Calorific value moist mineral matter-free

Fixed carbon limits (dry, mineral-matter-free basis), % Volatile matter limits (dry, mineral-matter-free basis), % Gi (moist OSS calorific value limits mineral-matter-free basis) ... 

The ASTM Glassification. The ASTM classification system was adopted in 1938 as a standard means of specification. This system is used in the United States and in many other parts of the world, and is designated D388 in the ASTM Standards (18). The higher rank coals are specified by fixed carbon >69%, or for volatile matter <31%, on a dry, mineral-free basis. Lower rank coals are classified by calorific value on the moist, mineral-matter-free... 

Such data are necessary for calculation of parameters in the classification of coal by rank dry, mineral-matter-free volatile matter (or fixed carbon) as well as moist, mineral-matter-free gross calorific value. For volatile matter and fixed-carbon data, it is also necessary to assume that 50% by weight of the sulfur is volatilized in the volatile matter test and therefore should not be included as part of the organic volatile matter (nor should the loss from clays and carbonate minerals) ... 

In the Parr formula for moist, mineral-matter-free calorific value, the moisture basis used is that of the inherent moisture of the coal in the seam (natural bed moisture, capacity moisture) ... 

Thus (Table 1.7), coal with a fixed carbon value in excess of 69% w/w or more, as calculated on a dry, mineral-matter-free basis, are classified according to the fixed-carbon value. Coal with a calorific value below 14,000 Btu/lb, as calculated on a moist, mineral-matter-free basis, is classified according to calorific value on a moist, mineral-matter-free basis, provided that the dry, mineral-matter-free fixed carbon is less than 69%. The agglomerating character is considered for coal... 

Class Group Fixed Carbon Limits (%, Dry, Mineral-Matter-Free Basis) Equal to or Greater Less Than Than Volatile Matter Limits (%, Dry, Mineral-Matter-Free Basis) Equal to or Greater Less Than Than Calorific Value Limits (Btu/lb, Moist, Mineral-Matter-Free Basis) Equal to or Greater Less Than Than Agglomerating Character... 

This classification does not include a few coals, principally nonbanded varieties, that have unusual physical and chemical properties and that come within the limits of the fixed-carbon or calorific value of the high-volatile bituminous and subbituminous ranks. All of these coals either contain less than 48% dry, mineral-matter-ffee fixed carbon or have more than 15,500 moist, mineral-matter-free British thermal units per pound. 

Inherent or equilibrium moisture is used for calculating moist, mineral-matter-free calorific values for the rank classification of high-volatile bituminous coals. It is also used for estimating free or surface moisture, since total moisture is equal to the sum of the inherent moisture and the free moisture and is considered the inherent moisture of the coal as it occurs in the unexposed seam, where the relative humidity is probably near 100%. However, due to physical limitations, equilibrium moisture determinations are made at 96 to 97% relative humidity and used as inherent moisture values. 

The classification of coal (ASTM D-388) depends on calculation of the volatile matter yield and fixed carbon values on a dmmf basis. Calorific values are calculated on a moist, mineral-matter-free basis. The Parr formula is used in the classification system to calculate the mineral matter from ash and sulfur data. 

High-volatile A bituminous coal rank of coal such that on a dry, mineral-matter-free basis, the volatile matter content of coal is greater than 31% (or the fixed carbon content is less than 69%), and its gross calorific value is equal to or greater than 14,000 Btu/lb of coal on a moist, mineral-matter-free basis, and the coal is commonly agglomerating. 

Cross Calorific Value Limits (Moist, Mineral Matter-Free Basis), MJ/kg... 

Other bases may be required for the expression of analytical data. Moist, ash-free basis (maf) assumes that the sample is free of ash, but with moisture (ASTM D388, Standard Classification of Coal by Rank, requires calorific value to be expressed on a moist, mineral matter-free basis (mmmf)). The various national standards organizations present different formulae for the calculation of mineral matter (which is not a generally determined value) reference to their publications is necessary to determine which calculation is appropriate in given circumstances. 

The basis for the two ASTM criteria (the fixed-carbon content and the calorific value calculated on a moist, mineral-matter-free basis) are shown in Fig.6.13 for over 300 typical coals of the United States. The classes and groups of Table 6.4 are indicated in Fig. 6.13. For the anthracitic and low- and medium-volatile bituminous coals, the moist, mineral-matter-free calorific value changes very little hence the fixed-carbon criterion is used. Conversely, in the case of the high-volatile bituminous, subbituminous, and lignitic coals, the moist, mineral-matter-free calorific value is used, since the fixed-carbon value is almost the same for aU classifications. 

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