Study On Cold Energy Utilization Of Small And Medium LNG Gasification Stations

At present,natural gas accounts for an increasing proportion of domestic energy consumption,and China has imported a large number of Liquefied Natural Gas?LNG?.The research on cold energy utilization of large LNG gasification station is extensive,and the cold energy utilization project is planned at the same time when the gasification station is constructed.There are few studies on the utilization of cold energy in small and medium gasification stations.Air gasifier is often used for gasification.In addition to waste of resources,cold fog is easy to form in the station,which will corrode the equipment and affect the health of the staff.Only effective utilization of LNG cold energy can ensure the healthy development of LNG industry.In this paper,numerical simulation and theoretical analysis are used to study the utilization of cold energy in small and medium LNG gasification stations.Based on the characteristics of small and medium gasification stations,the appropriate utilization of cold energy are selected.According to the location characteristics of the gasification station?whether there is industrial waste heat around?,different cold energy utilization schemes are proposed.For small and medium gasification stations with industrial waste heat available,two new processes of LNG cold energy used in Rankine cycle power generation and CO₂liquefaction recovery are proposed with industrial waste heat as heat source and LNG as cold source,and the processes are simulated and analyzed.For small and medium gasification stations without industrial waste heat available,a combined cycle of LNG cold energy and solar energy is proposed,And the simulation and performance analysis are carried out.The conclusions are as followsFor the small and medium gasification stations with industrial waste heat available,the proposed processes 1 and 2 have the highest efficiency of 49.70%and 51.03%,the specific work is 237.70 k J/kg LNG and 234.48 k J/kg LNG,and the liquefaction rate of CO2 is 0.60 kg/kg LNG.According to the analysis of heat exchanger loss,the ratio of heat exchanger loss is 68.17%and 67.88%.Based on the method of exergy analysis,the effects of the maximum temperature of exhaust gas,working medium pressure and flow rate on the specific work and exergy efficiency of the process were studied.The results show that the specific work and exergy efficiency increase with the increase of exhaust gas temperature and working medium pressure,the specific work of process 1 is higher than that of process 2,and the exergy efficiency is lower than that of process 2;the exergy efficiency increases first and then decreases with the increase of working medium flow rate,and the optimal flow rate of working medium is 3500 kg/h.For the small and medium gasification stations without industrial waste heat available,the proposed LNG cold energy and solar energy combined generation cycle is divided into LNG cold energy generation system and solar hot water system.The equipment in the LNG cold energy power generation system is analyzed.The results show that the exergy loss in the heat exchanger accounts for the majority of the total exergy loss?about 69.23%of the total exergy loss?in the process,and the exergy loss in the pump and expander accounts for 30.77%.The sensitivity analysis of the parameters which affect the performance of the system is carried out.The specific work and exergy efficiency of the system increase with the increase of hot water temperature.With the increase of LNG pressure P1 and P7,the specific work and exergy efficiency of the system increase.With the increase of primary expansion pressure?P5?,the specific work and exergy efficiency of the system decrease.With the increase of secondary expansion pressure?P9?,the specific work and exergy efficiency of the system first increase and then decrease.There is a maximum specific work and exergy efficiency.TRNSYS was used to simulate the solar heat water system.Taking Beijing,Dunhuang and Lasa as examples,the radiation amount,collector heat collection and auxiliary heat capacity were determined.Compared with the auxiliary heat capacity and LNG cold energy power generation system to determine whether the region is suitable for the combined generation cycle.This combined power generation system is not recommended in Beijing.The Dunhuang has strong solar radiation and high ambient temperature from April to November,this combined power generation system is suitable for this period.Due to the influence of precipitation,the amount of auxiliary heat required in Lasa from February to April is higher than the LNG cold energy power generation,and the combined power generation system is more suitable from May to January of the next year.The comprehensive analysis of the LNG cold and solar combined power generation cycle system is suitable for areas with large solar radiation and little rain.From December to March of the next year in Dunhuang and from February to April in Lasa,if they operate according to the original working conditions,they will not be able to make ends meet.In this period,the temperature of solar hot water will be adjusted to 50?,and the auxiliary heat capacity will be greatly reduced,which is lower than the power generation capacity,with a surplus of 3.30×10⁴k Wh and2.14×10⁴k Wh respectively.In summer,the cooled circulating water in the LNG cold power generation system can be used for cold water air conditioner.After cooling for the workshop in the station,it can enter the solar collector.