In parts of Europe and elsewhere, however, the lower heating value (LHV) is commonly used in reporting thermal efficiencies. In the United States LHV is commonly used to quote efficiencies based on natural gas as a fuel. The LHV assumes that water formed in combustion remains in a vapor state, as in actual combustion systems that discharge flue gases at temperatures of several hundred degrees. Thus, the energy potentially recoverable by condensing water in the flue gas is assumed to be unavailable and not credited to the fuel. Since the LHV assumes that fuel delivers less energy input than the HHV, any thermodynamic efficiency, E, based on LHV will be higher than one based on HHV in simple inverse proportion; that is, ELHV/EHHv = HHV/LHV.
The numerical difference between LHV and HHV depends on the fuel. The difference is smallest for coal (where LHV is roughly 4 percent less than HHV) and greatest for natural gas (where LHV is about 10 percent lower). Accordingly, a power plant efficiency of 40 percent based on HHV would be reported as 42 percent based on LHV using coal and about 44 percent based on LHV using natural gas.
Asea Brown Boveri
Atmospheric fluidized-bed combustion
Highest rank of economically useable coal, with a heating value of 15,000 Btu per pound, carbon content of 86 to 97 percent, and moisture content of less than 15 percent
Advanced pulverized coal
Advanced power system
Advanced research and environmental technology
Advanced research and technology development
Advanced turbine system
Baseload is the minimum amount of power required during a specified period at a steady state.
Type of coal most commonly used for electric power generation, with a heating value of 10,500 to 15,000 Btu per pound, carbon content of 45 to 86 percent, and moisture content of less than 20 percent
British thermal unit
Clean Air Act amendments
Clean coal technology
Clean Coal Technology Coalition