In-depth evaluation of a ZrO2 promoted CaO-based CO2 sorbent in fluidized bed reactor tests
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Date
2017-10-01Author
Antzara, Andy N.
Arregi Joaristi, Aitor
Heracleous, Eleni
Lemonidou, Angeliki A.
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Chemical Engineering Journal 333 : 697-711 (2018)
Abstract
Carbonate looping, based on the reversible gas-solid reaction of CaO with CO2, is
considered as a promising alternative to amine scrubbing for post-combustion CO2
capture. Solid sorbents suffer however from degradation, mainly due to thermal
sintering and elutriation of fine particles due to enhanced attrition rates in fluidized-bed
reactors. In this work, a previously developed synthetic Zr-promoted CaO-based CO2
sorbent was tested in a fluidized bed reactor unit to determine its performance in cyclic
CO2 capture over various operating conditions, relevant to industrial application. The
material exhibited very high carbonation conversion (60-85%) during pre-breakthrough
under all investigated conditions, with more than 75% CO2 removal. The addition of
steam in both the carbonation and calcination steps resulted, not only in higher
conversions, but also in significantly enhanced cyclic stability. Deactivation was less
than 16% after 20 consecutive cycles. The performance of the sorbent was further tested
under lower temperature difference between carbonation (680°C) and calcination
(750°C), a scheme more favourable for utilizing the heat generated by the highly
exothermic carbonation reaction for the thermal demands of the calciner in the actual
process. The material displayed similar carbonation conversion, but inferior
performance in terms of stability. Advanced post-reaction characterization with in-situ
XRD revealed that even though the sintering effect was more limited due to the lower
calcination temperature, calcination of CaCO3 was incomplete, rendering a small
fraction of the sorbent inactive for CO2 capture. Under severe calcination conditions
(920°C and 80 vol.% CO2 concentration) the sorbent maintained more than 70% of its
initial sorption capacity (7.1 moles of CO2/kg of sorbent after 20 cycles), a value more
than 5 times higher compared to natural limestone.