Interaction between phosphorus and alkali/alkaline earth metals and their effect on ash transformation thermal kinetics during phosphorus-rich biomass and coal co-gasification

Co-gasification of phosphorus-rich biomass with coal enables the clean and efficient conversion of both raw materials, but the interaction between phosphorus and alkali/alkaline earth metals (AAEMs) leads to more complex ash conversion. In this work, the release pattern of alkali metals during gasification of coal, blue-green algae (BG), and mixed raw materials was studied in-situ using a self-designed visual fixed bed and laser-induced breakdown spectroscopy system. Quantitative analysis of phosphorus migration and transformation during cogasification was performed using inductively coupled plasma emission spectroscopy. Various characterization methods and FactSage were used to investigate interactions between phosphorus and AAEMs in the slag along with their thermal kinetic characteristics during ash transformation. The results showed that coal inhibited the release concentration of potassium from biomass during co-gasification and increased the temperature at which the maximum release concentration of alkali metals occurred, promoting the conversion of non-apatite inorganic phosphorus to apatite inorganic phosphorus in the gasification residue. As the BG content increased, the total and maximum weight loss rate of the mixed ashes during ash conversion gradually decreased, raising the ash fusion temperature of the mixed ashes, and the slag system gradually formed alkaline earth-phosphate minerals from potassium and calcium minerals. And co-gasification of coal and phosphorus-rich biomass effectively alleviates the agglomeration issues caused by coal ash and improves the fouling and slagging problems associated with biomass. This work provided a theoretical basis for understanding the interaction between phosphorus and AAEMs and their influence on the thermodynamics of ash transformation during the co-gasification of coal and phosphorus-rich biomass.