Note: Descriptions are shown in the official language in which they were submitted.
3~
AGGLO~ERATION TYPE COAI. RECOVERY PROCESSES
The present invention relates to processes for recover-
ing coal in a commercially valuable form. It relates, more
specifically, to novel, improved processes of that character in
which an agglomeration promoting additive lor agglomerant) is
employed in conjunction with mechanical action to effect the
separation of coal particles from mineral m~tter associated there-
with in a slurry and the subsequent coalescence of those particles
into flocs or agglomerates which can b~ recovered from the slurry.
Certain terms used herein are defined as follows:
Raw coal -- a composite of coal and mineral matter which
constitutes the feedstock ~or a process designed to remove mineral
matter therefrom. The raw coal which the process disclosed and
claimed herein is designed to beneficiate is the black water from
a hydrobeneficiation plant, the culm from a sludge pond, or other
material of ~mall particle size~
Product coal -- the carbonaceous coal phase generated
in and recovered from a specified cleaning process.
Processes of the character first described above, using
2() liquid hydrocarbons as agglomeration promo ing additives, h~ve
been available for at least sixty years. Such processes are
disclosed in Brisse et al, Convertol Proces~, MINli~G ENGINEERING,
February 1958, pp. 258-261; AGGLO~ERATION 77, Vol. 2~ K.V.S. Sastry,
Ed., American Institute o Mining, Metallurglcal & Petroleum
Engineers, Inc., New York, New York, 1977, chapters 54-56, pp. 910-
951; and in U.S. Patents Nos. 2,744,626 i5sued May 8, 1956,
to R~erink et al; 2,769,537 issued November 6~ 1956, to
.. ..
~`,
-- 1 --
., 1.
Reerink et al; 2,769,538 issued November 6, 1956, to Reerink
et al; 2,781,904 issued February 19, 1957, to Reerink e-t al;
2,842,319 issued July 8, 1958, to Reerink et al; 3,045,818
issued July 24, 1962, to Muschenborn et al; 3,268,071 issued
August 23, 1966,to Puddington et al; 3,637,464 issued
January 25, 1972, to Walsh; and 4,033,729 issued July 5, 1977,
to Capes et al.
One disadvantage of this prior art process is that the
recovery of even a part of the agglomeration promoting additive
requires that the product coal agglomerates be heated at a tempera-
ture of 250-350C (482-662F). This is economically unattractive.
Furthermore, temperatures of the magnitude in question can cause
unwanted changes in the composition of the product coal.
Because of the cost of, and problems involved in, xecover-
ing agglomeration promoting additives of the conventional type,
they have heretofore apparently, for the most part, simply been
left on the product coal and lost to the process. At the current
elevated prices of the hydrocarbons employed as agglomerating
agents, this can make the above-described coal cleaning process
economically unattractive.
I have now discovered that the disadvantages of the here-
tofore proposed, agglomeration type coal cleaning process discussed
above can be overcome by employing as agglomeration promoting addi-
tives certain fluorinated derivatives of methane and ethane; i.e~,
compositions of the class generally designated by the generic texm
"fluorocarbonsO" Useful fluorocarbons include:
l-Chloro-2,2,2-trifluoroethane
1,1-Dichloro-2,2,2-trifluoroethane
Dichlorofluoromethane
1,1,2,2-Tetrachloro-1,2-difluoroethane
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: ~9~37~4
i
I l-Chloro-2-fluoroethane
i 1,1,2-Trichloro-1~2,2-trifluoroethane
Dichloro-1,2,2,2-tetrafluoroethane
Trichlorofluoromethane
Mixtures of the foregoing compounds can also be
employed.
O~ the listed compounds, ~11 but the last three are
at the present time prohably too expensive to be practical
from an economic viewpoint. And, of the latter, 1,1,2-trichloro- 1
!i ;
1, ,2 trifluoroethane and trichlorofluoromethane are preferred
because of their optimum physical properties, lack of chemical
;acti~ity, and relatively low cost.
The boiling points of the fluorocarbons I employ
are relatively low. Because of this and their low latent
heats of va~orization, they can be separated from the product
coal agglomerates at a modest co~t. P~ecovery rates approaching
100 percent are easily attainedO
Also, the fluorocarbons I employ do not form
azeotropes with moisture associated with the product coal to
;;any commexcially significant extent. This is important
because azeotropes can be xesolved into their components
! only at relatively high cost.
Yet another advantage of my novel process is that
it can be carried out at ambien~ temperature and pressure or
at temperatures and pressures approaching ambient.
