Experimental investigation on vapor-pump equipped gas boiler for flue gas heat recovery

To recycle the flue gas waste heat, a vapor-pump system is built and its performance is fully discussed in this paper. The vapor-pump system consists of a gas condenser, an air humidifier and a gas-water heat exchanger. The boiler oxidizing air is heated and humidified in the air humidifier. Thus the dew point of the boiler outlet flue gas is improved to above 60 degrees C. Then in the gas-water heat exchanger, the waste heat is recovered by the heating network return water. According to the experiment results, the exhaust flue gas temperature is reduced from 80-30.9 degrees C. The system efficiency improvement reaches over 10%. The return water temperature, the ambient air wet bulb temperature and the circulation water mass flow rate affect the system performance markedly. The system performance changes during a whole winter are simulated. Besides of energy saving, the vapor-pump system also can reduce the pollutant emission concentration. If the air is heated to over 50 degrees C, the concentration of NOx decreases from 33-24.6 ppm, the reduction is about 25.4%. The vapor-pump system achieves energy saving and emission reduction simultaneously. Techno-economic analysis is also proposed in this paper, the payback period is only 0.7 year.