Abstract
Chemical-Looping Combustion (CLC) of biofuels is a promising technology for cost-efficient CO2 separation and can lead to negative CO2 emissions when combined with carbon capture and storage. A potential challenge in developing CLC technology is the effects of alkali metal-containing compounds released during fuel conversion. This study investigates the interactions between alkali and an oxygen carrier (OC), CaMn0.775Ti0.125Mg0.1O3-δ, to better understand the fate of alkali in CLC. A laboratory-scale fluidized bed reactor is operated at 800–900 °C in oxidizing, reducing and inert atmospheres to mimic CLC conditions. Alkali is fed to the reactor as aerosol KCl particles, and alkali in the exhaust is measured online with a surface ionization detector. The alkali concentration changes with gas environment, temperature, and alkali loading, and the concentration profile has excellent reproducibility over repeated redox cycles. Alkali-OC interactions are dominated by alkali uptake under most conditions, except for a release during OC reduction. Uptake is significant during stable reducing conditions, and is limited under oxidizing conditions. The total uptake during a redox cycle is favored by a high alkali loading, while the influence of temperature is weak. The implications for the understanding of alkali behavior in CLC and further development are discussed.
Highlights
Global warming is increasing as humans continue to add heattrapping greenhouse gases (GHGs) to the atmosphere
If biomass is used as a fuel and combined with Carbon Capture and Storage (CCS) technology, it would result in negative carbon dioxide emissions [3]
The oxygen demand in the fuel reactor is provided by a solid oxygen carrier (OC) in the form of metal oxide particles, in contrast to conventional combustion where the oxygen demand is provided by mixing the fuel with air
Summary
Global warming is increasing as humans continue to add heattrapping greenhouse gases (GHGs) to the atmosphere. One way of reducing GHGs emissions is the implementation of Carbon Capture and Storage (CCS) systems, which capture the CO2 at the emission source and store it geologically [2]. The technology of chemical-looping combustion (CLC) is based on unmixed combustion, and it has the same net energy release as con ventional combustion. This is achieved by the use of two separate, interconnected, air and fuel reactors, which are commonly realized as circulating fluidized bed reactors [4,5]. The OC particles (MexOy) are reduced in the fuel reactor as they release oxygen that reacts with the fuel (CnH2m), forming carbon dioxide and water as main flue gases (Eq (1)). The reduced OC is transported to the air reactor, where it is regenerated by a chemical reaction with oxygen (Eq (2))
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