利用中低温余热的回热有机朗肯循环性能分析

Analysis of the Performance of Recuperative Organic Rankine Cycles Utilizing a Medium and Low Temperature Waste Heat

通过选取R227ea、R600和R141b 3种典型有机干流体作为工质,在热源流体进口温度设定为典型工业锅炉排烟温度423.15 K,冷却水进口温度和环境温度分别设定为283.15 K和293.15 K的条件下,分析蒸发温度、过热度和给水加热器出口处工质温度对回热有机朗肯循环性能的影响,比较回热有机朗肯循环与基本有机朗肯循环的性能。结果表明:随着蒸发温度的增大,循环总不可逆损失减小,循环热效率和第二定律效率增大,而循环输出净功率则先增大后减小;随着过热度的增大,循环总不可逆损失和循环输出净功率均减小,而循环热效率和第二定律效率的变化趋势则因工质而有所不同;随着给水加热器出口处工质温度的增大,循环总不可逆损失和循环输出净功率不断降低,而循环热效率和第二定律效率则先增后减;在相同工况下,回热有机朗肯循环的循环热效率和第二定律效率高于基本有机朗肯循环,但对于循环输出净功率和循环总不可逆损失,结果则相反。

The organic Rankine cycles are regarded as an effective approach for recovering and utilizing the medium and low temperature waste heat and to additionally design and arrange a recuperative link can use a part of heat originally transferred to the heat sink to heat the supercooled liquid working medium and reduce the heat absorbed from the heat source,thus enhancing the thermal efficiency of the cyclic system. With three kinds of typical organic dry fluid R227 ea,R600 and R141 b being chosen as the working medium respectively,under the condition that the temperature of the fluid in the heat source at the inlet was set at the typical flue gas temperature of 423. 15 K for industrial boilers and the temperature of the cooling water at the inlet and ambient temperature were set at 283. 15 K and293. 15 K respectively,the authors analyzed the influence of the vaporization temperature,superheating degree and the temperature of the working medium at the outlet of the feedwater heater on the performance of the recuperative organic Rankine cycle and compared the performance of the recuperative organic Rankine cycle and the basic organic Rankine cycle. It has been found that with an increase of the vaporization temperature,the total irreversible loss of the cycle will decrease and the thermal efficiency of the cycle and that of the second thermodynamic law will also increase while the net output power of the cycle will first increase and then decrease. With an increase of the superheating degree,both total irreversible loss and net output power of the cycle will decrease while the variation tenden-cy of the thermal efficiency of the cycle and that of the second thermodynamic law will somewhat differ depending on the working medium chosen. With an increase of the temperature of the working medium at the outlet of the feedwater heater,the total irreversible loss and net output power of the cycle will keep declining while the thermal efficiency of the cycle and that of the second thermodynamic law will first increase and then decrease. Under the same operating condition,the thermal efficiency of the recuperative organic Rankine cycle and that of the second thermodynamic law will he higher than that of the organic Rankine cycle,however,those results of the net output power andtotal irreversible loss of the cycle will be to this contrary.