Comprehensive Analysis of Air-Flue Gas Waste Heat Recovery in Air Cooling Units

Based on detailed analysis of operation characteristics of an air cooling unit, a combined air-flue gas waste heat recovery system was proposed, in which the hot air from air cooling unit is to be heated in air preheater for purposes of boiler combustion, and simultaneously, the low temperature economizer set at boiler tail is used to heat the low-pressure condensed water, thus saving the steam extracted from steam turbine. Taking a typical 600 MW subcritical direct air cooling unit as an example, the thermodynamic characteristics and energy-saving effects of its air-flue gas waste heat recovery system were analyzed. Results show that obvious economical effects can be obtained for the air-cooling unit under typical working conditions, with an increased inlet temperature of air preheater by 25 K, a reduced power supply coal consumption by 1.93 g/(kW·h), an annually economized standard coal consumption by 7 000 t, equivalent to 7 million RMB fuel cost (based on the coal price of 1 000 RMB/t with an annual running time of 5 500 hours).