FIELD OF THE INVENTION:
An improved way to produce low ash clean coal from high ash coal with total
solvent recovery.
BACKGROUND OF THE INVENTION:
As coal is a heterogeneous mixture of organic and inorganic constituents, the
process of solvolysis of coal varies with its constituents, maturity, and structural
characteristics. Since the mineral matter (non-combustible) in coals available in
specific geographical location, is very finely disseminated in the organic mass, it
is quite difficult to remove this non-combustible mineral matter by conventional
physical coal washing techniques. Presence of high percentage of near gravity
material in coal makes the scope of gravity process limited. It is known that
chemical benefication originates from the limitations of physical beneficiation
processes. Broadly, chemical beneficiation is possible by chemical leaching of
mineral matter present in coal or, dissolving organic matter of coal in various
organic solvents. This indicates that chemical treatment could be one of the
solutions to overcome the limitations of physical benefication methods. Prior art
teaches chemical beneficiation techniques that employ highly corrosive chemicals
(mostly acids and alkalis). Recovery or regeneration of these chemicals is very
important to make this technology viable. A parallel approach towards lowering

the ash-content could be recovery of the premium organic matter from coal by
solvent refining. Most of the prior art disclose that chemical leaching is basically
adapted to produce ultra clean coal or super clean coal with ash content less
than 0.2% for various high tech end uses. However, such conventional solvent
refining processes do not serve the objective of low ash coal requirement of steel
industries because of mainly low recovery which makes the process uneconomic
especially when such an ultra clean coal is not absolutely desired at the cost of
lowering the yields. Additionally, the operating cost of said prior art process is
high because of high cost of solvents and energy requirement in the process. In
prior art process, the extraction is being done at boiling point of the solvent
mixture making it difficult to recover the solvent from clean coal and reject.
Thus, there is a need to propose a process of washing clean coal and reject to
recover the remaining solvents. Also, there is a need to develop a process of
extraction of coal at a temperature lower than the boiling point of the solvent
mix.
By way of reference, the inventors observed that Indian patent application
numbers 1292/KOL/06, 1088/KOL/07, 1336/KOL/2008, 950/KOL/09,
1194/KOL/09, 611/KOL/09, 1581/KOL/08 are herein incorporated.

OBJECTS OF THE INVENTION:
It is therefore an object of this invention to propose a process to produce low
ash clean coal from high ash coal.
Another object of this invention is to propose a process to produce low ash clean
coal from high ash coal, in which coal is extracted at higher temperature than
the boiling point of solvent.
A still another object of this invention is to propose a process to produce low ash
clean coal from high ash coal, in which less amount of solvent is used.
Yet another object of this invention is to propose a process to produce low ash
clean coal from high ash coal, in which a washing step to recover solvent from
clean coal and reject is implemented.
A further object of this invention is to propose a process to produce low ash
clean coal from high ash coal, in which >99% solvent is recovered.

SUMMARY OF THE INVENTION:
According to the invention, coal, solvent (N-Methyl-2-Pyrrolidone, NMP) and co-
solvent (Ethylenediamine, EDA) are mixed thoroughly to produce coal slurry. The
coal slurry is extracted in a known manner which includes coal-solvent mixture.
According to the inventive process, coal is extracted by using solvent and co-
solvent in the reactor. The coal solvent mixture is separated in a separation unit
to produce a coarser fraction and a finer fraction. The finer fraction is fed to an
evaporator unit to allow 70 to 80% of solvent recovery. The hot concentrated
coal-solvent mixture is then flushed in a precipitation tank to precipitate the coal.
Where, water as an anti-solvent is being used. Water separates the solvent from
coal and we get water-solvent mixture, which is fed to distillation unit to
separate solvent and anti-solvent. And precipitated coal is separated in a filter. In
this inventive process, coal, solvent and co-solvent are being taken in a
predefined ratio. Coal to solvent ratio is varied from 1:4 to 1:25 (wt/vol, g/mL,
coal to solvent ratios are wt/vol and solvent: co-solvent ratios are vol/vol
wherever mentioned). Coal to co-solvent ratio is varied from 1:1 to 10:1 and co-
solvent to solvent ratio is varied from 1:1 to 1:50 (g/mL). Both clean coal and
reject is being washed in a sequence shown in figure 1. Following important
equipments were there in the system, such as thermic fluid heater, reactor, heat

