Case Study Hydrogen Recovery

Hydrogen recovery is applicable to several processes, divided into three main categories  

Similar membrane systems are already applied also for syngas ratio adjustment (H2/CO ratio) of the streams exiting reformers. Generally, membranes are employed for stripping hydrogen out of the syngas in order to reduce the H2/CO ratio. At the moment, several hundred hydrogen separation plants have been installed.  

Separation Process Traditional technology Membrane material 

H2/CO Adjustment of H2/CO ratio in syngas plant PSA Silicon rubber Polyimide Pd-based 

H2/hydrocarbons Hydrogen recovery in refineries PSA Silicon rubber Pol5fimide Pd-based 

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Case study I Hydrogen recovery from SMROG... 

Case Study Selection Guidelines for the Separation and Recovery of Hydrogen in Refineries... 

A comparison of membrane separation versus cryogenic separation in a typical large ammonia plant was made by Schendel et al. (1983). For the case study described in this paper, the operating conditions were modified to increase the methane content at the entrance to the synthesis loop to about double that allowed without hydrogen recovery. The pertinent process variables for the IS MMsefd feed stream are summarized in Table 15-5. To prevent densiflcation of the membrane or formation of an insoluble phase in the cryogenic system, the ammonia in the feed to both systems is reduced to very low levels in a water scrubber. To prevent formation of a solid phase in the cryogenic unit, molecular sieves are used to remove the water picked up in the scrubber. 

In order to compare the economics as well as the overall C02 emissions from each schematic studied in this joint venture, a reference case was analyzed. The reference case included only the process steps associated with coal gasification, shift, and hydrogen purification, but none of the steps associated with C02 sequestration or coalbed methane recovery. Three other process schemes were examined in this study and compared to the reference case. Figure 1 depicts simplified process flow diagrams for the reference case and the other three schemes (note the overall heat integration for each scheme is not shown). The top portion of the figure shows the process steps that are the same for each scheme up to hydrogen purification, while the operations inside the dashed boxes represent the steps that differ between the four cases. 

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