Professionals in the oil and gas industry are continually dealing with energy expressions. The Wobbe Index may be a frequent reference, but most people can’t quote you the Gross BTU of propane off the top of their heads or give you a precise definition of Inferior Heating Value. That’s why the Analytic Experts at Rosemount Analytical are bringing you a Review of Gas Energy Expressions in today’s blog. Check it out, save it, print it. It’s your handy reference guide.
Gross Heating Value (also referred to as higher heating value [HHV]): The heating value (Btu) produced by combustion at constant pressure with the following conditions:
(a) a volume of one cubic foot
(b) 60° Fahrenheit
(c) reference base pressure
(d) with air and gas having the same temperature and pressure
(e) recovered heat from the water vapor formed by combustion
Net Heating Value (also referred to as lower heating value [LHV]): The heating value produced under conditions similar to gross heating value conditions excepting the amount of heat potentially recovered from the water vapor produced at combustion. Net heating value is always less than gross heating value.
The Relationship of Gross Heating Value and Net Heating Value
Relative Density: The ratio of the density of a gas to the density of dry air under the same pressure and temperature conditions (it’s sometimes referred to as specific gravity), relative to 1.0000 (air).
CARI value: Combustion air requirement index, the amount of air required for complete stoichiometric combustion of the fuel. CARI directly relates to Wobbe. It is the most common value used for air/fuel control.
Wobbe Index: The ratio of the gross heating value of a gas to the square root of the relative density of the gas (WI = Hv /Ö RD).
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