using aspen hysys dynamics with columns

2013 Aspen Technology, Inc. AspenTech, aspenONE, the Aspen leaf logo, the aspenONE logo, and OPTIMIZE are trademarks of Aspen Technology, Inc. All rights reserved. 11-4407-1013

Jump Start: Using Aspen HYSYS Dynamics withColumns

A Brief Tutorial (and supplement to training and online documentation)

Nicholas Brownrigg, Product Marketing, Aspen Technology, Inc.Ajay Lakshmanan, Product Management, Aspen Technology, Inc.Zachary Peers, Product Management, Aspen Technology, Inc.Alex Rao, Product Management, Aspen Technology, Inc.


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Jump Start: Using Aspen HYSYS Dynamics with Columns

Table of ContentsIntroduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Preparing a Steady-State Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Debutanizer Column Specifics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Development of a Control Scheme . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Preparation of Flowsheet for Dynamic Simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Implementing and Sizing Control Valves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Activating Dynamic Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Column Equipment Sizing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Adding and Specifying Controllers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Strip Charts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Execution of Dynamic Simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Implementing Disturbances . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Additional Resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17



1

IntroductionColumns are an integral part of most processes. They are used to separate components in mixtures where the material

exiting columns often have stringent purity and flow constraints to maintain. It is also important to maintain flow through

columns to ensure safety.

For these reasonsand more, control schemes are usually implemented on columns in order to ensure that variables such

as temperature, pressure, and flow at critical points throughout the column remain constant. Control schemes also help to

maintain product purity and flow, ensuring that acceptable materials exit the column.

In order to obtain working simulation for a column in steady-state operation, Aspen HYSYS can be used. To obtain a

simulation of a column with an implemented control scheme, Aspen HYSYS Dynamics should be utilized. Using both of

these programs in concert provides a comprehensive summary of how a column will perform under varying plant

conditions and perturbations to the columns normal steady-state operation.

This guide will begin with a brief walkthrough of the process for setting up a steady-state column model. The steps

required towards developing and implementing a working control scheme, and studying column dynamic response using

Aspen HYSYS Dynamics, will then be outlined.

Four Aspen HYSYS files come compressed with this guide. The file Debutanizer SS Starter.hsc is the steady-state

simulation for the debutanizer column. Debutanizer Solution RefluxBoilup1 Control Case.hsc is a dynamics-ready file.

This guide will show the steps necessary to add the control equipment to the steady-state debutanizer file that is present

in the LV-1 control case.

In addition, two other alternative control scheme HYSYS files are included. These files are Debutanizer Solution

RefluxBottoms Control Case.hsc and Debutanizer Solution DistillateBoilup Control Case.hsc. The Aspen HYSYS

flowsheet for each of these files and a short description of the control schemes are included in the conclusion section of

this guide.

This document is not meant to be used as a stand-alone reference document. We recommend that a range of other

resources be called upon to give the user a comprehensive view of how to use Aspen HYSYS Dynamics. These may

include:

AspenTech support website (support.aspentech.com) this website has a wealth of information on the use of

AspenTech products and provides answers to frequently asked questions.

AspenTech courseware available in on-line and in-person versions

AspenTech business consultants

This document will show how to prepare a column and analyze its response to varying conditions using Aspen HYSYS

Dynamics. It assumes that the user has Aspen HYSYS V8.0 or higher installed on his or her computer and a functional

process design completed, as well as a very basic knowledge of dynamic simulation using Aspen HYSYS Dynamics.

2013 Aspen Technology, Inc. AspenTech, aspenONE, the Aspen leaf logo, the aspenONE logo, and OPTIMIZE are trademarks of Aspen Technology, Inc. All rights reserved.11-4030-0913

2


Preparing a Steady-State ModelIn order to properly use Aspen HYSYS Dynamics, a working steady-state process simulation model must first be obtained

in Aspen HYSYS. For more information about using Aspen HYSYS, please refer to the separate Aspen HYSYS Jump Start

Guide available at www.aspentech.com/JumpStart_HYSYSV8/.

