The Optimization Of Liquefied Natural Gas Cold Energy Air Separation Unit

Liquefied Natural Gas(LNG)is a kind of cryogenic liquid mixture,which is made of Natural Gas(NG)at normal temperature after removal of acid and water,through the process of freezing.It will release a large amount of cold energy(about 830kJ/kg)in the process of LNG vaporizing,LNG is usually heated and evaporated by seawater in LNG receiving station,and this will cause a great waste of energy and seawater cold pollution.In order to recycle and utilize LNG cold energy,many domestic and foreign experts and scholars propose many schemes on LNG cold energy recovery,the temperature of the air separation process is lower than that of LNG,which can make full use of LNG cold energy,so it is relatively reasonable way to use LNG cold energy in the air separation unit.At present,cold energy is applied to air separation unit in most of LNG receiving station,which has the great advantage of low production cost,but some widespread problems exist in the operation of LNG cold energy air separation unit,which have influence on economic benefit of LNG cold energy air separation project.This paper introduces the present situation and prospect of the development of liquefied natural gas industry,progress of research on LNG cold energy air separation,and the status of research on LNG cold energy recovery,and introduces LNG cold energy air separation unit of the CNOOC Air Products and Chemicals(Fujian)Co.Ltd,then proposes the problems existing in the production and operation of the device,simulates and calculates the process flow of LNG cold energy air separation with the help of chemical process simulation software Aspen Plus,analyzes the problems existing in the operation,provides support for device modification and optimization.Directing at the serious problems that exist in the production run,the paper carries out a detailed analysis and puts forward solutions.(1)By using Aspen Plus to simulate the process flow of LNG cold energy air separation,LNG temperature is one of the key factors that affect the yield of liquid nitrogen.Directing at the problem of low capacity of liquid nitrogen in LNG cold energy air separation unit,according to the cause analysis and simulation results,the solutions are put forward as follows:optimize the design of LNG cold energy supply,liquid nitrogen production can be increased by 3000t;improve and optimize glycol cooling water system,the heat generated by the HPN device is drew into glycol cooling water system of air separation unit,increase the yield of liquid nitrogen,the simulation data shows that the scheme is feasible,it can increase revenue for company 11200 hundred yuan per year.(2)Because of interruption of LNG supply,which causes the LNG cold energy air separation unit shutdown frequently,a scheme is put forward to use liquid nitrogen to supply cold energy for the device,by using Aspen Plus to simulate and optimize LNG cold energy air separation unit,it is proved that the scheme is feasible,avoiding the device open and shutdown frequently,it ensures the air separation unit is continuous and stable,achieving economic benefits more 900000 yuan per year.The above solutions not only reduce the loss of startup and shutdown,but also improve the yield of liquid nitrogen,eventually improve the economic benefit of LNG cold energy air separation project,those also provide reference for the production and optimization of the similar device in the future.