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Calculation of Gasoline Additives with Aspen Plus® V8.0 1. Lesson Objectives
Learn Learn how to specify a mixer
Learn how to use the Calculator block in Aspen Pl us to perform customized customized calculations for setting targets and for getting results
2. Prerequisites
Aspen Plus V8.0
3. Background Ethyl tert-butyl ether ethe r (ETBE) (ETBE) is an ox ygenate that is added to gasoli gasoline ne to improve Re search Octane Octane Number (RON) and to increase increase oxygen content. The goal goal is to have 2.7% 2.7% oxygen by weight in the final product. product. The legal limit li mit is that ETBE ETBE cannot ex ceed more than 17% 17% by volume . For simplicity, simplici ty, we use 2,2,4-trimethylpe 2,2,4-trimethylpentan ntane e to represent gasoline. gasoli ne. Since ETBE's ETBE's molecular weight wei ght is 102.18 102.18 g/mol, the ETBE in the product stream stream can be calculated as foll owing:
This yiel ds 17.2 17.243 43% % of ETBE by weight in the product stream. Given this, the Calculator block can can be utilized utilize d to target the ETBE feed f eed to achieve the desi red oxygen content. In this tutorial tutorial we will calculate calculate::
For a certain flow fl ow rate of gasoline (e.g ( e.g., ., 100 100 kg/hr), how much ETBE should be added to achieve the oxygen content of 2.7 2.7% % by weight in the blended gasoline. gasoline.
Check whether or not not the legal l imit of ETBE ETBE content is satisfied.
Two separate Calculator blocks are used to perform calculations on each criterion. Both targets targets should be met in the simulation. simulation. The examples example s presented are are solely intended to illustrat ill ustrate e specific concepts and principles. They may may not reflect refle ct an industrial application application or real si tuation.
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4. Aspen Plus Solution If you are unfamiliar with how to start Aspen Pl us, select components, define methods, or construct a fl owsheet, consult Get Started Guide for New Users of Aspe n Plus.pdf for instructions. 4.01.
Start a new simulation using the Blank Simulation template in Aspen Plus.
4.02.
The Components | Specifications | Selection sheet is displayed. In the Component ID column, enter GASOLINE and ETBE. In the Alias column, enter C8H18-13 for component GASOLINE. This sheet should look like the screenshot below.
4.03.
Define methods. Go to the Methods | Specifications | Global sheet. Select PENG-ROB for Base method.
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4.04.
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Move to the simulation environment by clicking the Simulation bar in the navigation pane. Add a Mixer from the Mixers/Splitters tab on the Model Palette to the flowsheet and add two material inlet stream and one material outle t stream. Rename the block and three streams so that your flowsheet looks like the one below.
4.05.
Navigate to the Streams | ETBE | Input | Mixe d sheet. Enter 25 for Temperature and 1 for Pressure. Select Mass for Total flow basis. Enter 17.243 for Total flow rate. Actually, you can enter a different value here because it wil l be overridden by results from a Calculator block defined later. Select MassFrac i n the Composition frame and enter 1 for ETBE value field.
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4.06.
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Go to the Streams | FEED | Input | Mixed sheet. Enter 25 for Temperature and 1 for Pressure. Select Mass for Total flow basis. Enter 82.757 for Total flow rate. Select Mass-Frac in the Composition frame and enter 1 for GASOLINE.
4.07.
Go to the Blocks | BLENDER | Input | Flash Options sheet. Confirm that Pressure has a value of 0 (interpreted by Aspen Plus as no pressure drop).
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4.08.
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In the navigation pane, select the Flowsheeting Options | Calculator node. The object manager for Calculator is displayed. Click the New… button to create a new calculator called ‘TARGET’. This calculator block will set the target for the ETBE flowrate. Go to the Flowsheeting Options | Calculator | TARGET | Input | Define sheet. New variables can be defi ned by clicking the New… button. Here, we defi ne three new variables: MSETBE, MSGASOLI, and MWETBE.
4.09.
For MSTEBE, select the Streams radio button in Category frame. Select Mass-Flow for Type, ETBE for Streams, MIXED for Substream, and ETBE for Component. Select Export variable in Information flow frame. This variable should update component ETBE’s mass flow rate for in stream ETBE.
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4.10.
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We defi ne variable MSGASOLI as foll ows. SelectStreams radio button in the Category frame. Select Mass-Flow for Type, FEED for Stream, MIXED for Substream, and GASOLINE for Component. In Information flow frame, select Import Variable radio button. This variable receives the value of the mass fl ow rate for component GASOLINE in stream FEED.
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4.11.
