of the parting liquid
** The coke button value (or more formally, free swelling index)
is a measure of cokability. FSI values range from 0-10 with
the higher value being ideal. Coals with a FSI of less than
5 are essentially useless as coking coals.
The above notes also apply to the tables which follow.
- 76
105~8~7
A number of significant points are shown by the data
- tabulated above.
The ash content o~ the coal was not only reduced, it
was reduced 36 percent below the leve,l which it theoretically
could be as determined by the standard washability study.
Total sulfur was reduced by 72.8 percent; this was
45 percent better than obtained in the standard washability
study. Pyritic sulfur was almost completely separated from
the coal, and there was a significant reduction in organic
sulfur. As mentioned above, this is a result which no other
- coal cleaning process known to us is capable of achieving.
Furthermore, the cokability of the coal was signifi-
cantly improved.
- - Example IV
To demonstrate that other surface active agents can
be employed and in varying amounts, bench scale coal cleaning
tests were made using Upper Freeport coal with the size consist
and other characteristics described in Example I.
The parting liquid was ~ichlorofluoromethane.
- The surface active agents employed in the tests and
the amounts,used were~
.
:
- 77 -
1051B;Z~
Table 5
Test Surface Active A~ent
A . Aerosol OT-100 tAmerican Cyanamid)
- -- anionic surfactant, dioctyl
- ester of sodium sulfosuccinic
acid; 0.06 pounds per ton of coal
B . Same as in Test A; 0.6 pounds per
ton of coal
C Witcomine 235 (Witco Chemical
Corp.) -- cationic surfactant,
l-polyaminoethyl-2n-alkyl-2-
imidazoline; three pounds per
. ton of coal
D Same as Test C; 0.03 pounds per
. ton of coal
E.............................. Same as Tests A ana B; 0.033
pounds per ton of coal plus
No. 6 fuel oil, 0.67 pounds
. per ton of coal
.
The results of tests A-E are tabulated in Table 6
below.
.
- . ......
.
~i . - 78 -
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105AL~Z7
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105182'7
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- 79a
lOS~18Z7
The data in Table 6 shows that the particular
surface active agent used is not critical, that both anionic
and cationic materials are satisfactory, and that the agent
need not be one which would conventionally be considered a
surfactant.
The tabulated data also shows that the amount of
surface active agent can be varied by as much as two orders
of magnitude (depending upon the particular agent employed?.
The larger amounts in general increase the efficiency of the
cleaning process though not in direct proportion to the amount
used.
Example V
In another test showing that the surface active
agents we employ need not be conventional surfactants, Ohio
No. 9 coal with a 60 mesh x 0 size consist was cleaned using
the bench scale procedure described above.
. ~ , . .
The parting liquid was CC13F plus S percent by
volume No.~4 fuel oil.
The results of the test are shown in Table 7.
- 80 -
, .. .
.... ,1
1051.8Z7
Table 7
Run-of -mine
Coal Test G
Ash % 24_ 82 12 . 61
96 Red'n/m BTU 58.5
Total Sulfur % 6.73 3.76
% Red'n/m BTU 54.2
Pyritic Sulfur % 4 . 34 1. 02
- % Red ' n/m BTU 8 0 . 6
Organic Sulfur % 2 . 31 2 . 68
% Red ' n/m ~STU 5 .1
BTU/~b .- 10,35~ 12,649
Weight Yield ~ 60.5
BTU - Yield . % . - 7 6 . 5
~oisture % - 6 . 5 6 . 0
.....
. - ' '., '. . .
-- 81 --
_ ., ,,, , . , , ,, , . , . . , . . . . . . ... _ . . . . , . . _, ..
1051827
Example VI
It was pointed out above that more efficient
cleaning can in some, if not all, cases be obtained if the
slurry of coal, 1,2-difluroethane or fluorochlorocarbon, and
surface active agent is agitated before the gravity separation of
the coal is effected.
This is shown by a test which duplicated test B,
Example IV except that the slurry of coal and parting liquid
(which contained 60 percent by weight solids) was mechanically
agitated using a blender for two minutes before gravity
separation was effected. The blending action did not reduce the
si~e consist significantly.
