Challenges and Solutions of Coal Preparation in the Context of Technology Upgradation and Bulk Handling / Volume Control
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The document discusses the challenges and solutions in coal preparation, highlighting the importance of coal quality in applications such as electricity generation and steel production. It outlines the processes of coal cleaning, beneficiation, and the effects of mineral impurities on coal's heating value. Additionally, there are comparisons between wet and dry processing methods, emphasizing the need for efficient technologies to enhance coal washability and minimize fines generation.
Challenges and Solutions of Coal Preparation in the Context of Technology Upgradation and Bulk Handling / Volume Control
- 1. CHALLENGES AND SOLUTIONS OF COAL PREPARATION IN THE CONTEXT OF TECHNOLOGY UPGRADATION AND BULK HANDLING / VOLUME CONTROL DEPARTMENT OF MINING ENGINEERING ACE
- 2. Coal is used mainly for Carbonization Combustion Gasification Liquefaction Where do we use COAL? Most significant uses of coal includes, Electricity generation Steel production Cement manufacturing Liquid fuel
- 3. Moisture Ash Volatile matter Fixed carbon Sulfur Mercury Heating value (BTU/lb, kcal/kg) Size & Specific Gravity Caking index Ash Melting Temperature 3 Coal Quality
- 4. 4
- 5. Distribution pattern of mineral impurities in Indian coals ------------------------------------------------------------------------------------------- Shale, Illite, montmorillonite, Frequent and Common 5-10 Musocovite ------------------------------------------------------------------------------------------- Kaolin Kaolinite Very Frequent and 60-85 Dominat Sulphide Pyrite, Mercasite Less Common 1-2 Pyrrhotite, etc Carbonate Calcite, Dolomite, Frequent and Common 1.0-2.5 Siderite, Ankerite Oxide Quartz Frequent and very common 2-20 Rutile, Anatase Frequent and common 0.5-1.0 Hematite Frequent and common 1-2 Other Feldspar, Apatite Common 0.5-1.0 Accessory Minerals ------------------------------------------------------------------------------------------- 5
- 6. Empirical Formula for Indian Coals Gross Calorific Value in Kcal/kg = 85.6 x (100-1.1A –M) – 60M A = Ash content, wt% M = equilibrated moisture content, wt% •40% ash, 10% M GCV = 3338 kcal/kg •30% ash, 10% M GCV = 4280 kcal/kg 1 ton of ROM Coal having 40% ash = 0.78 tons of washed coal having 30% ashTechno-economic feasibility analysis should be based on the above. The yield of washed coal at a given ash content is, therefore, of immense importance while selecting the appropriate coal washing technology. 6 Effects of Ash Content on Heat Value
- 7. Coal beneficiation is the process of removal of the contaminants and the lower grade coal to achieve a product quality which is suitable to the application of the end user - either as an energy source or as a reducing agent for metallurgical extraction of iron ores. A common term for this process is coal "washing" or "cleaning". Coal Processing forms a link between coal mining and coal utilization. Coal preparation is a broader term used to describe the complete process of sizing, handling and washing of the run-of-mine coal. It literally means increasing the commercial value of coal by suitable preparation. 7 What is Coal Preparation???
