Coal preparation survey. Final report Feb 82-Aug 82
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GCA identified 165 physical coal cleaning plants with a raw coal capacity of 500 tons/hr or greater. Of these 165 plants, additional information on the sulfur and ash content of the raw and prepared coals was collected for 49 coal preparation plants. Calculations were performed to determine the percent sulfur and ash reduction due to physical coal cleaning processes. The reduction in sulfur content varied from 0 to 57 percent by weight while the reduction in ash content varied from 10 to 85 percent by weight. These values are well within the range of results previously reported in the literature.Cite
The continuous testing of the Chemical and Electrochemical Coal Cleaning (CECC) bench-scale unit (Task 6) was completed successfully in this quarter using Middle Wyodak and Elkhorn No. 3 coal samples. The CECC unit was run under the optimum conditions established for these coal samples in Task 4. For the Middle Wyodak coal, the ash content was reduced from 6.96% to as low 1.61%, corresponding to an ash rejection (by weight) of about 83%. The ash and sulfur contents of the Elkhorn No. 3 coal were reduced to as low as 1.8% and 0.9%. The average ash and sulfur rejections were calculated to be around 84% and 47%. The CECC continuous unit was used to treat -325 mesh Elkhorn No. 3 coal samples and gave ash and sulfur rejection values of as high as 77% and 66%. In these test, the clean -325 mesh coal particles were separated from the liberated mineral matter through microbubble column flotation, instead of wet-screening.
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Clean coal
Fraction (chemistry)
Specific gravity
Froth flotation
Gravity separation
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The report gives results of tests at seven coal-preparation plants to evaluate the performance of froth flotation cells and dense-medium cyclones in removing ash and sulfur (S) from fine coal (Minus 28 mesh). Flotation circuits tested at four plants showed substantial reductions in coal ash content (64-88%), pyritic S content (48-65%), and sulfur dioxide (SO/sub 2/) emission (expressed as ng SO/sub 2//million Btu; 15-87%) at mean weight recoveries of 11-54%. Raw and clean coal data sets were found to exhibit statistical properties that can be characterized by time series models. The use of low-S coal, PCC, or chemical coal cleaning (CCC) was evaluated for compliance with potential SO/sub 2/ emission limits for industrial boilers. PCC can achieve moderate S reductions in (high S) Northern Appalachian and Midwestern coals, but few of these coals can be cleaned to meet a 516 ng SO/sub 2//million Btu standard. Many Southern Appalachian, Alabama, or Western coals are capable of meeting the standard as mined or after cleaning.
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moisture. Test results met or exceeded all of the program objectives. Nominal 3/8-inch size agglomerates with less than 20 percent moisture were produced. The clean coal ash content varied between 1.5 to 5.5 percent by weight (dry basis) depending on feed coal type. Ash reductions of the run-of-mine (ROM) coal were 77 to 83 percent. ROM pyritic sulfur reductions varied from 86 to 90 percent for the three test coals, equating to total sulfur reductions of 47 to 72 percent.
Agglomerate
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Clean coal
Coal slurry
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Coal is a major source of energy. The available Indian coal quality is very poor having very high ash content and low calorific value. Indian coal generates a large quantity of ash as a by-product of combustion. The objectives of the present study were to reduce the ash content of coal to produce ultra-clean coal. The coal was treated with a dual chemical leaching process consisting of NaOH followed by HCl.During experiments, the concentration of NaOH was varied from 2.5 to 10 M with 1.4 N HCl. Effect of shaking speed and time was analysed at 0, 50, 100, 150 and 200 rpm and 1, 2, 3 and 4 hours respectively. After chemical leaching, the ash content was reduced from 35.33 to 0.98% in the ultra-clean coal. The concentration of alkali, shaking speed and time of duration were found as highly influencing parameters for the reduction of ash content in the coal. Moreover, the current study should result in a better option for the removal of ash content from low-rank Indian coals.
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It is well known that froth flotation is inefficient for treating fine coal fractions containing a significant portion of middling particles. On the other hand, gravity-based processes can effectively remove middling particles containing only a small amount of coal. Falcon Concentrators Inc. and Knelson Gold Concentrators Inc. have developed full-scale, enhanced gravity separators for the treatment of heavy minerals. This project is evaluating the potential of using these concentrators to treat Illinois Basin coal fines. During this reporting period, -28 mesh run-of-mine Illinois No. 5 and No. 6 coal samples were processed using a continuous Falcon concentrator having a 10-inch bowl diameter. For the Illinois No. 5 coal sample, the ash content was reduced in the 100 {times} 325 mesh size fraction from about 18% to 8% while achieving a high combustible recovery value of nearly 97%. In addition, the total sulfur content was substantially decreased from 2.6% to 1.7%. Similar results were obtained from the treatment of the Illinois No. 6 coal sample where ash rejections ranged from 40%-70% for a 28 {times} 325 mesh feed having 7% ash. Combustible recovery values from these tests were greater than 87% while treating mass feed rates between 1 to 2 tons/hour. A parametric study found that lower feed solids contents provided marginally lower product ash and total sulfur contents while feed rate and bowl speed appeared to have no significant effect over the range of values tested.
