FIELD OF THE INVENTION
The present invention relates to a process to produce high quality clean coa!
from high ash coal with enhanced yield.
BACKGROUND OF THE INVENTION
As coa! is heterogeneous 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 (Gondwana coals) is very
finely disseminated in the organic mass, it is essential to ground the coal down to
-30 mesh to liberate mineral particle and also for providing a good suface area
towards solvolytic process. This solvolytic process is called organo-refining
process and it is able to extract about 30 to 40o/o as clean coa! with around 4olo
ash from parent coa! or discards having 400/o ash. Present work aims to protect
an alternative method to improve yield of the process along with a complete
solution of filtration technique used in Organo Refining Process. By way of
reference, the inventors obseryed that Indian patent application numbers
t292lKOU06, 1088/KOU07, 1336/KOU2008, 950/KOU09, Lt94lKOU09,
611/KOL/09, 158UKOU08 and 90UKOL/11 to produce clean coa! for various
metallurgica! applications relate to the similar field of technology.
Organo refining process is principally based on solvent extraction technique in
which it is known that fine coal, preferably with -30 mesh in size, is heated up in
a reactor with amine based organic solvent. A moderate temperature and
pressure is employed on the process to facilitate the extraction process. After
extraction, a suitable filter is provided to filter out extracted solvent from ineft
solid coal. It is well known that final coal always comes up with variable particle
3
size distribution, preferably in finer fraction. Although variable finer fraction still
present in the extraction system, it is extremely difficult to filter out those finer
fraction by known medium based filter like pressure filter. Further, one of the
prime objectives of filtration is to enhance dryness of untreated solid, which
cannot be achieved by the known steps of norma! gravity settling followed by
normal decantation, which wil! lead to a substantial amount of solvent loading on
the solid cake.
OBJECTS OF THE INVENTION
It is therefore an object of this invention to propose a process to produce high
quality clean coal from high ash coa! with enhanced yield.
Another object of the invention is to propose a process to produce high quality
clean coa! from high ash coal with enhanced yield, in which the end product
includes substantially lower ash percentage.
A still another object of this invention is to propose a process to produce high
quality clean coal from high ash coal with enhanced yield, which is capable to
provide more than 20olo yield than the conventional process.
Yet another object of this invention is to propose a process to produce high
quality clean coa! from high ash coal with enhanced yield, which introduces solid
bowl decanter filter for recovery of >40o/o product with high quality product.
A fufther object of invention is to propose a process to produce high quality
clean coal from high ash coal with enhanced yield, in which the reject coal is
dried to extract out higher quality component of clean coal from the reject.
4
A stil! further object of invention is to propose a process to produce high quality
clean coal from high ash coal with enhanced yield, in which a device capable of
exploiting density difference of the solid and solvent of the extraction process is
adapted to recover more yield with higher quality product.
Yet further object of the invention is to a process to produce high quality clean
coa! from high ash coal with enhanced yield, which operates as a continuous
process.
SUMMARY OF THE INVENTION
Organo refining process is principally based on solvent extraction technique in
which it is known that fine coal, preferably with -30 mesh in size, is heated up in
a reactor with amine based organic solvent. A moderate temperature and
pressure is employed on the process to facilitate the extraction process. After
extraction, a suitable filter is provided to filter out extracted solvent from ineft
solid coa!. It is well known that final coal always comes up with variable pafticle
size distribution, preferably in finer fraction. Although variable finer fraction still
present in the extraction system, it is extremely difficult to filter out those finer
fraction by known medium based filter like pressure filter. Further, one of the
prime objectives of filtration is to enhance dryness of untreated solid, which
cannot be achieved by the known steps of normal gravity settling followed by
normal decantation, which will lead to a substantial amount of solvent loading on
the solid cake.
The present inventors noted that pressure filter can although produce more dry
cake but causes choking of the porous medium by very fine solid coal, almost
instantaneously. Therefore, the inventors recognized that development of a filter
5
which is capable to operate without any filtration medium as well as enable to
elevate the process yield and quality of product is an impoftant factor for the
innovative process. For the filter to design the parameter called specific gravity
plays an influential role. The reason being that coal particle posses specific
gravity of 1.5, whereas the specific gravity of the solvent is around 1. It is
actually triggering a very effective filtration system which operate on density
difference principal. Solid bow centrifuge or horizontal decanter centrifuge
(HDC) is that kind of a system. The present invention exhibits the effectiveness
of the HDC in solving the above mentioned problem. It is not only enhanced the
yield, but enhanced product quality by many fold. The proposed invention
enhanced yield almost by 20olo with 600/o improvement in clean coal quality.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
Figure 1 shows a system for a process to produce high quality clean coal from
high ash coal with enhanced yield.
DETAILED DESCRIPTION OF THE INVENTION
In a two phase decanter, the liquid level is regulated by a plurality of dam plates.
When operating in a three phase mode, each phase discharges over a set of dam
plates into separate baffled compartments in the casing of the decanter. In
ceftain applications, a centripetal pump discharge that utilizes the pressure head
developed by the rotating liquid phase, is used to pump the liquid from the
decanter.
6
Centrifugal extraction is known to be the link between thermal and mechanical
process engineering. The choice of solvent is based on thermodynamic and
chemical/physical principles, whereas the design of the centrifuge and the
separating process are based on mechanical principles.
Organo refining process produces viscous slurry which needs to be separated at
ceftain operating conditions. The basic philosophy of the process is to get a
continuous solid liquid separation. The plan of work is depicted in figure 1.
As shown in figure 1, the inventive system consists of severa! unit operations. At
first, coal and solvent are getting mixed inside a reactor (1). The hot extract is
then sent to a horizontal decanter centrifuge tiller (2) for separating out
unreacted coal from the hot extract. The hot extract is then allowed to enter into
an evaporator (3) for clarification. From top of the evaporator (3), vapor are
coming out and subsequently condensed and collected at a first recycle solvent
storage (4). From the bottom of the evaporator (3), hot clarified extract is
directly fed into a Veftical Agitated Thin Film Dryer (5). From the top of the
VATFD (5), solvent vapor is getting condensed through a first condenser (6). A
first vacuum pump (7) is attached to maintain a high vacuum inside the system
which brings down the boiling point of the solvent substantially. Solvent vapor is
condensed and collected in a second recycle solvent storage tank (8). From the
bottom of the VATFD (5), hot dried clean coal is collected in powdery form. From
the hot filter (2), a reject coa! is received in slurry form. This slurry is then
pumped into a Horizontal Agitated Thin Film Dryer (HATFD). From the HATFD (9)
the solvent is heated off and condensed through a second condenser (10). From
the other end of the HATFD (9), a hot dried reject is collected (11). A high
vacuum is maintained by a second vacuum pump (12) throughout the dryer. Hot
condensed solvent is collected in a third recycle solvent storage tank (13).
7
The Horizontal decanter centrifuge of the invention, gives very encouraging
resutts in the regime of solid liquid separation particularly wherein solid contains
fine solid distribution. As the unreacted coal contains a very fine size distribution
and the extract contains dissolve coal, it gives tremendous improvement in yield
with more quality product. There is no method, other than gravity settling,
decantation procedure exists for handling this kind of slurry. In this respect,
adaptation of the solid bowl decanter has given very encouraging results. It
improves the yield by 2}o/o compared to prior art. The most interesting paft is
the reduction of ash from 6 to 2o/o, i.e. 600/o improvement in ash by maintaining
higher yield. The inventive systems achieves higher yields having higher quality
grade product. The comparative result is tabulated in table 1. According to the
invention, hot slurry is enter into the HDC for solid liquid separation. Solid
represents unreacted coal having specific gravity around 1.5. Liquid contains
dissolved coal with amine based solvent, having specific gravity around 1. This
difference in specific gravity implies that centrifugal separation shall be effective
as it has got 0.5 unit delta potential for separation. As per conventional design
rule, a 0.2 unit delta potential in specific gravity works efficiently in centrifugal
operation.
