Title of Invention	A PROCESS TO PRODUCE LOW ASH CLEAN COAL FROM HIGH ASH COAL/NON COKING COALS FOR METALLURGICAL AND THERMAL APPLICATION
Abstract	This invention relates to a process to produce low ash clean coal from high ash coals for coke making along with beneficiation of mineral values form coal comprising the steps of crushing clean coal obtained through froth-flotation or coal as received to -30 to -72 BS mesh size containing 15 to 16.5% ash, preparing a sample of the coal on oven drying at 105° C to 110° C and cooled, treating the cooled coal sample in a reactor with alkali (NaOH) solution at concentration of 10 - 50% at 80 85°C under reflux with or without stirring for 1.5-7 hours, washing the treated coal repeatedly with water and/or Hcl and then dried, treating the washed coal with 10-20% acidic (H2SO4/Hcl) solution for 1 to 5 hour at 80 - 85°C, filtering the treated coal, washing the filtered coal and dried followed by characterize evaluation of chemical, rheological and petroghaphical properties such as ash, volatile matter, alkali (Na2O and K2O) content, ash constituents - (Fe, CaO, SiO2, AL2O3, MnO, TiO2, P and S), calorific value and Crucible Swelling Number to ensure final ash content of the treated coal to around 5% suitable for coke making.

Title of Invention

A PROCESS TO PRODUCE LOW ASH CLEAN COAL FROM HIGH ASH COAL/NON COKING COALS FOR METALLURGICAL AND THERMAL APPLICATION

Abstract

This invention relates to a process to produce low ash clean coal from high ash coals for coke making along with beneficiation of mineral values form coal comprising the steps of crushing clean coal obtained through froth-flotation or coal as received to -30 to -72 BS mesh size containing 15 to 16.5% ash, preparing a sample of the coal on oven drying at 105° C to 110° C and cooled, treating the cooled coal sample in a reactor with alkali (NaOH) solution at concentration of 10 - 50% at 80 85°C under reflux with or without stirring for 1.5-7 hours, washing the treated coal repeatedly with water and/or Hcl and then dried, treating the washed coal with 10-20% acidic (H2SO4/Hcl) solution for 1 to 5 hour at 80 - 85°C, filtering the treated coal, washing the filtered coal and dried followed by characterize evaluation of chemical, rheological and petroghaphical properties such as ash, volatile matter, alkali (Na2O and K2O) content, ash constituents - (Fe, CaO, SiO2, AL2O3, MnO, TiO2, P and S), calorific value and Crucible Swelling Number to ensure final ash content of the treated coal to around 5% suitable for coke making.

