Introduction

The objective of this tutorial is to discover how to change the calculation options for the energy balance. There are two main options that the user can choose between. These are isothermal operation and non-isothermal operation.

During this tutorial, you will practise the following functions and different modes of calculating the energy balance within Cycad Process:

  1. Drawing the flowsheet
  2. Selecting isothermal operation
  3. Changing the temperature property
  4. Selecting the non-isothermal property
  5. Adding heat transfer coils to the operation
  6. Setting steam conditions
  7. Calculating the amount of steam required
  8. Examining the results

Option 1: Isothermal Operations

The first type of energy balance calculation that we will perform is an isothermal operation. In this type of operation the temperature is specifiedand the amount of energy required for the process is calculated.

Step 1: Set up the flowsheet

The first step in this tutorial is to do the following:

  • Draw the flowsheet
  • Add Components
  • Set the Equation
  • Set up the flows of materials in the various streams

Draw the flow diagram as shown in Figure 1.

1

Figure 1. Draw the flowsheet.


Then select the tank and in the Properties Viewer enter an evaporation rate of 0.1 t/hr.

Add the following components:

    1. Fe2O3 (s)
    2. HCl (aq)
    3. FeCl3 (aq)
    4. H2O (l)
    5. H2O (g)

Set the reaction equation as follows:

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

Set the extent to “ext = 0.85”

Set up the stream 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.


Step 2: Select isothermal operation

Select the tank so that the properties for the tank are displayed in the Properties Viewer.

The "Energy Balance" can be set to one of three options:

  • Isothermal (constant temperature)
  • NonIsothermal (non-constant temperature)
  • Adiabatic (no heat loss)

From these, select "Isothermal".

This is shown in Figure 2.

2

Figure 2. Select the isothermal operation.


Step 3: Enter the temperature of operation

The temperature of the operation is entered in the "Operating Conditions" section of the Properties Viewer.

Enter a value of 40oC as shown in Figure 3.

3

Figure 3. Temperature Property box in the Properties Viewer.

Step 4: Calculate

Run the project, as shown in Figure 4.

4

Figure 4. The Process Toolbar, with the cursor hovering over the Run button.


Step 5: Examine the results

The amount of energy required to perform the task is the main result.

This is viewed in the "Heat Transfer Duty" box of the Properties Viewer.

As can be seen from results displayed in Figure 5.This process would require an additional heating of 0.127 MW.

5

Figure 5. The energy required for this process to occur at 40oC is an additional 0.127 MW.



Option 2: Non-Isothermal Operations

Step 1: Selecting the Non-Isothermal Mode of Operation

Select the tank so that the properties for the tank are displayed in the Properties Viewer.

In the "Energy Balance" section, select "Energy Balance" and choose "NonIsothermal".

This is shown in Figure 6.

6

Figure 6. Setting the Energy Balance calculation option “NonIsothermal”.


Step 2: Add coils

With the Tank selected, change the Heat Transfer Equipment from "None" to "Coils" by first expanding the “Heat transfer” block under energy balance in the property viewer and then selecting the drop-down arrow next to the “heat transfer equipment” box. This is shown in Figure 7.

7

Figure 7. Adding coils to the tank.

This automatically draws coils in the tank.


Connect the coils to a source of steam as shown in Figure 8.

8

Figure 8. Connecting the coils to steam supply.


Step 3: Selecting the heat transfer fluid

It is necessary to specify the type of heat transfer fluid in order to perform the heat transfer calculations. This must already be in the list of components.

Select the tank and then expand the "Heat Transfer" property in the Properties Viewer.

In the "Fluid" box press the ellipsis button (...) to launch the component selection form.

Select H2O (g) as the component.

This is shown in Figure 9.

9

Figure 9. Selecting steam as the heat transfer fluid.


Step 4: Setting steam conditions

If you select the steam and then select Stream Manager, you will see that the flow of H2O (g) is zero – in other words there is no steam present. You need to provide some steam.

Add 1 t/hr of H2O (g) to the stream and set the temperature to 125°C.

Move the cursor opposite the Pressure item and right-click to launch the context menu.

Select the "Set Steam Conditions" item.

This automatically selects the pressure as that of saturated steam at 125°C – 130.4 kPaG.

This is shown in Figure 10.

 

10

Figure 10. Setting the temperature and pressure of the steam.


Step 5: Calculate

Run the project, as shown in Figure 11.

11

Figure 11. The Process Toolbar, with the cursor hovering over the Run button.

Step 6: Examine the results

Select the exit stream and then the Stream Manager.

This will reveal that the temperature has risen to 69°C.

Select the tank and then navigate to the "Heat Transfer Duty" box of the Properties Viewer to see that the duty that is used is 0.61 MW.

This is easily verified as the correct result since, 1 t/hr of steam releases about 2200kJ/kg, which is 1000 kg/h x 2200 kJ/kg x 1e-3 MJ/kJ x 1/3600 hr/s = 0.61MW.


Option 3: Extending the isothermal operation

In the previous two sections of this tutorial we examined how to use the isothermal and the non-isothermal properties when calculating the energy balance.

In this section we look at the effect of changing the "Energy Balance" property back to isothermal when we have coils. In this case the amount of steam is adjusted so that the isothermal condition is met.

Step 1: Change the energy balance property

Change the "Energy Balance" property to isothermal and set the temperature to 80°C.

This is shown in Figure 12.

12

Figure 12. Changing the Energy Balance Property


Step 2: Calculate

Run the project, as shown in Figure 13.

13

Figure 13. The Process Toolbar, with the cursor hovering over the Run button.

Step 3: Examine results

In this case the calculation has automatically changed the flow of steam so that the temperature is 80°C.

The required steam flow is determined to be 1.3 t/hr.