Patent ID: 8241400
Filing Date: 2012-08-14
Classification: B01D,C01B,F25J,Y02C,Y02P

Abstract:
1. A process for recovering gaseous hydrogen and gaseous carbon dioxide from a mixture of hydrocarbons utilizing a reformer unit in conjunction with a pressure swing adsorption unit and a cryogenic purification unit, the process comprising the steps of: a) generating a hydrogen rich effluent that also contains at least carbon monoxide, carbon dioxide, methane and water vapor from one or more hydrocarbon feed streams in a reformer unit; b) optionally treating the hydrogen rich effluent in a water gas shift reactor in order to further enrich the hydrogen content of the hydrogen rich effluent and to also increase the carbon dioxide content in the hydrogen rich effluent by oxidizing a portion of the carbon monoxide present in the effluent to carbon dioxide thereby obtaining a water shift effluent; c) providing a pressure swing adsorption unit having at least two adsorption vessels that each contain two or more adsorbent beds, the at least two adsorption vessels being parallel to one another and being independently operated on a cycle that includes an adsorption step, a co-feed step, a depressurization step, a regeneration step and a re-pressurization step, with the proviso that the cycles in the at least two adsorption vessels run consecutively with at least one of the adsorption vessels being in a different step of the cycle compared to at least one of the remaining adsorption vessels and the two or more adsorbent beds having an intermediate draw area positioned between at least two of the adsorbent beds thereby allowing for the withdrawal of a methane rich gas stream from the intermediate draw area during the co-feed step of the hydrogen pressure swing adsorption cycle; d) introducing the hydrogen rich effluent or water gas shift effluent into at least one of the adsorption vessels of the pressure swing adsorption unit during the adsorption step of the hydrogen pressure swing adsorption cycle in order to allow for the recovery of a high purity gaseous hydrogen stream from the hydrogen rich effluent or the water gas shift effluent and the adsorption of the carbon monoxide, carbon dioxide, methane, water vapor and remaining hydrogen onto the adsorbents in the adsorbent beds of the pressure swing adsorption unit, the adsorption step being carried out at a pressure from about 250 psig to about 700 psig; e) withdrawing the high purity gaseous hydrogen stream from the pressure swing adsorption unit during the adsorption step and passing this high purity gaseous hydrogen stream on for further use; f) allowing the at least one adsorption vessel to enter into the co-feed step while introducing a purified carbon dioxide stream obtained from the downstream cryogenic purification unit in order to allow the carbon dioxide to displace methane and carbon monoxide adsorbed onto the adsorbents in the adsorbent beds thereby producing a methane rich stream; g) withdrawing the methane rich stream from the intermediate draw area positioned between at least two of the adsorbent beds and recycling this methane rich stream to the reformer unit; h) allowing the at least one adsorption vessel to enter the depressurization step by depressurizing the adsorbent beds of the at least one adsorption vessel in order to release the carbon dioxide, carbon monoxide, methane, water vapor and hydrogen adsorbed to the adsorbents in the adsorbent beds thereby producing a carbon dioxide rich pressure swing adsorption tail gas having an increased concentration of carbon dioxide; i) withdrawing the carbon dioxide rich pressure swing adsorption tail gas from the pressure swing adsorption unit; j) regenerating and re-pressurizing the adsorbent beds for further use; k) compressing the carbon dioxide rich pressure swing adsorption tail gas in a compressor unit to a pressure that ranges from about 250 psig to about 1000 psig in order to obtain a compressed carbon dioxide rich pressure swing adsorption tail gas; l) introducing the compressed carbon dioxide rich pressure swing adsorption tail gas into a cryogenic purification unit in order to produce a carbon dioxide purified stream and an incondensibles stream that contains methane, carbon monoxide and hydrogen; and m) withdrawing the carbon dioxide purified stream from the cryogenic purification unit and recycling at least a portion of the carbon dioxide purified stream to the pressure swing adsorption unit where the carbon dioxide purified stream is introduced into the adsorption vessels during the co-feed step of the cycle in order to increase the concentration of carbon dioxide in the hydrogen pressure swing adsorption tail gas.