Experimental demonstration of CLC and the pressure effect in packed bed reactors using NiO/CaAl2O4 as oxygen carrier

Chemical-looping combustion is an emerging technology for power production with integrated CO2 capture. With this combination, the energy penalty is expected to be relatively low, provided that the reactors are operated at elevated pressures (20 bar). Packed bed reactors can better accommodate high pressures compared with interconnected fluidized bed systems, while the challenging gas/solid separation is circumvented. In this work, CLC is demonstrated in a lab scale pressurized packed bed reactor using NiO/CaAl2O4 as oxygen carrier material. H2 and syngas with a typical composition obtained from coal gasification are used as fuel in the reduction step. The pressure has been varied between 2 and 7.5 bar, while it is demonstrated that the pressure has quite a small effect on the overall performance of the CLC reactor. The experiments are well described by a one-dimensional pseudo-homogeneous reactor model, with which it is shown that the required high temperatures for power production can be reached in case the reactor is scaled-up (decreasing the heat losses). A drawback of the oxygen carrier used is that the reduction kinetics depend on the temperature during the previous oxidation, which has been fixed during all the experiments. The reduction kinetics decrease with the oxidation temperature, which is probably caused by interaction with the support material and therefore some further modifications on the support material are required for high temperature applications. In case the process is carried out with syngas and steam, the heat management strategy has to be adapted because of the heat produced by the water gas shift reaction.