Cleaner coal power

A new technique will help reduce mercury and other trace elements emitted from coal gasification and coal-fired power plants.

A licensing agreement recently signed by the US Department of Energy and Johnson Matthey will contribute to the reduction of mercury and other trace elements emitted from coal gasification and coal-fired power plants.

The agreement between Johnson Matthey and the Office of Fossil Energy’s National Energy Technology Laboratory (NETL) paves the way for the company to demonstrate a mercury-reduction process patented by two NETL researchers and to ultimately commercialise the process.

Johnson Matthey plans to demonstrate the process at larger bench- and pilot-scales to the point that it can be commercially sold to utility and related industries.

The process, patented as a ‘Method for High-Temperature Mercury Capture from Gas Streams,’ enables scientists to remove mercury from high-temperature gases by using metal sorbents to capture the mercury, as well as the trace elements arsenic and selenium. Once they capture the trace elements, the sorbents can be regenerated and used again in gas streams, primarily from coal gasifiers, coal-fired electric plants, and ore smelters.

Since the US Energy Department envisions the increased use of gasification, and a concurrent increase in trace element emissions over the next 20 years, the Department wants to ensure that technologies are in place to meet existing and future regulations.

The key to this new technology is that it has successfully removed mercury from fuel gases at high temperatures. Prior research had shown little progress in removing mercury from high-temperature gas streams because the adsorption of mercury on a sorbent typically decreases as temperature increases. As a result, nearly all of the mercury in coal ends up in the flue and fuel gases. The carbon-based sorbents typically used appear to be unsuited for capturing mercury contained in high-temperature fuel or flue gases.

In early tests, this patented process overcame obstacles related to heat and was able to perform at variable temperatures. Such successes at high temperatures preserve the high-temperature efficiency of gasifying systems, such as integrated gasification combined-cycle plants.