Design Of Membrane Coupling Process For Hydrogen And Hydrocarbon From Refinery Gas

Refinery gas is defined as the tail gas generated in processing crude oil, which is mainly composed of hydrogen and light hydrocarbons such as methane, ethane, propane and so on. Because of the single variety and low recovery of exisiting hydrogen and light hydrocarbon seperation processes, a large amount of surplus refinery gases are hard to be utilized and then have to be discharged into fuel gas pipelines.These disadvantages have resulted in a great waste of hydrogen and light hydrocarbon resources.Therefore, to find out a refinery process that can increase recovery rate of hydrogen and light hydrocarbons resources in refinery gases has become the problem demanding prompt solution in both petrochemical plants and scientific research departments.A refinery with a combined production of fuel gases about30000Nm3/h, in which hydrogen and light hydrocarbons are about42%(molar basis) and10%respectively. PSA was used to recycle hydrogen, however, because of the complexity of feed gas, some parts of the steams do not satisfy the feed conditions of PSA, which leads to the low recovery rate of hydrogen and light hydrocarbons.In this thesis, PSA/condensation/rectification process was designed on the base of traditional hydrogen and light hydrocarbon separation process. In order to increase recovery rate of hydrogen and light hydrocarbons, two processes, HM(hydrogen membrane)/PSA/condensation/rectification process and VM(vapor membrane)/HM/PSA/condensation/ectification were developed to optimize the process where HM and VM were respectively used to couple with PSA/condensation/rectification process. In these processes, HM was used for the purification of the feed gas while VM is used to recycle the desorption gas of PSA and non-permeate outlet gas of HM which contains some of the light hydrocarbons.By using UniSim Design to simulate and optimize three processes, the condensation temperature, membrane area and feed pressure were considered to analysis their effects on economic benefit and to find the optimal parameters. The recovery rates and economic benefits of three processes were calculated and then thevalues were compared.Compared with non-membrane process, when using VM/HM/PSA/condensation/rectification the recovery rates of hydrogen, LPG, C5+light oil have respectively increased by22%,30.37%and61.67%. Meanwhile the yields of LPG, C5+light oil and hydrogen are 27143t·a-1,5487t·a-1and6790t·a-1respectively which lead to a94.7million yuan economic benefit increasement per year.The study results showed that the condensation temperature, membrane area and feed pressure have adirect effects on the economic benefit and that membrane coupled process contributes to higher hydrogen and lighthydrocarbon recovery rate, thus rising economic benefits.