1.2.9 azeo distillation with ll extractor 3

Azeo Distillation with LL Extractor 1

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Azeo Distillation with LL Extractor

© 2000 AEA Technology plc - All Rights Reserved.Chem 9_3.pdf

2 Azeo Distillation with LL Extractor

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WorkshopAn azeotropic mixture of Benzene and Cyclo-Hexane is to be separated in a distillation column using Acetone as the entrainer. Nearly pure Benzene is produced from the bottom of the column, while a near azeotropic mixture of Acetone and Cyclo-Hexane is produced overhead. The overhead mixture will be separated in a Liquid-Liquid extractor using water as the solvent, with Cyclo-Hexane being recovered as the overhead product. The Acetone/Water mixture will then be separated in a vacuum tower with the Acetone and Water products being recycled through the flowsheet.

The process will be separated into four sections, the Azeotrope tower, the Liquid-Liquid extractor, the Solvent Recovery tower and finally the recycling system.

The problem could be solved with a single set of interaction parameters. However, the problem may be solved more accurately by using one set of binary coefficients which will predict the liquid phase splitting in the Extractor, and another set which will predict VLE behaviour in the Distillation Columns.

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

• Import Fluid Packages• Model Azeotropic Distillation Columns• Model Liquid-Liquid Extraction Columns

Process Overview


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Azeotropic Distillation Column

Solvent Recovery Tower


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Building the Simulation

Defining the Simulation BasisTwo Fluid Packages will be used in this example. Both Fluid Packages will use the UNIQUAC Activity Model, and contain the components Benzene, Cyclohexane, Acetone and H2O. The first Fluid Package (VLE-BASIS), will use the default library VLE binary interaction parameters and UNIFAC estimated parameters. The second Fluid Package (LLE-BASIS), will replace those interaction coefficients with UNIFAC LLE estimated binary coefficients and those regressed from HYSYS Conceptual Design Application.

1. Add the first Fluid Package in the usual manner and change the default name to VLE Basis.

2. On the Binary Coeffs tab, view the binary coefficients for the UNIQUAC activity model.

The binary coefficients for the Cyclohexane/Water pair are not available from the database, so it is necessary to obtain them by estimation or from another source.

In this example, the binary coefficients for the Cyclohexane/Water pair in the VLE Basis will be estimated by the UNIFAC VLE estimation method. Press the Unknowns Only button to estimate this pair.

The second Fluid Package (for the Liquid-Liquid Extractor) will be imported.

1. On the Fluid Pkgs tab of the Simulation Basis Manager, press the Import button and import the Fluid Package LLEBasis.fpk. This file should be located on the course disk supplied with this material.

2. Press the View button to see the new Fluid Package. Go to the Binary Coeffs tab to view the binary coefficients.

If you examine the LLE Coefficients for VLE Basis and LLE Basis you will see they are different, because they have been taken from different sources.

VLE Basis will be used for most of the simulation, while LLE Basis will be used as the Fluid Package for the Liquid-Liquid Extractor.

Enter the Simulation Environment.

Ensure that VLE Basis is the Default Fluid Package when you leave the Basis Environment.


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Adding the Feed Stream1. Enter the following stream Azeo Feed as follows:

2. Enter the stream Acetone as follows:

3. Enter a mass fraction of 1.0 for Acetone.

In this cell... Enter...

Conditions

Stream Name Azeo Feed

Temperature 77°C (170°F)

Pressure 101.3 kPa (14.7 psia)

Mass Flow 85 kg/h (190 lb/hr)

Composition - Mass Frac

Benzene 0.518

Cyclohexane 0.482

In This Cell... Enter...

Conditions

Stream Name Acetone





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Azeotrope TowerPublished documentation on this process indicates that the overhead composition from the Azeotrope Tower is a near azeotropic mixture of Acetone and Cyclohexane. Using less Acetone than is necessary to produce the azeotrope will prevent the original Benzene/Cyclohexane azeotrope from being separated.

