Chiller Plant - Part 1 PROBLEM Through guided practice, you will build a simulation of the process shown below. This is part of a chiller plant typical in natural gas processing. In subsequent parts of this example, you will add other sections of the plant to this simulation. Figure 1: Schematic of Chiller Plant Part 1 The process and equipment data are given in Table 3 and 4. Table 3: Feed Stream Data Component Mole % Component Mole % Nitrogen 1.0 i-Butane 1.25 Carbon dioxide 1.6 n-Butane 3.0 Methane 72.5 i-Pentane 0.55 Ethane 11.5 n-Pentane 1.10 Propane 6.75 C6PLUS (PETRO Component) 0.75 Total Flowrate 4 x 10 7 standard vap. ft 3 /day 1.0 x 10 6 normal vap. m 3 /day Temperature 120°F 50°C Pressure 205 psig 1520 kPa C6PLUS Properties NBP 210°F 99°C API Gravity 73 Specific Gravity 0.6919 PRO/II Getting Started Work Book
Transcript
Chiller Plant - Part 1
PROBLEM Through guided practice, you will build a simulation of the process shown below. This is part of a chiller plant typical in natural gas processing. In subsequent parts of this example, you will add other sections of the plant to this simulation.
Figure 1: Schematic of Chiller Plant
Part 1
The process and equipment data are given in Table 3 and 4.
Total Flowrate 4 x 107 standard vap. ft3/day 1.0 x 106 normal vap. m3/day
Temperature 120°F 50°C
Pressure 205 psig 1520 kPa
C6PLUS Properties NBP 210°F 99°C
API Gravity 73 Specific Gravity 0.6919
PRO/II Getting Started Work Book
Table 4: Equipment Data and Operating Conditions
Unit Description Data
D-1 Scrubber Temperature 85°F 203 psig
Pressure 30°C 1500 kPa
C-1 Compressor Outlet Pressure 600 psig 72%
Adiabatic Efficiency 4250 kPa 72%
HX-1 Cooler Hotside: Process Stream
Outlet Temperature 110°F 45°C
Pressure Drop 5 psi 35 psi
Coldside: Utility Air
Inlet Temperature 80°F 27°C
Outlet Temperature 100°F 38°C
D-2 Knockout drum Flash drum with no change of pressure and no duty
P-1 Pump Outlet Pressure 550 psig 3900 kPa
Efficiency 65% 65%
SOLUTIONStep 1 Create a New Simulation
Select New... from the File menu.
Note that several buttons on the toolbar, including the Run button have red borders. When you have satisfied PRO/II’s input requirements all red borders will disappear.
Step 2 Build the Process Flow Diagram
If the PFD palette is not already visible, click the PFD Palette button on the toolbar to bring it up. Click on the appropriate unit icons on the PFD palette to draw the PFD. To select and position a unit, just click on its icon.
A pointer with a box and flash drum attached appears. Move this to the main window and click again when the unit is in position.
In this manner, select and position the units as shown in the diagram using these PFD buttons:
Click on the red-bordered Streams on the PFD palette.
Note that the pointer now has an S attached to it. All available exit ports appear on PRO/II Getting Started Work Book
each unit once you select Streams. Required exit ports are red and optional exit ports are green.
Draw the streams on the flowsheet to connect the units.
After your first click, only the available feed ports are shown in red or green.
Note: Although not critical in this example, it is good practice to connect the FLASH DRUM hydrocarbon liquid product to the side port and to reserve the bottom port for a decanted water or second liquid product.
Double-click on each stream and unit and change its name to that shown on the diagram above. Do not change any other data in the dialog box.
Click OK to exit the dialog box. Note that spaces are not allowed in unit or stream names.
The completed PFD should now look like Figure 5 below.
