低温有机朗肯循环余热回收系统的工质优选

发布时间：2019-06-26 21:46

【摘要】：有机朗肯循环(Organic Rankine Cycle)以低沸点有机物为系统循环工质,吸收低温热能,推动膨胀机膨胀做功,其开发利用对提高能源利用率,减少环境污染具有重要意义。本文以热力学定律为依据,首先建立纯工质ORC系统模型,同时根据纯工质的选取原则,选取了R600、R601、异己烷、己烷、R601a、环己烷、庚烷、新戊烷、R123、R365mfc、R141b、R245ca、R245fa、苯十四种低沸点有机物作为系统工质,从热力学特性和经济特性两个方面,对纯工质ORC系统进行研究,结果表明,大部分烷类工质的热效率和压比相对其他类工质较高,而所需质量流量远小于其他类工质,且烷类工质cyclohexane以其较高的热效率、较低的单位功量质量流量和UA等特性,被认为是低品位余热回收系统中较理想的循环工质。其次,考虑到纯工质在换热过程中的缺点,对混合工质ORC系统进行分析,文中选取了具有阻燃特性的HFC类工质R245fa和循环性能较好的HC类工质cyclohexane组成非共沸混合物,同时建立非共沸混合工质ORC系统模型,以?损之比、系统热效率、压比、不可逆损失及UA等作为性能指标,从焓差与温度之间的线性度、热力学特性和经济特性三个方面对纯工质和混合工质的性能进行比较,结果表明,混合工质的?损之比和斜率平方差较纯工质更小,焓差和温度之间的线性度更好,换热过程更接近理想换热;大部分混合工质的热效率、系统净功量均高于纯工质,热力学性能较优,但其UA和质量流量也高于纯工质,经济特性较纯工质稍弱。同时,混合工质R245fa+cyclohexane(0.8,0.2)以其最低的?损之比和斜率平方差,最高的热效率和系统净功量,被认为是较纯工质更适合烟气余热回收系统的循环工质。
[Abstract]:The organic Rankine cycle (Organic Rankine Cycle) takes the low boiling point organic matter as the system circulation working fluid, absorbs the low temperature heat energy, promotes the expander to do the work, its development and utilization is of great significance to improve the energy utilization rate and reduce the environmental pollution. In this paper, based on the law of thermodynamics, the ORC system model of pure working fluid is established. At the same time, according to the selection principle of pure working fluid, the pure working fluid ORC system is studied from two aspects of thermodynamic and economic characteristics. The results show that the pure working fluid ORC system is studied from two aspects of thermodynamic and economic characteristics. The results show that R365mfc, R141b, R245ca, R245fa, benzene 14 kinds of low boiling point organic matter are used as working fluid in the system, and the pure working fluid ORC system is studied from two aspects of thermodynamic and economic characteristics. The thermal efficiency and pressure ratio of most alkane refrigerants are higher than those of other refrigerants, and the required mass flow rate is much lower than that of other refrigerants. Cyclohexane is considered to be an ideal circulating working fluid in low-grade waste heat recovery system because of its high thermal efficiency, low unit power mass flow rate and UA. Secondly, considering the shortcomings of pure working fluid in the heat transfer process, the mixed working fluid ORC system is analyzed. In this paper, the HFC working fluid R245fa with flame retardant property and the HC working fluid cyclohexane with good cycle performance are selected to form the non-azeotropic mixture. At the same time, the non-azeotropic mixed working fluid ORC system model is established. The ratio of loss, thermal efficiency, pressure ratio, irreversible loss and UA are used as performance indexes to compare the performance of pure working fluid and mixed working fluid from three aspects: linearity, thermodynamic and economic characteristics between enthalpy difference and temperature. The loss ratio and slope square difference are smaller than those of pure working fluid, the linearity between enthalpy difference and temperature is better, and the heat transfer process is closer to the ideal heat transfer process. The thermal efficiency of most mixtures is higher than that of pure working fluid, and the thermodynamic performance of the system is better, but its UA and mass flow rate are also higher than those of pure working fluid, and the economic characteristics are slightly weaker than those of pure working fluid. At the same time, the mixed working fluid R245fa cyclohexane (0.8, 0.2) is the lowest. The ratio of loss to slope square difference, the highest thermal efficiency and the net power of the system are considered to be more suitable for circulating working fluid of flue gas waste heat recovery system than pure working fluid.
【学位授予单位】：华北电力大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TK115

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