FIELD OF THE INVENTION
The present invention relates to organo-refining of coal. More particularly, the
present invention relates to a process to produce low ash dean coal from high
ash coal for various metallurgical applications.
BACKGROUND OF THE INVENTION
The concept and practice of chemical beneficiation process comes from the
limitation of physical beneficiation processes. Broadly, a chemical beneficiation
process 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 composition, maturity, and structural characteristics. Since the
mineral matter-(non-combustible) available in specific geographical locations is
very finely disseminated in the organic mass, it is really very difficult to remove
the non-combustible mineral matter by conventional physical coal washing
techniques. Presence of high percentage of near gravity material in such type of
coal makes the scope of implementing a gravity separation process limited. This
indicates that chemical treatment may be the right approach to overcome the
limitation of physical beneficiation methods. A plurality of technical 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 through 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
clear coal with ash content less than 0.2 % for high-tech end uses. This
conventional solvent refining process does not serve the objective of low ash
coal requirement of steel Industries mainly, because of low recovery which
makes the process uneconomic especially when such an ultra coal is not
absolutely desired, and the cost of the process to high entailed by low yields.
The main advantages of the prior art 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.
According to the existing process, 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. 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 % 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.
The existing processes require more co-solvent during solvent extraction of coal
which makes solvent and anti solvent separation in distillation more complex.
Further, the process increases impurity in top product in the distillation.
However, the inventors during the research undertaken in course of developing
the invention have identified that 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 and source (feed characteristics), particle size, coal-solvent ratio,
extraction time, extraction temperature etc.
By way of reference, the inventors observed that Indian patent application
numbers 1336/KOiy2008, 1088/KOL/07, and 1292/KOL/06 relate to the similar
field of technology.
OBJECT OF THE INVENTION
It is therefore an object of this invention is to propose a process to produce low
ash clean coal from high ash coal.
Another object of the invention is to propose a process to produce low ash clean
coal from high ash coal, which reduces consumption of co-solvent quality in the
extraction process.
A still another object of the invention is to propose a process to produce low ash
clean coal from high coal which exhibits high recovery of solvent.
Yet another object of the invention is to propose a process to produce low ash
clean coal from high ash coal, in which a substantially higher amount of pure
solvent and anti-solvent is obtained in distillation bottom and top product.
A further object of the invention is to propose a process to produce low ash
clean coal from high ash coal, in which vapor loss is minimized to obtain high
recovery of solvent.
SUMMARY OF THE INVENTION
According to the inventive process, coal solvent and co-solvent are provided in a
pre defined ratio. Coal to solvent ratio is varied from 1:6 to 1:17 (wt/vol, g/ml.
coal to solvent are wt/vol and solvent co-solvent ratios are vol/vol wherever
mentioned). Coal to co-solvent ratio is maintained asl:l (g/ml), while co-solvent
to solvent ratio is varied from 1:6 to 1:17. The boiling point of EDA, NMP and
water is 117°C, 202°C and 100°C respectively. According to the innovative
process, coal to solvent ratio is provided identical to that of the existing
processes. But co-solvent to solvent ratio is varied from 1:6 to 1:49.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 - shows a system and process to produce low ash clean coal from high
ash coal according to the invention.
DETAIL DESCRIPTION OF THE INVENTION
As shown in figure 1, the system consists of six units namely, (i) an Extractor (1)
(ii) a first filter (2) (separation size 500 mesh), (iii) a cooler (3), (iv) a
Precipitation tank (4), (v) a second filter (5) (for complete solid-liquid separation)
and (vi) a Distillation column (6).
Coal, solvent and co-solvent are mixed thoroughly in a coal-solvent feed tank
(not shown). Coal slurry is then pumped into the extractor (1) varies from 15
min 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
the first filter (2) i.e. the mixture is cut in two fractions; a coarser fraction
(+0.025 mm) and a finer fraction (-0.025 mm). The coarser fraction contains
high ash and is called as residue. The finer fraction or filtered extract is then fed
to the cooling unit (3) directly, by avoiding an evaporator unit. The cooled coal-
solvent mixture is flushed in the precipitation tank (4), where water acts as an
anti-solvent. As the solvents are strongly soluble in anti solvent, the extracted
coal gets separated from the solution phase and gets precipitated. This
precipitated coal is separated from a second filter (5). The filtrate consists of
solvent-anti solvent and solvent, wherein the anti-solvent is recovered through a
distillation unit (6).
According to the invention, the extractions are done with coal having -30 mesh
sizes and 28% ash content. Experiment with 5 gm sample of this coal is
undertaken, and extracted it in NMP and EDA as a solvent and co-solvent in
different ratio for one hour. Filtration is done through 500 stainless steel BSS
mesh (0.025 mm). Precipitation is done in water. These tests have been
repeated many times and clean coal yield has been found in the range of ± 2-
Results in Table -1 shows that dean coal yield was 48% at 1.9 anti-solvent to
solvent ratio and at, 1:24 ratio, dean coal yield was 50% with same clean coal
ash as 7-8%. With less co-solvent we get even better results than with more co-
solvent. So less co-solvent could be used in the solvent extraction of coal process
to get the low ash clean coal.
WE CLAIM:
1. A process for treating coal to lower ash content comprising (I) forming as
slurry of coal fines, in a solvent such as N-Methyl-2-pyrrolidone (NMP) with a co-
solvent such as Ethylenediamine (EDA), NMP and EDA, the ratio of solvent to co-
solvent in the solution being variable between 6:1 to 49:l.(ii) maintaining said
slurry in refluxed condition at a temperature of about boiling point (170-190°C)
of the slurry 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 the cut size being variable depending on the particle size
to be treated and the application of the end product such as filtrate or extract
and the residue (iv) recovering the solvent up to 80-85% 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 (vi)
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.
3. The process as claimed in claim 2 wherein said particle size is preferably -
0.5 mm, or any fine-size depending on the requirement.
4. The process as claimed in claim 2, wherein the ultra low ash clean coal or
super clean coal having ash content < 1% is produced by very fine filtration 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 < 1% and is adaptable to produce 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 about 8% is produced by coarse filtration of the refluxed
solution.
7. The process as claimed in claim 6 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 power generation.
8. The process as claimed in claim 1 wherein 98% recovery of the solvent is
achieved.
9. The process as claimed in claim 1 wherein the ultra low ash clean coal or
super clean coal having ash <8% is produced by lowering the co-solvent
quantity in solvent extraction (organo-refining) of coal process.
10. The process as claimed in claim 1 wherein ratio of co-solvent to solvent is
1:24 to produce low ash clean coal in the solvent extraction of coal process.
11. The process as claimed in claim 1 wherein ratio of co-solvent to solvent
varied from 1:6 to 1:49 to produce low ash clean coal in the solvent extraction of
coal process.
12. A process for treating coal to lower ash content substantially as herein
described and as illustrated in the accompanying drawings.

A process for treating coal to lower ash content comprising (i) forming as slurry
of coal fines in a solvent such as N-Methyl-2-pyrrolidone (NMP) with a co-solvent
such as Ethylenediamine (EDA), NMP and EDA, the ratio of solvent to co-solvent
in the solution being variable between 6:1 to 49:l.(ii) maintaining said slurry in
refluxed condition at a temperature of about boiling point (170-190°C) of the
slurry 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 the cut size being variable depending on the particle size to be treated
and the application of the end product such as filtrate or extract and the residue
(iv) recovering the solvent up to 80-85% 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 (vi) recovering the
rest of the solvent by distillation of water-solvent solution.