Method for de-ashing and transportation of coal

A method for de-ashing crushed coal and transporting it in the form of pellets, said method comprising the following steps: PA0 A. the step of mixing pulverized coal with a binder to cover the surfaces of coal particles with the binder; PA0 B. the step of adding water to the pulverized coal; PA0 C. the step of stirring the slurry to disperse ash particles in the pulverized coal into water and to agglomerate coal particles in the pulverized coal by tumbling, whereby forming pelletized coal; and PA0 D. the step of separating the pelletized coal from the ash particles, and transporting the pelletized coal. The above basic four steps may be combined with the following steps depending on the state and particle size of raw coal: PA0 E. the step of crushing raw coal and separating it into high-ash coal and purified crushed coal, and further pulverizing the purified crushed coal and supplying the resulting powder to the above step A; and PA0 F. the step of separating by gravity separation the pellets obtained in the above step D into high-ash pellets and purified pellets, and transporting the resulting purified pellets.

BACKGROUND OF THE INVENTION 
The present invention relates to a method for de-ashing and transportation 
of coal. More particularly, the present invention relates to a method for 
crushing, pelletizing, and de-ashing coal at coal mines and then 
transporting coal through slurry pipeline systems or bulk shipments by 
trains, trucks, conveyors, etc. 
The known methods for coal shipments include (1) slurry transportation in 
which pulverized coal is slurried in water and transported through 
pipelines and (2) bulk shipments in which coal is handled in the form of 
lumps. 
According to the slurry transportation method, coal is pulverized to an 
average particle size of about 0.1 mm and slurried in water and the coal 
slurry is transported through pipelines to the place of consumption. This 
method, however, has the following disadvantage. In order for the slurry 
to be stable enough to prevent coal particles from settling in the 
pipeline, the slurry should contain about 20% of fine coal particles less 
than 40 microns in size. If slurry is therefore made containing fine coal 
particles, by this the slurry can be made having an improved stability, 
but dewatering of the slurry is then made difficult as a matter of course, 
so that it is unavoidable in this case to carry out a powerful dewatering 
step at the destined place of consumption: For example, a slurry 
transported through a pipe line is put for a solid-liquid separation by a 
centrifugal separator, but there still tends to remain fine particles 
suspended in the separated liquid, so that it further is operated to pass 
the separated liquid through a thickener and to further refine it through 
a waste-water refining apparatus. 
As pointed out above, to directly slurry fine coal particles involves the 
serious shortcoming of being accompanied by an extreme difficulty for 
dewatering. 
On the other hand, the shipping of lump coal requires troublesome, costly 
loading and unloading and measures for environmental pollution with dust 
and spontaneous combustion during storage. 
Coal contains rocks and soil, and transporting them altogether is 
uneconomical. To solve these problems, the following methods have been 
proposed. (A) Removing rocks from coal by gravity separation. (B) Adding 
fuel oil or light oil to the coal slurry at the terminal of a pipeline 
system, whereby performing de-ashing and pelletization based on the 
principle of oil agglomeration in water (abbreviated as OAW hereinafter). 
(C) Adding water to a coal-oil mixture, whereby removing ash caught by 
water. 
The method (A) requires a coal dressing plant with additional cost for 
equipment and labor, and yet has the problem unsolved in the dewatering of 
slurry. 
The method (B) has inherent demerits mentioned below. 
(1) It is impossible to control the OAW operating conditions according to 
the fluctuation of coal rank. The rank of coal fluctuates even in the same 
coal mine, and the ash content and lipophilic property of coal vary 
accordingly. OAW utilizes the lipophilic property of coal, and the oil to 
be added should be controlled according to the rank of coal. However, this 
is impracticable in view of the fact that tens of thousand tons of coal is 
flowing in the pipe at all times. Even though the fluctuation of coal rank 
is found at the entrance of the OAW facility, it is impossible to cope 
with the time lag. As the result, slurry water is discharged, with 
agglomeration remaining incomplete. This might lead to water pollution 
with fine coal particles. 
(2) It is impossible to add oil in a proper quantity according to the 
pulverization of coal that occurs during slurry transportation. The 
quantity of oil to be added in the OAW process should be changed according 
to the particle size of coal powder, and the more the fine powder, the 
more the oil required. The ratio of pulverization varies depending on the 
rank of coal, but it is very difficult to estimate it beforehand. 
(3) The OAW process requires a great deal of powder and time and an 
apparatus of infeasibly large volume. For instance, if five million tons 
of coal is to be transported per year, the OAW apparatus would have to 
have a flow rate of 2000 m.sup.3 /h, assuming 30 wt % solids in the 
slurry. Such an apparatus would be 1000 to 2000 m.sup.3 in volume and 
require 4000 to 12000 kW for agitation, assuming a power consumption of 2 
to 6 kW.h for 1 m.sup.3 of slurry, according to the inventors' 
calculations. 
