Analysis of the heat losses of a natural-gas-fired boiler and its upper thermal efficiency

Based on an analysis of the heat losses of a Shanbei natural-gas-fired boiler, the latent heat of the water vapor contained in the flue gas is quantitatively characterized at different exit flue-gas temperatures. It is concluded that the thermal efficiency of the boiler can be substantially increased if the latent heat locked in the flue gas is recovered. When the exit flue-gas temperature is reduced to 40℃, 70% of the latent heat of the water vapor in the flue gas can be recovered for a Shanbei natural-gas-fired boiler, and the thermal efficiency can be increased by 13.5%~16.6% compared to conventional boilers with an exit flue-gas temperature of 180℃~250℃. The potential for efficiency improvement depends mainly on the fuel type fired, the exit flue-gas temperature, the process fluid temperature, the low-level heat required, and the excess air etc.