FIELD OF THE INVENTION
The present invention generally relates to cleaning of coal with mineral matter
finely disseminated in the organic-mass. More particularly, the invention relates
to a system and a process to produce low ash clean coal from high ash coal.
BACKGROUND OF THE INVENTION
As coal is a heterogenous mixture of organic and inorganic constituents,
solvolysis of coal varies with its constituents. Maturity, and structural
characteristics. Since the mineral matter (non-combustible) in Indian coals is
very finely disseminated in the organic mass, it is really very difficult to remove
this by conventional physical coal washing techniques. Presence of high
percentage of near gravity material in coal makes the scope of gravity process
limited. Concept of chemical beneficiation comes from the limitation 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 may be the right

approach to overcome the limitation of physical benefjciation methods. A lot of
literature is available on 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 ash could be recovering the premium organic matter from coal
by solvent refining. Literature reveals that most of the research work on this
subject was carried out with an objective to produce ultra clean coal or super
clean coal with ash content less than 0.2% for various high tech end uses. This
conventional solvent refining process does 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 coal is not absolutely
desired at the cost of restricting to low yields.
By way of reference, Indian patent application numbers 1292/KOL/06,
1088/KOL/07, 1336/KOL/20078, 950/KOL/09, 1195/KOL/09, 611/KOL/09 and
1581/KOL/08 are incorporated herein being related to the similar field of
technology.

Main advantages of this process are i) ease of recovery of solvent in the main
process stream, ii) solvolytic efficiency of recovered solvents as that of fresh
solvent, iii) 95-98% recovery of the solvent, iv) improved coking properties of
clean coal, and v) availability of industrial organic solvents. However, the
operating cost of this process is high because of high cost of solvents and energy
requirement in the process. The inventors made an effort to make this process
techno-economic initially through lab-scale process by improving the yield upto
50-60% with less than 8% ash content, including reduction in the cost of
solvent recovery.
According to the established process in the laboratory, coal, solvent (N-Methyl-2-
Pyrrolidone, NMP) and co-solvent (Ethylenediamine, EDA) are mixed thoroughly
to produce a coal slurry. The coal slurry is extracted in a known manner which
includes coal-solvent mixture. The 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% off solvent recovery. The hot concentrated

coal-solvent mixture is then flushed in a precipitation tank to precipitate the coal.
In this case, water as an anti-solvent is used. Water separates the solvent from
coal and a water-solvent mixture is obtained, which is fed to a distillation unit to
separate solvent and anti-solvent. The precipitated coal is separated in a filter. In
the process, coal, solvent and co-solvent are taken in a pre defined ratio. Coal to
solvent ratio is varied froml:6 to 1:17 (wt/vol, g/mL, coal to solvent ratios being
wt.vol, and solvent to co-solvent ratio are vol/vol). Coal to co-solvent as well as
co-solvent ratio is maintained as 1:1 (g/mL).
OBJECTS OF THE INVENTION
It is therefore an object of this invention to propose an industrial process to
produce low ash clean coal from high ash coal.
Another object of this invention is to propose a single reactor-based system to
produce low ash clean coal from high ash coal.

A further object of this invention is to propose a validation process to establish
the efficiency of the inventive system and process to produce low ash clean coal
from high ash coal, as compared to the output from the laboratory scale unit.
SUMMARY OF THE INVENTION
According to the invention, a process flow diagram for an industrial plant with a
single reactor is proposed. The important equipments constituting the inventive
system, are a thermic fluid heater, a reactor, a heat exchanger, a thermic fluid
pump, and an inert gas (N2) cylinder. Some of the associated equipments or
vessels comprise a water storage tank, a diesel storage tank, a thermic fluid
storage tank, and an expansion tank.
A reflux condenser (12) is used to maintain pressure at a specified condition.
The system also consists of about eighteen gate and ball valves, two pressure
gauges, at least one temperature gauge, and four temperature transmitters,

