LNG冷能用于朗肯循环和CO2液化新工艺

New processes for LNG cold energy utilized in Rankine cycle and CO2 liquefaction

关键词:  LNG冷能  液化CO₂  朗肯循环火用效率  敏感性分析

Key words:  LNG cold energy  CO₂ liquefaction  Rankine cycle  exergy efficiency  sensitivity analysis

摘要:

针对CO₂排放过量的问题,提出了两种利用液化天然气冷能进行朗肯循环发电和液化CO₂的新工艺流程。流程1在常规朗肯循环的基础上增加了再热循环和回热循环；流程2在保证预冷和液化CO₂所需冷能不变的情况下,在流程1的基础上集成了氮气液化系统,目的是降低蒸发器内冷热物流的品位差,提高蒸发器的火用效率。分析了烟气温度、循环工质压力和流量对流程比功和火用效率的影响。模拟计算得到,流程1、流程2的火用效率分别可达到49.70%和49.80%,对应比功分别为237.70 kJ/kg LNG和235.20 kJ/kg LNG,CO₂的液化率为0.60 kg/kg LNG。结合具体实例进行计算,证明新流程具有良好的经济效益和环境效益。

Abstract:

Based on the problems of excessive CO₂ emission, two new processes that liquefied natural gas (LNG) cold energy is utilized for Rankine cycle power generation and CO₂ liquefaction are proposed. Process 1 adds a reheat cycle and a regenerative cycle to the conventional Rankine cycle. Ensuring the cold energy required for pre-cooling and liquefying CO₂ to maintain constant, the process 2 integrates the nitrogen liquefaction system based on the process 1 to reduce the grade difference of the hot and cold streams in the evaporator and improve the exergy efficiency of the evaporator. The effects of exhaust gas temperature, circulating refrigerant pressure and flow rate on process specific work and exergy efficiency were analyzed. The simulation results show that the exergy efficiency of process 1 and 2 is 49.70% and 49.80% respectively, the specific work is 237.70 kJ/kg LNG and 235.20 kJ/kg LNG, and the same liquefaction rate of CO₂ is 0.60 kg/kg LNG. The calculation with a specific example proves that the new processes have good economic and environmental benefits.