For the purposes of this Jump Start Guide, a complete dynamic simulation of a column will be demonstrated utilizing a

previously completed steady-state Aspen HYSYS process involving a debutanizing column. The process developed is

shown in Figure 1.

Figure 1. Steady-State Process Simulation with Debutanizer Column

Debutanizer Column Specifics

It is important to appropriately design and rate the column that is going to be the focal point of the dynamic simulation by

double-clicking the column model block on the flowsheet. The parameters in Figure 2 were specified for the debutanizer,

including 15 separation stages, a feed on stage 8, a condenser pressure of 13.12 barg, and a reboiler pressure of 13.47 barg.

Feed2

Vent

Cond Duty

Feed1

Debutanizer

SS Specs

C5+

Reb Duty

Butanes



3

Figure 2. Column Design Parameters

Additional required column specifications of the reflux ratio, butane recovery from the condenser, and C5 exiting the

reboiler can be made in the Specs window. For the particular debutanizer column in this guide, the butane recovery is

96.25% and the C5+ in the condenser is set at 2.5%, which makes the percentage of C5+ in the bottoms 97.5%. From

these parameters, Aspen HYSYS calculates a reflux ratio of 3.697 and a molar reflux flow of 777.0 lbmole/hr. Figure 3

shows the Specs window and the setting up of the butane recovery in the condenser.


4


Figure 3. Setting Column Specifications

Once a steady-state column has been solved in Aspen HYSYS, the user can then continue to develop a control scheme

and add dynamic equipment to the flowsheet in order to begin a dynamic simulation using Aspen HYSYS Dynamics.

Development of a Control SchemeTo develop a control scheme for the column, the columns response to feed changes should be studied. Initially, for the

simulation set up in Figure 1, Feed 1 has a flowrate of 18,000 lb/hr, while Feed 2 has a flowrate of 9,000 lb/hr. Using the

Column Profiles window under the Performance tab for the column, it can be seen that the current feed flow scheme

results in the stage parameters shown in Figure 4.



5

Figure 4. Column Profile for Debutanizer

In order to develop an appropriate control scheme, the feed flow rates should be changed to discover which variables

within the column vary most. The following table shows feed flow changes made to the column and the corresponding

changes to column parameters that displayed the most variance with the feed change.

Table 1. Changes in Column Performance with Feed Changes

The temperature on tray 6 in the debutanizer increased and decreased according to a respective increase or decrease of

the flowrate of the Feed1 stream. Also, with an increase in the flowrate of Feed1, an increase in the i-C5 mass fraction and

decrease of condenser and reboiler duty was observed. For these reasons, the control scheme described in the following

section should be implemented.

Feed1 Flow(lb/hr)

Feed2 Flow(lb/hr)

Tray 6 Temperature(F)

Mass Fraction i-C5 inButanes Stream

Condenser Duty(Btu/hr)

Reboiler Duty(Btu/hr)

18,000 9,000 218.1 .0210 6.563e6 5.631e6

9,000 18,000 213.1 .0193 6.860e6 7.113e6

0 27,000 210.9 .0206 7.171e6 8.653e6

27,000 0 231.5 .0402 6.331e6 4.252e6


6


Preparation of Flowsheet for Dynamic Simulation(Note that the Dynamic Assistant can be used to guide the user in preparing a flowsheet for dynamic simulation. The

Dynamic Assistant will suggest all the steps covered in this section.)

Implementing and Sizing Control Valves

Dynamic simulation requires the proper equipment to be modeled on the flowsheet in order to work properly. The first

pieces of equipment that should be added are valves. For the case being used in this guide, four valves will be necessary

based on the control scheme identified. The valves should be connected to inlet streams Feed 1 and Feed 2 and outlet

streams Butanes and C5+, as depicted below in Figure 5. All valves should have a pressure drop of 7 psig.

Figure 5. Flowsheet with Valves Added

Valves 100 and 101 need to be sized. This is done by clicking on the Rating tab in the valve window and then clicking the

Size Valve button in the bottom left of the window.

