Title of Invention

A PROCESS FOR THE PRODUCTION CLEAN COALS FROM INFERIOR GRADE LOWER SEAM COALS

Abstract The invention describes an integrated process for the production of clean coals having ash content of below 34%, below 17.5% and below 60% from inferior grade lower seam coals These clean coals with varying ash contents are useful as power coal in thermal power stations( where clean coals are required to meet environmental pollution norms), metallurgical coke making and feedstock for fluid bed boilers respectively.
Full Text The present invention relates to a process for the production of clean coals from inferior grade lower seam coals.
The present invention finds its usage in production of clean coals for metallurgical furnaces and thermal power stations where clean coals are required to meet environmental pollution norms.
Known resources of coal and other solid carbonaceous fuel materials are far greater than the combined resources of petroleum and natural gas. The availability of cheaper, ecofriendly and transportable fuels, such as petroleum and natural gas, have, in the past, cast coal to a largely supporting role in the energy field. Current world events, however, have forced a new awareness of global energy requirements and of the availability of those resources which will adequately meet these needs. The realization that reserves of petroleum and natural gas are being rapidly depleted in conjunction with their skyrocketing prices and the unrest in the regions of the world which contain the largest quantities of these resources, has sparked a new interest in the utilization of solid carbonaceous materials, particularly coal, as primary energy sources . As a result, enormous efforts are being extended to utilize coal for better sources of energy, than petroleum or natural gas. In the case of coal, for example, much of this effort is directed to overcome the environmental problems associated with its production, transportation and utilization. For example, due to the increasing high ash content in presently mined coals, new legislation governing coal preparation and transportation are imposed. Furthermore, numerous techniques have been explored and developed to make coal cleaner, more suitable for specific uses and more readily transportable.
Regardless of the form in which the coal is ultimately employed, it must be cleaned because it contains substantial amounts of mineral matter along with sulfur and nitrogen compounds.
During combustion these materials enter into the environment as sulphur dioxides, nitrogen

oxides and particulates of impurities. If coal is to be accepted as primary energy source, it must be free from the detrimental impurities prior to its end use to prevent pollution of the environment.
Accordingly, physical as well as chemical coal cleaning processes have been extensively explored. However, chemical coal cleaning techniques are still in a very early stage of development. Based on the physical properties that effect the separation of the coal from the impurities, physical coal cleaning methods are divided into four general categories: gravity, flotation, magnetic and electrical methods in which gravity separation in general and flotation involving physico-chemical separation for fines are mostly followed in commercial practice. Physical methods of washing involve crushing the coal to release the impurities (liberation) and subsequent separation of the liberated impurities by suitable physical means (cleaning).
Reference may be made to U.S. Pat. No. 4,364,822 that describes a coal cleaning process involving two-stage cyclone separation and producing three products: clean coal, refuse, and middling. Middling is then crushed and recycled through the cyclones with the raw coal feed.
Reference may be made to US Patent No: 4,583,990 wherein the process steps consists of admixing pulverised low rank coal with a surface treating mixture comprised of water, a polymerisable monomer, a polymerisation catalyst and a coal derived oil and recovering the resulting clean coal. Coal derived oil consists of crude coal tar, tar acids, tar bases, naphtha, creosote, pitch and mixtures thereof. The process requires additional energy for bulk scale pulverisation and the results achieved have not been entirely satisfactory. Reference may be made to US Patent No: 4,133,747 wherein a process describing production of clean coal comprises of: cleaning the crushed coal in bulk in 'water-only-cyclone' and

obtaining wet clean coal and wet reject material and also a stream of effluent; drying the wet clean coal and wet reject material by agglomerating after the addition of a small amount of oil and then centrifuging to obtain a product of dry clean coal and solid reject material and also stream of effluent; treating the effluent stream from cleaning step and the effluent stream from the drying step by means of flocculation to recover a product of coal and reject sludge which is returned to pass through the drying step again. The clean water thus obtained is recycled and applied to the input of the cyclones in the cleaning step.
Reference may also be made to U.S. Pat. No. 3,908,912 that describes a process whereby refuse is initially separated out at high density, followed by a lower density separation to yield clean coal and middling. Middling is then crushed for further cleaning. However, small size coal is not removed from the coal feed prior to the initial high density separation which results in additional refuse in the clean coal product. Moreover, cyclone separation of small coal fines are inefficient in the sense that particles are frequently misplaced. Most of the processes of prior art dealt with good quality coals which are gradually depleting . Prior art search for high ash low grade coals was made based on literature survey and patent databases which did not yield any relevant references. In India, the lower seam coals, which constitute more than 60% of the total coking coal reserve are low volatile, high ash content (in the range of 35-50% or more) coals. These coals, hereinafter named as 'inferior grade' coals are found to be 'difficult to wash' by the processes of prior art as they contain higher percentage of inertinite materials associated with vitrinite grains and highly inter-banded mineral matter. They are mostly being treated as non-linked washery coals and are supplied to the thermal power plants, against augmenting the demand of metallurgical coal for coke making. However, due to increasing high ash content in presently mined coals, they may not

