Researchers at The Ohio State University (OSU) have successfully completed more than 200 hours of continuous operation of their patented Coal-Direct Chemical Looping (CDCL) technology - a one-step process to produce both electric power and high-purity carbon dioxide (CO2). The test, led by OSU Professor Liang-Shih Fan, represents the longest integrated operation of chemical looping technology anywhere in the world to date.
The test was conducted at OSU’s 25kWt CDCL combustion sub-pilot unit under the auspices of DOE’s Carbon Capture Program, which is developing innovative environmental control technologies to foster the use of the nation’s vast coal reserves. Managed by the Office of Fossil Energy’s National Energy Technology Laboratory, the program’s specific goal is to develop CO2 capture and compression technologies that can reduce the capital cost and energy penalty of CO2 capture by more than half—equivalent to CO2 capture at less than $40 per metric ton—when integrated into a new or existing coal fired power plant. The successful test moves chemical-looping a step closer to full scale.
Chemical looping is an advanced technology that offers several advantages over traditional combustion. In a chemical-looping system, a metal oxide, such as an iron oxide, provides the oxygen for combustion. The metal oxide releases its oxygen in a fuel reactor with a reducing atmosphere, and the oxygen reacts with the fuel. The reduced metal cycles back to an oxidation chamber where the metal oxide is regenerated by contact with air. The metal oxide is then reintroduced into the fuel reactor, thus completing the loop. Since CO2 separation occurs simultaneously with coal conversion, chemical looping offers a low-cost scheme for carbon capture. The process can produce power, synthesis gas, or hydrogen in addition to high-purity CO2.
OSU reports that the CDCL plant’s 200+ hours of operation, using metallurgical coke and subbituminous and lignite coals, shows the robustness of its novel moving-bed design and non-mechanical valve operation. The combination resulted in nearly 100% solid fuel conversion and a CO2 stream more than 99% pure, making it applicable to CO2 enhanced oil recovery operations.
The OSU project is expected to benefit the DOE Carbon Capture Program by identifying oxygen carriers and a chemical looping process having the potential to control multiple pollutants, including sulfur dioxide (SO2) and nitrogen oxides (NOx), along with CO2. OSU research aims to identify potential barriers and optimize the CDCL technology and provide realistic data for future technological and economic analysis.
In addition to DOE, OSU is partnering on the project with the Ohio Department of Development, Babcock & Wilcox Power Generation Group Inc., CONSOL Energy Inc., and Clear Skies Consulting LLC.
In a related project, DOE’s National Carbon Capture Center in Wilsonville, AL., will serve as the host site for the construction and operation of a fully integrated 250kWt pressurized syngas chemical looping pilot unit starting this year. The facility will be used to further prove the operability and economic feasibility of OSU’s advanced chemical looping technologies.