The temperature of natural gas-fired flue gas is high and its emissions waste a large amount of thermal energy. Recovery of waste heat is important to increase energy utilization efficiency. Four waste heat recovery techniques for natural gas-fired flue gas

including wall-type heat exchange

heat pipe exchanger and heat recovery by sprinkler + heat pump as well as flue gas cascade heat transfer(‘three towers' heat transfer) are systematically analyzed. The technical route of each technology and current research status are summarized. The advantages and limitations of the four techniques are explored

and the waste heat recovery and economy of the four technologies are compared quantitatively under the same operation conditions. The results show that

due to high dew point(50～57 ℃) of flue gas with considerable latent heat

the waste heat recovery technologies based on total heat transfer can fully recover the latent heat of the natural gas-fired flue gas below dew point

and improve the heating capacity by more than 9%

which has high economic efficiency.