exchanger, thermic fluid pump, inert gas (N2) cylinder, feed tank for evaporator,
double effect evaporator, feed pump, transfer pump, discharge pump, heat
exchanger, condenser, cooling tower, cooling pump, concentrate tank,
condensate tank, distillation feed tank, feed pump, distillation column,
condenser, condenser tank, reflux pump, reboiler, reboiler pump, discharge
pump, and bottom product tank. Some other equipments or vessels such as
water storage tank, diesel storage tank, thermic fluid storage tank, expansion
tank and centrifuge filter were also installed for this process.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING:
Fig-1 shows a system for washing clean coal and rejects.
DETAILED DESCRIPTION OF THE INVENTION:
As shown in fig - 1, the system consists of a plurality of units, each unit
comprising a precipitation tank, and a wash tank with stirrer system. Coal (reject
or clean coal) and washed liquid is obtained from each unit. The coal and reject
goes to next wash tank and washed liquid goes to previous wash tank.

Coal and solvent in predetermined ratio are loaded into a reactor. Nitrogen gas is
supplied through N2 cylinder for maintaining inert environment. Diesel is supplied
to a burner from a diesel storage tank. Thermic fluid is supplied into the system
from a thermic fluid storage tank. The thermic fluid is heated in a thermic fluid
heater. On heating, the thermic fluid's volume increases, and accordingly, an
expansion tank is used to store the extra thermic fluid. Hot thermic fluid is
pumped by a thermic fluid pump to heat the reactor. During extraction, a sample
is withdrawn from a sample port. On completion of the extraction, the burner is
switched off. To cool down the thermic fluid heater, the thermic fluid is passed
through a heat exchanger. Water is pumped in the heat exchanger through a
water pump from a water storage tank. A reflux condenser maintains pressure
and temperature at the reactor at a desired level.
Coal and solvents are loaded into the reactor in a predetermined ratio. Coal to
total solvent ratio is varied from 1:4 to 1:25 (wt/vol, g/mL, coal to solvent ratios
are wt/vol and solvent: co-solvent ratios are vol/vol wherever mentioned). Co-
solvent to solvent ratio is varied from 1:50 to 1:1. Nitrogen gas is purged into
the system for maintaining an inert environment. Thermic fluid is pumped into
the system from the thermic fluid storage tank. Thermic fluid is heated in the
thermic fluid heater by the diesel fired burner. The reactor is heated by hot

thermic fluid. Reactor pressure is varied from 1 to 4 kg/cm2. Reactor
temperature is varied from 100°C to 240°C. Extraction is done for 15 minutes to
4 h in the reactor.
Sample is withdrawn from the reactor through the sample port in predetermined
time intervals. This sample is filtered through a mesh. Filtration separates the
refluxed mix in two parts (i) reject and (ii) filtrate (extracted material with
solvents). Reject is washed thoroughly with an anti-solvent (water) for the
removal of the solvents from the reject. After drying and weighing, these rejects
are subjected to ash analysis. The filtrate is actually the extract containing very
low ash coal. For precipitation an anti solvent (water) is taken in a vessel.
Concentrated extract is then added in to the water. As these solvents are soluble
in water, the solvents move to water phase. It resulted in precipitation of solid
coal particles. The precipitated coal is then separated from the solvent-water
solution through filtration. This step is carried out in a conical flask-funnel type
arrangement with standard mesh. The reject of this filtration is the low ash clean
coal; filtrate consists of water and the solvents. After drying and weighing, the
clean coals are subjected to chemical and petro graphical analysis.

At a plant level, the recovery system comprises an evaporator feed tank, an
evaporator feed pump, a first evaporator, a vapour collector, a second
evaporator, a transfer pump, a discharge pump, a heat Exchanger, a concentrate
product tank, a condenser, a condensate tank, a cooling tower, a cooling pump,
a feed tank for distillation column, a feed pump for distillation, a distillation
column, a condenser, a condensate tank, a distillate pump, a reboiler, a reboiler
pump, a bottom product tank.
Reacted material in the reactor is taken out and filtered through a centrifuge
filter. Filtration separates the refluxed mix in two parts (i) reject and (ii) filtrate
(extracted material with solvents). Reject is washed thoroughly with an anti-
solvent (water) for the removal of the solvents from the reject (as shown in
figure 1). After drying and weighing, these rejects are subjected to ash analysis.
The filtrate is actually the extract containing very low ash coal. Filtrate (extracted
material along with solvents) are taken into the evaporator feed tank. Feed
material is fed to both the evaporators through the feed pump. Heating is started
in the second tank through hot thermic fluid. As the material is heated in the
second evaporator, vapour is generated. Vapour passes through the vapour
collector tank and then goes to the first evaporator to pre heat the input
material. Vapour generated in the first evaporator passes through the vapour

collector and finally passes through the condenser. The condensate is collected
in the condensate tank. The discharge pump is activated to allow discharge of
the concentrated material through the discharge pump to the concentrate
product tank with or without cooling. Concentrated product is continuously taken
out into the concentrate product tank. This cycle is allowed to continue till a
substantially concentrate material is obtained. About 80-85% solvent is
evaporated in this evaporator.
The concentrated material is precipitated in water in the mixing tank. As these
solvents are soluble in water, solvents move to water phase. It resulted in
precipitation of solid coal particles. Thus, precipitated coal is then separated from
solvent-water solution through the centrifuge filter. Clean coal is further washed
(as shown in figure 1) till all the solvent is removed from coal. Water-solvent
mixture is stored in a storage tank, which is separated in a distillation column.
Water-solvent mixture is fed to the distillation feed tank. The feed pump is
started to feed the material into the distillation column. The reboiler pump is
started to allow flow of thermic fluid in the reboiler to heat the material. This
water-solvent mixture is heated up by circulating it through the reboiler. After
some time this whole material is heated up and water vapour is generated. This

vapour comes out from top vapour line. The reflux (distillate) pump is started to
recycle the distillate into the distillation column. Vapour passes through the
condenser and condensed water goes to the distillate tank. This distillate is fed
to the distillation column till an equilibrium is achieved (based on reflux ratio).
The top product (distillate) can be taken out from the distillate line. This
continuous cycle of feeding material to the distillation column, heating it through
the reboiler and recycling it through the condenser continuous till the feed
material is distillated.
The bottom product discharge pump is operated to collect the bottom product
into the bottom product tank. Water and solvent is separated and stored in
different tanks, which can be used again in the process.
Clean coal and reject coal is washed as shown in the figure 1. Basically, it is a
countercurrent washing where fresh water is used, to wash last batch of clean
coal and reject (least contaminated with solvents) in the wash tank 8 and 9. Coal
extract along with wash liquid WOl and WEI is fed to precipitation tank (PPT
TANK 1). Coal is precipitated and clean coal (CO) and wash liquid (WOO) are
obtained. The clean coal is fed to next wash tank 2, and wash liquid WOO to
distillation column, where water and solvent is separated. In the wash tank 2

clean coal CO and wash liquid W02 is fed, which gives clean coal CI and wash
liquid WOl. Clean coal CI and wash liquid W03 is fed to wash tank 4, which
gives clean coal C2 and wash liquid W02. Clean coal C2 and wash liquid W04 is
fed to wash tank 6, which gives clean coal C3 and wash liquid W03. Clean coal
C3 and fresh water is fed to wash tank 8, which gives clean coal C4 and wash
liquid W04. Reject along with WE2 is fed to wash tank 3, which gives reject Rl
and wash liquid WEI. Reject Rl and wash liquid WEI. Reject Rl along with WE3
is fed to wash tank 5, which gives reject R2 and wash liquid WE2. Reject R2
along with WE4 is being fed to wash tank 7, which gives reject R3 and wash
liquid WE3. Reject R3 along fresh water is fed to wash tank 9, which gives reject
R4 and wash liquid WE4. Fresh water is given only at one stage and the same
water is used in all other steps in washing. By this strategy, water consumption
is less compared to conventional washing.
Many trials were conducted by varying different process parameters such as
temperature (100°C to 240°C), coal to solvent ratio (1:4 to 1:25), size fraction (-
1 mm, to -0.1 mm), different coal origin, filter pore size, co-solvent to solvent
ratio. The typical feed coal samples were run-of-mines (ROM) coal and flotation
clean coal having about 25-35% and 12-15% ash respectively. The feed particle

size varied from -1 mm to -0.1 mm and extraction was done at different
temperature.
Some of the typical results are shown here, for example, clean coal yield varied
from 45% to 60%. Clean coal ash was about 4%. It is possible to produce less
than 8% ash clean coal with 60% yield and about 80% combustible recovery
with this process. With the help of fine filtration even less than 1% ash clean
coal could be possible. With some typical coal, 70% of clean coal yield could be
achieved.

