A new technology invented by NETL researchers is changing the game for carbon capture by offering an effective way to separate carbon dioxide (CO₂) from flue gas.

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.

The innovation is one more example of how NETL develops technology solutions to enhance the nation’s energy foundation. This month, the Laboratory is highlighting technologies it has developed that are available for licensing or commercialization