Full Text	FIELD OF THE INVENTION The present invention relates to a process to produce low ash clean coal from high ash coal/non coking coals which is used for pulverized coal injection in blast furnaces, power generation in thermal power plants and any other value added application requiring low ash coat. More particularly the present invention relates to produce low ash coal for coke making by physical and chemical cleaning of high ash content coal on characterize evaluation of the cleansed coal to be processed for coke making. BACKGROUND OF THE INVENTION WITH PRIOR ART DIFFICULTIES Coal is a major fossil fuel that meets about 60% of the world's commercial energy demand. Known resources of coal and other solid carbonaceous fuel materials in the world are far greater than the known resources of petroleum and natural gas combined. Despite this enormous abundance of coal and related solid carbonaceous materials, reliance on these resources, particularly coal, as primary sources of energy, has been discouraged for the most part. The variability of cheaper, cleaner burning, more easily retrievable and transportable fuels, such as petroleum and natural gas, has in the past, cast coal to a largely supporting role in the energy field. Furthermore, coal is not a uniform substance but rather a mixture of combustible, metamorphic plant remains that varies in both physical and chemical composition. Ash producing substance, sulfur, and other materials may be present in amounts as high as sixty percent. Coal ash is the residue resulting from non-combustible acidic and basic components in the coal. The major acidic components are SiO2 and AI2O3. Basic components include magnesium oxide, calcium oxide, sodium oxide, potassium oxide, and hematite (Fe2O3). Acidic components also include phosphates and sulfates. Ash, as determined in coal analysis, may be defined as the noncombustible residue that remains when coal is burned. The ash forming materials occurring in coal are of two kinds: extraneous mineral matter and inherent ash. The extraneous mineral matter is composed mainly of clay and shale minerals, calcite, pyrite or marcasite and lesser chloride and fluoride minerals. Inherent ash includes inorganic elements combined with the organic part of the coal, the origin of which is the plant material from which the coal was formed. Inherent ash displays a reasonably uniform, essentially molecular distribution throughout the coal mass. Inherent ash seldom exceed 2 or 3 percent of the weight of the coal. The lower the inherent ash in the coal, the more reasonable of a reduction in the ash can be expected. Most of the coals are associated with mineral matter, which makes it unsuitable for efficient utilization, such as carbonisation, gasification, combustion, or liquefaction. Coking industries, and especially, blast furnaces, are more sensitive to high-ash contents in coals. As a result, enormous efforts are being extended to make coal and related solid carbonaceous materials equivalent or better sources of energy, than petroleum or natural gas. In the case of coal, for example, much of this effort is directed to overcoming the environmental problems associated with its production, transportation and combustion. Furthermore, numerous techniques have been explored and developed to make coal cleaner, more suitable for burning and more readily transportable. Regardless of the form in which the coal is ultimately employed, the coal or coal combustion products must be cleaned because they contain substantial amounts of sulfur, nitrogen compounds and mineral matter, including significant quantities of metal impurities like, aluminosilicates, metal oxides, metal pyrites, metal sulfates, etc. If coal is to be accepted as a primary energy source, it must be cleaned to prevent pollution of the environment either by cleaning the combustion products of the coal or cleaning the coal prior of burning. Accordingly, physical as well as chemical coal cleaning (benefidation) processes have been explored. In general, physical coal cleaning processes involve pulverizing the coal to release the impurities, wherein the fineness of the coal generally governs the degree to which the impurities are released. However, because the costs of preparing the coal rise exponentially with the amount of fines to be treated, there is an economic optimum in size reduction. Moreover, grinding coal even to extremely fine sizes may not be effective in removing all the impurities. Based on the physical properties that effect the separation of the coal from the impurities, physical coal cleaning methods are generally divided into four categories: gravity, flotation, magnetic and electrical. In contrast to physical coal cleaning, chemical coal cleaning techniques are in a very early stage of development. As far as Indian scenario is concerned, most of the coals present in India are of drift origin and low grade having high mineral matter contents varying from 5% to greater than 50%. Moreover, the mineral matter is finely disseminated inside the coal matrix and is at times firmly bound. Again, since washability characteristics of Indian coal is not good, it is difficult to remove the mineral matter from coal by conventional physical coal washing techniques based on specific gravity difference such as heavy media, dense media etc. Hence, physical methods of beneficiation, such as heavy media and froth floatation, are of limited use for applications in coal beneficiation to produce low ash coals for metallurgical coke making and power generation. Conventional methods of physical beneficiation separate the coal into clean coal (15-30 %), middling and rejects. The yields of clean coal are at the cost of the loss of coal in middlings, and rejects which is considerable. Hence, this present novel coal cleaning technique of Indian coals using chemicals to leach out the minerals to obtain clean, demineralized coal has been explored in details. Chemical leaching of coal is a technology to produce ultra clean coal where the ash content of clean coal is as low as ~ 1.0% basing on mineralogical composition of the feed coal. There are potential use of this ultra clean coal both as a fuel and nonfuel. Conventional chemical leaching processes have been explored mostly for thermal and non-coking coals. However, the present work on chemical cleaning process was aimed towards developing a process to produce low ash coal for coke making with high yield. An effort was made to decrease the ash content of high ash Indian coals up to ~ 5 % in clean coal without deteriorating the coking properties. The process has been established in laboratory scale as well as in bench scale. In the case of the chemical leaching processes for removing ash from coal, the inorganic substances constituting the ash content of coal are reacted with chemical agents and separated from the coal for removal. Various chemicals are used for the chemical beneficiation process. Some of these chemicals will have a tendency to dissolve certain inorganic constituents preferentially to others and the actual chemical to be used may depend upon the inorganic content of the carbonaceous material which is fed to the process. Following the end of World War II, it was learned that German coal processing plants treated coal with aqueous sodium hydroxide at elevated temperatures and pressures, and thereafter extracted the coal with aqueous hydrochloric acid. The process reduced the sulfur and ash content of the coal. (Crawford, BIOS Final Report No. 522, item No. 30, Feb, 19, 1946, British Intelligence Objectives Sub- Committee, London (A.T.I. - 118668, Central Documents Office, Wright- Patterson Airforce Base, Dayton, Ohio). Subsequently, the U.S. Bureau of mines evaluated a similar process for treating coal, involving leaching with aqueous sodium hydroxide at 225° C, both with and without a final stage extraction with aqueous hydrochloric acid. In a report made by Reggel et al in 1972, it was concluded that the sequence of sodium hydroxide treatment and hydrochloric acid extraction removed most of the mineral matter originally present in the coal. Am. Chem. Soc. Div. of fuel chem. Preprints, 17 (1): 44-48. Battelle Memorial Institute had developed a similar process, which is described in Stambaugh et al U.S. Patent No. 4,055,400 of 1977. An aqueous alkaline slurry of coal is heated at an elevated temperature and pressure to leach out sulfur and mineral matter. The Battelle process may optionally include last stage extraction with aqueous acid to reduce the final ash content. (Stambaugh et al, Hydrocarbon Processing, 54 (7): 115-116 (1975)). An alternative process has undergone extensive development at Iowa State University, Ames, Iowa. The "Ames" process uses oxidative desulphurisation in aqueous slurry of sodium carbonate. Typical conditions are 0.2 M Na2CO3 at an oxygen partial pressure of about 4 atmosphere and temperatures of 120-140° C for 1-2 hours. This development was reviewed in detail by Dr. T.D. Wheelock in 1981. (Chem. Eng. Commun., 12:137-159). In one representative test, using temperatures of 120-140° C, the total sulfur content of the coal was reduced 70% and the pyritic sulfur content was reduced 78%. (Wheelock (1981), above cited, at pages 148-149). In general, chemical leaching processes can be classified into the following four categories. 1. Dissolving with an acid 2. Dissolving with an alkali 3. Oxidation with air, nitrogen dioxide or the like, followed by dissolving with an acid or alkali 4. Treatment with hydrofluoric acid or hydrogen fluoride gas Such processes are known as processes for removing ash from coal or coke (Japanese Patent Publication No. 466/1942), a process for removing sulfur and ash from coals (Japanese Patent Publication No. 23711/1971) and a coal deashing process (Japanese Patent Disclosure No. 133487/1980). The processes (1) and (2) with use of an acid or alkali are practiced usually with the application of pressure and heat to dissolve the metallic components for the removal of ash. When practiced under moderate conditions, these processes were almost unable to achieve any ash removing effect and are therefore not suitable as deashing processes. The process (3) wherein oxidation is followed by an acid or alkali treatment is the same as the processes (1) and (2) in principle and is such that the FeS2 components which are difficult to dissolve are first oxidized and thereafter dissolved. With the process (4) wherein hydrofluoric acid or hydrogen fluoride gas is used for treatment, coal is treated with hydrogen fluoride gas since SiO2 is not easily soluble in acids or alkalis to separate Si in the form of gaseous SiF4 to achieve a deashing effect. However, the use of hydrofluoric acid or hydrogen fluoride gas, which is highly toxic and corrosive, involves many difficulties. Thus an actually effective and useful process for removing ash from coal still remains to be developed although the deashing of coal is a very important technique for the effective use of coal. The patent literature is replete with chemical coal beneficiation processes. For example, U.S. Patent No. 4, 424,062 discloses a process for chemically removing ash from coal by immersing ash containing coal in an aqueous solution containing hydrochloric acid or citric acid in combination with acidic ammonium fluoride. U.S. Patent No. 3,993,455 discloses a process for removing mineral matter from coal by the treatment of the coal with aqueous alkali such as sodium hydroxide, followed by acidification with strong acid. Similarly, U.S. Patent No. 4,055,400 discloses a method of extracting sulfur and ash from coal by mixing the coal with an aqueous alkaline solution, such as ammonium carbonate. U.S. Patent No. 4,071,328 discloses a method of removing sulfur from coal by first hydrogenating the coal and the hydrogenated coal is subsequently contacted with an aqueous inorganic acid solution. U.S. Patent No. 4,127,390 discloses a process for reducing the sulfur content of coal by treatment with an aqueous sodium chloride solution. U.S. Patent No. 4,134,737 discloses a process for the production of beneficiated coal wherein the coal is digested in caustic, then treated in mineral acid and then treated in nitric acid. U.S Patent No. 4,083,940 discloses a process for cleaning coal by contacting the coal with an aqueous leaching solution containing nitric and hydrofluoric acid. U.S. Patent No. 4,169,710 discloses comminuting and cleaning coal of sulfur and ash by contacting the coal with a hydrogen halide, such as HF (aqueous and/or anhydrous). U.S. Patent No. 4,408,999 discloses beneficiating coal by subjecting the coal to electromagnetic radiation in the presence of a strong inorganic acid, such as hydrofluoric acid. In turn, U.S. Patent No. 4,305,726 discloses a chemical method of treating coal to remove ash and sulfur comprising treating the coal with hydrochloric and hypochlorous acid in the presence of ferric and ferrous sulfate, while U.S. Patent No. 4,328,002 discloses a method of treating coal to remove ash and sulfur involving preconditioning coal particles in the presence of an aqueous solution of an oxidant, such as H2O2 or HF, washing the so-treated coal, treating the washed coal with further oxidant and then passivating the coal with for example, an ammonium salt and then neutralizing with alkali metal hydroxide. U.S. Patent No. 4,516,980 discloses a process for producing low-ash, low sulfur coal by a two-stage alkaline treatment using sodium carbonate or bicarbonate as the reagent. The alkaline treated coal is then extracted with aqueous mineral acid; and U.S. Patent No. 3,998,604 discloses a coal demineralization process whereby ground coal is treated with aqueous acid, such as HCI, H2SO4 or H2CO3 and then subjected to froth flotation in the presence of a gas selected from CI2,SO2, or CO2. In general, many inorganic acids can be used in the process of chemical leaching. Normally, the inorganic acid will be a strong acid such as hydrochloric acid, sulfuric acid, hydrofluoric acid, or nitric acid. Some of these acids will have a tendency to dissolve certain inorganic constituents preferentially to others and the actual acid used may depend upon the inorganic content of the carbonaceous material which is fed to the process. For example, hydrofluoric acid would be used when it is desired to remove silica. Hydrochloric acid or sulfuric acid alone may be used when it is desired to remove substantial portions of sulfur and other inorganic constituents. In general, the use of nitric acid is less desirable since it tends to oxidize the carbonaceous material. In some cases it may be preferable to use a mixture of acids in order to obtain complete solubilisation of the inorganic constituents. A combination of hydrochloric acid, nitric acid and hydrofluoric acid has been found to be a particularly effective mixture of acids. In general, it is preferable to use the acids in their strongest concentrations; however, in some cases more dilute aqueous solutions of the acids may be used. The actual amount of acid solution utilized is not critical as long as