even be accepted as such by the thermal power plants that are also looking for quality
products under environmental stringency.
The main object of the present invention is to provide a process for the production of clean
coals from inferior grade lower seam coals which obviates the drawbacks detailed above.
Another object is to provide coal of steel grade and at the same time, upgraded products for
pulverised fuel and fluidised bed-boilers.
Still another object of the invention is to provide a process of recovering products that suit
usage as metallurgical coal as well as power coal.
The process of the present invention constitutes an integrated process for the production of
clean coals having ash content of below 34%, below 17.5% and below 60% from inferior
grade lower seam coals. These clean coals with varying ash contents are useful as power coal
in metallurgical furnaces/thermal power stations, for coke making and feedstock for fluid bed
boilers.
Accordingly, the present invention provides a process for the production of clean coals from inferior grade lower seam coals which comprises crushing of raw coal to a nominal top size, screening to obtain coarser fraction and under size fraction; subjecting the coarser fraction to washing to produce clean coal having ash content within 34%; subjecting the undersize fraction to wet screening to obtain oversize as middle fraction and balance as slurry fraction, subjecting the middle fraction to washing and slurry fraction to deep beneficiation through a battery of flotation cells to get clean coal having ash content of less than 17.5%, mixing the rejects of coarse fraction, middle fraction washings and slurry beneficiation to get coal having ash percentage within 60%.
In an embodiment of the present invention the raw coal is crushed by conventional methods to a size in the range of 50 to 100 mm to obtain coarse fraction of less than 5%.

In yet another embodiment of the present invention screening is done to obtain coarser
fraction above 25 mm to 6 mm, preferably 13 mm and smaller fraction below 25 mm to 6
mm, preferably 13 mm.
In still another embodiment of the present invention the screening is effected using a
conventional vibrating screen having aperture diameter of 25 mm to 6 mm, preferably L";
mm.
In a further embodiment of the present invention the washing is carried out in a conventional
coal washery.
In another embodiment of the present invention the screening of the undersize fraction is
effected by desliming using a conventional . „' wet vibrating screen, preferably having
aperature diameter of 0.5 mm, to obtain middle and slurry fractions.
Figure 1 of the drawing accompanying this specification shows a block diagram depecting
the process of the present invention wherein raw coal, having high ash content in the range
of 35 to 50 percent, is crushed to a nominal top size of 100-50 mm in a crusher (1) under
feedback system and is screened in a vibrating screen ( 2) having aperture diameter above 25
mm to 6 mm preferably, 13 mm. The oversize ( coarse fraction ) is sent to one stream (3).
The coarse fraction is washed in a washer (5) to produce a clean coal (hereinafter named as
clean 1 for use as power coal (6)) having ash content within the limit of about 34% and a
reject (hereinafter named as 'Sink 1) is sent to a separate stream(7). The yield of'Power coal'
varies between about 30% to about 60% depending on the washability characteristics of the
coal used. The undersize that follow another stream (4) is further deslimed preferably at
0.5mm in a desliming screen (8) into two fractions,where the oversize ( middle fraction) is
sent to a stream (9) and the deslimed slurry (slurry) goes to a slurry thickener (10).

The middle fraction(9) is washed in a washer(l 1) to recover a clean product ( Clean 2) and is sent to a stream (14) ) and a sink ( Sink 2) which goes to another stream (13)). The ash content in 'Clean 2' has been maintained in between about 17.0% to about 18.0%, preferably more than 17.5%. The Slurry fraction from Thickener (10) is cleaned in a battery of flotation cells(12.), where finest coaly matter is separated as concentrate (Clean 3) from the tailings ( Sink3) and is sent to a stream (15). The tailings are sent to the other stream (16). The separation has been limited to the extent so that the ash content in 'Clean 3' lies in between about 14% to about 16% with a yield ranging between about 50% to about 70% of the 'Slurry' fed. The intention is to obtain a composite product from 'Clean 2' and 'Clean 3' (hereinafter named as Met. Cleans (17)) having ash content in the range of 17% to 18.0%, as desired for coke making in metallurgical industries. The rejects of the first stream, Sink 1, sinks from heavy medium washers, 'Sink 2' and tailings from froth flotation cells, 'Sink 3' are mixed together to obtain a product ( fluid bed combustion coal (18)), having ash in the range of 50-60%. This product is a feedstock for Fluid Bed Boilers.
The novelty of the present invention resides in providing clean coals from lower seam, inferior grade coals having ash content in the range of 35 to 50% which are otherwise difficult to wash in the existing washeries. The clean coals obtained have ash content of below 34%, below 17.5% and below 60%, which are useful as power coal in metallurgical furnaces, coke making and feedstock for fluid bed boilers, respectively. The above said novelty and usefulness has been achieved by the non-obvious inventive steps of the process of the present invention.
The following examples are given by way of illustration and should not be construed to limit the scope of the present invention.

Example 1:
Run of mine coal is crushed to 100mm in single roll crusher under feed back system until the oversize reduced to less than 5%. Raw coal ash was 39.3%.
Raw crushed coal was screened at 13mm in a vibrating screen into two fractions, which were fed to two different stream. In one stream, the 'Coarse fraction' was washed to recover two products, 'Power coal' having ash content restrained to less than 34% and rejects, 'Sink 1'. In other stream, the undersize of 13mm screen was deslimed at 0.5mm in a wet vibrating screen into 'Middle fraction' and 'Slurry'. The 'Middle fraction' was washed in a heavy medium Cyclone to recover 'Clean 2' and a sink, 'Sink 2'. The 'Slurry' was beneficiated in a battery of flotation cells after conditioning and separated into 'Clean 3' and 'Sink 3'.'Clean 2' and 'Clean 3' constitute the 'Met. Cleans' while the combined rejects, 'Sink 1', 'Sink 2' and 'Sink 3' provided the third product, 'fluid bed combustion(FBC) coal' having ash content less than 60%.
On the whole coal basis, recoveries were:
Yield. % Ash. %
Power coal 57-° 34-°
Clean 2 5.7 18.2
Clean 3 2.7 15.9
Met.Cleans 8.4 17.5
Sink 1 18.5 62.3
Sink 2 13.6 43.1
Sink 3 2.6 44.5
FBCcoal 34.7 53-4
Example 2:
Run of mine coal washed crushed to 75mm in single roll crusher under feed back system until the oversize reduced to less than 5%. Raw coal ash was 40.9%.

Raw crushed coal was screened at 13mm in a vibrating screen into two fractions, which were fed to two different stream. In one stream, the 'Coarse fraction' was washed to recover two products, 'Power coal' having ash content restrained to less than 34% and rejects, 'Sink 1'. In other stream, the undersize of 13mm screen was deslimed at 0.5mm wet vibrating screen into 'Middle fraction', and 'Slurry'. The 'Middle fraction' was washed in a heavy medium Cyclone to recover 'Clean 2' and a sink, 'Sink 2'. The 'Slurry' was beneficiated in a battery of flotation cells after conditioning and separated into 'Clean 3' and 'Sink 3'.'Clean 2' and 'Clean 3' constitute the 'Met. Cleans' while the combined rejects, 'Sink 1', 'Sink 2' and 'Sink 3' provided the third product, 'fluid bed combustion(FBC) coal'.
On the whole coal basis, recoveries were:
Yield. % Ash. %
Power coal 34.1 34.0
Clean 2 15.8 17.7
Clean3 6.8 15.6
Met. Cleans 22.6 17.1
Sinkl 22.1 64.0
Sink 2 17.4 53.2
Sink 3 3.8 52.5
FBC coal 43.3 58.6
Example 3:
Run of mine coal was crushed to 75mm in single roll crusher under feed back system until the oversize reduced to less than 5%. Raw coal ash was 37.2%.
Raw crushed coal was screened at 25mm in a vibrating screen into two fractions, which were fed to two different stream. In one stream, the 'Coarse fraction' was washed to recover two products, 'Power coal' and a rejects, 'Sink 1'. In other stream, the undersize of 25mm screen was deslimed at 0.5mm wet vibrating screen into 'Middle fraction' and 'Slurry'. The 'Middle fraction' was washed in a heavy medium Cyclone to recover 'Clean 2' and a sink, 'Sink 2'.

The 'Slurry' was beneficiated in a battery of flotation cells after conditioning and separated into 'Clean 3' and 'Sink 3'.'Clean 2' and 'Clean 3' constitute the 'Met. Cleans' while the combined rejects, 'Sink 1', 'Sink 2' and 'Sink 3' produced the third product, 'Fluid Bed Combustion (FBC) coal'.
On the whole coal basis, recoveries were:
Yield. % Ash. %
Power coal 45.8 33.8
Clean 2 19.4 17.2
Clean 3 3.4 16.8
Met. Cleans 22.8 17.3
Sink 1 12.7 68.9
Sink 2 17.4 48.1
Sink 3 1.5. 50.3
FBC coal 31.6 56.6
Example 4 :
Run of mine coal was crushed to 75mm in single roll crusher under feed back system until the oversize reduced to less than 5%. Raw coal ash was 38.99%.
Raw crushed coal was screened at 6 mm in a vibrating screen into two fractions, which were fed to two different stream. In one stream, the 'Coarse fraction' was washed to recover two products, 'Clean 1' having ash content restrained to less than 34% and a rejects, 'Sink 1'. In other stream, the undersize of 6 mm screen was deslimed at 0.5mm wet vibrating screen into 'Middle fraction', and 'Slurry. The 'Middle fraction' was washed in a heavy medium Cyclone to recover 'Clean 2' and a sink, 'Sink 2'. The 'Slurry' was beneficiated in a battery of flotation cells after conditioning and separated into 'Clean 3' and 'Sink 3'.'Clean 2' and

