If liquid-fuels are burned, the boiler efficiency is calculated with the direct method, by developing a balance between the heat introduced to the boiler and the usable heat. In case, when the boiler is fuelled with solid fuels – an indirect method is used. In this case one calculates heat losses that allow the non-measurable chemical energy stream supplied with the fuel to be balanced.
Boiler efficiency calculations are possible both if only primary fuels is burner as well as when multiple types of fuels are burned at the same time, e.g. coal and sludge; coal sludge and oil; coal and biomass. This allows boiler’s main heat losses to be also calculated with consideration for current operating conditions, including the volume of additive supplied in order to reduce the sulphur dioxide.
Boiler’s flue gas loss (being the main heat loss) as a function of oxygen content in combustion gas and flue gas temperature at the boiler outlet. This family of curves and the operating point are determined individually for current boiler operating conditions, e.g. air excess, temperature and flue gas moisture. Wszelkie Prawa Zastrzezone 2006 Enerbit.