Title of Invention	A PROCESS TO PRODUCE LOW ASH CLEAN COAL FROM HIGH ASH COALS FOR VARIOUS METALLURGICAL APPLICATIONS
Abstract	The invention relates to a process for treating coal to lower ash content comprising (i) forming a slurry of coal fines in a N-Methyl-2-pyrrolidona (NMP) with a small amount of Cyclohexylamine (CHA), NMP and CHA ratio may vary 14:1 to 24:1 solution, said slurry containing about 15 to 25 ml of solution per g of coal, (ii) maintaining said slurry in refluxed condition at a temperature of about 170.degree. C for a period of about 15 minutes to 2 hours depending on the requirement, (iii) separating the refluxed solution in two parts by coarse filtration at 0.025 mm filter cloth separation cut size being variable depending on the particle size to be treated and the use of the end product namely filtrate or extract and the residue, (iv) recovering the solvent up to 85% by distillation of the extract, (v) precipitating the coal by adding water in concentrated extract, (vi) separating the coal by filtration, said coal having a reduced ash content and (vii) recovering the rest of the solvent by distillation of water-solvent solution.

Title of Invention

A PROCESS TO PRODUCE LOW ASH CLEAN COAL FROM HIGH ASH COALS FOR VARIOUS METALLURGICAL APPLICATIONS

Abstract

The invention relates to a process for treating coal to lower ash content comprising (i) forming a slurry of coal fines in a N-Methyl-2-pyrrolidona (NMP) with a small amount of Cyclohexylamine (CHA), NMP and CHA ratio may vary 14:1 to 24:1 solution, said slurry containing about 15 to 25 ml of solution per g of coal, (ii) maintaining said slurry in refluxed condition at a temperature of about 170.degree. C for a period of about 15 minutes to 2 hours depending on the requirement, (iii) separating the refluxed solution in two parts by coarse filtration at 0.025 mm filter cloth separation cut size being variable depending on the particle size to be treated and the use of the end product namely filtrate or extract and the residue, (iv) recovering the solvent up to 85% by distillation of the extract, (v) precipitating the coal by adding water in concentrated extract, (vi) separating the coal by filtration, said coal having a reduced ash content and (vii) recovering the rest of the solvent by distillation of water-solvent solution.

