1 / 9

How much NO x can we form?

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

Download Presentation

How much NO x can we form?

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. 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?

  2. 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

  3. HANDS ON Example: Calculate Equilibrium NOx

  4. 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?

  5. 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?

  6. 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\

  7. 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?

  8. 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

  9. 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?

More Related