Solvents and coal are loaded into the reactor (10) with the help of opening on
the reactor top. Sampling system has been provided at the bottom of the reactor
(10) to draw the sample as and when required.
According to the invention, there is provided an industrial process for treating
coal to lower ash content in a system, the system comprising a first water
storage tank, a second water storage tank, a diesel storage thank, a thermic fluid
heater, a thermic fluid storage tank, a thermic fluid pump, a heat exchanger, a
thermic fluid expansion tank, a N2 gas cylinder, a reactor, a water pump, and a
reflux condenser, the method comprising (i) forming a slurry of coal fines in a N-
Methyl-2-pyrrolidone (NMP) with Ethylenediamine (EDA), the NMP and EDA ratio
varying between 5:1 to 25:1 solution, said slurry containing about 6 to 18 ml of
solution per g of coal, (ii) maintaining said slurry in the reactor at a temperature
range of 150°C to 220°C and at a pressure range of 1 to 4 gauge (kg/cm2) for a
period of about 1 to 3 hours, (iii) separating a sample of the slurry by coarse
filtration in a filter cloth, (separation cut size being variable depending on the

particle size to be treated and the end produce), to obtain a filtrate or extract
and a residue, (iv) precipitating the coal in water by adding concentrated extract,
and (vi) separating the coal by filtration, said coal having a reduced ash content.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
Figure 1 - shows a block diagram of a system to produce low-ash clean coal
from high-ash coal.
DETAILED DESCRIPTION OF THE INVENTION
As shown in figure 1, the inventive system comprises a first water storage tank
(1), a second water storage tank (2), a diesel storage tank (3), a thermic fluid
heater (4), a thermic fluid storage tank (5), a thermic fluid pump (6),a heat
exchanger (7), a termic fluid expansion tank (8)m a N2 gas cylinder (9), a reactor
(10), a water pump (11), and a reflux condenser (12).

Coal and solvent in a predetermined ratio are loaded into the reactor (10).
Nitrogen gas is supplied through the N2 cylinder (9) for maintaining inert
environment. Diesel is supplied to a burner from the diesel storage tank (3).
Thermic fluid is supplied into the system from the thermic fluid storage tank (5).
Thermic fluid is heated in the thermic fluid heater (4). On heating, the volume of
the thermic fluid increases. Thus, the expansion tank (8) is used to store extra
thermic fluid. The reactor (10) is heated by the hot thermic fluid, which is
pumped by the thermic fluid pump (6). During extraction, a sample is withdrawn
through a sample port with the help of valves (V9, V10). On completion of the
extraction step, the burner is switched off. To cool down the thermic fluid heater
(4), the thermic fluid is passed through the heat exchanger (7). Water is pumped
in the heat exchanger (7) through the water pump (11) from one of the first and
second water storage tank (1 or 2). The reflux condenser (12) maintains
pressure and temperature at a desired level.

The reactor (10) is configured with desired dimension and capacity for example,
diameter-630mm, height-850mm, conical height-175, capacity about 425 lit. Coal
and solvents are loaded into the reactor (10) through valve V7 in a
predetermined ratio. Coal to total solvent ratio is varied from 1:6 to 1:18 (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 1:25 to 1:5.
Nitrogen gas is purged into the system for maintaining inert environment.
Thermic fluid is pumped into the system from the thermic fluid storage tank (5).
Thermic fluid is heated in the thermic fluid heater (4) by the diesel fired burner.
The reactor (10) is heated by hot thermic fluid through limpet coils. Reactor
pressure is being varied from 1 to 4 gauge (kg/cm2). Reactor temperature is
varied from 150°C to 220°C. Extraction is being done for 1 to 3 hr in the reactor.
The sample is withdrawn from the reactor (10) through the sample port at
predetermined time intervals. This sample is filtered through a mesh. Filtration
step separates the refluxed mix in two parts (i) residue and (ii) filtrate (extracted

material with solvents. Residue is washed thoroughly with an anti-solvent (water)
for removal of the solvents from the residue. After drying and weighing, these
residues 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 container. Concentrated extract is then added in to the water. 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
the solvent-water solution through filtration. This step is carried out in a conical
flask-funnel arrangement with standard mesh. The residue 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.
The Experimental results are shown in table 1.


