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The heating value (or energy value or calorific value) of a substance, usually a fuel or food (see food energy), is the amount of heat released during the combustion of a specified amount of it. The calorific value is the total energy released as heat when a substance undergoes complete combustion with oxygen under standard conditions .
HCV = Higher Calorific Value (same as GCV, Gross Calorific Value) includes exhaust H 2 O condensed to liquid water Depending on which convention is used, a differences of 10% in the apparent efficiency of a gas fired plant can arise, so it is very important to know which convention, HCV or LCV (NCV or GCV) is being used.
The calorific value Q of coal [kJ/kg] is the heat liberated by its complete combustion with oxygen. Q is a complex function of the elemental composition of the coal [citation needed]. Q can be determined experimentally using calorimeters. Dulong suggests the following approximate formula for Q when the oxygen content is less than 10%:
Gross heating value accounts for water in the exhaust leaving as vapor, and includes liquid water in the fuel prior to combustion. This value is important for fuels like wood or coal, which will usually contain some amount of water prior to burning. Which definition of heating value is being used significantly affects any quoted efficiency.
The Wobbe index is expressed in MJ/Nm³ (where 'Nm³' indicates'm³ in Normal conditions), or sometimes in BTU/scf.In the case of natural gas (molar mass 17 g/mol), the typical heating value is around 39 MJ/Nm³ (1,050 BTU/scf) and the specific gravity is approximately 0.59, giving a typical Wobbe index of 51 MJ/Nm³ (1,367 BTU/scf).
Higher heating value The higher heating value (HHV) (also known as the gross calorific value or gross energy) of a fuel is defined as the amount of heat released by a specified quantity (initially at 25 °C) once it is combusted and the products have returned to a temperature of 25 °C. High-temperature shift
THis forular to estimate the CV of coal is very useful, however we could do with some more information: - full reference for this Dulong chap - is the calorific value (Q) gross or net? - are the elemental contents (C, H, O and S) 'as received' or 'dry ash free' etc. There are several other correlations which could go in to this article as well.
Gross caloric value, MJ/m 3: 43.01 Gross heating value, Btu/scf 1,093 Gross caloric value, MJ/kg 43.50 Gross heating value, Btu/gal : 150,000 Gross caloric value, MJ/kg 25.92 Gross heating value, Btu/lb 11,150 Molecular weight: 18 Specific gravity: 0.9626 Gravity, °API 15.5 Carbon/hydrogen ratio by weight 8.1 weight % carbon 61.2 weight % hydrogen