there is a sufficient amount present to retain the dissolved mineral matter in solution. But also most of these have got some disadvantages. For example, although HCI has been found effective in the removal of certain types of mineral matter from coal, processes that utilize HCI in any form run the risk of chlorinating the aromatic and heteroaromatic organic matrix found in coal. The chlorine cannot be removed from the chlorinated coals by simple washing or drying under vacuum. The corrosiveness of Chlorine liberated from combusted coal is well known. On the other hand, while it is also known that HF is very effective in removing silica and alumina from coal, it is not so effective in removing divalent alkali metals, such as calcium and magnesium. Furthermore, as also evidenced above, several prior art processes utilize oxidizing acids such as HNO3 and H2SO4. Although they may aid in the removal of mineral matter, they are also very capable of oxidizing the organic coal matrix, thereby decreasing the amount of volatile matter and the heating value of the coal. Several such processes have been developed. Besides, the amount and rate of removal of mineral matter from coal during chemical leaching process depend on various parameters such as type of mineral matter, percentage of mineral matter, porosity of coal, rank of coal, size of coal, reagents used for dissolution, time of dissolution, temperature, pressure etc. The present work on chemical cleaning process was aimed towards developing a process to produce low ash coal for coke making with high yield from high ash Indian coals. An effort was made to decrease the ash content up to ~ 5% in clean coal without deteriorating the coking properties. The process has been developed keeping in mind the high ash content and finely disseminated mineral matter content typical of Indian coals. DESCRIPTION OF THE INVENTION Leaching or solid extraction is done to dissolve mineral matter in coal using a solvent. The acidic and /or basic components present in mineral matter react with the solvents, gets dissolved and then removed. The present invention is a process of treating coals crushed to -30 to -72 BS mesh size (-0.25 to -0.50 mm) of fine clean coal obtained from flotation circuit coal for removal of ash-forming mineral which includes the steps of treating the coal in an aqueous alkaline solution at an elevated temperature under atmospheric pressure followed by reaction/extraction with an aqueous acidic solution. This is a process to produce low ash (~ 5% ash) clean coal for coke making from high ash Indian coals with 80-85% yield. Known processes to produce low ash clean coal have been developed mostly for power plant and other uses. In the present invention, the process has been developed and evaluated for coke making. The process has been established in laboratory scale as well as in bench scale where up to 2 kg of coal can be treated. Besides, Present invention is a step towards making chemical leaching process economically feasible for coke making. The present invention will be better understood from the following description with reference to the accompanying drawings in which Figure 1 represents photograph of experimental setup for the process in Laboratory scale. Figure 2 represents schematic diagram of experimental setup for the process in laboratory Scale. Figure 3 represents photograph of experimental setup for the process in bench scale. Figure 4 represents schematic diagram of experimental setup for the process in bench scale. The process was initially tried in laboratory scale. After successful experimentation and encouraging results, the process was also established using a bench scale unit where up to 2 kg of coal can be treated. In the first part of the description below, the methodology and results for the laboratory scale experimentations have been described. In the later part, the experimental procedure for the process using a bench scale reactor along with the test results has been stated. Laboratory Scale: Methodology of the claimed Process West Bokaro fine clean coal was taken initially as a feed sample to this process. This fine clean coal is generated in West Bokaro coal washery through froth flotation process. The feed sample can be taken directly as obtained after froth flotation treatment or can be crushed to -30 to -72 BS mesh size (-0.025 mm) for improving the kinetics of the process. Ash content of this coal sample was 15.0%. This West Bokaro fine clean coal is referred herein as feed coal and the clean coal produced from this process is referred herein as Product. The major minerals normally found in coals are silicates or shales, quartz and / or sandstone, pyrites and carbonates such as siderites and ankerites. It has been found that even at 373° K using dilute to moderately concentrated NaOH solution, kaolin is converted into a crystalline sodium derivative i.e. Na2O.Al2O3.1.8SiO2. The solubility of this sodium-aluminium-silicate derivative is not very high in alkali solutions but it is fairly soluble in dilute alkali followed by washing with mineral acid. Sample Preparation: Small amount (around 50-200 g) of coal was taken through coning quartering method from the received West Bokaro fine clean coal. This coal sample was dried in an oven at 105° C. After drying the coal sample was cooled in a desiccator. Chemicals used The experiments were carried out with various chemicals initially. However, since the presence of acidic compounds like silica and alumina in Indian coals are significantly higher, some chemicals tend to behave better than other chemicals. Treating such coals using diute aqueous NaOH solution under mild conditions at atmospheric pressure followed by acid leaching / washing results in substantial demineralization of the coal. The alkali and acid used can be recovered for re- use. This affords a convenient method for coal demineralization. Commercially available sodium hydroxide (NaOH) in combination with sulphuric acid (H2SO4) and HCI were used in the present method. The treatment process The experiments for chemical leaching of captive coals were carried out using the experimental setup as shown in Figures 1 and 2. The equipment assembly consisted of a three-necked 1000 ml round bottom flask, which is the reactor (B). The main centre neck was utilized for assembling the motor and the attached stirrer (D). The speed of the motor for stirring was controlled through a variac. A condenser (C) was connected to one of the other two necks which, in turn, was connected to a conical flask with water (F) for trapping the volatile gases generated during the reaction. The third neck (E) is used to facilitate addition of reagents using a dropping funnel and also to monitor the temperature of the reaction bath using a thermometer. Rotamantle (A) was the source of heat input for the reactor to raise the temperature to the reaction temperature of 80-85° C. This rotamantle does a two-fold job of controlling the temperature as well as speed of the stirring (when the magnetic stirrer is used). Both these parameters can be controlled through the variacs. The experiments for chemical leaching were carried out in the reactor assembly using two steps. In the first step, feed coals (5-50 gm) were treated with varying concentration (10-50%) of alkali (NaOH) (100-500 ml) at 80 - 85° C under reflux with or without stirring for particular length of time (1.5-5.0 hr) in the three-necked round bottom flask (B). The treated coal is then washed repeatedly with water and / or HCI (100ml - 300 ml) and then dried. The washed alkali treated coal (10-50 gm) is then reacted with 10-20% H2SO4 / HCI (100-500 ml) for 1.0-4.0 hr keeping the same condition as described above. Then, the treated coal is filtered, washed with water and dried before sending for their chemical, rheological and petrographical properties. Results obtained in laboratory Scale Exterimentation The chemical leaching technology is available. The most important factor for the successful commercialization of the chemical cleaning of coal to produce low ash coal for coke making is the cost involved. The process described here is simple as it operates under mild conditions under atmospheric pressure. The cost of chemicals needed, particularly the alkali and acid, would make the process unattractive. Hence, efficient methods of regeneration, recovery and recycling of both alkali and acid have been suggested here. Some changes have been made towards optimizing the whole process and minimizing the cost involved. The process has been for West Bokaro fine clean coal. This invention is valid for other coals as well. The experiments for chemical leaching of coal to remove mineral matter were conducted various levels of reagent concentration, coal weight, coal to solution ratio and type of washing (only water or water and 10% HCI combined together). The samples were analyzed for ash, volatile matter, alkali content (Na2O & K2O), ash constituents (Fe, CaO, SiO2, Al2O3, MgO, MnO, TiO2, phosphorous, Sulphur etc.), calorific value (kcal/kg), Crucible Swelling Number (CSN) and petrographical analysis {Reactive (Vitrinite+Semi-Vitrinite+Exinite), Inerts (Inertinite+Mineral matter) and Average Vitrinite Reflectance etc.}. Test results for West Bokaro fine clean coal (Table 1) are exemplified to express the effectiveness of this process and with improved result table 1 shows the test results with West Bokaro fine clean coal before and after the chemical treatment process. The chemical leaching in the first step, feed coals were treated also with Na2Co3 followed by treatment with H2SO4 or by Nacl followed by H2SO4. The test results are exemplified in that case in Table 2 as follows. From the above tests results, it is clear that significant amount of demineralization takes place incase of WB fine clean coal during the alkali and acid leaching and acid washing steps. The same process steps were tried for Jamadoba fine clean coal, and West Bokaro run-of-mine (ROM) coal as well. Few important test results are depicted below in Table 3. Invention was validated in all the three cases which ensure that this process can be used for other high ash coals as well. Table 3: Test results with Jamadoba fine clean Coal and West Bokaro Run-of mine (ROM) coal before and after the chemical treatment process Alkali treatment, depending on coals mineralogical composition, concentration and treatment time, may either decrease or increase the ash content. The gain in ash content or decrease in degree of demineralization of the coal samples with increase in alkali concentration is attributed to sodium aluminosilicate formation. The ash reduction is due to dissolution of sulphate and other water-soluble components present in the coal samples. Alkali also reacts with silica and alumina in clay and other silica and alumina-bearing materials present in the coal forming soluble silicates and aluminates as per the following simplified reactions. The concentrations of silicate and aluminate ions in the solution gradually increase with alkali concentration and treatment time till the same exceed the solubility product of sparingly soluble sodium aluminosilicates. The later is precipitated as per the following simplified reaction: The gel may convert either to zeolite or felspathoid like sodalite, nosalite etc. depending on the alkali concentration. In literature, it has been reported that formation of insoluble sodium complex takes place during leaching of some high ash coal. Some researchers observed formation of hydroxy-sodalite Na6[AIO2]6(SiO2)6.xNaOH. (8 - 2X)H2O on treatment of kaolinite and illite type of clay with sodium hydroxide solution. Continuous decrease in ash removal or gain in ash with alkali concentration and reaction period is therefore attributed to progressive precipitation and accumulation of aluminosilicates. This can happen when more and more amount of silica and alumina from the coal dissolves out. With the negative effect of alkali concentration on removal of mineral matter being more with few coals, it may be presumed that these coals contain larger amount of alkali soluble silica and alumina than coals where ash reduction takes place even at higher level of alkali concentration. Demineralisation by alkali alone or followed by acid depend on the nature of the coal. The cation exchange capacity (CEC) of some of the alkali-treated coal samples continuously increases with alkali concentration suggesting continuous accumulation of sodium aluminosilicate. Sodium aluminosilicates can entrap water molecules, alkali and soluble salt, and the sodium ions in it are exchangeable. The alkali treatment also leads to removal of considerable amount of inorganic sulphur from the coal samples. The following reaction takes place during the alkali leaching: Digestion of the coal samples in water indicates that sulphate leaching takes place over a long period. The pH of the medium gradually decreases during digestion and it is accompanied by small increase in the amount of dissolved . iron. This also confirms loss of some sulphur through oxidation of pyrite. Similar reactions take place during the leaching steps which results in reduction in ash content of the coal samples. Mineral acids are effective in deminerallsation of coals to different extent. However, the best results are obtained when it is combined with alkali treatment. Sulphuric acid treatment or hydrochloric acid washing of the alkali treated coal results in significant reduction of mineral matter. The ash reduction is more than that achieved with non-treated coal and is obviously due to formation of additional acid soluble components during alkali treatment. The alkali treatment results in formation and precipitation of sodium aluminosilicates gel as explained, which subsequently undergoes decomposition and solubilisation in presence of acid soluble forming salts. The reduction in ash content on acid treatment of the alkali treated coal was found to increase with increase in concentration of alkali. This is attributed to increase in dissolution of silica and alumina and consequently amount of aluminosilicate formation. A positive change is noticed in the Alumina (Al2O3) to Silica (SiO2) ratio which plays an important role during the steel making process. Alumina to silica ratio reduced from 0.45 to ~ 0.33 suggesting percentage removal of alumina being more that that of silica. There is no significant change in the phosphorous content of the coal samples after the first step where the treatment is done only with alkali. However, a sharp decrease in phosphorous content is noticed after acid treatment. There is no significant change in the alkali content either after alkali treatment or after the acid treatment or acid wash steps proving there is no accumulation of Na2O or K2O during the process. A marginal reduction in sulphur content is also observed after the alkali and acid treatment. The sulphur content of WB and Jamadoba fine clean coals are not very high, which suggests most of the inorganic sulphur may already have been removed during the physical coal cleaning processes and