A total heat recovery system between the flue gas and oxidizing air of a gas-fired boiler using a non-contact total heat exchanger

Highlights: • A novel non-contact total heat recovery system of gas-fired boiler is proposed. • The oxidizing air is heated and humidified by recovering total heat of flue gas. • The temperature of boiler flue gas after heat recovery is about 30 °C in winter. • The energy saving potential is close to the system using AHP for heat recovery. • The initial investment is so low that the payback period is shorter than 1 year. - Abstract: Recovering heat from the flue gas of a gas-fired boiler can both improve boiler efficiency and decrease pollutant emissions. To improve the efficiency of the gas-fired boiler in a more cost effective and higher efficient way, a non-contact total heat recovery (NCHR) system is proposed for recovering heat from flue gas for use in heating and humidifying the oxidizing air of the boiler. A mathematical model of a boiler with an NCHR system was established, and the performance of the NCHR system was compared with that of other heat recovery systems. It is shown that the efficiency of a boiler with an NCHR system can reach 103.4% for an inlet oxidizing air temperature of 0 °C, which is 13.4% higher than the efficiency of a traditional boiler. According to the case study, the energy saving potential of a boiler with an NCHR system is 12.97% compared to that of a traditional boiler. As for the economic analysis, the payback period of a boiler with an NCHR system to traditional boiler and the condensing boiler is 1 year and 3 years, respectively. In addition, the operation cost of an NCHR system is less than that of a boiler with an absorption heat pump for heat recovery (AHPB) system, indicating that the NCHR system has obvious economic benefits.