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The biomass gasification process in fixed bed was studied by means of computational fluid dynamics (CFD) numerical analysis. The aim was to evaluate the effect of the biomass packing factor on the thermochemical process. The fuel-wood used was Jacaranda Copaia in various shapes: chips, cylinders, and cubes with packing factors (PF) of 0.38, 0.48, and 0.59, respectively. The mathematical model is a transient 2D CFD model, which was developed through the implementation of User Defined Functions in ANSYS-Fluent. The model was extended to simulate the gasification process by expanding the chemical kinetic mechanism and by adapting the stages of pyrolysis, oxidation, and reduction. The model was validated with experimental data. The average relative error between experimental and numerical data was 5.45%. By means of the sensitivity analysis, it was found that with an increase in the packing factor from 0.38 to 0.59, the absorption of radiative heat transfer increases by 27% leading to increase the solid temperature in the reaction front, but due to a lower penetration of radiation, the drying and pyrolysis reaction rates decrease. But nevertheless, the higher solid temperature with packing factor favors the convective solid-gas heat transfer in the drying stage. [ABSTRACT FROM AUTHOR]

The objective of this work was to study the effect of torrefaction temperature on properties of patula pine (Pinus patula) wood that could be of interest for further thermochemical processing. Torrefaction temperature was varied from 200 to 300 °C for 30 minutes using a batch spoon type reactor. Raw and torrefied materials were characterized for proximate and ultimate analyses, thermogravimetry, and pyrolysis gas chromatography/mass spectrometry (Py-GC/MS). Results showed that torrefied pine has greater higher heating value and chemical exergy due to the reduction of O/C and H/C ratios. Compared with raw biomass, the material torrefied at 200 and 250 °C did not present significant changes in chemical composition and thermal behavior. Conversely, material torrefied at 300 °C did show important changes in both chemical composition and thermal behavior. Py-GC/MS results suggested that the main constituents of biomass, i.e., hemicellulose, cellulose and lignin, suffer a progressive thermal degradation with increase in torrefaction temperature. [ABSTRACT FROM AUTHOR]

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]

A detailed sensitivity analysis is performed on a one-dimensional fixed bed downdraft biomass gasification model. The aim of this work is to analyze how the heat transfer mechanisms and rates are affected as reaction front progresses along the bed with its main reactive stages (drying, pyrolysis, combustion and reduction) under auto-thermal conditions. To this end, a batch type fixed-bed gasifier was simulated and used to study process propagation velocity of biomass gasification. The previously proposed model was validated with experimental data as a function of particle size. The model was capable of predicting coherently the physicochemical processes of gasification allowing an agreement between experimental and calculated data with an average error of 8%. Model sensitivity to parametric changes in several model and process parameters was evaluated by analyzing their effect on heat transfer mechanisms of reaction front (solid–gas, bed–wall and radiative in the solid phase) and key response variables (temperature field, maximum solid and gas temperatures inside the bed, flame front velocity, biomass consumption and fuel/air ratio). The model coefficients analyzed were the solid–gas heat transfer, radiation absorption, bed–wall heat transfer, pyrolysis kinetic rates and reactor-environment heat transfer. On the other hand, particle size, bed void fraction, air intake temperature, gasifying agent composition and gasifier wall material were analyzed as process parameters. The solid–gas heat transfer coefficient (0.02 < correction factor < 1.0) and particle size (4 < diameter < 30 mm) were the most significant parameters affecting process behavior. They led to variations of 88% and 68% in process velocity, respectively. [ABSTRACT FROM AUTHOR]