(4) The OAW process, which is intended to separate pure coal by 
agglomeration from ash in pulverized raw coal, has an inherent demerit 
that it cannot separate ash particles enclosed by pure coal. This is the 
reason why the de-ashing ratio was 30 to 40% with the conventional OAW 
process. 
Finally, the method (C) is not economical because the oil used more than 50 
wt % based on coal is eventually burned. Using oil in such a large amount 
goes against the times when replacement of petroleum by coal is being 
advocated. 
SUMMARY OF THE INVENTION 
A first object of the present invention, which has been completed to 
overcome the above-mentioned disadvantages, is to provide a method for 
de-ashing and transportation of coal which can be controlled irrespective 
of the fluctuation of coal rank. 
A second object of this invention is to provide a method for de-ashing and 
transportation of coal which can be used in combination with each other 
according to the fluctuation of coal rank and can be controlled 
irrespective of fluctuation of hardness and pulverizability of coal. 
A third object of this invention is to provide a method for de-ashing and 
transportation of coal which saves the consumption of binder oil by 40 to 
60% as compared with the conventional OAW process. 
A fourth object of this invention is to provide a method for de-ashing and 
transportation of coal which can be carried out with much less power 
consumption than the conventional OAW process. 
A fifth object of this invention is to provide an effective method for coal 
de-ashing. 
A sixth object of this invention is to provide a method for de-ashing and 
transportation of coal which can be applied to coal of any variety. 
The method of this invention comprises the steps of mixing pulverized coal 
with a binder to cover the surfaces of coal particles with the binder, 
adding water to the pulverized coal to form coal slurry, stirring the 
slurry to disperse ash particles in the pulverized coal into water and to 
agglomerate coal particles in the pulverized coal by tumbling, whereby 
forming pelletized coal, separating the pelletized coal from the ash 
particles, and transporting the pelletized coal. Depending on the ash 
content in raw coal, the method is preceded by the pretreatment to 
separate the crushed coal into high-ash crushed coal and pure crushed coal 
by gravity separation and subsequently pulverize the pure crushed coal, in 
the case where raw coal contains about 30 to 50% of ash and ash particles 
greater than 1 mm, and/or the method may be followed by the post-treatment 
to separate the pelletized coal into high-ash pellets and pure pellets by 
gravity separation in the case where raw coal contains less than 30% of 
ash and ash particles smaller than 1 mm.

DETAILED DESCRIPTION OF THE INVENTION 
The invention is illustrated with reference to the following Examples. 
The process of Example 1 is shown in FIG. 1. According to this process, 
pulverized coal particles are coated with a binder and pelletized in 
water, while hydrophilic ash particles are dispersed into water, whereby 
de-ashing is accomplished. The process of Example 1 is fundamental to the 
processes of Examples 2 to 4. It is applicable to raw coal containing less 
than 15% of ash, such as bituminous coal, sub-bituminous coal, and brown 
coal. 
In FIG. 1, the raw coal 1 is crushed to a desired particle size by the 
crusher 2 which is a cage mill, rod mill, or ball mill. The particle size 
is selected properly in relation to the de-ashing ratio. If coal is 
pulverized to particles finer than 50 microns, more than 50% of ash can be 
removed in the subsequent de-ashing step. As the particle size becomes 
finer, more binder is required for the same quantity of coal. If coal is 
pulverized to coarse particles of 0.7 mm on average and finer than 5 mm, 
the quantity of binder required is about 5 wt % but the de-ashing ratio 
decreases to 35 to 45%. Thus, the particle size should be determined 
according to the de-ashing ratio or the quantity of binder, whichever is 
important from the standpoint of end use of coal. According to the 
inventors' economical estimate, the above-mentioned coarse particle size 
of 0.7 mm on average and finer than 5 mm is recommended. 
In the downstream of the crusher 2 is arranged the classifier 3 which 
separates coarse coal particles 4 from the crushed raw coal 5, permitting 
fine coal particles 6 to be transferred to the subsequent pelletizing 
step. 
According to another method which is preferably adopted to improve the 
overall economy of the invention, raw coal is crushed by the crusher to 
particle size of 0.7 mm on average and finer than 7 mm, and particles 
smaller than 0.5 mm are separated by a classifier and then pelletized. The 
pelletized coal is mixed with coal particles 4' of 0.5 to 7 mm in size to 
make the final product. This process is advantageously applied to coal of 
low ash content which is not pulverized easily during transportation. 
The fine coal 6, with coarse particulate coal 4 removed, is fed to the 
pelletizer 7 in which the fine coal 6 is mixed with the binder 8 which is 
described later. The atmosphere in the pelletizer 7 should preferably be 
replaced by nitrogen for brown coal which rapidly oxidizes during 
operation. 
