Technological Development And Applied Research Of LNG Cold Energy In Ice-storage Air Conditioning

With its high efficiency, energy saving, small volume, convenient transportation, andclean environmental protection, liquefied natural gas (LNG) has drawn the attention of theworld and become an important strategic energy reserves. LNG shipping and satellite stationsare the strong support of the development of LNG industry. It releases a lot of cold energyduring gasification, which is about830-860kJ/kg and is equivalent to power about231kw·h/t.Often, there are office, equipment maintenance room, dining room and other public buildingsnear the LNG Railway Station, and they need to consume a large amount of cold energy. Sostoring and recycling LNG cold energy with cold storage air-conditioning technology, storingcold energy during the gasification peak and releasing to the nearby public buildings duringcold peak, can break the limitation of time and space between the cold energy suppliers andusers, so as to expand the scope of application of LNG cold energy utilization, improve theutilization rate of cold energy, and save a lot of electricity consumed on refrigeration at thesame time.By studying the storage mode and LNG cold energy recovery methods, a process designof ice storage air conditioning utilizing LNG cold energy with two levels of refrigeranttransfer has been determined in this paper. By contrast, R404a is elected as the first-levelrefrigerant and30%of ethylene glycol aqueous solution the second-level refrigerant, and thekey equipment of the design has been compared and optimized. Simulating the workingcondition with Aspen plus software when LNG gasification1000Nm~3/h under1.6MPa andanalyzing the whole system with exergy analysis method, the exergy efficiency of the twoheat exchangers are respectively found as30.88%and43.86%. By analyzing the heat transfertemperature difference of two heat exchangers, LNG-R404a heat exchanger has become thefocus of the future scheme optimization due to that higher temperature difference leads tolower exergy efficiency.The process scheme is used in Meilin LNG railway station for engineering design. Thegasification quantity of the engineering is determine as1500Nm~3/h, and gasification pressure1.6MPa. According to the actual process, the selection of key equipment is completed, theheat load of two heat exchangers are242.3kW, heat transfer area of LNG-R404a heatexchanger and R404a-EGS heat exchanger are92.8m2and115.6m2respectively, the size ofthe ice storage tank1000RTH. The project invests2.73million yuan in total, the paybackperiod (after tax) is7.62years, suggesting that the project scheme has good economic benefits.Operation elasticity analysis has been done to ensure that the system is safe and reliable. By analyzing its development potential, high cold utilization and good energy-saving efficiencyare found in the scheme, and it is corresponding with the energy conservation and emissionsreduction policy in our country. The technology of putting heat transfer into pry and theparallel design of LNG refrigeration and electric compression refrigeration has make thescheme much more flexibility and practicability, and it is worthy of popularization.