How much NO x can we form? 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 –How much NO x will be formed? HAND S ON

Example:Calculate Equilibrium NO x HAND S ON 1.Create a New project, e.g., “myNOxEquil” –Drag an Equilibrium icon onto the Diagram and Update Project 2.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 Thermo data file 3.Fill in panels describing equilibrium conditions –Hint: Air consists of about 79% N 2 and 21% O 2 –Hint: Vary temperature using Continuations 4.Create input files and Run 5.Plot the resulting NO x components vs. T Temperature-dependence of NO x

Example: Calculate Equilibrium NO x HAND S ON

Example: Calculate Equilibrium NO x HAND S ON What is the dominant component of NO x –Does the answer change with Temperature? How many ppm of NO x is formed at T=2300 K? –Typical NO x emissions regulation: “…combined-cycle combustion turbines firing natural gas and distillate oil must limit NO x emissions to 42 and 65 parts per million” At what temperature does NO formation begin to become important?

Example:Calculate Equilibrium NO x HAND S ON 1.Create a New project to determine equilibrium conditions for varying pressure –Fix T = 2300 K –Hint: Air consists of about 79% N 2 and 21% O 2 –Vary P from 0.1 to 10 atm 2.Run 3.Plot the resulting NO x components vs. P Pressure-dependence of NO x How dependent is NO on Pressure?

Example: Use PFR to calculate the time to equilibrium Plug flow reactor model shows balance between flow times and kinetics Example: –Run air through a flow tube –Fix the temperature –Include N 2 /O 2 reaction kinetics Air 300 cm 3 /s 1 atm T = 2300 K ! 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 N+NO N2+O 2.700E N+O2 NO+O 9.000E N2O+O N2+O E N2O+O 2NO 2.900E N2O(+M) N2+O(+M) 7.910E LOW /6.370E / NO+O+M NO2+M 1.060E NO2+O NO+O E END HAND S ON 30 cm 2.54 cm...training\nox_emissions\plug_timescales_nOx\

Example:Use PFR to calculate the time to equilibrium HAND S ON 1.Create a New project, e.g., “myPFRNox” 2.Set the working dir to the training directory : –...training\NOx_Emissions\Plug_Timescales_NOx 3.Browse and select the “ Air_NOx.cks ” chemistry set –Note: reaction kinetics now included in the “ Air_chem.inp ” file 4.Set up the plug-flow problem –(settings on previous slide) 5.Create input and Run 6.Plot residence time vs. distance 7.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 equilibrium NO increases exponentially with temperature, as before For longer channel, we get closer to equilibrium Higher temperatures reach equilibrium faster T = 2300 K T = 2000 K T = 1500 K Equilibrium = ppm NO Time vs. Distance t = 0.49 s x = 28 cm HAND S ON

Summary: How do we reduce NO x ? Reduce time spent by gases at high temperatures (residence time) –Don’t let conditions approach equilibrium Keep combustion temperatures low Focus on NO; dominant NO x component Reduce nitrogen-containing compounds? Introduce additional chemistry so other species are formed? Calculations suggest: