(821d) Modeling the Ignition Phase of a Flash Carbonization Reactor

The prosperity of Silicon Valley is built upon a foundation of wood charcoal that is the necessary reductant for the manufacture of pure silicon from quartz.  Because ordinary pyrolysis processes offer low yields of charcoal from wood, the production of silicon makes heavy demands on the forest resource.  Prior work has shown that pyrolysis at elevated pressure, such as that accomplished by the Flash Carbonization process, realizes fixed-carbon yields of charcoal that approach the theoretical limit established by chemical equilibrium.  Flash Carbonization process is a semi-batch process in which a fire is ignited at elevated pressure at the bottom of a packed bed of biomass with no airflow.  This is the ignition phase of the process.  Thereafter air at elevated pressure is delivered to the top of the bed and flows downward against the upward movement of the flame.  The upward moving flame triggers the conversion of biomass into charcoal.  In this presentation we describe novel procedures for measuring transient peak temperatures and weight loss that occur during the ignition phase of the Flash Carbonization process.  These measurements are simulated using a numerical model based upon the division of the reactor’s packed bed into multiple (e.g. 50) compartments; wherein the equations of mass and energy conservation, chemical reactions and moisture evaporation and the ideal gas law are represented as a coupled set of ordinary differential and algebraic equations and are solved using IMSL software.  Various search algorithms are employed to identify parameters (e.g. heat transfer efficiency from the heater coil to the packed bed, heat loss and intra-bed heat transfer coefficients, reaction exothermicity and chemical kinetic parameters, etc.) that enable the model to fit the experimental data.  These parameters, which describe the performance of the pyrolysis/combustion system at pressures between 7 and 10 bar, are compared with those employed by other workers studying biomass gasification at 1 bar.