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Show combustion at the top of the furnace, with a reasonable oxygen concentration passing through the superheater. Description of CFD Code: The CFD software used for the numerical analysis is Fluent/UNS Version 4.2. The code works by first constructing a geometrical representation of the volume of interest, called the computational domain, that is subdivided into a large quantity of control volumes, or cells. For each of these cells, the code then simultaneously solves the governing fluid dynamic equations of continuity, momentum (Navier-Stokes equations), and energy to obtain a 3-D steady-state solution. Velocity and pressure coupling are resolved via the Semi-Implicit Method for Pressure Linked Equations (SIMPLE) algorithm. Turbulence closure by the well understood k-e turbulence model is employed. The turbulent boundary layer conditions for momentum and heat transfer in the near-wall region follow the logarithmic law of the wall. The transport Figure 8: Sander Dust Burner/Boiler equation for energy is solved using a conjugate heat Computational Domain transfer model, with radiative heat fluxes calculated by solving additional conservation equations. Gas phase combustion is modeled as a one step global reaction, with user-specified fuel and oxidant components reacting to form combustion products. Species transport and chemical reaction rates are governed by both mixing of the eddies and simple Arrhenius rate equations. It is important to note that the chemical reaction model used does not take molecular dissociation into account. Radiation modeling is conducted with the Discrete Transfer Radiation model. The following is a list of some of the specific models used in the CFD analysis for the current study. • Variable specific heat, thermal conductivity, and viscosity for the gas phase • Standard k-e turbulence model • Gray gas radiation using the P-l model with variable absorption coefficients based on water and carbon dioxide content • Thermal buoyancy • Chemical reaction according to Arrhenius reaction kinetics and the Magnussen mixing model Grid Development: A body-fitted grid system is developed for the boiler geometry represented in this model, see Figure 8. Only a part of the boiler is modeled for computational efficiency. The computational grid, shown as Figure 9, includes the radiative section of the furnace from a point between the wood grate and the nose of the furnace (bottom) to the superheater section 7 |