UDS-110-Depentaniser-debutanizer.pdf

De-Pentanizer & De-Butanizer 1

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De-Pentanizer & De-Butanizer

© 2005 Honeywell - All Rights ReservedUDS-110.03.R350.01

2 De-Pentanizer & De-Butanizer

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WorkshopSeparation of light products is typical of Refinery operations. In this module, two columns will be modeled to separate pentanes and butanes.

Because the Condenser temperature in the De-butanizer is below zero, the process stream will need to be cooled. The Propane Refrigeration Loop from the previous module will be used to cool the process stream, showing how templates can be linked into UniSim Design cases.

Learning ObjectivesOnce you have completed this section, you will be able to:

• Build columns using the Input Experts• Use the Spreadsheet• Link Templates

PrerequisitesBefore beginning this module you need to have completed the Getting Started and the Propane Refrigeration Loop modules.

Pro

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Column Overview

De-pentanizer

De-butanizer


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Building the SimulationFor this module you will continue building on the case you worked on in Module 1 by adding two distillation columns.

1. Open the case you saved at the end of module 1.

Make sure the temperature, pressure and flowrate for Feed stream are the following:

Adding the First Column: De-PentanizerThe De-pentanizer will be modelled with a Distillation column. The Column is a special type of Sub-Flowsheet, which contains equipment and streams, and exchanges information with the parent Flowsheet through the connected streams.

UniSim Design has several basic Column templates depending on the type of equipment your Column requires:

There are 12 ideal stages in the De-pentanizer, 10 in the tray section plus the Reboiler and Condenser.

1. Double-click on the Distillation Column icon in the Object Palette. The first Input Expert view appears.

In this cell... Enter...

Temperature 30°C (86°F)

Pressure 700 kPa (100 psia)

Molar Flow 100 kgmole/h (220 lbmole/h)

Basic Column Types Description

Absorber Tray Section Only

Liquid-Liquid Extractor Tray Section Only

Reboiled Absorber Tray Section and a bottom stage reboiler

Refluxed Absorber Tray Section and an overhead condenser

Distillation Tray Section with both reboiler and condenser

Distillation Column icon


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2. Input the following information into the first input expert page.

3. Click the Next button to proceed to the next page.

The Next button is only available when all of the necessary information has been supplied.

4. Supply the following information to the Pressure Estimates page.

In this field... Enter...

Column Name De-Pentanizer

Inlet Stream Feed

Inlet Stage 5_Main TS

Condenser Energy Stream Cond1 Q

Condenser Type Full Reflux

Overhead Vapour Outlet Ovhd Vap Prod

Reboiler Energy Stream Reb1 Q

Bottoms Liquid Outlet Pentanes+

Figure 1


Condenser Pressure 650 kPa (94 psia)

Reboiler Pressure 700 kPa (101 psia)

Input Expert is a tool that help to ensure all required information is entered. Once you are familiar with the column view, they can be turned off in your preference file.


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5. Click the Next button to proceed to the next page.

6. On this page, enter the temperature estimates. The Condenser temperature estimate will be 10°C (50°F), and the reboiler temperature estimate will be 120°C (248°F).

Temperature estimates are not required for the column to solve but they will aid in convergence.

7. Click the Next button to continue.

Figure 2

Figure 3


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8. On the last page supply a value of 2 for the Reflux Ratio.

9. Click the Done button. UniSim Design will open the Column Property View window. Access the Monitor page on the Design tab.

Two specifications must be filled so that the Degrees of Freedom are 0. You already have specified the Reflux Ratio. In this case you will use the i-C5 purity instead of the Ovhd Vap Rate.

Figure 4

Figure 5


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10. You need to deactivate the Ovhd Vap Rate by clicking on the Active check box. Now only the Reflux Ratio checkbox is checked and the Degrees of Freedom is 1.

11. To add a specification, click the Add Spec… button.

12.Select Column Component Fraction and click the Add Spec(s)… button.

13. Provide the following information.

Figure 6


Name iC5 Comp Fraction

Target Type Stream

Draw Pentanes+ @Col1

Basis Mole Fraction

Spec Value 0.27

Components i-Pentane

Figure 7


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14.When you are done, close the window to go back to the Monitor page of the Design tab. Check the Active ratio button for the Comp Fraction iC5 specification.

15.Click the Run button to begin calculations.

Once the column has converged, you can view the results on the Performance tab.

Adding the Second Column: De-ButanizerThe De-butanizer column is also modelled as a distillation column, with 17 stages, 15 trays in the column, plus the reboiler and condenser. The objective of this column is to produce a bottom product that has a molar fraction of butanes (both i-C4 and n-C4) of 0.97.

