Calcium Looping with Enhanced Sorbent Performance: Experimental Testing in A Large Pilot Plant

Abstract

Postcombustion CO2 capture by Calcium Looping (CaL) has been successfully carried out for more than 700 hours in a 1.7 MWth continuous pilot facility in La Pereda (Spain). The pilot is equipped with two interconnected circulating fluidized bed reactors: a CO2 carbonator, where CaCO3 is formed when CO2 is captured from a combustion flue gas in contact with fine particles of CaO, and an oxy-fired calciner, where a highly concentrated stream of CO2 is generated by decomposing the CaCO3 formed in the carbonator. CaL is a technology that has the potential to achieve a substantial reduction in the cost of CO2 capture because of the capability to recover waste heat and generate more power from the additional fuel fired in the calciner. However, one of the weaknesses of CaL systems is the rapid deactivation of the sorbent. The EU “ReCaL” project (http://recal-project.eu/) aims to develop a robust and simple reactivation process to stabilize sorbent activity in CaL systems, based on the thermodynamic and kinetic ability of the sorbent to increase its CaCO3 conversion under enhanced carbonation conditions. This paper presents a first attempt to demonstrate the concept at the scale of the La Pereda 1.7 MWth pilot plant. It describes the redesign and retrofitting exercise conducted in the pilot and discusses the initial experimental results achieved when one of the loop seals is used as “recarbonator” reactor (putting a small flow of pure CO2 in contact with partially carbonated particles arriving from the carbonator). The findings of this study suggest that recarbonation could be responsible for about 100% increase in the average CO2 carrying capacity of the material used in the CO2 capture step taking place in the carbonator. This could allow CaL systems to operate with very low limestone make-up flow requirements, making this emerging capture technology more competitive.