The flow of Acetone required to separate this azeotrope and produce a mixture near azeotropic Cyclo-Hexane/Acetone, can be calculated from the azeotrope composition, (0.688 Acetone and 0.312 Cyclo-Hexane mass fractions). These values can be obtained through HYSYS Conceptual Design Application or the HYSYS Extension Binary Plots.

The T-x-y diagrams for the Benzene/Cyclo-hexane and Acetone/Cyclo-hexane binaries are shown here:

The Binary extension is available on our website. www.aeat.software.com


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Calculation for Required Acetone Flow

Then, for an initial mass flowrate of the Azeo Feed stream of 85 kg/h with the given composition, the amount of Acetone required will be 90.34 kg/h (85*0.482*0.688/0.312). A slightly greater flow will be used (95 kg/h {210 lb/hr}) to ensure separation of the Benzene/Cyclohexane azeotrope.


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Adding the Azeotropic Distillation Column1. Insert a Distillation Column with the following data:

2. On the Parameters tab, Solver page, check the Azeotropic box and supply a Fixed Damping Factor of 0.5.

3. Run the column.


Connections

Column Name T-100

No. of Stages 28

Condenser Energy Stream Q-Cond

Inlet Streams Azeo Feed, Stage 6

Acetone, Stage 21

Condenser Type Total

Overhead Liquid Azeo Liq

Bottoms Liquid Outlet Benzene

Reboiler Energy Stream Q Reb

Pressures

Delta P 0

Condenser 95 kPa (13.75 psia)

Reboiler 101.3 kPa (14.7 psia)

Temp. Estimates

Condenser 55°C (130°F)

Reboiler 80°C (175°F)

Specifications

Benzene Recovery in Reboiler 0.998

Acetone Recovery in Cond 0.998

Reflux Ratio (Estimate) 10.0

Azeo Liq Draw (Estimate) 130 kg/h (285 lb/hr)

Because we expect an azeotrope to be present in this column, we must check the Azeotropic box on the Solver page.


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The Liquid-Liquid Extractor

Liquid-liquid extraction is used as an alternative to distillation in situations where distillation is either ineffective or very difficult. These situations can be found in all process industries. The extraction of penicillin from fermentation broth and the extraction of aromatics from lube oil fractions are two industrial examples. Extraction based on chemical differences is sometimes preferable to distillation, which is separation based on relative volatilities. Some examples of situations when extraction is preferred are listed below:

• Excessive amounts of heat are required for distillation - relative volatility of the components is near one

• Separation via distillation is limited due to the formation of azeotropes

• The high temperatures of distillation cannot be withstood by the components, even under vacuum conditions

• There are only small amounts of solute in the feed solution• The components to be separated are extremely different in

nature

Extraction involves the separation of a solute from a feed solution by mixing in a solvent in which the solute is preferentially soluble. In addition, the solvent must be insoluble, or have a limited solubility in the feed solution. The extraction operation, on a stage by stage basis, can therefore be discussed in terms of two processes:

• The mixing of a feed solution, a solvent, and any external feeds• The separation of the two immiscible liquid phases which result

from the mixing

HYSYS models the liquid-liquid extraction process using counter-current flow in a column similar to the absorber template.


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Property Package

The Liquid-Liquid Extractor cannot be used with the following property packages:

• Wilson• Antoine• BraunK10• Esso Tabular• Steam• Amine• Chao-Seader• Grayson-Streed• Sour PR• Sour SRK

Activity Models are recommended for most applications.

Overhead Estimate

You will not be required to provide an estimate for the Overhead Product Flow. The Extractor will generate an estimate from a mole weighted TP-Flash of the combined tower feeds.

Column Sizing Utility

The column sizing utility in HYSYS is designed for columns with vapour and liquid traffic; therefore, it is not applicable to the Extractor unit operation.

Stage Efficiencies

The HYSYS Extraction algorithm models the Extractor as a staged tower, allowing you to specify either ideal stages or actual stages with efficiencies.

