The primary objective of this study was to investigate the integration of combined calcium looping (CaL) and chemical looping combustion (CLC) with steam gasification of biomass through the utilization of composite pellets consisting of limestone, CuO, and a calcium aluminate cement binder. In this process, the heat released from the exothermic reduction of CuO is used to calcine CaCO 3 . The technologies can be integrated by combining an oxygen carrier such as CuO with limestone within a composite pellet, or by cycling CuO and limestone within distinct particles. Using a thermogravimetric analyzer, it was demonstrated that the use of composite CaO/CuO/calcium-aluminate-cement pellets for gasification purposes required oxidation of Cu to be preceded by carbonation as opposed to the postcombustion case in which the pellets are oxidized prior to carbonation. Composite pellets were thus tested under this CO 2 capture sequence using varying carbonation conditions over multiple cycles. While the pellets exhibited relatively high carbonation conversion, the oxidation conversion declined for all tested conditions likely because of the CaCO 3 product impeding passage of O 2 molecules to the more remote Cu sites. The reduction in oxygen uptake was particularly important when the pellets were precarbonated in the presence of steam. Limestone-based pellets and Cu-based pellets were subsequently tested in separate CaL and CLC loops, respectively, to assess their performance in a dual-loop process. A maximum Cu content of 50% could be accommodated in a pellet with calcium aluminate cement as support with no loss in oxidation conversion and no observable agglomeration.
Abstract:The combination of Chemical Looping Combustion (CLC) with Calcium Looping (CaL) using integrated pellets is an alternative CO 2 capture process to the current amine-based sorbent processes, but the pellets lose sorption capacity over time. In this paper, the deactivation behavior of CaO, CuO and CuO/CaO integrated pellets used for multiple (16)(17)(18)(19)(20) cycles in a thermogravimetric analyzer was studied. The impact of thermal treatment and the presence of steam on the deactivation were also investigated. Nitrogen physisorption and scanning electron microscopy/energy-dispersive X-ray analysis were used to characterize the pellets. The analysis revealed significant migration of the copper to the surface of the composite pellets, which likely suppressed carbonation capacity by reducing the accessibility of the CaO. While thermal pre-treatment and steam addition enhanced the performance of the base CaO pellets, the former led to cracks in the pellets. In contrast, thermal pretreatment of the CuO/CaO composite pellets resulted in worse CLC and CaL performance.
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