Case Study Hydrogen Separation in Refineries

In the following, after a brief desolption of the conventional separation processes (PSA and ayogenic) a comparison among these processes and membrane systems for hydrogen separation is reported, also introducing some project considerations such as process flexibility, reliability, ease of response to the variations, expansion capability and versatility [76]. 

Operating flexibility is the ability to operate under variable feed quality conditions, either on a short-term or long-term basis. 

The changes in feed composition occur very often in refinery applications, particularly when the source of the feed is a catalytic process or when the feedstock to the upstream unit changes. 

In membrane processes, the increase in feed impurity concentrations tend to cause a decrease in product purity, which, however, can be maintained for small feed composition changes by adjusting the feed-to-permeate pressure ratio. In most refinery membrane applications, however, the major product impurity is methane, and this can be allowed to increase slightly in the product without major downstream impact. The response time of membrane systems is essentially instantaneous, and corrective action has immediate results. The start-up time required by the process is extremely short. 

The cryogenic process has very low flexibility, because changes in the concentration of the lower boiling components of the feed affect the product purity directly. Recovery is not strongly affected. Response time is not as rapid as for PSA or m brane systems. Start-up is 8-24 hours, depending on the procedure used. 

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Membrane Engineering Progress and Potentialities in Cas Separations 301 14.4.1 Case Study Hydrogen Separation in Refineries... 

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