以燃煤废气为热源的LNG冷能三级利用系统

随着化石燃料的日益枯竭，回收工业过程中产生的低温余热已成为一种利用能源的重要方式，针对能量回收再利用的问题，将低温燃煤废气（70℃）及LNG（-162℃）冷能进行联合利用，以朗肯循环为基础，设计了一种可以在发电的同时，对CO₂进行液化的LNG冷能三级式利用系统。详细分析了膨胀机入口压力和温度对LNG冷能三级式利用系统热力性能的影响，确定了循环参数，利用HYSYS进行模拟计算，并与之相对应的LNG冷能二级式利用系统进行比较。结果表明：设计的三级式系统发电单元的热效率及（火用）效率较二级式系统分别提升了57.74%及36.67%；三级式系统总净输出功较二级式系统提升了61.16%，按90%发电效率，0.5元/（kW·h）电价计算，三级式系统每年可带来约52万元的经济效益，CO₂液化量为1580kg/h，每年可减排约CO₂ 1.365×10⁴t，具有可观的经济效益和较好的减排效果。

A three-stage utilization system of LNG cold energy with coal-fired waste gas heat source

With the increasing depletion of fossil fuels, recovering industrial low temperature waste heat is becoming an effective way to save energy. Aimed at the problem of energy recovery and reuse, based on the organic Rankine cycle and using low-temperature coal-fired waste gas (about 70℃) and cold energy of liquefied natural gas (LNG, about -162℃), this paper presents a three-stage system by which CO₂ liquefaction and power generation are achieved. The effects of expander inlet pressure and temperature on thermal performance of the LNG three-stage cold energy utilization system were analyzed in detail, and the optimal cycle parameters were obtained. HYSYS software simulation for the system was done with comparative analysis on a three-stage system and a two-stage system. The results show that for a three-stage cold energy utilization system, the thermal efficiency and energy efficiency of the generating unit increased 57.74% and 36.67% compared to those of a two-stage system;the net work output was 61.16% greater than that of a two-stage system. According to the efficiency of 90% power generation and 0.5 Yuan/(kW·h) calculation, the three-stage cold energy utilization system can result in saving of 0.52 million RMB every year. At the same time, the CO₂ liquefaction capacity is 1580kg/h which can reduce emission of CO₂ about 1.365×10⁴t/a. The system can bring considerable economic benefit and achieve better emission reduction.