Introduction

The objective of this tutorial is to demonstrate how to model reactions using reaction kinetics. In previous tutorials we discussed the modeling of reactions using conversions, sometimes referred to as extents. In this tutorial we will model the reaction more fundamentally by using reaction rates or kinetics.

The system that we will model is the dissolution of hematite in hydrochloric acid. The rate of this reaction is dependent on the concentration of acid in solution. This dependency will be accounted for explicitly.

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

  • Drawing the flowsheet
  • Setting up the mass balance
  • Adding the reaction kinetics
  • Running the model
  • Adding a Unit Designer to size of the tank; and,
  • Examining the results.

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

  1. Draw the flowsheet
  2. Set up the mass balance
  3. Add reactions and reaction kinetics
  4. Run the model
  5. Designing the tank size with a Unit Designer
  6. Examine the results

Step 1: Draw the flowsheet

The first step is to draw the flowsheet, as shown in Figure 1. The flowsheet consists of a tank that is fed by two streams. The product from the tank is a single stream.

To draw the flowsheet use the same techniques you used during the Challenge.

 Tut12 image1

Figure 1. The Overall flowsheet.

 


Step 2: Set up the mass balance

Add the components given in Table 1.

Table 1. Feed condition to the reactor.

. Feed condition to the reactor.

Stream Tag

     

10

20

Stream Description

     

FEED STREAM

HYDROCHLORIC ACID

H2O

(l)

water

t/hr

35.00

6.40

FeCl3

(aq)

ferric chloride

t/hr

0.00

0.00

HCl

(aq)

hydrochloric acid

t/hr

0.00

3.60

Fe2O3

(s)

ferric oxide

t/hr

1.00

0.00

H2O

(g)

water vapour

t/hr

0.00

0.00

SiO2

(s)

silica

t/hr

0.20

0.00


Step 3: Add the reactions to the tank

Select the tank and then navigate to the “Reactions” property in the Property Viewer. Select the ellipsis button to launch the Reaction editor.

Add the following reaction:

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

This reaction has the following rate equation:

rate = 0.185*[HCl(aq)]


To add this rate, select “Irreversible” in the Reversible column and HomogeneousLiquidPhaseReaction in the CalculationMethod column.

Type the rate expression in the Expression column.

The required selection is shown in Figure 2.

 Tut12 image2

Figure 2. The Reaction Grid Form.

Now for an important part but sometimes missed! The tank needs some volume for the reaction to occur in. Navigate to the “Volume” property of the tank and make the Liquid Volume 10m3.

(If the reaction is a gas phase reaction, the CalculationMethod in the Reaction Grid Form should be HomogeneousGas and the GasVolume should be greater than zero.)

 


Step 4: Run the model

Run the model by pressing the Run Project button in the Process Toolbar.

The results should be those shown in Table 2.

Table 2. Results for the Tank Reactor.

Stream Tag

     

10

20

30

Stream Description

     

FEED

ACID

PRODUCT

H2O

(l)

water

t/hr

35.00

6.40

41.58

FeCl3

(aq)

ferric chloride

t/hr

0.00

0.00

1.07

HCl

(aq)

hydrochloric acid

t/hr

0.00

3.60

2.88

Fe2O3

(s)

ferric oxide

t/hr

1.00

0.00

0.47

H2O

(g)

water vapour

t/hr

0.00

0.00

0.00

SiO2

(s)

silica

t/hr

0.20

0.00

0.20

             

Total Mass

   

t/hr

36.20

10.00

46.20

To see this tab click on the page without selecting anything, then select the Stream Manager to open this view.


Step 5: Designing the tank size with a Unit Designer

Add a Unit Designer to the Page.

Link it to the Tank and link the Measurement Point on the product stream to the Unit Designer. Link the Design Point on the Unit designer to the Design Point of the Tank.

This is shown in Figure 3.

 Tut12 image3

Figure 3. Linking the Unit Designer.


Select the Measurement to be 10 g/L of Fe(aq) in the exit stream.

The settings required to do this are shown in Figure 4.

 Tut12 image4

Figure 4. Settings for the Measurement values of the Unit Designer.

 


Set the Design variable to VolumeLiquid and the Design Range to between 1 and 20.

The design settings are shown in Figure 5.

This means that the Unit Designer will change the liquid volume of the tank between 1 m3 and 20m3 to achieve a concentration of 10 g/L Fe in solution at the exit.

 Tut12 image5

Figure 5. Settings for the Design values of the Unit Designer.

 


Step 6: Examine the results

Run the model by pressing the Run Project button in the Process Toolbar.

The Unit Designer should change the volume to 12.7 m3 to achieve the required Fe concentration of 10 g/L.

The Convergence Form is shown in Figure 6.

 Tut12 image6

Figure 6. Convergence Form showing that the volume has been changed to 12.7 m3.