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CO_(2)跨临界—有机朗肯复合循环的简单计算与特征分析

Simple Calculation and Characteristic Analysis of the Trans-critical CO_(2)-ORC Combined Cycle and the Correspondent Design Strategies
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摘要 由于我国地热资源以低品位热能为主,增强型地热系统在发电方面的应用会受限于过低的热效率。理论上,如直接将超临界CO_(2)与有机工质进行混合,确实有可能提升热动力系统的机械效率。根据该流程设计,对部分参数范围内的CO_(2)跨临界—异丁烷复合循环的效率进行了估算。计算使用了流量分别为1 kg/s的CO_(2)和0.25 kg/s的异丁烷流体。计算结果显示,特定状态下的超临界CO_(2)在膨胀为气态的过程中焦—汤效应显著,流体混合使得异丁烷先蒸发汽化,然后在膨胀中发生冷凝,使得膨胀机内部出现了两相流。冷凝后的异丁烷工质可再次注入压缩机与气体CO_(2)接触,使得CO_(2)升温减缓,同时自身获得预热。可借助异丁烷工质降低CO_(2)的温变范围,改变CO_(2)膨胀和压缩过程中的多变指数,使其更接近等温过程而非绝热过程,进而提高膨胀和压缩过程的效率。因此,该循环具备显著提高低品位CO_(2)热动力循环效率的潜力,在未来可用于基于CO_(2)的地热发电技术。 The application of geothermal power in China is limited by its low efficiency since most geothermal reservoirs developed for enhanced geothermal system are low grade heat source,which is not suitable for both water and CO_(2) to generate power effectively.Theoretically,a direct blending of supercritical carbon dioxide and organic working fluid may probably improve the mechanical efficiency of thermal power system,specifically in the CO_(2) based enhanced geothermal system(EGS).According to the process design,the efficiency of the CO_(2) transcritical-isobutane composite cycle is estimated within the parameter range.CO_(2) and isobutane flows of 1 kg/s and 0.25 kg/s were used in the calculation.Results showed that:with the decompression of scCO_(2) component,the Joule-Thomson effect of CO_(2) will come into play,leading to the condensation of organic working fluid,and thus the presence of multi-phased flow in the expander.From the computation,the condensates,if properly be re-utilized in the compression processes,will drastically shorten the range of temperature change of CO_(2) and reduce the energy cost for the compressors,while preheating the organic working fluid,paving the way for the fluids blending to complete the cycle.With mass flow rate 4∶1 for CO_(2) and isobutaneand a group of initial states of the working fluids carefully selected,increased efficiency can be expected from the design schematics,making the prototype a potentially promising candidate in low grade heat power generation and utilization for CO_(2)-based EGS in the future.
作者 周康 吕心力 余浩 庄庆祥 Zhou Kang;Lü Xinli;Yu Hao;Zhuang Qingxiang(Energy Research Association of Zhejiang Province, Hangzhou Zhejiang 310014, China;State Key Laboratory of Clean Energy Utilization, Zhejiang University, Hangzhou Zhejiang 310027, China;Department of Energy and Power Engineering, Tianjin University, Tianjin 300354, China;Academicians and Experts Workstation, Fujiansheng Xianghe Geothermal Exploitation Co., Ltd., Zhangzhou Fujian 363000, China)
出处 《工程地球物理学报》 2022年第1期43-50,共8页 Chinese Journal of Engineering Geophysics
关键词 增强型地热系统 二氧化碳 多变指数 热效率 enhanced geothermal system carbon dioxide polytropic index efficiency
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