Biomass and Coal Ash Sintering—Thermodynamic Equilibrium Modeling versus Pressure Drop Test and Mechanical Test

The problem of biomass combustion and co-combustion is a particularly important aspect of many district heating systems, where the use of biomass makes it possible to reduce CO2 emissions. The present article is a continuation of previous studies of the behavior of the mineral matter of selected fuels during the sintering processes. Three biomasses were studied: wheat straw, barley straw and rye straw, as well as two coals from Polish mines: bituminous coal and lignite. The study included ultimate and proximate analyses and oxide analysis. On the basis of the oxide analysis and using FactSage 8.0. software, the sintering process of ash from selected fuels was simulated. In particular, the content of the slag phase as well as the values of the specific heat cp and density were determined without considering the gas phase. The obtained results were compared with the results of measurements of fracture stress (mechanical method) and pressure drop (pressure drop test) determined during the sintering process of the ash samples. The study showed that there is a fairly pronounced correlation between the sintering temperatures determined by the mechanical and pressure drop test and the physical properties of the ashes, such as density and heat capacity, and chemical properties, i.e., the content of the slag phase. The completed research work indicates and confirms that nonstandard methods of studying ash sintering temperatures (mechanical and pressure drop test) are very promising because they directly reflect the behavior of coals and biofuels in combustion systems.