Title of Invention	PROCESS OF RECOVERING RESOURCES FROM COAL WASHERY EFFLUENTS FOR SUSTAINABILITY
Abstract	A large amount of water is required for coal washing and a huge quantity of effluent is generated. Coal washery effluents contain large amounts of suspended solids(TSS) and high chemical oxygen demand (COD) values and they create serious water pollution problem in which they are discharged. The solids in suspension are found to be colloidal in nature and they cannot be removed by ordinary settling. They possess high coking value and thus in addition to water pollution and siltation on the riverbed, a good quality coking coal is being lost. It shows the ineffectiveness of the present effluent treatment system. This process of invention relates to the recovery of coal fines as resource from the effluents. The effectiveness of the use of different conventional and synthetic polymeric flocculats for the removal of suspended solids has been evaluated. The process also involves the identification of a suitable flocculent and to evaluate the optimum size of a clarifier for the removal of suspended solids from the effluent. In this process a substantial amount of a good quality coal fines can be recovered as resource and the supernatant liquid can be recycled or safely discharged in the river. The process suggest a treatment scheme , which will make it feasible to design a cost-effective treatment plant for coal washery and the supernatant liquid can be recycled or safely discharged without causing surface water pollution. It would maintain the acceptable balance between environmental management and sustainable development of coal washeries in the region. This invention has got immense applications and socioeconomic benefits. The invention provides a sort of fundamental new scientific insight for the utilization of coal fines as resource and environmental protection as well.

Title of Invention

PROCESS OF RECOVERING RESOURCES FROM COAL WASHERY EFFLUENTS FOR SUSTAINABILITY

Abstract

A large amount of water is required for coal washing and a huge quantity of effluent is generated. Coal washery effluents contain large amounts of suspended solids(TSS) and high chemical oxygen demand (COD) values and they create serious water pollution problem in which they are discharged. The solids in suspension are found to be colloidal in nature and they cannot be removed by ordinary settling. They possess high coking value and thus in addition to water pollution and siltation on the riverbed, a good quality coking coal is being lost. It shows the ineffectiveness of the present effluent treatment system. This process of invention relates to the recovery of coal fines as resource from the effluents. The effectiveness of the use of different conventional and synthetic polymeric flocculats for the removal of suspended solids has been evaluated. The process also involves the identification of a suitable flocculent and to evaluate the optimum size of a clarifier for the removal of suspended solids from the effluent. In this process a substantial amount of a good quality coal fines can be recovered as resource and the supernatant liquid can be recycled or safely discharged in the river. The process suggest a treatment scheme , which will make it feasible to design a cost-effective treatment plant for coal washery and the supernatant liquid can be recycled or safely discharged without causing surface water pollution. It would maintain the acceptable balance between environmental management and sustainable development of coal washeries in the region. This invention has got immense applications and socioeconomic benefits. The invention provides a sort of fundamental new scientific insight for the utilization of coal fines as resource and environmental protection as well.

Full Text	1.0 Field of invention This invention relates to a noble method of recovering high quality coal fines from coal washery effluent as resource. The invention provides a sort fundamental new scientific insight for resource recovery from effluents, determining the optimum size of clarifier, for the control of environmental pollution and sustainable supply of water in washeries. The methodology can used on an industrial scale for various sites. 2.0 Background of the invention The reserve of coking coal is mainly centralized in the Jharia Coalfield of Bharat Coking Coal Ltd.(BCCL) But these coals are believed to be of drift origin and contains non-coal mineral matters embedded in them . These are released as pollution discharges at some point in the extraction cycle. Coal refuse consist of waste coal, state and clay associated with coal seams. The coking coal used in blast furnaces should have ash content 14-20%, where as Indian coals are having high ash content. So, demand for coal within the well-defined limits has led to the planning for the up gradation of coal . To do so, bigger sizes of coal as mined are crushed to smaller sizes and fed for washing in coal washeries. In this process lose mineral materials are eliminated by gravity separation process. Some non-coking coals are also washed for thermal power plants in washeries. A large quantity of water is required for coal washing. The quantity of water used per million tonnes of raw coal varies both with the size of the coal and with the type of process used. For every metric tonne of hourly capacity of the washery, 720-2400 gallons of water are required per hour. A plant with a capacity of 100 tonnes of coal per hour requires in the course of 8h shift from 600,000 to 2000,000 gallons of water. The feed water in the washing process comes out from the coal preparation plant in the form of effluent and contains dirty materials and impurities associated with the raw coal . The effluent from coal cleaning process contain large amount of suspended solids and they create serious problems of deterioration of water quality of the river or water bodies into which they are discharged. The fines produced during crushing and other processes are mixed with water and other liquid medium used in different processes, which led to the formation of slurry. The slurry formed is thickened in thickeners and the heavier underflow is filtered and normally mixed with clean coal. Thickener over flow together with the filtrate from the filter section and spill water from other sections of the plant form the washery effluent. The effluent contains large amount of coal fines in the form of suspended solids (TSS) and high chemical oxygen demand (COD) values and they create serious surface water pollution problem in which they are discharged There is no well defined process for combating this situation This 2 needs a search of proper technology to reduce pollution load within the desired limit before discharging the effluents to the river. Present invention relates to the identification of suitable regent for the recovery of coal fines as resource from coal washery effluent, determining the optimum size of clarifier, the control of environmental pollution and sustainable supply of water in washeries. and to maintain the sustainable supply of water in the region. 2.1 Working principle of washery Coal washing is mainly based on the differences in specific gravities between the coal and the impurities present in the coal. Since most of the impurities are heavier than the coal itself the coal is separated from its impurities by designed uses of these differences. Specific gravity of pure coal is between 1.23 to 1.7. A change in specific gravity is exhibited with a change in the ash content. Higher ash content gives higher specific gravity. The raw coal is crushed into smaller sizes and is introduced into a suspension or solution where specific gravity has been adjusted so that the coal floats at the surface, whereas the refuse sinks to the bottom. 2.2.Characteristics of coal washery effluent The quantity of water used per tonne of coal varies both with the size of coal and the type of the process used. The effluent contains very high-suspended materials, COD values and dissolved chemical substances. Coal washery effluents contain huge amounts of suspended solids. The solids in suspension are ultrafractions of coal fines, which are colloidal in nature, and possess high coking value. Thus, a good quality of coking coal is being lost along with the effluents. As the suspended particulates in the washery effluent are found to be colloidal in nature, it is difficult to remove the suspended solids by way of simple sedimentation. The large particles suspended in the range of 10-2 cm or natural settling or conventional filtration readily separates more. Particles of colloidal dimensions i.e. 3 This invention investigates to recover the coal fines as resource effectively from the effluent, which also abate water pollution problem and siltation on the riverbed. As such it will create or maintain sustainable supplies of water. 3.0 Drawback associated with the known art Associated impurities with coal are generally exposed when it is crushed and chances are favorable for a large proportion of dirt particle becoming detached from the coal. The fines produced during crushing and other processes are mixed with water and other liquid medium used in different processes lead to the formation of slurry. The slurry formed is thickened in thickeners and the thickener underflow is filtered and normally mixed with clean coal. Thickener overflow along with the filtrate from the filter section and spill water from other parts of the plant form the washery effluent. Most of the washeries face the acute problem of dewatering of coal fines. These solids in suspensions are found to be ultrafractions of coal, disperses to a long distance creating pollution problem and siltation on the riverbed. They cannot be removed by ordinary settling .The suspended solids were found to have high coking value. Apart from water pollution and siltation on the riverbed, a very good quality of coking coal is being lost in the river. It is a great loss to national economy in the context of energy crisis. Thus in addition to water pollution and siltation on the riverbed, a good quantity of coking coal was being lost in the river. Suspended solids present in the washery effluent also hinder the movement and development of aquatic life and making the river unsuitable for fish breeding. This also creates problem faced by downstream water works in settling and filtering the suspended solids from the polluted water. The present system of effluent treatment by ordinary settling and drying up in a series of lagoons has not been found to be successful and no well defined process in this regard has been reported 4.0 A summary of invention The colloids are destabilized or destroyed by causing them to aggregate or coagulate into larger particles and thus they can be effectively removed. Some specific structured compound known as coagulants does this. The salt of Al and Fe are found suitable for this purpose. The synthetic polyelectrolytes are very effective flocculants for suspended solid removal in aquatic medium. They combine with charged particles causing rapid flocculation and an increased rate of coagulation and settling. For optimum beneficial results, the molecular weight of polymers may be desirable in the range of 30,000 to 1,00,000 and even higher. The molecular weights should not however be so high as to yield insoluble polymers. 4 4.1 Destruction of colloids All colloidal particles are electrically charged. The colloidal particles are dependent upon electrical charge for their stability. Like charges repel, and as a result, similarly charged colloidal particles cannot come close enough to agglomerate into larger particles. Because of the primary charge on the particle, an electrical potential exists between the surface of the particle and the bulk of the solution. When two similar particles approach each other, the repulsive electrostatic force increases to keep them apart. However, if they can be brought sufficiently close together to pass this energy barrier the attractive Vander Wall's force will predominate and the particles will remain together. If it is desired to coagulate colloidal particles, they must be given sufficient kinetic energy to over come the energy barrier that exists, or else the energy barrier must be lowered by some means. There are four basic mechanisms by which colloids can be coagulated, i) Double layer compression ii) Charge neutralization iii) Entrapment in a precipitate iv) Interparticle bridging If a high concentration of an electrolyte added to a solution, the concentration of ions with in the different layer will increase and thickness of this layer will decrease. So particles can come together and aggregate. The charges on a colloid can some times be neutralized by addition of molecules on opposite charges, which have ability to absorb into the colloid. With the aid of sufficient metal salts of Al (iii) and Fe (iii) to the solution they may combine with OH rapidly to form OH precipitates. Colloidal particles may provide condensation sites where the precipitates may form and hence settles with it. The settling precipitates can also entrap colloids through which it passes, bringing them down. The precipitation of a colloid is effected by that ion of an electrolyte, which has the charge opposite in sign to that of the colloidal particles and the effect of such ion increases markedly with the number of charges it carries. The long chained charged synthetic and natural polymers (Polyelectrolytes) can act to destabilize colloids by forming inter particle bridge. The polymers that are anionic and non-ionic (usually anionic to a slight extent when placed in water) become attached at a number of adsorption sites to a surface of particles found in the settled effluent. A bridge is formed when two or more particles become intertwined with other bridge particles during the flocculation process, forming larger structural units that readily separated from aqueous dispersing medium 5 4.2 Measurable and likely impact of the invention A huge amount of water is required in coal beneficiation plants and a large quantity of effluent is formed. The effluent from the coal washery contain abnormally high amount of suspended solids ranging from 5 g/1 to 30 g/1. To fulfill the huge amount of water requirement, the maximum numbers of washereis are installed in the vicinity of the river Damodar in Jharia Coalfield in India. Presently there are 23 coal washereis in India out of which 13 are situated on the bank of the Damodar River only. A large quantity of effluent is formed in the process of coal washing and the discharge of the effluent to inland surface water, constitutes a serious threat to the environment. The ultrafine coal particles are being lost in the river. The presence of large amount of coal fines has blackened the color of the river water, which is visible everywhere. This needs a search of proper technology to reduce susbended songs of coal lines in the effluent to the desired river. The investigation relating to invention reveals the use of different conventional and synthetic polymeric flocculants for the removal of suspended solids present in the coal washery effluent. It has been found that the existing method of washery effluent treatment is not adequate to reduce the suspended solids in the final discharge to an acceptable limit. Studies involved to identify a suitable flocculent and to develop a methodology for the effective removal of suspended solids from the washery effluent. The work has made a distinct contribution to the advancement of knowledge in studying the characteristics of suspended coal fines and for its effective removal. The washery authority can design the effluent treatment plant which will be of smaller in size as the retention time is much less in comparison to conventional treatment process. In addition to this a substantial amount of good quality of fine coal can be recovered and the supernatant liquid can be recycled or safely discharged in the river with out causing pollution problem. Thus it will be of great economic benefit to the industry. These are the most significant and measurable impact of this work. The techniques adopted for the study have formed a guideline to remove the suspended solids from other coal washery effluent in the area. 5.0 Detailed description of the invention The coal washeris are most major contributors of pollutants to the river Damodar. The coal washery effluent contains extremely high amount of suspended solids. The study reveals that the existing method of washery effluent treatment system is inadequate to reduce the 6 suspended solids in the final discharge of effluent to an acceptable limit. The techniques to be adopted are specified below: 1. Characteristics of suspended solids in coal washery effluent depend on the quality of the raw coal used, process of washing and site-specific factors. Qualitative and quantitative assessment of the effluent is to be monitored. 2. The effluent containing known concentration of suspended solids is to be taken in a graduated cylinder to study the settling behavior. 3. The natural settling behavior is to be read by noting the height of interference between clear liquid and solid (settled sludge) at known interval of time. The zone settling curves are to be drawn with heights of interference and the corresponding time intervals. 4. Similar studies are to be conducted with suspended solids of different pulp density and with different coagulants and the zones of settling curves are to be drawn. 5. The suspended solids in the supernatant liquid are to be estimated at known interval of time and the percentage removal of the suspended solids is to be calculated. 6. The optimum pH for effective removal of suspended solids, optimum doze, retention, identification of the most coagulant, cost benefit analysis are to be made. 7. . Clarification area should be provided in the washery effluent treatment system. Sufficient retention time should be given for complete removal of suspended solids after the addition of coagulants. The design of the settling pond is to be made accordingly. 8. Clear overflow from the settling pond may be recirculated to the plant to save the raw water consumption and ultimately to low down the cost of running the plant. 6.0 Case study relates to this invention The user agencies of this invention are different coal washeries Ltd. For the application of this invention work Sudhamdih coal washery of BCCL (Bharat Coking Coal Ltd.) was chosen. The washery is at about 20 km. south of Dhanbad town and situated on the bank of the Damodar river. The average ash content of the raw coal used by the washery ranges from 27 to 30 %. The clean coal obtained as a product of the washery contains 18.5 to 19.5 % of ash content. The material balance of the coal washery is given Table 1 The washery requires 91 kl/h of water for the processing, which is being pumped from the Damodar river. The fed water comes out from the washery as a dirty blackened color effluent. Normally the effluent quantity from Sudamdih washery ranges from 300 to 500 cu.m per day. The suspended solids in the washery effluent were monitored on regular 7 oasis and were found to be ranging from 5000 to 30,000 mg/1 with an average value of 20,100 mg/1. The maximum permissible limit to discharge the industrial effluent in the inland surface water 100 mg/1. As the size of the suspended solids are found to be less then 0.3 MPD µ they posses all the properties of colloids and they do not settle down easily. They tend to remain suspended in surface water for indefinite period of time. These suspended solids posses high coking values. Thus a good quality of coking coal is being lost along with the effluent. The loss of huge amount of coal fines shows the in-effectiveness of the present effluent treatment system used in the washery. About 6-10 of coal fines are being lost every day in the Damodar river. The treatment of suspended solids is based on the principle of extended sedimentation with conventional coagulants like lime, alum and lime mixed with alum . Synthetic flocculent 'True floc' was also used. It is an anionic copolymer in powder form . Natural settling was found to be very slow and it took about 8 hours of settling. The supernatant after 8 hours of settling was not found even free from suspended solids. This is because of the colloidal nature of the suspended matters present in the effluent. The average settling rate was estimated to be 0.09 cm/min. The settling behavior by using lime as coagulant has been shown in Figure 3. The settling rate was found to be 0.39 cm/min. The suspended solid after 2 h settling time was found to be 642 mg/1. Alum doses of 400 mg/100g, 1.6 g/100g, 2.4 g/100g, 8 g/100g, 16 g/100g, of suspended solids S.S were used to the effluent containing 25 g/1 of S.S. The respective settling rates in cm/min were found to be 0.16 , 0.25 , 0.27 , 2.4 , 0.26 . On the basin of settling rate 1.6 g alum/100 S.S in the supernatant was found to be 642 mg/1 and the sludge volume was 405 ml. The settling rate was found to be 0.17 cm/min and sludge volume was 475 ml. The applied dose was 12 g lime + 2.4 g Alum/100 g of S.S. Synthetic flocculent " True floc" was used in the doses of 1 mg/100g S.S, 1.25 mg 100 g of S.S and 2 mg/100g S.S. The respective settling rates were found to be 2.75 cm/min , 2.2 cm/min , 1.5 cm/min for the effluent containing 10 g/1 S.S , 20 g/1 S.S and 25 g/1 S.S respectively. . It was found that "True floc" is the most effective in clarification of about 94% S.S. within 10 minutes and settling rate was enhanced by 15-28 times. After one-hour retention time S.S. were found to be 97 mg/1. Thus lime and alum were found to be equally effective in clarification of effluent. But "True floc" was found to be the most suitable for the treatment of washery effluent among the tasted coagulants. 8 6.1 Cost estimates Lime : Rs. 120/Kg (S=Rs43) Alum : Rs. 130/Kg "Turefloc" : Rs. 280/Kg The optimum does are Lime : 16g/100gS.S Alum : 1.6g/100gS.S "Turefloc" : 1.25 g/100g S.S The cost of treatment of the washery effluent with aid of above mentioned coagulants. Lime : Rs. 19,200/t of S.S Alum : Rs. 2,080/t of S.S "Turefloc" : Rs 3.5 A of S.S Thus it is clear that the treatment of washery effluent with aid of "True floc" is the cheapest than that of alum and lime. 6.2 Design of clarifier The rate at which the interface subsides is equal to the slope of the curve at that point10. According to this methodology critical area for thickening is given by where, A = Area in mz ;V = Subsidence velocity in m7h;and Q = Overflow rate in m7h Q and V were calculated with the data on output from tailing pond in m7h and settling test result. *Basic data Output from the tailing pond = 21 m3/h Subsidence velocity V from hindered settling portion of the curve: 9 6.3 A brief description of the accompanying drawing. The settling rates and % removal by different are given in Figure 1 .The test was also used for the slurry where suspended solid was 20 g/1 and the dose of True-floc was 1.25-mg/100 g of TSS. The advance of the interface between the water and settled solids was recorded with time and a graph was plotted between the heights of effluent slurry vs. time. The results are given in Table 2 and the curve plotted is shown in Figure 2. Using the data the area of decant pond of the washery effluent was calculated. Based on the results it was observed that the output of effluent from the tailing pond 21m3/h. Initially the height of the suspended coal fines in the cylinder was 40 cm. After the addition of coagulant the height of the coal fines was reduced by 25.8 cm. It may be seen from the curve that if the initial rate of settlement was continued the desired level of settlement would have been achieved after 8 min. But the rate of settlement continued to decline with the passage of time. A linear rate of settlement could be observed after 8 min, but after the lapse of 14 min the rate of settlement further reduced and the ultimate of 37.5 cm could be achieved after 25 min. It may be observed from the curve that, had there be no reduction in the rate of settlement after 8 min, ultimate settlement should have been achieved in 17 min. The cylinder test result also showed that the subsidence velocity V was 0.31 m/h, and' overflow rate Q was found to 7.875 m7h. The area required being 64.35 m2. At present the total area utilized for settling ponds was 36,800 m, 2 which is much more than the actually require, as calculated. With the addition of the synthetic flocculent suspended solids were removed in the clarifier. The sludge removed from underflow of the clarifier could be mixed with the clean coal and the clarified water could be recycled or disposed off in the river safely. Figure 3 shows the proposed scheme for design of the washery effluent treatment. 10 I claim 1. Coal fines in washery effluents in the form of suspended solids are found to having colloidal characteristics and they cannot be removed by ordinary settling. Process of recovering them as resource involves the evaluation of effectiveness of different conventional coagulants and synthetic flocculants, identification of a suitable flocculent for effective removal of coal fines at minimum cost. This invention identifies that with the aid of a synthetic flocculent, 90-95% of the coal fines can be removed from the effluent and solves the pollution problem as well. 2. The process determines the optimum size of the clarifier tank for the recovery of coal fines from the effluent. This additional unit operation for treatment is to be put before discharging the effluent to the water bodies and the supernatant can also be recycled , which will reduce the raw water consumption. The process can also minimize the cost of additional land requirement, land requirement, land degradation, surface and ground water pollution , siltation on the river bed , impact on social life and safety. 3. The process has suggested a treatment scheme , which will be feasible to design a cost effective effluent treatment plant for coal washery and the treated effluent can be recycled or safely discharged without causing surface water pollution. 11 the Material balance of the coal washery Item Throughput Yeld Ash in Fraction (t/d) (per cent) (per cent)Clean coals 700 23.7 18.5-19.5 Middlings 1,350 45.6 29.5-31.5 Rejects 900 30.4 33.1-35.9 Suspend solids 10 0.3 13.2-14.8 (Fine coals) Feed coal 2960 100.0 27-30 Table 2 Settling characteristics with the use of synthetic coagulant "true-floc" Suspended solids :20g/l,Dose : 1.25 mg/100g SS Time, Height of Settling Suspended Percentage min interface(cm) rate(cm/min) solids(g/l) removal0 40.0 0.00 20.0 0.00 5 16.0 5.00 10 4.0 3.7 0.801 91.0 15 3.1 2.5 20 2.4 1.93 -25 2.3 1.54 -30 2.0 1.30 0.454 95.46 50 2.0 0.78 0.325 98.37 60 2.0 0.65Average settling rate : 2.2 cm/min, sludge volume : 98.0 ml 12

Full Text

1.0 Field of invention
This invention relates to a noble method of recovering high quality coal fines from coal washery effluent as resource. The invention provides a sort fundamental new scientific insight for resource recovery from effluents, determining the optimum size of clarifier, for the control of environmental pollution and sustainable supply of water in washeries. The methodology can used on an industrial scale for various sites. 2.0 Background of the invention
The reserve of coking coal is mainly centralized in the Jharia Coalfield of Bharat Coking Coal Ltd.(BCCL) But these coals are believed to be of drift origin and contains non-coal mineral matters embedded in them . These are released as pollution discharges at some point in the extraction cycle. Coal refuse consist of waste coal, state and clay associated with coal seams. The coking coal used in blast furnaces should have ash content 14-20%, where as Indian coals are having high ash content. So, demand for coal within the well-defined limits has led to the planning for the up gradation of coal . To do so, bigger sizes of coal as mined are crushed to smaller sizes and fed for washing in coal washeries. In this process lose mineral materials are eliminated by gravity separation process. Some non-coking coals are also washed for thermal power plants in washeries. A large quantity of water is required for coal washing. The quantity of water used per million tonnes of raw coal varies both with the size of the coal and with the type of process used. For every metric tonne of hourly capacity of the washery, 720-2400 gallons of water are required per hour. A plant with a capacity of 100 tonnes of coal per hour requires in the course of 8h shift from 600,000 to 2000,000 gallons of water. The feed water in the washing process comes out from the coal preparation plant in the form of effluent and contains dirty materials and impurities associated with the raw coal . The effluent from coal cleaning process contain large amount of suspended solids and they create serious problems of deterioration of water quality of the river or water bodies into which they are discharged.
The fines produced during crushing and other processes are mixed with water and other liquid medium used in different processes, which led to the formation of slurry. The slurry formed is thickened in thickeners and the heavier underflow is filtered and normally mixed with clean coal. Thickener over flow together with the filtrate from the filter section and spill water from other sections of the plant form the washery effluent. The effluent contains large amount of coal fines in the form of suspended solids (TSS) and high chemical oxygen demand (COD) values and they create serious surface water pollution problem in which they are discharged There is no well defined process for combating this situation This
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needs a search of proper technology to reduce pollution load within the desired limit before discharging the effluents to the river. Present invention relates to the identification of suitable regent for the recovery of coal fines as resource from coal washery effluent, determining the optimum size of clarifier, the control of environmental pollution and sustainable supply of water in washeries. and to maintain the sustainable supply of water in the region. 2.1 Working principle of washery
Coal washing is mainly based on the differences in specific gravities between the coal and the impurities present in the coal. Since most of the impurities are heavier than the coal itself the coal is separated from its impurities by designed uses of these differences. Specific gravity of pure coal is between 1.23 to 1.7. A change in specific gravity is exhibited with a change in the ash content. Higher ash content gives higher specific gravity. The raw coal is crushed into smaller sizes and is introduced into a suspension or solution where specific gravity has been adjusted so that the coal floats at the surface, whereas the refuse sinks to the bottom. 2.2.Characteristics of coal washery effluent
The quantity of water used per tonne of coal varies both with the size of coal and the type of the process used. The effluent contains very high-suspended materials, COD values and dissolved chemical substances. Coal washery effluents contain huge amounts of suspended solids. The solids in suspension are ultrafractions of coal fines, which are colloidal in nature, and possess high coking value. Thus, a good quality of coking coal is being lost along with the effluents. As the suspended particulates in the washery effluent are found to be colloidal in nature, it is difficult to remove the suspended solids by way of simple sedimentation. The large particles suspended in the range of 10-2 cm or natural settling or conventional filtration readily separates more. Particles of colloidal dimensions i.e. 3

This invention investigates to recover the coal fines as resource effectively from the effluent, which also abate water pollution problem and siltation on the riverbed. As such it will create or maintain sustainable supplies of water. 3.0 Drawback associated with the known art
Associated impurities with coal are generally exposed when it is crushed and chances are favorable for a large proportion of dirt particle becoming detached from the coal. The fines produced during crushing and other processes are mixed with water and other liquid medium used in different processes lead to the formation of slurry. The slurry formed is thickened in thickeners and the thickener underflow is filtered and normally mixed with clean coal. Thickener overflow along with the filtrate from the filter section and spill water from other parts of the plant form the washery effluent. Most of the washeries face the acute problem of dewatering of coal fines. These solids in suspensions are found to be ultrafractions of coal, disperses to a long distance creating pollution problem and siltation on the riverbed. They cannot be removed by ordinary settling .The suspended solids were found to have high coking value. Apart from water pollution and siltation on the riverbed, a very good quality of coking coal is being lost in the river. It is a great loss to national economy in the context of energy crisis. Thus in addition to water pollution and siltation on the riverbed, a good quantity of coking coal was being lost in the river. Suspended solids present in the washery effluent also hinder the movement and development of aquatic life and making the river unsuitable for fish breeding. This also creates problem faced by downstream water works in settling and filtering the suspended solids from the polluted water. The present system of effluent treatment by ordinary settling and drying up in a series of lagoons has not been found to be successful and no well defined process in this regard has been reported 4.0 A summary of invention
The colloids are destabilized or destroyed by causing them to aggregate or coagulate into larger particles and thus they can be effectively removed. Some specific structured compound known as coagulants does this. The salt of Al and Fe are found suitable for this purpose. The synthetic polyelectrolytes are very effective flocculants for suspended solid removal in aquatic medium. They combine with charged particles causing rapid flocculation and an increased rate of coagulation and settling. For optimum beneficial results, the molecular weight of polymers may be desirable in the range of 30,000 to 1,00,000 and even higher. The molecular weights should not however be so high as to yield insoluble polymers.
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4.1 Destruction of colloids
All colloidal particles are electrically charged. The colloidal particles are dependent upon electrical charge for their stability. Like charges repel, and as a result, similarly charged colloidal particles cannot come close enough to agglomerate into larger particles. Because of the primary charge on the particle, an electrical potential exists between the surface of the particle and the bulk of the solution. When two similar particles approach each other, the repulsive electrostatic force increases to keep them apart. However, if they can be brought sufficiently close together to pass this energy barrier the attractive Vander Wall's force will predominate and the particles will remain together. If it is desired to coagulate colloidal particles, they must be given sufficient kinetic energy to over come the energy barrier that exists, or else the energy barrier must be lowered by some means.
There are four basic mechanisms by which colloids can be coagulated, i) Double layer compression ii) Charge neutralization iii) Entrapment in a precipitate iv) Interparticle bridging
If a high concentration of an electrolyte added to a solution, the concentration of ions with in the different layer will increase and thickness of this layer will decrease. So particles can come together and aggregate. The charges on a colloid can some times be neutralized by addition of molecules on opposite charges, which have ability to absorb into the colloid. With the aid of sufficient metal salts of Al (iii) and Fe (iii) to the solution they may combine with OH rapidly to form OH precipitates. Colloidal particles may provide condensation sites where the precipitates may form and hence settles with it. The settling precipitates can also entrap colloids through which it passes, bringing them down.
The precipitation of a colloid is effected by that ion of an electrolyte, which has the charge opposite in sign to that of the colloidal particles and the effect of such ion increases markedly with the number of charges it carries. The long chained charged synthetic and natural polymers (Polyelectrolytes) can act to destabilize colloids by forming inter particle bridge. The polymers that are anionic and non-ionic (usually anionic to a slight extent when placed in water) become attached at a number of adsorption sites to a surface of particles found in the settled effluent. A bridge is formed when two or more particles become intertwined with other bridge particles during the flocculation process, forming larger structural units that readily separated from aqueous dispersing medium
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4.2 Measurable and likely impact of the invention
A huge amount of water is required in coal beneficiation plants and a large quantity of effluent is formed. The effluent from the coal washery contain abnormally high amount of suspended solids ranging from 5 g/1 to 30 g/1. To fulfill the huge amount of water requirement, the maximum numbers of washereis are installed in the vicinity of the river Damodar in Jharia Coalfield in India. Presently there are 23 coal washereis in India out of which 13 are situated on the bank of the Damodar River only. A large quantity of effluent is formed in the process of coal washing and the discharge of the effluent to inland surface water, constitutes a serious threat to the environment. The ultrafine coal particles are being lost in the river. The presence of large amount of coal fines has blackened the color of the river water, which is visible everywhere. This needs a search of proper technology to reduce susbended songs of coal lines in the effluent to the desired river.
The investigation relating to invention reveals the use of different conventional and synthetic polymeric flocculants for the removal of suspended solids present in the coal washery effluent. It has been found that the existing method of washery effluent treatment is not adequate to reduce the suspended solids in the final discharge to an acceptable limit. Studies involved to identify a suitable flocculent and to develop a methodology for the effective removal of suspended solids from the washery effluent. The work has made a distinct contribution to the advancement of knowledge in studying the characteristics of suspended coal fines and for its effective removal.
The washery authority can design the effluent treatment plant which will be of smaller in size as the retention time is much less in comparison to conventional treatment process. In addition to this a substantial amount of good quality of fine coal can be recovered and the supernatant liquid can be recycled or safely discharged in the river with out causing pollution problem. Thus it will be of great economic benefit to the industry. These are the most significant and measurable impact of this work. The techniques adopted for the study have formed a guideline to remove the suspended solids from other coal washery effluent in the area. 5.0 Detailed description of the invention
The coal washeris are most major contributors of pollutants to the river Damodar. The coal washery effluent contains extremely high amount of suspended solids. The study reveals that the existing method of washery effluent treatment system is inadequate to reduce the
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suspended solids in the final discharge of effluent to an acceptable limit. The techniques to be adopted are specified below:
1. Characteristics of suspended solids in coal washery effluent depend on the quality of
the raw coal used, process of washing and site-specific factors. Qualitative and
quantitative assessment of the effluent is to be monitored.
2. The effluent containing known concentration of suspended solids is to be taken in a
graduated cylinder to study the settling behavior.
3. The natural settling behavior is to be read by noting the height of interference between
clear liquid and solid (settled sludge) at known interval of time. The zone settling
curves are to be drawn with heights of interference and the corresponding time
intervals.
4. Similar studies are to be conducted with suspended solids of different pulp density
and with different coagulants and the zones of settling curves are to be drawn.
5. The suspended solids in the supernatant liquid are to be estimated at known interval of
time and the percentage removal of the suspended solids is to be calculated.
6. The optimum pH for effective removal of suspended solids, optimum doze, retention,
identification of the most coagulant, cost benefit analysis are to be made.
7. . Clarification area should be provided in the washery effluent treatment system.
Sufficient retention time should be given for complete removal of suspended solids
after the addition of coagulants. The design of the settling pond is to be made
accordingly.
8. Clear overflow from the settling pond may be recirculated to the plant to save the raw
water consumption and ultimately to low down the cost of running the plant.
6.0 Case study relates to this invention
The user agencies of this invention are different coal washeries Ltd. For the application of this invention work Sudhamdih coal washery of BCCL (Bharat Coking Coal Ltd.) was chosen. The washery is at about 20 km. south of Dhanbad town and situated on the bank of the Damodar river. The average ash content of the raw coal used by the washery ranges from 27 to 30 %. The clean coal obtained as a product of the washery contains 18.5 to 19.5 % of ash content. The material balance of the coal washery is given Table 1
The washery requires 91 kl/h of water for the processing, which is being pumped from the Damodar river. The fed water comes out from the washery as a dirty blackened color effluent. Normally the effluent quantity from Sudamdih washery ranges from 300 to 500 cu.m per day. The suspended solids in the washery effluent were monitored on regular
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oasis and were found to be ranging from 5000 to 30,000 mg/1 with an average value of 20,100 mg/1. The maximum permissible limit to discharge the industrial effluent in the inland surface water 100 mg/1. As the size of the suspended solids are found to be less then 0.3 MPD µ they posses all the properties of colloids and they do not settle down easily. They tend to remain suspended in surface water for indefinite period of time. These suspended solids posses high coking values. Thus a good quality of coking coal is being lost along with the effluent. The loss of huge amount of coal fines shows the in-effectiveness of the present effluent treatment system used in the washery. About 6-10 of coal fines are being lost every day in the Damodar river.
The treatment of suspended solids is based on the principle of extended sedimentation with conventional coagulants like lime, alum and lime mixed with alum . Synthetic flocculent 'True floc' was also used. It is an anionic copolymer in powder form .
Natural settling was found to be very slow and it took about 8 hours of settling. The supernatant after 8 hours of settling was not found even free from suspended solids. This is because of the colloidal nature of the suspended matters present in the effluent. The average settling rate was estimated to be 0.09 cm/min. The settling behavior by using lime as coagulant has been shown in Figure 3. The settling rate was found to be 0.39 cm/min. The suspended solid after 2 h settling time was found to be 642 mg/1.
Alum doses of 400 mg/100g, 1.6 g/100g, 2.4 g/100g, 8 g/100g, 16 g/100g, of suspended solids S.S were used to the effluent containing 25 g/1 of S.S. The respective settling rates in cm/min were found to be 0.16 , 0.25 , 0.27 , 2.4 , 0.26 . On the basin of settling rate 1.6 g alum/100 S.S in the supernatant was found to be 642 mg/1 and the sludge volume was 405 ml. The settling rate was found to be 0.17 cm/min and sludge volume was 475 ml. The applied dose was 12 g lime + 2.4 g Alum/100 g of S.S.
Synthetic flocculent " True floc" was used in the doses of 1 mg/100g S.S, 1.25 mg 100 g of S.S and 2 mg/100g S.S. The respective settling rates were found to be 2.75 cm/min , 2.2 cm/min , 1.5 cm/min for the effluent containing 10 g/1 S.S , 20 g/1 S.S and 25 g/1 S.S respectively. . It was found that "True floc" is the most effective in clarification of about 94% S.S. within 10 minutes and settling rate was enhanced by 15-28 times. After one-hour retention time S.S. were found to be 97 mg/1.
Thus lime and alum were found to be equally effective in clarification of effluent. But "True floc" was found to be the most suitable for the treatment of washery effluent among the tasted coagulants.
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6.1 Cost estimates
Lime : Rs. 120/Kg (S=Rs43)
Alum : Rs. 130/Kg
"Turefloc" : Rs. 280/Kg
The optimum does are
Lime : 16g/100gS.S
Alum : 1.6g/100gS.S
"Turefloc" : 1.25 g/100g S.S
The cost of treatment of the washery effluent with aid of above mentioned coagulants.
Lime : Rs. 19,200/t of S.S
Alum : Rs. 2,080/t of S.S
"Turefloc" : Rs 3.5 A of S.S
Thus it is clear that the treatment of washery effluent with aid of "True floc" is the cheapest than that of alum and lime.
6.2 Design of clarifier
The rate at which the interface subsides is equal to the slope of the curve at that point10. According to this methodology critical area for thickening is given by

where, A = Area in mz ;V = Subsidence velocity in m7h;and Q = Overflow rate in m7h
Q and V were calculated with the data on output from tailing pond in m7h and
settling test result.
*Basic data
Output from the tailing pond = 21 m3/h
Subsidence velocity V from hindered settling portion of the curve:

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6.3 A brief description of the accompanying drawing.
The settling rates and % removal by different are given in Figure 1 .The test was also used for the slurry where suspended solid was 20 g/1 and the dose of True-floc was 1.25-mg/100 g of TSS. The advance of the interface between the water and settled solids was recorded with time and a graph was plotted between the heights of effluent slurry vs. time. The results are given in Table 2 and the curve plotted is shown in Figure 2. Using the data the area of decant pond of the washery effluent was calculated. Based on the results it was observed that the output of effluent from the tailing pond 21m3/h. Initially the height of the suspended coal fines in the cylinder was 40 cm. After the addition of coagulant the height of the coal fines was reduced by 25.8 cm. It may be seen from the curve that if the initial rate of settlement was continued the desired level of settlement would have been achieved after 8 min. But the rate of settlement continued to decline with the passage of time. A linear rate of settlement could be observed after 8 min, but after the lapse of 14 min the rate of settlement further reduced and the ultimate of 37.5 cm could be achieved after 25 min. It may be observed from the curve that, had there be no reduction in the rate of settlement after 8 min, ultimate settlement should have been achieved in 17 min. The cylinder test result also showed that the subsidence velocity V was 0.31 m/h, and' overflow rate Q was found to 7.875 m7h. The area required being 64.35 m2. At present the total area utilized for settling ponds was 36,800 m, 2 which is much more than the actually require, as calculated. With the addition of the synthetic flocculent suspended solids were removed in the clarifier. The sludge removed from underflow of the clarifier could be mixed with the clean coal and the clarified water could be recycled or disposed off in the river safely. Figure 3 shows the proposed scheme for design of the washery effluent treatment.
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I claim
1. Coal fines in washery effluents in the form of suspended solids are found to having
colloidal characteristics and they cannot be removed by ordinary settling. Process of
recovering them as resource involves the evaluation of effectiveness of different
conventional coagulants and synthetic flocculants, identification of a suitable
flocculent for effective removal of coal fines at minimum cost. This invention
identifies that with the aid of a synthetic flocculent, 90-95% of the coal fines can be
removed from the effluent and solves the pollution problem as well.
2. The process determines the optimum size of the clarifier tank for the recovery of coal
fines from the effluent. This additional unit operation for treatment is to be put before
discharging the effluent to the water bodies and the supernatant can also be recycled ,
which will reduce the raw water consumption. The process can also minimize the
cost of additional land requirement, land requirement, land degradation, surface and
ground water pollution , siltation on the river bed , impact on social life and safety.
3. The process has suggested a treatment scheme , which will be feasible to design a cost
effective effluent treatment plant for coal washery and the treated effluent can be
recycled or safely discharged without causing surface water pollution.
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the Material balance of the coal washery Item Throughput Yeld Ash in Fraction (t/d) (per cent) (per cent)Clean coals 700 23.7 18.5-19.5 Middlings 1,350 45.6 29.5-31.5 Rejects 900 30.4 33.1-35.9 Suspend solids 10 0.3 13.2-14.8 (Fine coals) Feed coal 2960 100.0 27-30
Table 2 Settling characteristics with the use of synthetic coagulant "true-floc" Suspended solids :20g/l,Dose : 1.25 mg/100g SS Time, Height of Settling Suspended Percentage min interface(cm) rate(cm/min) solids(g/l) removal0 40.0 0.00 20.0 0.00 5 16.0 5.00 10 4.0 3.7 0.801 91.0 15 3.1 2.5 20 2.4 1.93 -25 2.3 1.54 -30 2.0 1.30 0.454 95.46 50 2.0 0.78 0.325 98.37 60 2.0 0.65Average settling rate : 2.2 cm/min, sludge volume : 98.0 ml
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Patent Number

270221

Indian Patent Application Number

319/KOL/2007

PG Journal Number

49/2015

Publication Date

04-Dec-2015

Grant Date

02-Dec-2015

Date of Filing

06-Mar-2007

Name of Patentee

PROF. MRINAL K. GHOSE

Applicant Address

113 REGENT ESTATE KOLKATA-700092

Inventors:

#	Inventor's Name	Inventor's Address
1	DR. MRINAL K. GHOSE	CENTRE OF MINING ENVIRONMENT, INDIAN SCHOOL OF MINES UNIVERSITY, DHANBAD 826004 INDIA

PCT International Classification Number

C02F1/52

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA