Recovery of relatively pure hydrogen from refinery and petrochemical offgas streams such as from thermal hydrodealkylation (THDA), catalytic reformers, hydrotreaters and fluid catalytic crackers. Cryogenic processing is the optimal route to produce carbon monoxide (CO) from syngas.
Products: 90% to 98% pure hydrogen. Valuable product streams, such as LPG, may also be recovered.
A typical autorefrigerated cryogenic unit for recovery of hydrogen consists of two stages of cooling and partial condensation. Suitably pretreated feed gas is cooled and partially condensed against hydrogen product and fuel in the plate-fin heat exchanger (1). The hydrocarbon rich condensate is separated in the two-phase separator (2) and the vapor is further cooled and partially condensed in the second plate-fin heat exchanger (3). The methanerich condensate is separated in the second two-phase separator (4) giving relatively pure hydrogen product, which is reheated through both exchangers.
Autorefrigerated cryogenic units use refrigeration from Joule-Thomson expansion of the condensate streams and can generate hydrogen purities up to 96%.
Pretreatment ensures that the feed gas to the cryogenic unit is dry and contains no components which would freeze in the cold section. Depending on the pretreatment scheme, additional products can be obtained.
Depending on feed gas conditions and hydrogen product requirements, one, two or three stages of separation may be optimal.
Operating conditions: Typical hydrogen recoveries are 90% to 96%.
Economics: Cryogenic recovery of hydrogen is economically favored by the ability to recover other valuable products, e.g., olefins and LPG. Compared with alternative technologies, cryogenic processing is the most efficient and has the lowest utilities cost. Cryogenic recovery has been used to treat gases with hydrogen feed concentrations as high as 80% and pressures up to 80 barg.
Licensor: Costain Oil, Gas & Process Ltd.
