Coal cleaning process

Fine particle coal is beneficiated in specially designed dense medium cyclones to improve particle acceleration and enhance separation efficiency. Raw coal feed is first sized to remove fine coal particles. The coarse fraction is then separated into clean coal, middlings, and refuse. Middlings are comminuted for beneficiation with the fine fraction. The fine fraction is deslimed in a countercurrent cyclone circuit and then separated as multiple fractions of different size specifications in dense medium cyclones. The dense medium contains ultra-fine magnetite particles of a narrow size distribution which aid separation and improves magnetite recovery. Magnetite is recovered from each separated fraction independently, with non-magnetic effluent water from one fraction diluting feed to a smaller-size fraction, and improving both overall coal and magnetite recovery. Magnetite recovery is in specially designed recovery units, based on particle size, with final separation in a rougher-cleaner-scavenger circuit of magnetic drum separators incorporating a high strength rare earth magnet.

FIELD OF THE INVENTION 
The present invention is directed generally to the field of coal cleaning 
processes, and in particular, is directed to removal of refuse, such as 
sulfur-containing minerals, from fine coal particles. 
BACKGROUND OF THE INVENTION 
Coal is a widely used, but limited, fuel for generating electricity in the 
United States and around the world. However when burned, coal can emit 
significant amounts of pollutants which create environmental problems. 
Environmental concern is exemplified by the Clean Air Act Amendments of 
1990 creating new emissions limitations for coal of 2.5 pounds of sulfur 
dioxide per million BTU effective in 1995 and 1.2 pounds of sulfur dioxide 
per million BTU effective in the year 2000. 
A utility that burns high sulfur coal currently has the option of switching 
to a low sulfur coal or scrubbing flue gases to remove sulfur dioxide. 
Scrubbing sulfur dioxide requires significant capital investment and is 
operationally expensive. For many utilities, switching to low sulfur coal 
would be very expensive due to transportation costs for delivering coal 
from a distant source and capital costs associated with plant modification 
to accommodate coals with different combustion characteristics. 
Substantial deposits of high sulfur coal currently fuel many electrical 
power generation plants. A need exists to improve the cleaning of sulfur 
from such coals prior to combustion so that they may be efficiently used 
without producing excessive pollutants. 
Beneficiation of coal refers to the removal of non-coal material from raw 
coal to produce a relatively clean coal product. Raw coal is composed of 
high purity coal material and non-coal material. Non-coal material in 
coal, commonly referred to as ash, normally includes pyrite, clays, and 
other aluminosilicate materials. The presence of large amounts of these 
ash materials can create problems during combustion, such as slagging and 
fouling. Sulfur is present in raw coal in two forms, organic sulfur and 
inorganic sulfur. Organic sulfur is chemically bound as part of the coal 
matrix. Inorganic sulfur is all sulfur not chemically bound in the coal 
matrix. Pyrite sulfur is the predominate form of inorganic sulfur. Sulfate 
sulfur is another form of inorganic sulfur associated with ash forming 
materials. Physical beneficiation effectively removes only inorganic 
sulfur. Processes for beneficiating coal are varied, but commonly utilize 
dense medium separation, jigs, or froth flotation to separate clean coal 
from non-coal material. Because of its versatility, high efficiency and 
ease of operation, dense medium separation is perhaps the preferred 
separation technique. 
In dense medium separation, raw coal is introduced into a medium having a 
specific gravity intermediate between that of coal and non-coal material. 
The dense medium may be a homogeneous liquid, but is more often composed 
of water and magnetic particles, such as ferromagnetic particles. 
Magnetite is a commonly used magnetic particle. Separation can be carried 
out in a dense media bath or tank, or in a cyclone. When a cyclone is 
used, coal is generally removed as the overflow product while refuse 
becomes the underflow product. After separation of coal and refuse, it is 
advantageous to recover the magnetic particles from the coal and from the 
refuse for reuse. 
Raw coal feed, typically known as run-of-mine coal, is a mixture of three 
components, namely organic material, rock and pyrite. In raw coal, some 
particles are liberated, meaning that they constitute relatively pure 
components. Other particles are locked, meaning that these particles 
contain two or more of the three components locked together. Such locked 
particles are referred to as middlings. 
