Calcium looping for power generation with CO2 capture: The potential of sorbent storage for improved economic performance and flexibility

Abstract

Abstract The aim of this work is to investigate the potential of calcium looping (CaL) CO2 capture system for power plants with sorbent storage, for flexible and low-emission power generation from coal. Two different CaL systems have been analyzed for CO2 capture from a reference pulverized coal power plant: (i) a Baseline CaL system and (ii) a FlexiCaL system with sorbent storage. The sorbent storage systems can be exploited in two ways: the primary storage system allows to decouple the carbonator and the calciner load and reduce the size of the calciner island; the secondary storage unit allows to increase/reduce the maximum/minimum power output of the plant for improved grid services. Heat and mass balances have been computed at different loads with process simulation software, considering the off-design operation of the main plant components. A simplified economic analysis has been carried out to compute the cost of electricity and estimate the economic benefits of the primary sorbent storage system for a given power generation profile. The method used in this work allowed to compute the off-design behaviour of the CaL power plant the with the highest accuracy among the literature studies and to understand the potential of the secondary solids storage to provide grid services for the first time. The part-load analysis provided insights on the design of the carbonator reactor, that should limit the heat transfer surface in the riser to avoid excessive reactor cooling at part-load. Conversely, reaction heat should preferably be extracted from the external heat exchangers, where the heat transfer rate can be controlled more easily. From the thermodynamic standpoint, the two CaL plants feature similar efficiency on weekly cycling basis. The secondary storage allows increased operativity of the FlexiCaL plant on the secondary market, thanks to +2% of maximum power and -5% of minimum power output. The primary storage system allows reducing the capital cost of the CaL system, leading to LCOE reduction by 4-5% compared to the Baseline case, in a wide range of carbon tax and plant availability.