FIELD OF THE INVENTION
The present invention generally relates to an arrangement and a process to
obtain 100% regeneration of solvent with reduction in energy consumption in
organo-refining of coal process for producing of clean coal. More particularly, the
invention relates to an improved process to produce low ash clean coal from high
ash coal and almost 100% solvent recovery with 75% lower energy
consumption.
BACKGROUND OF THE INVENTION
Coal is a heterogeneous mixture of organic and inorganic constituents, the
solvolysis process of coal varies with its constituents, maturity, and structural
characteristics. Since the mineral matter (non-combustible) in Indian coals
(Gondwana coals) is very finely disseminated in the organic mass, it is
substantially difficult to remove the mineral matter from coals by conventional
physical coal washing techniques. Presence of high percentage of near gravity
material in coal makes application of known gravity process for the purpose less
effective. Concept of chemical beneficiation was originated 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 may be
a right approach to overcome the limitations of physical beneficiation methods.
Several literatures are available in the art 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
economically variable. Conventional chemical beneficiation processes generally

recover 99% solvent with expanse of huge energy which makes the process
uneconomical.
As per the conventional processes of washing the rejects and cleaning coal,
which can be considered as porous solids, with water to remove the last traces
of solvents and drying both of those, provided to be unsatisfactory. Examination
of the washed coal by microscope, showed that the solid particles were
somewhat coated with a solvent like material. It may be postulated that each
particle of solid was surrounded by a layer of solvent that still contained traces of
extract in solution when water was added during washing, the extract was
precipitated on to the surfaces of the particles. It is extremely difficult to wash of
the solvent as it enters into the capillary of solid coal.
Because of these difficulties encountered during washing including removal of
the last trace of solvent, the present inventors recognized that a direct drying
method which eliminate adsorption of the solvent during precipitate formation,
could be the right approach to regenerate solvent.
Organo refining process is well known process which is also able to remove
>99% recovery of solvent through conventional distillation approach. Coal
extract precipitates out in an anti solvent medium mainly in water. The waster
solvent mixture is distilled off to recover the solvent. Here, N methyl pyrollidone
(NMP) is used as a solvent. In this conventional process, a huge energy is
consumed as water is very stable liquid and also posses highest heat capacity
(540 cal/gm °C). Distillation is a costliest unit operation and also water
distillation is the maximum one. The present inventors noted that during this

known wet precipitation method, some amount of solvent and coal are discarded
due to the ineffective process. The disadvantages are :
1. A small portion of clean coal is discarded due to the formation of some
colloidal matter of coal extract in water, which goes out from the system
during filtration.
2. It is know that clean coal develop porous floppy mass which consumes
water 4 to 5 times of the solid mass, thus when the solvent enters into
the capillary of the clean coal, it becomes extremely difficult to wash out
completely, as a result some amount of solvent is lost during drying of the
coal.
Another prior art, solvent recovery process eliminated the costly distillation route
and yet could achieve recycling back almost 100% solvent. This prior art (NMP),
however substantial low value of lattent heat of evaporation (139 cal/gm °C)
which is noted from the difference in latent heat value. Thus, the inventors
recognized that a huge energy can be saved if NMP could be dried off directly
instead of distillation.
It is further known that almost 100% drying of solvent from solution is also
possible through the spray drying approach but due to the following limitations,
the spray drying concept has been discarded from the consideration:-
1. Spray drying is a direct drying method where the solution is heated
directly with a blast of hot air. As it posses flammable organic solvent, hot
N2 need to be used in place of air in order to avoid fire and explosion

hazard. As a huge amount of N2 is used, it leads the process towards
expansive operating zone.
2. As the solvent is costly, the object is to ensure that 100% solvent is
condensed back. However, in this known process, the closed loop spray
dryer consumes a huge amount of hot N2 for evaporation, which makes it
extremely difficult to condense out 100% of the solvent vapor.
By way of reference, the inventors herein incorporate the leaching of Indian
patent application numbers 1292/KOL72006. 1088/KOL/2007, 1336/KOU/2008,
950/KOL/2009, 1194/KOL72009, 611/KOL72009, 1581/KOL/2008 and an Indian
patent on bench scale (with one reactor only) plant set up and operation to
produce clean coal for various metallurgical applications.
OBJECTS OF THE INVENTION
It is therefore an object of this invention to propose a process to produce low
ash (4% ash) clean coal from high ash coal (40% ash) with lowest energy
consumption.
Another object of this invention is to propose an arrangement to produce low ash
clean coal from high coal.
A still another object of this invention is to propose an arrangement to produce
low ash clean coal from high coal, which includes a direct thin film drying system
for recovery of almost 100% solvent with very lower energy consumption.
Yet another object of invention is to propose a process to produce low ash (4%

