To produce a high-purity carbon monoxide (CO) stream, and a high-purity hydrogen stream, plus a ratio adjusted synthesis gas stream, if required, for use as a chemical feedstock. The synthesis gas stream is typically the product of steam methane reforming (SMR).
Feed gas for CO recovery is pretreated to remove carbon dioxide and water, which will freeze at the cryogenic temperatures encountered in the process. The pretreated feed gas is cooled in the main exchanger and fed to the bottom of the wash column (1). The column is refluxed with liquid methane to produce a hydrogen wash-product free of CO, but saturated with methane (2–3%). The hydrogen is then rewarmed and recovered as a product. The liquid from the wash column is preheated, reduced in pressure and separated in the flash column (2) where hydrogen dissolved in the methane (CH4) is rejected to fuel gas. To minimize CO losses, this column is also refluxed with liquid CH4.
The hydrogen-free liquid from the flash column is heated and flashed to the CO/CH4 splitter column (3). The CO from the overhead is rewarmed and compressed. Part of this stream is delivered as product; the remainder is cooled and recycled within the process. It is first used to reboil the splitter column and preheat the column feed streams. It is then flashed for refrigeration and the liquid is used as reflux for the splitter column. The CH4 liquid from the bottom of the splitter is pumped to the wash column for use as reflux. The net CH4 is vaporized in the main exchanger and leaves as the byproduct fuel gas.
Variations of this cycle have been developed to meet special requirements. In all cases, however, the hydrogen stream is produced at high pressure and the CO is available at low pressure. If CO is desired, a product compressor is usually required.
Licensor: Air Products and Chemicals, Inc.
