Abstract
This study describes how potassium salts representative of those in bio ash affect the reactivity of the oxygen carrier ilmenite under moist and dry conditions. Ilmenite is a bench-mark oxygen carrier for chemical-looping combustion, a technique that can separate CO2 from flue gases with minimal energy penalty. Different potassium salts were mixed with ilmenite to a concentration of 4 wt % potassium. The salts used were K2CO3, K2SO4, KCl, and KH2PO4. Experiments were performed at 850 °C under alternately oxidizing and reducing conditions in a dry atmosphere or in the presence of steam. Analyses of the oxygen carrier regarding changes in reactivity, structure, and composition followed the exposures. This study showed that salts such as K2CO3, K2SO4, and KCl increase the reactivity of the ilmenite. For the samples mixed with KCl, most of the salt was evaporated. KH2PO4 decomposed into KPO3, forming layers around the ilmenite particles that lead to agglomeration. Additionally, the KPO3 layer was more or less nonpermeable for CO and decreased the reactivity toward H2 significantly in both dry and wet conditions. This decreased reactivity indicates that the concentration of phosphorus in biofuel may have a significant effect on oxygen carrier degradation. It was also observed that the presence of steam changed the chemistry drastically for the nonphosphorus-containing salts. Alkali salts may react with steam, forming volatile KOH that evaporates partly. KOH may also form K-titanates by reaction with the oxygen carrier, leading to segregation of iron and titanium phases in the ilmenite.
Highlights
AND BACKGROUNDThe Paris Agreement aims to strengthen the global response toward the threats of climate change, stating goals such as remaining “well below 2 °C” and “pursuing efforts to limit the temperature increase to 1.5 °C”, compared to preindustrial temperatures.[1]
Ash from biomass may cause defluidization of the fluidized bed boilers because of alkali salts in the biomass interacting with the bed material
Ilmenite has been considered to be a bed material with oxygen carrier properties that is extra resistant toward agglomeration caused by potassium salts
Summary
The Paris Agreement aims to strengthen the global response toward the threats of climate change, stating goals such as remaining “well below 2 °C” and “pursuing efforts to limit the temperature increase to 1.5 °C”, compared to preindustrial temperatures.[1]. This phase separation is needed to obtain pig iron and the titanium oxide in the Becher process.[22−27] Alkali impregnation on ilmenite has been indicated to increase the reaction rate of the oxygen carrier in chemical looping applications.[28,29] as have been observed in a 100 kW CLC reactor with a mixture of ilmenite and manganese ore, a share of alkali is evaporated and found in both the FR and AR when operated under CLC.[30] it is unknown how different ash components interact with ilmenite during CLC operation under moist and dry conditions Understanding these interactions is of utmost interest because inhibition of oxygen carrier reactivity, agglomeration, and alkali evaporation with resulting corrosion may occur when combusting certain kinds of biomass. Potassium salts were used because potassium is the most common alkali metal in biomass,[4] and sodium and potassium are considered to be interconvertible regarding alkali roasting of ilmenite at temperatures below 860 °C.24,25 Potassium in biomass ash is present as carbonates, sulfates, chlorides, and phosphates.[4,31] these potassium salts have been used in this study
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
