EXAMPLES. UBAID UR REHMAN 2008-CHEM-19 ANAM ASIF 2008-CHEM-107 PRESENTED BY 2 CHEMICAL ENGINEERING DEPARTMENT, UET

EXAMPLES

ASPEN DYNAMICS

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C H E M I C A L E N G I N E E R I N G D E P A R T M E N T, U E T

UBAID UR REHMAN2008-CHEM-19

ANAM ASIF2008-CHEM-107

PRESENTED BY

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Introduction to Example

The Aspen Plus Simulation

Setting Up the Dynamic Simulation

Running the Batch Column Example

Initializing the Batch Column Example in Aspen Dynamics

PRESENTATION LAYOUT

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This is an example of a batch column simulation and illustrates these features of Aspen Dynamics:

• Use of scripts to automate initialization of an Aspen Dynamic flow sheet • Use of tasks to start up and operate the batch reactor

INTRODUCTION

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A mixture of methanol, ethanol and water is to be separated using a batch distillation column. The composition of the charge is 30% ethanol, 30% methanol and 40% water by weight.

The required product purity is 68% ethanol w/w.

STATEMENT

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• Aspen Plus has been used to set up the flow sheet for the batch column, which will be exported to Aspen Dynamics and initialized to be full of nitrogen at 20 C and 1 atmosphere

• The column has been modeled using a RadFrac block.

• Feed streams for the charge and nitrogen have been specified together with vapor and liquid distillate streams and a bottoms stream.

• The column has been specified with 10 stages, a partial vaporliquid condenser and a kettle reboiler.

THE ASPEN PLUS SIMULATION

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• The column dimensions have been specified on the RadFrac Dynamic form together with the sump and reflux drum size and geometry.

• The LMTD heat transfer option has been selected for the condenser and the cooling medium temperature specified as 200C

• The Constant temperature heat transfer option has been selected for the reboiler and the medium temperature has been specified as 120 C.

THE ASPEN PLUS SIMULATION

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USE OF SCRIPT To set up the dynamic simulation

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• A flowsheet level script called Setup and a RadFrac model script called Empty.

• The Flowsheet level script does the following: 1. Adds a reflux ratio controller 2. Sets the feed flow rates to zero 3. Calls the RadFrac Empty script to initialize the column to be full of nitrogen at 20 C and 1 atmosphere. 4. Performs an initialization run. 5. Saves a snapshot

SETTING UP THE DYNAMIC SIMULATION

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To run the BatchColumn example: 1. In Aspen Plus, open BatchColumn.bkp. If you installed Aspen Dynamics in the default location, BatchColumn.bkp is in:

C:\Program Files\AspenTech\Aspen Dynamics 12.1\Examples\BatchColumn.

2. Perform a run. 3. Export it as a flow-driven dynamic simulation file. 4. Exit Aspen Plus.

RUNNING THE BATCH COLUMN EXAMPLE

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1. In Aspen Dynamics, open BatchColumn.dynf 2. In the All Items pane of the Simulation Explorer, ensure Flow sheet is selected. In the Contents pane, double-click Add Script. 3. Enter a name for the script, for example, Setup.

INITIALIZING THE BATCH COLUMN EXAMPLE IN ASPEN

DYNAMICS

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4. In the text editor window, click the right mouse button and point to Insert, then click File. Insert BatchColumnScript.txt.5. Again click the right mouse button and click Invoke Script. Close the text editor window.

INITIALIZING THE BATCH COLUMN EXAMPLE IN ASPEN DYNAMICS

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6. Now create a task called BatchOperation. To do this: 7. In the Contents pane of the Simulation Explorer, double-click Add Task. Enter the name BatchOperation. 8. In the text editor window, select all of the existing text with the mouse (or use Ctrl-A). Click the right mouse button and point to Insert, then click File. Insert BatchOperationTask.txt. 9. Again click with the right mouse button and click Compile or press F8. Close the text editor window. 10. In the Contents pane of the Simulation Explorer, double-click the task to activate it. 11. Change the run mode to Dynamic and perform a dynamic run.

INITIALIZING THE BATCH COLUMN EXAMPLE IN ASPEN DYNAMICS

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USE 0F TASKTo start up and operate the batch

reactor

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The operating sequence defined by the tasks is: At time = 0.5 hours: 1. Ramp the mass flow rate of the Feed stream to 1000 kg/hr over 0.1 hours. 2. Wait until the cumulative mass flow of stream Feed is >= 1000 kg.

OPERATING SEQUENCE

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3. Step the mass flow rate of the Feed stream to 0 kg/hr. 4. Wait for 3 minutes.

OPERATING SEQUENCE

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5. Increase the flow of the Nitrogen feed stream to 0.1 kmol/hr. This is needed to maintain the pressure in the column.

OPERATING SEQUENCE

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6.Ramp the reboiler medium temperature to 80 C over 30 minutes. 7. Wait until the reflux drum level >= 0.3 m.

OPERATING SEQUENCE

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8. Start the reflux flow. 9. Wait for 3 minutes. 10. Start the product draw. 11. Ramp the reboiler medium temperature to 90 over 30 minutes. 12. Wait until the mass fraction of methanol in the distillate receiver reaches 0.68. 13. Pause the simulation.

OPERATING SEQUENCE

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14. Use plots and tables to view the results of the simulation during the dynamic run. 15. If you wish to repeat the simulation, rewind to saved snapshot Empty_Initial and then run again.

OPERATING SEQUENCE

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Documents

EXAMPLES. UBAID UR REHMAN 2008-CHEM-19 ANAM ASIF 2008-CHEM-107 PRESENTED BY 2 CHEMICAL ENGINEERING DEPARTMENT, UET