Successful 200+ Hour Continuous Operation of Coal-Direct Chemical Looping Combustion Technology

The Ohio State University successfully demonstrated 200+ hours of continuous operation of a fully integrated chemical looping combustion pilot plant for solid fuel conversion last quarter. The Coal-Direct Chemical Looping (CDCL) is an advanced oxy-combustion carbon capture technology for coal-fired power plants. This demonstration represents the first long-term integrated operation of any chemical looping technology in the world.

Directed by Professor Liang-Shih Fan and his team of graduate students, the successful operation of the 25 kWth CDCL sub-pilot unit conducted at Ohio State’s Clean Energy Research Laboratory signifies the commercial potential for the Ohio State-patented CDCL technology.

Chemical looping technology is a transformational process for converting carbon-based fuels such as coal, syngas and natural gas to electricity, liquid fuels and/or hydrogen with low to negative net carbon emissions. As one of the ultimate technologies in the U.S. Department of Energy’s Carbon Emission Control Technology Roadmap, the chemical looping technology utilizes the reduction-oxidation reactions of an oxygen carrier to segregate the air source from the fuel. This eliminates the need for energy intensive CO2 separation systems that require high capital and operating costs.

CONSOL Energy, in collaboration with Ohio State, performed an economic analysis of the CDCL process using DOE’s economic and boiler performance assumptions for a coal-fired, supercritical power plant. The results indicate that Ohio State’s CDCL process can meet and exceed DOE’s target of less than 35% increase in cost of electricity with greater than 90% carbon capture. 

The CDCL sub-pilot unit successfully demonstrated the integrated performance of the two major process components: the counter-current moving bed reducer and the fluidized bed combustor, establishing the viability of the process for the direct conversion of coal to electricity. The CDCL process utilizes an iron-based oxygen carrier cycling between the reducer and combustor reactors.

Under DOE’s Carbon Capture Program, the fully integrated, streamlined CDCL plant is unique in both design and operation because of its moving bed design and non-mechanical valves. The CDCL system uses an in-situ ash removal system in the reducer to eliminate the need for additional fines removal devices, which lowers the unit capital and operating costs and simplifies the process design and operation.

The 200+ hours of continuous operation, using metallurgical coke and sub-bituminous and lignite coals, demonstrated the robustness of the unique moving bed reducer design and non-mechanical valve operation by achieving nearly 100% solid fuel conversion with more than 99% carbon dioxide purity.

The concentrated CO2 stream produced from the reducer contained very low concentrations of methane, oxygen, and carbon monoxide. From the reducer to the combustor, minimal carbon carry-over was observed from the transfer of oxygen carrier particles contributing to nearly 100% carbon capture efficiency. Additionally, pollutant analyses during the operation showed comparable NOx and SOx concentrations in the reducer as compared to concentrations in a conventional pulverized coal combustion boiler equipped with a low NOx burner, and negligible amounts of both pollutants observed in the combustor effluent gas. The long-term demonstration validated the oxygen carrier particle performance in terms of its reactivity, recyclability and attrition resistance.

This program was primarily sponsored by DOE’s National Energy Technology Laboratory (Project #: DE-NT0005289, Project Title: Coal-Direct Chemical Looping Retrofit to Pulverized Coal Power Plants System for In-Situ CO2 Capture) and the Ohio Development Services Agency. In addition, Ohio State has conducted this research in collaboration with multiple industrial partners: Babcock & Wilcox Power Generation Group, Inc. (B&W PGG), CONSOL Energy, Inc., and Clear Skies Consulting LLC.

Further, a fully integrated 250-kWth pressurized Ohio State Syngas Chemical Looping (SCL) pilot unit is being designed and constructed at DOE’s National Carbon Capture Center in Wilsonville, Alabama and is expected to be in operation in late 2013 to further verify the operability and economic feasibility of advanced chemical looping technologies. Combined, more than 800 operating hours have been achieved using the SCL and CDCL sub-pilot units, which demonstrate the reliability and operability of the Ohio State design.

This remarkable feat follows the recent awarding of Phase I DOE funding for advanced oxy-combustion technologies. Ohio State is working with B&W PGG, the Phase I project principal investigator, to conduct a techno-economic study of a commercial 550 MWe power plant using the CDCL process. The CDCL process can be implemented as a greenfield plant or as a cost-effective repowering option to existing coal-fired power plants.