Determination and comparison of ash melting temperature of a biomass blend by laboratory methods and thermodynamic modelling

Ash melting could cause severe problems in boiler operation such as agglomeration of the fluidized bed. The blending of fuels could lead to eutectics and extremely low melting points. Sophisticated methods are needed to investigate and understand the chemical mechanisms taking place under thermal treatment causing ash melting. Reed and wheat straw were used as parent fuels and their ashes were blended in the ratio of 50%/50%. The aim of this study is to investigate the ash melting behaviour of biomass blend to determine the starting point of ash melting and extent of the melting process, when the melt fraction could cause severe problems in boiler operation. The ash melting behaviour was investigated using a number of laboratory methods, such as simultaneous thermal analysis, heating microscope and scanning electron microscopy (SEM). Thermodynamic modelling was carried out using FactSage software. The results revealed that the melting was started at 660-680 °C when the Na and K salts were melted. Intensive melting took place in the temperature range of 800-980 °C. The rapid melting occurring between 950 and 980 °C was caused by the melting of SiO₂ and K2MgSi₅O₁₂.