Investigation of the polygeneration system integrated with gas engine-driven heat pump system and CO2 Brayton cycle for waste heat recovery

Abstract

A gas engine-driven heat pump system could provide cooling and heating, and fully recover the waste heat. The temperature of the waste heat recovered from the gas engine cylinder jacket and exhaust gas was more than 90℃ and 350℃, respectively. The supercritical CO2 Brayton power cycle is considered a promising primary mover of the combined cooling, heating, and power system to potentially provide higher efficiency. Therefore, a polygeneration system composed of gas engine-driven heat pump system and CO2 Brayton cycle was proposed for cooling, heating, and electricity. Experiments of gas engine-driven heat pump system were conducted and the performances were also investigated in the cooling mode. Meanwhile, the thermodynamic performances of the CO2 Brayton cycle were analyzed. The results indicated that the cooling capacity and waste heat increased with the increase of gas engine speed and decreased with the decrease of evaporator water inlet temperature, the primary energy ratio was 1.032, 0.963, and 0.893 at the gas engine speeds of 1260 r/min, 1510 r/min, and 1820 r/min, respectively, and the increasing range was over 43.5 %. In addition, the maximum net power output of CO2 Brayton cycle was 0.97, 1.68, and 2.14 kW, and the gas engine fuel economy was 12.05, 12.35, and 12.10 kg/kWh at the gas engine speeds 1260 r/min, 1510 r/min, and 1820 r/min, respectively. The decreasing range of gas engine fuel with CO2 Brayton cycle system was 8.6 %, 12.3 %, and 12.5 %, respectively.