Process For Providing A Low-Carbon Fuel For Refining Operations

CATEGORY: HYDROGEN
PATENT
Process For Providing A Low-Carbon Fuel For Refining Operations
United States Patent Application 20130081328
Inventors:
Jadhav, Raja Ankush (Benicia, CA, US)
Application Number:
13/248952
Publication Date:
04/04/2013
Assignee:
Chevron U.S.A. INC. (San Ramon, CA, US)
Abstract:
An integrated process provides a low-carbon fuel gas for use in refinery equipment such as heaters and boilers. The process utilizes a hydrogen separation membrane to separate a refinery fuel gas into a first hydrogen-enriched stream and a hydrogen-depleted stream containing methane. The hydrogen-depleted stream is subjected to reforming and water gas shift, and the resulting shifted gas mixture containing hydrogen and carbon dioxide is subjected to separation into a second hydrogen-enriched stream and a carbon dioxide stream. The first and second hydrogen-enriched streams are combined and utilized as low-carbon fuel gas containing at least about 50 mol % hydrogen. Sweep gas is provided across the permeate side of the hydrogen separation membrane to improve the performance of the membrane unit. The sweep gas can be taken from the exhaust of the refinery equipment, from an air separation unit and/or from a carbon dioxide-depleted stream generated in the reforming process.
FIELD
The present disclosure relates to a process for treating a gaseous mixture such as a refinery fuel gas to provide a low-carbon fuel gas. The disclosure further relates to the use of such low-carbon fuel gas as fuel for refinery equipment.
BACKGROUND
Within operations for refining petroleum products, refinery equipment such as heaters and boilers are a significant source of carbon dioxide emissions. Such equipment is typically fueled by refinery fuel gas (RFG) used throughout the refinery and containing hydrogen, methane as well as other hydrocarbon components. The carbon dioxide emissions can be controlled using a known amine solvent-based post-combustion carbon capture process. However, this requires a large amount of area which is not always available in a refinery.
It has been proposed that refinery equipment be fueled by hydrogen fuel produced by reforming RFG in a steam methane reformer (SMR) or autothermal reformer (ATR) fitted with a carbon dioxide capture technology. Since the RFG can contain as much as 30 mol % hydrogen, it is advantageous to separate a majority of the hydrogen from the RFG first. Known hydrogen separation membranes can be used for this purpose. The pressure differential across the membrane determines the flux, i.e. the flow rate of hydrogen per unit area per unit time across the membrane. In order to achieve high recovery of hydrogen, the size in terms of area of the membrane can be increased, the feed can be compressed to increase the pressure on the feed side and/or the pressure on the permeate side of the membrane can be reduced. Each of these has disadvantages in terms of cost, space requirements and energy usage for compression of the feed or recompression of the permeate.
It would be desirable to provide an integrated process that would produce a low-carbon fuel gas for use in refinery equipment in a way that is energy efficient and reduces carbon dioxide emissions from such refinery equipment.
SUMMARY
According to one embodiment, the present disclosure relates to a process for providing a fuel gas for refining operations, in which a first gaseous mixture containing hydrogen and methane is passed across one side of a first hydrogen separation membrane to form a first hydrogen-enriched stream and a first hydrogen-depleted retentate stream containing methane. A sweep gas is passed across the other side of the membrane to enhance hydrogen flux across the membrane. The first hydrogen-depleted retentate stream is subjected to a reforming operation to form a second gaseous mixture containing hydrogen, carbon monoxide, carbon dioxide and water. The second gaseous mixture is passed through a water gas shift reactor to form a third gaseous mixture containing hydrogen and carbon dioxide. The third gaseous mixture is separated into a second hydrogen-enriched stream and a carbon dioxide stream. The first and second hydrogen-enriched streams are combined to form a low-carbon fuel gas stream containing at least about 50 mol % hydrogen.
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