Note: Descriptions are shown in the official language in which they were submitted.
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AGGLOMERATION TYPE COAL CLEANING PROC~SSES
This invention relates to processes for re-
covering coal in a commercially valuable form. It relates,
more specifically, to novel, improved processes of that
character in which an agglomeration promoting additive is
employed in conjunction with mechanical action to effect
the separation of coal particles from mineral matter
associated therewith in a slurry and the subsequent coales-
cence of those particles into flocs or agglomerates which
can be recovered from the slurry.
Certain terms used herein are deEined as
follows:
Raw coal -- a composite oE coal and mineral
matter, a term used herein for the sake of convenience -to
include impurities other than inorganic material associated
with coal. In general, raw coal will constitute the feed-
stock for a process designed to remove mineral matter there-
from. The raw coal may be as mined with or without having
been subjected to preliminary preparation; or it may be
the black water from a hydrobeneficiation plant or the
culm from a sludge pond, etc.
Product coal -- the carbonaceous coal phase
generated in and recovered from a specified cleaning
process.
Processes of the character described above,
using liquid hydrocarbons as an agglomeration promoting
additive, have been available for at least sixty years.
Such processes are disclosed in Convertol Process,
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Brisse et al, MINING ENGINEERING, February 1958, pp. 258- 261;
AGGLOMERATION 77, Vol. 2, K.V.S. Sastry, Ed., American
Institute of Mining, Metallurgical & Petroleum Enyineers,
Inc., New York, New York, 1977, chapters 54-56, pp. 910-951;
and in U.S. Patents Nos. 2,74~,626 issued December 15, 1952,
to Reerink et al; 2,769,537 issued November 6, 1956, to
Reerink et al; 2,769,538 issued November 6, 195~, to Reerink
et al; 2,781,904 issued February 19, 1957, to Reerink et al;
2,842,319 issued`July 8, 1958, to Reerink et al; 3,0~5,818
issued July 24, 1972, to Muschenborn et al; 3,26~,071 lssued
April 23, 1966, ko 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 oE kh~s prior art process is
that the recovery of even a part of the agglomeration promot-
ing additive requires that the product coal agylomerates be
heated at a temperature 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 coa].
Because of the cost of, and ~roblems involved in,
recovering agglomeration promoting additives of -the conven-
tional type, they have hereto~ore 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.
We have now discovered that, unexpectedly, the
- agglomeration promoting additive can be recovered from the
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; product coal generated by the process in question at a low
enough cost and with a degree of efficiency which makes the
process commercially attractive. More particularly, we
have found that this novel, and important, objective can be
attained by washing the product coal agglomerates with
certain halogenated derivatives of methane and ethane which
prove to have a high solvent power for the conventional
additives. The solvent is then separated from the additive,
and both compositions are recycled.
Those solvents which we consider suitable for use
in the novel process just described because of their high
solvent power, low latent heat of vaporization, low viscosity
and surface tension and their chemical inertness toward coal
and materials emplo~ed in the process equipment are certain
fluorinated derivatives of methane and ethane; i.e., compos:i-
tions of the class generally designated by the generic form
"fluorocarbons". Useful fluorocarbons include:
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-Dichloro-1,2,2,2-tetrafluoroethane
Trichlo.ofluoromethane
~ixtures of the foregoing compounds can also be
employed.
Of the listed compounds~ all but the last three
are at the present time probably too expensive to be practical
from an economic viewpoint. And, of the latter,
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1,1,2-trichloro-1,2,2-trifluoroethane and trichlorofluoro-
methane are preferred because of their optimum physical
properties, lack of chemical activity, and relatively low
cost.
The boiling points of the fluorocarbons we employ
are relatively low. Because of this and their Iow latent ~;
heats of vaporization, they can be separated from the
agglomeration promoting additive which they strip from the
product coal agglomerates at a modest cost. Recovery rates
approaching 100 percent are easily attained.
Also, the fluorocarbons we employ in the novel
process described above do not form azeotropes with moisture
associated with the product coal to any commercially signifi-
cant extent. This is important because azeotropes can be
resolved into their components only at relatively high cost.
~et another advantaye of our novel process is
that the separation of the fluorocarbon solvent from the
; agglomeration promoting additive can be carried out at ambient
temperature and pressure or at temperatures and pressures
approaching ambient.
Still another important advantage of our inven-
tion, alluded to above, is that the fluorocarbons employed
to recover the agglomeration promoting additives do not
react chemically with coal under the process conditions we
employ. This is important because contaminated coals are
undesirable. In the case of steaming coals chemical con-
- taminants can cause boiler corrosion. Contaminated coking
coals can alter the chemistry of the reactions in which they
are employed in unwanted directions.
Chemical contamination may also make it necessary
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to purify the fluorocarbon and/or the agglomera-tion promoting
additive before they are recycled to the process. This,
potentially, makes the entire process economically unattrac-
tive.
Furthermore, because the fluorocarbons we employ
are chemically inert under process conditions, our novel
process can be carried out without generating the pollutants
attributable to many coal cleaning processes.
From the foregoing, it will be apparent to -the
reader that the primary objec-t of the present invention
resides in the provision of novel, improved methods for
separating coal from mineral matter associated therewith.
Another important but more specific object of
the invention resides in the provision of a process of the
character just described in which an additive is introduced
into an aqueous slurry of the raw coal to promote the
separation of the coal particles from the mineral matter
associated therewith and the coalescence of said coal into
agglomerates and in which provision is made for subse~uently
- recovering the agglomerati~n promoting additive from the
product coal agglomerates.
Other important but still more specific objects
o our invention reside in the provision of processes.in
accord with the preceding object in which:;
the agglomeration promoting additive can be
recovered from the product coal agglomerates with only a
modest, commercially viable eY~penditure of energy;
the agglomeration promoting additive can be
recovered from the product coal agglomerates without generat-
3C ing ecologically undesirable wastes;
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the agylomeration promoting additive can be
recovered from the product coal agglomerates under conditions
which are, or approach, ambient, thereby eliminating the
safety and other problems appurtenan-t to the use of high
temperatures and/or non-atmospheric pressures.
Still ano-ther important object of the present
invention resides in the provision of coal cleaning processes
which employ a soluble ag~lomeration promoting ad~itive alld
in which the additive is recovered from thc product coal
agglomerates by washing the agglomerates wi-th a fluorocarbon
in which the additive is soluble, mechanical].y se~arating the
fluorocarbon and additive from the agcJlomerates, separating
the ~luorocarbon from the a~glomeration promo~incJ adclitive,
and recycling bo-th the fluorocarbon and the additive.
P~elated, but more spec~fic, objects o~ our inven-
tion reside in the provision of processes in accord with the
preceding object:
which employ a fluorocarbon that can be separated
from the a~glomeration promot.in~ additive by evaporation and
then purged oE non-condensible gases, condensed, and recycled
Witil only modest expenditures of ener~y;
which employ a fluorocarbon that has high solvent
power and low viscosity, surface tension, and latent hcat of
vaporization and which is chemically inert with respect to
coal under the process conditions;
which employ fluorocarbons that are non-flammable,
odor free, non-corrosive, and non-toxic.
Those objects are broadly a-ttained by the invelltion
which contemplates a process for recovering coal from a
particulate composite in which the coal is associated w.it~
mineral matter and which comprises the steps of treating
the composite in an aqueous carrier with a non-aqueous,
organic agglomeration promo-ting additive wi-th respect to
which the coal is hydrophobic to effect a coalescence of
the coal particles into product coal agglomerates, and the
e~ection of mineral matter into dispersion in the aqueous
carrier. The product coal agglomerates are recovered from
the aqueous carrier, and the product coal agglomerates
are washed with a fluorocarbon in which the additive is
soluble to thereby effect a recovery of the agylomeration
promoting additive from the product coal agylomerates.
O-ther important objects, advantages, and
features of the present inven-tion will be apparen-t from the
foregoing and the appended claims and as the ensuing detailed
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description and discussion proceeds in conjunction ~ th the
appended drawing in which the single figure is a flow diagram
of one process for beneficating coal in accord with the
principle of the present invention.
Referring now to the drawing, the separation of
coal from the mineral matter associated therewith, the sub-
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 ~o. 2,744,626 issued ~ .
December 15, 1952, to Reerink et al; a tumbler as described
in U.S. Patent No. 3,471,267 issued October 7, 1965, to
Capes et al; or a ball, beater, buhr, cage, Chilean, colloid,
disc, distintegrating, hammer, pebble, pendulum, pin,
Raymond, rod, or comparable mill.
The separation may be carried ou-t at ~mbient
temperature and pressure.
Agglomerator 10 p~ovides mechanical forces which
jam the coal particles in the raw coal into agglomerates of
- the wanted character and which eject the mineral matter and
water from the agglomerates. In addition, it generates
.forces which knead or work the agglomerates to expel addi-
tional mineral matter and water therefrom.
Also, if a mill type agglomerator is employed,
the agglomerator reduces the size of the material fed to it,
perhaps liberating additional product coal from the mineral
matter to which it is bound, and exposing fresh surfaces on
the coal particles. Exposure of fresh surfaces to the
agglomerating agent can be important because the agglomera-
tion of the product coal particles involves surface active
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phenomena which~ at least generally, operate most efficiently
only on freshly exposed coal particle surfaces.
Raw coal and the selected agg]omeration promoting
additive are introduced into agglomerator 10 through transfer
devices indicated generally by reference characters 12 and
14. Such water as may be necessary to form a slurry wi-th
appropriate characteristics is introduced into mill 10
through conduit 16.
The amount of additive we employ is th.~t
necessary for an efficient agglomeration o the particles of
product coal to be effected. As discussed in the reerences
cited above, this can range from G0 to over 200 pounds of
additive per ton of coal.
As indicated above, the additive employed in ou~
novel process is a hydrocarbon whlch is soluble in the
fluorocarbon used -to recover it. The addi-tive, which must be
one with respect to which the coal particles are hydrophobic,
will typically be, or include:, a petroleum distillate or
solvent; a nitrobenzene; a kerosene; a lubricating, fuel, or
residual oil; or a chlorinated biphenyl.
As discussed in copending Cdn. Serial No. 33g,~11,
iled November 2, 1979, it is also desirable, in many cases,
to add calcium oxide in either hydrated or anhyclrous form to
the slurry during the agglomeration process. The calci.um
oxide, if employed, is introduced into agglomerator 10
through transfer device 17. From 0.5 to 3 percent of calcium
oxide (calculated as CaO) based on the weight of the raw coal
is employed. It is preferred that the calcium oxide be
dosed or metered to the agglomerator over the period of coal
~30 particle separation and agglomeration.
g _
, . . _ ~ .
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..:
Tlle ac~ueous carri~r and mineral mat-ter are dis-
charged- from agglol~erator 10 through a screen 18 on which the
agglomerates of product coal are retained. This aclueous
phase is transferred through conduit 20 to a conventlonal
thickener (not shown). Suitable thickeners ~re described in
Taggart, HANDBOOK OF MI~ERAL DR~SSING, John r.~iley & Sons,
Inc., New York, New ~or~, 1927, pp. 15-0~ -- 15-~6~ rrhe
mineral matter consol~da-ted in -the -thickener may be
transferred to a refuse heap or landfill, for example;
and the water can be recycled.
Up to 200 pounds per ton or more of agglomeration
promoting additive may remain on the product coal agglomerates
retained on screen 18. This additive is recove~red b~ trans-
ferrincJ the agglomerates throucJIl concluit 22 ko a wasllc.~r 2~l
wher~ -the aclditive is w~shcd or leached Erom the agcJlorner~tc!s
with a fluorocarbon solvent of the charac-ter clescribed akove
and introduced into the washer through line 26.
The deslgn of the washer is not critical. It may,
as one example, be a countercurrent extractor of the character
descriked in U.S. Patent No. 3,941,679 issued r~arch 2, 1976,
to Smith e-t al.
The process conditions described in -tha-t patent
are directly applicable in stripping or washing the acJglomera-
tion promoting additive from the product coal acJ~lomerates
in washer 24.
One effluent from the washer consists of product
coal agglomerates wetted with the solvent and dispersed in
the solvent-additive phase generated in the washer.
This efElucnt is transferred through line 28 to
a cen-trifuge 30 to separate -the agglomerates fro~ the solvent
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and additive. Product coal agglomerates with their accompany-
ing burdens of fluorocarbon solvent and in at leas-t the
majority of cases, at least some surface ~ater, are trans-
ferred through line 32 to an evaporator 34 where at least the
fluorocarbon is stripped from the agglomerates. Moisture
associated therewith ~ay also be stripped from the coal in
evaporator 34.
However, it is not in every case necessary that
all, or even any, of this moisture be removed; and it :is an
important feature of our invention tha-t an essentiall~
quantitative (99~ plus) recovery of the fluorocarbon can be
made without removing the water. It is also important that,
if a reduction in product coal moisture content does prove
necess~ry, evaporation oE the fluorocarbon solvent 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.
. Suitable evaporatdrs are described in U. S. Patent
No. 4,173,530.
Dried agglomerates discharged from evaporator 3
are ready for utilization as indicated by arrow 36.
Vapor generated i.n evaporator 34 flows through
line 38 to a condensor-purge unit 40.
The solvent-additive mixture discharged from
centrifuge 30 is pumped through line 42 to an evaporator 44
where the solvent is stripped from the higher boiling point
agglomeration promoting additive. The additive is trans-
ferred through line 41 to an additive storage facility or tank
48 from which it can be recirculated to agglomerator 10
through transfer device 1~.
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.,
Vaporized parting llquid generated in eva~orator
44 is transferrecl through line 50 to condensor-purge unit 40
where it is combined with the vapor flowin~ to that unit ~-~
through line 38. Condensed, degassed parting li~uid is -~
pumped from unit 40 through line 52 to storage facility tank
54.
Numerous embodiments of our inven-tion have been
described above, and that invention may be embodied in still
other specific forms without departing fxom the spirit or
essential characteristics thereof. The present embodiments
are therefore to be considered in all respects as illustra-
tive and not restrictive, the scope of the invention being
indicated by the appended claims rather than by the foregoing
description; and all chan~es which come within the meanin~
and range of equivalency of the claims are therefore intended
to be ernbraced therein.
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