Study On LNG Process From Coke Oven Gas

China's coke production ranks first in the world.While producing coke,a large amount of coke oven gas is produced by-product.Coke oven gas contains more combustible components and has great value in utilization.Therefore,how to make rational use of coke oven gas has attracted much attention.How to realize the efficient utilization of coke oven gas is an important issue related to environmental protection,creating a low carbon environment and creating economic value.Faced with the increasingly serious environmental pollution problem,people rely more and more on natural gas as a clean and efficient primary energy,which increases the demand and becomes an indispensable and important part of people's daily life.The process of LNG production from residual coke oven gas was studied in detail,and the process simulation and optimization were carried out,and the flow field simulation of methanation reactor was carried out.The coke oven gas with 15,000 Nm~3/h raw material comes from the remaining coke oven gas in the coking plant.The process of LNG production from coke oven gas can be divided into four parts.The first part is hydrogen and sulfur produced by high temperature pyrolysis of hydrogen sulfide.After the coke oven gas is preliminarily treated in a coking plant,most of the organic and inorganic sulfur are removed and hydrogen sulfide is enriched.Compared with traditional Claus process,hydrogen sulfide is converted into sulfur and water.By high temperature pyrolysis,the sulfur with 99.2%mass fraction is obtained and the hydrogen with 85.84%mass fraction is obtained at the same time.The hydrogen generated can be used for hydrode sulfurization in the next section,and the economy is greatly enhanced.The second part is the purification and compression process of coke oven gas.After the coke oven gas passes through the conventional treatment process in the coking plant,further purification process is needed to prevent the phenomenon of catalyst poisoning in the subsequent process.The third part is the methanation process.The adiabatic multi-stage methanation technology is selected in this paper.The waste heat boiler is used behind the former methanation adiabatic furnace to recover high temperature heat source and produce medium pressure steam.The recovery energy is 1.561*10~7 kJ/h.At the same time,the carbon monoxide conversion rate can reach 100%,the carbon dioxide conversion rate is 99.67%,and the methane content in the product is 63.35%,higher methane content is conducive to the next step of separation and liquefaction process.Activated Energy Analysis is used for economic accounting of methanation process,with a total investment of 139.89 million and a total expected return of 20%.The fourth part is cryogenic separation process.The methane-rich gas after methanation contains a small amount of hydrogen,nitrogen and a small amount of water.After gradual cooling,it is separated.The liquid methane is sent to LNG tank as LNG product.The molar fraction of LNG obtained from the bottom of cryogenic distillation column is 99.995%,and the separation efficiency of methane is 98.90%.The molar fraction of hydrogen and nitrogen at the top of the tower is 95.43%.Compared with the traditional process,this process achieves a higher purity of LNG.The production cost of LNG process from coke oven gas is estimated.After estimating,the annual gross profit reaches 50.3946 million,which has good economic benefits.Aiming at the local high temperature problem in the methanation reactor,which is the key point of the methanation reactor,and affects the methane content at the outlet of the reactor,a gas distributor at the top of the methanation reactor was designed and improved.The flow field inside the reactor was simulated by using the Fluent flow field simulation software,and the velocity field,temperature field and component field distribution in the reactor were obtained.The reactions in the methanation reactor were investigated by these flow field distribution.Distributor installed at the top of the reactor can effectively improve the uneven distribution of gas in the reactor,improve the local high temperature problem in the reactor.The methane content at the outlet of the reactor is increased.The methane content at the outlet of the methanation reactor was increased.The average methane content at the outlet of the three reactors was 0.5157,0.5592 and0.5622,respectively.