The results of this test, identified as "H", are
compared to those obtained in Test B in Table 8 below.
- 82 -
105~827
Table 8
Run-of-mine Test B Test H
Coal
Volatile Matter % 26 . 09 36.01
Fixed Carbon % 37.34 57.73
Ash % 35.57 6.55 6.26
lbs/m BTU 40.1 4. 4
% Red'n/m BTU 88.9
$otal sulfur % 1. 55 0.87
lbs/m BTU 1.70 0.62
% Red ' n/m BTU 63.7
Pyritic Sulfur % 1. 22 0.31
lbs/m BTU 1. 33 0.22
% Red ' n/m BTU 83.5
Organic Sulfur % 0 . 31 0.50
lbs/m BTU 0 . 34 0.35
96 Red ' n/m BTU
BTU/lb 9,128 14,113
BTU/lb (MAF) 14,391 15,056
Weight Yield % 52.3 52.3
BTU Yield % 80 . 9
Specific Gravity . 1. 51 1. 51
- 83 - .
10518Z7
As shown by the tabulated data, agitation of the
coal and parting liquid slurry resulted in a further, significant
reduction in the ash content of the coal without reducing the
weight yield or otherwise adversely effecting the cleaning
process.
Example VII
As indicated above, our novel process has the
capability of cleaning coal of different size consists.
This was demonstrated by repeating the test described
in Example III after having first ground the coal to a size
consist of 60 mesh x 0. The results of the two tests are
compared in $able 9.
- 84 -
Tabl~ 9
10518Z7
Run-of-mine Example III 60 Mesh
Coal Tèst x 0 Coal
Vola~ile Matter 96 28 . 42 34 . 77 36 . 61
Fixed Carbon % 46.03 59.55 57.84
Ash % 25.55 5.68 5.55
lbs/m BTU 23 . 5 3 . 98 3 . 89
% Red'n/m BTU 83 83.4
Total Sulfur % 1.46 0.52 0.73
lbs/m BTU 1. 34 0. 36 0.51
% Red 'n/m BTU 72 . 8 61. 8
Pyritic Sulfur % 1. 09 0 .16 0 .10
lbs/m BTU 1.00 0.11 0.07
% Red ' n/m BTU 8 8 . 8 9 3
Organic Sulfur % 0. 35 0 O 32 . 0. 59
lbs/m BTU Q.32 0.22 0.41
% Red'n/m BTU . 30
BTU/lb 10~ 891 14t 262 14 ~ 253 ~ -- -
BTU,~lb (M~F) . 14, 629 15,:121 15! 091
Weight Yield % 6 8 . S 6 8 . 8
BTU Yield %. 89 . 7 90 . 0
Specific Gravity 1. 51 1. ~1
Moisture (input) 7.1 7.1 7.1
Coke Button . 7 8 . 5 8
Recovered Coal
Moisture 2 .18 2 . 22
-- 85 --
.,. i
10518Z7
The results were nearly the same and probably within
the limits of experimental error. The significant point in
this test is that there was essentially no loss in BTU Yield
even though in one case (Example III) the particle size was
3/8 inch x 0 and in the other 60m x 0.
Example VIII
.
We also pointed out above that the specific gravity
of the 1,2-difluoroethane and fluorochlorocarbons we employ
as parting liquids can be readily adjusted in applications where
this is advantageous. As an example, t-he specific gravity may
be lowered to separate more ash from the coal in applications
where the customer's specifications so dictate.
That the specific gravity of our parting liqulds can
be readily adjusted was demonstrated by a series of bench scale
- tests in which petroleum ~th~r was mixed with trichlorofluoro-
methane in amounts which reduced the specific gravity of the
mixtures to 1.47 and 1.43. These mixtures and trichlorofluoro-
methane alone, all with three pounds of Pace Perk per ton of
coal, were used as parting liquids.
Upper Freeport coal with the size consist described
in Example I was cleaned.
The results are tabulated in Table 10.
- 86 -
1051827
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- 87a -
~051827
The data shows that the percentage of ash reduction
increased as the specific gravity of the parting liquid was
lowered. There was a corresponding beneficial increase in the
percentage of sulfur reduction, and the removal of more ash and
sulfur was accomplished without a sacrifice in BTU yield.
