Process Optimization Of 200000 T/a Methanol Production From Coke Oven Gas

Coke Oven Gas?COG?is a by-product of coking process,mainly composed of H₂,CH₄,CO,N₂,CO₂ and so on.The annual output of coke oven gas in China reaches179.6 billion m³.50%of coke oven gas is used as fuel and the rest is emptied after burning,which results in resources waste and greenhouse gas emissions.COG to methanol?CTM?is a highly-valued utilization method of coke oven gas.Compared with other coke oven gas utilization methods,it has the advantages of high industrialization and good economic benefit.Due to the low conversion ratio of coke oven gas synthesis methanol and the high recycle flowrate of unreacted gas,high energy consumption,and low methanol yield were generated.Coke oven gas is rich in hydrogen,and purge gas contains a large amount of hydrogen and some carbon dioxide,resulting in resources waste and carbon dioxide emissions.In order to improve the utilization ratio of elements,increase methanol production and save energy and reduce emissions,the carbon supplement method of buying pure CO₂ or building new CO₂-generation unit is often used in industry.However,the problem of hydrogen resource waste and carbon dioxide emissions can not be thoroughly solved,and the production cost and total energy consumption will be increased accordingly.Based on this,two optimization schemes are proposed in this paper.The whole process model of the process was established by using the process simulation software Aspen Plus,and the technical-economic-environmental performance analysis of the schemes was carried out.The main work of this article is as follows:?1?Using Aspen Plus software,established a full process model of CTM process with the annual output of 200000 t/a methanol.The simulation results are in good agreement with the factory data,which lay the foundation for subsequent process optimization.?2?In view of the low conversion rate of methanol synthesis,a CTM process optimization scheme based on by-product steam downgrade is proposed.In methanol synthesis reactor,medium-pressure boiling water is often used as coolant,and so by-product of medium-pressure steam.The coolant temperature?that is,reflecting boiling water pressure?is a key parameter affecting methanol synthesis and process energy consumption.The results show that,when the coolant temperature is reduced to 187?,the low-pressure steam is generated,which increase the conversion rate of the methanol synthesis by 25%,increase the methanol yield by 3%,save energy cost of 28.2%,increase income of 5.397 M$/a,and reduce the carbon dioxide emission by 21.3%.?3?In view of the problem of hydrogen resource waste and carbon emissions caused by the purge gas,a new process for methanol production from coke oven gas assisted by purge gas is proposed.The new technology adds an H₂&CO₂ separation and recycle unit on the basis of the original process,so all the recycled CO₂ and some H₂are circulated to the methanol synthesis unit,and the rest H₂ is as a product.After the analysis of technical-energy-economic performance,the key parameters of the new process,the hydrogen recycle ratio,the coolant temperature and the unreacted gas recycle ratio are set as 0.6,187,and 0.89,respectively.The new process requires an investment cost of 2.319 M$,which can achieve zero emissions of carbon dioxide,increase methanol yield by 16%,save energy costs by 15.5%,and increase income by23.485 M$/a.