Integration of coal gasification and packed bed CLC for high efficiency and near-zero emission power generation

Abstract

A detailed thermodynamic analysis has been carried out of large-scale coal gasification-based power plant cycles with near zero CO2 emissions, integrated with chemical looping combustion (CLC). Syngas from coal gasification is oxidized in dynamically operated packed bed reactors (PBRs), generating a CO2-rich stream ready for sequestration. PBRs have recently been proposed for CLC as an alternative for an interconnected fluidized bed reactors system operated at high pressure, to circumvent difficulties associated with solids circulation and gas/solid separation at high temperature and pressure. However, in view of the dynamic operation, the heat management in PBRs needs to be carefully assessed, since it affects the temperature and gas flow rates at the reactor outlet during the different cycles. The present work investigates the effect on plant performance of two different PBRs heat management strategies proposed in a previous work, with the aim of avoiding problems related to oxygen carriers featuring low reduction kinetics at moderate temperatures. The system is designed to achieve full integration of the steam cycle with the other units of the plants in order to improve the overall plant efficiency. A sensitivity analysis on the CLC operating pressure, the steam cycle parameters and the effect of syngas dilution with exhaust recirculation and steam addition was performed. The mass and energy balances of the integrated plant are presented in detail and the plant performance is compared with reference technologies. The net electric efficiency approaches 41% (based on the coal LHV) with a CO2 capture efficiency over 97%. Moreover, it has been found that the heat management strategies adopted do not significantly affect the maximum net electric efficiency, even if different power shares between the gas and steam turbines are obtained, with consequent implications in the plant design and economics.