【作者】 张亮；

【导师】 王怀信； 李志游；

【作者基本信息】 天津大学 ， 工程（专业学位）， 2023， 硕士

【摘要】 近年来,由于我国能源结构调整,进入油气替代煤炭的更替期,我国天然气消费快速增长,液化天然气(LNG)进口量逐年上涨。在LNG再气化过程中引入冷能发电系统,可有效回收利用LNG冷量(火用),具有重要的节能意义,有助于实现“碳达峰”、“碳中和”目标。目前,上海洋山港LNG接收站落地实施了国内首台套冷能发电装置,而对于数量众多、容量较小的LNG卫星站引入冷能发电系统的可行性,尚有待研究。本文旨在探讨LNG卫星站引入冷能发电系统,从而充分回收利用LNG冷量(火用)的可行性。通过构建与LNG卫星站工况相对应的小型LNG冷能发电系统模型,基于已有的热经济性评价指标和优化目标函数,分析不同冷能发电系统的热经济性。主要研究内容包括:(1)动力循环的选择。在系统最简和LNG冷量(火用)利用最充分两个极端目标之间,选择了直接膨胀(DE)系统、有机工质朗肯循环(ORC)系统、ORC+DE系统、并联(Parallel)ORC系统、Parallel ORC+DE系统、复叠式(Cascade)ORC系统等六种系统;(2)LNG冷能发电系统热经济性分析模型的建立。包括换热器设计,部件造价估算,系统经济分析等模块;(3)在LNG质量流量0.5～2.5 kg/s,输气压力300 k Pa,热源水温15～25 ~oC的条件下,对六种冷能发电系统开展以净输出功率最大和单位发电成本最低为双优化目标的热经济性优化研究,热经济性影响规律研究,基于优化目标函数的六种冷能系统的热经济性对比分析研究。主要研究结果如下:两种简单冷能发电系统中,DE系统各项热力性能指标和经济性指标均优于ORC系统,原因在于ORC系统的工质优选受到冷凝过程压力不低于环境大气压力这一条件的限制,使得冷凝器内循环工质与LNG之间温差超过43.50 K,ORC系统难以充分利用LNG冷量(火用)。较之ORC系统和DE系统,四种复合系统可梯级利用LNG冷量(火用),因而热力性能有所提高,但系统的复杂性导致投资成本增加。四种复合系统中,ORC+DE和Parallel ORC+DE系统的热经济性较优,值得注意的是Parallel ORC+DE系统最为复杂,投资成本最高;Parallel ORC系统中仍存在循环工质优选受冷凝器微正压要求的限制,同时投资成本增加,因此其经济性能最差;Cascade ORC系统引入了以甲烷为工质的底部循环,意在更充分的利用LNG冷量(火用),但并未给出优于ORC+DE系统和Parallel ORC+DE系统的热力性能,且经济性较差。更多还原

【Abstract】 In recent years,due to the adjustment of China’s energy structure and the replacement period of oil and gas substituting coal,the consumption of natural gas in China has grown rapidly,and the import volume of liquefied natural gas(LNG)has increased year by year.Introducing a cold exergy power generation system in the LNG regasification process can effectively recover and utilize the cold exergy of LNG,which has significant energy-saving significance and helps to achieve the goals of"carbon peak"and"carbon neutrality".Currently,the first cold exergy power generation device in China has been implemented at the Shanghai Yangshan Port LNG receiving station.However,the feasibility of introducing cold exergy power generation systems for numerous small-capacity LNG satellite stations remains to be studied.This article aims to explore the feasibility of introducing cold exergy power generation systems in LNG satellite stations to fully recover and utilize the cold energy of LNG.By constructing a small-scale LNG cold exergy power generation system model corresponding to the working conditions of LNG satellite stations,based on existing thermal-economic evaluation indicators and optimization objective functions,the thermal-economic performance of different cold exergy power generation systems is analyzed.The main research content includes:(1)selection of power cycles.Among the extremes of the simplest system and the most complete utilization of LNG cold exergy,six systems were selected:direct expansion(DE)system,organic Rankine cycle(ORC)system,ORC+DE system,parallel ORC system,parallel ORC+DE system,and cascade ORC system;(2)establishment of thermal-economic analysis model for LNG cold exergy power generation system.Including heat exchanger design,component cost estimation,and system economic analysis modules;(3)under the conditions of LNG mass flow rate of 0.5-2.5 kg/s,gas transmission pressure of 300 k Pa,and heat source water temperature of 15-25°C,six cold exergy power generation systems were studied for thermal-economic optimization with the dual optimization objectives of maximum net output power and minimum unit power generation cost,as well as research on the impact of thermal-economic performance and comparative analysis of the six cold exergy systems based on optimization objective functions.The main research results are as follows:In the two simple cold exergy power generation systems,the thermal and economic performance indicators of the DE system are superior to those of the ORC system.The reason is that the optimal selection of working fluids for the ORC system is limited by the condition that the pressure in the condenser should not be lower than atmospheric pressure,which causes a temperature difference of over 43.50 K between the circulating working fluid and LNG in the condenser,making it difficult for the ORC system to fully utilize the cold exergy of LNG.Compared with the ORC and DE systems,the four composite systems can cascade utilize the cold exergy of LNG,thus improving the thermal performance,but the complexity of the system increases the investment cost.Among the four composite systems,the thermal-economic performance of the ORC+DE and parallel ORC+DE systems is better,and it is noteworthy that the parallel ORC+DE system is the most complex and has the highest investment cost.The parallel ORC system still has the limitation of optimal working fluid selection due to the requirement of a slightly positive pressure in the condenser,and the investment cost increases,resulting in the worst economic performance.The cascade ORC system introduces a bottom cycle using methane as the working fluid,aiming to make full use of the cold exergy of LNG,but it does not give better thermal performance than the ORC+DE and parallel ORC+DE systems,and its economic performance is poorer.更多还原