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For variable MWETBE, select Physical Property Parameter in the Category frame. Select Unary-Param for Type, MW for Variable, ETBE for ID1 and 1 for ID2. In the Information flow frame, select Import variable. This variable stores the value of ETBE’s molecular weight .
4.12.
Now, all three variables are displayed on the Flowsheeting Options | Calculator | TARGET | Input | Define sheet.
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4.13.
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Navigate to the Flowsheeting Options | Calculator | TARGET | Input | Calculate sheet. Select Excel in the Calculation method frame. Click the Open Excel Spreadsheet button.
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4.14.
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An Excel spreadsheet opens in a new window. The user can import or export variables by selecting a variable in the drop-down list under the Add-Ins tab, as shown in screenshot below. Import both MSGASOLI and MWETBE to the Excel spreadsheet to cell C3 and cell C6 respectively . Enter the label and value for Target oxygen content (weight) in cell s B1 and C1. Enter the label and value for ETBE content limit in cells B2 and C2. The label for Target ETBE content (weight) is entered in cell B7. The formula for calculating its value is “ =MWETBE/C5*2*C1” and is entered in cell C7. Fill i n the remaining
text so your spreadsheet looks like the one below. See the next step for defining cell C8.
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4.15.
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The formula for Target mass flow rate of ETBE is “=C7*C3/(1-C7)” and is entered in cell C8. Also, C8 is linked to variable MSETBE. Thus, the value from C8 is sent to MSETBE. When finished filling out the spreadsheet, close the spreadsheet and return to the Aspe n Plus user interface.
4.16.
Navigate to the Flowsheeting Options | Calculator | TARGET | Input | Sequence sheet. SelectBefore for Execute, Unit operation for Block type, and BLENDER for Block name.
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4.17.
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In the navigation pane, select Flowsheeting Options | Calculator. The object manager for Calculator is displayed. Click the New… button to create another Calculator block named CHECK. We will create two variables: VETBE and VGASOLI. This calculator block will be used to check the results.
4.18.
In the Flowsheeting Options | Calculator | CHECK | Input | Define sheet, click the New … button to create a new variable called VETBE. For VETBE, select Streams for Category. Select StdVol-Flow for Type, ETBE for Stream, MIXED for Substream, and ETBE for Component. Select the Import variable radio button in Information flow frame. This variable will provide the volumetric flow rate of component ETBE in stream ETBE.
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4.19.
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Click the New … button on the Flowsheeting Options | Calculator | CHECK | Input | Define sheet again to create another variable called VGASOLI. For VGASOLI, select Streams for Category. Select StdVolFlow for Type, FEED for Stream, MIXED for Substream, and GASOLINE for Component. Also select Import variable for Information flow. This variable will provi de the volumetric flow rate of component GASOLINE in stream FEED.
4.20.
At this point, these two variables are displayed on the Flowsheeting Options | Calculator | CHECK | Input | Define sheet.
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4.21.
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Navigate to the Flowsheeting Options | Calculator | CHECK | Input | Calculate sheet. Select Excel for Calculation method. Click the Open Excel Spreadsheet button to open Excel spreadsheet in a new Excel window. Link variable VETBE to cell C2 and VGASOLI to cell C3. The formula for calculating ETBE content in PRODUCT stream (vol %) is “=VETBE/(VGASOLI+VETBE)*100” and is entered in cell C5. Enter text so your flowsheet looks like the following.
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4.22.
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Close the Excel spreadsheet window. Navigate to the Flowsheeting Options | Calculator | TARGET | Input | Sequence sheet. Select Last for Execute.
4.23.
Press F5 to run the simulation. After the simulation is complete, check the results from both calculators to confirm that both targets have been met.
4.24.
The legal limit of ETBE content of 17% by vol ume is met according to the calculator block CHECK.
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4.25.
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For a gasoli ne mass flow rate of 82.757 kg/hr, the target mass flow rate of ETBE i s calculated to be 17.24293 kg/hr according to calculator block TARGET.
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5. Conclusions For a spe cified gasoline mass flow rate of 82.757 kg/hr, 17.24293 kg/hr of ETBE is needed to achieve 2.7% oxygen content by weight in the final product. Furthermore, after blending, the product does not exceed the legal limit for ETBE of 17% by volume. If gasoline contains a single component, manual calculation should be easy without a simulator. However, real gasoline contains many unknown components and gasoline’s contents
vary as feedstock or plant operation conditions change. Therefore, manual calculation becomes very difficult and the use of a simulator such as Aspen Plus can be helpful to carry out the calculation.
6. Copyright Copyright © 2012 by Aspen Technology, Inc. (“AspenTech”). All rights res erved. This work may not be
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