A flexible CO2 capture system for backup power plants using Ca(OH)2/CaCO3 solid storage

Abstract

CO₂ capture technologies are required to address intermittent sources of CO₂, such as the natural gas combined cycle (NGCC) used for backup power applications. The high reactivity of Ca(OH)₂ powder facilitates the design of low cost carbonators to capture diluted CO₂ (typically below 4%_v in NGCC flue gases) as CaCO₃. By storing CaCO₃ and Ca(OH)₂ it is possible to decouple the CO₂ capture step in the carbonator from the oxy-calciner/hydrator block in which Ca(OH)₂ is regenerated and CO₂ extracted. This facilitates the integration of CO₂ capture elements in backup power systems. Simulations of the completely integrated backup power plant with and without capture indicated that for a NGCC capacity factor (CF) of 0.1, the thermal capacity of the oxy-calciner was just 2% of the gross power output of the NGCC gas turbine. Capture efficiencies of 90% can be reached without modifying the operating conditions of the gas power plant, while achieving a global efficiency of 38% for the system with CO₂ capture. A basic economic analysis indicated that the proposed scheme would lead to a cost of CO₂ avoided of approximately 200 $ per tCO₂, making it suitable for retrofitting natural gas-based power plants.