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In this work is studied the effect of biomass packing factor (PF) and oxygen enriched air as gasifying agent (GA) on fixed bed biomass gasification. Oxygen concentrations in GA are 21, 24 and 29% vol. The biomass used as fuel is Jacaranda Copaia wood with three defined particle forms: square prism, cylindrical and chips. Flame front velocity and biomass consumption rate increase with oxygen concentration in the GA. These results are due to smaller amount of nitrogen involved in the process, which leads to decrease thermal energy losses by nitrogen heating. Moreover, lower convective cooling effect of gas over solid phase and lower radiation attenuation in the solid are reached with less nitrogen concentration in GA. The efficiency slightly increases when PF increases, this is due to less radiation penetration from the oxidation zone to drying and pyrolysis stages, thereby biomass consumption rate decreases. [ABSTRACT FROM AUTHOR]

Abstract: The main objective of this paper is to study the effect of operating and design parameters, mainly reactor geometry, air superficial velocity, biomass moisture content, particle size and biomass type (pine bark and sewage sludge), on the performance of the gasification/combustion process of waste biomass in fixed bed downdraft reactors. This experimental approach allows optimizing the dynamic behavior of the thermochemical process. Emphasis was put on interactions between the mentioned parameters with output or response variables, such as biomass consumption rate, fuel/air equivalence ratio, producer gas heating value and composition, tars concentration, and flame front velocity. The effect of the operating and design parameters on response variables was studied by means of multifactorial experimental designs. The statistical R 2 obtained through the data fitting of the multifactorial experimental designs indicated that the factors taken into account explained between 80.8% and 98.8% of the variability of the response variables. For the particular experiments carried out, the optimal gasification conditions were obtained with the following set of inlet conditions: air superficial velocity of 0.06m/s, biomass particle size between 2 and 6mm, and biomass moisture content of 10.62%. The corresponding response variables were: flame front velocity=11mm/min, fuel air equivalence ratio=3.2, biomass consumption rate=125kg/h/m2, lower heating value of the producer gas=2965.6kJ/Nm3, tar concentration=7.73g/Nm3, and an average composition of the producer gas of 8.0% H2, 13.0% CO, 1.4% CH4, 14.9% CO2, and 62.7% N2. [Copyright &y& Elsevier]

Biochar (BC) is a solid byproduct of gasification and could be valorized looking for contributing to the feasibility of gasification projects. In this study, the effect of airflow during fixed-bed gasification of pelletized fallen leaves to BC was evaluated at 0.075 and 0.150 kg/s/m2. The influence of glycerol in the leaf feedstock was also studied, and the gasification products were characterized. BC formation under gasification conditions was simulated using a two-dimensional (2D) unsteady computational fluid dynamics (CFD) model. When airflow was increased, convective heat transfer from the gas to the solid phase increased by 250%, and absorption of radiative heat transfer in the solid phase increased by 59%. This was ascribed to the increase in the process temperature, which also promoted the release of volatile matter. The H:C and O:C ratios in the feedstocks were reduced by 80% and 92%, respectively. The surface areas and pore volumes of the samples increased by up to 50%. The BC with the largest surface area (68.63 m2/g) also had the highest total organic carbon content (21.3%) and the highest water retention capacity (408.13%). The pH of the BCs obtained in the study ranged from 8.7 to 10, making them suitable for acid soils. • Gasification's cold gas efficiency of fallen leaves pellets (FLP) is up to 60%. • Convective and radiative heat transfer affect physicochemical properties of biochar. • If glycerol increases, biochar (BC) density decreases and BC temperature increases. • FLP's BC as a byproduct of fixed-bed gasification is suitable for acid soils. • FLP's BC is not suitable as a solid fuel due to its high ash content (∼58 wt%). [ABSTRACT FROM AUTHOR]

Abstract: A one-dimensional stationary model of biomass gasification in a fixed bed downdraft gasifier is presented in this paper. The model is based on the mass and energy conservation equations and includes the energy exchange between solid and gaseous phases, and the heat transfer by radiation from the solid particles. Different gasification sub-processes are incorporated: biomass drying, pyrolysis, oxidation of char and volatile matter, chemical reduction of H2, CO2 and H2O by char, and hydrocarbon reforming. The model was validated experimentally in a small-scale gasifier by comparing the experimental temperature fields, biomass burning rates and fuel/air equivalence ratios with predicted results. A good agreement between experimental and estimated results was achieved. The model can be used as a tool to study the influence of process parameters, such as biomass particle mean diameter, air flow velocity, gasifier geometry, composition and inlet temperature of the gasifying agent and biomass type, on the process propagation velocity (flame front velocity) and its efficiency. The maximum efficiency was obtained with the smaller particle size and lower air velocity. It was a consequence of the higher fuel/air ratio in the gasifier and so the production of a gas with a higher calorific value. [Copyright &y& Elsevier]