Through a research planning visit, Dr. Kevin Whitty of the University of Utah will initiate a collaborative project with Swedish partners, Drs. Anders Lyngfelt, Tobias Martison, and Henrik Leion, at the Chalmers University in Gothenburg. Together, they intend to pursue questions related to chemical looping combustion by drawing on the renowned expertise in chemical looping at Chalmers and the well established strengths in chemical kinetics at the University of Utah. The Swedish partners offer bench-scale pilot facilities for chemical looping combustion with interconnected fluidized beds that can be used to oxidize a variety of gaseous fuels and coals. This is complemented by the Utah group's progress in developing kinetic parameters needed to model the combustion of coal and petroleum coke with an oxygen carrier. The initial collaboration is expected to help the U.S.-Swedish team extend their research with the goal of accelerating progress in the field of chemical looping with oxygen uncoupling (CLOU) . If successful, results may contribute to the fundamental engineering required to understand and develop a CLOU process that effectively reduces the residence time for solids in fuel reactors by a significant percent.

Likely broader impacts include advances in knowledge of theoretical and practical CO2 capture. Envisioned long-term applications could lead to designs for continuous reactors to demonstrate CLOU at larger scales and at reduced costs. To build on preliminary findings, the principal investigator plans to submit a follow-on application to the National Science Foundation for cooperative research on related transport and thermal fluids phenomena. Furthermore, one U.S. graduate student from the University of Utah will travel with Dr. Whitty to Gothenburg and participate in joint activities at Chalmers, thereby gaining beneficial international research experience. This early career access to expert Swedish engineers and specialized reactor scaling should lead to a beneficial professional network in the increasingly important fields related to energy and combustion.

Project Report

" funded travel of researchers from the University of Utah to Chalmers University of Technology in Gothenburg, Sweden to stimulate collaboration between these universities. Chalmers is a leading institution in chemical looping combustion research and activities there cover a range of scales, from fundamental development of oxygen carrier particles to pilot-scale testing of dual bed systems. The University of Utah has extensive experience in lab and pilot-scale research of combustion and gasification systems and is building up its chemical looping combustion research program. Major activities under this program included (1) collaboration on experimental determination of oxidation and reduction kinetics for copper-based chemical looping carriers, (2) design of a pilot-scale dual fluidized bed chemical looping system at the University of Utah and (3) joint modeling and simulation of dual fluidized bed chemical looping systems. Under the first activity, the University of Utah and Chalmers collaborated to evaluate rates of oxidation of copper-based oxygen carriers in lab-scale tests using thermogravimetric analyzers and small electrically heated batch fluidized bed systems. The experimental work was funded by other projects, but the collaborative nature was promoted by this project. Several types of carriers were evaluated, including materials prepared at Chalmers. Rates of oxidation were measured at various temperatures and oxygen partial pressures and evaluated with consideration to the extent of carrier conversion. Experimental evaluation is complicated by the fact that both equilibrium oxygen partial pressure and the rate of the reversible oxidation reaction change with temperature. The evaluation and an expression describing oxidation of copper-based carriers was published and has been presented at international meetings. A similar evaluation was performed for reduction of copper-based carriers, which fall into the category of "oxygen uncoupling" carriers that spontaneously release gaseous oxygen in low-O2 environments. The rate of oxygen release, which is an important determiner of overall performance of solid fuel conversion in a copper-based chemical looping system, was investigated using carrier material supplied by Chalmers. A universal expression describing the rate of carrier reduction versus temperature and local oxygen concentration was developed. A key outcome of these studies is that both oxidation and reduction are rapid enough at combustion temperatures that copper-based chemical looping with oxygen uncoupling is feasible even for low-reactivity fuels such as bituminous coal and petroleum coke. The second major activity involved cooperation on the design of a 100 kWth dual fluidized bed chemical looping combustion system at the University of Utah that is being built under separate funding. In addition to the overall system design, specific design decisions such as whether the fuel reactor should be a bubbling or circulating bed and whether at this scale it is preferable to construct externally heated metal reactors or build refractory-lined systems, needed to be resolved. Under this project, researchers from the University of Utah visited Chalmers University of Technology to learn details of the design of their dual-bed pilot system and to discuss operating experience of that system. Meetings during that trip as well as afterwards provided valuable input for the design of the Utah system. The design of the University of Utah system was completed during this project and construction of the pilot-scale chemical looping process development unit is currently in progress. The final collaborative activity involved modeling and computational simulation of dual fluidized bed reactors of the kind used in chemical looping systems. Both institutions have modeling projects and have constructed clear acrylic cold flow models of their respective pilot-scale systems. Under this program a University of Utah graduate student traveled to Sweden to work with the Chalmers researchers performing the modeling and learned about operation and analysis of the cold flow system. The collaboration that has developed in this area continues, with focus on computational simulation of dual fluidized bed system. The two universities are now working on two joint publications regarding cold flow modeling and simulation of interconnected dual-bed chemical looping systems. Through the collaboration developed under this program and resulting publications, there is now a better scientific understanding of chemical and physical processes that take place during chemical looping with oxygen uncoupling. Researchers and students from the University of Utah and Chalmers have benefitted from the opportunity to work with world experts, and the impacts of this program include establishment of valuable international cooperation. Successful deployment of advanced technologies such as chemical looping combustion requires a global effort, and this program has been a step in that direction.

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University of Utah
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