Full Text	FIELD OF THE INVENTION The invention relates to a process to produce low ash clean coal from high ash coals for various metallurgical applications. BACKGROUND OF THE INVENTION 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. As coal is heterogeneous mixture of organic and inorganic constituents, solvolysis of coal varies with its constituents, maturity, and structural characteristics. Main advantage 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. There is an attempt to make this process techno-economic through improving the yield to 70- 80%. However, further research may be required to make the process economically viable through reducing the cost of solvent recovery. Recovery of clean coal and its ash content depend on various operating parameters and feed characteristics like faster and convenient filtration of refluxed solution at different size, solvent and co-solvent of choice, coal source, particle size, coal-solvent ratio, extraction time, extraction temperature, etc. This may thus offer the room for the trade off between the yield and the ash contents desired in the clean coal obtained by this process. Since the mineral matter (non-combustible) in Indian coals (Gondwana coals) is very finely disseminated in the organic mass, it is extremely difficult to remove this by conventional physical coal washing techniques. High percentage of near gravity material in coal makes the scope of gravity process limited. This indicates that chemical treatment may be the right approach to overcome the limitation of physical beneficiation 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. Organo-refining or, solvent-refining, or, solvent extraction of coal is a well-established technology. Abundant literature is available on the subject. However, the primary objective in most of those cases is to provide a process to produce ultra clean coal or super clean coal with ash contains less than 0.2%. The same process has been tried in our laboratory to produce suitable coal for coke making from medium coking coal. -0.5 mm fine clean coal from flotation process has been used as parent coal for organo-refining process. The ash content of this parent coal (flotation product) is 12%. Exploratory study revealed that it is possible to extract only 30% of parent coal through this process of extraction of coal under reflux conditions at atmospheric pressure. The coal so expected contains 1% ash. Losing 70% of the parent coal (with having only 12% ash) as rejects is not acceptable. The solvent extraction of coal process involves mainly the mass transfer operations. This involves the diffusion of solvents in the solid coal matrix which results in the swelling of coal. Then as the extraction proceeds, desorption of solvent containing the extracted molecules from the swollen coal matrix results in the extraction of coal molecules. It has been observed that there is a synergistic extraction enhancement of coal by using a suitable co-solvent which may aid the swelling of coal matrix for the enhanced extraction. Solvent extraction proceeds with the shrinking of cores of the coal particles as the extraction progresses. This shrinking cores result in the demineralization of coal particles. This may thus afford the chemical designing of the process of the solvent extraction of coal in such a way that the ash reduction in coal particles may be tailored to different ash levels. Since the solvent extraction leaches or cuts down the coal particles to different ash levels, therefore a suitable selection of the separation aid may help in obtaining the extracts of the coal macerals i.e., super clean coal having ash contents of different cuts or extent. Therefore there is a need to find out a convenient co-solvent for the N-methyl-2- pyrrolidone (NMP) to obtain a designer solvent. There is also a need to find out the filter of a specific pore size i.e., mesh size to obtain a coal extract having ash contents in the suitable range for coke making. OBJECTS OF THE INVENTION It is therefore an object of the invention to propose a process to produce low ash clean coal from high ash coal. Another object of the invention is to propose an economic and environment-friendly solvent-co solvent combination which is for suitable industrial extraction of coal. A further object of the invention is to propose a corresponding device to carry-out the innovative process. A still further object of the invention is to propose a process to produce low ash clean coal from high ash coals which ensures high recovery with low ash content. A still another object of the invention is to propose a process to produce low ash clean coal from high ash coals which provides faster filtration. BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING Figure 1 - Schematically shows a device for bench scale operation of the process according to the invention. SUMMARY OF THE INVENTION Accordingly there is provided in one aspect of the invention a process to produce low ash clean coal from high ash coals for various metallurgical applications. According to the innovative process, coal, solvent and co- solvent 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 a distillation unit to allow extraction of 80 to 85% of solvent recovery. The concentrated coal- solvent mixture is then flushed in a precipitation tank to precipitate the coal. Thus precipitated coal is separated in a rorary drum filter. The obtained clean coal contains less than 4% ash. The filtrate comprises a solution of solvent and water from which the solvent is recovered in a second distillation unit. The by-product from the second distillation unit being steam which can be used as a heat source in the extractor. According to a second aspect of the invention, there is provided a device for carrying-out the innovative process. The device essentially comprises an extractor to receive coal slurry from a coal-solvent feed