Feed2To Feed2 VLV-101

Vent

Cond Duty

VLV-102

VLV-103

Feed1 Butane Product

Liquid ProductDebutanizer

To Feed1 VLV-100

C5+

Reb Duty

Butanes

SS Specs



7

Figure 6. Sizing a Valve

Activating Dynamic Specifications

The next step in moving towards dynamic simulation is to activate the pressure specifications under the Dynamics tab

for streams To Feed1, To Feed2, Butane Product, and Liquid Product, by checking the box shown in Figure 7.


8


Figure 7. Activating Dynamic Parameters

In a similar fashion, check the flow specification box for the streams Vent and Reflux. Reflux is located within the

column subflowsheet environment. Also ensure that no dynamic specifications are checked for streams Feed1 and

Feed2.

Column Equipment Sizing

Next, the reboiler, condenser, and tray section must be given sizes. In order to define the reboiler and condenser volumes,

open the column window and move to the Rating tab and click Vessels in the navigation pane, shown in Figure 8. Enter

530 ft3 for both the reboiler and condenser for the purposes of this guide.

Figure 8. Sizing Reboiler and Condenser



9

To size the trays for the column, open the Tray Section window and then double click the named Tray/Packed Section,

shown in Figure 9. This will open the sizing form for that tray section.

Figure 9. Sizing Tray Section

Enter a tray diameter of 4.5 ft, a tray spacing of 1.8 ft, a Weir height of 0.15 ft, and a Weir length of 4.0 ft to complete tray

sizing.

Adding and Specifying Controllers

Six controllers should be added to the flowsheet for process control. The process variables, output targets, and acceptable

tuning parameters for each valve are listed in Table 2.


10


Table 2. Controller Connections and Variables Controlled

After implementing the control scheme from the above table, the flowsheet should then appear as Figure 10 displays

below.

Figure 10. Flowsheet with Controllers Implemented

To Feed2

Vent

Cond Duty

VLV-102

VLV-103

Feed1 Butane Product

Liquid Product

Debutanizer

To Feed1 VLV-100

C5+

Reb Duty

Butanes

VLV-101

Feed2 FIC

Feed1 FIC

Cond PC

Column TC

Reboiler LCCond LC

Feed2

SS Specs

Controller Process Variable Source Output Target ObjectTuningParameters

Action Range

Feed1 FIC Feed1 Mass FlowVLV-100

Actuator Desired PositionKc = 0.5Ti = 1.0

Reverse0 lb/hr

30,000lb/hr

Feed2 FIC Feed2 Mass FlowVLV-101

Actuator Desired PositionKc = 0.5Ti = 1.0

Reverse0 lb/hr

30,000lb/hr

Cond PCCondenser Vessel

PressureCondenser Duty Control Valve

Kc = 1.0Ti = 2.0

Direct 180 psia - 220 psia

Cond LCCondenser Liquid Volume Percent

VLV-102 Actuator DesiredPosition

Kc = 2.0Ti = 5.0

Direct210F 260F

Column TCColumn Stage 6Temperature

Reboiler Duty Control ValveKc = 2.0Ti = 5.0

Reverse 0% - 100%

Reboiler LCReboiler Liquid Volume

PercentVLV-103 Actuator Desired

PositionKc = 2.0Ti = 5.0

Direct 0% - 100%



11

Strip Charts

Strip charts help users to view the results of dynamic simulation to disturbances. Four strip charts are automatically

available under the Dynamics tab once the control scheme is implemented. These strip charts show the liquid percent

level in the condenser and reboiler versus time, the two feed mass flows versus time, condenser pressure and column

stage 6 temperature versus time, and the composition in the Butanes product stream versus time. These strip charts can

be found by clicking the Strip Charts button under the Dynamics header in the ribbon, then selecting the desired

graph, shown in Figure 11.

Figure 11. Opening Strip Charts

Execution of Dynamic SimulationAfter following the steps towards setting up a steady-state flowsheet for dynamic simulation, the dynamic simulation can

be run. To accomplish this, click the Dynamics tab on the main ribbon in Aspen HYSYS, shown below. Alternatively,

hitting F7 with Aspen HYSYS open will automatically enter dynamics mode. Once the Dynamics tab has been opened,

activate Dynamics Mode by clicking the appropriate button, shown in Figure 12. Then, to run a dynamic simulation, either

click the Run button, or press F9.

Figure 12. Navigating to the Dynamics Tab from the Main Ribbon and Running a Dynamic Simulation

If the steps in this guide are followed, the Dynamics Assistant will indicate that there are changes suggested before

running the dynamic simulation. The suggested changes would revert some of the set up steps listed in this guide. Simply

press No when prompted to run the dynamic simulation.


12


Implementing Disturbances

Some process modification suggestions to view dynamic response for the control scheme implemented include:

Change the feed flowrate

Change the feed composition

Change the temperature setpoints

Change the pressure setpoints

Change both temperature and pressure setpoints

To change the composition or feed flowrates, once the dynamic simulation has been initialized, the feed streams

definition worksheet can be opened by double clicking the appropriate stream. Then, the streams flow or composition can

be modified. Additionally, flow controller setpoints can be modified to initiate disturbance in the simulation.

To change the setpoints for either temperature or pressure, the controllers Parameters tab can be used or the face plate

for a controller can be opened by double clicking the appropriate controller and selecting the Face Plate option, shown

in Figure 13.

Figure 13. Changing the Setpoint and Opening a Face Plate for a Controller



13

In the Parameters tab, the setpoint can be manually typed to the desired value. If the face plate is used, the setpoint can

be modified by dragging the red arrow highlighted in Figure 14.

Figure 14. Face Plate with Highlighted Setpoint Control

To test the implemented control scheme, a dynamic simulation was run. After letting the process come to steady-state

operation, the flowrate of the stream To Feed1 was increased from 18,000 lb/hr to 28,000 lb/hr. The control response

was evident in the Feed Flows strip chart, shown below in Figure 15.

Figure 15. Feed Flows Strip Chart from Dynamic Simulation of Debutanizer

The increased flow to 28,000 lb/hr to the column can be seen, as well as a small perturbation to the Feed 2 stream from

the steady-state value of 9000 lb/hr.


14


Additional strip charts showing the dynamic response for the simulation can be generated for the temperature on tray 6 of

the column and condenser vessel pressure. This strip chart is shown in Figure 16.

Figure 16. Strip Chart Showing Tray 6 Temperature and Condenser Pressure

It can be observed that both the temperature and condenser pressure show fluctuations when the column feed

experienced disturbancebefore each parameter returned to its original value due to the control response.

Figure 17 shows another strip chart for the liquid level percent present in the reboiler and condenser.

Figure 17. Strip Chart Showing Liquid Percent Level in Condenser and Reboiler

For this strip chart, neither the liquid level percent in the reboiler nor the condenser fully reaches its steady-state value of

50% before the feed flow disturbance is activated. However, upon control response, the liquid levels both move towards

their steady-state values.



15

ConclusionDynamic simulation is a very powerful tool that allows users to view how processes will behave when deviations from

steady-state operation occur. Aspen HYSYS Dynamics is the premier dynamic simulator, combining the simulation power

of Aspen HYSYS with the ability to view rigorous dynamic process response.

Aspen HYSYS Dynamics is especially effective for its use in viewing column dynamic response and exploring various

control schemes to limit steady-state operation deviations in columns. The control scheme shown in this guide is a reflux-

boilup control. Reflux-boilup control responds well to feed disturbances. The reflux flow rate controls the distillate

composition while the heat input to the reboiler controls the bottoms composition.

Other suggestions for control schemes to be implemented on the debutanizer column, as well as the scheme shown in

this guide, are included in Table 3.

Table 3. Alternate Control Scheme Configurations

Figure 18 shows the flowsheet of Aspen HYSYS file Debutanizer Solution DistillateBoilup Control Case.hsc, which is an

example of Distillate-Boilup control. This Aspen HYSYS file was downloaded along with this guide and is available for

examination and modification inside of Aspen HYSYS and Aspen HYSYS Dynamics.