hence the scope for removal of inorganic sulphur during the alkali-acid leaching process is low. The sulphur present may be of organic origin which is very difficult to leach out or remove. The increase in calorific value is expected because the decrease in mineral matter content of the coal samples due to leaching is associated with an increase in fixed carbon content which adds to the heating value. To study the influence of alkali-acid leaching process on captive coals, the Crucible Swelling Number (CSN) of the coal samples after the alkali and acid treatment were determined. The results suggest that CSN of WB fine clean coal (6.5) improves to 7.5 after H2SO4/HCI treatment when followed by NaOH treatment. This shows coal washings with aqueous acids have been effective in improving coking properties of coals. The process hence can be especially very effective for the conversion of lower-ranking coals including subbituminous coals. Even some of their inert minerals can be converted into fusible or reactive forms through the removal of ion-exchangeable cations. Addition of alkali aiso acts in a similar way by affecting the macromolecular structure of coal. However, structural change of coals in terms of such aggregate form of macromolecules, pores, and reactivity of oxygen functional groups by such pretreatment have not been fully clarified. Additives of inorganic substance (alkali/acid etc.) can influence the thermoplastic properties but the effect depends on the nature of the additive used, amount added and also on the structure of the parent coal. The WB fine clean coal samples before and after the chemical leaching are also evaluated for their petrographical properties. As expected, because of the reduction in mineral matter content of the coal samples after leaching, there is an increase in total reactives content and a decrease in total inerts content. Reductionin Inertinite content is seen in addition to the reduction in mineral matter contents. There is no significant change in the Avg. Vitrinite Reflectance (Ro) and vitrinite distribution (V9-V13)/petrographical make up. Bench Scale: Methodology of the claimed Process Here also, West Bokaro fine clean coal (different sample than that was used in laboratory scale) was taken as a feed sample to this process initially. This fine clean coal is generated in West Bokaro coal washery through froth flotation process. The feed sample can be taken directly as obtained after froth flotation treatment or can be crushed to -72 BS mesh size (-0.025mm) for improving the kinetics of the process. Ash content of this coal sample was 13.1%. This West Bokaro fine clean coal is referred as feed coal and the clean coal produced from this process is referred as Product. Sample Preparation: 1-2 kg of coal was taken through coning quartering method from the received West Bokaro fine clean coal. This coal sample was dried in an oven at 105° C to 110° C. Chemicals Used: The experiments were carried out with various chemicals initially. However, since the presence of acidic compounds like silica and alumina in Indian coals are significantly higher, some chemicals tend to behave better than other chemicals. Treating such coals using dilute aqueous NaOH solution under mild conditions at atmospheric pressure followed by acid leaching/washing results in substantial demineralisation of the coal. The alkali and acid used can be recovered for re- use. This affords a convenient method for coal demineralization. Commercially available sodium hydroxide (NaOH) in combination with sulphuric acid (H2SO4) and HCI were used in the present method. The treatment process The manner of control of operation at reaction chamber through DAS, Host computer, TC and TT is described below. The bench scale unit consists of a batch reactor (1) of nearly 23 litres capacity with heating arrangements, condenser (2) with provision for reflux, the data acquisition and control system (DAS) - 3, sparkler horizontal filter (5). The reactor is heated with four heating coils of 1-kilowatt capacity each which are fitted outside the circumference of the reactor. A stirrer (6), which extends up to nearly 2 inch from the bottom of the reactor is fixed at the middle. A D.C. motor runs the stirrer and its speed can be measured using a sensor, which is mounted in front of the stirrer. It gives the stirrer speed by magnetic induction principle. The maximum rpm can go up to ~ 1500 and it can be controlled using a variac. However, the stirrer is usually operated at around 600 - 900 rpm. Prepared reagents are kept inside bottles at a height from the reactor from where those are fed to the reactor using a manifold, pipes and connectors. There is facility for filling the reactor with coal slurry using pipes. Three resistance temperature detectors (RTD) (not shown) are mounted at bottom and 4 inch and 8 inch from the bottom of the reactor. The resistance temperature detectors (RTD) at the bottom is connected to the PID controller (7) via a temperature transmitter TT (8) through which the temperature inside the reactor can be controlled using relay switches connected to the heaters. The four relay switches can also be controlled manually by switching the relays on or off. Remaining two RTDs are connected to the data acquisition module (3) through a signal conditioning element. There is a sensor (energy meter) (not shown) to sense the amount of current passing through the "Live wire" which provides electricity supply to the four heating coils. The output from this device (current data) is send to host computer (4). The temperature data from data acquisition module as well as controller, energy data etc can be seen on the host computer (4) through a graphical user interface developed particularly for this set up. The data acquisition modules, PID controller, signal conditioning elements, 24 V battery, variac and display unit of stirrer etc are placed inside a panel. The experiments for chemical leaching were carried out in the reactor assembly using two steps. In the first step, feed coals (1-2 kg) were treated with varying concentration (10-50%) of alkali (NaOH) (10 lit) or Na2CO3 / Nacl at varying temperatures under refulx with stirring for particular length of time (1.5-7.0 hr) in the bench scale reactor described above. The treated coal is then washed repeatedly with water and/or HCI and then dried. The washed alkali treated coal (10-50gm) is then reacted with 10-20% H2SO4/HCI for 1.0-5.0 hr keeping the same condition as described above. Then, the treated coal is filtered, washed with water and dried before sending for their chemical, rheological and petrographical properties. The coal to slurry ratio is maintained at 1:10 or 1:5 keeping the total volume 10 liters. The moment the feed is fed to the reactor, the stirrer and the data acquisition system are switched on. The readings are checked in the host computer using the GUI to ensure the proper working of the sensors. Once checked, the datas are capture using the save command which saves the data to a text file. At the start of the experiment all the four heaters are switched on. Any of the four heaters can be switched on or off basing on requirement. For example, once the set point is reached, the set temperature can be controlled using only one heater. During the test, intermediate samples can be collected any time from the sampling pipe present at the bottom of the reactor. Different amount of sample can be collected at various length of time during the test basing on subsequent analysis to be one with the samples. The samples collected can be washed with water and/or 10-20% HCI/H2SO4 solution. These samples are dried and analyzed for various properties. After the completion of the experiment, the remaining sample present inside the reactor is taken out from the bottom and filtered using the sparkler horizontal filter. The filter cake is dried inside a drying oven and analyzed for various properties. Multi-stage experiments as well as intermediate dosing experiments were also carried out using the experimental set up. The experiments for chemical leaching of coal to remove mineral matter were conducted at various levels of reagent concentration, coal weight, coal to solution ratio and type of washing (only water or water and 10-20% H2SO4/HCI combined together). The samples were analyzed for ash, volatile matter, alkali content (Na2O & K2O), ash constituents (Fe, CaO, SiO2, Al2O3, MgO, MnO, TiO2, phosphorous, and Sulphur etc.), calorific value (kcal/kg) and Crucible Swelling Number (CSN) etc. Using this set up when chemical treatment of West Bokaro fine clean coal were carried out, the ash content reduced from 13.1 % to nearly 5.0%. All the test results obtained were similar to those obtained with the laboratory scale set up. The crucible swelling number (CSN) improved from 6.5 to 7.5. Nearly 50% silica and 75% alumina can be removed from coal using this process. The alkali content in the product remained nearly same as that of the feed. Experiments were also carried out for Jamadoba fine clean coal, West Bokaro run-of-mine (ROM) coal, West Bokaro Middling samples. Invention was validated in all the four cases which prove that this process can be used for other coals as well. Detail thermodynamic and kinetic study as well as energy requirement for this process was evaluated using the bench scale unit. This will help in optimization as well as scaling up the chemical leaching process to commercial scale and low ash coal can be produced economically for coke making. Despite the incongruity of the words 'ultra clean' and 'coal', they can't help but resonate when coupled together. The most important factor for the successful commercialization of the chemical cleaning of coal to produce low ash coal is the cost involved. The process is simple as it operates under mild conditions under atmospheric pressure, but the cost of chemicals needed, particularly the alkali and acid, would make the process unattractive. Hence, efficient methods of regeneration, recovery and recycling of both alkali and acid are suggested here. The dissolved minerals after chemical leaching can be precipitated as gypsum and aluminium silicates, which can be used in the building and ceramics industries, white the alkalis/acids can be regenerated for reuse. Alkali can be regenerated by reacting with lime, where as acid can be regenerated by distillation or by treating the silicic acid produced with gypsum. The regenerated alkali can be concentrated to desired level using a multiple effect evaporator. The acid treatment process can be eliminated here by just the acid washing step as both produce product with almost same level of ash content which will substantially reduce the process operating cost and acid regeneration difficulty. Though the invention as herein described with a few exemplary embodiments, various modifications, alterations and adaptations are possible within the scope and ambit of the invention as defined in the encompassed appended claims. WE CLAIM; 1. A process to produce low ash clean coal from high ash coal/non coking coals for metallurgical, and thermal applications comprising the steps of crushing clean coal obtained through froth-flotation or coal as received to -30 to -72BS mesh size containing 15 to 16.5% ash, preparing a sample of the coal on oven drying at 105°C to 110°C and cooled, treating the cooled coal sample in a reactor with alkali (NaOH) or with Na2CO3 or NaCl solution at concentration of 10-50% at 80-85°C under reflux with or without stirring for 1.5-7 hours, washing the treated coal repeatedly with water and/or HC1 and then drying, treating the washed coal with 10-20% acidic (H2SO4/HCl) solution for 1 to 5 hour at 80 - 85°C, filtering the treated coal, washing the filtered coal and drying followed by evaluation of chemical, Theological and petroghaphical properties whereby the final ash content of the treated coal is around 5%, which is suitable for coke making. 2. A process to produce low ash clean coal as claimed in claim 1, wherein the minerals of coal such as silicates or shales, quartz and/or sandstone, pyrites and carbonates such as siderites and ankerites during chemical leaching get dissolved as silicates and aluminates and sulphates to be precipitated as gypsum and aluminium silicates which are used in the building and ceramic industries. 3. A process to produce low ash clean coal as claimed in claim 1, wherein alkali used in the process is regenerated by treating the filtrate and alkali wash of the chemically treated coal with lime and acid is regenerated by distillation or by treating the silicic acid produced with gypsum. 4. A process to produce low ash clean coal as claimed in claim 1, wherein the temperatures and pressure in the reaction vessel are maintained optimizingly low such that the treated coal does not decompose resulting in diminishing coking properties. 5. A process to produce low ash clean coal as claimed in the preceding claims wherein the chemically treated coal is substantially demineralised of phosphorus, sulphur, Al2O3/SiO2, iron and calcium oxide. 6. A process as claimed in the preceding claims wherein the calorific value and crucible swelling Number (CSN) of the treated clean coal are improved to meet specification for coke producing. 7. A process to produce low ash clean coal as claimed in claims 1 and 2, wherein silicate and aluminate ions in the solution are precipitated as sodium-aluminosilicate gel according to the reaction Na2SiO3(aq)+NaAl(OH)4(aq)+NaOH(aq)+H2O→[Naa(AlO2)b(SiO)c.NaOH.H2O] 8. A process to produce low ash clean coal as claimed in claims 1, 2 and 7, wherein considerable amount of inorganic sulphur from coal samples are removed according to the reaction 2NaOH+FeS2→ Na2S +Fe(OH)2+S Na2S+2H2O→2NaOH+H2S 2FeS2+2H2O+7O2 →2FeSO4+2H2SO4 9. A process to produce low ash clean coal as claimed in claim 3, wherein alkali used in the process is regenerated according to the equation NaSiO3+Ca(OH)2→CaSiO3+2NaOH H2SiO3+CaSO4→CaSiO3+H2SO4 This invention relates to a process to produce low ash clean coal from high ash coals for coke making along with beneficiation of mineral values form coal comprising the steps of crushing clean coal obtained through froth-flotation or coal as received to -30 to -72 BS mesh size containing 15 to 16.5% ash, preparing a sample of the coal on oven drying at 105° C to 110° C and cooled, treating the cooled coal sample in a reactor with alkali (NaOH) solution at concentration of 10 - 50% at 80 85°C under reflux with or without stirring for 1.5-7 hours, washing the treated coal repeatedly with water and/or Hcl and then dried, treating the washed coal with 10-20% acidic (H2SO4/Hcl) solution for 1 to 5 hour at 80 - 85°C, filtering the treated coal, washing the filtered coal and dried followed by characterize evaluation of chemical, rheological and petroghaphical properties such as ash, volatile matter, alkali (Na2O and K2O) content, ash constituents - (Fe, CaO, SiO2, AL2O3, MnO, TiO2, P and S), calorific value and Crucible Swelling Number to ensure final ash content of the treated coal to around 5% suitable for coke making.

