NZ623465B2 - A process flow sheet for pre-treatment of high ash coal to produce clean coal - Google Patents

Abstract

Disclosed is a process to produce low ash clean coal from high ash coal with substantially complete solvent recovery, the process comprising: (i) forming a slurry of coal fines in a solvent mixture of N-Methyl-2-pyrrolidone (NMP) with Ethylenediamine (EDA); (ii) maintaining said slurry in a reactor at a temperature range of 100°C to 240°C and a pressure range of 1 to 4 gauge (kg/cm2) for a period of 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 obtained in step (iii) in an anti-solvent (such as water); (v) separating the washed reject obtained in step (iv) by filtration, said separated reject having a high ash content; (vi) feeding the extract obtained in step (iii) into an evaporator to recover 80-85% solvent and to obtain concentrated material; (vii) precipitating the concentrated material obtained in step (vi) into an anti-solvent tank to separate coal from solvent; (viii) separating the precipitated concentrated material of step (vii) by filtration to obtain separated coal, said separated coal having a reduced ash content; (ix) feeding anti-solvent and solvent resulting from step (vii) as a mixture in a distillation column to separate remaining solvent from the anti-solvent for reuse in the process. at a temperature range of 100°C to 240°C and a pressure range of 1 to 4 gauge (kg/cm2) for a period of 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 obtained in step (iii) in an anti-solvent (such as water); (v) separating the washed reject obtained in step (iv) by filtration, said separated reject having a high ash content; (vi) feeding the extract obtained in step (iii) into an evaporator to recover 80-85% solvent and to obtain concentrated material; (vii) precipitating the concentrated material obtained in step (vi) into an anti-solvent tank to separate coal from solvent; (viii) separating the precipitated concentrated material of step (vii) by filtration to obtain separated coal, said separated coal having a reduced ash content; (ix) feeding anti-solvent and solvent resulting from step (vii) as a mixture in a distillation column to separate remaining solvent from the anti-solvent for reuse in the process.

Description

A PROCESS FLOW SHEET FOR PRE-TREATMENT OF HIGH ASH COAL TO PRODUCE CLEAN COAL FIELD OF THE INVENTION: An improved way to produce low ash clean coal from high ash coal with total solvent recovery.

OUND OF THE INVENTION: As coal is a heterogeneous mixture of organic and inorganic constituents, the process of solvolysis of coal varies with its constituents, maturity, and structural characteristics.

Since the l matter (non-combustible) in coals available in specific geographical location, is very finely disseminated in the organic mass, it is quite difficult to remove this non-combustible l matter by conventional physical coal washing techniques.

Presence of high percentage of near gravity material in coal makes the scope of gravity s limited. It is known that chemical benefication originates from the limitations of physical beneficiation processes. Broadly, chemical iation ispossible by chemical leaching of mineral matter t in coal or, dissolving organic matter of coal. in various organic ts. This indicates that chemical treatment could be one of the solutions to overcome thelimitations of physical benefication methods. Prior art teaches chemical beneficiation techniques that employ highly, corrosivechemicals (mostly acids and alkalis). ry or regeneration of these chemicals is very important to make this technology viable. A parallel approach towards-lowering the ash-content could be recovery of the premium organic matter from coal by Solvent refining. Most of the prior art disclose that chemical leaching is basically adapted to produce ultra clean coal or super clean coal. with ash content less than 0.2% for s high tech end uses. However, such conventional solvent refining processes do not serve the lobjective of low ash coal requirement of steel industries because of mainly low recovery which makes the process uneconomic especially when such an ultra clean coal is not absolutely desired at the cost of lowering the yields. Additionally, the operating cost of said prior art process is high e of high cost of ts and energy requirement in the process. In prior art process, the extraction is being done at boiling point of the solvent mixture making it difficult to recover the solvent trom clean coal and reject. Thus, there is a need to propose a process of g clean coal and reject to recover the remaining solvents. Also, there is a need to develop a process of extraction of coal at a temperature lower than the boiling point of the solvent mix.

By way of reference, the inventors observed that Indian patent ation numbers 1292/KOL/06, OL/07, OL/2008, 950/KOL/09, 1194/KOL/09, 611/KOL/09, 1581/KOL/08 are herein incorporated.

This invention therefore proposes a process to produce low ash clean coal from high ash coal.

This invention also proposes a process to produce low ash clean coal from high ash coal, in which coal is extracted at higher temperature than the boiling point of solvent.

This invention further proposes a process to produce low ash clean coal from high ash coal, in which less amount of solvent is used.

In addition, this invention es a process to e low ash clean coal from high ash coal, in which a washing step to recover solvent from clean coal and reject is implemented.

This invention also es a process to produce low ash clean coal from high ash coal, in which >99% solvent is recovered.

