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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

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

introduction
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

governing equations
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

boundary conditions
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

formulation
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

formulation6
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

solution
Solution
  • Much portion of reactants is converted in the inlet of the reactor
  • NH3 slip should be considered when NH3 is injected
validation
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
parametric study10
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
conclusion
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