coal power plant

Improved fossil fuel process scrubs CO2 from the atmosphere

US researchers have developed a chemical process for producing useful products, including electricity, from fossil fuels such as shale gas, coal and biomass without emitting carbon dioxide (CO2).

Under certain conditions the technology actually consumes all the carbon dioxide it produces plus additional carbon dioxide from an outside source. In this scenario the process would actually act as a net positive force to counteract global warming and climate change.

The technology, known as chemical looping, uses metal oxide particles in high-pressure reactors to ‘burn’ fossil fuels and biomass without the presence of oxygen in the air. The metal oxide provides the oxygen for the reaction.

Chemical looping is capable of acting as a stopgap technology that can provide clean electricity until renewable energies such as solar and wind become both widely available and affordable, the engineers said.

“Renewables are the future,” said Liang-Shih Fan (pictured), Ohio State University professor, who leads the research team.

“We need a bridge that allows us to create clean energy until we get there – something affordable we can use for the next 30 years or more, while wind and solar power become the prevailing technologies.”

Five years ago, the team demonstrated a technology called coal-direct chemical looping (CDCL) combustion, in which they were able to release energy from coal while capturing more than 99 per cent of the resulting carbon dioxide, preventing its emission to the environment.

The key advance of CDCL came in the form of iron oxide particles which supply the oxygen for chemical combustion in a moving bed reactor. After combustion, the particles take back the oxygen from air, and the cycle begins again.

The challenge then, as now, was how to keep the particles from wearing out, said Andrew Tong, research assistant professor of chemical and biomolecular engineering at Ohio State.

While five years ago the particles for CDCL lasted through 100 cycles for more than eight days of continuous operation, the engineers have since developed a new formulation that lasts for more than 3,000 cycles, or more than eight months of continuous use in laboratory tests.

“The particle itself is a vessel, and it’s carrying the oxygen back and forth in this process, and it eventually falls apart. Like a truck transporting goods on a highway, eventually it’s going to undergo some wear and tear. And we’re saying we devised a particle that can make the trip 3,000 times in the lab and still maintain its integrity,” Tong said.

This is the longest lifetime ever reported for the oxygen carrier, he added. The next step is to test the carrier in an integrated coal-fired chemical looping process.

Another advancement involves the engineers’ development of chemical looping for production of syngas, which in turn provides the building blocks for a host of other useful products including ammonia, plastics or even carbon fibres.

This is where the technology really gets interesting: It provides a potential industrial use for carbon dioxide as a raw material for producing useful, everyday products.

Today, when carbon dioxide is scrubbed from power plant exhaust, it is intended to be buried to keep it from entering the atmosphere as a greenhouse gas. In this new scenario, some of the scrubbed carbon dioxide wouldn’t need to be buried; it could be converted into useful products.

Taken together, Fan said, these advancements bring the chemical looping technology much closer to commercialisation.

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