SUMMARY OF THE ION: The present es a process to produce low ash clean coal from high ash coal with substantially complete solvent recovery, the s comprising : (i) forming a slurry of coal fines in a N-Methylpyrrolidone (NMP) with Ethylenediamine (EDA); (ii) maintaining said slurry in a reactor at a ature range of 100°C to 240°C and a re range of 1 to 4 gauge (kg/cm2) for a period of 15 minutes to 4 hours; (iii) separating the produced sample after awal from the reactor, separation cut size being variable depending on the particle size to be d 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 obtained in step (iii) in an anti solvent; (v) separating the washed reject obtained in step (iv) by filtration, said separated reject having a high ash content; (vi) feeding the extract obtained in step (iii) into an evaporator to recover 80-85% solvent and to obtain concentrated material; (vii) precipitating the concentrated material obtained in step (vi) into an anti solvent tank to separate coal from solvent; (viii) separating the precipitated concentrated material of step (vii) by tion to obtain separated coal, said separated coal having a reduced ash content; (ix) feeding anti solvent and solvent resulting from step (vii) as a mixture in a distillation column to separate remaining solvent from the anti solvent for reuse in the process.

According to the invention, coal, solvent (N-MethylPyrrolidone, 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. ing to the inventive s, coal is extracted by using solvent and co-solvent in the reactor. The coal solvent mixture is separated in a separation unit to produce a r 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 e 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. In this inventive process, coal, solvent and cosolvent are being taken in a predefined ratio. Coal to solvent ratio is varied from 1:4 to 1:25 l, g/ml, coal to solvent ratios are wt/vol and solvent: co-solvent ratios are vol/vol wherever mentioned). Coal to co-solvent ratio is varied from 1: 1 to 10: 1 and co-solvent to t ratio is varied from 1:1 to 1:50 (g/ml). Both clean coal and reject is being washed in a sequence shown in figure 1. Following important equipments were there in the system, such as thermic fluid heater, reactor, heat exchanger, thermic fluid pump, inert gas (N2) er, feed tank for evaporator, double effect evaporator, feed pump, transfer pump, discharge pump, heat exchanger, condenser, cooling t0wer, cooling pump, concentrate tank, condensate tank, distillation feed tank, feed pump, distillation column, condenser, condenser tank, reflux pump, reboiler, reboiler pump, discharge pump, and bottom product tank. Some other equipments or vessels such as water storage tank, diesel storage tank, thermic fluid storage tank, expansion tank and centrifuge filter were also installed for this process.

BRIEF DESCRIPTION OF THE ACCOMPANYING G: Fig-'1 shows a system for washing clean coal and s.

DETAILED DESCRIPTION OF THE INVENTION: As shown in fig — 1, thesystem consists of a plurality of units, each unit sing a- itation tank, and a wash tank with stirrer system. Coal (reject or clean coal) and washed liquid is obtained from each unit. The coal and reject goes to next wash tank and washed liquid goes to previbus wash tank.

Coal and solVent in ermined ratio are loaded into a reactor. Nitrogen 'gas is supplied through N2 cylinder for ining inert nment. Diesel is ed to a burner from a diesel e tank. Thermic fluid is supplied into the system from a thermic fluid storage tank. The thermic fluid is heated in a thermic fluid heater. On heating, the thermic fluid’s volume increases, and accordingly, an expansion tank is used to Store the extra thermic fluid. Hot thermic fluid is pumped‘ by a thermic fluid pump to heat the reactor. During extraction, a sample is withdrawn from a sample port.

On completion of the extraction, the burner is switched off. To cool down the thermic fluid heater, the thermic fluid is passed through a heat exchanger. Water is pumped in the heat exchanger through a water pump from a water storage tank.. A reflux condenser maintains pressure and temperature at the reactor at a desired level.

Coal and solvents are loaded into the reactor in a predetermined ratio, Coalf‘to total solvent ratio is varied from 1:4 to 1:25 (wt/vol, g/mL, coal to solvent ratios are wt/vol and solvent: co-solvent ratios are vol/vol wherever mentioned). Co-solvent to solvent ratio is-varied from 1:50 to 1:1. Nitrogen gas is purged into the system for maintaining an inert environment. Thermic fluid is pumped into the system from the thermic fluid storage tank. VThermic fluid is heated in the thermic fluid heater by the diesel fired burner. The reactor is heated by hot thermic fluid. Reactor pressure is varied from 1 to 4 kg/cmz. Reactor temperature is varied from 100°C to 240°C. Extraction is done for 15 minutes to 4 h in the r.

Sample is withdrawn from the reactor h the sample port in predetermined time intervals. This sample is filtered through a mesh. Filtration tes the refluxed mix in two parts (i) reject and (ii) filtrate (extracted material with solvents). Reject is washed ‘ thoroughly with an anti-solvent'(water) for the removal of the solvents from the .

