Effect of gas nonlinearity on boilers equipped with vapor-pump (BEVP) system for flue-gas heat and moisture recovery
Lin Fu and
Energy, 2020, vol. 198, issue C
Conventional condensing heat exchangers are considered inefficient in the recovery of surplus heat in flue gas from gas boilers. Different waste heat recovery schemes have emerged for improving the efficiency. The boilers equipped with vapor-pump system (BEVP system) is one of such schemes. This paper focuses on the investigation of gas nonlinearity effect on the overall performance of a BEVP system. It is found that gases are varied-heat-capacity fluids during heat exchange in a BEVP system. Due to gas nonlinearity effect, there is an operation limit for the Subsystem II and thereby the overall system. With the increase of thermal-network return (TNR) water temperature from 45 °C to 65 °C, the maximum system efficiency declines from 92.5% to 74.6%. Also, the maximum TNR water temperature that becomes to cause a significant adverse impact on the operation of the BEVP system appears to be 81.8 °C. To mitigate the gas nonlinearity effect, an optimized configuration is proposed for the BEVP system. Under the optimized configuration, the heat exchange efficiency of the Subsystem II is elevated considerably, namely latent heat exchange efficiency and total heat recovery efficiency both climbing by 14%. In addition, if there were infinite stages inside the Subsystem II, the total heat recovery efficiency would be 100%.
Keywords: Gas nonlinearity; Total heat recovery; Flue gas; Air humidification; Vapor pump; District heating (search for similar items in EconPapers)
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