WE CLAIM:
1. An improved process to produce low ash clean coal from high ash coal
with substantially complete solvent recovery, the process comprising :
(i) forming a slurry of coal fines in a N-Methyl-2-pyrrolidone (NMP)
with a small amount of Ethylenediamine (EDA);
(ii) maintaining said slurry in a reactor at a temperature range of
100°C to 240°C and a pressure range of 1 to 4 gauge (kg/cm2)
for a period of about 15 minutes to 4 hours;
(iii) separating the produced sample after withdrawal from the
reactor, separation cut size being variable depending on the
particle size to be treated including application of the end
product, a first part of the separated sample being a filtrate or
extract and the second part being a reject;
(iv) washing the reject in an anti solvent by adding second part
called reject;
(v) separating the reject by filtration, said separated reject having a
high ash content;
(vi) feeding the extracted part into an evaporator to recover 80-
85% solvent;
(vii) precipitating the concentrated material into an anti solvent tank
to separate coal from solvent;

(viii) separating the coal by filtration, said separated coal having a
reduced ash content;
(ix) feeding anti solvent and solvent mixture in a distillation column
to separate remaining solvent from the anti solvent for reuse in
the process.
2. The process as claimed in claim 1 wherein said coal comprises run of mine
coal.
3. The process as claimed in claim 1 wherein said coal comprises flotation
clean coal.
4. The process as claimed in claim 2 wherein said particle size is preferably, -
0.5 mm or any fine size depending on the requirement.
5. The process as claimed in claim 1 wherein an ultra low ash clean coal or
super clean coal produced in step (viii) is having ash content < 1%, and
produced by said fine filtration of the extracted solution.

6. The process as claimed in claim 5, wherein said ultra low ash clean coal or
super clean coal having ash content < 1% is applicable to produce
graphite, liquid fuels, aromatic polymers, special chemicals, carbon
materials such as carbon nanotubes.
7. The process as claimed in claim 1 wherein a moderate ash clean coal
produced at step (iii) is having ash content <8%, and produced by coarse
filtration of the extracted solution.
8. The process as claimed in claim 7 wherein said moderate ash clean coal
having ash content <8% can be used for coke making and blast furnace
injection in iron and steel industries and in power generation.
9. The process as claimed in claim 1 wherein said moderate ash clean coal
having <8% ash content is produced in the process constitutes about
60% clean coal yield.
10. The process as claimed in claim 1 wherein coal ash having <8% is
produced in the process contains about 80% combustible recovery in the
clean coal.

11. The process as claimed in claim 1 wherein coal ash having <8% is
produced in said process at coal to solvent ratio of 1:4 to 1:25.
12. The process as claimed in claim 1 wherein coal ash having <8% is
produced in said process at co-solvent to solvent ratio of 1:1 to 1:50.
13. The process as claimed in claim 1 wherein coal ash having < 8% is
produced in said process at a temperature range of 100°C to 240°C.
14. The process as claimed in claim 1 wherein coal ash having <8% is
produced in said process at a pressure range of 1 to 4 gauge (kg/cm2).
15. The process as claimed in claim 1 wherein coal ash having <8% is
produced in said process coal to co-solvent ratio is varied from 1:1 to
10:1.
16. The process as claimed in claim 1 wherein coal ash having <8% is
produced with >99% solvent recovery from the system.

17. The process as claimed in claim 1 wherein coal ash having <8% is
produced in said process in which clean coal and reject is being washed at
least five stages to recover the solvents.

ABSTRACT
An improved process to produce low ash clean coal from high ash coal with
substantially complete solvent recovery, the process comprising forming a slurry
of coal fines in a N-Methyl-2-pyrrolidone (NMP) with a small amount of
Ethylenediamine (EDA); maintaining said slurry in a reactor at a temperature
range of 100°C to 240°C and a pressure range of 1 to 4 gauge (kg/cm2) for a
period of about 15 minutes to 4 hours; separating the produced sample
withdrawn from the reactor, separation cut size being variable depending on the
particle size to be treated including application of the end product, one part
being a filtrate or extract and other a reject; precipitating the coal in an anti
solvent by adding concentrated extract; separating the coal by filtration, said
separated coal having a reduced ash content; feeding the extracted part into an
evaporator to recover 80-85% solvent; precipitating the concentrated material
into an anti solvent tank to separate coal from solvent, feeding anti solvent and
solvent mixture in a distillation column to separate remaining solvent from the
anti solvent for reuse in the process.