Specific gravity
Gravity separation
Fraction (chemistry)
Beneficiation
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Fifteen 1-ton bulk samples of Indiana coal were studied in detail by the Indiana Geological Survey in an attempt to reduce the sulfur content. Laboratory techniques of crushing, screening, and making separations based on specific gravity simulated the cleaning processes used in modern industry-operated coal preparation plants. Sulfide, sulfate, organic sulfur, and total sulfur were determined for each fractional sample of coal obtained by screening and float-sink methods. Only the sulfate (about 0.1% of coal) and the sulfide or pyritic sulfur (0.7 to 5.4% of coal) can be reduced by this mechanical cleaning technique. Organic sulfur (0.2 to 2.8 % of coal) cannot be reduced by this method. Although about half of the pyritic sulfur can be removed at the 80% recovery level, Seelyville coal (III) and Springfield coal (V) still contain, in most places, more than 3% sulfur; Buffaloville coal, Hymera coal (VI), and Danville coal (VII), 2 to 3%; and Survant coal (IV) and Upper Block coal, 2% or less.
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Thermal Power plants in India burn high ash content coal of 40-60 ash % due to the paucity of low ash coal. Combustion of high ash coals creates a lot of environmental issues like atmospheric pollution, generation of high quantities of fly/bottom ash, water and soil pollution. The common practice for reduction of mineral matter and undesirable pollutants in coal is by wet washing or cleaning. The disadvantages of wet coal cleaning are high water requirement, increase in moisture content of washed coal thereby decrease in heat value, chemical breakdown of coaly material, physical degradation & generation of excessive fines, disposal of slurry water in addition to high capital investment, high processing cost and cumbersome handling. A new dry coal beneficiation system namely COAL WINNOWING SYSTEM has been designed & developed. Various coals from Wardha Valley Coalfields of WCL had been experimented in Coal winnowing system. Studies on Coal of size fractions; 50-25 mm, 25-13 mm, 13-6 mm were conducted. One experiment conducted with size fractions of 25-13 mm WCL -Marki Mangli mine coal shows overall ash percentage reduction from 47.4% to 43.1% with cleans yield of 79.5%. The parameters like air velocity, horizontal distribution of particles and handling of higher sized coal, 100-50 mm was optimized. Studies on ROM coal from New Sasti Mines, Wardha Valley Coalfield, Maharashtra on size fraction of 100-75 mm shows overall ash percentage reduction from 55.8% to 37.0% with cleans yield of 48.17%.Winnowing Index is calculated and Tromp curve has been drawn for different size fractions of coal. The probable error (Ep) values for different size fractions are between 0.065 to 0.155 which seems better than the Allair Jig which has Ep value 0.18 during bench scale test in the laboratory. These studies show that Coal winnowing technique can be effectively applied to physically separate the coal & shale/stone particles. The developed technique can be easily applied to dry coal cleaning of non-coking coals for
thermal power plant use and will be more useful in as the coal will have low moisture, no chemical breakdown, no physical degradation as well as low capital investment, low processing cost and easy handling.
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Winnowing
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A series of thrigy-three coal/oil agglomerations experiments and subsequent analyses and testing provided much information on the use of this process for the pretreatment of coal liquefaction feeds. Coal derived oils were identified that will deash Burning Star coal (10% ash) by coal/oil agglomeration. The results indicate that it is possible to achieve 45% ash removal with 96% recovery of organic matter and product size larger than 1 mm. Acceptable oils included recycle oils produced by the ITSL, H-Coal and SRC-II processes. Under donor liquefaction conditions, the deashed coal gave conversions and yield structures similar to the raw coal. The ash elements Ti, Fe, K, Mg and P are selectively retained in the product. The ash elements Ca, Al and S are selectively rejected. The pyrite/ash ratio and the percentage of Fe/sub 2/O/sub 3/ in the ash are both increased in the product by approximately 1.5 times relative to the feed coal. This result should prove beneficial to processes such as SRC-II that rely on mineral matter catalysis because overall feed ash levels could be reduced while maintaining high concentrations of catalytic iron-bearing minerals. The cleaned coal is expected to give better hydro-liquefaction behavior than raw coal with similar ashmore » levels. It may be possible to further enrich the iron in the ash by using run-of-mine coal. The donor liquefaction behavior of several foreign and domestic coals (candidates for ITSL) were tested in the microautoclave with ITSL pasting solvents at a variety of conditions. Yield structures were determined for some of the runs. Preliminary analyses are presented for the samples from the early Illinois 6 coal ITSL runs. 1 figure, 32 tables.« less
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