1. Double click on the Distillation Column button on the Object

Figure 8

What is the flowrate of the Pentanes+ Stream? ___________________________


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Palette and enter the following information:

Save your case as Crude3.usc.


Connections

Name De-butanizer

No. of Stage 15

Feed Stream/Stage Ovhd Vap Prod / 9

Condenser Type Full Reflux

Overhead Vapour Product Light Products

Bottom Product Butanes

Condenser Duty Cond2 Q

Reboiler Duty Reb2 Q

Pressure

Condenser 550 kPa (80 psia)

Reboiler 600 kPa (87 psia)

Temperature Estimates

Condenser -20°C (-4°F)

Reboiler 50°C (122°F)

Specification

Reflux Ratio 2

Component Recovery (i-butane) 0.97

What is the Molar Flow of Light Products streams? _________________________

And the flowrate of i-C4 and n-C4 in Light Products?

i-C4_________, n-C4__________

What is the molar fraction of butanes in Light Products? _________________________

What is the recovery of butanes?

_________________________

Save your case!


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Using the SpreadsheetTo answer the previous questions you had to add the fraction of i-C4 and n-C4 somewhere outside the simulation. UniSim Design has a Spreadsheet operation, which allows you to import stream or operation variables, perform calculations, and export calculated results.

You are going to create a spreadsheet to calculate the molar fraction both of pentanes and butanes in their respectively streams and their recoveries.

1. To install a Spreadsheet and display its property view, double-click on the Spreadsheet icon in the Object Palette.

2. Click the Add Import button, and the Select Import view will appear.

3. Choose the Object, Variable, and Variable Specific as shown:

Notice that UniSim Design assigned the imported variable to Spreadsheet cell A1, by default. Change this cell location to B1. The reason for doing so will become apparent on the Spreadsheet tab.

4. Before continuing you need to add more rows to the spreadsheet. Do this by clicking in the Parameters tab and entering 16 in the Number of Rows field.

In this field... Select...

Object Feed

Variable Comp Molar Flow

Variable Specifics i-Pentane

Figure 9

Spreadsheet icon


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5. In many ways, the UniSim Design Spreadsheet behaves similarly to commercial spreadsheets packages; you enter data in the cells, and calculated results are returned. You can introduce the variables directly in the spreadsheet. Change to the Spreadsheet tab.

6. Right-click in the cell where you want to import the variable. Do this in cell D1. The following view will appear:

7. Select Import Variable.

8. Select the Object, Variable, and Variable Specific as shown:

9. Enter the following names in the spreadsheet:

Figure 10

In this field... Select...

Object Feed

Variable Comp Molar Flow

Variable Specifics n-Pentane


A3 PENTANES+

A4 iC5 Frac

A5 nC5 Frac

A6 iC5 Flow

A7 nC5 Flow

A10 iC4 Ovhd Vap Flow

A12 BUTANES

A13 iC4 Frac

A14 nC4 Frac

A15 iC4 Flow

A16 nC4 Flow

C5 Pentane Frac

C7 Pentane Recovery

C14 Butane Frac

C16 Butane Recovery


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10.Complete the rest of the spreadsheet by importing the following values into the specified cell.

You can move to a cell by clicking it, or by clicking the arrow keys.

The values are those corresponding the variable named to the left. Import them. Fractions and Flows are in molar basis

11. To enter the formulas place the cursor on the cell and write it. Remember to use a "=" symbol before mathematical operations. Enter the following formulas

Cell Object Variable Variable Specifics

B4 Pentanes+ Comp Mole Frac i-Pentane

B5 Pentanes+ Comp Mole Frac n-Pentane

B6 Pentanes+ Comp Molar Flow i-Pentane

B7 Pentanes+ Comp Molar Flow n-Pentane

B10 Ovhd Vap Prod Comp Molar Flow i-Butane

B13 Butanes Comp Mole Frac i-Butane

B14 Butanes Comp Mole Frac n-Butane

B15 Butanes Comp Molar Flow i-Butane

B16 Butanes Comp Molar Flow n-Butane

D10 Ovhd Vap Prod Comp Molar Flow n-Butane

Figure 11

Cell Formula

D5 =b4+b5

D7 =(b6+b7)/(b1+d1)*100

D14 =b13+b14

D16 =(b15+b16)/(b10+d10)*100


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Clicking in the Function Help button you can see all the operations that are available in UniSim Design.

Once the cell is completed, you can export the variable to the simulation. This is done by clicking with the right button in the cell. The spreadsheet allows you to use your own correlations, for example, for pressures drop, etc.

Save your case as Crude3_Recovery.usc

Figure 12

What is the pentanes recovery? _____________________________________________

And that of butanes? _____________________________

Save your case!


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Another easy way to view the component recovery is to go to the Performance-Summary view of the column properties, and then select the Recovery radio button. From this view, the users can find the component recovery for each individual component.

Figure 13


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Linking TemplatesOnce you have completed the recovery fractionation train you can link it to the Propane Loop Template, and use the Propane Loop to refrigerate the De-butanizer.

The duty of the Condenser, Cond2 Q, in this module, will be linked to the duty of the Chiller, Chill-Q in the Propane Refrigeration Loop template.

1. Double-click on the Sub-Flowsheet icon on the Object Palette.2. Select the Read an Existing Template button.

3. Open the template file saved in the Propane Refrigeration Loop module, C3loop.tpl.

4. The Sub-Flowsheet Operation view appears. Click the Sub-Flowsheet Environment button at the bottom of the view.

5. The PFD of the Propane Refrigeration Loop appears. Double-click on the energy stream of the Chiller, Chill-Q.

6. Delete the Heat Flow value of the stream by pressing the DELETE key on the keyboard.

7. Close the Energy stream view. Click the Enter Parent Simulation Environment icon on the toolbar to return to the Sub-Flowsheet Operation view.

Figure 14

Sub-Flowsheet icon

To connect the template without conflicts, the heat flow value of Chiller-Q is deleted in the template prior to connecting the internal and external energy stream.

This is to prevent over specifying the flowsheet; if the heat flow value of Chiller-Q is not deleted, a consistent error will occur as there are two different heat flow values for the same energy stream.

Enter Parent Simulation


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8. In the Feed Connections to Sub-Flowsheet group, connect the External Stream, Cond2 Q, to the Internal Stream Chill Q.

Once the connection is complete, both streams, (Internal and External) will have the same name and heat flow value, that of the External stream.

Figure 15

What is the flowrate of propane in the Refrigeration Loop? _________________________________________

What is the compressor duty? _________________________________________

Advanced Modelling 19

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Advanced ModellingThe Column is a special type of SubFlowsheet in UniSim Design. SubFlowsheets contain equipment and streams, and exchange information with the Parent Flowsheet through the connected streams. From the Main Environment, the Column appears as a single, multi-feed multi-product operation. In many cases, you can treat the Column in exactly that manner.

The Column SubFlowsheet provides a number of advantages:

• Isolation of the Column Solver. The Column Build Environment allows you to make changes and focus on the Column without the re-calculation of the entire Flowsheet.

• Optional use of different Fluid Packages. UniSim Design allows you to specify a unique (different from the Main Environment) fluid package for the Column SubFlowsheet. This may be useful in instances when a different fluid package is better suited to the Column (Gas Plant using PR may contain an Amine Contactor that needs to use the Amines Property Package), or the Column does not use all of the components used in the Main Flowsheet and so by decreasing the number of components in the column you may speed up column convergence.

• Construction of custom templates. In addition to the default column configurations which are available as templates, you may define column setups with varying degrees of complexity. Complex custom columns and multiple columns may be simulated within a single SubFlowsheet using various combinations of SubFlowsheet equipment. Custom column examples include replacement of the standard Condenser with a Heat Exchanger, or the standard kettle reboiler with a thermosyphon reboiler.

• Ability to solve multiple towers simultaneously. The Column SubFlowsheet uses a simultaneous solver whereby all operations within the SubFlowsheet are solved simultaneously. The simultaneous solver permits the user to install multiple interconnected columns within the SubFlowsheet without the need for Recycle blocks.

The presence of the green "Up Arrow" button in the Button Bar and the Environment: Name (COL1) indicates that you are in the Column SubFlowsheet.

It is also written at the right in the Icons bar.

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You can enter the Column SubFlowsheet by clicking the Column Environment button on the Column Property View. Once inside the Column Environment you can return to the Parent Environment by clicking either the Parent Environment button on the Column Runner view or the Enter Parent Simulation Environment icon in the toolbar.

Exploring with the Simulation

Exercise 1Study the influence of the number of stages on the propane fraction in bottoms. Increase the number of stages until the propane recovery in the tower overhead is higher than 0.998.

Exercise 2

What is the Molar Enthalpy for streams Reflux and Boilup?

Reflux___________,Boilup__________________

Enter Parent Simulation Environment icon

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UDS-110-Depentaniser-debutanizer.pdf