After drying and weighing, these rejects are subjected to ash analysis. The filtrate is actually the extract containing very low ash coal. For precipitation an anti solvent (water) is taken in a vessel. Concentrated extract is then added in to the water. As these solvents are soluble in water, the solvents move to water. phase. It resulted in precipitation Of solid coal particles. The precipitated coal is then separated from the solvent-water solution through ion. This step is carried out in a conicalfiask-funnel type arrangement with standard mesh. The reject of this filtration is the low ash clean coal; filtrate consists of water and the solvents. After drying and weighing, the clean coals are subjected to al and petro graphical analysis.

' At a plant level, the recovery system ses an evaporator feed tank, an evaporator feed pump, a first evaporator, a vapour collector, a second evaporator, a transfer pump, a discharge pump, a heat Exchanger, a concentrate product tank, a condenser, a sate tank, a cooling tower, a cooling pump, a feed tank for distillation column, a feed pump for distillation, a distillation , a condenser, alcondensate tank, a distillate pump, a reboiler, a reboiler pump, a bottom product tank.

'Reacted material in the reactor is taken out and filtered through a centrifuge filter.

Filtration separates the refluxed mix in two parts (i) reject and (ii) filtrate (extracted. material with solvents). Reject is washed thoroughly with an anti-solvent (water) for the removal of the sOlvents from_the reject (as shown in figure 1_). After drying and weighing, these s are subjected to ash analysis. The filtrate is actually the extract containing very low ash coal. te (extracted material along with solvents) are taken into the ator feed tank. Feed material is fed to both the evaporators through the feed pump. 'Heating is started in the second tank through hot thermic fluid. As the material is heated in the second evaporator, vapour is generated. Vapour passes through the vapour collector tank and then goes to the first evaporator to ‘pre heat. the ' input material. Vapour ted in the first evaporator passes through the vapour collector and finally passes through the condenser. The condensate is collected in the condensate tank. The discharge pump is activated to allow discharge of the concentrated material through the discharge pump to the concentrate product tank with or without g. Concentrated product is continuously taken out into the concentrate t tank. This cycle is allowed to continue till a substantially concentrate material is obtained. About 80-85% solvent is evaporated in this evaporator.

The concentrated material is precipitated in water in the mixing tank. As these solvents are soluble in water, solvents move to water phase. It resulted in precipitation of solid coal particles. Thus, precipitated coal is then separated from t-water solution through the centrifuge filter. Clean coal is further washed -(as shown in figure 1) till all the solvent is removed from coal. Water-solvent mixture is stored in ’ a storage tank,' which is separated in a distillation .

Water-solvent e is fed to the distillation feed tank. The feed pump is started to feed the material into the distillation . The reboiler pump is started to allow flow ‘of. thermic 'fluid in the reboiler to heat the material. This water- . solvent e is heated up by circulating it through the reboiler. After some time. this whole material is heated up and water vapour is generated. This WO 44972 vapour comes out from top vapour line. The reflux (distillate) pump is started to recycle the distillate into the distillation column. Vapour passes through the condenser and condensed water goes to the distillate tank. This distillate is fed to the distillation column till an equilibrium is achieved (based on reflux ratio). The top product (distillate) can be taken out‘from the distillate line. This uous cycle of feeding material to the distillation column, heating it through the reboiler and ing it through the condenser continuous till the feed material is distillated.

The bottom product discharge pump is operated to collect the bottom t into the . bottom product tank. Water and solvent is separated and stored in different tanks, which can be used again in the process.

Clean c0al and reject coal is washed as shown in the figure 1.'Basical|y, it is a countercurrent washing where fresh water is used, to wash last batch of clean coal and reject (least contaminated with solvents) in the wash tank 8 and 9. Coal extract along with wash liquid W01 and WE1 isfed to precipitation tank (PPT TANK 1). Coal is precipitated and clean coal (CO) and wash liquid (W90) are obtained.

'The clean coal is fed to next wash tank 2, and wash liquid WOO to distillation column, where water and solvent is separated. In the wash tank2 clean coal C0 and wash liquid W02 is fed, which gives clean coal C1 and wash liquid W01. Clean coal C1 and wash liquid W03 is fed to wash tank 4, which gives clean coal C2 and wash liquid W02. Clean coal C2 and wash liquid W04 is fed to wash tank 6, which gives clean coal C3 and wash liquid W03. Clean coal C3 and fresh water is fed to wash tank 8, which gives clean coal C4 and wash liquid W04. Reject along with WE2 is fed to wash tank 3, which gives reject R1 and wash liquid WE1. Reject R1 and wash liquid WEI. Reject R1 along with WE3 is fed to wash tank 5, which gives reject R2 and wash liquid WE2. Reject R2 along with WE4 is being fed to wash tank 7, which gives reject R3 and wash liquid WE3. Reject R3 along fresh water is fed to wash tank 9, which gives reject R4 and wash liquid WE4. Fresh water is given only at one stage and the same water is used in all other steps in washing. By this strategy, water consumption is less compared to conventional g.