Each of the raw coal components has a characteristic specific gravity. To 
illustrate, organic material has a specific gravity of about 1.25, rock 
has a specific gravity of about 2.85 and pyrite has a specific gravity of 
about 5.0. A raw coal feed contains particles with many specific gravities 
as a result of the differing specific gravities of the three separate 
components and the combination of components which are locked together. 
While dense medium beneficiation has been effective for large size coal 
feed particles, those greater than approximately 0.5 mm in size, it has 
typically not been used for smaller-size coal particles. In this regard, 
the separation efficiency for small particle coal feeds has not been 
satisfactory. As a result, small coal particles are often discarded. 
One way to improve the separation of coal from non-coal material is to 
crush or otherwise comminute the raw feed to liberate high purity coal and 
non-coal material in the middlings. Generally, as the average size of the 
particles in the raw coal feed becomes smaller, more coal and non-coal 
material are liberated and the percentage of particles constituting 
middling decreases, potentially allowing the recovery of more coal 
product. Crushing or grinding a coal feed to liberate coal locked with 
non-coal material in middlings has not been practical because there was no 
process for treating fines which efficiently separates coal from non-coal 
material. Middlings material, therefore, either reports to the clean coal, 
which introduces pyrite and other unwanted minerals into the fuel, or 
reports to the refuse resulting in an undesirable loss of coal. 
Comminution of an entire coal feed is, however, costly and not 
commercially practical. The expense of comminution is significant and it 
would be desirable to minimize the costs. 
As indicated above, in order to recover coal from middlings to produce a 
high purity coal product, it is necessary to comminute the middlings and 
then to separate the coal from refuse. If middlings are not processed for 
further coal recovery, a substantial quantity of useable coal in the 
middlings will be discarded along with non-coal material. Accordingly, to 
maximize recovery of a clean coal product, it is essential to develop 
beneficiation processes designed to handle small particle raw coal feed. 
U.S. Pat. No. 4,364,822, by Rich, issued Dec. 21, 1982, describes a coal 
cleaning process involving two-stage cyclone separation that produces 
three products, clean coal, refuse, and middlings. Middlings are then 
crushed and recycled through the cyclones with the raw coal feed. Rich, 
however, specifically teaches away from a dense medium process using 
magnetic particles based on problems with the recovery of magnetic 
particles. 
U.S. Pat. No. 3,908,912 by Irons, issued Sep. 30, 1975, describes a process 
whereby refuse is initially separated out at high density, followed by a 
lower density separation to yield clean coal and middlings. Middlings are 
then crushed for further cleaning. However, in Irons small size coal is 
not removed from the coal feed prior to the initial high density 
separation which results in additional refuse in the clean coal product. 
Moreover, Irons discloses that cyclone separations of small coal fines are 
inefficient in that particles are frequently misplaced. As such, Irons 
teaches the use of secondary cyclones followed by flotation to eliminate 
refuse in the coal. 
Many attempts have been made to clean fine particle coal, with varying 
results. In dense medium cycloning, separation efficiency drops as coal 
feed particles become smaller. In particular, considerable difficulty is 
encountered in cleaning a coal feed made up of particles less than about 
0.5 mm in size. Also, recovery of the magnetic particles from the dense 
medium after beneficiation becomes more difficult as coal feed particles 
become smaller. 
Accordingly, there is a need for an effective and efficient means for 
beneficiating coal feed particles less than about 0.5 mm in size where the 
separation efficiency is sufficient such that the coal product meets 
desired specifications. The separation efficiency of a coal cleaning 
process is frequently illustrated through probability curves known as 
partition curves. These curves describe the probability that a given 
particle in the feed will report to the clean coal rather than refuse. The 
measure of the slope of the vertical portion of a partition curve is the 
separation's probable error, or Ep. The more vertical the center portion 
of the partition curve, the more efficient the separation and the smaller 
the probable error. 
In order to avoid the difficulties associated with cleaning small size 
particles, many methods for processing fine coal particles discard 
particles below a threshold size prior to beneficiation typically referred 
to as desliming. Desliming has traditionally been based o limitations of 
the beneficiation process. For example, U.S. Pat. No. 3,794,162 by Miller 
et al., issued Feb. 26, 1974, discloses a heavy medium beneficiating 
process for particles down to 150 mesh (0.105 mm). Particles smaller than 
150 mesh are screened-out prior to beneficiation by dense medium cyclone. 
