Reactor design and operation strategies for a large-scale packed-bed CLC power plant with coal syngas

This paper deals with the design and operation strategies of dynamically operated packed-bed reactors (PBRs) of a chemical looping combustion (CLC) system included in an integrated gasification combined cycle (IGCC) for electric power generation with low CO2 emission from coal. The CLC reactors, that employ ilmenite as oxygen carrier, are operated sequentially across the following phases: oxidation, purge, reduction and heat removal. Two different layout configurations have been considered: in the first configuration, all the inlet streams are fed to the PBRs from the same side ("co-current"), while in the second configuration the coal syngas for the reduction and the N2-rich stream for the heat removal phases are fed from the opposite side ("counter-current"). The number of reactors required for continuous operation of a large-scale power plant has been assessed to comply with an 8% maximum pressure drop across the reactor for different internal reactor diameters and reactor lengths. A sensitivity analysis on the number of reactors has been carried out by varying the particle size, while accounting for the effect of internal mass transfer limitations. A novel strategy for the dynamic operation of the reactors is proposed to reduce gas temperature fluctuations at the inlet of turbomachines and heat exchangers by switching the reactors in parallel with a proper phased displacement. A comprehensive analysis has been carried out on the dynamic reactor behaviour by using a one-dimensional adiabatic reactor model. The outcomes from the reactor model have been used to calculate the resulting conditions of the gases that are leaving the reactors operated in parallel. The results obtained indicated that 14-16 units (for the co-current and counter-current configuration respectively) with 5.5m of internal diameter and 11m of length are required for continuous operation of a 350-400MWe coal-fired power plant. Although packed-bed reactors are dynamically operated, the gases released by the CLC units do not exhibit significant transient temperature changes (only about 6°C for the gas turbine) and the system seems promising for future large-scale power plant applications with integrated CO2 capture.