The binder 8 is selected from coal tar, artificial petroleum obtained from 
coal, fuel oil, and asphalt obtained from petroleum, which are readily 
available at low prices and are effective for agglomeration of fine coal 
particles. When in use, the binder is heated to adjust the viscosity 
properly. 
The quantity of the binder 8 to be added is determined according to the 
particle size of crushed coal as above-mentioned; at least 20 wt % is 
required when particle size is smaller than 50 microns, and about 5 wt % 
will be sufficient for coal particles of about 0.7 mm on average. The 
average particle size of 0.7 mm is preferably used according to the 
inventors' economical estimate. 
The binder 8 is preferably incorporated with a surface active agent 9 which 
is effective to reduce the quantity of the binder 8 to be added and to 
shorten the pelletizing time. Some examples of the surface active agent 9 
are shown below. 
##STR1## 
(where R is an alkyl group of C.sub.6 to C.sub.20, and n is an integer 
from 1 to 30.) 
This surface active agent is added in an amount from 0.05 to 0.2 wt % based 
on raw coal. 
The binder 8 incorporated with the surface active agent 9 may be further 
incorporated with approximately the same quantity of water 32, and the 
binder 8 is dispersed into water in the form of fine particles in the 
order of microns. For dispersion, the supersonic emulsifier 33 is 
preferably used. 
The binder may contain 30 to 60 wt % of coal powder finer than 10 microns 
in addition to the surface active agent. 
The fine coal powder for such incorporation may comprise any of the 
pelletized coal particles according to the Example 1 of the present 
invention, the purified pellets according to Examples 2 and 3 to be later 
described, and the pelletized particles according to Example 4 of the 
invention and pulverized to a particle size below 10 .mu.. 
The dry pelletizer 7 is preferably a Henschel type powder mixer or an 
inclined tumbling disc mixer with an eccentric rotary rake which is 
intended for mixing solids. 
In the pelletizer 7, the binder is dispersed among the coal particles so 
that the binder uniformly covers the surface of the coal particles. During 
this process, coal particles lose the oxidized layer on the surface due to 
friction between coal particles, and water on the surface of coal 
particles is replaced by the binder. 
The residence time in the pelletizer 7 is usually 3 to 10 minutes and the 
agitator blade is turned at a peripheral velocity of 3 to 30 m/s. 
The binder 8 may be charged into the pelletizer 7 all at once, or charged 
by spraying from a nozzle while the coal powder is stirred. The latter 
method is preferable for uniform dispersion and rapid coating onto the 
surface of coal particles. 
As the result of the above-mentioned step, the surfaces of the coal 
particles are coated with a thin film of the binder. 
The binder-coated coal particles 10 are charged to the mixer 11, into which 
water 12 is added to yield the coal slurry 13 containing 30 to 60 wt % of 
solids. 
If the solid content of the coal slurry is less than 30 wt %, agglomeration 
takes a longer time because coal particles are less likely to collide with 
each other in the forming machine 14. In addition, power is wasted to stir 
water needlessly. 
If the solid content of the coal slurry is higher than 60 wt %, free 
release of ash particles is prevented and the slurry lacks flowability 
when supplied to the forming machine 14. The mixer 11 is usually a 
vessel-type mixer with a vertical stirrer. 
The coal slurry 13 obtained in the above step is then fed to the wet-type 
forming machine 14, in which coal particles coated with the binder film 
are caused to agglomerate as if oil droplets dispersed in water 
agglomerate, while hydrophilic ash particles release the binder film and 
the resulting bare ash particles disperse into water. 
The forming machine 14 is usually a vessel-type mixer with a stirrer, and a 
vertical or horizontal cylindrical mixer with a multi-blade stirrer is 
also preferably used. The residence time in the forming machine 14 is 
usually about 3 to 15 minutes and the blade is turned at a peripheral 
velocity of 6 to 30 m/s. 
In the first half (at the inlet side) of the forming machine 14, the high 
shear force generated by the stirring blades strips off the binder film 
from ash particles and disperses the resulting bare ash particles into 
water, and simultaneously, agglomerates coal particles coated with the 
binder film. 
In the second, half (af the outlet side) of the forming machine 14, the 
centrifugal force generated by the stirring blades causes the coal 
agglomerates to tumble, under the pressing force against the inside wall 
of the cylinder. The coal agglomerates finally become spherical pellets. 
The slurry 15 containing pellets and ash particles is then passed through 
the screen having 0.3 to 0.7 mm openings. The oversize particles are 
pellets of 0.3 to 0.5 mm and up in particle diameter, and the undersize 
particles are ash particles dispersed in the slurry 18. 