tank and for extraction of the same. A first rotary drum filter is connected to the extractor which on receiving the extracted coal-solvent mixture, cut the mixture into two fractions. The finer fraction is fed from the first rotary drum filter to a first distillation unit for solvent recovery. A precipitation tank is flowably connected to the first distillation unit. The precipitated coal is then separated in a second rotary drum filter. The solvent is recovered through a second distillation unit, wherein the bi-product in the second distillation unit which is steam is used as a heat source for the extractor. DETAILED DESCRIPTION OF THE INVENTION A suitable solvent-co-solvent combination has been identified for convenient, environmental friendly and economical industrial extraction operation. N-methyl-2-pyrrolidone (NMP) with a small amount of Cyclohexylamine (CHA) is found as the best suitable solvent for the present. The ratio of NMP and CHA may vary from 14:1 to 24:1 and the coal (g) to solvents (ml) ratio may vary from 1:15 to 1:25. A study of the behaviour of the conventional treatment for medium coking coal from West Bokaro, a clean coal (ash content has been produced with an objective to obtain maximum possible high yield and to have faster and quick filtration. With this objective, the particle size of feed and both the products (clean coal and residual coal) have been studied. From the size analysis of feed and the two products, it is revealed that the process changes the size analysis of feed and the two products, it is revealed that the process changes the size distribution of coal i.e., this follows a shrinking core model. Therefore, the coal sample is refluxed with NMP and a small amount of CHA for 2 h at atmospheric pressure. Then the refluxed mixture using 500 stainless steel BSS mesh (0.025 mm) cloth is filtered. This arrangement allowed coarser and faster filtration at 0.025 mm size in comparison to that observed by using Whatman filter paper. Therefore, increase in yield of clean coal and simultaneously increase in ash content of clean coal, have been clearly established. However, this arrangement is found to be advantageous to produce high yield clean coal with low ash content ( faster filtration process. For NMP with small amount of CHA test, the results obtained are shown in the Table 1. A mass balancing of the ash content, reveals as under: (28.6)(1.0)+(62.6-28.6)(x)=(62.6)*(3.2) (1) Where x is the ash content of extra yield. From equation (1) it is found that x=5.05. However, it can be seen from Table 2 that ash content of -0.025 mm fraction of feed sample is 14.05%. So, it is very clear that this improvement in result is not because of simply coarser cut; rather it is because of partial dissolution phenomena during the process. Comparison of the extraction yields obtained by using NMP alone (32%) with that obtained by using a convenient co-solvent i.e., CHA (62.6%) showed the synergism of using CHA as a co-solvent. This invention thus enables producing low ash ( making purpose with very high yield through a relatively faster filtration. The extraction yields on dry mineral matter basis will be still higher. A device has been developed for bench scale operation which is shown in Fig. 1. The device consists of six units namely, (i) an Extractor (1), (ii) a first Rotary drum filter (2) (separation size 500 mesh), (iii) a first Distillation column (3), (iv) a Precipitation tank (4), (v) a second Rotary drum filter (5) (for complete solid-liquid separation, and (vi) a second Distillation column (6). Coal, solvent and co-solvent are mixed thoroughly in coal -solvent feed tank. Coal slurry is then pumped into the extractor (1). A temperature around 170°C is achieved in the extractor (1) slowly. Residence time in the extractor (1) may vary form 15 mins to 2 h and i.e. dictated by the techno economics of the process and its specific requirement. Extracted coal-solvent mixture is then separated through a first rotary drum filter (2) or any separation unit which may cut the mixture in two fractions: coarser fraction (+0.025 mm) and finer fraction (-0.025 mm). Coarser fraction contains high ash and is called as residue. The finer fraction or filtered extract is then fed to a first distillation unit (3). Maximum 80-85% solvent recovery may be allowed through the first distillation unit (3). The concentrated coal-solvent mixture is flushed in a precipitation tank (4). As NMP-CHA solvents are soluble in water, extracted coal gets separated from the solution phase and gets precipitated. This precipitated coal is separated through a second rotary drum filter (5). Thus obtained clean coal contains less than 4% ash. The filtrate consists of solvent-water solution and solvent is recovered through a second distillation unit (6). The secondary product of the second distillation unit (6) is steam, which may be used as a heat source in the extractor (1) at a high pressure. It is possible to recover around 98% of solvent through the distillation units (3,6). The important safety measures comprises: a. As the solvent of use are organic and are flammable in nature, it may catch fire in contact with oxygen at high temperature. Therefore, there is provision for Nitrogen flashing in the extractor (1) and the first Rotary drum filter unit (2). b. There may be a need to guard moisture for the co-solvent i.e. CHA.