Waste Heat Recovery System Using Coal-Fired Boiler Flue Gas to Heat Heating Network Return Water

At present, exhaust flue gas temperature of coal-fired boiler is generally above 120 °C, while the temperature of boiler burning high sulfur coal may be higher in China. Meanwhile, the boiler burns large amount of fuel to heat the heating network return water to the supply temperature. A specially designed waste heat recovery system, which can reduce exhaust flue gas temperature to 60–70 °C and recycle large amount of sensible heat and latent heat in the flue gas to heat the return water, is designed. This paper included three parts. In the first part, the return water temperature duration in the heating season of 99, 64, 29 MW boilers which are three typically used in Harbin are calculated. The feasibility of the system is verified with the results that the return water temperature kept lower than 55 °C for a long period of time. In the second part, the system implementation plan including the material of heat transfer equipment and the choice of heat pump concerned are discussed. The titanium alloy plate heat exchanger and first absorption heat pump are selected. Then thermodynamic and hydraulic calculations of the system are done to determine the amount of flue gas heat recovery, structure of water spray chamber, plate heat exchangers, and absorption heat pump design. In the third part, the dynamic payback periods of waste heat recovery system used in these three boilers are calculated and the results are less than the life cycle of the heat recovery system.