NGCC post-combustion CO2 capture with Ca/carbonate looping: Efficiency dependency on sorbent properties, capture unit performance and process configuration

This paper evaluates the potential of post-combustion CO2 capture from a natural gas combined cycle (NGCC) through the use of solid sorbents at high temperatures. Experimental deactivation and residual sorption capacity parameters for various sorbents reported in the literature, as well as from own lab, are reviewed and the performance of three different Ca-based sorbents is studied in more detail: natural CaCO3, natural dolomite and synthetic CaO. Results from steady-state simulations of the Ca/carbonate looping unit show how the energy requirement for sorbent regeneration varies with sorbent properties, sorbent make-up ratio, internal heat recuperation and CO2 recirculation temperature. Net electric efficiency for a reference NGCC power plant without CO2 capture is 58.1% on a lower heating value basis and 49.5% for 90% CO2 capture rate with MEA. In comparison, an NGCC combined with looping of synthetic CaO sorbent and an advanced secondary steam cycle reaches a net electric efficiency of 53.1% for a capture rate above 90%. It is concluded that in addition to improved sorbent capacity and stability, heat recuperation in the solid streams between the carbonator and calciner as well as high CO2 recycle temperature are important for obtaining the high overall power plant efficiency.