Effect of Particle Geometry and Microstructure on Fast Pyrolysis of Beech Wood

Abstract

The influence of particle geometry and microstructure in fast pyrolysis of beech wood has been investigated. Milled wood particles (<0.08−2.4 mm) and natural wood cylinders (2−14 mm) with different lengths (10−50 mm) and artificial wood cylinders (D p = 0.5−14 mm) made of steel walls, filled with small milled wood particles (<0.08−0.140 mm), have been pyrolyzed in a fluidized bed at 500°C. From the results of the experiments, the influence of particle geometry and microstructure on char, gas, and pyrolysis oil yield and pyrolysis oil composition has been derived. The product yields of large cylinders with diameters of 6−14 mm are primarily determined by the outer diameter and resulting heating rate. The microstructure of these cylinders, being either natural channels or randomly packed small milled wood particles, has turned out to be much less important. For the smaller milled wood particles, the microstructure does have a profound effect on the product yields. The smallest particles (<0.140 mm), which consist only out of cell wall material and have lost their typical wood channel structure, show a clearly higher oil yield and lower char yield. It is postulated that the high pyrolysis oil yield can be explained by larger mass transfer rates of pyrolysis products from these smallest particles, as compared to mass transfer from particles containing channels.

Thermochemical and Catalytic Conversion Technologies for the Development of Brazilian Biomass Utilization

“…The heating rate of the biomass particles is of utmost importance for the pyrolysis process, impacting process control, product yields, and product quality [110,111,[118][119][120]. Kersten et al [118] affirm that the individual particle decomposition is controlled by external heat transfer and thermal diffusivity for wood particles larger than 1 mm, where this decomposition takes place very close to the reactor temperature for smaller particles, being, therefore, kinetics driven, an opinion shared with other authors [121][122][123][124].…”

“…Various kinds of pyrolysis reactors have been developed, in which the design and optimization require a deep comprehension of the reaction and transport phenomena participating in the degradation of the solid feedstock. One area of direct influence that requires further research is the meaning of both the shape and size of the feedstock particles on the final product distribution [110].…”

Transportation fuels from biomass fast pyrolysis, catalytic hydrodeoxygenation, and catalytic fast hydropyrolysis

“…In order to achieve a high oil yield with the fluid bed reactor, the biomass particles should preferably be smaller than a few mm in diameter [107][108][109][110][111]. A low moisture content of the feed biomass is also preferred, because a high moisture content limits the heat transfer and thereby increases the char yield [112,113].…”

Progress in understanding the four dominant intra-particle phenomena of lignocellulose pyrolysis: chemical reactions, heat transfer, mass transfer, and phase change

“…117,206,207 These aerosols can be trapped inside the solid matrix after ejection and the collision probability will increase with particle size. 106,207,208 Heat transfer Effect of particle size and pore structure on heat transfer…”