Carbon capture technology moves toward power plant integration

Powered by $7.5 million in federal and state funding, chemical engineering researchers are advancing their iron-based coal direct chemical looping (CDCL) technology closer to commercialization.

Liang-Shih Fan, distinguished professor of chemical and biomolecular engineering and director of Ohio State’s Clean Energy Research Laboratory, pioneered the CDCL technology, which chemically harnesses coal’s energy and efficiently captures the carbon dioxide produced before it can be released into the atmosphere. His research team recently began two new projects co-funded by the Department of Energy’s National Energy Technology Laboratory and the Ohio Development Services Agency.

One of the projects is focused on completing the front-end engineering design of a 10 MW_e (megawatts electric) CDCL large pilot plant. The Ohio State research team has successfully demonstrated a 25 kW_th (kilowatts thermal) sub-pilot CDCL process for more than 1,000 hours of operation, testing a wide range of solid fuels from anthracite coals to lignite and biomass. One MW_e can power approximately 750 homes.

Babcock & Wilcox Company, Inc. (B&W) is leading the commercial design effort for this novel technology. Research and testing of a 250 kW_th CDCL small pilot unit are ongoing at the B&W Research Center in Barberton, Ohio, and at Ohio State’s labs.

In a chemical-looping system, a metal oxide, such as iron oxide, provides the oxygen for combustion. The metal oxide reacts with the fuel in the reducer, donating its oxygen to produce a highly concentrated stream of carbon dioxide. The reduced metal cycles to an oxidation chamber, the combustor, where the metal oxide is regenerated by contact with air. The metal oxide is then reintroduced into the reducer, thus completing the loop. The oxygen carrier oxidation reaction releases a large amount of heat for steam production. The produced steam is sent to a steam turbine for electricity generation.

“In the simplest sense, combustion is a chemical reaction that consumes oxygen from air and produces heat,” Fan said. “We found a way to release the heat and easily contain the carbon dioxide produced. We carefully control the chemical reaction so that the coal is consumed chemically, and the carbon dioxide is inherently produced as a concentrated gas that can be directly stored and/or utilized.”

The design of the 10 MW_e large pilot plant will incorporate advanced combustion and control features that have been verified through performance testing on the 25 kW_th sub-pilot unit at Ohio State and further testing in a 250 kW_th pilot at B&W currently in operation.

“The reason we’ve been so successful is how simple and effective our reactor system design really is compared to other groups working with chemical looping,” said Research Assistant Professor Andrew Tong.

Tong is the principal investigator on the team’s second project receiving funding, aimed at improving the heat exchanger network design and optimizing the process efficiency for the CDCL technology. This project also entails dynamic modeling of the 10 MW_e CDCL process, which will directly influence the eventual design and operation control of the large pilot plant. B&W is a sub-awardee of this project as well.

“Researchers here at Ohio State are working to scale up the technology, looking at how we can use and size the different reactor components and systems, and understanding the reaction kinetics of materials and hydrodynamics of the flow in each,” explained Tong. “B&W’s role will be to come up with the detailed designs of the reactors, heat exchangers, and interconnected components for power plant-wide integration.”

Projects funded by DOE’s Advanced Combustion Systems Program—including those at Ohio State—are focused on driving down costs and collecting engineering data for scale-up of advanced coal-based power systems. The program’s goal is to develop technologies that capture greater than 90 percent of the CO₂ without the need for post-combustion capture systems. According to Tong, Ohio State’s CDCL system is achieving a 96.5 percent capture rate.

“For utility companies, the primary benefit of our CDCL technology is regulation compliance in a very efficient manner,” said Tong. “For the benefit of us all, it reduces greenhouse gas emissions from power plants.”

Industry partners involved in one or both projects include Particulate Solid Research, Inc. (PSRI), Johnson Matthey Company, Electric Power Research Institute (EPRI), Clear Skies Consulting and Nexant. Dover (Ohio) Light & Power is also a partner and a possible test site host for the 10MW_e large pilot plant. 

Tong added that if all goes well, the 10 MW_e power plant could be in development by 2020.