ash) clean coal from high ash coal (40% ash) with lowest energy consumption,
which implements vertical thin film drying for drying out solid coal product from
solution phase.
A further object of the invention is to propose a process to produce low ash (4%
ash) clean coal from high ash coal (40% ash) with lowest energy consumption,
which implements Horizontal thin film drying for drying out solid reject from
slurry phase.
A still further object of this invention is to propose a process to produce low ash
(4% ash) clean coal from high ash coal (40% ash) with lowest energy
consumption, which is economic.
SUMMARY OF THE INVENTION
According to the invention, an arrangement having a single reactor and a solvent
recovery system (double effect evaporator and Agitated thin film drying
technique) has been proposed. As it is imperative to obtain solvent-free extracts,
several techniques of separating solvent from the extract were experimented.
The most common type of separation, and precipitation of the extract by addition
of a large volume of water, proved unsatisfactory because 1) a gelatinous
precipitate was formed that prevented quantitative filtration and absolute drying
of the precipitate, and 2) with a dilution ratio of water to solvent-plus-extract
originally set at 8 to 1, the filtrate had a yellowish hue, indicating a
nonquantitative precipitation of extract. When the ratio was increased to 50 to 1,
the filtrate remained clear, but a gelatinous precipitate appeared in it after 48
hours. This result explains the difficulties in getting almost 100% regeneration of

solvent through the conventional wet or precipitation method. As the solvent is
very costly, the inventive solution to obtain ~100% solvent regeneration with
lowest energy consumption, resides in adapting a drying system in the process.
Direct drying from a solution phase is not generally possible unless an unique
type of equipments is used. The known spray drying could be one of the
alternative solutions but for organic solution it may not work effective due to the
following reasons.
a. In a flammable organic medium, hot air blast is not desirable being highly
susceptible to fire.
b. As the solvent is very costly, an effective solvent recovery system is
required to maintain almost 100% recycling of solvent.
Due to the above limitations, the known direct drying concept couldn't be
implemented on organic refining process. Accordingly, an Agitated thin film
drying system was envisage, which can break the barrier of above mentioned
constraints. In this systems, a very thin film is maintained along the wall of the
dryer to avoid charring. Dryer is heated indirectly by steam. As direct heating is
not used in the system, a condenser is attached at the top of the dryer to
condense out the evaporating vapor. A vacuum is maintained throughout to keep
the evaporating temperature substantially low. It actually prevents heat
degradation of material. After extraction, hot filtered material is directly sent to
the ATFD. Form the ATFD, a solid product is achieved. All the solvent from the
evaporator and the ATFD is condensed out and collected. In this way >99.9%
solvent regeneration is achieved with very low energy consumption.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 - shows a flow diagram of the process of the present invention
Figure 2 - shows a photographic view of dry clean coal powder obtained through
the inventive process before the drying of the rejects.
Figure 3 - shows a pictorial view of the dry rejects of the coal before complete
reduction according tot the process of the invention.
DETAIL DESCRIPTION OF THE INVENTION
Accordingly, there is provides a highly feasible process, and an arrangement as
shown in figure 1. High feasibility of the process is achieved by incorporation of
Agitated Thin Film Drying (ATFD) concept. In this way it is possible to remove
solvent through a dry method as opposed to prior art precipitation of the solvent
in water, and recover almost 100% solvent by complete evaporation.
As shown in figure 1, the process consists of several unit operations. At first, coal
and solvent are admixed inside a reactor (1). The hot extract is then sent to a
filter (2) for separating out unreacted coal. The hot extract is then entered into
an evaporator (3) for clarification. From top of the evaporator (3), vapor coming
out is subsequently condensed and collected at a recycle solvent storage (4).
From the bottom of the evaporator (3), hot clarified extract is directly fed into a
Vertical Agitated Thin Film Dryer (5). From the top of the VATFD (5), the solvent
vapor is condensed through a first condenser (6) and collected in a recycle
solvent storage tank (8). A first vacuum pump (7) is attached to maintain a high
vacuum inside the arrangement, which lowers the boiling point of the solvent