- The main advantages of the invention achieved i. Recovery increases by two folds. High recovery improves the techno- economics remarkably. ii. The shrinking core based extraction affords a trade off between extraction yield and ash contents in the super clean coal obtained. iii. An environment friendly, economic and convenient solvent-co solvent mix was identified as suitable solvents. These solvents are industrial solvents and easy to handle. Therefore, there is no concern from industrial application point of view. iv. CHA is a cheaper solvent as that of Ethylenediamine (EDA). It helps in improving the process economy, v. CHA has lesser atomic N/C ratio than that of EDA, which is good from coke making point of view as less N-contents helps in coke making, vi. Filtration becomes relatively faster by using 500 BSS mesh filter cloth, thus saving a lot of operation time, vii. Depending upon the ash contents in the super clean coal obtained, this may be studied for its other non-fuel uses as well, viii. The process is also applicable to non-coking coal for producing low ash clean coal for blast furnace injection, power generation and converting coals into liquid fuels/chemicals, ix. Maximum extraction rate is observed at the beginning of the process. Rate of extraction decreases with time. 59.6%, 63.1% extraction yield has been obtained for extraction time 0.25 h, 0.75h and 1.25 h respectively, x. Extraction yield improves for fine size; e.g. it is possible to recover 76% of parent coal if -0.25 mm fraction of coal is taken for treatment, xi. The process is useful to lower the ash contents from run of mine (ROM), middlings, and clean coal from physical beneficiation processes. Table 3 shows the effect of solvent- refining treatment of these three coals. Table 3. Test results of solvent-refining for ROM, middlings and clean coal xii. The process can also be useful to produce super clean coal or ultra low ash clean coal (ash contents potential end uses in obtaining graphite, aromatic polymers, specially chemicals, carbon materials such as carbon nanotubes etc. xiii. 98% of the solvent is easily recovered. This recovered solvent is as good as that of fresh solvent in terms of solvolytic efficiency. xiv. The super clan coal obtained showed good coking prosperities. Vitrinite contents increases significantly (Table 4). WE CLAIM; 1. A process for treating high ash coal to lower ash content comprising (i) forming a slurry of coal fines in a N-Methyl-2-pyrrolidone (NMP) with a small amount of Cyclohexylamine (CHA), NMP and CHA ratio may vary 14:1 to 24:1 solution, said slurry containing about 15 to 25 ml of solution per gm of coal, (ii) maintaining said slurry in refluxed condition at a temperature of about 170.degree. C for a period of about 15 minutes to 2 hours depending on the requirement, (iii) separating the refluxed solution in two parts by coarse filtration at 0.025 mm filter cloth separation cut size being variable depending on the particle size to be treated and the use of the end product namely filtrate or extract and the residue, (iv) recovering the solvent up to 85% by distillation of the extract, (v) precipitating the coal by adding water in concentrated extract, (vi) separating the coal by filtration, said coal having a reduced ash content and (vii) recovering the rest of the solvent by distillation of water- solvent solution. 2. The process as claimed in claim 1 wherein said coal comprises run of mine coal, middlings or fine clean coal. 3. The process as claimed in claim 2 wherein said particle size is preferably, -2mm, -0.5 mm, more preferably 0-.25 mm or any fine size depending on the requirement. 4. The process as claimed in claim 1 wherein the ultra low ash clean coal or super clean coal having ash content of the refluxed solution. 5. The process as claimed in claim 4 wherein said ultra low ash clean coal or super clean coal having ash content graphite, liquid fuels, aromatic polymers, specially chemicals, carbon materials such as carbon nanotubes etc. 6. The process as claimed in claim 1 wherein the moderate ash clean coal having ash content solution. 7. The process as claimed in claim 6 wherein said moderate ash clean coal having ash content injection in iron and steel industries and power generation. 8. The process as claimed in claim 1 wherein 98% recovery of the solvent is achieved. 9. A device for treating high-ash content coal to lower ash content, the device comprising: - an extractor (1) for receiving coal-slurry from a coal-solvent feed tank (7) and for extraction of coal-solvent mixture; - a brief rotary drum filter (2) connected to the extracted (1) which cut the solvent mixture into two fractions; - a first distillation unit (3) for receiving the finer fraction out of said two fractions form the first rotary drum filter (2) and for carrying out solvent recovery; - a precipitation tank (4) flow ably connected to the first distillation unit for receiving there from the concentrated coal-solvent mixture and following precipitation of the coal including separation of the filtrate: - a second rotary drum filter (5) for separating the precipitated coal containing less than about 4% ash; and - a second distillation unit (6) for recovery of the solvent from said filtrate containing solvent-water solution. ABSTRACT TITLE: A PROCESS TO PRODUCE LOW ASH CLEAN COAL FROM HIGH ASH COALS FOR VARIOUS METALLURGICAL APPLICATIONS The invention relates to a process for treating coal to lower ash content comprising (i) forming a slurry of coal fines in a N-Methyl-2-pyrrolidona (NMP) with a small amount of Cyclohexylamine (CHA), NMP and CHA ratio may vary 14:1 to 24:1 solution, said slurry containing about 15 to 25 ml of solution per g of coal, (ii) maintaining said slurry in refluxed condition at a temperature of about 170.degree. C for a period of about 15 minutes to 2 hours depending on the requirement, (iii) separating the refluxed solution in two parts by coarse filtration at 0.025 mm filter cloth separation cut size being variable depending on the particle size to be treated and the use of the end product namely filtrate or extract and the residue, (iv) recovering the solvent up to 85% by distillation of the extract, (v) precipitating the coal by adding water in concentrated extract, (vi) separating the coal by filtration, said coal having a reduced ash content and (vii) recovering the rest of the solvent by distillation of water-solvent solution.

