洁净煤技术

2020, v.26;No.129(05) 70-76

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中高温烟气余热动力回收的复叠跨临界CO_2动力循环热力学分析
Thermodynamic analysis of cascading transcritical power cycle using CO_2 for waste heat recover from medium and high temperature flue gas

李成宇;高振强;高明云;高升堂;王有镗;
LI Chengyu;GAO Zhenqiang;GAO Mingyun;GAO Shengtang;WANG Youtang;School of Transportation and Vehicle Engineering,Shandong University of Technology;Shandong Yancheng Air Conditioning Co.,Ltd.;

摘要(Abstract):

工业窑炉存在大量的中高温烟气余热,现有的动力循环或工质存在难以有效回收大温降烟气余热的问题。提出以CO_2为工质的复叠跨临界动力循环,以单位质量烟气的循环净功率最大为优化目标,在400和500℃的烟气热源条件下,研究循环参数对循环性能的影响规律。重点分析了工质分流质量比、吸热压力对回热过程换热匹配特性以及循环性能的影响,并对简单循环、回热循环和复叠循环进行了优化对比。结果表明,复叠循环中,上下级循环的回热匹配是影响循环性能的重要因素,通过调节工质泵出口的工质分流比x以改善回热匹配性,烟气初温400和500℃下,最优的工质分流比0.6和0.7。吸热压力的增加有利于循环净输出功率的增加,烟气初温500℃下,吸热压力由20 MPa增至35 MPa时,净功率由117.4 kW增至143.8 kW,增幅为22.49%;对各部件而言,提高吸热压力可增加高、低温透平输出功率,但对回热功率的作用相反; 20~35 MPa内随吸热压力的升高,低温透平输出功率占比由31.4%降至27.3%,吸热压力对高温透平的性能影响更明显。对比3种跨临界CO_2循环,简单循环的热效率和净功率均最低,回热循环具有最高的热效率,复叠循环输出最高的净功率。烟气初温400℃下,复叠循环的净功率比简单循环和回热循环分别高22.2%和6.1%;烟气初温500℃下,分别高35.7%和12.5%。
Large quantities of waste heat from medium and high temperature flue gas are generated from industrial kilns. However,the present power cycles or working fluids is difficult to effectively recover the waste heat of flue gas with the temperature drop. A cascading transcritical power cycle using CO_2 as working fluids was proposed. The maximum net power output per unit mass flue gas was selected as objective function. The effects of parameters on cycle thermodynamic performance were investigated under flue gas temperature of 400 and 500 ℃ .The influence of mass split flow ratio and high pressure on thermal matching in regenerator and cycle performance were mainly analyzed. The optimization and comparative analysis was conducted among basic transcritical cycle,regenerative transcritical cycle and cascading transcritical cycle. The results indicate that the thermal matching in regenerator is key influence factor on cycle performance of the cascade cycle. By adjusting mass split flow ratio x at the outlet of the working medium pump to improve the regenerative matching,the optimal value of of working medium is 0.6 and 0.7 under flue gas temperature of 400 and 500 ℃ . The increase of endothermic pressure is beneficial to the increase of net power output,and when the endothermic pressure increases from 20 MPa to 35 MPa under flue gas temperature of 500 ℃,the net power increases from 117.4 kW to 143.8 kW,with an increase of 22.49%. The higher pressure also promotes power output for both high-and low-temperature turbines,but the deteriorates heat exchange amount in regenerator. The ratio of low-temperature turbine power output to total ranges from 31.4% to 27.3% with high pressure increasing from 20 to 35 MPa,which means that the hightemperature turbine is more affected by high pressure. Compared with the three transcritical CO_2 cycles,the basic transcritical cycle has the lowest thermal efficiency and net power output. The regenerative transcritical cycle achieves the highest thermal efficiency. The cascading transcritical cycle outputs the maximum net power. The net power output of cascading transcritical cycle is 22.2% and 6.1% higher than that of basic and regenerative cycle under flue gas temperature of 400 ℃,respectively,and the values is 35.7% and 12.5% under flue gas temperature of 500 ℃ .

关键词(KeyWords): 中高温烟气;余热回收;CO_2;复叠跨临界循环;参数优化;热力学性能
medium and high temperature flue gas;waste heat recovery;CO_2;cascading transcritical power cycle;parametric optimization;thermodynamic performance

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基金项目(Foundation): 淄博市校城融合发展计划资助项目(2019ZBXC081)

作者(Author): 李成宇;高振强;高明云;高升堂;王有镗;
LI Chengyu;GAO Zhenqiang;GAO Mingyun;GAO Shengtang;WANG Youtang;School of Transportation and Vehicle Engineering,Shandong University of Technology;Shandong Yancheng Air Conditioning Co.,Ltd.;

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DOI: 10.13226/j.issn.1006-6772.IF20080614

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