Modeling of downdraft gasification process: Part II - Studies on the effect of shrinking and non-shrinking biomass geometries on the performance of gasification process

This study investigated the effect of shrinking and non-shrinking biomass geometries in a fixed bed reactor. Model simulation was performed to analyze the effect of biomass moisture content, gasification temperature, air flow rate, oxygen content in the primary air, and mass transfer coefficient on product yield for spherical, tabular, and cylindrical biomass briquettes. The model matched well with the experimental data. The production of hydrogen and carbon dioxide increased with an increase in moisture content. With an increase in gasification temperature, the water–gas shift reaction proceeded faster than the Boudouard reaction, leading to a decrease in the carbon dioxide composition and an increase in the carbon monoxide composition. Tabular shrinking particles with a H2/CO ratio of 1.44 and a CO/CO2 ratio of 0.22 at 1175 K were more favorable for producing value-added chemicals than the particles of all other geometries. The non-shrinking spherical particles had the highest low heating value (LHV) of 4.65 MJ/m3, whereas the tabular non-shrinking particles had the lowest LHV of 1.33 MJ/m3 among the shrinking and non-shrinking particles with all the other geometries considered. The gasification temperature was the most sensitive parameter, whereas moisture content and the mass transfer coefficient were the least sensitive parameters.