采用螺杆膨胀机的ORC系统特性试验研究
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摘要
有机工质朗肯循环(Organic Rankine cycle,ORC)能回收工业余热产生高压蒸气,并由膨胀机输出机械功,是一种具有广泛应用前景的节能技术。工质泵和膨胀机作为ORC循环运行的两大核心机械,实现不同热源流量或温度条件下,工质泵频率和膨胀机转速的匹配,可有效提高ORC循环效率。基于ORC循环的热力学分析,选用R245fa作为循环工质,采用适用性广、可靠性高的螺杆膨胀机,设计并搭建了ORC系统试验台,根据试验结果,重点研究螺杆膨胀机转速、工质泵频率及蒸发器出口过热度对系统性能的影响。结果表明:膨胀机转速的增加会使得系统中工质的循环流量上升,但对蒸发压力的影响较小;存在与工质泵频率相匹配的最佳膨胀机转速,使得系统的循环热效率达到最大;工质泵频率增加时,工质的循环流量和蒸发温度也随之增大,蒸发器换热量、膨胀机输出功率及系统循环热效率都有所上升;蒸发器出口过热度的变化基本不会影响系统热效率。
The organic Rankine cycle(ORC) is a promoting energy saving technology which recycles the heat of low temperature and converts it to mechanical power. The expander as a key component has great influence on the system's efficiency. Among different types of expander, twin-screw expanders draw much attention due to its advantages of high reliability, strong adaptability and less parts. An ORC system with twin screw expander is designed and a corresponding test rig is developed choosing R245 fa as its working fluid. Then, an experimental study of the ORC system is carried out to analyze the influence of the expander speed, working medium pump frequency and the superheat degree of the vapor into the expander. The results show that the mass flow rate of working fluid increases with the increase of expander rotational speed, but the evaporating pressure is less affected by the expander speed. The system efficiency exists an optimal value when the expander speed matches well with the pump frequency. The mass flow rate of working fluid and the evaporating pressure increase with the increase of working medium pump frequency. As a result, the expander output power and system efficiency will also increase. The superheat degree of working fluid has little effect on the system efficiency.
The organic Rankine cycle(ORC) is a promoting energy saving technology which recycles the heat of low temperature and converts it to mechanical power. The expander as a key component has great influence on the system's efficiency. Among different types of expander, twin-screw expanders draw much attention due to its advantages of high reliability, strong adaptability and less parts. An ORC system with twin screw expander is designed and a corresponding test rig is developed choosing R245 fa as its working fluid. Then, an experimental study of the ORC system is carried out to analyze the influence of the expander speed, working medium pump frequency and the superheat degree of the vapor into the expander. The results show that the mass flow rate of working fluid increases with the increase of expander rotational speed, but the evaporating pressure is less affected by the expander speed. The system efficiency exists an optimal value when the expander speed matches well with the pump frequency. The mass flow rate of working fluid and the evaporating pressure increase with the increase of working medium pump frequency. As a result, the expander output power and system efficiency will also increase. The superheat degree of working fluid has little effect on the system efficiency.
引文
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[3]RAYEGAN R,TAO Y X.A procedure to select wotking fluids for solar organic Rankine cycles(ORCs)[J].Renewable Energy,2011,36(2):659-670.
[4]张新欣,何茂刚,曾科,等.发动机余热利用蒸气动力循环的工质筛选[J].工程热物理学报,2010,31(1):15-18.ZHANG Xinxin,HE Maogang,ZENG Ke,et al.Selection of working fluid used in vapor power cycle for waste heat recovery of vehicle engine[J].Journal of Engineering Thermophysics,2010,31(1):15-18.
[5]汪健生,岳开红.窄点温差匹配对ORC系统性能的影响[J].机械工程学报,2017,53(8):158-165.WANG Jiansheng,YUE Kaihong.Effect of pinch point temperature difference assignment on the thermal perfoemance of ORC system[J].Journal of Mechanical Engineering,2017,53(8):158-165.
[6]ALJUNDI I H.Effect of dry hydrocarbons and critical point temperature on the efficiencies of organic Rankine cycle[J].Renewable Energy,2011,36(4):1196-1202.
[7]HUNG T C,WANG S K,KUO C H,et al.A study of organic working fluids on system efficiency of an ORC using low-grade energy sources[J].Energy,2010,35(3):1403-1411.
[8]BAO J,ZHAO L.A review of working fluid and expander selections for organic Rankine cycle[J].Renewable and Sustainable Energy Reviews,2013,24:325-342.
[9]LIU B,CHIEN K,WANG C.Effect of working fluids on organic Rankine cycle for waster heat recovery[J].Energy,2004,29(8):1207-1217.
[10]CHEN H,GOSWAMI D Y,STEFANAKOS E K.A review of thermodynamic cycles and working fluids for the conservation of low-grade heat[J].Renewable and Sustainable Energy Reviews,2010,14(9):3059-3067.
[11]SALEH B,KOGLBAUER G,WENDLAND M,et al.Working fluids for low-temperature organic Rankine cycles[J].Energy,2007,32(7):1210-1221.
[12]LI W,FENG X,YU J L,et al.Effects of evaporating temperature and internal heat exchanger on organic Rankine cycle[J].Applied Thermal Engineering,2011,31(17-18):4014-4023.
[13]邢子文,崔天生,束鹏程.滑片膨胀机基本特性的实验研究[J].西安交通大学学报,1998,32(1):38-41.XING Ziwen,CUI Tiansheng,SHU Pengcheng.Experimental investigation on the fundamental performance of rotary vane expander[J].Journal of Xi’an Jiaotong University,1998,32(1):38-41.
[14]刘广彬,赵远扬,李连生,等.小型低温余热发电系统膨胀机输出特性实验研究[J].西安交通大学学报,2009,43(11):100-103.LIU Guangbin,ZHAO Yuanyang,LI Liansheng,et al.Experiment on output characteristics of scroll expander in small power generation system with low–temperature waste heat[J].Journal of Xi’an Jiaotong University,2009,43(11):100-103.
[15]CHANG J,HUNG T,HE Y,et al.Experimental study on low-temperature organic Rankine cycle utilizing scroll type expander[J].Applied Energy,2015,155:150-159.
[16]张业强,吴玉庭,夏国栋,等.单螺杆膨胀机在有机朗肯循环系统中的性能研究[J].机械工程学报,2015,51(16):156-163.ZHANG Yeqiang,WU Yuting,XIA Guodong,et al.Performance study on single-screw expander in organic rankine cycle system[J].Journal of Mechanical Engineering,2015,51(16):156-163.
[17]吴华根,唐昊,陈文卿,等.双螺杆水蒸气膨胀机的研究与开发[J].西安交通大学学报,2014,48(3):1-5.WU Huagen,TANG Hao,CHEN Wenqing,et al.Research and development of steam twin screw expander[J].Journal of Xi’an Jiaotong University,2014,48(3):1-5.
[18]TANG H,WU H G,WANG X L,et al.Performance study of a twin-screw expander used in a geothermal organic Rankine cycle power generator[J].Energy,2015,90:631-642.