Figure 3 : Chiller Plant PFDinPRO/ll
Step 3 After you finish building the flowsheet, the labels of all the internal streams are black and the available ports of all the units are green. At this point, all the unit labels have red borders and the border of the feed stream label is also red because you must still add data. Note that the border of Streams is black, indicating that you have entered all necessary data for this function. To exit the stream connection mode, right-click, or click on Streams so that it turns gray, indicating that the mode is no longer active.
Before continuing, save the simulation as CHILL1.PRZ
Modify the Input Units of Measure
Click on the green-bordered Units of Measure (UOM) button on the toolbar to verify the units of measure used in this simulation.
For this example you will use either modified SI Units or modified English units. Click Initialize from Library.... and select ENGLISH-SET1 or SI-SET1 from the drop-down list.
Check each item that it matches the input data given in the tables above.
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Make any necessary changes and click OK
Notice that the border of the UOM button is now blue indicating that you have modified the data.
Step 4 Define the Components
Click on the red-bordered Component Selection button on the tool bar.
Click Select from Lists....
Select the Hydrocarbon Lightends Component Family and select components from the list displayed. Select a single component or a group of components (using the shift or control keys) and then click Add Components to add them to the component list below.
Add the components in the order presented in Table 3. Figured 4: Component,
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S election
When Finished click OK to return to the Component Selection dia-log box,
Click Petroleum... to enter data for the petroleum component C6PLUS.
Enter its name, NBP and gravity data, and click OK Note that Petroleum... and List of Selected Components box now have blue borders.
Click OK to exit the dialog box.
Step 5 Select the Thermodynamic Method Click on the red-bordered Thermodynamic Data button on the tool-bar.
Select the Most Commonly Used Category, and then select Peng-Robinson as the Primary Method.
Double-click on Peng-Robinson, or click Add-> to add your method selection to the Defined Systems box.
To specify the transport property methods, click Modify... and then Transport Properties
Check the Compute Transport Properties box and select Petroleum Correlations from the Transport System drop-down list, as shown in Figure.
Figure 5: Transport Properties
Click OK in each of the three dialog boxes to save the entered data.
Step 6 Define the External Feed Stream Double-click on the feed stream INLET_GAS. Make sure that the
stream type is Composition Defined.
Enter the stream's thermal condition:
• Select Temperature as the first specification and enter value.
• Select Pressure as the second specification and enter value.
Click Flowrate and Composition...
Select Total Fluid Flowrate and enter value.
You will need to locally override the flowrate dimensional units. To do so, with the cursor in the fluid flowrate field, click UOM at the top of the dialog box
PRO/II Getting Started Work Book
and change the basis to vapor volume and the units to ft3 or m3 and day. Click Change Units to return to the dialog box.
Enter the individual component mole percentages into the component grid. You can move down the list using the <Tab> key. After entering the composition data, check that the total equals 100.
Click OK to exit each dialog box and return to the PFD. You do not need to enter data for any streams other than the INLET_GAS (the external feed stream to the process) because PRO/II calculates the others for you, based on your process conditions.
Step 7 Enter Operating Conditions for Each Unit Operation
Double-click on each unit in turn and enter the required data including the unit identifier.
Enter data for flash drum D-l. The First Specification is Pressure and the second Specification is Temperature.
Enter data for flash drum D-2. The First Specification is Pressure Drop and the Second Specification is Duty. The duty of an adiabatic flash is zero.
Note: As you return to the PFD after each unit operation, its unit identifier has changed from red (data missing) to black (data satisfied).
Enter data for heat exchanger HX-1.
Note: By default, the horizontal stream is the hot side and the vertical stream is the cold side. Here this means that the utility stream is the cold side. You could use this dialog box to change the stream allocations if the reverse were true.
Click Specification... to set the heat exchanger specification.
Select Hot Product Temperature from the list and enter value.
PRO/II Getting Started Work Book
PRO/II Getting Started Work Book
PRO/II Getting Started Work Book
Plant - Part 2 Chiller
PROBLEM Continue to build the chiller plant. Since you already entered the units of measure, components, and feed stream data in Part 1 you won't need to add these data again. Figure 11 shows the process schematic for this part. The portion of the flowsheet that you entered in Part i is gray, and the new units and streams you will now add are black.
