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.


ABB

Asea Brown Boveri

AFBC

Atmospheric fluidized-bed combustion

Anthracite

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

APC

Advanced pulverized coal

APS

Advanced power system

AR&ET

Advanced research and environmental technology

AR&TD

Advanced research and technology development

ATS

Advanced turbine system


Baseload

Baseload is the minimum amount of power required during a specified period at a steady state.

Bbl

Barrel

Bituminous coal

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

Btu

British thermal unit


CAAA

Clean Air Act amendments

CCT

Clean coal technology

CCTC

Clean Coal Technology Coalition

CE

Combustion Engineering

CH4

Methane

Cl

Chlorine

CO

Carbon monoxide

CO2

Carbon dioxide



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