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Thursday, January 04, 2018

Zero-emissions ‘chemical looping’ converts fossil fuels into electricity

Engineers at The Ohio State University are developing technologies that have the potential to economically convert fossil fuels and biomass into useful products including electricity without emitting carbon dioxide to the atmosphere.

In the first of two papers published in the journal Energy & Environmental Science, the engineers report that they've devised a process that transforms shale gas into products such as methanol and gasoline-all while consuming carbon dioxide. This process can also be applied to coal and biomass to produce useful products.

Under certain conditions, the technology consumes all the carbon dioxide it produces plus additional carbon dioxide from an outside source.

In the  second paper, they report that they've found a way to greatly extend the lifetime of the particles that enable the chemical reaction to transform coal or other fuels to electricity and useful products over a length of time that is useful for commercial operation.

Prof Liang-Shih Fan

Finally, the same team has discovered and patented a way with the potential to lower the capital costs in producing a fuel gas called synthesis gas, or "syngas," by about 50 percent over the traditional technology.

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, Distinguished University Professor in Chemical and Biomolecular Engineering, who leads the effort. "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, Fan and his research 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 percent 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. A similar formulation has also been tested at sub-pilot and pilot plants.

"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.

Read the full story here