PRO/II Getting Started Work Book
Figure 6: Schematic of Chiller Plant - Part 2
The new equipment data and operating conditions are provided below. Table 5:
Equipment Data
Unit Description Data HX-2 Gas to Gas a Hotside ∆P 5 psi 35 kP
Exchanger Coldside ∆Pi 5 psi 35 kPa Approach Te 10°F 5°C mp (Hot In - Cold Out)
SOLUTION Use the previous example, CHILLI.PRZ as the basis for this example.
Select File/Save As... from the menu bar and save the example as CHILL2.PRZ.
Step 1 Add to the Process Flow Diagram Using Figure 11 as a guide, add units HX-2, HX-3, D-3, and V-1 to the flowsheet.
Connect the vapor product stream from D-2 to HX-2.
Add the remaining streams to the flowsheet. Enter the unit and stream names. The PFD now looks like Figure 7.
Figure 7: ChillerPlant in PRO/II
PRO/II Getting Started Work Book
Step 2 Enter Operating Conditions for Each New Unit Operation
Enter data for the new units.
In the Heat Exchanger dialog box for HEAT EXCHANGER HX-3 (Chiller), click Utility Stream... and choose Refrigerant as the Utility Type. Select Propane from the Component list and enter the saturation temperature.
Note: PRO/H's refrigerant utility, used in unit HX-3, considers only latent heat effects, so the refrigerant inlet and outlet conditions are a saturated liquid and a saturated vapor, respectively.
At this point there should not be any red borders on the flowsheet. All stream and unit labels should have black borders. If any of the unit or stream labels has a red border, dou . ble-click on it and check the data
Step the Simulation and View the Results 3 Run Run the simulation.
Highlight the cold separator overhead stream 10, click the View Results button and look at the thermal recycle rate.
As you can see, the stream is all vapor.
Generate an output report by clicking the Generate Report button or by choosing Generate Report from the Output menu.
Look at the HEAT EXCHANGER summary for HX-3. Find the flowrate of the refrigerant. You will use this rate as an initial estimate in the Part 3 of this exercise.
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PRO/II
Getting Started Work Book
Chiller Plant-Part 3 PROBLEM Continue to build the chiller plant. Suppose that the refrigerant for the chiller HX-3
consists of a mixture rather than pure propane. You want to determine the flowrate of that mixture required to maintain a process stream (hotside) outlet temperature of -15°F (-26°C). Instead of using the HEAT EXCHANGER refrigerant utility in PRO/II, which is designed for use with single components, you now must introduce a refrigerant stream, with the correct composition, and use a CONTROLLER to determine the refrigerant flowrate.
The diagram shows part of the process schematic. The portion of the flowsheet that you entered previously is gray, and the new units and streams you will now add are black.
Figure 8: Schematic of
PRO/II Getting Started Work Book
Chiller Plant-Part 3
The equipment and refrigerant stream data are shown in Table 6.
Table 6: Refrigerant Stream Data
Component Mole%
Ethane 2.5
Propane 97
i .5 -Butane 0
Pressure 11.5 psig 180 kPa
Condition Bubble Point
SOLUTION sis for this example and save the Use the previous example, CHILL2.PRZ, as the baexample as CHILL3.PRZ.
Step 1 Change the Flowsheet Configuration Add a controller unit to the flowsheet.
Remove the utility stream on HEAT EXCHANGER HX-3 by double-clicking on the unit and deactivating the check box for the utility stream.
Add inlet and outlet streams to the cold side of HX-3. Name the inlet stream 50 and the outlet stream 51.
Figure 9: Chiller Plant PFD in PRO/II
Step 2 Enter Stream Data
Enter the composition data and define the thermal conditions for stream 50.
Even though the flowrate of this stream is going to be calculated by the controller, you must enter a flowrate here. This not only satisfies the data requirements of the dialog box but also serves as an initial estimate.
Use the propane refrigerant rate from the previous example as the initial flow ate rfor this stream.
Step 3 Enter Unit Data
Change the specification for HEAT EXCHANGER HX-3 so that the new refrigerant stream exits at its dew point. Select the Cold Product Liquid Fraction specification and set the value to 0.00.
Double-click on the CONTROLLER. The Feedback Controller dialog box appears.
You want to vary stream 50 flowrate so that the temperature of stream 9 is-15°F (-26°C).
In the Specification group:
Click on Parameter.
Choose the hotside outlet stream for HEAT EXCHANGER HX-3 (stream 9) as the stream to specify.
Click on Parameter in the Parameter dialog box.
Select Temperature and return to the Feedback Controller dialog box.
Enter-15°F(-26°C) as the islue of the hotside outlet temperature.
In the Variable group box:
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Click on Parameter.
Choose stream 50 as the stream to vary. Click on Parameter and choose Flowrate as the variable.
When complete, the Feedback Controller dialog box looks like Figure 16.
Click OK to save the entries and return to the flowsheet.
Save the simulation before continuing.
Step 4 Run the Simulation and View the Results
Run the simulation.
Create a STREAM PROPERTY TABLE for stream 50 with the Stream Summary list selected.
A portion of this table is shown below. Compare the quantity of refrigerant required to that obtained in the previous example. Why are the results different?
PRO/II Getting Started Work Book
PRO/II Getting Started Work Book
Chiller Plant - Part 4
P ntinue to build the chiller plant. Add a COLUMN and a COMPRESSOR. Use MIXER ROBLEM Counits to combine the plant liquid streams into one product and the plant vapor streams into another product.
PRO/II Getting Started Work Book
Figure 11: Schematic of Chiller Plant Part 4
SOLUTION Use the previous example, CHILL3.PRZ, as the basis for this example and save the example as CHILL4.PRZ.
Step 1 Add to the Process Flow Diagram
Place a COMPRESSOR, two MIXERs and a COLUMN on the PFD. Connect the streams as shown in Figure 11. Name the units and stream.
When you place the column, you will be asked to give the number of theoretical trays and to state whether the column has a condenser and a reboiler. Note that the Table 7 gives actual trays and tray efficiency. From this you must calculate the number of theoretical trays in the body of the column (22*55% =12 stages). The kettle reboiler is simulated as a theoretical stage and thus is stage 13. This column has no condenser.
When complete, the PFD should look similar to Figure 19.
Figure 12: Complete Chiller Plant in PRO/II
Step 2 Enter the Unit Data
The mixers require no data. Enter the COMPRESSOR data from the table.
Double-click on the COLUMN. Check that the Number of Trays is correct and that the default selections for Algorithm and Calculated Phases are appropriate to your simulation.
Click Pressure Profile... and enter the Top Tray Pressure and the Pressure Drop for the entire Column.
Click Feeds and Products.... to set the feed tray number. Check that the default entry for the Phase of each Product is correct.
Estimate
PRO/II Getting Started Work Book
t
he rate of the overhead product. You can make a good guess from the results of the previous run. You could also use t Define procedhe ure, assuming that the overhead stream gh Methane from the column feed (Figure 13). consists of all the Nitrogen throu
Figure 13: Overhead Flowrate Definition
Click Reboiler... to check that Kettle (Conventional) has been selected.
Click Initial Estimates... to select the Conventional initial estimate method.
Click Performance Specifications... to enter the true vapor pressure specification. Check the Add Specifications and Variables box. In the Specifications grid, click on Parameter; choose the bottoms stream, 15, and select Vapor Pressure and True from the lists. Return to the Specifications and Variables dialog box and enter a value of 235 psig (1720 kPa).
In the Variables grid, click on Parameter, choose Column and select Heat Duty of the Reboiler from the lists. The completed dialog box is shown in Figure 14.
