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Selective Catalytic Reduction (SCR) by NH 3 in a Fixed-Bed Reactor

Selective Catalytic Reduction (SCR) by NH 3 in a Fixed-Bed Reactor. HEE JE SEONG The Department of Energy and Geo-Environmental Engineering The Pennsylvania State University. Introduction. NOx emissions are a major pollutant from engines, incinerators and power plants

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Selective Catalytic Reduction (SCR) by NH 3 in a Fixed-Bed Reactor

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  1. Selective Catalytic Reduction (SCR) by NH3 in a Fixed-Bed Reactor HEE JE SEONG The Department of Energy and Geo-Environmental Engineering The Pennsylvania State University

  2. Introduction • NOx emissions are a major pollutant from engines, incinerators and power plants - unavoidable at conditions where air is involved at high combusting temperature • Selective catalytic reduction with NH3 has been successfully used to remove NOx 4NO + 4NH3+ O2  4N2 + 6H2O • Kinetic parameters depend much on a catalyst - V2O5-WO3/TiO2, CuHM and etc

  3. Governing Equations • Mass equation - Convection and diffusion where R : -rNO, -rNH3 • Momentum equation - Navier-Stokes equation (Brinkman eqn. involved) • Energy equation - Assumed as an isothermal state due to a small amount of heat evolved

  4. Boundary Conditions • Inlet - Velocity : 1, 2, 4m/s - CNO = 8.16x10-3mol/m3 CNH3 = 8.16x10-3mol/m3 CNH3 = 6.94x10-3mol/m3 CNH3 = 9.38x10-3mol/m3 - Pin : 1.01325x105Pa • Outlet - P : Pin – ΔP (according to Ergun eqn.) Inlet 0.1(m) Wall/ Insulation Wall/ Insulation 0.076(m) Outlet

  5. Formulation • Mass conservation - Convection and diffusion - Chemical reaction ENO : Enthalpy of NO reduction ENH3 : Enthalpy of NH3 oxidation HNH3 : Heat of NH3 adsorption kNO : Reaction rate constant of NO reduction kNH3 : Reaction rate constant of NH3 oxidation KNH3 : Adsorption equilibrium constant for NH3

  6. Formulation • Air is assumed as the fluid flowing through the reactor - small amounts of NO and NH3 - ρ and η are temperature-dependent - pressure drop is calculated using Ergun eqn. - Permeability is calculated using Darcy’s law

  7. Solution • Much portion of reactants is converted in the inlet of the reactor • NH3 slip should be considered when NH3 is injected

  8. Validation SV = 100,000 h-1 SV = 200,000 h-1 • Detailed information in Chae et al’s model is missing • This COMSOL model simulates similar trends of results to • those of Chae et al.’s model for both conditions

  9. Parametric Study

  10. Parametric Study • Conversion of NO is higher at a dry condition than at a wet condition • due to the competition between H2O and NH3 • This COMSOL model also reflects a general phenomenon of SCR • when water is involved in the reaction

  11. Conclusion • SCR model using COMSOL well describes a general trend of NO removal performance - Valid result compared to the reference - Water effect is predictable • The model also indicates that NH3/NO should be controlled considering NH3 slip and performance at operating temperatures

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