Research On Zero Emission System Of LNG Power Plant

LNG (Liquefied Natural Gas) is a kind of mixed cryogenic liquid (-162℃,0.14MPa), which goes through dehydration, desulfurization, removing of heavy metals. The cold energy that contains in the LNG is about 840kWh/tLNG.The "12th Five-Year Plan" points out that, by 2030, China is expected to imports more than 50 million tons LNG, which accounts 10% of primary fossil energy. According to this plan, we can calculate that along with China’s annual LNG imports, approximately 14.532 X 109kWh high-quality cold energy will also be imported. The traditional method of sea water and combustion LNG gasification is a serious waste of cold energy. In recent years, along with the increasing greenhouse effect, CO2 recycling is concerned by many people. Combining with the characteristics of LNG power plant flue gas generation, this paper designed a set of LNG cold energy combined utilization plan, which would achieve the goal of cold energy cascade utilization, efficient LNG gasification, waste gas zero emission in LNG power plant.Firstly, the equation of state of real gas Peng-Robinson was chosen to calculate LNG parameter in different conditions. The impact of ambient temperature, LNG composition, gasification pressure on LNG cold energy and standard exergy released was discussed. Secondly, Through the study of pure cold energy utilization, pure power cold energy utilization and combined utilization, using the method of energy level analysis, a practical evaluation and guidance of cold energy utilization was gained. Lastly, the refrigerant and low-temperature generating system was studied, a set of LNG cold energy cascade utilization system which integrated low temperature power system was designed, carbon dioxide recovery system, nitrogen and oxygen separation system, the detailed process and parameters was designed.The research results show:1) Through calculation and simulation, zero emission system designed in this paper can realize the power plant LNG cold energy cascade utilization, LNG high efficiency gasification, zero emissions targets, and can make a by-product of liquid carbon dioxide and oxygen.2) The cold energy and cold exergy of LNG has a characteristic of cascaded releasing, LNG cold energy should adopt the method of cascade recovery.3) For low temperature power generation, recycling of carbon dioxide and nitrogen oxygen separation, the best matching temperature of LNG are given.4) Working in with the refrigerant R152a and R407c, the longitudinal double stage cascade power system is adopted, which achieve a better generating capacity.5) System liquefied carbon dioxide recovery is 2.1kg/s, the recovery rate is 84%, liquid oxygen recovery is 2.7kg/s. Power waste comes mainly from the compression mechanism. The unit mass consumption of carbon dioxide and oxygen is about 7kW/kg, which saves nearly half energy comparing to the traditional air separation unit.