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Interest in biomass to produce heat, power, liquid fuels, hydrogen, and value-added chemicals with reduced greenhouse gas emissions is increasing worldwide. Gasification is becoming a promising technology for biomass utilization with a positive environmental impact. This review focuses specifically on woody biomass gasification and recent advances in the field. The physical properties, chemical structure, and composition of biomass greatly affect gasification performance, pretreatment, and handling. Primary and secondary catalysts are of key importance to improve the conversion and cracking of tars, and lime-enhanced gasification advantageously combines CO2 capture with gasification. These topics are covered here, including the reaction mechanisms and biomass characterization. Experimental research and industrial experience are investigated to elucidate concepts, processes, and characteristics of woody biomass gasification and to identify challenges.

The influence of the distributor configuration on interphase mass transfer, gas axial dispersion and bubble size was studied in a 2-D fluidised bed reactor for two types of distributor configurations; a novel multi-vortex (MV) distributor with tuyéres directed vertically and horizontally at different heights and a standard perforated plate distributor (baseline). The linear inlet velocity (U 0 ) ranged between 0.1 m/s and 0.35 m/s, with air as fluidising medium at ambient conditions. The ozone decomposition reaction over Fe 2 O 3 impregnated FCC catalyst was used as an indirect measure of the performance of the FBR and it was found that the MV distributor causes a significant improvement (15% average) in the conversion efficiencies at all velocities tested. Bubble size measurements (using two separate techniques) indicated larger bubbles for the MV distributor, while the visual bubbling to turbulent transition boundary (U c ) for the MV distributor was found to be lower than the baseline distributor. The interphase bubble-emulsion mass transfer was quantified using the model derived by Thompson et al. (1999) and was found to be 52% higher for the MV distributor than the baseline distributor. In addition the MV distributor exhibited near plug flow characteristics at velocities exceeding U c , while this was not the case for the baseline distributor.

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Gas-solid fluidization experiments were performed in two separate experimental setups with similar dimensions. Fast X-Ray Tomography (XRT) was used in setup 1, while ozone decomposition experiments were performed in setup 2. Packing and operation characteristics for the two setups were close to identical. The hydrodynamic measurements from the XRT acquisitions were used to evaluate the interphase mass transfer characteristics obtained from the ozone decomposition results. Superficial velocities (U 0 ) spanning the bubbling up to the onset of the turbulent regime (U c ) were employed. Traditional specific interphase mass transfer (k be ) correlations are based on incipiently fluidized beds; however, results suggested that a distinction should be made between the low-interaction bubbling regime and the highinteraction bubbling regime. A change in mass transfer behaviour occurred around a U 0 /U c value of 0.25. An empirical correlation for k be of the high-interaction bubbling regime is 1