Selective Catalytic Selective Catalytic Reduction (SCR) by NHReduction (SCR) by NH33 in a in a

Fixed-Bed ReactorFixed-Bed Reactor

HEE JE SEONG

The Department of Energy and Geo-Environmental Engineering

The Pennsylvania State University

IntroductionIntroductionNOx emissions are a major pollutant from

engines, incinerators and power plants - unavoidable at conditions where air is

involved at high combusting temperatureSelective catalytic reduction with NH3 has

been successfully used to remove NOx 4NO + 4NH3 + O2 4N2 + 6H2OKinetic parameters depend much on a

catalyst - V2O5-WO3/TiO2, CuHM and etc

Governing EquationsGoverning EquationsMass 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 ConditionsBoundary 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 : 1.01325x105PaOutlet - P : Pin – ΔP (according to

Ergun eqn.)

Inlet

Wall/Insulation

Outlet

Wall/Insulation

0.1(m)

0.076(m)

FormulationFormulationMass conservation - Convection and diffusion - Chemical reaction

ENO : Enthalpy of NO reductionENH3 : Enthalpy of NH3 oxidationHNH3 : Heat of NH3 adsorptionkNO : Reaction rate constant of NO reductionkNH3 : Reaction rate constant of NH3 oxidationKNH3 : Adsorption equilibrium constant for NH3

FormulationFormulation 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

SolutionSolution

- Much portion of reactants is converted in the inlet of the reactor- NH3 slip should be considered when NH3 is injected

ValidationValidation

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 StudyParametric Study

Temperature (oC)Porosity = 0.5 Porosity = 0.7

ΔP (Pa) K (m2) ΔP (Pa) K (m2)

200 29492 3.33x10-10 4390 2.23x10-9

250 33308 3.49x10-10 4861 2.40x10-9

300 37529 3.62x10-10 5353 2.54x10-9

350 42119 3.72x10-10 5921 2.65x10-9

400 47057 3.80x10-10 6539 2.73x10-9

450 52323 3.86x10-10 7205 2.80x10-9

500 57901 3.90x10-10 7915 2.86x10-9

Parametric StudyParametric Study

Kineticparamete

rDry Wet

Ea,NO

Ea,NH3

ΔHNH3

ko,NO

ko,NH3

Ko,NH3

11.542.821.5

2.79x106

6.38x105

59.6

12.157.622.2

3.04x106

9.98x108

69.1

- 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

ConclusionConclusionSCR model using COMSOL well

describes a general trend of NO removal performance

- Valid result compared to the reference- Water effect is predictableThe model also indicates that NH3/NO

should be controlled considering NH3 slip

and performance at operating temperatures