Enhancement of ash properties on alkali and alkaline earth metal retention by coal additives in the gasification condition

Abstract

Biomass gasification is a promising technology to realize low carbon emission and clean energy generation processes, while the ash-related problem is the main limitation of its large-scale application. The coal additives can effectively alleviate ash sintering and melting issues. The in-situ ash fusion behavior, mineral transformation, and potassium retention process were explored in the co-gasification condition of soybean straw and coal. The formation of alkali and alkaline earth metal (AAEMs) based minerals led to the low ash slagging propensity with the coal additives due to the reaction between SiO2, Al2O3 and AAEMs. Then the in-situ observation indicated that the formation of refractory minerals promoted the reduction of shrinkage and the increase of AFTs. In this sense, the mineral evolution at different quenching temperatures further revealed that the alkaline earth metals were prone to react with SiO2 or Al2O3. Moreover, the decreasing amount of gaseous potassium meant that the K could be effectively retained by coal additives. Based on this in-situ analysis, the combinative thermodynamic calculation suggested that the priority areas were in the anorthite, melilite and leucite primary phase zones to ensure the smooth operation of the co-gasification process.