基于[火积]耗散理论的烟气-水接触式换热优化

Study on Reducing Entransy Dissipation of Gas-Water Heat Transfer by Two-Segment Spraying

天然气作为供热能源在北方城市得以广泛应用,其燃烧产生的烟气中含有大量余热,采用接触式换热可实现对其高效回收.本文基于[火积]耗散理论,研究如何减少接触式换热中的[火积]耗散以提高换热效率.本文推导了烟气-水接触式换热表达式,从而得到烟气-水换热曲线方程,并对一段喷淋中的烟气-水换热流程进行了改进,分析了烟气-水换热产生的[火积]耗散及本文的优化方向:如何减少烟气露点温度以下的烟气-水换热[火积]耗散.研究了在两段喷淋方式下,如何选择分段点可使得[火积]耗散最小,并以设计排烟温度30℃为例进行了具体计算,进而得到了不同典型热源在不同排烟温度下对应的喷淋水分段点温度.当设计排烟温度为30℃时,对于典型燃气锅炉和热电厂,相对于一段喷淋,两段喷淋下的[火积]耗散可分别减少58%和29%以上.

As heating energy,natural gas has been widely used in northern cities. There is a lot of waste heat in the flue gas,which can be recovered efficiently through contact heat exchange. Based on entransy dissipation,this paper studied how to reduce the entransy dissipation in the contact heat exchange to improve the heat exchange efficiency. Gas-water heat-transfer equations were derived to obtain heat transfer curve equation. Gas-water heat exchange was partially optimized in single-segment spraying and the entransy dissipation was analyzed. So,the optimization direction of entransy dissipation was defined: how to reduce gas-water entransy dissipation under dew point of flue gas. By two-segment spraying ways,this paper studied how to find segment points to minimum gaswater entransy dissipation. Taking flue-gas temperature of 30 ℃ as an example,calculation was carried out,and then the spraying water temperature of segment points corresponding to different typical heat sources under different flue-gas temperature was obtained. When flue gas temperature was designed as 30 ℃,in typical gas-fired boiler and thermal power plant,entransy dissipation of two-segment spraying can be respectively decreased by over 58%and 29% compared with single-segment spraying.