Sour Water Stripper

Dist-017H Revised: November 6, 2012

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Sour Water Stripper with Aspen HYSYS® V8.0

1. Lesson Objectives Configure distillation column

Configure heat exchanger

Optimize column feed temperature

2. Prerequisites Aspen HYSYS V8.0

Introduction to distillation

3. Background Many refinery operations produce what is called sour water. Any refinery process water that contains sulfides is

considered to be sour water. Sour water typically contains ammonia and hydrogen sulfide, which must be

removed before the water can be repurposed or sent to a wastewater system. In this lesson we will simulate

this process as well as analyzing the effect that feed temperature has on the column.

The examples presented are solely intended to illustrate specific concepts and principles. They may not

reflect an industrial application or real situation.

4. Problem Statement and Aspen HYSYS Solution

Problem Statement

Construct a simulation of a sour water stripper using Aspen HYSYS. A sour water stream containing mass

fractions of 0.988 water, 0.005 ammonia, and 0.007 hydrogen sulfide is produced from a crude tower. This

stream is at 37.78°C, 2.758 bar, and has a mass flow of 328,900 kg/h. The goal is to produce a pure water

stream with a maximum of 0.00005 mole % ammonia while recovering 99% of the water in the feed stream.


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Aspen HYSYS Solution

4.01. Create a new simulation in Aspen HYSYS V8.0.

4.02. Create a component list. In the Component List folder select Add. Add Water, Ammonia, and

Hydrogen Sulfide to the component list.

4.03. Define property package. In the Fluid Packages folder select Add. Select Sour PR as the property

package. The Sour PR model combines the Peng-Robinson equation of state and Wilson’s API-Sour

Model for handling sour water systems.

4.04. Enter the simulation environment by clicking the Simulation button in the bottom left of the screen.

4.05. Add a Material Stream to the flowsheet from the Model Palette. This stream will serve as our sour

water feed.


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4.06. Double click on the material stream (1). In the Worksheet tab, rename this stream Sour Water. Enter a

Temperature of 37.78°C, a Pressure of 2.758 bar, and a Mass Flow of 328,900 kg/h.


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4.07. In the Composition form under the Worksheet tab, enter Mass Fractions of 0.988 for H2O, 0.007 for

H2S, and 0.005 for Ammonia. The stream should now be fully defined and will solve.

4.08. Add a Heater to the flowsheet from the Model Palette. This heater will serve to heat the sour water

stream before it enters the column.

4.09. Double click on the heater (E-100). Select stream Sour Water as the Inlet, create an Outlet stream

called StripperFeed, and create an Energy stream called Q-Heat.


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4.10. In the Parameters form under the Design tab, specify a Delta P of 0.6895 bar.

4.11. In the Worksheet tab enter an outlet Temperature of 100°C. The heater should solve.


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4.12. Add a Distillation Column Sub-Flowsheet from the Model Palette.

4.13. Double click on the column (T-100). The Distillation Column Input Expert will open. On page 1 of the

input expert enter the following information and click Next when complete.


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4.14. On Page 2 of the Input Expert, leave the default settings for a Once-through, Regular Hysys reboiler.

Click Next.

4.15. On Page 3 of the Input Expert, enter a Condenser Pressure of 1.979 bar and a Reboiler Pressure of

2.255 bar. Click Next when complete.


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4.16. On Page 4 of the Input Expert leave all fields for temperature estimates blank. Click Next. On the final

page of the Input Expert leave all fields blank and click Done to configure the column.

4.17. The Column: T-100 window will automatically appear. Go to the Specs form under the Design tab to

complete the column specifications. First we will create a specification for the mole fraction of

ammonia in the reboiler. Click Add and select Column Component Fraction. Select Reboiler for Stage,

enter 0.00005 for Spec Value, and select Ammonia for Component.

4.18. We also would like to recover 99% of the water from the feed stream. Create this specification by

clicking Add and selecting Column Component Recovery. Select Water for Draw, enter 0.99 for Spec

Value, and select H2O for Component.


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4.19. Go to the Specs Summary form and make sure that the only active specifications are Comp Fraction and

Comp Recovery. Once these two specifications are made active the column will attempt to solve. If the

solver fails to converge you may need to take a look at the Damping Factor.

4.20. Go to the Solver form under the Parameters tab. You will notice a default Damping Factor of 1. The

damping factor serves to reduce the amplitude of oscillations that occur in the solver. Often times

convergence can become cyclic, which can prevent the solver from finding a solution. This is where a

damping factor becomes useful. If you click the Troubleshooting icon on the ribbon under Get Started

and search for ‘damping factor’ you will see the following guidelines.

4.21. We are working with a sour water stripper, therefore the recommended damping factor is between 0.25

and 0.5. In the Solver form under the Parameters tab, enter a Fixed Damping Factor of 0.4. After

clicking Run, the column should solve.


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4.22. Save this file before continuing.

4.23. If you look at the Water stream leaving the reboiler, you will notice that this stream contains

superheated water. We can potentially use the energy of this stream to heat the column feed stream,

thus lowering the energy input required for this process. Delete the heater block ( E-100) and place a

Heat Exchanger block onto the flowsheet. Note that you can right click on the Heat Exchanger block

and select Change Icon to select a different icon to display.


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4.24. Double click on the heat exchanger (E-100). Select stream Sour Water as the Tube Side Inlet,

StripperFeed as the Tube Side Outlet, Water as the Shell Side Inlet, and create a stream called Water-

Cool for the Shell Side Outlet.

4.25. In the Parameters form under the Design tab enter a Pressure Drop of 0.6895 bar for both the Shell and

Tube side. Also change the number of Tube Passes to 1. The heat exchanger should solve.


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4.26. We will now perform a case study to determine the optimal column feed temperature. In the

Navigation Pane click the Case Studies folder and select Add. In Case Study 1, add the StripperFeed

Temperature and the Heat Flows of energy streams Q-Cond and Q-Reb.

4.27. For the Independent Variable (StripperFeed Temperature), enter a Low Bound of 80°C, a High Bound of

115°C, and a Step Size of 2°C.

4.28. Click Run to begin the calculations. To view results go to the Results or the Plots tab.


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4.29. From the case study, you can see that at higher feed temperatures we have a lower reboiler duty but a

higher condenser duty. Since the cost of steam is generally higher than the cost of cooling water, we

should increase the temperature of the column feed stream to 115°C.

5. Conclusions In this lesson we learned how to simulate a sour water stripping process. We configured a distillation column as

well as a heat exchanger. It was determined through the use of a case study that a higher column feed

temperature will lead to lower energy costs for this separation.

6. Copyright Copyright © 2012 by Aspen Technology, Inc. (“AspenTech”). All rights reserved. This work may not be

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Sour Water Stripper

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