To produce hydrogen from light hydrocarbons using steam-methane reforming.
Feedstock: Natural gas, refinery gas, liquefied petroleum gas (LPG) and naphtha.
Product: High-purity hydrogen and steam.
Light hydrocarbon feed (1) is heated prior to passing through two fixed-catalyst beds. Organic sulfur compounds present in feed gas (e.g., mercaptans) are converted to hydrogen sulfide (H2S) and mono-olefins in the gas phase are hydrogenated in the first bed of cobalt molybdenum oxide catalyst (2). The second bed contains zinc oxide to remove H2S by adsorption. This sulfur-removal stage is necessary to avoid poisoning of the reforming catalysts.
Treated feed gas is mixed with steam and heated before passing to the reformer where the hydrocarbons and steam react to form synthesis gas (syngas). Foster Wheeler supplies proprietary side-fired Terrace Wall reformers, with natural draft mode option for increased reliability, compact plot layout with convection section mounted directly above the radiant section and modular fabrication option. Foster Wheeler supplies top-fired reformer options for large capacity plants.
Syngas containing hydrogen, methane, carbon dioxide (CO2), carbon monoxide (CO) and water leaves the reformer and passes through the waste-heat boiler to the shift reactor (3) where most of the CO is converted to CO2 and hydrogen by reaction with steam. For heavier feedstocks, prereforming is used for conversion of feedstock upstream of the reformer.
The syngas is cooled through a series of heat-recovery exchangers before free water is recovered in a knockout drum. The resultant raw hydrogen stream passes to the pressure swing adsorption (PSA) unit for purification (4) to typically 99.9% hydrogen product quality. Tail gas from the PSA unit provides a substantial proportion of the firing duty for the reformer. The remaining fuel is supplied from the feed gas or other sources (e.g., refinery fuel gas).
Demineralized water makeup is de-aerated, mixed with recovered condensate and preheated through a series of heat-recovery exchangers before passing to the steam drum. Saturated and superheated steam is raised by heat exchange with the reformed gas and flue gas in the convection section of the reformer. Steam export quantities can be varied between 1,250 and 5,750 lb/million scfd of hydrogen produced using air pre-heat and auxiliary firing options.
Licensor: Foster Wheeler