Experimental Validation of the Calcium Looping CO₂ Capture Process with Two Circulating Fluidized Bed Carbonator Reactors

Abstract

[EN] Postcombustion CO2 capture using CaO as a regenerable solid sorbent in a circulating fluidized bed
\n(CFB) carbonator is emerging as a promising CO2 capture technology. Experimental validation of this
\nconcept is provided through a comparative analysis of the results obtained in two laboratory-scale dual
\nfluidized bed (DFB) installations located at INCAR-CSIC (Spain) and IFK (Germany). The analysis is focused on the performance of the CFB carbonator reactors operated with continuous solid circulation of
\nCaO. A reasonable closure of the carbon balances (i) between the CO2 that has disappeared from the gas
\nphase, (ii) the CaCO3 circulating between the reactors and (iii) the CaCO3 that is formed within the
\ncarbonator bed has been established. A necessary condition for the capture of a given molar flow of CO2
\nis experimentally demonstrated and requires that a slightly over-stoichiometric molar flow of active CaO
\nis supplied to the carbonator. The deactivation behavior of the sorbents during continuous looping
\nconditions has been measured. The key parameter to interpret the carbonator reactor results has been the
\nactive space time, that is indicative of the CaO inventory per molar flow of CO2 participating in the
\ncarbonation reaction and of the reaction rate of the solid inventory in the reactor. Two different
\napproaches have been utilized in order to find a suitable expression for this parameter, thus achieving its
\ncorrelation with the CO2 capture efficiency. A simple model assuming instant mixing of solids and plugflow
\nof the gas has been tested. Based mainly on carbonator active space time variation, the CO2 capture
\nefficiency are shown to lie between 30 % and above 90 %. These results confirm the technical viability
\nof the calcium looping postcombustion CO2 capture process. They have been used for designing the
\ncurrent pilot-plant facilities which are scaled up 20-50 times in regard to the lab-scale units. Moreover,
\nthe lab-scale results obtained allow for simulation work to be initiated in regard to the full scale Ca looping application.