Hydrogen Production from Natural Gas (Partial Oxidation Process)

The process under analysis comprises four major sections: (1) Sulfur Removal; (2) Partial Oxidation; (3) Water-gas Shift; and (4) Purification.

Sulfur Removal. Natural gas feedstock is purified by catalytic treatment with recycled hydrogen for removal of sulfur impurities. A pressurized mixture is fed to a hydrotreater with platinum-based catalyst, where hydrogen reacts with sulfur compounds present in the feed stream forming hydrogen sulfide, which is then adsorbed in zinc oxide beds in the desulfurizer.

Partial Oxidation. Purified natural gas is partially oxidized by being mixed with pressurized air in the Partial Oxidation (POX) Reactor, forming CO and hydrogen. Steam is also fed in the reactor to promote a CO shift reaction, in which carbon monoxide reacts with water, generating carbon dioxide and more hydrogen.

Water-gas Shift. Steam is added to the POX Reactor outlet stream, and reacts with the bulk of the carbon monoxide still present in it, forming Hydrogen and carbon dioxide. The shift conversion is firstly carried out in a high temperature (350-400 °C) reactor, over a bed of iron oxide/chromium oxide catalyst, and then in a low temperature (200-220 °C) reactor, in the presence of a catalyst containing copper oxide, zinc oxide and aluminum oxide.

Purification. The shifted gas is then cooled to near ambient temperature, causing water to condense, which is then removed in a knockout drum. Carbon dioxide and other impurities are removed from the hydrogen stream in a pressure swing adsorption (PSA) system. A small portion of pure hydrogen is recycled to the Sulfur Removal section, and the remainder is compressed and sent to storage facilities.