Silane Reactions in a Fluidized Bed

An innovative technology with numerous potential applications, fluidized-bed combustion offers a highly efficient means to generate low-cost electricity from coal and other fuels with minimal environmental impact. It promises improved efficiency at substantially less cost to build than conventional non-fluidized bed combustion units used in power generation, and it offers a clean method to rely on coal as a fuel to meet growing energy needs.

Along with coal, fluidized-bed combustion can use waste materials as fuel - such as municipal trash and hospital medical waste - burning them to produce electricity while reducing the need for waste disposal. Because pollutants are incinerated or captured in the bed as they're generated, they aren't released to the air.

NETL carries out extensive programs of research in fluidized-bed combustion. Among the tools it has developed is simulation software called MFIX (Multiphase Flow with Interphase Exchanges). MFIX realistically models the gas-particle dynamics, chemical reactions and heat transfer processes that occur in fluidized-bed combustion.

In a recent MFIX study, NETL researchers used PSC's CRAY T3E to model the chemical reactions of silane, a chemical precursor of silicon, when injected into a fluidized bed. Carried out in collaboration with Dow Corning, this project investigated fluidized-bed technology as a production method for ultra-pure silicon, which deposits on the bed of particles as silane decomposes at high temperature.

This sequence of images, from an animation produced by PSC visualization specialist Greg Foss, depicts some of the simulation results. Color (decreasing from black through red to purple) corresponds to the fraction of gas versus solid material visible at a cross-sectional slice through the combustor. These results told the NETL researchers that the reaction occurs rapidly at the bottom of the combustor, where the silane is injected, and that "bubbles" of gas (black) tend to form along the walls of the combustor and migrate toward the center as they rise.