(60dh) Technology Development for Coal-Direct Chemical Looping Power Generation: Experimental Demonstration and Process Assessment

Authors: 
Zhang, Y., The Ohio State University
Wang, D., The Ohio State University
Fan, L. S., The Ohio State University
Flynn, T., Babcock & Wilcox Company
Velazquez-Vargas, L. G., Babcock & Wilcox Company
Tong, A., The Ohio State University
Chemical looping combustion (CLC) is recognized as a promising technology for the conversion of carbonaceous fuel with inherent CO2 capture. The coal-direct chemical looping (CDCL) technology is a CLC technology that uses coal as feedstock for power generation. Previous research has shown that CDCL process can cost-effectively generate clean electricity with higher net plant energy efficiency compared to conventional pulverized-coal process with CO2 capture. In the CDCL process, coal is introduced into a moving bed reducer reactor and fully oxidized to form carbon dioxide (CO2) and steam using iron-based oxygen carrier particles. The reduced particles are transported to a fluidized bed combustor reactor. They are regenerated using air and transported back to the reducer. High purity CO2 stream can be obtained from the reducer gas outlet after water removal, as the CDCL process avoids direct contact between fuel and air. High quality heat can be extracted from the hot gas outputs from each reactor and from in-bed heat exchangers in the reactors for power production.

Experiments have been conducted in support of process scale-up. The Ohio State University (OSU) has conducted experiments on a 25 kWt sub-pilot CDCL facility. The results showed the sub-pilot facility is capable of producing CO2 at 99% purity with the coal conversion higher than 97%. In collaboration with The Babcock & Wilcox Company (B&W), a 250 kWt pilot CDCL facility was designed, constructed, and successfully demonstrated with over 2-week continuous operation and similar performance as compared to sub-pilot facility. The feasibility of CDCL technology was further validated and knowledge associated with process scale-up was obtained through these experiments.

In addition to sub-pilot and pilot testing, a comprehensive process analysis was performed to evaluate and optimize the process efficiency as well as minimize the overall cost of electricity production using the CDCL process. A process model of CDCL power plant was developed in Aspen Plus based on the results of sub-pilot and pilot plant experiments and references. The results indicate that the CDCL technology shows a higher exergy efficiency and is more economically favorable as compared to conventional coal-based power generation technology with CO2 capture.