Title of Invention

A PROCESS FOR THE PRODUCTION OF COAL WATER SLURRY FUEL.

Abstract

This invention relates to a process for the production of coal water slurry fuel. The main usage of the invention is in the preparation of high concentration coal-water slurry fuel achieving desirable flow property and stability. The coal water slurry fuel may be used as substitute for petroleum based oil & gas for direct & continuous self sustained combustion Without the aid of any auxiliary fuel. The novelty of the invention resides in the stability in the range of 65-70% as the concentration of solids in the slurry as against below 65% using known additives in one step as against multi steps mentioned in the prior art. The additive package consisting of 0.5 to 1.5 wt% of ammonium salt of humic acid, 0.5 to 1.5 wt% stabilizers such as tannin extract, carboxy methyl cellulose and poly acrylates or mixture thereof has been used in the preparation of coal water slurry fuel.

Full Text

This invention relates to a process for the production of coal water slurry fuel. The main usage of the invention is in the preparation of high concentration coal-water slurry fuel achieving desirable flow property and stability. This particularly relates to a process for the production of low viscous, stabilised, water based slurry of high solids loading useful as fuel from coal, suitable for pipeline transportation. The coal water slurry fuel may be used as substitute for petroleum based oil & gas for direct & continuous self sustained combustion without the aid of any auxiliary fuel. The use of such high concentration water based slurry would therefore cause considerable impact in the field of coal transportation and cleaner use of coal, conservation of oil and savings in foreign exchange due to lower import of fuel oil. Water based slurry fuel conveniently prepared from coal is usually high viscous and becomes very thick as the concentration of coal in the slurry exceeds 65% by using known additives. Stability of the slurry though fairly good, needs further improvement. Using coal in place of expensive petroleum has become popular. However, coal in the form of a solid fuel is difficult to handle and also the cost of its transportation is great. Thus the development of techniques of converting coal into a slurry to make it possible to handle coal in the form of a fluid has been energetically carried out. AS one of the techniques, a process of Coal Oil Mixture obtained by mixing coal with heavy oil has been known. This process, however, is directed to a mixture of coal with heavy oil in a ratio by weight of about 1:1, hence it cannot be regarded as a completely oil free fuel and also its merit in cost is small. Further, a mixture of coal with methanol, the so called methacoal, has also been known, but since expensive methanol is used therein, the mixture is also expensive so that it has not yet reached a stage of practical use. On the other hand, Coal Water Mixture which is a mixture of coal with water is fully practical also in cost; hence it has been most noted. Coal Water Mixture, however, has problem that if the water content therein is high, its heat efficiency at the time of combustion decrease, and contrarily if it is low, the viscosity of Coal Water Mixture rises to increase the pressure loss at the time of transportation. Further, since Coal Water Mixture consists of coal particles and water, there is a problem of storage that coal particles settle with lapse of time and separate from water. In order to overcome these problems, there has been made an attempt of adjusting the particle diameter of coal particles to thereby produce a coal water mixture having a low viscosity and a good stability. In order to produce a coal water mixture having a high coal concentration, a low viscosity and a good stability, it is said to be preferable to mill coal so as to give such a particle diameter distribution that the packing fraction of coal may be made as high as possible. As one of the processes for milling coal so as to give such a particle diameter distribution, a high concentration wet milling process has generally been known. However, when the coal concentration becomes so high, the viscosity of slurry also becomes high, which inevitably results in a problem-of reduction in the milling efficiency, i.e; increase in the power, it is necessary for promoting the milling to add an additive such as surfactant( dispersing agent), but since the amount necessary amounts to about 1% of the weight of coal used, its influence upon the production cost of Coal Water Mixture cannot be ruled out. Reference may be made to US Patent No: 4747548 wherein a process has been mentioned for producing a coal water slurry in a wet mill having plurality of stages serially arranged to have an inlet and an exit. The said process comprises of : continuously operating the wet mill for milling coal fed to the mill; feeding coal and water to the wet mill at the plurality of stages, thereby causing concentration of the coal at the inlet to be lower than concentration of the coal at the exit of the mill; said step of feeding includes feeding a first type of coal having a Hardgrove index of grindability of sixty or less and feeding a second type of coal having a Hardgove index of grindability being greater by at least eight than the Hardgrove index of the type first type of coal; and passing the first and second types of coal and water as a coal water slurry serially through the plurality of stages and milling the coal in the stages, thereby obtaining a broader width of particle size distribution resulting in less viscosity being obtained for the coal water slurry. Reference may also me made to US Patent No: 4613084 wherein high concentration coal water slurry is produced by feeding coal, water and dispersing agent( not disclosed ) into a wet, continuous ball mill and subjecting them to wet milling, which process "comprises feeding the dispersing agent in a multi- stage manner along the milling direction of coal within the ball mill. The drawbacks of the above processes are that reactions have to be carried out in several stages with various types of specific compounds and the final additive package requires extensive pretreatment and selective purification methods, thus making the process tedious and uneconomical. Besides, the performance of the additive packages was not up to the desired level of stability in the range of 60-70%. Owing to these disadvantages, the Japanese developed and additive, namely sodium polystyrene sulphonate which is used for commercial production of water slurry. Reference may be made to H.Arai and T.Ukigaki, Proc. 16 Int. Tech. Conf. Coal Utilization and fuel system, Florida, 1991, 423-433. Sodium polystyrene sulphonate being the proprietary additive package of Japanese company, its preparation methods are fully guarded and the additive is highly expensive. Reference may also be made to work of J.L. Morrison, B.G. Miller and A.W. Scaroni, Proc. 18 Int. Tech. Conf. Coal utilization and fuel systems, April 26-29 (1993) 361-368, Florida, USA wherein an ammonium based sulphonated naphthalene condensate has been used as the dispersant for coal-water slurry fuels. However, the slurry formulation with this dispersant requires a pH modifier and a stabilizer. The main objective of the present invention is to provide a process for the production of coal water slurry fuels which obviates the drawbacks as detailed above. Another objective of the present invention is to provide a process for the production of high concentration, 70% solids loading and above, water based slurry which obviates the drawback of viscosity, stability and concentration. Accordingly, the present invention provides a process for the production of coal water slurry fuel in one step which comprises wet grinding by conventional methods to -72 to 0200 mm size, a mix of 65 to 70 wt% coal, 30 to 35 wt% deionised water and characterized in that 1.0 to 3.0 wt% additive system essentially containing 0.5 to 1.5 wt% ammonium salt of humic acid, 0.5 to 1.5 wt% stabilizers such as tannin extract, carboxy methyl cellulose, poly acrylates or mixture thereof, for a time period in the range of 25 to 60 minutes, screening the oversize and recirculating the oversize so obtained for further grinding, if required, to obtain coal water slurry fuel. In an embodiment of the present invention the mixing and grinding is effected at temperature in the range of room temperature to 60 degree Celsius. In another embodiment of the present invention the pH of the slurry is maintained in the range of 6 to 8 by adding an alkali solution, if required. In yet another embodiment of the present invention slurry of coal water mixture is prepared and stored in an air tight container/vessel or under nitrogen pressure to eliminate/minimize evaporation of water. Coal is crushed in dry disintegrate like jaw crusher and double roll crusher to a size 100 percent below 10 mm. The crushed material below 10 mm is then subjected to mixing in ball mill, containing spherical, hardened steel balls of assorted sizes in specified numbers occupying 45 to 50 percent of the ball mill volume. The raw coal is crushed to the desired size in the range of-72 to -200 mm, in the presence of just adequate quantity of deionised water and suitable additive system containing ammonium salt of humic acid and tannin extract for a time period in the range of 25 to 60 minutes, screening the oversize and re-circulating for further grinding. Water based slurry prepared in this manner is sufficiently fluid and fairly stable. The increase in solids loading and the reduction in grinding time as well as viscosity achieved by this technique is substantial. The solids concentration in the slurry is in the range of 65 to 70 percent. The pH of the slurry is kept within the range of 6 to 8 by adding, if necessary, an alkali solution. The low viscous slurry so obtained is stored in an airtight vessel or under nitrogen pressure to eliminate or minimise evaporation of water of the slurry. The slurry thus prepared and stored is pumpable and can be transported through pipeline, injected and atomised in modified oil designed and/or specially designed burner. The novelty of the invention resides in the stability in the range of 65-70% as the concentration of solids in the slurry as against below 65% using known additives in one step as against multi steps mentioned in the prior art. The inventive step comprises of providing an additive package consisting of 0.5 to 1.5 wt% of ammonium salt of humic acid, 0.5 to 1.5 wt% stabilisers such as tannin extract, carboxy methyl cellulose and poly acrylates or mixture thereof. The stabilisers used may be selected from compounds such as carboxy methyl cellulose, tannin extract, poly- acrylates and the like. The process of the present invention is explained by means of the following examples which should not be construed to limit the scope of the invention. Example-l Run- of- Mine(ROM) Challang Coal of Meghalaya, containing moisture 5.7%, Ash 8.2%, Vplatile Matter(VM) 38.5% and Fixed Carbon(FC) 47.6% is crushed in a jaw and double roll crusher to less than 10 mm size. 20 kg of crushed coal sample is charged in a 120 capacity ball mill containing spherical, hardened steel balls of assorted sizes( ball diameter 50 mm, 40 mm and 20 mm) filling approximately 47.5 % of the mill volume. 300 gms of additive is added to 9700 gms of demineralised water ( conductivity 0.9 ms/cm) and mixed thoroughly in a mixer for one or two minutes & then sent to the ball mill. The mill is run (Rpm 42/minute for 40 minutes). 600 ml of 12% alkali solution is added to the slurry and thoroughly mixed to adjust the pH to 6.3. The slurry so prepared is then transferred to an air tight container. The slurry prepared is stable for more than 20 days and pseudoplastic in nature and its viscosity is 960 mPas at 128/sec shear rate. Example-2 Run- of- Mine(ROM) Ledo Coal of Assam, containing moisture 3.3%, Ash 9.7%, Volatile Matter(VM) 37.7% and Fixed Carbon(FC) 49.3% is crushed in a jaw and double roll crusher to less than 10 mm size. 20 kg of crushed coal sample is charged in a 120 capacity ball mill containing spherical, hardened steel balls of assorted sizes( ball diameter 50 mm, 40 mm and 20 mm) filling approximately 47.5 % of the mill volume. 300 gms of additive is added to 9700 gms of demineralised water ( conductivity 0.9 ms/cm) and mixed thoroughly in a mixer for one or two minutes & then sent to the ball mill. The mill is run (Rpm 42/minute for 45 minutes). 600 ml of 12% alkali solution is added to the slurry and thoroughly mixed to adjust the pH to 6.3. The slurry so prepared is then transferred to an air tight container. The slurry prepared is stable for more than 20 days and pseudo plastic in nature and its viscosity is 1002 mPas at 128/sec shear rate. ExampIe-3 Run- of- Mine(ROM) Challang Coal of Meghalaya containing moisture 5.7%, Ash 8.2%. Volatile Matter(VM) 38,5% and Fixed Carbon(FC) 47.6% is crushed in a jaw and double roll crusher to less than ]0 mm size. 19 85 kg of crushed coal sample is charged in a 120 capacity ball mill containing spherical, hardened steel balls of assorted sizes( ball diameter 50 mm, 40 mm and 20 mm) filling approximately 47.5 % of the mill volume. 150 gms of additive is added to 10000 gms of demineralised water ( conductivity 0.9 ms cm) and mixed thoroughly in a mixer for one or two minutes & then sent to the ball milL The mill is run (Rpm 42/minute for 40minutes). 600 m! of 12% alkali solution is added to the slurry and thoroughly mixed to adjust the pH to 6.3. The slurry so prepared is then transferred to an air tight container. The slurry prepared is stable op to 05 days and pseudo plastic in nature and its viscosity is 1370 mPas at 118 sec shear rate. Example-4 Run- of- Mine(ROM) Challang Coal of Meghalaya containing moisture 5.7%, Ash 8.2%, Volatile Ma^er(VM) 38.5% and Fixed Carbon(FC) 47.6% is crushed in a jaw and double roll crusher to less than 10 mm size. 20.7 kg of crushed coal sample is charged in a 120 capacity ball mill containing spherical, hardened steel balls of assorted sizes( ball diameter 50 mm, 40 mm and 20 mm) filling approximately 47.5 % of the mill volume. 300 gms of additive is added to 9000 gms of demineralised water ( conductivity 0.9 ms/cm) and mixed thoroughly in a mixer for one or two minutes & then sent to the ball mill. The mill is run (Rpm 42/minute for 40minutes). 600 ml of 12% alkali solution is added to the slurry and thoroughly mixed to adjust the pH to 6.3. The slurry so prepared is then transferred to an air tight container. The slurry prepared is stable for more than 20 days and pseudo plastic in nature and its viscosity is 1270 mPas at 128/sec shear rate. Example-5 Run- of- Mine(ROM) Challang Coal of Meghalaya containing moisture 5.7%, Ash 8.2%, Volatile Matter(VM) 38.5% and Fixed Carbon(FC) 47.6% is crushed in a jaw and double roll crusher to less than 10 mm size. 20.55 kg of crushed coal sample is charged in a 120 capacity ball mill containing spherical, hardened steel balls of assorted sizes( ball diameter 50 mm, 40 mm and 20 mm) filling approximately 47.5 % of the mill volume. 450 gms of additive is added to 9000 gms of demineralised water ( conductivity 0.9 ms/cm) and mixed thoroughly in a mixer for one or two minutes & then sent to the ball mill. The mill is run (Rpm 42/minute for 40minutes). 600 ml of 12% alkali solution is added to the slurry and thoroughly mixed to adjust the pH to 6.3. The slurry so prepared is then transferred to an air tight container. The slurry prepared is stable for more than 20 days and pseudo plastic in nature and its viscosity is 1250 mPas at 128/sec shear rate. Table-1 (Table Removed) The main advantages of this invention are— 1. Grinding & Mixing( Slurry Making) are combined to a single step 2. Grinding time is reduced 3. Product being liquid discharge & handling is easier 4. Pollution during grinding & product discharge is eliminated 5. Viscosity of the slurry reduces appreciably 6. Fluidity of the slurry improves 7. Stability of the slurry improves We Claim: 1. A process for the production of coal water slurry fuel in one step which comprises wet grinding by conventional methods to -72 to 0200 mm size, a mix of 65 to 70 wt% coal, 30 to 35 wt% deionised water and characterized in that 1.0 to 3.0 wt% additive system essentially containing 0.5 to 1.5 wt% ammonium salt of humic acid, 0.5 to 1.5 wt% stabilizers such as tannin extract, carboxy methyl cellulose, poly acrylates or mixture thereof, for a time period in the range of 25 to 60 minutes, screening the oversize and recirculating the oversize so obtained for further grinding, if required, to obtain coal water slurry fuel. 2. A process as claimed in claim 1 wherein the pH of the slurry is maintained in the range of 6 to 8 by optionally adding an alkali solution. 3. A process for the production of coal water slurry fuel substantially as herein described with reference to the examples.

Documents:

328-del-2001-abstract.pdf

328-del-2001-claims.pdf

328-del-2001-correspondence-others.pdf

328-del-2001-correspondence-po.pdf

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

328-del-2001-form-1.pdf

328-del-2001-form-18.pdf

328-del-2001-form-2.pdf

328-del-2001-form-3.pdf