How much no x can we form
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How much NO x can we form? PowerPoint PPT Presentation


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How much NO x can we form?. HANDS ON. Equilibrium calculations tell us the eventual concentrations of species, for a given set of conditions Example : Start with pure air (N 2 + O 2 ) Constrain temperature and pressure Let P = 1 atm, vary T = 300 to 2300 K

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How much NO x can we form?

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How much no x can we form

How much NOx can we form?

HANDS ON

  • Equilibrium calculations tell us the eventual concentrations of species, for a given set of conditions

  • Example:

    • Start with pure air (N2 + O2)

    • Constrain temperature and pressure

      • Let P = 1 atm, vary T = 300 to 2300 K

    • How much NOx will be formed?


Example calculate equilibrium no x

Example:Calculate Equilibrium NOx

HANDS ON

Temperature-dependence of NOx

  • Create a New project, e.g., “myNOxEquil”

    • Drag an Equilibrium icon onto the Diagram and Update Project

  • Create a new chemistry set

    • Set Working Directory to a new directory,e.g., “MyNOxEquil”

    • Create new Gas-phase chemistry file

    • Only need elements and species: N, O, NO, NO2, N2O, N2, O2

    • Select the standard Thermodata file

  • Fill in panels describing equilibrium conditions

    • Hint: Air consists of about 79% N2 and 21% O2

    • Hint: Vary temperature using Continuations

  • Create input files and Run

  • Plot the resulting NOx components vs. T


How much no x can we form

HANDS ON

Example: Calculate Equilibrium NOx


Example calculate equilibrium no x1

Example: Calculate Equilibrium NOx

HANDS ON

  • What is the dominant component of NOx

    • Does the answer change with Temperature?

  • How many ppm of NOx is formed at T=2300 K?

    • Typical NOx emissions regulation:

      “…combined-cycle combustion turbines firing natural gas and distillate oil must limit NOx emissions to 42 and 65 parts per million”

  • At what temperature does NO formation begin to become important?


Example calculate equilibrium no x2

Example:Calculate Equilibrium NOx

HANDS ON

Pressure-dependence of NOx

  • Create a New project to determine equilibrium conditions for varying pressure

    • Fix T = 2300 K

    • Hint: Air consists of about 79% N2 and 21% O2

    • Vary P from 0.1 to 10 atm

  • Run

  • Plot the resulting NOx components vs. P

How dependent is NO on Pressure?


Example use pfr to calculate the time to equilibrium

Example: Use PFR to calculate the time to equilibrium

HANDS ON

  • Plug flow reactor model shows balance between flow times and kinetics

  • Example:

    • Run air through a flow tube

    • Fix the temperature

    • Include N2/O2reaction kinetics

T = 2300 K

Air

300 cm3/s

1 atm

2.54

cm

! Air reactions extracted from GRI-Mech Version 3.0

ELEMENTS

O H N AR

END

SPECIES

O O2 N NO NO2 N2O N2

END

REACTIONS

2O+M<=>O2+M 1.200E+17 -1.000 .00

N+NO<=>N2+O 2.700E+13 .000 355.00

N+O2<=>NO+O 9.000E+09 1.000 6500.00

N2O+O<=>N2+O2 1.400E+12 .000 10810.00

N2O+O<=>2NO 2.900E+13 .000 23150.00

N2O(+M)<=>N2+O(+M) 7.910E+10 .000 56020.00

LOW /6.370E+14 .000 56640.00/

NO+O+M<=>NO2+M 1.060E+20 -1.410 .00

NO2+O<=>NO+O2 3.900E+12 .000 -240.00

END

30 cm

...training\nox_emissions\plug_timescales_nOx\


Example use pfr to calculate the time to equilibrium1

Example:Use PFR to calculate the time to equilibrium

HANDS ON

  • Create a New project, e.g., “myPFRNox”

  • Set the working dir to the training directory :

    • ...training\NOx_Emissions\Plug_Timescales_NOx

  • Browse and select the “Air_NOx.cks” chemistry set

    • Note: reaction kinetics now included in the “Air_chem.inp” file

  • Set up the plug-flow problem

    • (settings on previous slide)

  • Create input and Run

  • Plot residence time vs. distance

  • Plot NO vs. residence time

How long does it take for NO to reach the equilibrium value?


Example use pfr to calculate the time to equilibrium2

t = 0.49 s

x = 28 cm

Example:Use PFR to calculate the time to equilibrium

HANDS ON

T = 2300 K

  • NO increases exponentially with temperature, as before

  • For longer channel, we get closer to equilibrium

  • Higher temperatures reach equilibrium faster

Equilibrium = 15400 ppm

T = 2000 K

NO

Time vs. Distance

T = 1500 K


Summary how do we reduce no x

Summary: How do we reduce NOx?

Calculations suggest:

  • Reduce time spent by gases at high temperatures (residence time)

    • Don’t let conditions approach equilibrium

  • Keep combustion temperatures low

  • Focus on NO; dominant NOx component

  • Reduce nitrogen-containing compounds?

  • Introduce additional chemistry so other species are formed?


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