'Clean 3' constitute the 'Met. cleans' while the combined rejects, 'Sink 1', 'Sink 2' and 'Sink 3' produces the third product, 'Fluid Bed Combustion(FBC) coal'.
On the whole coal basis, recoveries are:
Yield, % Ash, %
Clean 1 58.0 33.8
Clean 2 8.8 17.1
Clean 3 3.8 15.8
Met.clean 12.6 16.7
Sinkl 21.8 61.1
Sink 2 4.8 52.0
Sink 3 3.0 41.8
FBC coal 29.4 57.7
The main advantages of the present invention are:
1. The process provides optimal utilisation of inferior grade high ash (35-50%) lower seam
coals.
2. The present process provides up-graded products which can be used in metallurgical
furnaces and in thermal power stations.
3. Selective cleaning of the coarser fraction produces clean coal having less moisture
comparatively than cleaning of whole coal.






We claim :
1. A process for the production of clean coals from inferior grade lower seam coals which
comprises crushing of raw coal to a nominal top size, screening to obtain coarser fraction
and undersize fraction; subjecting the coarser fraction to washing to produce clean coal
having ash content within 34%; subjecting the undersize fraction to wet screening to
obtain oversize as middle fraction and balance as slurry fraction, subjecting the middle
fraction to washing and slurry fraction to deep beneficiation through a battery of flotation
cells to get clean coal having ash of less than 17.5%, mixing the rejects of coarse,middle
fraction washings and slurry beneficiation to get to get coal having ash percentage within
60%.
2. A process as claimed in claim 1 wherein the raw coal is crushed by conventional
methods to a size in the range of 50 to 100 mm to obtain coarse fraction of less than 5%.
3. A process as claimed in claims 1 & 2 wherein the crushing of raw coal is carried out in a
conventional crusher with feed back system.
4. A process as claimed in claim 1, wherein screening is done to obtain coarser fraction
above 25 mm to 6 mm, preferably 13 mm 'and smaller fraction below 25 mm to 6 mm,
preferably 13mm.
5. A process as claimed in claim 1 & 4, wherein the screening is effected using a
conventional vibrating screen having aperture diameter of 25 mm to 6 mm, preferably 13
mm.
6. A process as claimed in claim 1, wherein the washing is carried out in a conventional coal
washkry.
7. A process ac claimed in claim 1, wherein the screening of the undersize fraction is
effected by desliming using a wet vibrating screen, preferably having aperature of 0.5
mm, to obtain middle and slurry fractions.

8. A process for the production of clean coals from inferior grade lower seam coals substantially as herein described with reference to the examples and drawing accompanying this specification.



Documents:

1091-del-2001-abstract.pdf

1091-del-2001-claims.pdf

1091-del-2001-correspondence-others.pdf

1091-del-2001-correspondence-po.pdf

1091-del-2001-description (complete).pdf

1091-del-2001-drawings.pdf

1091-del-2001-form-1.pdf

1091-del-2001-form-18.pdf

1091-del-2001-form-2.pdf

1091-del-2001-form-3.pdf


Patent Number 227104
Indian Patent Application Number 1091/DEL/2001
PG Journal Number 04/2009
Publication Date 23-Jan-2009
Grant Date 01-Jan-2009
Date of Filing 30-Oct-2001
Name of Patentee COUNCIL OF SCIENTIFIC & INDUSTRIAL RESEARCH
Applicant Address RAFI MARG, NEW DELHI-110 001, INDIA.
Inventors:
# Inventor's Name Inventor's Address
1 KALYAN SEN CENTRAL FUEL RESEARCH INSTITUTE, P.O. F.R.I.-828108, DHANBAD (INDIA)
2 BIMAL KANTI DUTTA CENTRAL FUEL RESEARCH INSTITUTE, P.O. F.R.I.-828108, DHANBAD (INDIA)
3 NIKHILENDU SEKHAR DAS CENTRAL FUEL RESEARCH INSTITUTE, P.O. F.R.I.-828108, DHANBAD (INDIA)
4 RAHUL DASGUPTA CENTRAL FUEL RESEARCH INSTITUTE, P.O. F.R.I.-828108, DHANBAD (INDIA)
PCT International Classification Number C01B 55/00
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA