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.

No abstract

The onset of thermal convection in a 2D porous box is investigated analytically. The lateral walls are partly heat conducting and partly penetrative. The top and bottom are impermeable and perfect heat conductors. The linear stability problem is solved only for the symmetric configuration of equal conditions at each sidewall. The problem is degenerate when the parameters of semi-conduction and semi-penetration coincide. The degenerate problem has one symmetric and one antisymmetric eigenfunctions, and the cell width varies with minimum cell width in the middle. Our primary model for the partly penetrative wall is a thin and highly permeable layer near a closed wall. We also study a secondary model of a partly penetrative wall, with a thin layer of small permeability near a hydrostatic reservoir.

Molten salt pyrolysis is a thermochemical conversion process in which biomass is fed into and heated up by a molten salt bath. Molten salts have very high thermal stability, good heat transfer characteristics, and a catalytic effect in cracking and liquefaction of large molecules found in biomass. In this study, the heat transfer characteristics of molten salts are studied by recording the thermal history of wood particles in molten salt pyrolysis. Experiments have been carried out with cylindrical beech and pine wood particles with constant length (L = 30 mm) and varying diameter (d = 1–8 mm) in a FLiNaK melt with a temperature of 500 °C. The thermal history at the particle center has been used to evaluate the reaction temperatures, the heating rates, and the devolatilization times. Results have been compared with a similar study in a fluidized sand bed. It is found that FLiNaK gives significantly higher heating rates for cylinders with d ≤ 4 mm. For larger cylinders, the process is dominated by heat transfer within the wood particle, and the heat transfer medium is of less importance. For the smallest cylinders (d = 1 mm), heating rates as high as 218 ± 6 and 186 ± 15 °C/s were observed for beech and pine wood, respectively. The average heating rate for wood cylinders until the main degradation takes place has been found to follow the empirical correlation β = (k eff/ρ)103(24 + 390e–0.49d ), and the total devolatilization time has been found to follow the empirical correlation t dev = ρ(0.146 e–k eff – 1.09)d 1.05.

No abstract

No abstract

No abstract

No abstract