Performance of a Bench-Scale Fast Fluidized Bed Carbonator

Abstract

The carbonate looping process is a promising technology for CO2 capture from flue gas. In this process, the CO2 capture efficiency depends on the performance of a carbonator that may be operated as a circulating fluidized bed (CFB). In this paper, the carbonator performance is investigated by applying a new experimental method with accurate control of the particle recirculation rate. The experimental results show that the inlet calcium to carbon molar ratio is the main factor on the CO2 capture efficiency in the carbonator, that is, increasing the inlet Ca/C from 4 to 13 results in increasing the CO2 capture efficiency from 40 to 85% with limestone having a maximum CO2 capture capacity of only 11.5%. Furthermore, a reactor model for a carbonator is developed based on the Kunii–Levenspiel’s model. A key parameter in the model is the particle distribution along the height of the reactor, which is estimated from experiments under stable operating conditions with constant bed inventory, reactor temperature and exit CO2 concentration. The validated CFB carbonator model was used to simulate different operating conditions relevant for CO2 capture from a power plant and from a cement plant. The results show that particle recirculation rates of 2–5 kg/(m2s) or ratio of bed inventory to recirculation rates of 70–176 s are sufficient for attaining 90% CO2 capture efficiency depending on the inlet Ca to C ratio.