Still another important advantage of my invention,
suggested above, is that the ~luorocarbons I employ do not react
chemically with coal under the process conditions I use. This i5
important because contaminated coals are undesirable. In the case
of steaming coals chemical contaminants can cause boiler corrosion.
Co~taminated coking coals can alter the chemistry of the
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: '
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~31~7~
reactions in which they are employed in unwanted directiorls.
Chemical contamination may also make it necessary to
purify the fluorocarbon before it is recycled to the process.
This, potentially, makes the entire process economically unattrac-
tiv~.
Furthermore, because the fluorocarbons I employ are
chemically inert under p~ocess conditions, my novel process can
be carried out without generating the pollutants attributable
Ito many coal cleaning processes.
, ~ther coal beneficiation processes which employ fluoro-
~car~ons are described in U.S. patent No. 4,173,530 issued November
.; 6, 1979, to Smith et al and in a series o~ divisional cascs based
on the same disclosure as that patent.
' Speci~ically, Smith e~ al disclose a process of the
:' gravity separation or sink-float type in which a fluorocarbcn
is used as the parting or gravi$y separation liquid. Gravity
; separation employs Archimedes' principle to resolve raw coàl into
product coal and ~ineral solids. Agglomeration-type processes,
the type disclosed herein~ on the other hand involve quite
different physical phenomena as is evident from, for example,
. the introductory portions of the Puddington et al patent identified
Il above.
From the foregoing, it will be apparent to the
reader that the primary object of the present invention resides
in the provis.ion of novel~ improved methods for separating coal
I~ .
from mineral matter associated therewith.
, Another important but more specific object of the
:invention resides in the provision of a process of ~he character
just described in which an additive is introduced into an
,.aqueous sluxry of the raw coal to promote the separation of
..;, 11
.. _ . . . .. . _ . .. . .. . .
7~
the coal particles from the mineral matter associated therewi~h
and the coalescence oE said coal into agglomerates and in
which provision i.s made for subseqently recovering the agglomer-
ation promoting additive from the product coal agglomerates.
Other important but still more specific objects
of my invention reside in the provision of processes in accord
with the preceding object in which:
the agglomeration promoting additive can be reco~ered
from the product coal agglomerates with only a modest, commercially
viable expenditure of energy;
the agglomeration promoting additive can be recovered
from the product coal agglomerates without generating ecologically
undesirable wastes;
~ he agglomeration ~}o,.loting additive can.be recovered
from the product coal agglomerates under condition~ which are,
or approach, ambient, thereby eliminating the safety and other
problems appurtenant to the use of high temperatures and
pressures.
The oh~ects are broadly attained hy the invention
which contemplates a process or recovering particles of coal
from a particulate composite having a top size of ca 0.6 mm in
which the particles of coal are mixed with particles of mineral
matter to effect a physical separation of the existent coal
particles from the existent particles of mineral matter essen-
tially without further liberation of mineral matter from the
coal. The process comprises the steps of: agitating the
composite, wlthout any significant reduction in size o~ the
particles making up the composite 9 in an aqueous carrier contain-
ing a fluorocarbon agglomeration promoting additive with
0 respect to whlch the coal is hydrophobic, to effect a coalescence
of the coal particles into product coal agglomerates and the
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e~ection of mineral matter particles into dispersion in the
aqueous carrier, and recovering the product coal agglomerates
from the aqueous carrier. The agglomera-tion promoting addi~ es
that can be used in the inventive process are the eight listed
as useful above in this disclosure at page 2, line 28 to page 3,
line 5.
Other important objects, advantages, and features
of the present invention will be apparent from the foregoing
and the appended claims and as the ensuing detailed description
and discussion proceeds in conjunction with the appended
drawings in which:
Figure 1 is a flow diagram of one process for
beneficiating coal in accord with the principles of the present
invention; and
Figure 2 is a graph showing the effect of the
important process variables on the ash content of the product
coal.
Referring now to Figure 1, the separation of coal
from the mineral matter associated therewith, the su~sequent
agglomeration of the coal particles, and the ejection of
mineral matter and water from the agglomerates is carried out
in an agglomerator 10 which may be, for example, a homogenizer
as described in U.S. Patent No. 2,744,626 issued May 8,
1956, to Reerink et al or a tumbler as described in U.S. Patent
No. 3,471,267 issued October 7, 1965, to Capes et al. Or, as
shown in the drawing, the agglomerator may simply be a casing
1~ housing propellor-type agitators 14 rotated by a drive 16
of conventional construction~ This arrangement moves the raw
coal along casing 12 as the separation and agglomeration of the
product coal and the ejection of water and mineral matter from
the agglomerates take place.
Agglomerator 10 provides mechanical forces which
jam the coal particles in the raw coal into agglomerates of
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~9~3'7~39~
the wanted character and which eject the mineral matter ana
water from the agglomerates. In addition, it generates
forces which knead or work the agglomerates to expel additional
mineral matter and water therefrom.
; The separation may be carried out at ambient temperature
and pressure.
Raw coal and the selected agglomeration promoting
additive are introduced into agglomerator 10 through transfer
devices indicated generally by reference characters 18 and 20.
Such water as may be necessary to form a slurry with appropriate
characteristics is introduced through a separate conduit (not
shown) or premixed with the coal, depending upon the character
of the agglomerator.
For my process to operate efficiently, the size consist
of the coal should not exceed 0.6 mm; i.e., it is e~ficient
fox coals with size consists up to 0.6 mm x 0. On the other hand
; coals with si~e consists of 0.02 mm x 0 (and even smaller)
can be readily cleaned with my process.
- The minimum amount of additive I employ is that
necessary for an efficient agglomeration o~ the particles of
product coal to be effected. Three to ten percent by weight
of the additive based on the weight of the liquid carrier-
raw coal-additive system serves that purpose.
Typically, nothing will be gained by employing more
than 500 pounds of agglomerant per ton of coal; but the
efficiency of the process will begin to deteriorate, and the
amount of ash in the product coal will begin to increase, as
; the amount of agglomerant is decreased below that level.
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7~'~
~ minimum of 70 percent water based on the weight
of the raw coal-additive-liquid system is maintained in
agglomerator 10. Lower amounts do not provide a sufficiently
large body of liquid to keep the mineral matter suspended in
~the aqueous carrier.
The maximum amount of water and agglomeration promoting
additive that can be tolerated in agglomerator 10 depends upon
, I
the type of e~uipment that is employed and can range up to
' 98 percent of water and additive combined based upon the weight
10 of the raw coal.
Typically, the solids content of the raw coal-
agglomerant-water system will be in the range of five to ten
weight percent.
" The time for which agglomeration is carriedout is
also important in the successful practice of my invention.
Typically, an agglomeration (or throughput) time of
abou~ one minute will be employed. Reductions to shorter
perlods result in higher product coal ash contents while
~ longer periods produce increased energy consumption and
component wear without producing any significant additional
reduction in product coal ash content.
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1~98'7~'~
` A strictly optional step in the process as so far
described is to subject the coal particles to particle size
reduction prior to agglomeration. This technique can be employed
to reduce the sulfur content of the product coal and/or its
mineral content. The particle size reduction can be carried out
in a ball mill such as is shown at 21, for example.
The foregoing technique is readily distinguishable from
the process disclosed and claimed in U.S. patent No. 4,186,887
which is assigned to the same assignee as thepresent case. In
10 the previously patented process, milling (or size reduction) is
employed in the agglomeration process to reduce the mineral content
of the coal being cleaned to an absolute minimum.
Figure 2 illustrates, graphically, the effect that
actual tests showed the major process variables to have on the
ash content of the product coal. Each of these variables was
investigated with the other variables optimized. Generally,
as the percentage of solids in the water-agglomerant-raw coal
system increased, the ash in the product coal increased. ~gglomerat-
ing times shorter than one minute resulted in increased ash.
2~ Agglomerant concentrations of less than 0.3 gms/gm of coal also
produced an increase in ash.
i
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As discussed in copending Canadian application No.
339,011, filed November 2, 1979, now Canadian patent No.
1,130,231, it is deslrable, in many cases, to add calcium
oxide in either hydrated or anhydrous form to the slurry
during the agglomera-tion process to promote the separation of
pyritic sulfur from the product coal.
Pyritic sulfur content~ of only a fraction of one
percent have consistently been obtained by employing that
technique.
Also, in the course of agglomeration, the calcium
oxide is associated with the product coal in a manner which
increases the hydrogasification and steam gasification
reactivities of the coal, another benefit of decided economic
importance~
Furthermore, when coal fortified with calcium
oxide in the manner just described is burned, the calcium
ions react with sulfur remaining in the coal, ~ormin~ a
p1-ecipitate that can be readily removed from the combustion
products. Thus, the presence of calcium ions in the coal
produced by my novel process actually facilitates the removal
of pollutants from the combustion products.
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The calcium oxide, i employed, is introduced into
agglomerator 10 through transfer device 2~. From 0.15 to
0.53 percent of calcium oxide (calculated as CaO) based on the
weight of the water in the agqlomerator is employed. It is
preferred that the calcium oxide be dosed or metered ko the
ag~lomerator over the period of coal particle separation and
agglomeration as this much more effectively promotes the
rejection of pyritic sulfur from the pxoduct coal agglomerates
than a one-time addition does.
The product coal agglomerates, the aqueous carrier,
and the mineral matter are discharaed from agglomerator 10
through a conventional sieve bend or Vor-sieve 24 here the
mineral matter and water are separated from the product coal
agqlomerates.
The ~ater and mineral matter are optionally directed
to a conventional scrubber 26 to recover agglomeration promoting
additive carried from ag~lomexator 10 therewith (typically about
200 ppm) and then to a thickener 28. Suitable thickeners are
described in Taggart, HA~DBOOK OF MINERAL DRESS IMG, John Wiley
o & So~s, Inc., New York, New York, 1927, pp. 15-04 -- 15-26.
The mineral matter consolidated in the thickener
may be transferred to a refuse heap or landfill, for example;
and the water can be recycled.
The product coal agglomerates with their accompanying
burdens of agglomeration promoting additive and moisture are
transferred to an evaporator 30 where at least the additive
is stripped from the agglcmexates. Moisture associated there~
with may also be stripped from the coal in evaporator 30.
However, it is not in every case necessary that all, or even
30 any, of this moisture be removed; and it i5 an important feature
~~ ,tJ
7~
o~ my invention that an essentially quantitative (9g% plus)
recovery of additive can be made without removing the water.
I Suitable evaporators are described in patent No.
4,173,530.
Dried agglomerates discharged from evaporator 30 are
ready for utilization.
The aqueous phase istreate~ as described above.
It is a feature of the present invention that evaporation
;of the fluorocarbon additive as just described can be effected
at a fast enough rate to substantially reduce the vapor pressure
over, and, as a consequence, the cost of recovering the moisture
- from the coal. This has been demonstrated by evaporating
15% by weight of trichlorofluoromethane from a bed of fine coal
containing 6% by weight moisture at a temperature only 6C
above the 24C (75F) boiling point o~ that compound. In less
than 10 minutes the moisture content o~ the coal had been
reduced by ca. 2%. At the same temperature it would have taken
several hours for the coal to have lost that much moisture
absent the codistillation effected by the fluorocarbon.
1 Other of the agglomerants I employ, notably 1,1,2-
trichloro-1,2,2-trifluoroethane, exhibit this novel codistillation
,1 "'
capability to an even greater, and therefore more beneficial,
extent.
! Mechanical removal of liquid can be employed in
association with evaporator 30 to reduce the load on and the
cost of operating the latter. Product coal from sieve bend 2~
will typically have a 40 weight percent water content. Simply by
.. ..
` passing typical agglomerants through the nip between two conven-
tional wringer rolls, as shown diagrammatically in the drawing
at 32, the moisture content of the agglomerates can be reduced
to on the order of 8 percent by weight.
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The fluorocarbon agglomeration promoting additive
and any moisture recovered from the evaporator -therewith are
transferred to a fluorocarbon recovery unit 34 of the type
described in patent ~o. 4,173,530, for example, as is the
~luorocarbon vapor recovered in scrubber 26. The water and
additive are co-condensed and can then be readily separated
due to their vir~ually complete immiscibility.
The fluorocarbon additive is then purged o non-
condensible gases and recycled by way of an agglomerant
storage tank 35, and the water may also be recycl~d.
The examples which rollow describe representative
tests which illustrate various facets of my novel coal
cleaning process.
In each run ca. 100 g of the coal in aqueous slurry
was agitated with the agglomeration promoting additive in
a conventional ~itchen blender for two minutes~
` !
The agglomerates were separated from the aqueous
mineral matter phase of the slurry with a 6 in. by 2 in. curved
sieve bend and then expressed between two steel rolls, reducing
the moisture content of the agglomerates rom ca. 40 to less
than 10 weight percent.
The "dryl' agglomerates were then recovered and
subjected to proximate analysis.
All data are on a dry bàsis, and all percentages
except for ~TU yield are based on weight.
EXA~IPLE I
Sludge from the thickener of an existlng hydro-
beneficiation plant containing ca. 10 weight percent solids
was subjected to agglomeration type benefi~iation using the
process and equipment described above and 1,1,2-trichloro-
:1~98'~
1,2,2-trifluoroethane as the ag~lomerant.
The results are tabulated below:
Table l
.,
!
