Design of a Novel Fluidized Bed Reactor To Enhance Sorbent Performance in CO2 Capture Systems Using CaO

Abstract

This work deals with the modeling and design of a novel bubbling fluidized bed reactor that aims to improve the CO2 carrying capacity of CaO particles in CO2 capture systems by calcium looping (CaL). Inside the new reactor (the recarbonator) the particles that arrive from the carbonator of the CaL system react with a concentrated stream of CO2, thereby increasing their carbonate content up to a certain value, which can be predicted by means of the model proposed. The recarbonator model presented in this work is based on the Kunii and Levenspiel model for bubbling bed reactors of fine particles. The reduction in the gas volume due to the reaction of CO2 with CaO is taken into account by dividing the recarbonator into a number of reactor elements where the bubble properties are recalculated, whereas the solids are perfectly mixed throughout the bed. The model has been used to test the conceptual design of a CaL system that incorporates an additional recarbonator reactor to more than double the residual CO2 carrying capacity of the sorbent (from 0.07 to 0.16). In a reference design case of a 1000 MWth coal-fired power plant it was found that the recarbonator cross section needs to be between 80 and 100 m2 (about 40–50% the area of the carbonator reactor), the solid inventories around 1200–1500 kg/m2, and the inlet CO2 gas velocities between 0.6 and 0.9 m/s. This set of operating and design windows predicts an increase in the carbonate content of the particles in the recarbonator of around 0.02, which has been shown to be sufficient to sustain the increased average CO2 carrying capacity of the sorbent.