The ash particle slurry 18 is separated into ash particles 20 and clear 
water 21 by the solid-liquid separator 19. A precipitator used for 
treatment of clay-containing waste water may be used as the solid-liquid 
separator 19. 
The clear water 21 is recycled to the mixer 11 after being combined with 
replenishing water 12. 
The ash particles 20 are used, after dewatering, to fill up the spaces left 
after mining. 
The pellets 17 prepared in the above steps are mixed with water 23 in the 
conditioning vessel 22 to make the slurry 24 of proper solid content, say 
30 to 50 wt %, which is suitable for transportation to the place of 
consumption by the pump 25. 
At the terminal of the pipeline, the pellets are dewatered by the 
solid-liquid separator 26 prior to combustion. Being hydrophobic, the 
pellets are dewatered easily. 
The pellets can be burned in the conventional pulverized coal burner 27 
after re-crushing to a desired particle size by the crusher 2. Also, the 
pellets can be burned as received in a fluidized bed boiler (not shown). 
In slurry transportation, the slurry pumps 25, which may be common sand 
pumps, are installed at intervals of 100 km. The pellets 17, which are not 
crushed under agitation by the stirring blade at a peripheral velocity of 
5 to 30 m/s in the forming machine 14, are not crushed as a matter of 
course when they pass through the pump 25 and the pipeline 24. 
If a 0.3 to 1 mm vibrating screen is used as the solid-liquid separator, it 
is possible to reduce the water content of the pellets 17 to 12 wt %. If a 
cage-type centrifugal separator of about 100G is used, it is possible to 
reduce the water content to 7 wt % or less. 
Instead of slurry transportation through pipeline 24, the pellets may be 
shipped by sea or land. For bulk shipment by sea or land, the pellets 17 
are passed through the dryer 34, if required, for water content 
adjustment, and then piled up (29) by the stacker 28 at the open-air 
storage yard. 
The pellets 29 piled up at the open-air storage yard are loaded by a 
reclaimer 30 onto freight cars 31. At the destination, the pellets 29 are 
piled up again at the open-air storage yard and then fed to the crusher 2 
and boiler 27. The pellets as received can be burned in a fluidized bed 
boiler. 
If pellets are to be transported by water after slurry transportation 
through ground pipelines, the slurry may be dewatered by screens prior to 
loading and the loaded slurry may be dewatered through screens at the 
bottom of the ship's hold, so that carrying unwanted water is avoided. 
The process of this invention as shown in FIG. 1 is further described 
theoretically in comparison with the conventional OAW method. 
FIGS. 2A to 2D illustrate the principle of the OAW method, and FIGS. 3A to 
3D illustrate the principle of the present invention. 
FIG. 2A schematically shows coal slurry composed of water W and coal 
particles C and ash particles A suspending therein. 
When a binder is added to the slurry, the binder in the form of droplets B 
disperses among coal particles B and ash particles A as shown in FIG. 2B. 
The binder droplets B stick selectively to lipophilic coal particles A, 
forming coated coal particles P, as shown in FIG. 2C. The coated coal 
particles P agglomerate as shown in FIG. 2D, and the agglomerates form 
pellets Q when tumbled in water. 
On the other hand, hydrophilic ash particles A remain suspended in water, 
and finally pellets Q are sieved out from the slurry containing ash 
particles. 
It is to be understood from this principle that the conventional OAW method 
is dependent on the degree of lipophilic property of coal. Therefore, the 
conventional OAW method cannot pelletize brown coal having no lipophilic 
property, and involves problems such as low yields of pellets and 
increased transfer of binder to ash slurry, which all result from the 
lipophilic property of coal. 
According to the principle of this invention, pulverized coal and binder 
are mixed in the dry pelletizer 7 so that the surfaces of coal particles 
are coated with the binder. This is schematically shown in FIG. 3A, in 
which coal particle C and ash particle A are coated by binder Z and coated 
particle X is formed. 
During dry mixing, coal particles C are rubbed with each other and water 
and oxidized layer are removed from the coal particles. Thus, the film of 
binder Z is formed on the fresh surfaces of coal particles. 
On addition of water W, followed by agitation, the binder separates from 
hydrophilic ash particle A, and thus bare ash particles disperse into 
water, as shown in FIG. 3B. 
After continued agitation, coal particles X coated with binder Z 
agglomerate, forming agglomerate particles Y or pellets on tumbling in 
water, as shown in FIG. 3C. 
The agglomerate particles Y are sieved out from the slurry containing ash 
particles A, and the resultant pellets 17 (FIG. 1) are shipped by slurry 
transportation or bulk transportation as mentioned earlier. 
The slurry containing ash particles A, shown in FIG. 3D, is separated into 
ash particles 20 and clear water 21 by the solid-liquid separator 19, as 
mentioned above. 
