Experimental Demonstration of Two-Stage Packed Bed Chemical-Looping Combustion Using Syngas with CuO/Al2O3 and NiO/CaAl2O4 as Oxygen Carriers

Recently, a novel two-stage reactor configuration for packed bed chemical-looping combustion (CLC) has been proposed and studied by numerical simulations. This two-stage CLC consists of two pressurized packed bed reactors connected in series, where the first bed contains an oxygen carrier material which is reactive at relatively low temperatures (450 degrees C) such as CuO/Cu, while the second bed contains an oxygen carrier which is resistant to relatively high temperatures (typically 1200 degrees C) such as NiO/Ni. In this work, this two-stage CLC concept has been experimentally demonstrated using CuO/Al2O3 and NiO/CaAl2O4 as bed materials in a high-pressure, high-temperature packed bed reactor. The influence of the operating conditions has been examined, and a validated reactor model has been used to scale up the process to industrial scale. The two-stage CLC concept is successfully demonstrated with a maximum temperature of 839 degrees C in the second bed. The operating pressure, the throughput during the reduction cycle, and the fuel concentrations have been found to result in small or negligible influences on the maximum temperature rise. This means that they do not affect the TS-CLC performance as long as the cycle time is adopted such that the heat produced in the first reactor bed is exactly transferred to the second bed. It has also been demonstrated that operation at higher pressures (to reach a higher overall process efficiency) does not affect the performance of the TS-CLC reactor. However, the fuel type (H-2, syngas, CO, or CH4) strongly influences the temperature increase in the reactor, since it influences to what extent the oxygen carriers can be reduced. The experimental results could be well described by a one-dimensional packed bed reactor model provided that the extent of heat losses and the response time of the thermocouples are properly taken into account. The validated reactor model shows that the desired gas flow rate at 1200 degrees C can indeed be produced after some small changes in the operating conditions and the active weight content of the oxygen carriers. Therefore, TS-CLC can be regarded as a feasible technology for power production with inherent CO2 capture with high LHV efficiency.