Coal higher heating value basis

Analytical results (Table 1) show that SRC have very high volatile matter and nitrogen contents (52-60% and 1.8-1.9%, respectively, on a dry-ash-free basis) and very low moisture and ash contents (0.1-0.3%, as-received basis in each case). The Higher Heating Values for the SRC (15,920-16,115 Btu/lb, dry-ash-free basis) are much higher than those of reference coals (13,290 and 14,110 Btu/lb for the WSB and KHB coals, respectively). 

The most commonly used system of classification refers to the American standard (ASTM D-388 [13]) using fixed carbon combined with volatile matter on a dmmf basis for higher-rank coals and higher heating value (HHV) on moist mineral matter-free (mmmf) basis for lower-rank coals. The moisture used should be as close as possible to the natural bed moisture content and is obtained by exposing the sample to 30 °C and a relative humidity of 97%. To convert the analysis data to the mentioned reference state, the Parr formulas must be used assuming that a part of the ash sulfur leaves with the volatile matter ... 

The coal exergy flow, calculated on an higher heating value (HHV) basis, is constant (525.7 MW) and clearly dominates the input stream. Most of the exergy is conserved in the gas phase, as can be seen from the respective values of gas chemical exergy flow, which reflect the cold gas efficiency to a certain extent. 

Subbituminous coal that has been subjected to an increased level of organic metamorphism, which has driven off some of the oxygen and hydrogen in the coal. That loss produces coal with higher carbon content (71%-77% on a dry ash-free basis). Subbituminous coal has a heating value between 8,300 and 13,000 Btu/lb on a mineral matter-free basis. On the basis of heating value, it is subdivided into subbituminous A, subbituminous B, and subbituminous C ranks. 

Bituminous is the most abundant rank of coal. It accounts for about 50% of the coal produced in the United States. Bituminous coal has a carbon content of between 77% and 87% on a dry ash-free basis and a heating value that is much higher than lignite or subbituminous coal. On the basis of volatile matter content, bituminous coals are subdivided into low-volatile bituminous, medium-volatile bituminous, and high-volatile bituminous. Bituminous coal is often referred to as soft coal but this designation is a Layman s term and has httle to do with the hardness of the coal. 

Relative to lignite, metamorphic processes have decreased the oxygen content and the hydrogen content to produce coal with a higher carbon content (71%-77% w/w on a dry ash-free basis) and a heating value from 8,300 to 13,000 Btu per pound (mineral matter-free basis) subbituminous coal is subdivided into the following subbituminous A coal, subbituminous B coal, and subbituminous C coal on the basis of heating value... 

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