Use of in-bed primary catalyst in pressurized biomass fluidized bed gasification: Strategies for optimal use

Pressurized fluidized bed gasification is advantageous for efficient integration with downstream processes operating under pressurized conditions. This study presents a detailed analysis of product gas’s composition and yields, using different natural minerals, including magnesite, dolomite, olivine, and silica sand at 8 bar in a pressurized biomass fluidized bed gasifier, investigating the mechanisms of selected natural minerals in catalytic tar-cracking and reforming. The used bed particles were further analyzed and examined using H₂-TPR, TPO, and XPS analysis. In comparison with used olivine, the used dolomite exhibited a higher amount of carbon deposited on the surface; however, the carbon starts reacting with H₂ at around 550 °C, which could not be observed from the used olivine. The used dolomite contains more $C-O$ on the surface while the used olivine has a relatively higher level of $C=O$. The non-active chemical status of main elements (Fe, Mg, Ca) on the surface of used olivine was also determined by the XPS analysis. The mechanisms for the evolution of light and heavy hydrocarbons were also elucidated. A linear correlation between the concentrations of benzene and naphthalene was observed in tests using dolomite and magnesite. Dolomite is effective in increasing H₂ concentration, which could be attributed to dolomite’s catalytic tar cracking capacity. The optimal use of dolomite may be achieved via selecting a proper steam-to-biomass-ratio (SBR) and optimizing the internal circulation and hydrodynamics of bed particles in the pressurized fluidized bed gasifier to continuously converting deposited carbon and regenerating dolomite particles.