Abstract
Entrained flow gasification of biomass provides the opportunity to convert low-grade biogenic feedstocks to
high-grade synthetic fuels. For a top-fired entrained flow slagging biomass gasifier, the thermophysical
properties of the ash and slag limit process operation and affect process energy efficiency. The biomass ash
has to be molten and slag viscosity has to be in a certain range for it to flow out of the gasifier. However, direct
sampling, analysis, and evaluation of slag formation and behaviors are often challenging as entrained flow
biomass gasification operates at high temperatures (i.e., 1200-1500°C) continuously. One alternative is to study
synthetic ash's melting and sintering behaviors at elevated temperatures, which represent the major inorganic
constituents in biomass ash. For thermochemical conversion of biomass, K, Ca and Si are typically the most
common ash-forming elements. In this work, the synthetic ashes were prepared by mixing model compounds
K2O, CaO and SiO2 in different mole ratios, which were pressed to form pellets. The selection of mole ratios
was based on thermodynamic calculations that indicate that the tested model compound mixtures melt and flow
with desired viscosity at certain temperature ranges. The pressed synthetic ashes were preheated at 900 °C for
8 hours to thermally homogenize them. Then the premelted synthetic ashes were heated at 1000 and 1400 °C
in a muffle furnace with a residence time of 1 and 8 hours in air to study fusion behaviors and slag formation
tendency, and were cooled down to room temperature gradually after the sintering test. The sintered residues
were collected and analyzed by SEM/EDX to study the interactions of the model compounds and identify
chemical compositions. The results showed that the mole ratios of model compounds have recognizable impacts
on the composition, formation and transformation of mineral phases in residues from sintering tests. A strong
correlation was also found between the sintering intensity of the synthetic ash and the mole ratios of model
compounds.
high-grade synthetic fuels. For a top-fired entrained flow slagging biomass gasifier, the thermophysical
properties of the ash and slag limit process operation and affect process energy efficiency. The biomass ash
has to be molten and slag viscosity has to be in a certain range for it to flow out of the gasifier. However, direct
sampling, analysis, and evaluation of slag formation and behaviors are often challenging as entrained flow
biomass gasification operates at high temperatures (i.e., 1200-1500°C) continuously. One alternative is to study
synthetic ash's melting and sintering behaviors at elevated temperatures, which represent the major inorganic
constituents in biomass ash. For thermochemical conversion of biomass, K, Ca and Si are typically the most
common ash-forming elements. In this work, the synthetic ashes were prepared by mixing model compounds
K2O, CaO and SiO2 in different mole ratios, which were pressed to form pellets. The selection of mole ratios
was based on thermodynamic calculations that indicate that the tested model compound mixtures melt and flow
with desired viscosity at certain temperature ranges. The pressed synthetic ashes were preheated at 900 °C for
8 hours to thermally homogenize them. Then the premelted synthetic ashes were heated at 1000 and 1400 °C
in a muffle furnace with a residence time of 1 and 8 hours in air to study fusion behaviors and slag formation
tendency, and were cooled down to room temperature gradually after the sintering test. The sintered residues
were collected and analyzed by SEM/EDX to study the interactions of the model compounds and identify
chemical compositions. The results showed that the mole ratios of model compounds have recognizable impacts
on the composition, formation and transformation of mineral phases in residues from sintering tests. A strong
correlation was also found between the sintering intensity of the synthetic ash and the mole ratios of model
compounds.