NETL carbon capture system using supersonic expansion

Jan 03 2018

NETL researchers have patented a cost effective CO2 separation technology.

Mainstream CO2 capture technologies use solvents to dissolve CO2 from other constituents in power plant flue gas, such as nitrogen and water vapor. Capturing CO2 prevents the gas from entering the atmosphere, but use of solvents can greatly reduce a plant’s energy efficiency. An alternative approach to separate CO2is to use mechanical gas separation in which specific components of the gas stream are changed to either a liquid or solid phase, facilitating more effective separation.

NETL’s patented invention applies a novel approach to this mechanical separation method. In the first step, flue gas is expanded by passing through a small opening, or nozzle, from a region of high pressure into a region of low pressure. This process, called supersonic expansion, cools the gas to the point where molecules of a specific component, such as CO2, condense. During expansion of a typical effluent stream, the gas flow cools to a point where CO2 vapor changes into a liquid or solid, forming a CO2 precipitate carried by the gas stream. Once CO2 has changed phase, the carrier gas is slowed down and slightly recompressed so that the precipitate can be mechanically separated.

According to the technology inventor, NETL Research Scientist John VanOsdol, Ph.D., the technology has applications in other areas beyond CO2 capture: “For example, a mechanical separator, such as the one in the current invention, can be used to selectively remove components like H2O, CO2, and CO directly out of a syngas stream that is produced by a typical high-pressure gasification unit. This would result in a stream of relatively pure H2, which would enhance the performance of ultra-efficient, low-emission gas turbine-fuel cell hybrid systems while removing CO2 at the same time. The operating costs for using mechanical separation in this area would be much lower compared to the operating costs for separating CO2 directly out of the effluent stream.”

Other mechanical separation techniques rely on cryogenic refrigeration to bring the gas stream to the conditions needed to condense CO2 out so it can be mechanically separated. However, the refrigeration requirements impose additional energy penalties making this approach inefficient and expensive.

NETL’s mechanical CO2 separator offers a competitive way to extract CO2 from fossil fuel power generation, enabling more effective, sustainable use of our nation’s abundant coal resources.

National Energy Technology Laboratory

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Issue 64 - July - Aug 2018

CCS in Australia - CS-Cap: Development of an SO2 tolerant post combustion CO2 capture process .. CSIRO pilot plant demo of aqueous ammonia CO2 capture How OGCI is trying to enable a commercial CCUS industry .. NET Power project achieves first fire .....

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