Process Design And Optimization Of Membrane Separation Of H₂/CO₂ Based On Coal Gasification Coupling With Gasoil Hydrogenation

Hydrogen is an important raw material gas for realizing petroleum hydrocracking in oil refineries and improving the quality of oil products.Hydrogen production by coal gasification is a relatively mature and common method in refineries.The shifted gas produced by coal gasification has an H₂ content of about 41mol%and a CO₂ content of about 30mol%.Conventional separation processes use pressure swing adsorption（PSA）,membrane,cryogenic separation to achieve hydrogen purification,and the problems of complex equipment,huge investment and energy consumption are common.The rapid development of membrane separation technology in the past two decades proves the advantages of simple operation,easy coupling,investment and low energy consumption.Therefore,it was proposed to use multi-stage membrane separation and its coupling technology to achieve hydrogen purification from shifted gas,and to couple the design process with the gasoil hydrogenation process,and use Unisim Design to simulate and optimize the process.A two-stage hydrogen membrane series process and a two-stage carbon membrane-two-stage hydrogen membrane combined process were established for hydrogen purification.Firstly,a two-stage hydrogen membrane series process was established to optimize the gas flow rate,membrane area and hydrogen purity in the exhaust gas at different pressure ratios.It was found that this process can only ensure the purity of hydrogen and the recovery rate is very low.Then,based on this,a two-stage carbon membrane-two-stage hydrogen membrane combined process was established,and the effects of membrane area on compressor power,product purity and recovery rate under different pressure ratios were studied and the most suitable operating conditions were determined by economic evaluation.The results show that the design can simplify the traditional PSA operation,which is technically feasible,but the economy is poor.A carbon membrane-PSA combined process was established.CO₂ was separated by carbon membrane and compressed condensation,and H₂ was purified by PSA.Optimized membrane area,condensing pressure and temperature,gas flow rate and composition on both sides of the membrane,product purity and recovery rate,etc.,determined the optimal operating parameters,and carried out process investment and energy consumption was compared with the traditional VPSA-PSA process.The results show that the carbon membrane-PSA combined process can simplify the traditional operations,and also the investment and energy consumption are better than traditional processes.In the gasoil hydrogenation process,the circulated hydrogen accounts for a large proportion,and the conventional operation uses PSA or membrane separation to purify it to a purity of 99 mol%of make-up hydrogen,and then enters the reactor.These two kinds of shifted gas purification processes designed are coupled to the gasoil hydrogenation,and the hydrogen effluent or PSA unit in the hydrogen extraction process is used to purify the circulated hydrogen,and a separate purification device for circulating hydrogen is no longer needed.The optimization of the purity of the new hydrogen in the two-stage carbon membrane-two-stage hydrogen membrane coupling gasoil hydrogenation process shows that the two-stage carbon membrane-first-order hydrogen membrane can meet the production needs,thus improving the process and improving the process.An economic evaluation was conducted,and the results showed that the economics of the multi-stage membrane combination process was still poor.Then,the carbon membrane-PSA combined coupling gasoil hydrogenation process has better economical efficiency.Compared with the traditional process,the total investment of the coupling process is reduced by 194.99 million yuan,the annual operating cost is reduced by50.97 million yuan/year,and the total annual cost is reduced by 14.2%.