Some of the experimental results are shown in table 1. The feed coal is run-of-
mines (ROM) coal having about 26% ash. The feed particle size is -0.5 mm and
extraction is done at 2.5 and 1 kg/cm2 pressure. Results are shown at two
different coal to solvent ratio, 1:6 and 1:10. Clean coal ash is about 7% when
pressure is 2.5 kg/cm2 and it is about 4% when pressure is 1 kg/cm2. Clean coal
yield is about 48% and 50% for 1:10 and 1:6 coal to solvent ratio respectively. It
is possible to produce less than 8% ash clean coal in the inventive step. With the
help of fine filtration even less than 1% ash clean coal can be obtained. This
proves that the results contained in the system, are similar to that obtained at
laboratory scale.

WE CLAIM:
1. An industrial process for treating coal to lower ash content in a system,
the system comprising a first water storage tank (1), a second water storage
tank (2), a diesel storage tank (3), a thermic fluid heater (4) , a thermic fluid
storage tank (5), a thermic fluid pump (6), a heat exchanger (7), a thermic fluid
expansion tank (8), a N2 gas cylinder (9), a reactor (10), a water pump (11), and
a reflux condenser (12), the method comprising (i) forming a slurry of coal fines
in a N-Methyl-2-pyrrolidone (NMP) with Ethylenediamine (EDA), the NMP and
EDA ratio varying between 5:1 to 25:1 solution, said slurry containing about 6 to
18 ml of solution per g of coal, (ii) maintaining said slurry in the reactor at a
temperature range of 150°C to 22°C and at a pressure range of 1 to 4 gauge
(kg/cm2) for a period of about 1 to 3 hours, (iii) separating a sample of the slurry
by coarse filtration in a filter cloth, (separation cut size being variable
depending on the particle size to be treated and the end produce), to obtain a
filtrate or extract and a residue, (iv) precipitating the coal in water by adding
concentrated extract, and (vi) separating the coal by filtration, said coal having a
reduced ash content.

2. The process as claimed in claim 1 wherein said coal comprises run of mine
coal.
3. The process as claimed in claim 2 wherein said particle size is preferably, -
0.5 mm or any fine size depending on the end use.
4. The process as claimed in claim 1 wherein said ultra low ash clean coal or
super clean coal having ash content < 1% is produced by fine filtration of the
extracted solution.
5. The process as claimed in claim 4 wherein said ultra low ash clean coal or
super clean coal having ash content < 1% can be used to produce graphite,
liquid fuels, aromatic polymers, specially chemicals, carbon materials such as
carbon nanotubes.
6. The process as claimed in claim 1 wherein clean coal having ash content
< 8% is produced by coarse filtration of the extracted solution.

7. The process as claimed in claim 6 wherein said clean coal having ash
content < 8% can be used for one of coke making, blast furnace injection in iron
and steel industries, and power plants.
8. The process as claimed in claim 1 wherein said clean coal having ash
content < 8% is produced in said system at an yield rate of about 50% clean
coal.
9. The process as claimed in claim 1 wherein said cleaning coal having ash
content < 8% is produced in said system with a varying coal to solvent ratio of
1:6 to 1:18.
10. The process as claimed in claim 1 wherein said clean coal having ash
content < 8% is produced in said system at an yield rate equivalent to that of a
laboratory set-up.

An industrial process for treating coal to lower ash content in a system, the
system comprising a first water storage tank (1), a second water storage tank
(2), a diesel storage tank (3), a thermic fluid heater (4), a thermic fluid storage
tank (5), a thermic fluid pump (6), a heat exchanger (7), a thermic fluid
expansion tank (8), a N2gas cylinder (9), a reactor (10), a water pump (11), and
a reflux condenser (12), the method comprising (i) forming a slurry of coal fines
in a N-Methyl-2-pyrrolidone (NMP) with Ethylenediamine (EDA), the NMP and
EDA ratio varying between 5:1 to 25:1 solution, said slurry containing about 6 to
18 ml of solution per g of coal, (ii) maintaining said slurry in the reactor at a
temperature range of 150°C to 220°C and at a pressure range of 1 to 4 gauge
(kg/cm2) for a period of about 1 to 3 hours, (iii) separating a sample of the slurry
by coarse filtration in a filter cloth, (separation cut size being variable
depending on the particle size to be treated and the end produce), to obtain a
filtrate or extract and a residue, (iv) precipitating the coal in water by adding
concentrated extract, and (vi) separating the coal by filtration, said coal having a
reduced ash content.