Info

Qloss

= heat losses (Btu/hr),

Ldf

= dry flue gas heat loss (%),

Lfh

= fuel hydrogen heat loss (%),

Lam

= combustion air moisture heat loss (%),

Lrad

= radiation heat loss (%),

Lconv

= convection heat loss (%),

Linc

= incombusted fuel loss (%),

Lbd

= blowdown heat loss (%),

Lunacct

= unaccounted for heat losses (%).

Using this method the flue gas losses (sensible and latent heat) due to radiation and convection, incomplete combustion, and blowdown are accounted for. in most boilers the flue gas loss is the largest loss, which can be determined by a flue gas analysis. Flue gas losses vary with flue gas exit temperature, fuel composition and type of firing.110 Radiation and convection loss can be obtained from the standard curves.111 Unaccounted for heat losses can also be obtained from published industry sources,112 which cite losses of 1.5% for solid fuels, and 1% for gaseous or liquid fuel boilers. Losses from boiler blowdown should also be measured. Typical values can be found in various sources.113'114

Indirect Combustion Method

The indirect combustion method can also be used to measure boiler efficiency. The combustion efficiency is the measure of the fraction of fuel-air energy available during the combustion process, calculated from the folowing:115,116

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