U.S. Pat. No. 4,282,088 by Ennis, issued Aug. 4, 1981, discloses a process 
where particles smaller than 0.1 mm are separated out in a cyclone 
classifier and discarded prior to beneficiation by dense medium cyclone. 
When all particles below 0.1 mm or 0.105 mm in size are discarded, pure 
coal is also discarded both as small coal particles and as coal locked in 
small middling particles. 
The ability to deslime by screening or sieving is limited by available 
screen and sieve construction. Screening or sieving large quantities of 
material below a size of about 150 mesh is not practical. Classifying 
cyclones, which separate particles based on different particle settling 
velocities, have been used to classify coal feeds, but have not been 
effective for making a size classification of coal feed at 0.015 mm. 
Rejecting only the smallest coal particles in raw coal feed, on the order 
of 0.015 mm and smaller, presents a major problem. Particles smaller than 
this size are predominately refuse material which should be discarded. 
One parameter in cyclone design which has received relatively little 
attention is the size of the inlet orifice through which feed enters the 
cyclone. Arterburn, in a paper entitled, "The Sizing of Hydrocyclones" 
(Krebbs Engineers 1976), notes that feed orifices usually have an area 
between 6 percent and 8 percent of the area of the cyclone feed chamber. 
The modification of inlet diameters has not been identified as a factor to 
improve a classifying cyclone separation capability. 
Multiple classifying cyclones arranged in a countercurrent flow circuit 
have been used for size classification of starch. U.S. Pat. No. 4,282,232 
by Best, issued Aug. 11, 1981, describes a countercurrent cyclone circuit 
designed primarily to wash starch. As far as the inventor knows, a 
countercurrent arrangement of classifying cyclones is not practiced in the 
coal cleaning industry and has not been used to separate particles of the 
magnitude of 0.015 mm and smaller. 
Attempts have been made in the coal industry to eliminate the need for 
desliming by improving the beneficiation process. For example, U.S. Pat. 
No. 4,802,976, by Miller, issued Feb. 7, 1989, discloses a process in 
which froth flotation is used to recover coal particles smaller than 28 
mesh (0.595 mm) downstream of a dense media cyclone. But this process is 
not appropriate for all coals. A raw coal feed often contains oxidized 
coals which do not float. Also, pyrite tends to float, along with clean 
coal, thereby contaminating the clean coal product. Devising a process to 
treat all types of fine particle coal and to effectively remove pyrite 
from the smallest size fractions, has been problematic. 
Cyclones for use in connection with dense medium beneficiation have varying 
size parameters and can be subject to varying operating conditions. In 
general, cyclones do not operate as effectively when used to beneficiate 
small size particles. A problem with the use of cyclones for the 
beneficiation of small coal particles is the need to assure that the 
particles correctly report to either the underflow as refuse or overflow 
as coal. Small particles often become misplaced, thereby decreasing the 
separation efficiency of the cyclone. 
One cyclone parameter is the area of the inlet orifice through which raw 
coal feed enters the cyclone. U.S. Pat. No. 2,819,795 by Fontein, issued 
Jan. 14, 1958, discloses a cyclone design where the area of the inlet is 
calculated to equal between 0.1 and 0.4 times the area available for 
overflow. Fontein also specifies a cyclone diameter between two and three 
times the diameter of the overflow. Fontein does not discuss the inlet 
diameter as related to the cyclone diameter or particle velocity. U.S. 
Pat. No. 4,341,382 by Liller, issued Jul. 27, 1982, discloses a design for 
an eighteen inch diameter cyclone where the inlet tube diameter is 
calculated to equal between 0.25 and 0.35 times the cyclone diameter. 
Fourie et al., "The Beneficiation of Fine Coal by Dense-Medium Cyclones", 
Journal of South African Institute of Mining and Metallurgy, pp. 357-361 
(October 1980), discloses the use of magnetite particles in beneficiating 
minus 0.5 mm coal by dense medium cycloning where at least 50 percent of 
the magnetite is finer than 10 microns (0.010 mm). Finer size magnetite 
is, however, more difficult and costly to recover from clean coal and 
refuse. Fourie discloses the recovery of magnetite in a 
rougher-cleaner-scavenger arrangement of wet drum magnetic separators and 
reported serious problems with magnetite loss. There is a need for a 
process which employs magnetite small enough to separate fine size coal 
and refuse effectively, but allows for sufficient recovery of magnetite 
after beneficiation. 