Full Text

FIELD OF THE INVENTION
The present invention relates to a process to produce low ash clean coal from
high ash coal/non coking coals which is used for pulverized coal injection in blast
furnaces, power generation in thermal power plants and any other value added
application requiring low ash coat.
More particularly the present invention relates to produce low ash coal for coke
making by physical and chemical cleaning of high ash content coal on
characterize evaluation of the cleansed coal to be processed for coke making.
BACKGROUND OF THE INVENTION
WITH PRIOR ART DIFFICULTIES
Coal is a major fossil fuel that meets about 60% of the world's commercial
energy demand. Known resources of coal and other solid carbonaceous fuel
materials in the world are far greater than the known resources of petroleum and
natural gas combined. Despite this enormous abundance of coal and related
solid carbonaceous materials, reliance on these resources, particularly coal, as
primary sources of energy, has been discouraged for the most part. The
variability of cheaper, cleaner burning, more easily retrievable and transportable
fuels, such as petroleum and natural gas, has in the past, cast coal to a largely
supporting role in the energy field.

Furthermore, coal is not a uniform substance but rather a mixture of
combustible, metamorphic plant remains that varies in both physical and
chemical composition. Ash producing substance, sulfur, and other materials may
be present in amounts as high as sixty percent. Coal ash is the residue resulting
from non-combustible acidic and basic components in the coal. The major acidic
components are SiO2 and AI2O3. Basic components include magnesium oxide,
calcium oxide, sodium oxide, potassium oxide, and hematite (Fe2O3). Acidic
components also include phosphates and sulfates. Ash, as determined in coal
analysis, may be defined as the noncombustible residue that remains when coal
is burned. The ash forming materials occurring in coal are of two kinds:
extraneous mineral matter and inherent ash. The extraneous mineral matter is
composed mainly of clay and shale minerals, calcite, pyrite or marcasite and
lesser chloride and fluoride minerals. Inherent ash includes inorganic elements
combined with the organic part of the coal, the origin of which is the plant
material from which the coal was formed. Inherent ash displays a reasonably
uniform, essentially molecular distribution throughout the coal mass. Inherent
ash seldom exceed 2 or 3 percent of the weight of the coal. The lower the
inherent ash in the coal, the more reasonable of a reduction in the ash can be
expected.

Most of the coals are associated with mineral matter, which makes it unsuitable
for efficient utilization, such as carbonisation, gasification, combustion, or
liquefaction. Coking industries, and especially, blast furnaces, are more sensitive
to high-ash contents in coals. As a result, enormous efforts are being extended
to make coal and related solid carbonaceous materials equivalent or better
sources of energy, than petroleum or natural gas. In the case of coal, for
example, much of this effort is directed to overcoming the environmental
problems associated with its production, transportation and combustion.
Furthermore, numerous techniques have been explored and developed to make
coal cleaner, more suitable for burning and more readily transportable.
Regardless of the form in which the coal is ultimately employed, the coal or coal
combustion products must be cleaned because they contain substantial amounts
of sulfur, nitrogen compounds and mineral matter, including significant quantities
of metal impurities like, aluminosilicates, metal oxides, metal pyrites, metal
sulfates, etc. If coal is to be accepted as a primary energy source, it must be
cleaned to prevent pollution of the environment either by cleaning the
combustion products of the coal or cleaning the coal prior of burning.
Accordingly, physical as well as chemical coal cleaning (benefidation) processes
have been explored. In general, physical coal cleaning processes involve
pulverizing the coal to release the impurities, wherein the fineness of the coal

generally governs the degree to which the impurities are released. However,
because the costs of preparing the coal rise exponentially with the amount of
fines to be treated, there is an economic optimum in size reduction. Moreover,
grinding coal even to extremely fine sizes may not be effective in removing all
the impurities. Based on the physical properties that effect the separation of the
coal from the impurities, physical coal cleaning methods are generally divided
into four categories: gravity, flotation, magnetic and electrical.
In contrast to physical coal cleaning, chemical coal cleaning techniques are in a
very early stage of development. As far as Indian scenario is concerned, most of
the coals present in India are of drift origin and low grade having high mineral
matter contents varying from 5% to greater than 50%. Moreover, the mineral
matter is finely disseminated inside the coal matrix and is at times firmly bound.
Again, since washability characteristics of Indian coal is not good, it is difficult to
remove the mineral matter from coal by conventional physical coal washing
techniques based on specific gravity difference such as heavy media, dense
media etc. Hence, physical methods of beneficiation, such as heavy media and
froth floatation, are of limited use for applications in coal beneficiation to
produce low ash coals for metallurgical coke making and power generation.
Conventional methods of physical beneficiation separate the coal into clean coal
(15-30 %), middling and rejects. The yields of clean coal are at the cost of the
loss of coal in middlings, and rejects which is considerable. Hence, this present

novel coal cleaning technique of Indian coals using chemicals to leach out the
minerals to obtain clean, demineralized coal has been explored in details.
Chemical leaching of coal is a technology to produce ultra clean coal where the
ash content of clean coal is as low as ~ 1.0% basing on mineralogical
composition of the feed coal. There are potential use of this ultra clean coal
both as a fuel and nonfuel. Conventional chemical leaching processes have been
explored mostly for thermal and non-coking coals. However, the present work
on chemical cleaning process was aimed towards developing a process to
produce low ash coal for coke making with high yield. An effort was made to
decrease the ash content of high ash Indian coals up to ~ 5 % in clean coal
without deteriorating the coking properties. The process has been established in
laboratory scale as well as in bench scale.
In the case of the chemical leaching processes for removing ash from coal, the
inorganic substances constituting the ash content of coal are reacted with
chemical agents and separated from the coal for removal. Various chemicals are
used for the chemical beneficiation process. Some of these chemicals will have a
tendency to dissolve certain inorganic constituents preferentially to others and
the actual chemical to be used may depend upon the inorganic content of the
carbonaceous material which is fed to the process.

Following the end of World War II, it was learned that German coal processing
plants treated coal with aqueous sodium hydroxide at elevated temperatures and
pressures, and thereafter extracted the coal with aqueous hydrochloric acid. The
process reduced the sulfur and ash content of the coal. (Crawford, BIOS Final
Report No. 522, item No. 30, Feb, 19, 1946, British Intelligence Objectives Sub-
Committee, London (A.T.I. - 118668, Central Documents Office, Wright-
Patterson Airforce Base, Dayton, Ohio). Subsequently, the U.S. Bureau of mines
evaluated a similar process for treating coal, involving leaching with aqueous
sodium hydroxide at 225° C, both with and without a final stage extraction with
aqueous hydrochloric acid. In a report made by Reggel et al in 1972, it was
concluded that the sequence of sodium hydroxide treatment and hydrochloric
acid extraction removed most of the mineral matter originally present in the coal.
Am. Chem. Soc. Div. of fuel chem. Preprints, 17 (1): 44-48. Battelle Memorial
Institute had developed a similar process, which is described in Stambaugh et al
U.S. Patent No. 4,055,400 of 1977. An aqueous alkaline slurry of coal is heated
at an elevated temperature and pressure to leach out sulfur and mineral matter.
The Battelle process may optionally include last stage extraction with aqueous
acid to reduce the final ash content. (Stambaugh et al, Hydrocarbon Processing,
54 (7): 115-116 (1975)). An alternative process has undergone extensive
development at Iowa State University, Ames, Iowa. The "Ames" process uses
oxidative desulphurisation in aqueous slurry of sodium carbonate. Typical

conditions are 0.2 M Na2CO3 at an oxygen partial pressure of about 4
atmosphere and temperatures of 120-140° C for 1-2 hours. This development
was reviewed in detail by Dr. T.D. Wheelock in 1981. (Chem. Eng. Commun.,
12:137-159). In one representative test, using temperatures of 120-140° C, the
total sulfur content of the coal was reduced 70% and the pyritic sulfur content
was reduced 78%. (Wheelock (1981), above cited, at pages 148-149).
In general, chemical leaching processes can be classified into the following four
categories.
1. Dissolving with an acid
2. Dissolving with an alkali
3. Oxidation with air, nitrogen dioxide or the like, followed by dissolving with
an acid or alkali
4. Treatment with hydrofluoric acid or hydrogen fluoride gas
Such processes are known as processes for removing ash from coal or coke
(Japanese Patent Publication No. 466/1942), a process for removing sulfur and
ash from coals (Japanese Patent Publication No. 23711/1971) and a coal
deashing process (Japanese Patent Disclosure No. 133487/1980). The processes
(1) and (2) with use of an acid or alkali are practiced usually with the application

of pressure and heat to dissolve the metallic components for the removal of ash.
When practiced under moderate conditions, these processes were almost unable
to achieve any ash removing effect and are therefore not suitable as deashing
processes. The process (3) wherein oxidation is followed by an acid or alkali
treatment is the same as the processes (1) and (2) in principle and is such that
the FeS2 components which are difficult to dissolve are first oxidized and
thereafter dissolved. With the process (4) wherein hydrofluoric acid or hydrogen
fluoride gas is used for treatment, coal is treated with hydrogen fluoride gas
since SiO2 is not easily soluble in acids or alkalis to separate Si in the form of
gaseous SiF4 to achieve a deashing effect. However, the use of hydrofluoric acid
or hydrogen fluoride gas, which is highly toxic and corrosive, involves many
difficulties. Thus an actually effective and useful process for removing ash from
coal still remains to be developed although the deashing of coal is a very
important technique for the effective use of coal.
The patent literature is replete with chemical coal beneficiation processes. For
example, U.S. Patent No. 4, 424,062 discloses a process for chemically removing
ash from coal by immersing ash containing coal in an aqueous solution
containing hydrochloric acid or citric acid in combination with acidic ammonium
fluoride. U.S. Patent No. 3,993,455 discloses a process for removing mineral
matter from coal by the treatment of the coal with aqueous alkali such as sodium

hydroxide, followed by acidification with strong acid. Similarly, U.S. Patent No.
4,055,400 discloses a method of extracting sulfur and ash from coal by mixing
the coal with an aqueous alkaline solution, such as ammonium carbonate.
U.S. Patent No. 4,071,328 discloses a method of removing sulfur from coal by
first hydrogenating the coal and the hydrogenated coal is subsequently contacted
with an aqueous inorganic acid solution. U.S. Patent No. 4,127,390 discloses a
process for reducing the sulfur content of coal by treatment with an aqueous
sodium chloride solution. U.S. Patent No. 4,134,737 discloses a process for the
production of beneficiated coal wherein the coal is digested in caustic, then
treated in mineral acid and then treated in nitric acid.
U.S Patent No. 4,083,940 discloses a process for cleaning coal by contacting the
coal with an aqueous leaching solution containing nitric and hydrofluoric acid.
U.S. Patent No. 4,169,710 discloses comminuting and cleaning coal of sulfur and
ash by contacting the coal with a hydrogen halide, such as HF (aqueous and/or
anhydrous).
U.S. Patent No. 4,408,999 discloses beneficiating coal by subjecting the coal to
electromagnetic radiation in the presence of a strong inorganic acid, such as
hydrofluoric acid. In turn, U.S. Patent No. 4,305,726 discloses a chemical