As is apparent from FIG. 3A to 3D, the process of this invention is 
characteristic in that the binder sticks to coal particles regardless of 
the degree of carbonization of raw coal. 
Example 2 is described with reference to FIG. 4, in which the steps of 
preparing the slurry 15 containing pellets and ash particles from raw coal 
1 and sieving the slurry are carried out in the same manner as in Example 
1 (FIG. 1). The process of Example 2 includes the additional 
post-treatment step for improved de-ashing, in which the pellets 17 sieved 
out by the screen 16 are subjected to the gravity separator 35. 
In other words, the process of Example 2 is intended to further de-ash the 
pellets 17 obtained in the process of Example 1, whereby to obtain 
purified pellets 36. Since the pellets 17 are more uniform in particle 
size as compared with conventional pulverized coal, de-ashing by gravity 
separation can be achieved effectively. 
The purified pellets 36 contain more coal and carry more binder than 
pellets 17, and therefore have a lower specific gravity than pellets 17 
and release ash easily. 
In addition, the purified pellets 36 contain bubbles, although very small 
in quantity, and therefore float more easily than pellets 17. This 
property also improves the de-ashing by gravity separation. 
When raw coal powder which is not pelletized is subjected directly to the 
conventional gravity separation, separation of coal and ash becomes 
blurred due to fine coal particles in the raw coal. In other words, the 
fine coal particles form a black slurry which prevents the separation of 
low-ash coal that floats and high-ash coal that settles down. 
This Example 2 is intended to overcome the above-mentioned disadvantages 
and to produce purified pellets by effective de-ashing. 
The process of Example 2 can be applied to raw coal such as bituminous coal 
and sub-bituminous coal containing 15 to 45 wt % of ash, and particularly 
to raw coal in which ash is present in the form of particles of 1 to 2 mm 
in size. 
Referring to FIG. 4, pellets 17 separated by screen 16 are introduced to 
gravity separator 35 in which purified pellets 36 float and high-ash 
pellets 37 settle down. 
It is also possible to introduce pellet-ash slurry 15 directly into gravity 
separator 35. 
It is to be noted that high-ash pellets 37 contain coal particles of such 
structure that carbon encloses ash particles, or contain ash particles of 
the same particle size as the pellets. 
As the gravity separator 35, a heavy-media cyclone or water concentrator 
can be used. They are operated at a separation ratio of 90% floating and 
10% settling based on the flow rate of the pellets. 
The settle high-ash pellets 37 are disintegrated by the wet mill 38 and 
then recycled to the mixer 11. The floated purified pellets 36 pass 
through the solid-liquid separator 39 for separation of water 40, and then 
combined with fresh water, as in Example 1, for slurry transportation to 
the place of consumption. Instead of slurry transportation, the pellets 36 
may be shipped by bulk transportation 41 as in Example 1. 
According to the principle of Example 2, the pellets Y shown in FIG. 3C 
(Example 1) are subjected to a gravity separator, whereby the high-ash 
pellets S containing ash as shown in FIG. 5A are separated from the 
purified pellets R as shown in FIG. 5B. The removal of high-ash pellets S 
improves the de-ashing ratio further. 
Example 3 is described with reference to FIG. 6, in which the pretreatment 
steps of crushing raw coal and performing de-ashing by gravity separation 
are added to the process of Example 2. The process of Example 3 can be 
preferably applied to treatment of raw coal containing rock layers thicker 
than 1 mm and ash particles smaller than 1 mm. 
As compared with the process of Example 2, the process of Example 3 is 
advantageous in that de-ashing is performed prior to addition of binder 
and therefore the content of pure coal at the time of binder addition is 
increased and the quantity of ash in de-ashing step after binder addition 
is decreased. In proportion to this decrease, the quantity of binder to be 
added can be reduced and pellets of high purity can be obtained at high 
yields. 
In FIG. 6, raw coal 1 is crushed by the crusher 2 and then screened by the 
classifier 3. Lump coal in size from 7 to 100 mm is fed to the gravity 
separator 42, and fine coal 6 in size less than 7 mm is fed to the dry 
pelletizer 7. 
As the gravity separator 42, a heavy-media cyclone or water concentrator 
can be used, as in the case of the gravity separator 35 used for post 
treatment in Example 2 (FIG. 4). The settled high-ash lump coal 43 is used 
for, for example, land reclamation. 
On the other hand, the floated, de-ashed purified lump coal 44 is separated 
from water 46 by the solid-liquid separator 45, crushed into particles 
smaller than 7 mm, 0.5 to 0.8 mm on average, by the crusher 47, and then 
fed to the dry pelletizer 7. Thereafter, the pellets undergo the same 
treatment as in Example 2 (FIG. 4). 
The water 46 separated from the solid-liquid separator 45 still contains 
suspending fine coal particles; it is purified by the thickener 48 and the 
purified water 49 is recycled to the gravity separator 42. 
Example 4 is described with reference to FIG. 7, in which the pretreatment 
process for de-ashing crushed raw coal by a gravity separator is added to 
the process of Example 1 (FIG. 1). This de-ashing pretreatment process is 
performed in the same manner as the de-ashing pretreatment in Example 3 
(FIG. 6). 
The process of Example 4 can be applied to the treatment of raw coal 
containing rock layers greater than 1 mm, providing an economical effect 
that the quantity of discarded coal is decreased and the yield of coal is 
improved. 
The present invention has the following effects. 
(1) Since the binder is applied directly to the surface of pulverized coal 
particles by dry agitation, the sticking of binder is not affected by the 
rank of coal or the degree of lipophilic property of coal. Thus, it is 
possible to apply the de-ashing and pelletizing treatment to brown coal to 
which the conventional process has not been applicable. 
(2) The dry mixing of coal particles and binder provides good sticking of 
binder in thin film to the surface of coal particles. It is also possible 
to prevent the binder from being discharged into slurry from ash 
particles. This saves the consumption of binder by 40 to 60% as compared 
with the conventional process in which the binder is added to the fine 
coal slurry. 
(3) In the conventional process, it is necessary to stir a large quantity 
of slurry medium (water) with a great deal of power energy in order to 
attain oil to coal particles by adding oil to coal slurry, whereas 
according to the present invention, the binder is attached directly to 
coal particles in air and consequently the power requirement can be 
reduced to an extreme extent. 
(4) According to the conventional OAW method, it is difficult to carry out 
de-ashing and pelletizing when the surfaces of coal particles are oxidized 
and less lipophilic, whereas according to the present invention, coal 
particles are rubbed with each other and the oxidized layer is removed 
when the binder is added. Therefore, oxidation of coal particles causes no 
problem. 
(5) In the case of coal particles carrying a large amount of water, the 
surface water is replaced by the binder. Thus, it is possible to attach 
binder while carrying out dewatering. 
(6) Ash such as soil and rocks in coal is allowed to disperse into water by 
utilizing the hydrophilic property of ash which permits water to be 
adsorbed with a force as high as 10,000 kg/cm.sup.2 in terms of pressure. 
Because of this hydrophilic property, ash particles which have been once 
enclosed with the binder release the binder into water. Thus, de-ashing 
can be performed effectively irrespective of the kind of coal. 
(7) According to the present invention, de-ashing treatment by gravity 
separation can be combined depending on the state of presence of ash in 
raw coal, the size of ash particles, and the content of ash. Thus, it is 
possible to remove by sedimentation ash particles enclosed by pure coal 
which cannot be removed by the conventional method. Sink float separation 
can be performed more effectively for uniform pellets than for as-received 
coal particles. 
(8) In addition, according to the present invention, coal and binder are 
recovered by recrushing high-ash coal separated by gravity separation. 
This increases the de-ashing ratio and the yield of pure coal and 
decreases the usage of binder. 
(9) Slurry transportation or bulk transportation of pellets containing 
reduced ash saves the waste of transporting ash. In addition, according to 
the present invention, pipelines for slurry transportation are protected 
effectively from corrosion, and the pellets with ash removed and with 
surface coated with binder (oil) float well during slurry transportation. 
Pellets can be easily dewatered at the terminal of pipelines for slurry 
transportation. 
(10) Bulk transportation in the form of pellets prevents almost completely 
dust from occurring. 
(11) The process of this invention can be applied without any modification 
to coking coal as well as steaming coal. The process of this invention is 
also applicable to oil shale, brown coal, sub-bituminous coal, and 
bituminous coal. 
The invention will be described in detail with reference to the following 
examples. 
EXAMPLE 1 
The process of this invention was evaluated by operating a pilot plant 
according to the flow diagram shown in FIG. 1, with a coal flow rate of 
100 kg/h in the de-ashing and pelletizing processes from the crusher 2 to 
the screen 16. 
(1) De-ashing ratio 
The de-ashing ratio in relation to the stirring time in the dry agitator 7 
was investigated for brown coal produced in the arctic zone. The raw coal 
was pulverized to an average particle size of 0.7 mm. 
The results are shown in FIG. 8. In FIG. 8. the double circle at the zero 
agitation time indicates the result of operation in which dry agitation 
was omitted and only the wet forming machine 14 was used in the same 
manner as in the conventional OAW process. The power consumption (kW) 
throughout the entire process was the same. 
It is to be noted from FIG. 8 that the conventional method achieved 30% of 
de-ashing ratio, whereas the process of this invention having the dry 
agitator 4 improved the de-ashing ratio to about 50%. 
