Solid Fuels Coals and Cokes

Specific enthalpy of combustion reported per unit mass of fuel (i.e., C, H, S) 

Fusain consists of opaque to translucent irregularly shaped masses. On the other hand, the microscopical examination of polished coal carried out under reflected light, a methodology first initiated in France, led to four different classes also called lithotypes (macerals) vitrain, clarain, durain, and fusain. Each group is characterized by a particular reflectivity and aspect. The major maceral groups are vitrinite, exinite and inertinite. 

The quantitative characterization of coals and cokes can be performed in several ways. Usually, a classical ultimate chemical analysis provides the elemental chemical composition usually expressed in mass percentages of the major elements such as carbon (C), hydrogen (H) and oxygen (O), minor elements like sulfur (S) and nitrogen (N) and finally metals such as alkali and alkaline-earth metals, aluminum, iron, and vanadium. For most practical uses, the chemical composition of coal and coke are reported using the following technical characteristics  

The fixed carbon (FC) represents the mass percentage of free carbon contained in the coal or coke, as received, excluding the carbon contained in volatile matter (hydrocarbon). In theory, it corresponds to the solid residue other than ash obtained after a destructive distillation performed under inert atmosphere. In practice, it is a value calculated, according to standard ASTM D3172, by subtraction of the mass of the volatile matter, ash content and moisture, with the result being expressed as a percentage of the total mass. 

Volatile matter (VM) represents the mass percentage of compounds contained in the coal or coke given-off upon heating at 950°C but excluding moisture. In practice, it corresponds to the weight loss other than moisture determined on the sample as received according to standard ASTM D3175. 

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