Reaction Kinetics for the Ammonia Slip Catalyst (ASC)
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In the Home toolbar, click  Add Physics to open the Add Physics window.
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Go to the Add Physics window.
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In the tree, select Chemical Species Transport > Reaction Engineering.
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Click the Add to Component 1 button in the window toolbar.
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In the Home toolbar, click  Add Physics to close the Add Physics window.
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In the Settings window for Reaction Engineering, type Ammonia Slip Catalyst (ASC) in the Label text field.
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Locate the Reactor section. From the Reactor type list, choose Plug flow.
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Locate the Energy Balance section. From the Energy balance list, choose Include.
Add the reactions.
(1) Desired NH3 oxidation: 4 NH3 + 3 O2 => 2 N2 + 6 H2O
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In the Reaction Engineering toolbar, click  Reaction.
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In the Settings window for Reaction, locate the Reaction Formula section.
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In the Formula text field, type 4 NH3 + 3 O2 => 2 N2 + 6 H2O.
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In the Label text field, type (1) Desired NH3 oxidation: 4 NH3 + 3 O2 => 2 N2 + 6 H2O.
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Locate the Reaction Rate section. From the list, choose User defined.
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In the rj text field, type re2.kf_1*re2.c_NH3*re2.c_O2/(1+K_NH3_ASC*re2.c_NH3).
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Locate the Rate Constants section. Select the Use Arrhenius expressions checkbox.
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In the Af text field, type A1_ASC.
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In the Ef text field, type E1_ASC.
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Locate the Reaction Orders section. Find the Volumetric overall reaction order subsection. In the Forward text field, type 2.
(2) Undesired NO formation: 4 NH3 + 5 O2 => 4 NO + 6 H2O
1
In the Reaction Engineering toolbar, click  Reaction.
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In the Settings window for Reaction, locate the Reaction Formula section.
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In the Formula text field, type 4 NH3 + 5 O2 => 4 NO + 6 H2O.
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In the Label text field, type (2) Undesired NO formation: 4 NH3 + 5 O2 => 4 NO + 6 H2O.
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Locate the Reaction Rate section. From the list, choose User defined.
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In the rj text field, type re2.kf_2*re2.c_O2*re2.c_NH3/G_ASC.
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Locate the Rate Constants section. Select the Use Arrhenius expressions checkbox.
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In the Af text field, type A2_ASC.
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In the Ef text field, type E2_ASC.
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Locate the Reaction Orders section. Find the Volumetric overall reaction order subsection. In the Forward text field, type 2.
(3) Equilibrium: 2 NO + O2 <=> 2 NO2
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In the Reaction Engineering toolbar, click  Reaction.
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In the Settings window for Reaction, locate the Reaction Formula section.
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In the Formula text field, type 2 NO + O2 <=> 2 NO2.
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In the Label text field, type (3) Equilibrium: 2 NO + O2 <=> 2 NO2.
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Locate the Rate Constants section. Select the Specify equilibrium constant checkbox.
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Select the Use Arrhenius expressions checkbox.
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In the Af text field, type A4.
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In the Ef text field, type E4.
(4) Undesired NO2 formation: 4 NH3 + 7 O2 => 4 NO2 + 6 H2O
1
In the Reaction Engineering toolbar, click  Reaction.
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In the Settings window for Reaction, locate the Reaction Formula section.
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In the Formula text field, type 4 NH3 + 7 O2 => 4 NO2 + 6 H2O.
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In the Label text field, type (4) Undesired NO2 formation: 4 NH3 + 7 O2 => 4 NO2 + 6 H2O.
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Locate the Reaction Rate section. From the list, choose User defined.
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In the rj text field, type re2.kf_4*re2.c_NH3*re2.c_O2/G_ASC.
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Locate the Rate Constants section. Select the Use Arrhenius expressions checkbox.
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In the Af text field, type A4_ASC.
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In the Ef text field, type E4_ASC.
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Locate the Reaction Orders section. Find the Volumetric overall reaction order subsection. In the Forward text field, type 2.
Couple the interface to the Thermodynamics System and edit the volumetric flow rate and the reactor pressure.
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In the Model Builder window, click Ammonia Slip Catalyst (ASC).
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In the Settings window for Reaction Engineering, locate the Mixture Properties section.
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Select the Thermodynamics checkbox.
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Locate the Species Matching section. In the table, enter the following settings:
Species
From Thermodynamics
H2O
H2O
N2
N2
NH3
H3N
NO
NO
O2
O2
Define the initial condition for the system. The gas entering the ammonia slip catalyst is that exiting the upstream SCR catalyst. Use Ctrl+Space in the text field to see a list of valid inputs, for example the variable names defined by the SCR system.
Initial Values 1
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In the Model Builder window, click Initial Values 1.
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In the Settings window for Initial Values, locate the General Parameters section.
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In the T0,in text field, type re.T.
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Locate the Volumetric Species Initial Values section. In the table, enter the following settings:
Species
Molar flow rate (mol/s)
H2O
re.F_H2O
N2
re.F_N2
NH3
re.F_NH3
NO
re.F_NO
NO2
re.F_NO2
O2
re.F_O2
The ammonia slip catalyst interface now looks like this:
Now, investigate the temperature operating window for the first part of the reactor, the SCR catalyst. Investigate this by varying the temperature of the inlet exhaust gas using Auxiliary Sweep. The Ammonia to NOx Ratio (ANR) is set to 1.3 (see Parameters: Flow and Composition) and the mass flow rate of exhaust gas corresponds to engine load case 2, that is, intermediate engine speed.