1.2 Steady State Simulation
1.2.10 Optional Study
In the following sections, the effects of the LTS temperature on the SalesGas dew point and heating value are determined. Before proceeding, re-specify the temperature of ColdGas back to its original value of 0oF:
1. Click the Workbook icon on the toolbar.
2. On the Material Streams tab of the Workbook, click in the
3. Type 0, then press ENTER.
Using the Spreadsheet
HYSYS has a Spreadsheet operation that allows you to import stream or operation variables, perform calculations, and export calculated results.
To install a Spreadsheet and display its property view: 1. Click Flowsheet > Add Operation.
2. In the Add Operation window, click Spreadsheet and then
Add.
The Spreadsheet property view appears.
3. On the Connections tab, change the spreadsheet name to
Heating Value.
The heating value of the sales gas is calculated by importing the stream composition into the Spreadsheet then
multiplying the mole fraction of each component by its individual heating value.
Importing Variables - First Method
In this section you will import variables on the Connections tab.
1. Click the Add Import button, and the Select Import for cell property view appears.
2. Choose the SalesGas Object, Phase Comp Mole Frac Variable, and Methane Variable Specific as shown.
NO2 and CO2 are not included in the calculation as their individual heating values are negligible.
3. Click the OK button.
4. Click the Add Import button again, then select the
SalesGas Object, Comp Mole Frac Variable, and Ethane
Variable Specific. 5. Click the OK button.
6. Repeat steps 4 and 5 to add the Propane Variable Specific. For illustration purposes, the two remaining components will be added later using an alternative import method. HYSYS assigned the imported variables to Spreadsheet cells A1 through A3, by default.
7. Change the cell locations to B3 through B5 as shown in the following figure; the reason for doing so will become
apparent on the Spreadsheet tab.
8. No information is required on the Parameters and Formulas tabs, so click the Spreadsheet tab.
9. Enter the column headings as shown in the table below.
You can move to a cell by clicking it, or by pressing the arrow keys. The HYSYS Spreadsheet behaves similarly to commercial spreadsheet packages; you enter data and formulas in the cells, and calculated results are returned. 10. Enter the components in the Component column as shown
as shown in the table below.
Figure 1.108
Column/Row Heading
A1 Component
B1 Mole Fraction
C1 Comp Heat Value
D1 Total Heat Value
Row Component 3 C1 4 C2 5 C3 6 iC4 7 nC4
11. Enter the component net heating values in the Comp Heat
Value column as shown in the figure below.
Importing Variables - Second Method
The next task is to import the remaining two variables’ mole fractions in the Sales Gas.
1. Select the Spreadsheet cell B6, which is reserved for the i- C4 mole fraction.
2. Right-click and select Import Variable from the Object Inspect menu.
The Select Import for cell property view appears.
3. Select the SalesGas Object, Comp Mole Frac Variable, and
i-Butane Variable Specific.
4. Click the OK button to accept the input and close the property view.
5. Follow steps 1 to 4 to import the mole fraction for n-C4 into cell B7.
• Position the cursor over cell B7.
• Right-click once, and select Import Variable.
• Select the SalesGas Object, Comp Mole Frac Variable,
• Click the OK button.
Entering Formulas
The next task is entering the formulas for calculating the component and total sales gas heating values.
1. Click in cell D3.
2. Type +b3*c3, then press ENTER.
This multiplies the Methane mole fraction by its Net Heating Value.
3. Enter the following formulas in cells D4 through D7.
4. The table should appear as shown in the figure below.
5. Click in cell C9, and type Sales Gas NHV. 6. Click in cell D9.
All formulas must be preceded by a “+”.
Cell Formula D4 +b4*c4 D5 +b5*c5 D6 +b6*c6 D7 +b7*c7 Figure 1.110
7. Enter +d3+d4+d5+d6+d7 in cell D9 to sum the individual heating values.
The result is the NHV of SalesGas in Btu/scf.