Side Draw

If you require a Side Draw on the Extractor, you can choose to draw either the Light or Heavy phase from a stage. HYSYS will perform a three phase flash on the entire contents of the stage to produce the conditions and composition of the specified draw.

Use only property packages that support 2 liquid phases.


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The purpose of the Liquid-Liquid Extractor is to determine the required solvent flow (in this case water) which will cause a mixture to phase split, forming two liquid phases. A rough estimation of the solvent flow can be obtained by using a Mixer, and then examining the phase separation while varying the solvent flow. However, because the extractor is divided into stages, the flow determined can only be used as an estimate. Use a flow of 200 kg/h (440 lb/hr) of Water.

1. Enter the following data for the stream Water:


Conditions

Stream Name Water




Mass Fraction H20 1.0


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2. Add the Liquid-Liquid Extractor with the following data:

3. On the Parameters tab, Profiles page, supply an estimate of 48 kg/h (105 lb/hr) for the overhead light liquid.

In this cell... Enter...

Connections

Column Name T-101

No. of Stages 20

Top Stage Inlet Water

Bottom Stage Inlet Azeo Liq

Ovhd Light Liquid CycloC6

Bottoms Heavy Liquid Rich Solv

Pressures

Top Stage 101.3 kPa (14.7 psia)

Bottom Stage 101.3 kPa (14.7 psia)

Temperature Estimates

Top Stage 25°C (77°F)

Stages 2-18 25°C (77°F)

Stage 19 28°C (82°F)

Stage 20 33°C (91°F)

The Temperature Estimates for Stages 2-19 can be supplied on the Parameters tab, Profiles page of the column property view.


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4. Go to the Basis Environment and select LLE Basis as the Fluid Package for the Liquid-Liquid Extractor. Return to the Simulation Environment.

5. Run the column.


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Adding the Solvent Recovery Tower

The Solvent Recovery tower, which separates the Acetone from the Water, presents a difficult separation at atmospheric pressure. To keep the number of stages reasonable, an overhead pressure of 53 kPa will be used. (Once again the data was obtained from HYSYS Conceptual Design Application).

1. Add the Solvent Recovery Tower as a Distillation Column with the following data:

2. Supply a Damping Factor of 0.8.

3. Run the column.


Connections

Column Name T-102

No. of Stages 20

Inlet Streams RichSolv, Stage 17

Condenser Type Total

Overhead Liq AcetRich

Bottoms Liquid Outlet H2O Rich

Condenser Energy Stream RecCond Q

Reboiler Energy Stream RecReb Q

Pressures

Condenser Pressure 53 kPa (7.75 psia)

Reboiler Pressure 56 kPa (8 psia)

Temperature Estimates

Condenser 35°C (95°F)

Reboiler 80°C (175°F)

Specifications

Reflux Ratio 7

Acetone Recovery (Cond) 0.9998


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Solvent Recycles

Finally, the two products from the Solvent Recovery tower have to be recycled to the previous two towers. Because of the temperature and pressure of the Solvent Recovery tower, each recycle stream will require a Pump and a Cooler/Heater operation to return the stream to the necessary tower conditions.

Add a Pump

Add a Pump to the stream H2O Rich with the following information:

The pressure of stream H2O Atm is 101.3 kPa (14.7 psia).


Connections

Name P-100

Inlet H2O Rich

Outlet H2O Atm

Energy Q 100

Parameters

Adiabatic Efficiency 75%


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Add a Cooler

Add a Cooler downstream of P-100 with the following information:

The temperature of stream H2O Cool is 25°C (77°F).


Connections

Name E-100

Inlet H2O Atm

Energy Q102

Outlet H2O Cool

Parameters

Delta P 0 kPa


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Add the Second Pump

Add another Pump from the T-102 product with the following information:

The pressure of Acet Atm is 101.3 kPa (14.7 psia).

Add a Heater

Add a Heater operation downstream of Acet Atm with the following information:

The temperature of Acet Warm is 55°C (130°F).


Connections

Name P-101

Inlet Acet Rich

Outlet Acet Atm

Energy Q 101

Parameters

Adiabatic Efficiency 75%


Connections

Name E-101

Inlet Acet Atm

Energy Q 103

Outlet Acet Warm

Parameters

Delta P 0 kPa


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Adding the Recycles

Make-up streams are necessary to compensate for the losses of Acetone and Water in the process product streams. To calculate the exact amount that is lost in the products, Balance operations are used. These are not real operations but only mathematical ways of obtaining the make-up values.

A Mole Balance operation will be used to create two streams (Rec Acet and Rec Water) with the same flowrates and compositions as the tower product streams Benzene and CycloC6, respectively.

These streams are then sent to a Component Splitter and split into two streams: one containing the product and the other containing traces of the lost solvent.

The streams containing the lost solvents are the make-up streams which will be mixed with the recycled streams from the solvent Recovery Tower.


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Add the Balance Operations

Add two Balance operations with the following data:

1. On the Parameters tab, specify the Balance Type as Mole.

2. Specify the Temperature and Pressure of Rec Acet to be 55°C (130°F) and 101.3 kPa (14.7 psia).

3. Add the second balance operation with the following information.

1. On the Parameters tab, specify the Balance Type as Mole.

2. Specify the Temperature and Pressure of Rec H2O to be 25°C (77°F)and 101.3 kPa (14.7 psia).


Connections

Name BAL-1

Inlet Streams Benzene

Outlet Streams Rec Acet


Connections

Name BAL-2

Inlet Streams CycloC6

Outlet Streams Rec H2O


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Add the Component Splitters

Add two Component Splitters with the following information:

Specify the temperature of one of the product streams to be 25°C (77°F). The temperature in the other stream will be calculated from the energy balance around the operation.


Connections

Name X-100

Inlets Rec H2O

Overhead Outlet H2O Make-up

Bottoms Outlet Frac CycloC6

Parameters

Overhead Pressure 101.3 kPa (14.7 psia)

Bottoms Pressure 101.3 kPa (14.7 psia)

Splits

Benzene 0

CycloC6 0

Acetone 1.0

H2O 1.0


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Specify the temperature of the product streams to be 55°C (130°F).


Connections

Name X-101

Inlets Rec Acet

Overhead Outlet Acet Make-up

Bottoms Outlet Frac Benzene

Parameters

Overhead Pressure 101.3 kPa (14.7 psia)

Bottoms Pressure 101.3 kPa (14.7 psia)

Splits

Benzene 0

CycloC6 0

Acetone 1.0

H2O 1.0


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Add the Mixer Operations

Add two Mixer operations with the following information:


Connections

Name MIX-100

Inlets Acet Warm

Acet Make-up

Outlet Acet to Rec

Connections

Name MIX-101

Inlets H2O Cool

H2O Make-up

Outlet H2O to Rec


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Add the Recycles

The input for the recycles is shown below. Note that because of the nature of the process, the Flow Tolerance is set to 1 and the Composition Tolerance is set to 1. The Recycles are installed as Simultaneous. Put the case in Hold mode before adding the recycles.


Connections

Name RCY-1

Inlet H2O to Rec

Outlet Water

Parameters

Vapour Fraction 10.0

Temperature 10.0

Pressure 10.0

Flow 1.0

Enthalpy 10.0

Composition 1.0

Connections

Name RCY-2

Inlet Acet to Rec

Outlet Acetone

Parameters

Vapour Fraction 10.0

Temperature 10.0

Pressure 10.0

Flow 1.0

Enthalpy 10.0

Composition 1.0


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Press the Go button to begin calculations.

Having completed the recycles and converged the whole flowsheet, operations can be opened again in order to be examined.

Save your case!


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1.2.9 azeo distillation with ll extractor 3

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