substantially. From the bottom of the VATFD (5), hot dried clean coal is
collected in powdery form. Form the hot filter (2), the reject coal is received in
slurry form. This slurry is then pumped into a Horizontal Agitated Thin Film Dryer
HATFD (9) the solvent is heated off and condensed through a second condenser
(10). A high vacuum is maintained by a second vacuum pump (12) throughout
the dryer. From the other end, the hot dried reject is collected in a second
storage tank (11). Hot condensed solvent is collected in a third recycle solvent
storage tank (13).
The present inventors accordingly, concluded that an improved process of
Agitated film drying process with unique drying arrangement is the solution to
the technical disadvantages of prior art for the followings:-
1. Being an indirect heating system, solution indirectly, reduces evaporation
cost drastically compared to known spray drying.
2. as a substantially lower amount of hot N2 is mixed within the system,
condensation of the solvent vapor is easily achievable.
Due to the above reasons ATFD outperforms the prior art process
A solid liquid solution like dissolved solid is solvent can be easily treated through
VATFD. As the solution is easily pumpable, it is pumped up to the top part of
VATFD. Feed is distributing through the feed distributor. With the help of a rotor
a thin film is maintained throughout the dryer for effective drying. The impeller
of agitator is playing a vital role during drying. Depending upon specification of
solution impeller bed is designed. The VATFD has a jacketed cylinder with a
closely fitting rotor at the centre. During operation the rotor revolves at high
speed. The feed distributor spreads the incoming feed uniformly over the

cylinder top periphery. The rotor blades pick up the material, spread it over
heated surface in a thin film and agitate the film intensely, as it rapidly travels
down. The material transform from solution to slurry, wet cake, wet powder and
finally dry powder as it travels from top to bottom. The vapour generated rises
counter-currently to the inbuilt entrainment separator. Here the entrained
droplets are separated from the vapour stream. The clean vapour leaves the
dryer through the vapour nozzle at top. The dry powdery coal is collected at the
bottom of the chamber. A typical result of VATFD during coal extract drying is
explained as follows
Feed 10 Kg (4% dissolve coalin 96% NMP)
Recycle Solvent = 9.5 kg
Coal powder = 400gm
Temp inside= 179 Centigrade, Vacuum 0.05 atm)
Table 1: Result of VATFD trial for coal extract

From Table 1 it can be found, Loss of drying (LOD) at 200 C and 0.05 Vacuum is
0.5% which is a negligible quantity. So it proves that the solvent content of the

product coal is almost negligible. The amount of recycle solvent is 9.5 kg.
Amount of dried coal powder is 400 gm. So altogether it gives 9.9 kg mass
compared to feed of 10 kg mass. As the mass balance substantially matches, it is
concluded that the recovery of solvent is done with >99.9% accuracy for coal
extract. Figure 2 demonstrates the proof of dry clean coal powder from VATFD.
Now the horizontal version of the dryer is used for drying of wet cake, pastes,
wet powders. This is why reject coal from filter is pumped towards the HATFD.
The wet slurry enters at one end and dry powder leaves from the opposite end.
The vapors move counter currently to the powder flow and leave through vapor
nozzle. A high vacuum is maintained around at 0.05 atm through out the HATFD.
The trial results are as follows
Solid content of feed is 40% alongwith 60% NMP.
Feed 10 Kg (40% suspended coal, reject)
Recycle Solvent= 4.5 kg (solid content in recycle solvent due to entrapment is
0%)
Dry Reject Coal = 5.4 Kg
Inside temp is maintained at 180 °C and vacuum is maintained at 0.05 atm.


