Total heat recovery of gas boiler by absorption heat pump and direct-contact heat exchanger

• A new technology for condensing heat recovery from gas boiler is presented.
• Absorption heat pump and direct-contact heat exchanger are combined in this system.
• Field test shows that the temperature of the flue gas can be cooled below 30 °C.
• This technology can improve the heat capacity of gas boiler by nearly 12%.

This paper presents a new technology which combines the absorption heat pump and the direct-contact heat exchanger. Based on the analysis of natural gas features and thermal efficiency of the gas boilers, it analyzes existing and new techniques for heat recovery, focusing upon removing heat from the flue gas to a point where it can be below the dew point as significant to realizing the total heat recovery for the gas boiler. Through field test and experimental analysis of an actual case in a district heating system operating at various system load, this paper strives to identify challenges related to high return water temperature, achieving a low-temperature cold source, and enhancing the heat transfer effect; while observing if the system performance is satisfactory, and whether the system can achieve very stable performance under different working conditions and realize the total design heat capacity improvement of 12%. Data will be examined for boiler load and its influences on the condensing rate with suggestions for further improvements.