Preparations and Starting the program

Transcription

1 Preparations and Starting the program

2 1) Create a working directory on your computer for your Chemkin work, and 2) download kinetic mechanism files AAUmech.inp and AAUtherm.dat into your working directory Click to get

3 Start / launch the software Chemkin 2 3 1

4 Start a new Chemkin project

5 1) Close whatever project is by default open 2) Create New project, provide Project Name

6 Save project 1) Under Project tab, select Save Save project 2) Save in your working directory

7 Choose reactor into your project

8 As result of 1) these apperar As result of 2) this 1) From the Models panel click Plug Flow Reactor icon 2) Under Miscellaneous, click Outlet Flow icon 3) You can move the icons around in the Diagram View panel 4) To connect the Plug Flow Reactor (PFR) to the Outflow, place the mouse/cursor on the edge of the PFR icon (the mouse turns into a cross. Press down the left mouse button and draw a line from the PFR to the Outflow (see next slide for how result should look like)

9 1 PFR connected to Outflow After pressing 2) Update Project, the screen should look something like this 3 PFR with inlet and outflow connected Project tab 2

10 Import and pre-process chemistry

11 2) Browse to your working directory 1) Double-click Pre-Processing 2) When there, press Select

12 3) Select Gas-Phase Kinetics File 4) Press Open/Create 1) Click New Chemistry Set 2) Select the ÅA mechanism files that you downloaded: Gas-Phase Kinetics File, and Thermodynamics file

13 1) After selecting both mechanism files, provide a name for the new mechanism 2) Press SaveAs, and save in your working directory

14 1) Press Run Pre-Processor (Run Calculations should become black = available for use) 2) Close Pre-Processing tab 3) You are now ready to start defining calculation conditions and calculation input Before that, Save your project

15 Defining reactor parameters and input species

16 1) Double-click PFR (C1) to open selection tree. Under C1_PFR you can define reactor conditions, and C1_Inlet1 you can use to define input gas species 2) Double-click C1_PFR, and choose Fix Gas Temperature. This choice defines the PFR to have a constant temperature. Next slide shows the panel that opens after you have chosen problem type. To note: Selecting Solve Gas Energy Equation results in gas temperature changing as result of chemical reaction (heat release). Depending on the purpose of your calculation, you can choose this when needed.

17 In this panel you can define reactor conditions 1) Constant temperature or solve temperature 2) Length of reactor (and units) 3) The reactor needs to a have a numeric value for the diameter. We will later define inflow as velocity, so the diameter value does not affect our calculation results 4) Reactor temperature. This is either the fixed temperature value, or the starting temperature, depending on if the energy equation is solved or not 5) Pressure, 1 atm or 1 bar 6) To close panel

18 4) Select the Species-specific Properties panel (see next slide) 3) Set gas velocity. The gas velosity in combination with the reactor length determine the reactor residence time (sec) 1) Double-click C1_Inlet1 2) Press OK to this

19 Provide input species 1) For example a ) choose to define amounts in mole fraction / mole b) write O2 in Species field c) the amount 2 in the Data field d) press the Add button 2) Input species for methane combustion with air at air factor 1 3) You can press Normalize, which normalizes the input to sum to 1. This is equivalent to having mole fractions 4) Close the C1_Inlet1 panel (cross in upper-right corner) These correspond to stoichimetry 1 mol CH4 + 2 mol O2 + 2/21*79 mol N2 1 mol CH4 + 2 mol O mol N2

20 Running calculation and plotting results

21 2 1 1) Double-click Run Calculations 2) Press Begin

22 1) Maintain default option to Plot Results by Selecting New Settings 2) Press Nex Step

23 1) Maintan default options. If you want you can scroll down to see what options can be selected Var refers to variable, for example species mole fractions and temperature ROP refers to Rate-of-Production, which is the reaction rates 2) Press Process Solution Data

24 Options for presenting / managing results 1) Tabs for type of plot, or for export results 2) For the line plot (xy-plot) x-variable (choose distance or res. time) y-variable (choose one or several species) or temperature

25 1) To select several species have the Ctrl button pressed down while selecting the species. Select for example CH4, CO, CO2, H2, H2O, O2 (these are in different order in the menu) 2) Press Create Plot

26 You can zoom in on the profiles by pressing the mouse wheel down and selecting the area by drawing a rectangle from the top-left corner to bottom-right corner. To zoom out, do the opposite: rectangle from bottom-right to top-left You can also go back to reactor parameters and define the reactor length to be longer or shorter After testing, close plot window, and close also other windows related to result plotting.

27 Calculating by solving also the energy equation

28 3) Close C1_PFR panel 2) Choose to Solve Gas Energy Equation 1) Double-click C1_PFR

29 2) Press Begin 1) Double-click Run Calculations 3) Plot using Previous Settings (press Next Step) Here you can choose other settings as needed, but the Previous Setting should be ok for the Purpose of this exercise

30

31 Alternatives for result treatment

32 You can test plotting species mole fractions on logarithmic scale (y-axis) For example CH 4 is not in the strictest sense zero. However, for practical purposes a mole fraction of 1E-15 can be considered zero

33 To export results to, for example, be read into Excel 1) Choose Export Variables tab 2) Select variables to be exported 3) Choose where to export the data to (your working directory is default). give file name, and press Save 4) Press Export

34 You are now ready to start working on the exercise At this point, save your project before continuing. This way you have something to go back to, in case the program crashes etc.

35 Task 1: Methane combustion Methane combustion at 1000 C 1) Calculate input (mol) of CH 4, O 2, and N 2 depending on air factor 2) Set up and carry out kinetics calculations using Chemkin: - plug flow reactor length 10 m, - axial velocity 10 m/s, - constant temperature at 1000 C - species input depending on air factor 3) What is the final (chemical equilibrium) gas composition? Update the table below and plot your results in Excel (species mole fractions as function of air factor) Air factor T ( C) Mole fractions O 2 CH 4 CO CO 2 H 2 H 2 O

36 Task 2: Methane combustion Use you model to estimate how quickly a pre-mixed mixture of methane and air would burn if the initial temperature was 1000 C and the gas velocity is 10 m/s. To judge when combustion is completed, you can use as criteria that CH 4, CO, CO 2 have leveled out and their mole fractions are not changing. Note this location in the PFR in terms of distance along the PFR and as time (residence time). This correspond to having a Bunsen burner with gas flow 10 m/s, and seeing how far (or short ) the gas needs to travel from the burner nozzle before combustion is completed. The point is not to fixate on decimals, but instead to be able to say in which kind of range the time needed for complete combustion is (order of magnitude, is it 1 millisecond, 1 second, or 10 seconds) You should be able to use the model from the previous task: - Calculate methane combustion in air at air factor Test the sensitivity of your calculations to temperature by keeping temperature constant and doing calculations using temperatures of 600, 800, 1000, 1200 C

37 Task 3: study NOx chemistry Step 1: Use the model from previous tasks to study to which extent NH 3 forms NO, depending on O 2 level. Consider O 2 at 1vol-% and at 20 vol-% Chemkin input Mixture mol O mol N 2-100E-6 mol NH 3 (when you normalize this, these approximatily 100 ppm NH 3 in approximately 20 vol-% O2) Mixture mol O mol N 2-100E-6 mol NH 3 For both cases (mixtures) plot NH 3 and NO in the same plot, and note to which extent NH 3 forms NO (approximately which per cent of NH 3 forms NO)