Coal preparation

Coal preparation serves several purposes. One important purpose is to increase the heating value of the coal by mechanical removal of impurities. This is often required in order to find a market for the product. ROM coal from a modem mine may incorporate as mnch as 60% reject materials. 

The energy content of coal is related to its rank (degree of coalification) (Table 6.1) which is influenced by the content of nonfuel components (e.g., minerals and moisture) (Chapters 7 through 9). Thus, a primary objective of coal cleaning is to maximize the recovery of the heat value of the coal, consistent with achieving standard specifications for ash, moistme, and sulfur contents. 

Briefly, the grade of a coal establishes its economic value for a specific end use. Grade of coal refers to the amount of mineral matter that is present in the coal and is a measure of coal quality. Sulfm content, ash fusion temperature (measurement of the behavior of ash at high temperatures). 

In fact, long-range transportation of lignites, more than one-third of which consists of water, can more than triple the initial mine-mouth costs calculated on an energy basis. There may however be some trade-off in transportation costs if the low-rank coal is sufficiently low in sulfur which, in turn, means a lower cost in terms of stack gas cleanup (Nowacki, 1980). 

The need for coal cleaning can be reduced by choice of suitable mining methods many mines include the methods by which oversize coal is reduced in size but the cleaning of ROM coal is, more often than not, a separate operation which is performed as a surface operation that is usually close to the mine-mouth. However, the term coal preparation includes, by definition, not only sizing (i.e., crushing and breaking) methods but also all of the handling and treatment methods that are required to prepare the coal for the market. 

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J. Abbott and co-workers, paper presented at The International Coal Preparation Congress, Paris, France, 1972, paper 20E VI. 

Mechanical Properties. Mechanical properties (4,6,55) are important for a number of steps in coal preparation from mining through handling, cmshing, and grinding. The properties include elasticity and strength as measured by standard laboratory tests and empirical tests for grindabiUty and friabihty, and indirect measurements based on particle size distributions. 

One significant advantage of pulverized coal boilers is the ability to use any kind of coal, including mn-of-mine or uncleaned coals. However, with the advent of continuous mining equipment, the ash content frequently is ca 25%, and some preparation is frequently practiced. There were 931 coal preparation plants in the United States in 1988, mainly in Kentucky, West Virginia, and Peimsylvania. 

J. L. Anastasi and co-workers, 5th Annual Coal Preparation, Utilisyation and Environmental Control Contractors Conference, U.S. Department of Energy, Pittsburgh, Pa., July 31—Aug. 3, 1989. 

Additions of new flocculants after conventional thickening produce further dewatering of mineral slimes. A clay flocculated with polyacrylamides and rotated in a dmm can produce a growth of compact kaolin pellets (84), which can easily be wet-screened and dewatered. A device called a Dehydmm, which flocculates and pelletizes thickened sludges into round, 3-mm pellets, was developed for this purpose. Several units reported in commercial operation in Japan thicken fine refuse from coal-preparation plants. The product contains 50% moisture, compared with 3% soflds fed into the Dehydmm from the thickener underflow (85). In Poland, commercial use of the process to treat coal fines has been reported (86), and is said to compare favorably both economically and technically to thickening and vacuum filtration. 

M. Yusa and co-wotkets, in A. C. Partridge, ed.. Proceedings of the 7th International Coal Preparation Congress, AustraUan National Committee, Sydney, 1976. 

T. A. Sladek and C. H. Cox, Coal Preparation LsingMagnetic Separation, Vol. 4, Evaluation of Magnetic Fluidsfor Coal Beneficiation, EPRI Report CS1517, Energy Electric Power Research Institute, Palo Alto, Calif., July 1980. 

Coal-preparation plants Materials handling conveyors, elevators, chutes Particulates (dust) Local exhaust system and cyclones... 

Coal preparation plants are used to reduce noncombustibles and other undesirable materials in coal before it is burned. 

Fugitive particulate emissions during material handling (coal preparation)... 

These yields are also given on the basis of 100 g of original dry coal before fractionation. The bottom line of the table shows the mass of each fraction obtained from 100 g of dry coal. For every 100 g of original dry coal an additional 100 g of extraneous material was present. Elemental balances and other evidence (]J showed this to be made up almost entirely of phenol chemically combined with the coal material, with traces present of residual solvent associated with the fractions as a result of the coal preparation and fractionation scheme. Note that with fractions A and B no solid residue was obtained. 

Figure 3.5 shows the complete process for the production of hydrogen from coal. The process consists of the following components coal preparation, air separation, coal gasification,... 

At the Fabius Coal Preparation Plant in Jackson County, Alabama, a constructed wetland treatment system was built to treat acid drainage from a coal pile. In 1985, the total cost of the wetlands was 43,000. The annual costs from 1985 to 1990 were approximately 13,000 due to repairs and extensive monitoring. In 1991, operation and maintenance costs were estimated to be 1000 annually (D12459E, p. 164). 

In 1990, an anoxic limestone drain was installed upstream of a wetland treating acid drainage from another coal-contaminated area of the Fabius Coal Preparation Plant. The total installation cost was approximately 19,000 (D124607, p. 135). 

To assure optimum performance, it was also necessary for us to become expert in tuning and troubleshooting the electrostatic precipitator units, the coal preparation and feed equipment,as well as the general operation of the utility boiler. Such capabilities proved to be vital in successfully running this business. It required that we recruit and train a technical service department and mechanical staff,which became the largest organizational units within our company. 

Take quicksilver and gold leaf, making to the consistency of wax. Clean the vase with alum, and taking a little of the waxy material, spread it on the vase with the polisher and let it stand to fix. Do this five times. Take the vase with a linen cloth so that it he not soiled, and removing it from the coals, prepare ashes, smooth with the polisher and use it as a gold vase. It will stand the test for real gold. 

Fate of trace metals in coal preparation and conversion processes... 

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