Coal: Predominantly Upper Freeport
Weight Yield % - 81.30
BTU Yield ~ - 94.50
,;
* M/BTU = 106 BTU
** MAF = moisture and ash free
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1 EXAMPLE II
. . .
Slurries (40 weight percent solids) of Upper Freeport
coal drawn from the same thlckener circult were similarly
beneficiated. "Best run" results follow:
.1
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Table 2
~,
Sa~,E,leSample lA7t.% Total Lbs. Sulfur/ Wt.~ BrU
Number Description Wt.~ Ash Sulfur B~7~1b. 106 BTU Wt.% Yield Yield
Raw Slurry 22.65 1.09+0.04 11,9570.91
Coal-5Slurry 6.27 0.76+0.03 14,6400.52 77.1 87.7
Raw
Coal-7Slurry 22.03 1.15~0.03 11,9720.96 - -
Coal-7Slurry 8.14 1.31~0.03 14,3470.91 89.3 99.5
Coal-8Slurry 24.92 1.52+0.04 11,4641.33 _ _
ProdllctSlurry 4.92 1.02+0.05 14,862* 0.69 62.0 80.4
* Calcu~ated BTU/lb value from the ash-BTU/lb relationship: BTU/lb = -167.6 (Wt.~ Ash) ~ 15,687
1: L98~7~
EX~PLE III
That my novel process is capable of producing agglomer-
ates with a high degree of structural integxity as well as
efficiently separating the coal from the mineral matter associated
therewith was demonstrated by size consist before and after
beneficiation analyses of a sludge, again taken from the sarne
thickener circuit. The results follow:
Table 3
Raw Coal Product Coal
10 Size Fraction(Wet Screened)(Dry Screened)
+9m* - 17.2
9m x 16m - 43.6
16m x 28m 1.5 23.1
28m x 60m 5.5 11.7
60m x 100m 6.6 1.5
100m x 200m 14.1 0.7
200m x 325m 9.4 0.7
325m x 400m 6.0 0.4
400m x 0 57.0, 1.1
20 TOTAL 100.1 100.0
* m = Tyler mesh
The larger size consist of the product coal is due to
solid particle adhesion. That these agglomerates have consider-
able strength is evident as the very act of sieve sizing places
severe mechanical stresses on the particles as they are vibrated
i~
across the sieve surface and through the respective sieves.
. :
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EXAMPLE IV
Seven agglomeration type beneficiations as described
in EX~IPLF I were made of an Upper Freeport "grab" sam~le having
the following size consist~
Table 4
Particle Weight
Si~e Percent
~60m* 0. 3
60;n x lOOm 8 . 9
10 '' lOOm x 200m21. 0
' 200m x 32Sm12. 4
325m x 400mS. 0
400m x 0 52 ~ 4
,
;~ * m = Tyler mesh
: . ,
The results are tabulated below:
Table 5
Raw Product
Coal Coal
B C D E F G H
20 Ash 18.17 7.45 4.01~ 6.033.93 5.654.08 5.36
Total Sulfur% 1.24 1.06 0.771.03 0.771.06 - 1.06
Weight Yield96 - 85.60 61.50* 86.60 74.60* 84.40 72020 83.90
* Average~ Yield~;
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E~AMPLE V
That rny novel process can be used ~ith equal effective-
ness to clean other coals has been demonstrated hy a large number
cf tests conducted on 60m x 0 coals in the same manner as the
test reported in EX~MPIE I. The results of representative ones
of those tests are tabulated below:
I`able 6
RAW CO~. PRODUCT COAL
Coal Se~m County, S-tate ~sh BTU/~ Ash PTU/lb
Pittsburgh* Washington, PA 31.23 9,448 5.54 13,944
er hittal~ing* Washinyton, PA 24.87 11,024 5.74 14,332
Ridge~lountain** Ca~pbell, TN 8.52 13,326 3.59 14,125
Hazal^d** PeL~, .~ 7.48 13,513 3.53 14,103
Illillois No. 6** Fran].lin, IL 7.68 13,388 3.13 14,087
I'e rles5 Iayette, ~14.8812,983 2.60 14,700
Oh-io No. 9 ~lorg~n, OII 23.25 10,700 7.70 13~20
* Slurry Pond SouLce
** Washed Coal Source
'~3
r~
The invention may be embodied in other specific forms
without departing from the spirit or essential characteristics
thereof. The presen-t 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 descri~tion; and all changes which come
within the meaning and range of equivalency of -the claims are
therefore intended to be embraced therein.
"
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