Full Text

FIELD OF THE INVENTION
The invention relates to a process to produce low ash clean coal from high
ash coals for various metallurgical applications.
BACKGROUND OF THE INVENTION
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. As coal is heterogeneous
mixture of organic and inorganic constituents, solvolysis of coal varies
with its constituents, maturity, and structural characteristics. Main
advantage 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. There is an attempt to
make this process techno-economic through improving the yield to 70-
80%. However, further research may be required to make the process
economically viable through reducing the cost of solvent recovery.

Recovery of clean coal and its ash content depend on various operating
parameters and feed characteristics like faster and convenient filtration of
refluxed solution at different size, solvent and co-solvent of choice, coal
source, particle size, coal-solvent ratio, extraction time, extraction
temperature, etc. This may thus offer the room for the trade off between
the yield and the ash contents desired in the clean coal obtained by this
process.
Since the mineral matter (non-combustible) in Indian coals (Gondwana
coals) is very finely disseminated in the organic mass, it is extremely
difficult to remove this by conventional physical coal washing techniques.
High percentage of near gravity material in coal makes the scope of
gravity process limited. This indicates that chemical treatment may be the
right approach to overcome the limitation of physical beneficiation
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.

Organo-refining or, solvent-refining, or, solvent extraction of coal is a
well-established technology. Abundant literature is available on the
subject. However, the primary objective in most of those cases is to
provide a process to produce ultra clean coal or super clean coal with ash
contains less than 0.2%. The same process has been tried in our
laboratory to produce suitable coal for coke making from medium coking
coal. -0.5 mm fine clean coal from flotation process has been used as
parent coal for organo-refining process. The ash content of this parent
coal (flotation product) is 12%. Exploratory study revealed that it is
possible to extract only 30% of parent coal through this process of
extraction of coal under reflux conditions at atmospheric pressure. The
coal so expected contains 1% ash. Losing 70% of the parent coal (with
having only 12% ash) as rejects is not acceptable.
The solvent extraction of coal process involves mainly the mass transfer
operations. This involves the diffusion of solvents in the solid coal matrix
which results in the swelling of coal. Then as the extraction proceeds,
desorption of solvent containing the extracted molecules from the swollen
coal matrix results in the extraction of coal molecules. It has been
observed that there is a synergistic extraction enhancement of coal by
using a suitable co-solvent which may aid the swelling of coal matrix for
the enhanced extraction. Solvent extraction proceeds with the shrinking of
cores of the coal particles as the extraction progresses. This shrinking
cores result in the demineralization of coal particles. This may thus afford
the chemical designing of the process of the solvent extraction of coal in
such a way that the ash reduction in coal particles may be tailored to

different ash levels. Since the solvent extraction leaches or cuts down the
coal particles to different ash levels, therefore a suitable selection of the
separation aid may help in obtaining the extracts of the coal macerals i.e.,
super clean coal having ash contents of different cuts or extent. Therefore
there is a need to find out a convenient co-solvent for the N-methyl-2-
pyrrolidone (NMP) to obtain a designer solvent. There is also a need to
find out the filter of a specific pore size i.e., mesh size to obtain a coal
extract having ash contents in the suitable range for coke making.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose a process to produce
low ash clean coal from high ash coal.
Another object of the invention is to propose an economic and
environment-friendly solvent-co solvent combination which is for suitable
industrial extraction of coal.
A further object of the invention is to propose a corresponding device to
carry-out the innovative process.
A still further object of the invention is to propose a process to produce
low ash clean coal from high ash coals which ensures high recovery with
low ash content.

A still another object of the invention is to propose a process to produce
low ash clean coal from high ash coals which provides faster filtration.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
Figure 1 - Schematically shows a device for bench scale operation of the
process according to the invention.
SUMMARY OF THE INVENTION
Accordingly there is provided in one aspect of the invention a process to
produce low ash clean coal from high ash coals for various metallurgical
applications. According to the innovative process, coal, solvent and co-
solvent 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 a distillation unit to allow
extraction of 80 to 85% of solvent recovery. The concentrated coal-
solvent mixture is then flushed in a precipitation tank to precipitate the
coal. Thus precipitated coal is separated in a rorary drum filter. The
obtained clean coal contains less than 4% ash. The filtrate comprises a
solution of solvent and water from which the solvent is recovered in a
second distillation unit. The by-product from the second distillation unit
being steam which can be used as a heat source in the extractor.

According to a second aspect of the invention, there is provided a device for
carrying-out the innovative process. The device essentially comprises an
extractor to receive coal slurry from a coal-solvent feed tank and for extraction
of the same. A first rotary drum filter is connected to the extractor which on
receiving the extracted coal-solvent mixture, cut the mixture into two fractions.
The finer fraction is fed from the first rotary drum filter to a first distillation
unit for solvent recovery. A precipitation tank is flowably connected to the first
distillation unit. The precipitated coal is then separated in a second rotary
drum filter. The solvent is recovered through a second distillation unit, wherein
the bi-product in the second distillation unit which is steam is used as a heat
source for the extractor.

DETAILED DESCRIPTION OF THE INVENTION
A suitable solvent-co-solvent combination has been identified for
convenient, environmental friendly and economical industrial extraction
operation. N-methyl-2-pyrrolidone (NMP) with a small amount of
Cyclohexylamine (CHA) is found as the best suitable solvent for the
present. The ratio of NMP and CHA may vary from 14:1 to 24:1 and the
coal (g) to solvents (ml) ratio may vary from 1:15 to 1:25.
A study of the behaviour of the conventional treatment for medium coking
coal from West Bokaro, a clean coal (ash content has been produced with an objective to obtain maximum possible high

yield and to have faster and quick filtration. With this objective, the
particle size of feed and both the products (clean coal and residual coal)
have been studied. From the size analysis of feed and the two products, it
is revealed that the process changes the size analysis of feed and the two
products, it is revealed that the process changes the size distribution of
coal i.e., this follows a shrinking core model. Therefore, the coal sample is
refluxed with NMP and a small amount of CHA for 2 h at atmospheric
pressure. Then the refluxed mixture using 500 stainless steel BSS mesh
(0.025 mm) cloth is filtered. This arrangement allowed coarser and faster
filtration at 0.025 mm size in comparison to that observed by using
Whatman filter paper. Therefore, increase in yield of clean coal and
simultaneously increase in ash content of clean coal, have been clearly
established. However, this arrangement is found to be advantageous to
produce high yield clean coal with low ash content ( faster filtration process. For NMP with small amount of CHA test, the
results obtained are shown in the Table 1.

A mass balancing of the ash content, reveals as under:
(28.6)*(1.0)+(62.6-28.6)*(x)=(62.6)*(3.2) (1)
Where x is the ash content of extra yield.
From equation (1) it is found that x=5.05. However, it can be seen from
Table 2 that ash content of -0.025 mm fraction of feed sample is 14.05%.
So, it is very clear that this improvement in result is not because of simply
coarser cut; rather it is because of partial dissolution phenomena during
the process. Comparison of the extraction yields obtained by using NMP
alone (32%) with that obtained by using a convenient co-solvent i.e., CHA
(62.6%) showed the synergism of using CHA as a co-solvent. This
invention thus enables producing low ash ( making purpose with very high yield through a relatively faster filtration.
The extraction yields on dry mineral matter basis will be still higher.

A device has been developed for bench scale operation which is shown in
Fig. 1. The device consists of six units namely, (i) an Extractor (1), (ii) a
first Rotary drum filter (2) (separation size 500 mesh), (iii) a first
Distillation column (3), (iv) a Precipitation tank (4), (v) a second Rotary
drum filter (5) (for complete solid-liquid separation, and (vi) a second
Distillation column (6).
Coal, solvent and co-solvent are mixed thoroughly in coal -solvent feed
tank. Coal slurry is then pumped into the extractor (1). A temperature
around 170°C is achieved in the extractor (1) slowly. Residence time in
the extractor (1) may vary form 15 mins to 2 h and i.e. dictated by the
techno economics of the process and its specific requirement. Extracted
coal-solvent mixture is then separated through a first rotary drum filter (2)
or any separation unit which may cut the mixture in two fractions: coarser
fraction (+0.025 mm) and finer fraction (-0.025 mm). Coarser fraction
contains high ash and is called as residue. The finer fraction or filtered
extract is then fed to a first distillation unit (3). Maximum 80-85% solvent
recovery may be allowed through the first distillation unit (3). The
concentrated coal-solvent mixture is flushed in a precipitation tank (4). As
NMP-CHA solvents are soluble in water, extracted coal gets separated
from the solution phase and gets precipitated. This precipitated coal is
separated through a second rotary drum filter (5). Thus obtained clean
coal contains less than 4% ash. The filtrate consists of solvent-water
solution and solvent is recovered through a second distillation unit (6).
The secondary product of the second distillation unit (6) is steam, which
may be used as a heat source in the extractor (1) at a high pressure. It is

possible to recover around 98% of solvent through the distillation units
(3,6).
The important safety measures comprises:
a. As the solvent of use are organic and are flammable in nature, it may catch
fire in contact with oxygen at high temperature. Therefore, there is provision for
Nitrogen flashing in the extractor (1) and the first Rotary drum filter unit (2).
b. There may be a need to guard moisture for the co-solvent i.e. CHA.-
The main advantages of the invention achieved
i. Recovery increases by two folds. High recovery improves the techno-
economics remarkably.
ii. The shrinking core based extraction affords a trade off between extraction
yield and ash contents in the super clean coal obtained.
iii. An environment friendly, economic and convenient solvent-co solvent mix
was identified as suitable solvents. These solvents are industrial solvents and
easy to handle. Therefore, there is no concern from industrial application point
of view.

iv. CHA is a cheaper solvent as that of Ethylenediamine (EDA). It
helps in improving the process economy,
v. CHA has lesser atomic N/C ratio than that of EDA, which is good
from coke making point of view as less N-contents helps in coke
making,
vi. Filtration becomes relatively faster by using 500 BSS mesh filter
cloth, thus saving a lot of operation time,
vii. Depending upon the ash contents in the super clean coal
obtained, this may be studied for its other non-fuel uses as
well,
viii. The process is also applicable to non-coking coal for producing
low ash clean coal for blast furnace injection, power generation
and converting coals into liquid fuels/chemicals,
ix. Maximum extraction rate is observed at the beginning of the
process. Rate of extraction decreases with time. 59.6%, 63.1%
extraction yield has been obtained for extraction time 0.25 h,
0.75h and 1.25 h respectively,
x. Extraction yield improves for fine size; e.g. it is possible to
recover 76% of parent coal if -0.25 mm fraction of coal is taken
for treatment,
xi. The process is useful to lower the ash contents from run of
mine (ROM), middlings, and clean coal from physical
beneficiation processes. Table 3 shows the effect of solvent-
refining treatment of these three coals.

Table 3. Test results of solvent-refining for ROM, middlings and clean
coal

xii. The process can also be useful to produce super clean coal or
ultra low ash clean coal (ash contents potential end uses in obtaining graphite, aromatic polymers,
specially chemicals, carbon materials such as carbon nanotubes
etc.
xiii. 98% of the solvent is easily recovered. This recovered solvent is
as good as that of fresh solvent in terms of solvolytic efficiency.
xiv. The super clan coal obtained showed good coking prosperities.
Vitrinite contents increases significantly (Table 4).

WE CLAIM;
1. A process for treating high ash coal to lower ash content comprising (i)
forming a slurry of coal fines in a N-Methyl-2-pyrrolidone (NMP) with a
small amount of Cyclohexylamine (CHA), NMP and CHA ratio may vary
14:1 to 24:1 solution, said slurry containing about 15 to 25 ml of
solution per gm of coal, (ii) maintaining said slurry in refluxed condition
at a temperature of about 170.degree. C for a period of about 15 minutes
to 2 hours depending on the requirement, (iii) separating the refluxed
solution in two parts by coarse filtration at 0.025 mm filter cloth
separation cut size being variable depending on the particle size to be
treated and the use of the end product namely filtrate or extract and the
residue, (iv) recovering the solvent up to 85% by distillation of the
extract, (v) precipitating the coal by adding water in concentrated extract,
(vi) separating the coal by filtration, said coal having a reduced ash
content and (vii) recovering the rest of the solvent by distillation of water-
solvent solution.
2. The process as claimed in claim 1 wherein said coal comprises run of
mine coal, middlings or fine clean coal.
3. The process as claimed in claim 2 wherein said particle size is preferably,
-2mm, -0.5 mm, more preferably 0-.25 mm or any fine size depending on
the requirement.
4. The process as claimed in claim 1 wherein the ultra low ash clean coal or
super clean coal having ash content of the refluxed solution.
5. The process as claimed in claim 4 wherein said ultra low ash clean coal
or super clean coal having ash content graphite, liquid fuels, aromatic polymers, specially chemicals, carbon
materials such as carbon nanotubes etc.
6. The process as claimed in claim 1 wherein the moderate ash clean coal
having ash content solution.

7. The process as claimed in claim 6 wherein said moderate ash clean coal
having ash content injection in iron and steel industries and power generation.
8. The process as claimed in claim 1 wherein 98% recovery of the solvent is
achieved.
9. A device for treating high-ash content coal to lower ash content, the
device comprising:
- an extractor (1) for receiving coal-slurry from a coal-solvent feed tank
(7) and for extraction of coal-solvent mixture;
- a brief rotary drum filter (2) connected to the extracted (1) which cut
the solvent mixture into two fractions;
- a first distillation unit (3) for receiving the finer fraction out of said two
fractions form the first rotary drum filter (2) and for carrying out solvent
recovery;
- a precipitation tank (4) flow ably connected to the first distillation unit
for receiving there from the concentrated coal-solvent mixture and
following precipitation of the coal including separation of the filtrate:
- a second rotary drum filter (5) for separating the precipitated coal
containing less than about 4% ash; and
- a second distillation unit (6) for recovery of the solvent from said filtrate
containing solvent-water solution.

ABSTRACT

TITLE: A PROCESS TO PRODUCE LOW ASH CLEAN COAL FROM HIGH ASH
COALS FOR VARIOUS METALLURGICAL APPLICATIONS
The invention relates to a process for treating coal to lower ash content
comprising (i) forming a slurry of coal fines in a N-Methyl-2-pyrrolidona
(NMP) with a small amount of Cyclohexylamine (CHA), NMP and CHA ratio
may vary 14:1 to 24:1 solution, said slurry containing about 15 to 25 ml of
solution per g of coal, (ii) maintaining said slurry in refluxed condition at a
temperature of about 170.degree. C for a period of about 15 minutes to 2
hours depending on the requirement, (iii) separating the refluxed solution in
two parts by coarse filtration at 0.025 mm filter cloth separation cut size
being variable depending on the particle size to be treated and the use of the
end product namely filtrate or extract and the residue, (iv) recovering the
solvent up to 85% by distillation of the extract, (v) precipitating the coal by
adding water in concentrated extract, (vi) separating the coal by filtration,
said coal having a reduced ash content and (vii) recovering the rest of the
solvent by distillation of water-solvent solution.

Documents:

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Patent Number

272335

Indian Patent Application Number

1088/KOL/2007

PG Journal Number

14/2016

Publication Date

01-Apr-2016

Grant Date

30-Mar-2016

Date of Filing

06-Aug-2007

Name of Patentee

TATA STEEL LIMITED

Applicant Address

JAMSHEDPUR

Inventors:

#	Inventor's Name	Inventor's Address
1	PRADIP KUMAR BANERJEE	TATA STEEL LIMITED, JAMSHEDPUR, 831001
2	MR. D.K. SHARMA	INDIAN INSTITUTE OF TECHNOLOGY, DELHI,
3	MITALI CHINA	TATA STEEL LIMITED, JAMSHEDPUR, 831001

PCT International Classification Number

C10L 5/00; C10G 1/00

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA