Biomass ash chemistry in oxygen carrier aided combustion: Interaction between potassium and red mud

Oxygen Carrier Aided Combustion (OCAC) is a process that uses oxygen carrier particles to improve oxygen distribution in circulating fluidized bed reactors. Its application using biomass as fuel can increase fuel conversion, thus enhancing combustion efficiency. However, ash generated during combustion is a major challenge, with potassium-based ash being particularly problematic. Red mud is considered a potential low-cost oxygen carrier. In this study, the interaction mechanism of organic potassium (CH3COOK), as well as inorganic potassium (K2CO3, KCl, K2SO4, K3PO4) and red mud oxygen carriers, was investigated under an oxidizing atmosphere at 950 degrees C. Experiments were carried out on a TGA test bench and a fixed bed reactor. XRD and SEM-EDS were used to characterize the reaction products of the mixtures. Thermodynamic equilibrium calculations to support the experimental data. The results show that K enters the red mud oxygen carrier and forms mainly KAlSiO4 and KAlSi3O8. Some of the potassium salts lead to the formation of K-Fe-O material. The agglomeration of the bed material depends on the proportion of elements in the oxygen carrier and ash mixture. CH3COOK and K2CO3 are more likely to cause the reacting particles to stick together. KCl, K2SO4, and K3PO4 react with the red mud particles but have no obvious effect on the particles' agglomeration.

Automated summary

Oxygen Carrier Aided Combustion (OCAC) is a process that improves combustion efficiency by using oxygen carrier particles. This study found that red mud is a potential low-cost oxygen carrier and investigated the interaction mechanism between organic and inorganic potassium and red mud oxygen carriers, as well as their effect on particle agglomeration.