Introduction

The objective of this tutorial is to calculate the exit concentration in a reactor in which iron oxide is dissolved with hydrochloric acid.

The reaction is exothermic causing the temperature in the exit stream to rise. The objective is also to determine by how much the temperature will rise.

During this tutorial you will practice the following functions within Cycad Process:

  • Drawing the flowsheet
  • Adding components to the balance
  • Changing stream compositions
  • Adding reactions to the process unit
  • Calculating the balance
  • Interpreting the results displayed Convergence Form
  • Examining the results

In this tutorial you will go through the following six steps:

  1. Draw the flowsheet
  2. Add components to the mass balance
  3. Add reactions
  4. Set up the feed flows
  5. Run the balance
  6. Examine the results

Step 1: Draw the flowsheet

The first step is to add a tank. Add Stream flags and process streams such that the drawing of the system looks like that shown in Figure 1.

1

Figure 1. Flow diagram for the dissolution of ferric oxide by hydrochloric acid.

Add an equipment tag and description for the tank and Agitator. The tags and descriptions can be edited in the Process Unit section of the Properties Viewer when the tank is selected.

This is shown in Figure 2.

2

Figure 2. Adding tag numbers and equipment descriptions for the tank.

Note: Leave the temperature of the unit set to the default 25oC.


Step 2: Add components to the mass balance

Add Fe2O3 (s), HCl (aq), H2O (l), and FeCl3 (aq) to the list of components.

This is achieved as follows:

Press the "Add Components" Button on the Process Toolbar, as illustrated in Figure 3, to launch the Components Selection Form.

3

Figure 3. The Add Components Button on the Setup Balance Process Toolbar.

The Components Selection Form is shown in Figure 4.

To select a component find it in the list and then double click on it. This will add the component to the selected components list. Should you wish to remove an accidently selected component simply double click on the component in the selected component list.

After selecting all the required components, click the OK button to send the components to Stream manager.

Click the Stream manager tab to check if all components have been added and are in their correct physical states.

4

Figure 4. The Component Selection Form.


Step 3: Add the reactions

Select the Tank and click on Reactions in the Properties Browser.

Launch the Reaction editor by selecting the button with the ellipsis (...) on it.

Add the reaction as exactly shown in Figure 5:

Fe2O3 (s) + 6 HCl (aq) --> 2 FeCl3 (aq) + 3 H2O (l)

(Note that the ‘aq’ is lower case AQ for aqueous, not AG!)

Set the conversion to be 85% by typing “ext = 0.85” in the Expression block.

5

Figure 5. The Reaction Editor for the tank, showing the dissolution reaction.

Click “Apply” and then the “OK” button to launch reaction equation.

Select the tank. In the Properties Window under Energy balance select the Non-Isothermal option for temperature change determination.


Step 4: Setup the stream compositions and flows

Select the hydrochloric acid feed stream and set the flow rates to:

  • H2O (l) = 6.4 t/hr

  • HCl (aq) = 3.6 t/hr.

Next, select the solids feed stream and set the flow rates to:

  • Fe2O3 (s) = 1 t/hr,

  • H2O (l) = 10 t/hr.

Stream 20 is shown in Figure 6.

6

Figure 6. Setup the Process Streams in the Stream Manager.


Step 5: Calculate

Press one of the Run buttons on the process toolbar. The Process Toolbar is shown in Figure 7.

7

Figure 7. The Calculate Process Toolbar, with the cursor hovering over the Run button.

Once the project has run the Convergence Form will be displayed. An example of this form is shown in Figure 8.

8

Figure 8. Convergence form.

The main thing to examine in this form is the mass balance error for each of the elements. Since there is no error for any of the elements, the results can be accepted.


Step 6: Examine results

Select the exit stream and then select the Stream Manager to view the results of the calculation.

The exit stream should have the value shown in Figure 9.

The obvious observation is that 85% of the Fe2O3(s) dissolved as required and that this reaction affected the concentrations of ferric chloride and hydrochloric acid in solution.

It is also evident that the reaction caused the temperature of the solution to heat up from 25°C to about 36.5°C. This is because we chose the "Non-isothermal" option for the calculation of the energy balance for this reactor.

9

Figure 9. Results of the calculation.

The solution heats up because the reaction is exothermic. To get a value for the heat of reaction, go to the equipment tab in the Design Criteria and then navigate to the reactions table.

After selecting the Design Criteria report, then select page 1. The heat of reaction is given as -1.2e+05 J/mol of the first component. The negative value implies that the reaction is exothermic therefore heat is given off during the reaction.

The screen view of this is shown in Figure 10.

10

Figure 10. Design criteria for the tank reactor.