CHEMCAD Batch Reactor – Vessel Heat Transfer, page 1 of 25 10December2006

Department of Chemical and Biomedical Engineering FAMU–FSU College of Engineering

Unit Operations Laboratory

Vessel Heat Transfer (VHT) Dominque Foxx and Loren B. Schreiber

The authors give permission to download and print any part or all of the text for any nonprofit educational purpose.

Purpose The purpose of this tutorial is to introduce the application of the Batch Reactor module in CHEMCAD (version 5.6.1) for dynamic simulation of heat transfer in jacketed vessels. This tutorial is geared toward novice CHEMCAD users who are already familiar with the basics of heat exchangers. Problem Statement The heat-transfer characteristics of a laboratory jacketed reactor are evaluated by means of a simulated experiment with hot/cold water. The vessel is assumed to be well mixed and at atmospheric pressure. The vessel is initially charged with 1000 g of water at 40 °C. Water at ambient temperature then flows at a rate of 50 g/min continuously to the vessel, while simultaneously water at 60 °C flows at a rate of 3.5 L/min to the jacket. The liquid volume in the reactor is maintained at 1 L by an overflow device. Using CHEMCAD, predict the vessel temperature as a function of time. Procedure Step 1: Creating the flow sheet Step 2: Entering the engineering units Step 3: Entering the components Step 4: Entering the thermodynamic model Step 5: Entering the composition of the feed streams Step 6: Labeling the product streams Step 7: Entering the reactor specifications Step 8: Running the simulation and retrieving the results Step 9: Running more simulations

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Step 1: Creating the flow sheet

Open CHEMCAD and start a new job. On the toolbar change to Flowsheet mode. Select the batch reactor (2nd row 3rd column) from the palette and paste it to the

workspace. Select two feed arrows (4th row 1st column) and paste it to the workspace. Select two product arrows (5th row 6th column) and paste it to the workspace. Connect the batch reactor, feed arrows and product arrows with streams (1st row

9th column) from the palette. Change the ID number of the Batch reactor to 242. Change the ID number of the vessel feed and product stream ID numbers to single

digit and the ID numbers of the jacket supply and return streams to double digits in order to readily distinguish between the two.

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Step 2: Entering the engineering units

In the Format menu click on Engineering Units and click on Alt SI at the bottom. Change the Time to min. Change the Mass/Mole to g. Change the Pressure to Pa. Change the Enthalpy and Work to kJ. Change the Liquid Volume to liter and the Liquid Vol. Rate to liter/min. Change the Thickness, Diameter and Length to mm.

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Select the Options and references tab. Confirm that Total Flow is set to Default mole/mass. Confirm that Component Flow is set to Default mole/mass. Click OK to continue.

(Note: You can return later to the Engineering Unit Selection and change the units as needed to make your work easier.)

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Step 3: Entering the components

On the toolbar change to Simulation mode. Go to the Thermophysical on the menu bar and click on Component List (or click

on the shortcut button on the toolbar). Add water from the CHEMCAD component list by searching for the

component by name or chemical formula and clicking Add. Click OK.

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Step 4: Entering the thermodynamic model

This screen appears after you have added the components. If the min/max for the temperature and pressure ranges looks ok, then nothing

needs to be done. Click OK. Click OK on the two screens that follow.

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Step 5: Entering the composition of feed streams

Double-click on the stream ID number for the reactor feed stream. Enter the Stream Name as Feed. Enter the Temp C as 22. Enter the Press Pa as 101325. Enter the desired water flow rate as 50 g/min. Click Flash to fill in the remaining specifications. Click OK.

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Double-click the stream ID number for the jacket feed stream (i.e., water supply). Enter the Stream Name as WS. Enter the Temp C as 60. Enter the Press Pa as 101325. Enter the jacket flow rate as 3500 g/min. Click Flash to fill in the remaining values. Click OK.

Step 6: Labeling the product streams

Double-click the stream ID number for the reactor product stream. Enter the Stream Name as Product. Click OK. Double-click the stream ID number for the jacket product or return stream. Enter the Stream Name as WR. Click OK.

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Step 7: Entering the reactor specifications

Double-click on the reactor to bring up the Batch Reactor Menu.

Click on Initial Charge.

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Add the initial specifications of 1000 g of water and atmospheric pressure. Enter the Temp C as 40.

Click Flash. Click OK.

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Next, click on General Information on the Batch Reactor Menu. Leave the number of reactions blank. Select Liquid only, liquid phase reaction for the reactor phase. Select Specify jackets/coils for the thermal mode. Set the constant pressure to atmospheric pressure.

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Select the Semi-Batch tab. Set the Feed stream 1 to Stream 1. Set the Liquid product stream to Stream 2. Set the Reactor Holdup to 1 liter.

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Select the Convergence tab. Set the Integration method to Semi-implicit RK4 (for stiff systems).

Click OK.

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Go to Reactor Specifications on the Batch Reactor Menu. Enter 50 °C for the Initial wall temperature (i.e. the midpoint between the initial

temperature of the vessel contents and the temperature of the water supply). Enter the reactor volume (the total volume including the volume of the bottom

dish), diameter, wall thickness, wall density (based upon borosilicate glass), wall heat capacity, and thermal conductivity*.

Enter the # of jackets and coils as 1. (Note that a tab now appears for Jacket/coil 1.)

Enter the Holdup as 1 liter.

* Physical property data were obtained for N-51A glass from the document “TECHNICAL INFORMATION: Physical Properties of Glass” at the Kimble Kontes website http://www.kimble-kontes.com/pdfs/physical_properties_glass.pdf

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Select the Process side tab. Enter the Impeller diameter as 38 mm. Enter the Impeller speed as 18.75 Hz (i.e., 1125 rpm).

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Select the Jacket/Coil 1 tab. Select the Jacket type as Unbaffled jacket. Enter the jacket total volume, jacket height, jacket annulus and inlet diameter

(jacket nozzle diameter). Enter the initial conditions with atmospheric pressure, a temperature of 60 °C and

an initial liquid fraction of 1. Enter the minimum reactor volume (volume of the bottom dish), maximum

reactor volume (vessel volume to the top of the jacket), and the maximum active area (area inside of the vessel wall).

Select the Utility stream 1 as Stream 11 and the Utility origin stream ID as 11.

Click OK.

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Go to the Product draw schedule on the Batch Reactor Menu. Select Maintain holdup for the Product rate units.

Click OK. Press Exit on the Batch Reactor Menu and save.

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Step 8: Running the simulation and collecting the results

In the upper toolbar select Run and select Dynamics (or click on the shortcut button on the toolbar).

Click on Set run time. Set the number of operation steps to 1. Select the Step 1 tab and set the Run time for 60 min with a Step size of 0.1

min.** Click OK to save.

** Note: On the Step 1 menu, entries must be made with caution. We choose the step size with care. If the value is too large, the numerical algorithm may give incorrect results. On the other hand, if the step size is too small, the computation time may be excessive. We start with a step size of 0.1 min, recognizing that this value may have to be changed in subsequent simulations. We also consider making simulation trials at a variety of values of step size (e.g., 0.01 min and 0.5 min) to confirm that the simulation results are the same.

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Select Run from initial state (or click on the shortcut button on the toolbar). A message box will appear with any errors or warnings. Warnings usually can be

ignored, but errors need to be corrected. If there are no errors, click yes to continue.

To retrieve a time vs. temperature graph, in the upper toolbar select Plot, then Batch Reactor/DSVL History.

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Change the time unit to minutes. Under Reactor properties select Temperature.

Click OK.

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If the simulation is correct, the graph of temperature vs. time should be similar to the one below.

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All graphs are available under the Window menu and can be copied to Microsoft Word, or printed from CHEMCAD.

To export the data to Excel, select Graph from the toolbar, then select Data to Excel CSV file.

An Excel file with the data will open automatically.

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Step 9: Running more simulations

Return to the flowsheet. In the upper toolbar select Run and select Dynamics.

Click on Restore to initial state (or click on the shortcut button on the toolbar).

Press Exit. Select the feed stream and change the water flow rate to 150 g/min. Press OK and save. Return to the Dynamics menu, select Run from initial state. Plot the time vs. temperature graph.

What happened? What do you think happens to the temperature of the water in the vessel if the

jacket supply rate is reduced from 3500 g/min to 1300 g/min?

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Helpful Figures

Figure 1. Top View of CSTR walls

Jacket Water

A. Inside diameter of vessel wall – 100 mm B. Outside diameter of vessel wall – 110 mm C. Inside diameter of jacket wall – 140 mm D. Outside diameter of jacket wall – 150 mm

A

B C

D

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Figure 2. Side View of CSTR

Jacket Nozzle Diameter (6.4 mm)

Volume of Bottom Dish (0.024 L)