Study on the optimal temperature for flue gas waste heat recovery of the heat pump with new working fluid

doi:10.3969/j.issn.2097-0706.2023.04.003

Abstract

Abstract:

Since the flue gas emitted from natural gas boilers is of high temperature and contains high latent heat of steam， it is worthy to be reused. To pursuit the "dual carbon" target， the waste heat in natural gas boiler flue gas is recovered by electric heat pumps with new working fluids to rise the return water temperature. In order to improve the coefficient of performance of electric heat pumps， their performances under different working conditions are studied. Six types of mixed working fluids， R134a+R245fa， R152a+R245fa， R227ea+R245fa， R134a+R142b， R152a+R142b and R227ea+R142b， show different cycling properties. Under the actual operating condition of a boiler room，the thermodynamic properties of different mixed working fluids are compared when the inlet and outlet hot water temperatures of the condenser are 50/65 ℃，and the inlet and outlet cold water temperatures of the evaporator are 40/35 ℃ or 40/30 ℃. The conclusion is that the optimal working fluid under this working condition is the mixture of R134a and R245fa whose mole fractions are 0.41 and 0.59. The benefits of the waste heat recovery system and the costs of the heat pump with the optimized flue gas temperature and selected working fluid are analysed， and the variation law of the economy of waste flue gas recovery with flue gas temperature is obtained. The analysis is beneficial for the future design of waste heat recovery systems.

Key words: dual carbon target, natural gas boiler, exhaust gas temperature, waste heat recovery, electric heat pump, mixed working fluid

CLC Number:

TK115

SUN Jian, QIN Yu, WANG Yinwu, WU Kexin, GE Zhihua. Study on the optimal temperature for flue gas waste heat recovery of the heat pump with new working fluid[J]. Integrated Intelligent Energy, 2023, 45(4): 19-25.

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物性参数	R134a	R152a	R245fa	R227ea	R142b
临界温度/℃	101.0	113.3	154.0	102.8	137.2
临界压力/MPa	4.1	4.5	3.7	3.0	4.1
分子量	102.0	66.1	134.0	170.0	100.5
汽化潜热（0 ℃）/（kJ·kg^-1）	197.0	324.2	196.1	131.0	233.0
沸点/℃	-26.2	-25.0	15.1	-17.0	-10.0

余热回收价格/（元·GJ^-1）	最佳排烟温度/℃	机组利润/（元·h^-1）
40	36	291
60	31	496
80	26	720

电价/[元·（kW·h）^-1]	最佳排烟温度/℃	机组利润/（元·h^-1）
0.5	31	496
0.7	35	446
0.9	38	412