Many trials were conducted by varying ent process parameters such as temperature (100°C to 240°C),.coa| to solvent ratio (1:4 to 1:25), size fraction (-1 mm, to -0.1 mm), different coal origin, filter pore size, co-solvent to solvent ratio. The typical feed coal samples were run—of-mines (ROM) coal and flotation clean coal having about 25-35% and 12-15% ash respectively... The feed particle size varied from -1 mm to -0.1 mm and extraction was done at different temperature.

Some of the typical results are shown here, for example, clean coal yield varied from 45% to 60%. Clean coal ash was about 4%. It is possible to produce less than 8% ash clean coal with 60% yield and about 80% combustible ry with this process. With the help of fine filtration even less than 1 % ash clean coal could be possible. With some l coal, 70% of clean coal yield could be achieved.

Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" and "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

The reference in this specification to any prior publication (or ation derived from it), or to any matter which is known, is not, and should not be taken as an acknowledgment or admission or any form of suggestion that that prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavour to which this ication relates.

WE

Claims (18)

CLAIM :

1. A process to produce low ash clean coal from high ash coal with ntially complete solvent recovery, the process comprising : (i) forming a slurry of coal fines in a N-Methylpyrrolidone (NMP) with Ethylenediamine (EDA); (ii) maintaining said slurry in a reactor at a temperature range of 100°C to 240°C and a pressure range of 1 to 4 gauge (kg/cm2) for a period of 15 minutes to 4 hours; (iii) separating the produced sample after awal 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 obtained in step (iii) in an anti solvent; (v) separating the washed reject obtained in step (iv) by filtration, said separated reject having a high ash t; (vi) g the extract obtained in step (iii) into an evaporator to r 80- 85% solvent and to obtain concentrated material; (vii) precipitating the concentrated material ed in step (vi) into an anti solvent tank to separate coal from solvent; (viii) separating the precipitated concentrated material of step (vii) by filtration to obtain separated coal, said separated coal having a reduced ash content; (ix) feeding anti solvent and solvent resulting from step (vii) as a mixture in a distillation column to separate remaining solvent from the anti solvent for reuse in the process.

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 flotation clean coal.

4. The process as d in claim 2 wherein said particle size is 0.5 mm or less.

5. The process as claimed in claim 1 n an ultra low ash clean coal or super clean coal is produced in step , has an ash content of < 1 %, and is ed by said fine filtration of the extracted on.

6. The process as claimed in claim 5, wherein said ultra low ash clean coal or super clean coal having an ash content of < 1 % is applicable to produce graphite, liquid fuels, aromatic polymers, special chemicals, or carbon materials.

7. The process as claimed in claim 6, wherein the carbon materials comprise carbon nanotubes.

8. The process as claimed in claim 1 wherein a moderate ash clean coal is produced at step (iii) has an ash content of <8%, and is produced by coarse filtration of the ted solution.

9. The process as claimed in claim 8 wherein said te ash clean coal having an ash content of <8% can be used for coke making and blast furnace injection in iron and steel industries and in power generation.

10. The process as claimed in claim 1 wherein moderate ash clean coal having < 8% ash t is produced in the process and constitutes about 60% clean coal yield.

11. The process as claimed in claim 1 wherein coal ash having < 8% ash content is produced in the process, providing for about 80% combustible recovery in the clean coal.

12. The process as claimed in claim 1 wherein coal ash having < 8% ash content is ed in said process at coal to t ratio of 1:4 to 1:25.

13. The process as claimed in claim 1 wherein coal ash having < 8% ash content is produced in said process at co-solvent to solvent ratio of 1:1 to 1:50.

14. The process as claimed in claim 1 wherein coal ash having < 8% ash content is produced in said process at a temperature range of 100°C to 240°C.

15. The s as claimed in claim 1 wherein coal ash having < 8% ash content is produced in said process at a pressure range of 1 to 4 gauge (kg/cm2).

16. The s as claimed in claim 1 wherein coal ash having < 8% ash content is produced in said process, and coal to co-solvent ratio is varied from 1:1 to 10:1.

17. The process as claimed in claim 1 wherein coal ash having < 8% ash content is produced with > 99% solvent ry from the system.

18. The process as claimed in claim 1 wherein coal ash having < 8% ash content is produced in said process, and in which clean coal and reject are being washed in at least five stages to recover the solvents.