18/3/2014 ChemCAD tutorials

http://www.isr.umd.edu/Labs/CACSE/A-Team/ChemCAD/tutorials/preheat.html 1/2

ChemCADpreheaterexample

1 mole/sec ofmethane is used asfuel for a fired heater.If a stoichiometricamount of air is to befed to the heater,compute

1. the necessaryrate at whichheat must besupplied to theair stream (inkW), and

2. the resultingtemperature ofthe air/methanemixture prior tocombusion

if the air and methaneboth are available at

20o C and the air is to

be preheated to 400o

C. Approximate thecomposition of air asa 20/80 mixture ofoxygen and nitrogenand the air andmethane are availableat 2 atm pressure.

ChemCAD implementation

1. Start the ChemCAD application; choose menu item File -> Save As...and save as a file on your computer's desktop.

2. In the Palette box, click on Heat Exchanges tab, then click on theHeat exchangers #1 symbol. Once the unit is selected, click on apoint in the work space where you want the unit placed. Right clickingwill unselect the heat exchanger.

3. Then place, by selecting from the main palette (clicking on All UnitOps returns all process unit icons), the Feed and Product arrows.Place the 2 feed and 1 product arrows accordingly near the heatexchanger.

4. Click on the Piping and flow tab and add a mixer between the heat

18/3/2014 ChemCAD tutorials

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exchanger and product arrow.5. While still in Piping and flow, click on the Stream icon (first row, first

column) and use this to connect1. one feed arrow to the heat exchanger inlet;2. the heat exchanger outlet to one mixer inlet;3. the other feed arrow to another mixer inlet;4. the mixer outlet to the product arrow.

In all cases, blue dots represent equipment feed streams and red dotsrepresent equipment outlet streams.

6. Select Thermophysical -> Select Components and add methane (2),nitrogen (46) and oxygen (47). Click OK until you are through all of themenus that subsequently appear..

7. Choose menu item Format -> Engineering Units to select Formal SIunits for this problem. Change pressure to atmospheres, temperatureto C, enthalpy to kJ, and time to sec. Component flows should be molefractions - to make that change, click on the Options and Referencestab and change Component Flows to mole fractions. After makingthese choices, click OK.

8. Double-click on the input stream arrow connected to the heatexchanger; set the correct feed temperature and pressure and theoxygen and nitrogen flows to 2 and 8 mol/s, respectively.

9. Double-click on the other input stream arrow (connected to the mixer);set the correct feed temperature and pressure and the methane flowto 1 mol/s.

10. Double-click on the heat exchanger; set the outlet temperature to

400o C and 0 pressure drop.11. From the main menu, select Run -> Run All; correct errors, if any.12. Using the mouse, examine the heat exchanger duty and stream

temperatures on the flowsheet.13. From the solution report obtained from Report -> Consolidated

Report click on the Generate button.

Created and maintained by R. A. Adomaitis of the University of Maryland,2012.