Magnetite used in Fourie was prepared by milling magnetite ore. But milling 
ore to ultra-fine sizes is very expensive, and milling gives little 
control over particle size distribution. Magnetite for use in dense media 
separation can also be produced by chemical reduction of hematite. U.S. 
Pat. No. 4,436,681 by Barczak, issued Mar. 13, 1984, discloses a process 
whereby hematite prepared by spray roasting of iron chloride is reduced to 
magnetite. However, Barczak does not discuss magnetite particle size or 
recognize problems encountered during magnetite recovery following dense 
medium separation. 
U.S. Pat. No. 4,777,031 by Senecal, issued Oct. 11, 1988, discloses a 
process whereby magnetite is produced by pyrohydrolysis of iron chloride 
at temperatures between 1000.degree. C. and 1600.degree. C. However, 
Senecal is directed to producing magnetite particles between 0.02 and 0.2 
microns (0.00002 mm to 0.0002 mm) in size that are well suited for binder 
systems such as those used in magnetic recording media. Senecal's process 
results in magnetite particles too small to be used effectively in dense 
medium separation of coal due to problems with recovering such small 
particles following dense medium separation. 
Magnetite used in dense medium separation has traditionally been recovered 
for reuse by first draining the medium from the separated product over 
screens and then rinsing the product over screens to remove the remaining 
magnetite. Magnetite is then separated from the rinse water, dilute 
medium, by magnetic separation. However, when cleaning fine size coal 
particles, screens are not effective to keep coal and refuse particles 
from passing through with the medium and rinse water. These fine particles 
of coal and non-coal material contaminate the dense medium and are 
difficult to separate from the magnetite in conventional magnetic drum 
separators. 
Another problem with the recovery of small magnetite particles is that it 
is difficult to separate the magnetite from rinse water by magnetic 
separation. U.S. Pat. No. 4,802,976 by Miller, issued Feb. 7, 1989, 
proposes recovering magnetite as the sink from froth flotation cells, 
thereby avoiding the problem of fine coal and non-coal particles entrained 
with magnetite during magnetic separation. Froth flotation systems are, 
however, complex and difficult to operate. The use of a magnetic separator 
incorporating a high density gradient magnet in a matrix design could be 
employed. However, high density gradient magnets are expensive and matrix 
separators complicate operation compared to traditional magnetic drum 
separators. There is a need for an effective separation process using 
easier to operate magnetic separators and more economical designs for 
magnetic separation. 
In order to satisfy utility combustion requirements, the clean coal product 
from beneficiation must be dewatered to reduce its moisture content. Fine 
particle coal is more difficult to dewater than larger-size coal because 
of its greater surface area. 
In light of the foregoing, what is needed is an improved process for 
beneficiating fine particulate coal such that desired specifications, such 
as sulfur content, can be met. Many of the problems impeding development 
of such a process have been described, and they are formidable. A need 
exists for a process that maximizes the recovery of coal without the 
expense of comminuting the entire coal feed. Also, methods of classifying 
coal particles based on size must be improved, particularly methods using 
classifying cyclones. Improved separation efficiency of fine particle coal 
in high throughput dense medium cyclones is desired. Methods to 
effectively recover ultra-fine size magnetic particles for reuse following 
dense medium separation are needed to improve the viability of dense 
medium separation of fine particle coal. Improved methods are also needed 
for producing magnetic particles of optimum size to effect good dense 
medium separation while maximizing magnetic particle recovery. 
SUMMARY OF THE INVENTION 
In accordance with one embodiment of the present invention, a process for 
beneficiating fine particle coal in specially designed dense medium 
cyclones to improve particle acceleration and to enhance separation 
efficiency is provided. Raw coal feed is first sized to isolate the coarse 
and fine coal fractions. The coarse fraction is then separated into clean 
coal, middlings, and refuse. Middlings are comminuted for beneficiation 
with the fine fraction. The fine fraction is deslimed in a countercurrent 
classifying cyclone circuit and then separated into multiple fractions 
according to size prior to dense medium cycloning. 
