Biomass gasification in a 1.5 MWth fluidized bed reactor: A sustainable route for biofuel production

The production of syngas through biomass gasification has attracted considerable attention due to its potential to promote circularity, enhance sustainability, and address emerging needs, including those driven by socio-political events, to improve energy self-sufficiency.

Nonetheless, concerns arise when biomass is used as fuel to produce syngas, and they are mainly focused on the heterogeneous composition of these materials, which may negatively affect both the gasifier performance and the generation of undesired compounds, such as tar, condensable organic compounds produced along with syngas that are commonly not accepted in the devices for end-use application of the syngas. Proper selection of gasifier design and operating conditions, use of a catalyst during gasification, and cleaning of the syngas (e.g., by thermo-catalytic tar cracking or filtering) are means to address this issue. In this context, ?uidised bed (FB) reactors are widely recognised as appropriate gasifiers, due to the very good mass and heat transfer coefficients provided by FB ?uid dynamics, and to the possibility of controlling emissions through proper gasifier design and operating conditions.

This study investigated biomass gasification in a 1.5 MWth bubbling ?uidised bed demonstration plant, employing air or an air/steam mixture as the gasifying agent and olivine as the bed material. Gasification tests were conducted under autothermal conditions with a constant equivalence ratio of 0.30. The gasification products—including producer gas, elutriated particles, tar, and contaminant gases—were comprehensively characterised. The performance of the entire gasification plant and its individual process units was quantitatively assessed through material and energy ?ow analyses. Results demonstrated that steam addition enhanced producer gas quality by promoting the conversion of tar and char into permanent gases, thereby increasing the specific yield of producer gas, although the lower heating value and cold gas efficiency of the producer gas decreased slightly.

Material ?ow analysis revealed that carbon conversion efficiency was primarily affected by carbon loss associated with solid particles collected by the cyclone. Energy ?ow analysis indicated that cold gas efficiency was significantly in?uenced by the energy required to convert the initial biomass into producer gas. The efficiency of biomass conversion into electrical energy was approximately 24%.