The purpose of this unit is to provide an abundant supply of the high purity hydrogen required as feed for the Hydrocracker Reaction Unit, Gas Oil Unit and Naphtha/Jet Hydrotreating Unit. There the hydrogen is consumed by hydrogenation, desulpherization, and denitrification reactions. The hydrogen requirement is met through steam reforming of natural gas (methane) in the presence of a catalyst. The steps in this process are: desulpherization of the feed gas, reforming, carbon monoxide shift, and purification. The natural gas required by the process is supplied from a source outside the Upgrader.
The feed gas contains small quantities of organic sulphur compounds detrimental to the catalyst used in the reforming process. These compounds are removed by mixing a small stream of recycle hydrogen with the feed gas, heating the mixture and passing it over fixed beds of catalyst. In the first catalyst bed, the hydrogen reacts with the sulphur compounds to form hydrogen sulphide which is absorbed by another catalyst in the second bed.
The desulphurized feed gas is mixed with super-heated steam and preheated in coils situated in the convection section of the reformer furnace. The feed stream then passes through catalyst-filled tubes in the furnace radiant section where methane reacts with the stream to produce hydrogen, carbon monoxide, and carbon dioxide.
The hot reformer effluent is partially cooled by generating high pressure steam, which is consumed by the process and is passed over a high-temperature-shift catalyst where carbon monoxide and steam (water) are catalytically converted to hydrogen and carbon dioxide. Following cooling to recover waste heat and separate free liquid, the shift converter effluent enters a Pressure Swing Adsorption (PSA) Unit for removal of impurities (carbon dioxide, carbon monoxide, nitrogen and methane) through adsorption by molecular sieve type materials. The PSA Unit tail gas is used as fuel in the reformer furnace. The purified hydrogen gas leaving the PSA Unit is filtered, compressed, and sent to the Hydrocracker Reaction Unit, the Gas Oil Unit and the Naphtha/Jet Hydrotreating Unit.
Diagram used with permission (© SAIT Polytechnic, MacPhail School of Energy, 2009)