- 8. To increase the commercial value of coal to meet consumer demands Greater environmental constraints than in the past Due to the incorporation of non-coal bands, mineral aggregates and possibly a certain amount of roof and floor rock in the mined material. Due to Mechanized Mining Operation Need for Coal Preparation
- 9. To Remove extraneous, non-combustible material from coal To Reduce ash handling at power station For Sulfur reduction (lower SOX emissions) For Carbon and NOX Emissions Reduction To Reduce transportation costs per unit of heat To Provide Guarantee consistent heat value To Improve plant efficiency 9 Purpose of Coal Preparation
- 10. • Washability of a coal broadly means its amenability to improvement in quality by washing. • Washability characteristics of coal vary from locality to locality and from seam to seam due to variance in the extent and nature of impurities associated with coal. It is therefore necessary to assess the cleaning potentiality of a coal, before assigning it to a preparation plant. • Float and sink tests are based on the difference in specific gravity of coal and impurities. Specific gravity of clean coking coal, e.g., is about 1.2 (1.12 to 1.35), while specific gravity of impurities typically varies from 1.6 to 2.6. 10 Washability
- 11. Organic Liquids : Bromoform (2.89) and Carbon Tetrachloride (1.59) Salts : Zinc Chloride (2.9 ) 11 Sink-float Tests
- 12. Specific Gravity Ranges Wt% Ash% Wt% Ash% Below 1.3 29.1 6.4 29.1 6.4 1.3-1.4 5.5 16.1 34.6 7.9 1.4-1.5 17.6 23.0 52.2 13.0 1.5-1.6 21.2 31.7 73.4 18.4 1.6-1.7 15.7 41.7 89.1 22.5 1.7-1.8 6.1 50.2 95.2 24.3 Above 1.8 4.8 67.2 100.0 26.3 Direct Cumulative Float 12 Typical Coal Washability Data
- 14. Circuit Feed SIZING CLEANING DEWATERING Raw Coal Deslime Screens D&R Screens Dense Medium Vessel D&R Sizer Screens Stoker Centrifuge D&R Screens D&R Screens Centrifugal Dense Medium Dryer Cyclones Sieve Bends/ Clean Coal Dewatering Cyclones Classifying Compound Screen Cyclones Spirals Clean Coal Screen-Bowl Deslime Cyclones (Optional) Advanced Flotation Thickener Waste Disposal 14 Typical Process Flow Sheet For Steam Coal Production
- 15. FOR OPTIMUM PERFORMANCE, INDIAN COALS ARE COMMINUTED INTO THREE SIZE FRACTIONS: COARSE COAL: (–50+13) MM - JIGS AND HEAVY MEDIA BATHS MEDIUM AND SMALL COAL: (-13+0.5) MM - DENSE MEDIUM CYCLONES (DMC) FINE COAL: (–0.5) MM - FROTH FLOTATION 15 Coal Sizes for Washing
- 16. • Deterioration with ROM Coal Quality • Enhanced Proportion of Fine Coal Fraction due to Mechanized Mining and Liberation at Finer Sizes • Construction of High Capacity Plants with Efficient Technologies • Utilization of Large Volume of Washery Rejects 16 Challenges in Coal Preparation with Enhanced Production
- 17. Mine to Mill Process Optimisation – An Option? 17 How do we minimize fines generation?
- 18. »Innovative Circuit Configuration »Modular Design »Linkage of Existing Units with Improvised Unit Operations »A Database to Elicit Merits of Replacing Existing Equipment with Modern Units 18 Strategies to be Adopted for Efficient Coal Washing
- 19. Jigging Good for Deshaling but Performance Drops Significantly with Decreasing Coal Particle Size 19 Major Unit Operations for Coal Washing
- 20. Included angle Underflow Overflow Feed Diameter of Cyclone Spigot 20 Dense Medium Cyclone Dense Medium Cyclones Seem to be the Most Promising
- 21. Sharp, efficient, separation of fine coal is possible. Low relative density cut points can be achieved. The density of separation can be controlled. Oxidised or weathered coal can be processed. Oversize particles can be handled. The process is flexible and suited to almost any type of coal. High magnetite consumption. Problems associated with magnetite recovery. The medium density is difficult to control. In spite of the sharp separation possible, it is not easy to consistently produce low-ash coal. The plants previously built were notoriously ‘troublesome’. Advantages Disadvantages 21 Pros-and-Cons of DMC
- 23. No water consumption Environment friendly Low operating cost Easy maintenance Potential Benefits 23 Emerging trends? Dry Beneficiation
- 24. FGX Separator Air dense medium fluidized bed Separator24 Dry Beneficiation
- 25. (DRY PROCESSING VERSUS DENSE MEDIUM PROCESSING FOR PREPARING THERMAL COAL - GJ DE KORTE, 2013) 25 Case Study
- 27. Poor separation performance Cannot upgrade raw coal to the required quality – especially when the coal contains high amounts of near-gravity material. Misplacement rate of fine and ultrafine coal is high The question is whether it is economically viable in the longer term to implement dry processing? 27 Drawbacks
- 28. In specific cases, where the coal is easy to process, where there is a shortage of water and when only de-stoning of the coal is required, dry processing technologies may prove the most viable processing option. The separation efficiency of dry processes is, however, not nearly as good as that of dense medium and, as a result, it is difficult to effectively beneficiate coals with a high near-dense content. The product yield obtained from some raw coals is lower than expected and control of product quality is not always easy with dry processes. 28 Remarks
- 29. Need to think twice before using Dry beneficiation!!! Dry processing is less efficient than wet processes and hence it is necessary to consider the economic impact of the lower product recovery from raw coal mined and processed.
Editor's Notes
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