(321c) Investigation ON REACTION MECHANISM of Chemical Looping Combustion of COAL Utilizing OXYGEN Carriers

Chemical looping combustion (CLC) is an emerging technology for clean energy production from fossil and renewable fuels. CLC produces sequestration-ready CO2-streams without significant energy penalty. A solid fuel such as coal is rarely used in CLC since the process with solid fuels faces many challenges. The reaction mechanism of coal and metal oxides has not been well established. The generally accepted mechanism is that the coal de-volatilization products initiate the chain reaction with the metal oxide to complete the combustion reaction: CO +MeO = CO2 +Me [1] CO2 +C = 2CO [2]

Other researchers have proposed utilization of oxygen from the metal oxide decomposition for combusting solid fuel (CLOU). This research work focused in understanding the reaction mechanism of solid fuels with oxygen carriers.

Thermo-gravimetric studies, flow reactor studies, in-situ high temperature XRD, SEM and XPS studies were conducted with various solid fuels such as coal, coal char and carbon mixed with various metal oxide in the presence of both nitrogen and carbon dioxide. Theoretical calculations with density functional theory (DFT) were performed to understand the orbital interactions when metal oxide approaches solid carbon. These studies indicated that the combustion reaction of carbon with metal oxides can occur at low temperatures (~500-700 0C). Type of fuel, particles sizes, and separation distance of the fuel and the oxygen carrier had a significant influence on the reaction temperature. Our experimental data suggest that presence of fuels in the vicinity of metal oxide is necessary for oxygen release. Identification of reaction mechanisms and rate information obtained from these studies will also be presented.