As From Table 2, it can be found that, loss of drying at 200 C and 0.05 atm
Vacuum isO.5% and also mass balance with feed matches closely, which
established almost 100% recovery of the solvent with HATFD. Figure 3
demonstrating the proof of dry reject coal coming from HATFD.
Now in terms of energy saving estimation following calculation were done:
1 kg extract evaporation consumes = (sensible + Latent) (1x0.5 x 180 + 129) =
219 Kcal
1 kg WATER evaporation consumes = (sensible + Latent) (1x1 x 75 + 540)+ 615
Kcal
So Energy consumption will be reduced by 3 times directly. Distillation can be
omitted from the loop very efficiently with help of ATFD concept. So it provides
that almost 75% of energy can be saved by going through this route instead of
conventional one.
Further, the inventive process operates operating through minimum number of
process equipments. Distillators, precipitators, washing filters, wash tanks, coal
dryer, slurry pumps are not required in the invention, thereby eliminating several
equipments used in the prior-art arrangement.

WE CLAIM
1. An improved process to produce low ash clean coal from high ash coal
involving 100% solvent recovery with 75% lower energy consumption, the
process comprising:
(i) forming a slurry of coal fines in organic solvent with a small
amount of co-solvent;
(ii) maintaining said slurry in a reactor at a temperature range
between 100°C to 240°C and 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 the second
separates part called reject;
(v) drying the reject by a horizontal dryer, said separated reject
having high ash content;
(vi) feeding the extracted part into an evaporator to recover the
solvent; and
(vii) feeding the concentrated material (bottom product of
evaporator) into a vertical dryer to separate coal from the
solvent, said separated 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 1, wherein said coal comprises washery
discards such as middling's.
4. The process as claimed in claim 1, wherein said coal comprises washery
discards such as tailings.
5. The process as claimed in claim 1, wherein said coal comprises thermal
coals (non-coking coals).
6. The process as claimed in claim 1, wherein said particles size is fine size
depending on end use, preferably, -0.5 mm.
7. The process as claimed in claim 1, wherein said solvent is N-Methyl-2-
pyrrolidone (NMP).
8. The process as claimed in claim 1, wherein said co-solvent is selected
from a group consisting of Ethylenediamine (EDA), Monoethanolamine
(MEA), Diethanolamine (DEA), Triethanolamine (TEA), Cyclohexylamine
(CHA), and Trybutylamine (TBA).
9. The process as claimed in claim 1, wherein ash content in the produced
coal is <8% at a coal to solvent ratio of 1:4 to 1:25.
10. The process as claimed in claim 1, wherein the content in said produced
coal is <8% at a co-solvent to solvent ratio of 1:1 to 1:50.
11. The process as claimed in claim 1, wherein ash-content in the product
coal is <8% at a temperature range of 100°C to 240°C.

12. The process as claimed in claim 1, wherein ash-content in the produced
coals is <8% at a pressure range of 1 to 4 gauge (kg/cm2).
13. The process as claimed in claim 1, wherein ash-content in the produced
coal is <8%, and wherein coal to co-solvent ratio is varied from 1:1 to
10:1.
14. The process as claimed in claim 1, wherein said horizontal dryer is HATFD
(Horizontal agitated thin film dryer) which is used to dry the reject coal
having high ash content.
15. The process as claimed in claim 1, wherein said vertical dryer is VATFD
(Vertical agitated thin film dryer) is used to recover the solvents and dry
the clean coal in an economical way.
16. The process as claimed in claim 1, wherein said VATFD and HATFD
reduces the energy consumption significantly in the process.
17.The process as claimed in claiml, wherein the produced 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.

ABSTRACT

The invention relates to an improved process to produce low ash clean coal from
high ash coal involving 100% solvent recovery with 75% lower energy
consumption, the process comprising:
(i) forming a slurry of coal fines in organic solvent with a small
amount of co-solvent;
(ii) maintaining said slurry in a reactor at a temperature range
between 100°C to 240°C and 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) drying the reject by a horizontal dryer, said separated reject
having high ash content;
(v) feeding the extracted part into an evaporator to recover the
solvent; and
(vi) feeding the concentrated material (bottom product of
evaporator) into a vertical dryer to separate coal from the
solvent, said separated coal having a reduced ash content.