method of treating coal to remove ash and sulfur comprising treating the coal
with hydrochloric and hypochlorous acid in the presence of ferric and ferrous
sulfate, while U.S. Patent No. 4,328,002 discloses a method of treating coal to
remove ash and sulfur involving preconditioning coal particles in the presence of
an aqueous solution of an oxidant, such as H2O2 or HF, washing the so-treated
coal, treating the washed coal with further oxidant and then passivating the coal
with for example, an ammonium salt and then neutralizing with alkali metal
hydroxide.
U.S. Patent No. 4,516,980 discloses a process for producing low-ash, low sulfur
coal by a two-stage alkaline treatment using sodium carbonate or bicarbonate as
the reagent. The alkaline treated coal is then extracted with aqueous mineral
acid; and U.S. Patent No. 3,998,604 discloses a coal demineralization process
whereby ground coal is treated with aqueous acid, such as HCI, H2SO4 or H2CO3
and then subjected to froth flotation in the presence of a gas selected from
CI2,SO2, or CO2.
In general, many inorganic acids can be used in the process of chemical
leaching. Normally, the inorganic acid will be a strong acid such as hydrochloric
acid, sulfuric acid, hydrofluoric acid, or nitric acid. Some of these acids will have
a tendency to dissolve certain inorganic constituents preferentially to others and

the actual acid used may depend upon the inorganic content of the
carbonaceous material which is fed to the process. For example, hydrofluoric
acid would be used when it is desired to remove silica. Hydrochloric acid or
sulfuric acid alone may be used when it is desired to remove substantial portions
of sulfur and other inorganic constituents. In general, the use of nitric acid is
less desirable since it tends to oxidize the carbonaceous material. In some cases
it may be preferable to use a mixture of acids in order to obtain complete
solubilisation of the inorganic constituents. A combination of hydrochloric acid,
nitric acid and hydrofluoric acid has been found to be a particularly effective
mixture of acids.
In general, it is preferable to use the acids in their strongest concentrations;
however, in some cases more dilute aqueous solutions of the acids may be used.
The actual amount of acid solution utilized is not critical as long as there is a
sufficient amount present to retain the dissolved mineral matter in solution. But
also most of these have got some disadvantages. For example, although HCI has
been found effective in the removal of certain types of mineral matter from coal,
processes that utilize HCI in any form run the risk of chlorinating the aromatic
and heteroaromatic organic matrix found in coal. The chlorine cannot be
removed from the chlorinated coals by simple washing or drying under vacuum.
The corrosiveness of Chlorine liberated from combusted coal is well known. On

the other hand, while it is also known that HF is very effective in removing silica
and alumina from coal, it is not so effective in removing divalent alkali metals,
such as calcium and magnesium. Furthermore, as also evidenced above, several
prior art processes utilize oxidizing acids such as HNO3 and H2SO4. Although
they may aid in the removal of mineral matter, they are also very capable of
oxidizing the organic coal matrix, thereby decreasing the amount of volatile
matter and the heating value of the coal.
Several such processes have been developed. Besides, the amount and rate of
removal of mineral matter from coal during chemical leaching process depend on
various parameters such as type of mineral matter, percentage of mineral
matter, porosity of coal, rank of coal, size of coal, reagents used for dissolution,
time of dissolution, temperature, pressure etc.
The present work on chemical cleaning process was aimed towards developing a
process to produce low ash coal for coke making with high yield from high ash
Indian coals. An effort was made to decrease the ash content up to ~ 5% in
clean coal without deteriorating the coking properties. The process has been
developed keeping in mind the high ash content and finely disseminated mineral
matter content typical of Indian coals.

DESCRIPTION OF THE INVENTION
Leaching or solid extraction is done to dissolve mineral matter in coal using a
solvent. The acidic and /or basic components present in mineral matter react
with the solvents, gets dissolved and then removed. The present invention is a
process of treating coals crushed to -30 to -72 BS mesh size (-0.25 to -0.50 mm)
of fine clean coal obtained from flotation circuit coal for removal of ash-forming
mineral which includes the steps of treating the coal in an aqueous alkaline
solution at an elevated temperature under atmospheric pressure followed by
reaction/extraction with an aqueous acidic solution. This is a process to produce
low ash (~ 5% ash) clean coal for coke making from high ash Indian coals with
80-85% yield. Known processes to produce low ash clean coal have been
developed mostly for power plant and other uses. In the present invention, the
process has been developed and evaluated for coke making. The process has
been established in laboratory scale as well as in bench scale where up to 2 kg of
coal can be treated. Besides, Present invention is a step towards making
chemical leaching process economically feasible for coke making.
The present invention will be better understood from the following description
with reference to the accompanying drawings in which

Figure 1 represents photograph of experimental setup
for the process in Laboratory scale.
Figure 2 represents schematic diagram of experimental
setup for the process in laboratory Scale.
Figure 3 represents photograph of experimental setup
for the process in bench scale.
Figure 4 represents schematic diagram of experimental
setup for the process in bench scale.
The process was initially tried in laboratory scale. After successful
experimentation and encouraging results, the process was also established using
a bench scale unit where up to 2 kg of coal can be treated. In the first part of
the description below, the methodology and results for the laboratory scale
experimentations have been described. In the later part, the experimental
procedure for the process using a bench scale reactor along with the test results
has been stated.
Laboratory Scale:

Methodology of the claimed Process
West Bokaro fine clean coal was taken initially as a feed sample to this process.
This fine clean coal is generated in West Bokaro coal washery through froth
flotation process. The feed sample can be taken directly as obtained after froth
flotation treatment or can be crushed to -30 to -72 BS mesh size (-0.025 mm) for
improving the kinetics of the process. Ash content of this coal sample was
15.0%. This West Bokaro fine clean coal is referred herein as feed coal and the
clean coal produced from this process is referred herein as Product. The major
minerals normally found in coals are silicates or shales, quartz and / or
sandstone, pyrites and carbonates such as siderites and ankerites. It has been
found that even at 373° K using dilute to moderately concentrated NaOH
solution, kaolin is converted into a crystalline sodium derivative i.e.
Na2O.Al2O3.1.8SiO2. The solubility of this sodium-aluminium-silicate derivative is
not very high in alkali solutions but it is fairly soluble in dilute alkali followed by
washing with mineral acid.
Sample Preparation:
Small amount (around 50-200 g) of coal was taken through coning quartering
method from the received West Bokaro fine clean coal. This coal sample was

dried in an oven at 105° C. After drying the coal sample was cooled in a
desiccator.
Chemicals used
The experiments were carried out with various chemicals initially. However,
since the presence of acidic compounds like silica and alumina in Indian coals are
significantly higher, some chemicals tend to behave better than other chemicals.
Treating such coals using diute aqueous NaOH solution under mild conditions at
atmospheric pressure followed by acid leaching / washing results in substantial
demineralization of the coal. The alkali and acid used can be recovered for re-
use. This affords a convenient method for coal demineralization. Commercially
available sodium hydroxide (NaOH) in combination with sulphuric acid (H2SO4)
and HCI were used in the present method.
The treatment process
The experiments for chemical leaching of captive coals were carried out using
the experimental setup as shown in Figures 1 and 2. The equipment assembly
consisted of a three-necked 1000 ml round bottom flask, which is the reactor
(B). The main centre neck was utilized for assembling the motor and the
attached stirrer (D). The speed of the motor for stirring was controlled through

a variac. A condenser (C) was connected to one of the other two necks which,
in turn, was connected to a conical flask with water (F) for trapping the volatile
gases generated during the reaction. The third neck (E) is used to facilitate
addition of reagents using a dropping funnel and also to monitor the
temperature of the reaction bath using a thermometer. Rotamantle (A) was the
source of heat input for the reactor to raise the temperature to the reaction
temperature of 80-85° C. This rotamantle does a two-fold job of controlling the
temperature as well as speed of the stirring (when the magnetic stirrer is used).
Both these parameters can be controlled through the variacs.
The experiments for chemical leaching were carried out in the reactor assembly
using two steps. In the first step, feed coals (5-50 gm) were treated with
varying concentration (10-50%) of alkali (NaOH) (100-500 ml) at 80 - 85° C
under reflux with or without stirring for particular length of time (1.5-5.0 hr) in
the three-necked round bottom flask (B). The treated coal is then washed
repeatedly with water and / or HCI (100ml - 300 ml) and then dried. The
washed alkali treated coal (10-50 gm) is then reacted with 10-20% H2SO4 / HCI
(100-500 ml) for 1.0-4.0 hr keeping the same condition as described above.
Then, the treated coal is filtered, washed with water and dried before sending
for their chemical, rheological and petrographical properties.

Results obtained in laboratory Scale Exterimentation
The chemical leaching technology is available. The most important factor for the
successful commercialization of the chemical cleaning of coal to produce low ash
coal for coke making is the cost involved. The process described here is simple
as it operates under mild conditions under atmospheric pressure. The cost of
chemicals needed, particularly the alkali and acid, would make the process
unattractive. Hence, efficient methods of regeneration, recovery and recycling of
both alkali and acid have been suggested here. Some changes have been made
towards optimizing the whole process and minimizing the cost involved. The
process has been for West Bokaro fine clean coal. This invention is valid for
other coals as well.
The experiments for chemical leaching of coal to remove mineral matter were
conducted various levels of reagent concentration, coal weight, coal to solution
ratio and type of washing (only water or water and 10% HCI combined
together). The samples were analyzed for ash, volatile matter, alkali content
(Na2O & K2O), ash constituents (Fe, CaO, SiO2, Al2O3, MgO, MnO, TiO2,
phosphorous, Sulphur etc.), calorific value (kcal/kg), Crucible Swelling Number
(CSN) and petrographical analysis {Reactive (Vitrinite+Semi-Vitrinite+Exinite),
Inerts (Inertinite+Mineral matter) and Average Vitrinite Reflectance etc.}. Test

results for West Bokaro fine clean coal (Table 1) are exemplified to express the
effectiveness of this process and with improved result table 1 shows the test
results with West Bokaro fine clean coal before and after the chemical treatment
process.

The chemical leaching in the first step, feed coals were treated also with Na2Co3
followed by treatment with H2SO4 or by Nacl followed by H2SO4.
The test results are exemplified in that case in Table 2 as follows.

From the above tests results, it is clear that significant amount of
demineralization takes place incase of WB fine clean coal during the alkali and
acid leaching and acid washing steps. The same process steps were tried for
Jamadoba fine clean coal, and West Bokaro run-of-mine (ROM) coal as well.

Few important test results are depicted below in Table 3. Invention was
validated in all the three cases which ensure that this process can be used for
other high ash coals as well.
Table 3: Test results with Jamadoba fine clean Coal and West Bokaro
Run-of mine (ROM) coal before and after the chemical treatment
process

Alkali treatment, depending on coals mineralogical composition, concentration
and treatment time, may either decrease or increase the ash content. The gain
in ash content or decrease in degree of demineralization of the coal samples with

increase in alkali concentration is attributed to sodium aluminosilicate formation.
The ash reduction is due to dissolution of sulphate and other water-soluble
components present in the coal samples. Alkali also reacts with silica and
alumina in clay and other silica and alumina-bearing materials present in the coal
forming soluble silicates and aluminates as per the following simplified reactions.

The concentrations of silicate and aluminate ions in the solution gradually
increase with alkali concentration and treatment time till the same exceed the
solubility product of sparingly soluble sodium aluminosilicates. The later is
precipitated as per the following simplified reaction:

The gel may convert either to zeolite or felspathoid like sodalite, nosalite etc.
depending on the alkali concentration. In literature, it has been reported that
formation of insoluble sodium complex takes place during leaching of some high
ash coal. Some researchers observed formation of hydroxy-sodalite
Na6[AIO2]6(SiO2)6.xNaOH. (8 - 2X)H2O on treatment of kaolinite and illite type of
clay with sodium hydroxide solution. Continuous decrease in ash removal or

gain in ash with alkali concentration and reaction period is therefore attributed to
progressive precipitation and accumulation of aluminosilicates. This can happen
when more and more amount of silica and alumina from the coal dissolves out.
With the negative effect of alkali concentration on removal of mineral matter
being more with few coals, it may be presumed that these coals contain larger
amount of alkali soluble silica and alumina than coals where ash reduction takes
place even at higher level of alkali concentration. Demineralisation by alkali
alone or followed by acid depend on the nature of the coal. The cation exchange
capacity (CEC) of some of the alkali-treated coal samples continuously increases
with alkali concentration suggesting continuous accumulation of sodium
aluminosilicate. Sodium aluminosilicates can entrap water molecules, alkali and
soluble salt, and the sodium ions in it are exchangeable. The alkali treatment
also leads to removal of considerable amount of inorganic sulphur from the coal
samples. The following reaction takes place during the alkali leaching:

Digestion of the coal samples in water indicates that sulphate leaching takes
place over a long period. The pH of the medium gradually decreases during
digestion and it is accompanied by small increase in the amount of dissolved

.
iron. This also confirms loss of some sulphur through oxidation of pyrite. Similar
reactions take place during the leaching steps which results in reduction in ash
content of the coal samples.
Mineral acids are effective in deminerallsation of coals to different extent.
However, the best results are obtained when it is combined with alkali treatment.
Sulphuric acid treatment or hydrochloric acid washing of the alkali treated coal
results in significant reduction of mineral matter. The ash reduction is more than
that achieved with non-treated coal and is obviously due to formation of
additional acid soluble components during alkali treatment. The alkali treatment
results in formation and precipitation of sodium aluminosilicates gel as explained,
which subsequently undergoes decomposition and solubilisation in presence of
acid soluble forming salts. The reduction in ash content on acid treatment of the
alkali treated coal was found to increase with increase in concentration of alkali.
This is attributed to increase in dissolution of silica and alumina and
consequently amount of aluminosilicate formation.
A positive change is noticed in the Alumina (Al2O3) to Silica (SiO2) ratio which
plays an important role during the steel making process. Alumina to silica ratio
reduced from 0.45 to ~ 0.33 suggesting percentage removal of alumina being
more that that of silica. There is no significant change in the phosphorous

content of the coal samples after the first step where the treatment is done only
with alkali. However, a sharp decrease in phosphorous content is noticed after
acid treatment. There is no significant change in the alkali content either after
alkali treatment or after the acid treatment or acid wash steps proving there is
no accumulation of Na2O or K2O during the process. A marginal reduction in
sulphur content is also observed after the alkali and acid treatment. The sulphur
content of WB and Jamadoba fine clean coals are not very high, which suggests
most of the inorganic sulphur may already have been removed during the
physical coal cleaning processes and hence the scope for removal of inorganic
sulphur during the alkali-acid leaching process is low. The sulphur present may
be of organic origin which is very difficult to leach out or remove. The increase
in calorific value is expected because the decrease in mineral matter content of
the coal samples due to leaching is associated with an increase in fixed carbon
content which adds to the heating value.
To study the influence of alkali-acid leaching process on captive coals, the
Crucible Swelling Number (CSN) of the coal samples after the alkali and acid
treatment were determined. The results suggest that CSN of WB fine clean
coal (6.5) improves to 7.5 after H2SO4/HCI treatment when followed by NaOH
treatment. This shows coal washings with aqueous acids have been effective in
improving coking properties of coals. The process hence can be especially very

effective for the conversion of lower-ranking coals including subbituminous coals.
Even some of their inert minerals can be converted into fusible or reactive forms
through the removal of ion-exchangeable cations. Addition of alkali aiso acts in a
similar way by affecting the macromolecular structure of coal. However,
structural change of coals in terms of such aggregate form of macromolecules,
pores, and reactivity of oxygen functional groups by such pretreatment have not
been fully clarified. Additives of inorganic substance (alkali/acid etc.) can
influence the thermoplastic properties but the effect depends on the nature of
the additive used, amount added and also on the structure of the parent coal.
The WB fine clean coal samples before and after the chemical leaching are also
evaluated for their petrographical properties. As expected, because of the
reduction in mineral matter content of the coal samples after leaching, there is
an increase in total reactives content and a decrease in total inerts content.
Reductionin Inertinite content is seen in addition to the reduction in mineral
matter contents. There is no significant change in the Avg. Vitrinite Reflectance
(Ro) and vitrinite distribution (V9-V13)/petrographical make up.
Bench Scale:
Methodology of the claimed Process

Here also, West Bokaro fine clean coal (different sample than that was used in
laboratory scale) was taken as a feed sample to this process initially. This fine
clean coal is generated in West Bokaro coal washery through froth flotation
process. The feed sample can be taken directly as obtained after froth flotation
treatment or can be crushed to -72 BS mesh size (-0.025mm) for improving the
kinetics of the process. Ash content of this coal sample was 13.1%. This West
Bokaro fine clean coal is referred as feed coal and the clean coal produced from
this process is referred as Product.
Sample Preparation:
1-2 kg of coal was taken through coning quartering method from the received
West Bokaro fine clean coal. This coal sample was dried in an oven at 105° C to
110° C.
Chemicals Used:
The experiments were carried out with various chemicals initially. However,
since the presence of acidic compounds like silica and alumina in Indian coals are
significantly higher, some chemicals tend to behave better than other chemicals.
Treating such coals using dilute aqueous NaOH solution under mild conditions at
atmospheric pressure followed by acid leaching/washing results in substantial

demineralisation of the coal. The alkali and acid used can be recovered for re-
use. This affords a convenient method for coal demineralization. Commercially
available sodium hydroxide (NaOH) in combination with sulphuric acid (H2SO4)
and HCI were used in the present method.
The treatment process
The manner of control of operation at reaction chamber through DAS, Host
computer, TC and TT is described below.
The bench scale unit consists of a batch reactor (1) of nearly 23 litres capacity
with heating arrangements, condenser (2) with provision for reflux, the data
acquisition and control system (DAS) - 3, sparkler horizontal filter (5). The
reactor is heated with four heating coils of 1-kilowatt capacity each which are
fitted outside the circumference of the reactor. A stirrer (6), which extends up to
nearly 2 inch from the bottom of the reactor is fixed at the middle. A D.C. motor
runs the stirrer and its speed can be measured using a sensor, which is mounted
in front of the stirrer. It gives the stirrer speed by magnetic induction principle.
The maximum rpm can go up to ~ 1500 and it can be controlled using a variac.
However, the stirrer is usually operated at around 600 - 900 rpm. Prepared
reagents are kept inside bottles at a height from the reactor from where those

are fed to the reactor using a manifold, pipes and connectors. There is facility
for filling the reactor with coal slurry using pipes.
Three resistance temperature detectors (RTD) (not shown) are mounted at
bottom and 4 inch and 8 inch from the bottom of the reactor. The resistance
temperature detectors (RTD) at the bottom is connected to the PID controller (7)
via a temperature transmitter TT (8) through which the temperature inside the
reactor can be controlled using relay switches connected to the heaters. The
four relay switches can also be controlled manually by switching the relays on or
off. Remaining two RTDs are connected to the data acquisition module (3)
through a signal conditioning element.
There is a sensor (energy meter) (not shown) to sense the amount of current
passing through the "Live wire" which provides electricity supply to the four
heating coils. The output from this device (current data) is send to host
computer (4).
The temperature data from data acquisition module as well as controller, energy
data etc can be seen on the host computer (4) through a graphical user interface
developed particularly for this set up. The data acquisition modules, PID
controller, signal conditioning elements, 24 V battery, variac and display unit of
stirrer etc are placed inside a panel.

