Abstract:

An improved ammonia-power cycle activated by low temperature waste heat is operated under three pressure stages,which consists of two turbines. Since there exists many degrees of freedom for ammonia-water power cycle and they are coupled, once the waste heat and condensation temperature are fixed, the selection range of degrees of freedom like three pressure levels and ammonia mass fraction are confined by the cycle constraints. A graphic aid is proposed to select the optimum cycle with various pairs of waste heat temperature and turbine inlet pressure under fixed condensation temperature. For the typical working condition like waste heat and condensation temperature of 190℃ and 30℃, the optimization results shows that the thermal efficiency of 21.6% is obtained and the corresponding second law efficiency is 62%. The thermal efficiency is increased by around 8% when the temperature of waste heat is from 130℃ to 190℃ under a fixed turbine inlet pressure(3500 kPa). The improved cycle increases the performance compared with Rankine cycle and ORC cycle in low temperature waste heat application (>150℃).

Key words: binary mixture, thermodynamics, optimization, ammonia water solution, power cycle, Kalina cycle

摘要：

提出了一种高效利用余热的以氨水溶液为工质的三级压力动力循环，该循环包含了两个膨胀做功过程。由于氨水动力循环存在多个自由度且耦合在一起，当余热温度和冷凝温度确定时，循环约束条件能确定高、中、低压力和氨质量分数自由度的取值范围。当冷凝温度确定时，对于不同的余热温度和膨胀机进口压力，最佳循环的选择可以用图表显示且做出参考。在典型工况下当余热温度190℃、冷凝温度30℃时，以热效率为目标函数的优化计算结果表明热效率为21.6%，相应的热力学第二效率为62%。当膨胀机进气压在3500 kPa时，余热温度在130～190℃范围内，与KCS11相比改进循环的热效率提高了8%。在低温余热下（>150℃），改进循环的热效率要明显高于Rankine循环和ORC循环。

关键词: 二元混合物, 热力学, 优化, 氨水溶液, 动力循环, Kalina循环