Thermodynamic performance assessment and comparison of IGCC with solid cycling process for CO2 capture at high and medium temperatures

Abstract

Solid sorbents can be used to capture CO2 from pre-combustion sources at various temperatures. MgO and CaO are typical medium- and high-temperature CO2 sorbents. However, pure MgO is not active toward CO2. The addition of Na2CO3 increases the operating temperature and significantly increases the reactivity of sorbents to capture CO2. Na2CO3-promoted MgO is a promising medium-temperature CO2 sorbent. In this study, the thermodynamic performance of integrated gasification combined cycle (IGCC) systems with Na2CO3–MgO-based warm gas decarbonation (WGDC) and CaO-based hot gas decarbonation (HGDC) is evaluated and compared with that of an IGCC system with methyldiethanolamine (MDEA)-based cold gas decarbonation (CGDC). Assuming that the average CO2 capture capacities of solid sorbents are one-third of their theoretical maxima, we reveal that the IGCC system undergoes approximately 2.8% and 3.6% improvement on net efficiency when switching from CGDC to WGDC and to HGDC, respectively. The net efficiency of the system is increased by improving the CO2 capture capacity of the sorbent. The IGCC with Na2CO3–MgO experiences more significant increase in efficiency than that with CaO along with the improvement of sorbent average CO2 capture capacity. The efficiency of the IGCC systems reaches the same value when the average CO2 capture capacities of both sorbents are 53% of their theoretical levels. The effects of gas turbine combustor fuel gas inlet temperature on IGCC system performance are analyzed. Results show that the efficiency of the IGCC systems with HGDC and WGDC increases by 0.74% and 0.53% respectively as the fuel gas inlet temperature increases from 250 °C to 650 °C.