The current heating value of the sales gas is 1080 Btu/scf. Whenever flowsheet changes are made that result in the re- calculation of the stream SalesGas, the compositional changes will be automatically transferred to the
Spreadsheet, and the heating value updated accordingly. 8. Close the Heating Value property view.
Optional, you can add the value of Sales Gas NHV to the Databook by:
1. Click the Parameters tab of the Heating Value property view.
2. In the Exportable Cells table, enter a Variable Name for cell
D9 (for example NHV).
3. Open the Databook by pressing CTRL D.
4. On the Variables tab, insert the variable, selecting the
Heating Value operation as the Object and NHV as the
variable.
Installing an Adjust for Calculating
the LTS Temperature
Suppose the market price of your liquid product is currently unfavourable and you want to raise the LTS temperature to leave more of the heavier components in the gas phase. This will increase the sales gas heating value, resulting in a bonus from the transmission company. The sales gas must, however, still comply with the dew point specification.
An Adjust operation can be used to adjust the temperature of the LTS (ColdGas stream) until the sales gas dew point is within a few degrees of the pipeline specification. In effect, this
increases the gas heating value while still satisfying the dew point criteria.
Installing, Connecting, and Defining the
Adjust
1. Click the PFD icon to display the PFD and access the Object Palette by pressing F4.
2. Click the Adjust icon on the Object Palette.
3. Position the cursor on the PFD to the right of the SalesDP stream icon.
4. Click to drop the Adjust icon onto the PFD.
A new Adjust object appears with the default name ADJ-1. 5. Click the Attach Mode icon on the PFD toolbar to enter
Attach mode.
6. Position the cursor over the left end of the ADJ-1 icon. The connection point and pop-up Adjusted Object appears. 7. With the pop-up visible, left-click and drag toward the
ColdGas stream icon.
8. When the solid white box appears on the ColdGas stream, release the mouse button.
The Adjust operation performs automatic trial-and-error calculations until a target value is reached.
The Select Adjusted Variable property view appears.
At this point, HYSYS knows that the ColdGas should be adjusted in some way to meet the required target. An adjustable variable for the ColdGas must now be selected from the Select Adjusted Variable property view.
9. From the Variable list, select Temperature. 10. Click the OK button.
11. Position the cursor over the right corner of the ADJ-1 icon. The connection point and pop-up Target Object appears. 12. With the pop-up visible, left-click and drag toward the
SalesDP stream icon.
13. When the solid white box appears at the cursor tip, release the mouse button.
The Select Target Variable property view appears. 14. From the Variable list, select Temperature. 15. Click the OK button.
16. Click the Attach Mode icon to leave Attach mode. 17. Double-click the ADJ-1 icon to open its property view.
Figure 1.112
The connections made in the PFD have been transferred to the appropriate cells in the property view.
Adjusting the Target Variable
The next task is to provide a value for the target variable, in this case the dew point temperature. A 5°F safety margin will be used on the pipeline specification of 15°F, so the desired dew point is 10°F.
1. In the Connections page, enter 10°F in the Specified
Target Value field.
2. Click the Parameters tab.
3. In the Parameters page, enter 0.1°F in the Tolerance cell. 4. In the Step Size cell, enter 5°F.
No values will be entered in the Minimum and Maximum field, as these are optional parameters.
5. Click the Monitor tab.
This tab enables you to view the calculations. 6. Click the Start button.
The Adjust converges on the target value within the specified tolerance in five iterations. An LTS temperature (adjusted variable) of 4.4°F gives a sales gas dew point (target variable) of 10°F.
Figure 1.115
The Adjust has changed the LTS temperature from the original value of 0°F to 4.4°F. The new sales gas heating value can now be compared to the previous value to see the effect of this change.
7. Click the Close icon on the Adjust property view.
Results of the Study
1. Open the Workbook to access the calculated results for the entire flowsheet.
The Material Streams and Compositions tabs of the Workbook appear below.