A New System of Absorption Heat Pump Vs. Boiler for Recovering Heat and Water Vapor in Flue Gas

Abstract

Conventional natural gas-fired boiler exhaust flue gas contained large amount of waste heat and water vapor direct to the atmosphere at high temperature which results in relatively low thermal efficiency. In traditional ways only a part of sensible heat are recovered. The latent heat, contained in the water vapor, which is the majority of the waste heat in the flue gas, cannot be recovered. Using a heat pump system with a boiler, the temperature of flue gas of the boiler can be drooped to dew point and the waste heat in the flue gas and condensation heat can be recovered deeply. In this paper, a new type of system, absorption heat pump vs. boiler, is proposed in which the waste and vapor in flue gas can be recovered efficiently. In this system, not only the evaporator is used to absorb the waste heat from flue gas, but also the generator is used to get the heat from the flue gas at high temperature. At the same time, a heat exchanger is used to transfer the heat from the flue gas to the backwater. A collector is installed on the evaporator to collect the condensed water from flue gas which will be used to a feed-water for the boiler room after they are purified. The performance of system is evaluated basing on a practical project, the installed capacity of which is 31.5MW. Results show that with the system, 13793.84MJ of heat is recovered per hour, in a whole heating season, 1.14 million cubic meter of natural gas will be saved. The efficiency of boiler rises about 11.8%. The recycled condensed water is 1177.344m3. 227 tons of CO2 can be cut into atmosphere per year.