According to the invention, the HDC separates solid coal and its liquid phases,
which is the solvent e*ract, in one single continuous process. This is done using
centrifugal forces that can be well beyond 3000 times greater than gravity. When
subjected to such forces, the denser solid particles are pressed outwards against
the rotating bowl wall, while the less dense liquid phase forms a concentric inner
layer. Different dam ptates are used to vary the depth of the liquid - the socalled
pond as required. The sediment formed by the solid pafticles is
continuously removed by a screw conveyor, which rotates at different speeds
than the bowl. As a resutt, the solids are gradualty "ploughed" out of the pond
I
and up the conical "beach". The centrifugal force compacts the solids and expels
the surplus liquid. The dried solids are then discharged from the bowl. The
clarified liquid phase or phases overflow the dam plates situated at the opposite
end of the bowl. Baffles within the centrifuge casing direct the separated phases
into the correct flow path and prevent any risk of cross-contamination. The prior
art HDC are capable of handling solid particles with diameters less than 0.5 mm.
Decanter units can also handle slurries with a solid content from as low as 2o/o
w/w to more than Llo/o wlw. HDC can accept variations in the feed more
effectively than other types of centrifuge or separation devices. As per the
results tabulated in table 1, the inventive process gives 30o/o more yield.
Simultaneously, with the elevation of yield, the process also refines the product
by 600/o. In prior aft practice, 60/o ash clean coal is achieved wherein the
inventive process, 2o/o ash clean coal is achieved. So finally it can be concluded
that the present process enhances the yield by 30o/o with 600/o more refining in
the product quality.
Table 1 : Comparative performance study between conventional filter and
horizontal decanter centrifuge filter :
SN FEED
RATE
(M3/H
R)
FEED
CONCE
tIT
RATION
(o/o
w/w)
PULLE
Y SIZE
(MM)
DIFF.
SPEED
(RPM)
DECANTER PERFORMANCE CONVENTIONAL FILTER
REPORT
CAKE
MOIS
T
URE
e/o)
CENTARATE QUAUTY
(APPX.)
CAKE
MOIS
T
URE
(o'/o)
CENTARATE
QUAUTY (APPX.)
ASH
(vo)
\TE
LD
(vo)
TS
(vo)
ASH
(o/o)
\TE
LD
(o/"TS
(vo)
1 (0.3
to
0.s)
10 135 40.5 50 2 33 3.4
60 6 30 3.1
2 10 135 40.5 50 2 40 4,L
WE CLAIM :
1. An improved process to
with high recovery of
comprising :
(i) forming a slurry of coal fines in organic solvent with a small amount of cosolvent;
(ii) maintaining said slurry in a reactor at a temperature range of 1000C to
2400C and at a pressure range of 1 to 4 gauge (kg/cm2) for a period of
about 15 minutes to 4 hours;
(iii) separating the produced product after withdrawal from the reactor in a
separation unit, 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 product being a filtrate or extract and a second part
being a reject;
(iv) washing the reject in an anti solvent by adding second part called rejecU
(v) drying the reject by a horizontal dryer, said separated reject having high
ash content;
(vi) feeding the extracted paft into an evaporator to recover solvents;
(vii) feeding the concentrated material (bottom product of evaporator) into a
veftical dryer to separate coal from solvent, said separated coal having a
reduced ash content;
The process as claimed in claim 1 wherein said coal comprises run of mine
coals, washery discards such as middling's tailings and thermal coals.
The process as claimed in claim 1 wherein said particle size is preferably, -
0.5 mm or any fine size depending on the requirement.
produce low ash clean coal from high ash coal
enhanced quality of clean coal, the process
3.
9
10
4. The process as claimed in claim 1 wherein said solvent is N-Methy!-2-
pyrrolidone (NMP) and co-solvent is Ethylenediamine (EDA).
5. The process as claimed in claim 1 wherein coal ash having <2o/o is
produced in said process at coal to solvent ratio of 1:4 to 1:25 and cosolvent
to solvent ratio of 1:1 to 1:50 and temperature range of 1000C to
2400C.
6. The process as claimed in claim 1, wherein said separation unit is a
horizontal decanter centrifuge filter which separates clean coal extract and
fine reject.
7. The process as claimed in claim 1 wherein said separation unit is enabled
to enhance process yield by 30% and product quality by 60%.