Example IX
Numerous bench scale tests conducted in the manner
described above show that our novel process is useful for
cleaning coals in general as opposed to coal from a particular
seam. Results of various tests involving coal from the Upper
Freeport seam are described in the preceding examples, and
results of exemplary tests involving other coals are tabulated
in Table 11.
Trichlorofluoromethane plus 0.5 volume percent of
Pace Perk was used as a parting liquid in cleaning the
Midwestern (Illinois No. 5) coal, and CC13F was used alone
as a parting liquid to clean the Appalachian (Lower Kittanning)
coal.
- 88 -
- 10518Z7
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-- 89 --
105~8Z7
- The data shows that our process can be employed to
clean coals of widely divergent character. The run-of-mine ash
contents of the coals, for example, vary by a ratio of 2.9:1.
Also, the tabulated data again demonstrates that a fluorochloro-
carbon alone can be used as a parting liquid in our process.
Example X
A bench scale test conducted as described above and
using trichlorofluoromethane plus Aerosol OT-100 (0.3 lbs/ton
coal) as the parting liquid demonstrates that our novel process
is so efficient that it can even be used to separate substantial
amounts of ash and sulfur from the product coal of a modern
hydrobeneficiation plant.
The coal employed was Pittsburgh No. 8 Washing Plant
Product. It was ground to 5 mesh x 0 before it was cleaned.
The results of the test are shown in Table 12.
-- 90 --
Table 12lOS18;Z7
Washing Plant
Product CoalTest Product
Ash % 15.96 7.52
%Red ' n/m BTU 57 . 6
Total Sulfur % 4. 30 3. 8S
%Red'n/m BTU 10.4
Pyritic Sulfur %2 . 70 1. 74
%Red ' n/m BTU 35 . 5
Organic Sulfur % 1. 59 2 .10
%Red ' n/m BTU
BTU/lb 12,375 13,740
Weight Yield % 82 . 6
BTU Yield % 91. 7
Moisture % 6 . 0 6 . 0
-- 91 --
~os~sz7
In this test, the ash and sulfur contents of coal
already cleaned in a modern facility were reduced by values
of 57 and 10 percent with no loss of BTU Yield by cleaning the
coal with our novel process.
~ _ _ _ _ _ __
- 92 -
H
10518Z7
Example XI
In an even more demanding test than that described
in Example X, slurry pond coal was cleaned by our process.
~eretofore1 there has not been any way to recover coal from
slurry ponds because of the small size of the particles and
the high moisture content.
The size consist of the coal in the slurry pond
was 85 percent less than 200 mesh and 67 percent less than
325 mesh.
Trichlorofluoromethane with approximately one
pound of Aerosol OT-100 per ton of coal was used as the
parting liquid.
In Table 13 below we have compared the raw slurry
pond coal and the product coals obtained by cleaning that coal
at input bed moistures of eight and 14 percent.
- 93 -
Table 13
1~51827
T~st Product Test Product
Raw Slurry Coal - 8% Coal - 14%
Pond Coal Moisture Input Moisture Input
Volatile Matter ~ 22.60 28.01 27.43
Fixed Carbon % 47.75 66.71 66.24
r Ash % 29.65 5.28 6.33
lbs/m BTU .29.1 3.64 4.43
~ Red'n/m BTU 87.5 -84.8
Total Sulfur % 0.85 0.81 0.80
lbs/m BTU 0.83 0.56 . 0.56
% Red'n/m BTU 32.5 32.5
Pyritic Sulfur ~ 0.41 0.19 0.16
lbsJm BTU 0.40 0.13 0.11
% Redln/m BTU . 6 7 . 5 72.5
Organic Sulfur % 0.39 0.56 0.58
lbs/m BTU 0.38 0.39 0.41
% ~ed'n/m BTU
BTU/lb 10,189 14,520 14,297
BTU/lb (MAF) 14,483 15,329 15,263
Weight Yield % 37.1 - 37.3
BTU Yield % 53 - 5Z.3
Specific Gravity % 1.50 1.50
Raw Coal % . 8 14
tInput Moisture)
Product Coal % 4.24 4.3
~Moisture)
Coke Button 1 9 9
- - 94 -
, ~., .
~ . ~ , .
.
1051827
The recovered coal is higllly marketa~le.
The cost of recovering and cleaning slurry pond coal
as employed Ln the just described test is, conservatively
calculated, $3.00 per input ton. On the other hand, the current
F.O.B. market price for the product is at least $25.00 to S35.00
- per ton, which shows that this application of our process is one
of considerable economic importance.
This test is also significant because of the large
amount of water that reported to the sinks in the cleaning process.
As shown in Table 13, this results in a reduction of water
content from 14 to 4.3 percent. That is, without any additional
steps, over two-thirds of the initially present water was
removed from ~he coal. - - ~
That this large proportion of the water can be caused -
to report to the sinks is attributable to the novel 1,2-difluoro-
ethane or fluorochlorocarbon and additive systems we employ as
- parting liquids. Because the parting liquids are essentially
chemically inert under the process conditions, we can mix ~ith
~hem a surface active agent which will disrupt the water films
on the surfaces of the coal particles and remove the water to the
sinks.
This is opposite to what has heretofore been aone in
coal cleaning processes such as described in the Foulke et al
patents identified above. Those processes employ parting
liquids which, because of their chemical reactivity and!or
high boiling points, can not be recovered in amounts which make
the process practical if they are allowed to directly contact
the coal. Therefore, these processes use surfactants of a
character which, instead of disrupting the water films on the
coal particles, stabilize these films so they will isolate the
coal particles from the parting liquid. No water is removed
r
~ ~ .;
, .. . . , . _ . , .. .. . _ _,
~OS18Z7
from the 'coal by these processes, and additional processing may
be necessary to reduce the moisture content of the product to an
acceptable,level.
~xample XI I
- The following tests are representative of m~ny which
show that the results described and discussed in the preceaing
examples are equally attainable when coal is cleaned by our
process on a much larger scale.
' The tests were conducted in the pilot plant i71ustrated
, 10 in'Figure 11 using the pilot plant test procedure described
above.
'' The coal was that described in Example I. Trichloro-
fluoromethane with one pound of Aerosol OT-100 per ton of coal
, was used as the parting liquid.
, The test results are reported in Table 15.
They are compared with the results obtained in the 1.51 specific
gravity parting liquid test described in Example VIII.- The
latter was a bench scale test, but otherwise the same.
- Throughputs in the range of six tons per hour were
employed. Six hundred and ten pounds of coal were cleaned
in the first test and 582 pounds in the second test.
.
.
, .
- 96 -
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'
p
~ m ~ ~ d
U
,S2 R ~
~ .q P~ ~ ~ ~ u
h ~ E~, ''I D
o a~ m :~ m u~
,; - ~
, .
- 97a -
- 1~51~327
The data shows that the results of the two pilot
plant runs were consistent and, if anything, superior to those
obtained in the bench scale tests although the differences
may be within the level of experimental error.
- Tests on other coals produced similar results. Those
obtained in cleaning Lower Kittanning coal ana the hydrobeneficia-
t;on plant product (Example X) are typical.
The coal and parting liquids were as described in
Example X except that the hydrobeneficiation product had a
size consist of S mesh x 0, and the Lower Rittanning coal haa a
size consist of 3/8 inch x O rather than 30 mesh x O as in the
~ench scale test.
Results of the tests appear in Table 15.
.
.
....
,Ik
~ - 98 -
1051B27
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E.,
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H
p
a)
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X O o ~ Ln ~ o _I
W
.
U~
E~
O ~ ~
to o _I ~1
n o _I co ~1 u~
~o o o~r ~r 117
u). ~r ~1 _I u, co
~a
a~
~n
a
E-l
o o ~r o In
~' o . .
_-- ~ o o ~ ~ U~ ~ ~ ~1
o
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O _I ~r co
~ o o
dP ~ dP
S~ D -,1
O ~ O
~,~ ~ ~ Q Q ~ r~ ~
~d ~ ~ ~ ~ ~ U
b) ~1 ~ D ::~ rl D
o m m m u~
- 98a -
~0518Z7
Table 15
Hydrobeneficiation
- . Lower Kittanning Product Coal
Bench Pilot Bench Pilot
Scale Plant Scale Plant
Ash % 9063 10.73 7.52 6.08
%Red'n/m BTU 70;8 67.4 57.6 64.0
Total Sulfur % .73 .77 3.85 . 3.53
. g6Red'n/m BTIJ 60.2 57.9 10.4 29.4
Pyritic Sulfur % .25 _25 1.74 - 1.49
%Red'n/m BTU 81.0 81.0 35.5 51 0
Organic Sulfur % .46 .50 2.10 ~.02
%Red'n/m BTU 6_0 -
BT~/Lb 13,595 13,53513,740 13,964
Weight Yield 67.9 70.5 82.6 80
BTU Yiela 85.0 - 88.0 91.7 89.5
Moistore %5.0 5.0 ~ 6.0 6.0
-
.
H
99
10518Z7
Table 15 shows that the results of the pilot plant
and bench scale tests involving the cleaning of Lower Kittanning
and hydrobeneficiated coals were very much alike. Again, the
pilot plant was slightly superior to the bench apparatus.
Example XIII
It was pointed out above that our invention includes
a novel process for uniformly dispersing additives on coal and
that one application of this process is the dustproofing of
coal.
A goal in dustproofing coal is to agglomerate the
smaller particles into larger ones, thereby making the product
easier to handle, less subject to attrition in storage, etc.
To illustrate how coal can be dedusted in accord with
the principles of the present invention, No. 6 fuel oil was
dissolved in trichlorofluoromethane with stirring at room
temperature in a ratio of one part of fuel oil to 250 parts of
fluorochlorocarbon.
The liquid was mixed with coal which was ground to
a 30 mesh x 0 size consist in amounts providing approximately
two pounds of fuel oil per ton of coal.
The coal was first drip dried, and the remaining
fluorochlorocarbon was then removed by evaporation.
The size consists of the treated and untreated coals
are compared in Table 16.
In the table which follows, the numerical entries
are the weight percent of the sample which passed through a
sieve of the mesh size indicated on the same horizontal line
as the numerical entry.
-- 100 --
- 1051~327
Table 16
Sieve Mesh Size Untreated Treated
.
30 x 0 98.5 96.6
60 x 0 71.7 58.0
100 x 0 53.4 25.9
200 x 0 ' ' 36.1 4.7
The tabulated data shows that the treatment effectively
reduced the proportion of small particles. Furthermore, the
aedustea particles that did pass the finer mesh sieves had a
marked tendency to agglomerate and to support an angle of
repose exceeding 90~
.
Example XIV-
As discussed above, another application of our
novel coating and additive dispersing process is the waterproof-
- ing of coal to keep it from spontaneously igniting following
the absorption of water and/or to keep the lumps or particles
fro~ freezing together under low temperature conditions.
The effectiveness of our process in waterproofing
coal is demonstrated by a test in which a kilogram of a Wyoming
coal with a size consist of 3/4 inch x 0 and an inherent
moisture content of thirty percent was completely dried in
a vacuum oven at 105C. The coal was divided into two samples,
and one was immediately transferred to a gas ight container.
The secona sample was with equal alacrity immersed
in a mixture of 97 percent by volume trichlorofluoromethane
and 3 percent by volume No. 6 fuel oil. The mixture was
stirrea for 0.5 minute to promote intimate contact between
the coal and the mixture of carrier and waterproofing agent.
~?~ - 101 -
lOSl~Z7
The coal was then extracted from the bath ana the
trichlorofluoromethane removea by evaporation.
Both the treated and untreatea samples were immersed
in deionized water undex ambient conditions. One hour later the
water was removed by shaking the samples of coal on a screen.
The water recovered from the coal was compared to the~
amount present a~ the beginning of the test, the difference
~eing water absorbed on and adsorbed by the coal.
The untreated coal acquired a 50 percent moisture
content almost instantaneously and equiliberated through air
drying to a 30 percent moisture content. In contrast, the shake
aried, treated sample had a moisture content of only twenty
percent after the one hour submersion.
When air dried to the same extent as the first sample,
i.e., to 30 percent moisture, the treated sample had only
l.S percen~ absorbed moisture as determined by vacuum oven
drying at 105C. This indicated that the porous structure
of the coal had, indeed, been inhibited from carrying moisture.
The level was well below the limit of 5 percent needed to
insure against spontaneous combustion and freezing of the
coal into a mass.
Exa~ple XV
Another previously discussed aspect of our invention
is the conversion of coal particles into briquettes and similar
artifacts which facilitate transportation, reduce storage
losses, and permit proper gas flow through the system in applica-
tion such as coking.
Exemplary briquettes were made by immersing 60 x O
mesh Pittsburgh coal in a mixture of 97 percent volume trichloro-
fluoromethane and 3 percent No. 6 fuel oil and manually stirringthe mixture for less than a minute.
... .
- 102 -
10518Z~
The coal was recovered and the trichlorofluoromethane
removed by evaporation, leaving the coal coated with the fuel oil
in an amount of approximately one gallon of fuel oil per ton of
coal.
The coated coal was transferred to a die and compacted
into one-inch diameter by two-inch long cylinders under 3000
pounds pressure by a hydraulic machine.
Without further treatment the briquettes were dropped
onto a~concrete floor from a height of four feet.
This did not cause any substantial damage to the
briguettes. ~ ~
Numerous embodiments of our invention have been
described above in varying degrees of detail. However, the
invention may be embodied in still other specific forms without
aeparting from the spirit or essential characteristics thereof.
The present em~odiments are therefore to be considered in all
respects as illustrative and not restrictive, the scope o~ the
in~ention bëing indicated by the appended claims rather than
by the foregoing description; and all changes which come within
the meaning and range of equivalency of the claims are therefore
to be embraced therein.
.
~j;. ~j,
.,,., ",
- 103 -
1051827
The coal was then extracted from the bath and the
trichlorofluoromethane removed by evaporation.
Both the treated and untreated samples were immersed
in deionized water under ambient conditions. One hour later the
water was removed by shaking the samples of coal on a screen.
The water recovered from the coal was compared to the
amount present at the beginning of the test, the difference
being water absorbed on and adsorbed by the coal.
The untreated coal acquired a 50 percent moisture
content almost instantaneously and equiliberated through air
drying to a 30 percent moisture content. In contrast, the shake
dried, treated sample had a moisture content of only twenty
percent after the one hour submersion.
When air dried to the same extent as the first sample,
i.e., to 30 percent moisture, the treated sample had only
1.5 percent absorbed moisture as determined by vacuum oven
drying at 105C. This indicated that the porous structure
of the coal had, indeed, been inhibited from carrying moisture.
The level was well below the limit of 5 percent needed to
insure against spontaneous combustion and freezing of the
coal into a mass.
Example XVI
I Another previously discussed aspect of our invention
- is the conversion of coal particles into briquettes and similar
artifacts which facilitate transportation, reduce storage
losses, and permit proper gas flow through the system in applica-
tion such as coking.
Exemplary briquettes were made by immersing 60 x 0
mesh Pittsburgh coal in a mixture of 97 percent volume trichloro-
fluoromethane and 3 percent No. 6 fueI oil and manually stirring
the mixture for less than a minute.
,~0~ '
1051827 l,
!
The coal was recovered and the trichlorofluoromethane
removed by evaporation, leaving the coal coated with the fuel oil
in an amount of approximately one gallon of fuel oil per ton of
coal.
The coated coal was transferred to a die and compacted
into one-inch diameter by two-inch long cylinders under 3000
pounds pressure by a hydraulic machine.
Without further treatment the briquettes were dropped
onto a concrete floor from a height of four feet.
This did not cause any substantial damage to the
briquettes.
Numerous embodiments of our invention have been
described above in varying degrees of detail. However, the
invention may be embodied in still other specific forms without
departing from the spirit or essential characteristics thereof.
The present embodiments are therefore to be considered in all
respects as illustrative and not restrictive, the scope of the
invention being indicated by the appended claims rather than
by the foregoing description; and all changes which come within
the meaning and range of equivalency of the claims are therefore
to be embraced therein.
What is claimed and desired to be secured by Letters
Patent of the United States is:
