High Temperature CO2 Capture with Modified CaO-Based Pellet Sorbents

High temperature CO₂ capture with modified CaO-based pellet sorbents

Yinghai Wu, Ian He, Vasilije Manovic and Edward J. Anthony

CanmetENERGY, Natural Resources Canada

1 Haanel Dr. Ottawa, ON K1A1M1

Abstract

It is generally accepted that increasing greenhouse gases, in particular CO₂, contribute to global warming. Currently, one third of all anthropogenic CO₂ emissions come from fossil fuel combustion for power generation. CO₂ capture from large stationary sources is therefore necessary to stabilize the atmospheric concentration of CO₂ in order to prevent more severe climate change effects in the future. CaO-based sorbent looping cycles, which utilises reversible carbonation and calcination reactions, offer a promising technology to separate CO₂ from flue or syngas to produce a high purity CO₂ stream suitable for sequestration or use and in the case of syngas application, for sorption enhanced H₂ production. Naturally occurring limestones (mostly calcitic) have so far been the subject of intensive research. However, natural sorbents lose their CO₂ carrying capacity quickly with increasing numbers of reaction cycles. Hence, hydration of the spent sorbents has been proposed as a method to recover the lost carrying capacity, but the resulting reactivated sorbents tend to be fragile and are unsuitable for fluidized bed conditions. To overcome this drawback with natural sorbents, a novel method using pelletization of the sorbents is proposed here. In this study, the performance of the pelletized sorbents was tested in a small bubbling fluidized bed reactor. Calcium aluminate cements and bentonite were investigated as different types of binders for pelletization. It was shown that pelletized sorbent can maintain their capacity over many cycles. The effect of sintering and attrition of the pellet sorbents are also discussed and the morphology changes of these sorbents during carbonation and calcination cycles are examined by SEM.