The dense medium contains ultra-fine magnetic particles of a narrow size 
distribution that aids separation and improves subsequent recovery of the 
magnetic particles. Magnetic particles are recovered from the clean coal 
and refuse fractions independently. Magnetic particle recovery is in 
specially designed recovery units, based on particle size, with the more 
conventional drain-and-rinse approach applied to coarser fractions, but 
with final separation in a rougher-cleaner-scavenger circuit of wet drum 
magnetic separators incorporating a high strength rare earth magnet. The 
overall coal processing circuit can be arranged so that the non-magnetic 
effluents from the magnetite recovery systems of coarser coal fractions, 
which may contain some unrecovered fine magnetite, ultimately flow to the 
rougher-cleaner-scavenger circuit which recovers virtually all fine 
magnetite. 
One advantage of the present invention is that it constitutes an effective 
process for beneficiating coal particles smaller then 0.5 mm. An advantage 
of one embodiment of the invention is that it provides a process for 
desliming of raw feed coal prior to beneficiation which minimizes the 
amount of coal discarded as slimes and aids in subsequent magnetic 
particle recovery and dewatering of the coal product. 
In accordance with an embodiment of the present invention, a process is 
provided for classifying ultra-fine particles employing a classifying 
cyclone having an inlet area within a specified range. In another 
embodiment of the invention, a process is provided for classifying small 
particles by size using multiple classifying cyclones. While reference to 
the partitioning of particles by classification cyclones to overflow and 
underflow is described as being by size, it is recognized that 
classification is by settling velocity which is influenced not only by 
size but also by other particle parameters including particle specific 
gravity and shape. Another embodiment provides a process for recovering 
magnetic particles used in dense medium cycloning involving sizing and 
classifying the coal feed into narrow size fractions for processing. 
In accordance with one embodiment of the invention, a process for 
beneficiating extremely fine coal by dense medium separation using 
magnetic particles of a particular particle size and size distribution is 
provided. In accordance with another embodiment, magnetite is produced by 
reduction of hematite, which magnetite exhibits properties desirable for 
dense medium separation and for which recovery is improved following 
separation. In accordance with another embodiment, a process of dense 
medium separation of extremely fine particle coal in a cyclone with inlet 
area sized within a specific range is provided. 
In accordance with another embodiment of the present invention, a process 
for recovering magnetic particles following dense medium separation is 
provided whereby the non-magnetic effluent from the magnetite recovery 
unit of a larger-particle-size coal fraction containing both unrecovered 
clean coal and magnetite is sent to circuits treating smaller-size coal 
fractions, which circuits employ a rougher-cleaner-scavenger magnetite 
recovery circuit which captures virtually all the magnetite while also 
recovering the coal. In accordance with another embodiment of the present 
invention, a process of wet drum magnetic separation using a rare earth 
magnet is provided. In accordance with another embodiment, a process for 
dewatering and agglomerating extremely fine coal involving the addition of 
paper fibers to the coal is provided.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
The present invention relates to a process of beneficiating fine particle 
coal through use of a dense medium separation process. In particular, the 
present invention involves a process for beneficiating particulate coal 
particles smaller than about 0.5 mm. The process of the present invention 
results in an exceptionally clean coal product with high heating value, 
low ash and low inorganic sulfur content. The process of the present 
invention can be used to produce a clean coal product which, during 
combustion, can meet desired emission specifications. It has been found 
that an improved coal product can be produced by application of one or 
more of the following methods, and preferably by application of each of 
the following methods. 
LIBERATION 
In one embodiment of the present invention, prior to beneficiation, 
substantially pure coal and high ash refuse are removed from the raw coal 
feed. Coarse coal (coal which is at least 0.5 mm in size) is relatively 
easy to clean and satisfactory cleaning processes are known in the 
industry. Cleaning of fine coal (coal which is less than about 0.5 mm in 
particle size) is more complex. For example, small particle coal is much 
more difficult to separate in dense medium cyclones because the small 
particles have large surface areas and experience high viscous drag, and 
because dense media have not traditionally been designed for such 
particles. Accordingly, it is preferable to remove clean coarse coal prior 
to beneficiation of coal fines. 
A process for treating fine coal which incorporates comminution of coarse 
middlings to liberate coal from non-coal material is advantageous. Such a 
need is heightened by recent environmental concerns and regulatory 
impositions. Coal with high sulfur content will not be acceptable for 
electrical generation without expensive scrubbing. Comminution, however, 
is expensive; moreover, cleaning the resulting fines is costly. 
Comminution should, therefore, be minimized. 
