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Tuesday, June 26, 2007

Bioenergy Conversion Factors

Bioenergy Conversion Factors: "This is a quick-reference list of conversion factors used by the Bioenergy Feedstock Development Programs at ORNL. It was compiled from a wide range of sources, and is designed to be concise and convenient rather than all-inclusive. Most conversion factors and data are given to only 3 significant figures. Users are encouraged to consult other original sources for independent verification of these numbers."

Energy contents are expressed here as Lower Heating Value (LHV) unless otherwise stated (this is closest to the actual energy yield in most cases). Higher Heating Value (HHV, including condensation of combustion products) is greater by between 5% (in the case of coal) and 10% (for natural gas), depending mainly on the hydrogen content of the fuel. For most biomass feedstocks this difference appears to be 6-7%.

The appropriateness of using LHV or HHV when comparing fuels, calculating thermal efficiencies, etc. really depends upon the application. For stationary combustion where exhaust gases are cooled before discharging (e.g. power stations), HHV is more appropriate. Where no attempt is made to extract useful work from hot exhaust gases (e.g. motor vehicles), the LHV is more suitable. In practice, many European publications report LHV, whereas North American publications use HHV.
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