Coupled CLC and CLOU behaviour for Solid Fuels Conversion

Other conference contribution, 2011

There are two main strategies for using solid fuels in chemical-looping. The first is conventional Chemical-Looping Combustion (CLC) where the fuel is directly introduced to the fuel reactor with the gasification of the solid fuel and subsequent reactions with the oxygen carrier occurring simultaneously. The second is referred to as Chemical-Looping with Oxygen Uncoupling (CLOU) and requires an oxygen carrier which releases gas-phase O2 in the fuel reactor. The solid fuel is in this case oxidized through normal combustion which is a considerably faster reaction path than in conventional CLC. CLOU also makes it easier to obtain full conversion of the fuel since the oxidation of intermediates can occur in the gas-phase above the bed of oxygen carrier. The difference between CLOU and conventional CLC is determined by the oxygen carrier. If the carrier releases gas-phase O2 it is CLOU, if not it is CLC. But the situation can occur when the rate of O2 release from a CLOU oxygen carrier is comparably slow, and consequently the major reaction mechanism may be CLC. Nevertheless, the oxygen released could be very helpful in improving gas conversion as well as char conversion. This paper presents experimental results and discussed the benefits with this kind of coupled CLC and CLOU behaviour. Experiments were performed in a batch fluidized bed reactor with wood char and petroleum coke used as fuel. The primary oxygen carriers used were manganese-based with different additives such as Fe or Ca. These experiments were compared to both conventional CLC experiments with the iron-titanium mineral ilmenite as oxygen carrier, and to pure CLOU experiments where CuO on Zr2O was used as oxygen carrier. The results indicate that it is possible to utilize a combination of CLOU and conventional CLC. The rate of conversion of char for the combined system is lower as compared to pure CLOU but high compared to conventional CLC. The system also had more or less full char and gas conversion similar to the CLOU case.