The upgrading of the raw hot gas from a bubbling fluidized bed biomass gasifier is studied using cheap calcined minerals or rocks downstream from the gasifier. Biomass gasification is made with steam (not air) at 750-780 °C and about 0.5-1.0 kg of biomass/h. Calcined solids used are dolomite (MgO-CaO), pure calcite (CaO), and pure magnesite (MgO). Variables studied have been temperature of the secondary bed (780-910 °C), time of contact or space-time of the gas (0.08-0.32 kg‚h/m 3 n), and particle diameter (1-4 mm) and type of mineral. Their effects on tar conversion, tar amount in the exit gas, product distribution, and gas composition are presented. Using a macrokinetic model for the tar disappearance network, the activities of the stones are expressed by their apparent kinetic constant. Apparent energies of activation for tar elimination (42-47 kJ/mol) and preexponential and effectiveness factors are given for all tested solids of which the most active is the calcined dolomite.

Calcined dolomites, limestones, and magnesites are active and inexpensive solids for cleaning raw hot gas from biomass gasifiers with steam. The variations of their activities with time-on-stream are studied here. Simultaneous coke formation and coke elimination by steam gasification increases the life of these “naturally occurring” catalysts under some circumstances. The lives of these solids are studied at different temperatures (800−880 °C), space times (0.08−0.32 kg of dolomite·h/nm3), particle diameters (1−4 mm), and types of solid. Not much deactivation was observed for tar concentration in the raw gas below 48 g/nm3, particle diameters of less than 1.9 mm, temperatures above 800 °C, and space times above 0.13 kg·h/nm3. The effectiveness of these calcined minerals is compared with that of an inert material (silica sand) and with a commercial steam reforming catalyst (R-67 from Haldor Topsøe).

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A mathematical model for the discharge of a metal-hydride electrode was developed. The model was used to study the effect of various parameters on predicted discharge curves. The simulations obtained using the mode] show the expected decrease of charge utilization as the rate of discharge is increased. Increasing the particle size of the alloy and decreasing the diffusion coefficient of the hydrogen atoms in the hydride showed a similar effect on the discharge curves. The model simulations also show the critical role that the kinetic and transport parameters play in determining the overall shape of the predicted discharge curves for a metal-hydride electrode. The kinetic parameters used in the model predictions are those for TiMnI.~H~ (x < 0.31).