ControlConfigurationName

ManipulatedVariable forCondenser LC

ManipulatedVariable forReboiler LC

Manipulated Variable for Primary Composition

Control (Stage 6 Temperature)

Manipulated Variable for Secondary Composition

Control (Fixed in Base Case)

ManipulatedVariable for

Pressure Control

Reflux-Boilup 1

Distillate FlowRate

Bottoms FlowRate

Reboiler Duty Reflux Flow Rate Condenser Duty

Reflux-Boilup 2

Distillate FlowRate

Bottoms FlowRate

Reflux Flow Rate Reboiler Duty Condenser Duty

Distillate-Boilup 1

Reflux Flow RateBottoms Flow

RateReboiler Duty Distillate Flow Rate Condenser Duty

Distillate-Boilup 2

Reflux Flow RateBottoms Flow

RateDistillate Flow Rate Reboiler Duty Condenser Duty

Reflux-Bottoms 1

Distillate FlowRate

Reboiler Duty Bottoms Flow Rate Reflux Flow Rate Condenser Duty

Reflux-Bottoms 2

Distillate FlowRate

Reboiler Duty Reflux Flow Rate Bottoms Flow Rate Condenser Duty


16


Figure 18. Distillate-Boilup Control Case Flowsheet

Distillate-Boilup control is effective for columns operating at high reflux. The distillate flow rate controls the distillate

composition while the heat input to the reboiler controls the bottoms composition.

Figure 19 shows the flowsheet of the Aspen HYSYS file Debutanizer Solution RefluxBottoms Control Case.hsc, which is

an example of Reflux-Bottoms control. This file was also downloaded in conjunction with this guide.

Reflux-Bottoms control is effective when the boilup ratio of a column is high. The reflux controls distillate composition

while the bottoms flow controls the bottoms composition.

To Feed1

Vent

Cond Duty

VLV-102

VLV-103

Feed2Butane Product


To Feed2 VLV-100

C5+

Reb Duty

Butanes

VLV-101

Feed1 FC

Feed 2 FC

Cond PC

Cond LC

Column TC

Reboiler LC Key Compositions

Feed1

To Feed 2

P/F Specs Pressure

Pressure 198.5 psig

To Feed 1

P/F Specs Pressure

Pressure 199.2 psig

Vent

P/F Specs Flow

Molar Flow 0.0

Butane Product

P/F Specs Pressure

Pressure 182.6 psig

Liquid Product

P/F Specs Pressure

Pressure 186.9 psig



17

Figure 19. LB Control Case Flowsheet

In-depth exploration of these control schemes, as well as others that would be appropriate for a users specific process,

ultimately leads to safer and more profitable column operation.

Additional ResourcesPublic Website:

http://www.aspentech.com/products/aspen-hysys-dynamics.aspx

Online Training:

http://www.aspentech.com/products/aspen-online-training

AspenTech YouTube Channel:

http://www.youtube.com/user/aspentechnologyinc

To Feed1

Vent

Cond Duty

VLV-102

VLV-103

Feed2Butane Product


To Feed2 VLV-100

C5+

Reb Duty

Butanes

VLV-101

Feed 1 FC

Feed2 FC

Cond PC

Cond LC

Column TC

Reboiler LC Key Compositions

Feed1

To Feed 2

P/F Specs Pressure

Pressure 198.5 psig

To Feed 1

P/F Specs Pressure

Pressure 199.2 psig

Vent

P/F Specs Flow

Molar Flow 0.0

Butane Product

P/F Specs Pressure

Pressure 182.6 psig

Liquid Product

P/F Specs Pressure

Pressure 186.9 psig

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phone: +17812216400fax: [email protected]

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For a complete list of offices, please visit www.aspentech.com/locations

2013 Aspen Technology, Inc. AspenTech, aspenONE, the Aspen leaf logo, the aspenONE logo, and OPTIMIZE are trademarks of AspenTechnology, Inc. All rights reserved. 11-4407-1013

About AspenTech

AspenTech is a leading supplier of software that optimizes process manufacturingfor energy, chemicals,

engineering and construction, and other industries that manufacture and produce products from a

chemical process. With integrated aspenONE solutions, process manufacturers can implement best

practices for optimizing their engineering, manufacturing, and supply chain operations. As a result,

AspenTech customers are better able to increase capacity, improve margins, reduce costs, and become

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