The process of the present invention provides an efficient and effective 
means for removing especially clean coal particles and refuse particles 
substantially barren of coal from a coarse coal feed. By removing coarse 
clean coal and refuse, only the middling fraction need be comminuted for 
further processing as fine particle coal. Thus, the process has the 
advantages of reducing the load on fine particle coal separation 
equipment, minimizing the cost of comminution and minimizing the amount of 
fines in the final clean coal product. 
In the process of the present invention, raw coal feed is separated by size 
into coarse and fine fractions by an suitable method, preferably with 
screens. The separation is preferably made at a particle size from about 
0.25 mm to about 1.0 mm, more preferably from about 0.6 mm to about 0.4 
mm, and most preferably at a size of about 0.5 mm. The oversize coal is 
then subjected to dense medium separation, preferably by dense medium 
cycloning, at a low specific gravity such that an exceptionally clean coal 
product is removed as the overflow product. Preferably, the overflow 
product contains at least about 95 percent coal. Preferably, the density 
of separation is no more than about 0.1 specific gravity units in excess 
of the specific gravity of the pure coal being treated. The density of 
separation refers to the specific gravity for which there is an equal 
probability that a particle of feed having a density corresponding to that 
specific gravity will report to overflow or underflow. For example, for a 
1.25 specific gravity bituminous coal, the density of separation should be 
less than about 1.35, preferably about 1.30, and for a 1.55 specific 
gravity anthracite coal, the density of separation should be less than 
about 1.65, preferably about 1.60. 
The underflow product of this initial separation is preferably subjected to 
an additional dense medium separation, preferably by dense medium 
cycloning, at a high specific gravity such that non-coal material can be 
removed as the underflow product. Preferably, the gravity of separation of 
this second dense medium separation is at least about 0.5 specific gravity 
units in excess of the specific gravity of the pure coal, and more 
preferably at least about 0.75 specific gravity units in excess of the 
specific gravity of the pure coal. This underflow product is substantially 
free of coal and is discarded as refuse. Preferably, the underflow product 
contains less than about 25 percent coal, more preferably less than about 
15 percent coal. In the alternative, the coal feed could be subjected to a 
high gravity separation followed by a low gravity separation. 
The overflow product of the high gravity separation consists of middlings 
containing a combination of coal and non-coal materials such as pyrite and 
other ash-forming minerals. These coal and non-coal materials are locked 
together in the middling product. To liberate the coal from the non-coal 
material in the middlings, it is necessary to crush, grind or otherwise 
comminute the middlings to a fine particle size, preferably to less than 
about 0.5 mm in size. Following comminution, the liberated middlings are 
then processed with the fine particle coal initially sized away from the 
coarse fractions. 
To assure that no coarse particles pass with the comminuted middlings to be 
processed with the fine particle coal, the comminuted middlings may be 
recycled to the raw coal feed stream so as to again pass through the 
initial sizing step. The undersize from the sizing step, including 
comminuted middlings, is then processed in a separation unit specifically 
designed to treat fine particle coal. If desired, prior to the low and 
high density separations, the coarse coal can be divided into multiple 
fractions by sizing, and these multiple fractions individually subjected 
to low and high density separations in order to liberate coal from 
non-coal material. By processing coarse and fine coal separately, and by 
comminuting only the middlings, advantages, as previously mentioned are 
realized. 
As illustrated in FIG. 2, clean coal and refuse are liberated from a raw 
coal feed. A raw coal feed 80 is sized 82 at 0.5 mm. The undersize 84 is 
recovered and sent to the dense medium cycloning circuit for small 
particle coal 85. The oversize 86, which is made up of plus 0.5 mm 
particles, is subjected to a first dense medium separation 88 at a low 
specific gravity of approximately 1.3. Clean coal 90 is removed as the 
float product of the first dense medium separation 88. The sink product 92 
from the first dense medium separation 88 is subjected to a second dense 
medium separation 94 at a higher specific gravity of approximately 2.0. 
The high gravity sink product 100 is discarded as refuse. The float 
product 96 of the second dense medium separation 94 is subjected to 
comminution 98. The comminuted product 102 is subjected to additional 
sizing 82 until the entire coal feed is less than about 0.5 mm in size 
and, therefore, reports to the dense medium cycloning circuit for small 
particle coal 85. 
SIZING AND