Abstract:

In order to capture carbon dioxide (CO₂) from the flue gas of a natural gas-fired power plant and to recover the cold energy of liquefied natural gas (LNG), a hierarchical process for recovering the cold energy of LNG is proposed. The process divides LNG into deep, medium, and shallow cold by temperature and matches each segment of cold energy separately to the circulating medium to recover LNG cold energy, water, and captured CO₂ while delivering electricity to the outside world. In the Organic Rankine Cycle (ORC), the heat source is flue gas and the cold source is LNG. The thermodynamic analysis of the system shows that the heat recovery efficiency, cold energy utilization, power generation efficiency, and exergy efficiency of the system are 41.55%, 14.34%, 10.80%, and 53.60%, respectively. The CO₂ capture and cold energy generation are 177.30 kg/t and 25.86 kWh/t, respectively. In addition, the LNG regasification pressure is investigated and the maximum CO₂ capture rate is achieved at a gasification pressure of 1.00 MPa. The higher exergy efficiency indicates the novelty of the hierarchical cold energy utilization process design and the suitability of the working fluid for use in ORC.

Key words: CO₂ capture, LNG, thermodynamic analysis, ORC power generation, cold energy utilization

摘要：

为了从天然气发电厂的烟气中捕获二氧化碳（CO₂）并回收液化天然气（LNG）的冷能，提出了一种分级回收LNG冷能的工艺。该工艺将液化天然气按温度分为深冷、中冷和浅冷，并将每一段冷能分别与循环介质相匹配，以回收LNG冷能、水和捕获CO₂，同时向外界输送电力。在有机朗肯循环（ORC）中，热源是烟道气，冷源是液化天然气。系统的热力学分析表明，该系统的热回收效率、冷能利用率、发电效率和㶲效率分别为41.55%、14.34%、10.80%和53.60%。CO₂捕获量和冷能发电量分别为177.30 kg/t和25.86 kWh/t。此外，对LNG再气化压力进行了研究，在气化压力为1.00 MPa时，CO₂捕集率达到最大。较高的㶲效率表明了分级冷能利用工艺设计的新颖性以及工作流体在ORC中使用的适宜性。

关键词: 二氧化碳捕集, 液化天然气, 热力学分析, ORC发电循环, 冷能利用