Incidentally, the de-ashing ratio (.eta.) is defined as follows: 
EQU (.eta.)=1-(A.sub.a .times.R)/A.sub.r 
where 
A.sub.a :ash content in pellets 
A.sub.r :ash content in raw coal 
R:yield 
(2) Pure coal yield 
As in above (1), the relation between the de-ashing ratio and the dry 
agitation time was investigated. Results are shown in FIG. 9. It is to be 
noted from FIG. 9 that the yield was improved from 94% to 99%. 
(3) Quantity of oil discharged into waste water 
As in above (1), the relation between the quantity of oil discharged into 
waste water (% of oil added) and the agitation time. Results are shown in 
FIG. 10. 
It is to be noted from FIG. 10 that the quantity of oil discharged was 
greatly improved from about 9% to about 1.5%. 
In the above investigations from (1) to (3), the process of this invention 
required about one half the power for the conventional OAW method to 
achieve the same result (indicated by the double circle). This is because 
the conventional process needs vigorous agitation of water to attach oil 
to coal particles, whereas the process of this invention needs no water 
agitation. 
EXAMPLE 2 
The same experiment as Example 1 was carried out for high-ash bituminous 
coal produced in Australia, using fuel oil C as the binder. Results are 
shown in Table 1. 
TABLE 1 
______________________________________ 
Raw coal 
Water content (wt %) 
5.0 
Ash content (wt %) 
36.0 
Average particle size (mm) 
0.085 
Conventional 
Process of 
process the invention 
Binder added (% on raw coal) 
19.0 12.0 
Ash in pellets (wt %) 
13.0 12.5 
______________________________________ 
It is to be noted that the quantity of binder to achieve the same de-ashing 
ratio was reduced almost by half in the process of this invention as 
compared with the conventional process. 
EXAMPLE 3 
The same experiment as Example 1 was carried out for high-water brown coal 
produced in Australia. Results are shown in Table 2. 
TABLE 2 
______________________________________ 
Raw coal 
Water content (wt %) 
60 
Ash content (wt %) 
4.8 
Average particle size (mm) 
0.285 
Conventional 
Process of 
process the invention 
Kind and quantity of 
Coal tar Fuel oil C 
binder added (%) 30 16 
Water in pellets (wt %) 
15.0 12.0 
Ash in pellets (wt %) 
2.5 2.9 
______________________________________ 
In the conventional process, it was impossible to produce pellets with 30 
wt % of fuel oil C, and it was only possible to produce pellets with 30 wt 
% of coal tar. This means that the conventional process is industrially 
unfavorable in recent years when coal tar is not available in large 
quantities. 
In the process of this invention, it was possible to produce pellets with 
half as much binder (fuel oil C) as in the conventional process. 
The relation between the quantity of fuel oil added and the particle size 
of pulverized raw coal was investigated. Results are shown in FIG. 11. 
The particle size distribution of raw coal was such that the slope of 
Rosin-Rammler distribution is about 45.degree. (tan .theta.=1). 
FIG. 11 indicates that the binder in the process of this invention (line H) 
is nearly halved as compared with the conventional OAW process (line G). 
EXAMPLE 4 
In the process of this Example shown in FIG. 4, the post-treatment step by 
gravity separation was added to the process shown in FIG. 1. 
Using the same raw coal as in Example 2, the relation between gravity 
separation and ash content of pellets was investigated. Results are shown 
in FIGS. 12 and 13. 
In FIGS. 12 and 13, point K (indicated by a double circle) on curve J 
indicates the ash content of raw coal (33 wt %). The broken line from 
point K to point L (indicated by a triangle) is the so-called gravity 
separation curve of raw coal. In the conventional gravity separation of 
raw coal, purified coal containing 20 wt % ash represented by point L can 
be obtained if settled coal amounting to 20 wt % of the total coal is 
discarded. However, the discarded coal still contain about 15 wt % of pure 
coal and the discard gives rise to a great problem in energy economy and 
environmental protection. 
Point N (indicated by a circle) on curve M indicates the ash content of 
pellets (pellets 17 in FIG. 4) prior to gravity separation in the process 
of this invention. The curve from point N to point O (indicated by an X) 
is the gravity separation curve of the pellets. This curve indicates that 
according to the process of this invention it is possible to reduce the 
ash content to 11 wt % for the purified pellets defined by point O. 
Settled coal or high-ash pellets to be recycled to the de-ashing step 14 
after crushing contain about 45% of pure coal which corresponds to about 7 
wt % of coal before treatment. This pure coal is recovered in the steps 
from mixer 11 to separator 19 in FIG. 4. 
Incidentally, in FIG. 13, chain line P indicates an imaginary line for 100% 
yield of pure coal. 
According to the process of this invention, it is possible to accomplish a 
very high de-ashing ratio while reducing by half the quantity of binder 
and keeping the yield higher than 98%. 
EXAMPLE 5 
In the process of this Example shown in FIG. 6, the pre-treatment step by 
gravity separation was added to the process shown in FIG. 4. 
FIG. 14 shows the relation between the ash content and the weight ratio of 
floating coal of the resulting pellets. 
In this Example, high-ash bituminous coal containing 35 wt % ash was used. 
In FIG. 14, broken line J from point P (raw coal) to point S via point T 
represents the flotation curve of lump coal obtained by crushing raw coal 
to 20 to 100 mm size. As compared with FIG. 13, this curve J greatly 
deviates from the imaginary line PQ representing 100% yield of pure coal. 
As shown in FIG. 6, raw coal is subjected to gravity separation so as to 
obtain purified coal (represented by T in FIG. 14) containing 23 wt % ash. 
This purified coal undergoes dry pelletizing and underwater forming to 
yield pellets containing 13 wt % ash as represented by U in FIG. 14. The 
pellets U are then subjected to gravity separation to yield purified 
pellets as final products containing ash less than 10 wt % (represented by 
R). 
If it is attempted to obtain purified coal containing 10 wt % ash simply by 
subjecting raw coal (point P) to gravity separation, the yield is 40 wt % 
as indicated by point S, whereas the process shown in FIG. 6 makes it 
possible to increase the yield to 62% (point R) with a significant 
economical effect. 
EXAMPLE 6 
In the process of this Example shown in FIG. 7, the pre-treatment step for 
de-ashing by gravity separation was added to the process shown in FIG. 1. 
FIG. 15 shows the relation between the ash content and the weight ratio of 
floating coal of the resulting pellets. 
In this Example, high-ash bituminous coal containing 40 wt % ash was used. 
In FIG. 15, the straight line drawn from point P representing ash content 
of raw coal to point Q representing 60 wt % yield of floated coal 
represents the imaginary line for 100% yield of pure coal. The broken line 
J from point P to point S via point T represents the flotation curve of 
lump coal obtained by crushing raw coal to 20 to 100 mm size. 
So long as the flotation curve J is close to the straight imaginary line 
for 100% yield of pure coal, or in the range in which ash content is 
decreased from 40 wt % to 20 wt %, it is adequate to subject raw coal to 
gravity separation. In other words, raw coal undergoes gravity separation 
until 77% yield (point T) is achieved, and the floating purified coal 
undergoes dry pelletizing and underwater forming. The coal is further 
de-ashed from point T to point R, and purified pellets containing 9 wt % 
ash can be obtained. 
If it is attempted to obtain purified coal containing 10 wt % ash simply by 
subjecting raw coal to gravity separation as shown in curve J from point P 
to point S via point T, the yield is less than 50 wt % as indicated by 
point S, whereas the process shown in FIG. 7 makes it possible to increase 
the yield to 66% (from point P to point R via point T) with a saving of 
discarded coal and improved economy. 
EXAMPLE 7 
Slurry transportation was investigated using the pellets obtained in 
Example 1. 
In view of the fact that pipes used for slurry transportation of pellets 
are larger in diameter than those used for slurry transportation of dust 
coal, one is inclined to think that slurry transportation of pellets 
requires a greater critical flow rate and involves difficulties 
accordingly. 
However, it was confirmed in the pilot plant of Example 1 that pellet 
slurry of 50 wt % solids can be transported satisfactorily through a pipe 
having a nominal diameter of 3B (3 inches) and a total length of 100 
meters, at a flow rate of 1.5 m/s which is the standard flow rate for dust 
coal slurry. This results from the fact that pellets have a low true 
specific gravity because they are free of heavy ash (.rho..gtoreq.2) and 
contains fuel oil (.rho.=0.9 to 0.95) and air which has been entrapped in 
voids during the dry agitation process. 
In the case of coal slurry containing powder of bituminous coal produced in 
Eastern Australia, the resulting slurry is acid at pH 3 to 5 and corrodes 
pipelines. However, the slurry carrying the same coal which has been 
formed into pellets is neutral at pH 7.3 and does not corrode pipelines. 
The pellets obtained in Example 1 were passed through the centrifugal pump 
in the pilot plant 185 times and passed through the piping for 9 hours to 
see if the pellets are pulverized during slurry transportation. It was 
found that particles smaller than 0.5 mm in size were formed in an amount 
of about 10% based on the total quantity of pellets larger than 0.5 mm in 
size. It was also found that the fine particles formed by disintegration 
are still agglomerates and are not particles of size in microns which 
cause trouble in the dewatering process. 
It has been proved that the process of this invention is superior to the 
conventional OAW arranged at the terminal of a pipeline for dust coal 
slurry. Needless to say, the process of this invention has a significant 
effect that the wase of transporting ash is reduced.