The experiments for chemical leaching were carried out in the reactor assembly
using two steps. In the first step, feed coals (1-2 kg) were treated with varying
concentration (10-50%) of alkali (NaOH) (10 lit) or Na2CO3 / Nacl at varying
temperatures under refulx with stirring for particular length of time (1.5-7.0 hr)
in the bench scale reactor described above. The treated coal is then washed
repeatedly with water and/or HCI and then dried. The washed alkali treated coal
(10-50gm) is then reacted with 10-20% H2SO4/HCI for 1.0-5.0 hr keeping the
same condition as described above. Then, the treated coal is filtered, washed
with water and dried before sending for their chemical, rheological and
petrographical properties.
The coal to slurry ratio is maintained at 1:10 or 1:5 keeping the total volume 10
liters. The moment the feed is fed to the reactor, the stirrer and the data
acquisition system are switched on. The readings are checked in the host
computer using the GUI to ensure the proper working of the sensors. Once
checked, the datas are capture using the save command which saves the data to
a text file.
At the start of the experiment all the four heaters are switched on. Any of the
four heaters can be switched on or off basing on requirement. For example,

once the set point is reached, the set temperature can be controlled using only
one heater. During the test, intermediate samples can be collected any time
from the sampling pipe present at the bottom of the reactor. Different amount
of sample can be collected at various length of time during the test basing on
subsequent analysis to be one with the samples. The samples collected can be
washed with water and/or 10-20% HCI/H2SO4 solution. These samples are dried
and analyzed for various properties.
After the completion of the experiment, the remaining sample present inside the
reactor is taken out from the bottom and filtered using the sparkler horizontal
filter. The filter cake is dried inside a drying oven and analyzed for various
properties. Multi-stage experiments as well as intermediate dosing experiments
were also carried out using the experimental set up.
The experiments for chemical leaching of coal to remove mineral matter were
conducted at various levels of reagent concentration, coal weight, coal to
solution ratio and type of washing (only water or water and 10-20% H2SO4/HCI
combined together). The samples were analyzed for ash, volatile matter, alkali
content (Na2O & K2O), ash constituents (Fe, CaO, SiO2, Al2O3, MgO, MnO, TiO2,
phosphorous, and Sulphur etc.), calorific value (kcal/kg) and Crucible Swelling
Number (CSN) etc. Using this set up when chemical treatment of West Bokaro
fine clean coal were carried out, the ash content reduced from 13.1 % to nearly

5.0%. All the test results obtained were similar to those obtained with the
laboratory scale set up. The crucible swelling number (CSN) improved from 6.5
to 7.5. Nearly 50% silica and 75% alumina can be removed from coal using this
process. The alkali content in the product remained nearly same as that of the
feed.
Experiments were also carried out for Jamadoba fine clean coal, West Bokaro
run-of-mine (ROM) coal, West Bokaro Middling samples. Invention was validated
in all the four cases which prove that this process can be used for other coals as
well. Detail thermodynamic and kinetic study as well as energy requirement for
this process was evaluated using the bench scale unit. This will help in
optimization as well as scaling up the chemical leaching process to commercial
scale and low ash coal can be produced economically for coke making.
Despite the incongruity of the words 'ultra clean' and 'coal', they can't help but
resonate when coupled together. The most important factor for the successful
commercialization of the chemical cleaning of coal to produce low ash coal is the
cost involved. The process is simple as it operates under mild conditions under
atmospheric pressure, but the cost of chemicals needed, particularly the alkali
and acid, would make the process unattractive. Hence, efficient methods of
regeneration, recovery and recycling of both alkali and acid are suggested here.
The dissolved minerals after chemical leaching can be precipitated as gypsum

and aluminium silicates, which can be used in the building and ceramics
industries, white the alkalis/acids can be regenerated for reuse. Alkali can be
regenerated by reacting with lime, where as acid can be regenerated by
distillation or by treating the silicic acid produced with gypsum.

The regenerated alkali can be concentrated to desired level using a multiple
effect evaporator. The acid treatment process can be eliminated here by just the
acid washing step as both produce product with almost same level of ash
content which will substantially reduce the process operating cost and acid
regeneration difficulty.
Though the invention as herein described with a few exemplary embodiments,
various modifications, alterations and adaptations are possible within the scope
and ambit of the invention as defined in the encompassed appended claims.

WE CLAIM;
1. A process to produce low ash clean coal from high ash coal/non
coking coals for metallurgical, and thermal applications comprising the
steps of crushing clean coal obtained through froth-flotation or coal as
received to -30 to -72BS mesh size containing 15 to 16.5% ash,
preparing a sample of the coal on oven drying at 105°C to 110°C and
cooled, treating the cooled coal sample in a reactor with alkali (NaOH) or
with Na2CO3 or NaCl solution at concentration of 10-50% at 80-85°C
under reflux with or without stirring for 1.5-7 hours, washing the treated
coal repeatedly with water and/or HC1 and then drying, treating the
washed coal with 10-20% acidic (H2SO4/HCl) solution for 1 to 5 hour at
80 - 85°C, filtering the treated coal, washing the filtered coal and drying
followed by evaluation of chemical, Theological and petroghaphical
properties whereby the final ash content of the treated coal is around
5%, which is suitable for coke making.
2. A process to produce low ash clean coal as claimed in claim 1, wherein
the minerals of coal such as silicates or shales, quartz and/or sandstone,
pyrites and carbonates such as siderites and ankerites during chemical
leaching get dissolved as silicates and aluminates and sulphates to be
precipitated as gypsum and aluminium silicates which are used in the
building and ceramic industries.

3. A process to produce low ash clean coal as claimed in claim 1, wherein
alkali used in the process is regenerated by treating the filtrate and alkali
wash of the chemically treated coal with lime and acid is regenerated by
distillation or by treating the silicic acid produced with gypsum.
4. A process to produce low ash clean coal as claimed in claim 1, wherein
the temperatures and pressure in the reaction vessel are maintained
optimizingly low such that the treated coal does not decompose resulting
in diminishing coking properties.
5. A process to produce low ash clean coal as claimed in the preceding
claims wherein the chemically treated coal is substantially demineralised
of phosphorus, sulphur, Al2O3/SiO2, iron and calcium oxide.

6. A process as claimed in the preceding claims wherein the calorific
value and crucible swelling Number (CSN) of the treated clean coal are
improved to meet specification for coke producing.
7. A process to produce low ash clean coal as claimed in claims 1 and 2,
wherein silicate and aluminate ions in the solution are precipitated as
sodium-aluminosilicate gel according to the reaction

Na2SiO3(aq)+NaAl(OH)4(aq)+NaOH(aq)+H2O→[Naa(AlO2)b(SiO)c.NaOH.H2O]
8. A process to produce low ash clean coal as claimed in claims 1, 2 and
7, wherein considerable amount of inorganic sulphur from coal samples
are removed according to the reaction
2NaOH+FeS2→ Na2S +Fe(OH)2+S
Na2S+2H2O→2NaOH+H2S
2FeS2+2H2O+7O2 →2FeSO4+2H2SO4
9. A process to produce low ash clean coal as claimed in claim 3, wherein
alkali used in the process is regenerated according to the equation
NaSiO3+Ca(OH)2→CaSiO3+2NaOH
H2SiO3+CaSO4→CaSiO3+H2SO4

This invention relates to a process to produce low ash clean coal from high ash
coals for coke making along with beneficiation of mineral values form coal
comprising the steps of crushing clean coal obtained through froth-flotation or
coal as received to -30 to -72 BS mesh size containing 15 to 16.5% ash,
preparing a sample of the coal on oven drying at 105° C to 110° C and cooled,
treating the cooled coal sample in a reactor with alkali (NaOH) solution at
concentration of 10 - 50% at 80 85°C under reflux with or without stirring for
1.5-7 hours, washing the treated coal repeatedly with water and/or Hcl and
then dried, treating the washed coal with 10-20% acidic (H2SO4/Hcl) solution for
1 to 5 hour at 80 - 85°C, filtering the treated coal, washing the filtered coal and
dried followed by characterize evaluation of chemical, rheological and
petroghaphical properties such as ash, volatile matter, alkali (Na2O and K2O)
content, ash constituents - (Fe, CaO, SiO2, AL2O3, MnO, TiO2, P and S), calorific
value and Crucible Swelling Number to ensure final ash content of the treated
coal to around 5% suitable for coke making.

Documents:

01072-kol-2007-abstract.pdf

01072-kol-2007-claims.pdf

01072-kol-2007-correspondence others 1.1.pdf

01072-kol-2007-correspondence others 1.2.pdf

01072-kol-2007-correspondence others 1.3.pdf

01072-kol-2007-correspondence others-1.4.pdf

01072-kol-2007-correspondence others.pdf

01072-kol-2007-description complete.pdf

01072-kol-2007-drawings.pdf

01072-kol-2007-form 1 1.1.pdf

01072-kol-2007-form 1-1.2.pdf

01072-kol-2007-form 1.pdf

01072-kol-2007-form 18.pdf

01072-kol-2007-form 2.pdf

01072-kol-2007-form 3.pdf

01072-kol-2007-gpa.pdf

1072-KOL-2007-ABSTRACT 1.1.pdf

1072-KOL-2007-AMANDEDCLAIMS.pdf

1072-KOL-2007-CORRESPONDENCE.pdf

1072-KOL-2007-DESCRIPTION (COMPLETE) 1.1.pdf

1072-KOL-2007-DRAWINGS 1.1.pdf

1072-KOL-2007-EXAMINATION REPORT REPLY RECIEVED.pdf

1072-KOL-2007-EXAMINATION REPORT.pdf

1072-KOL-2007-FORM 1-1.1.pdf

1072-KOL-2007-FORM 13.pdf

1072-kol-2007-form 13.pdf.PDF

1072-KOL-2007-FORM 18.pdf

1072-KOL-2007-FORM 2-1.1.pdf

1072-KOL-2007-FORM 3.pdf

1072-KOL-2007-GPA.pdf

1072-KOL-2007-GRANTED-ABSTRACT.pdf

1072-KOL-2007-GRANTED-CLAIMS.pdf

1072-KOL-2007-GRANTED-DESCRIPTION (COMPLETE).pdf

1072-KOL-2007-GRANTED-DRAWINGS.pdf

1072-KOL-2007-GRANTED-FORM 1.pdf

1072-KOL-2007-GRANTED-FORM 2.pdf

1072-KOL-2007-GRANTED-SPECIFICATION.pdf

1072-KOL-2007-OTHERS 1.1.pdf

1072-KOL-2007-REPLY TO EXAMINATION REPORT.pdf

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Patent Number

249940

Indian Patent Application Number

1072/KOL/2007

PG Journal Number

47/2011

Publication Date

25-Nov-2011

Grant Date

23-Nov-2011

Date of Filing

01-Aug-2007

Name of Patentee

TATA STEEL LIMITED

Applicant Address

JAMSHEDPUR

Inventors:

#	Inventor's Name	Inventor's Address
1	DASH, PRATIK SWARUP	TATA STEEL LIMITED, JAMSHEDPUR-831 001
2	BHATTACHARJEE, DEBASHISH	TATA STEEL LIMITED, JAMSHEDPUR-831 001
3	MUKHERJEE, T.	TATA STEEL LIMITED, JAMSHEDPUR-831001
4	BANERJEE, PRADIP KUMAR	TATA STEEL LIMITED, JAMSHEDPUR-831001

PCT International Classification Number

C10L 5/00; C10G 1/00

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA