A method is described for significantly improving the predictive capability of equilibrium-based calculation tools for the estimation of fuel gas composition in high-temperature biomass gasification processes. It is based on acknowledgment of the fact that the overall thermochemical conversion occurs in two stages: fast biomass-particle devolatilization, followed by the much slower, and hence often nonequilibrium, conversion of methane and char. Inputs to the equilibrium calculation routine, modified in relation to this latter phenomenon, are proposed that can be readily implemented in commercial flow sheet calculation routines for chemical reactors. The method provides estimates for the yields of specific compounds, such as hydrogen and carbon monoxide, and is shown to predict well the performance trends relating to changes in operating conditions. None of the available kinetic models is able to offer comparable predictive capability. Nor too do thermodynamic equilibrium model methods that fail to take into account the two-stage nature of the gasification process and, as a result give rise to substantial deviations from available experimental data: underprediction of both the methane content in the product gas and the unconverted carbon in the solid phase; negative findings similar to these have been reported in analogous literature studies of coal gasification.
The efficiency of rejection of sand from Athabasca oil sands in a cold water process based on mechanical upgrading in rotating contactors was found to depend upon the time of contact, the rate of rotation, the linear velocity of the lifter, the water to oil sands ratio, the depth of charge to lifter height ratio, and the internal diameter of the contactor. The efficiency of the process in rejecting sand may be described in terms of a rate constant. Sand rejection is promoted in general by lifter-oil sands and contactor wall-oil sands impacts and by the action of shear fields within vortices created by the lifter. The depth of charge to lifter height ratio and the linear velocity of the lifter are important parameters.
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