Dist-017H Dist -017H
Revi sed: November 6, 2012 2012
Sour Water Stripper with Aspen HYSYS® V8.0 1. Lesson Objectives
Configure distillatio di stillation n column
Configure heat exchanger
Optimize Optimi ze column feed temperature
2. Prerequisites
Aspen HYSYS V 8.0
Introduction to distill ation
3. Background Many ref inery operations produce what is calle called d sour water. Any refi nery process process water that that contains sulfides is considered to be sour water. Sour water typicall y contains ammonia ammonia and hydrogen sulfide, which which must be removed before the water can be repurposed or sent to a wastewater syst em. In this lesson we wil l simulate simulate this process as wel l as analyzing the eff ect that feed fee d temperature temperature has on the column. column. The examples example s presented are are solely intended to illustrat ill ustrate e specific concepts and principles. They may may not reflect refle ct an industrial application or real situation.
4. Problem Statement and Aspen HYSYS Solution Problem Statement Construct a simulati on of a sour water stripper using Aspen HYSYS. HYSYS. A sour water stream containing mass fractions of 0.988 0.988 water, w ater, 0.00 0.005 5 ammonia, and 0.007 0.007 hydrogen sulf id e is produced from a crude crude tower. towe r. This stream is at 37.78°C, 37.78°C, 2.758 2.758 bar, and has a mass flow of 328,90 328,900 0 kg/h. The goal is to produce a pure water stream with a maximum of 0.0000 0.00005 5 mole % ammonia while recovering 99% 99% of the water in the fee d stream.
1
Dist-017H
Revi sed: November 6, 2012
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 handli ng sour water systems.
4.04.
Enter the simul ation 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.
2
Dist-017H
4.06.
Revi sed: November 6, 2012
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.
3
Dist-017H
4.07.
Revi sed: November 6, 2012
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 full y 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.
4
Dist-017H
Revi sed: November 6, 2012
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.
5
Dist-017H
Revi sed: November 6, 2012
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 fol lowing information and click Next when complete.
6
Dist-017H
4.14.
Revi sed: November 6, 2012
On Page 2 of the Input Expert, leave the default settings for a Once-through, Regular Hysys reboile r. 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.
7
Dist-017H
4.16.
Revi sed: November 6, 2012
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 fi elds blank and click Done to configure the column.
4.17.
The Column: T-100 window wil l 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 f rom 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.
8
Dist-017H
4.19.
Revi sed: November 6, 2012
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 oscil lations 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.
9
Dist-017H
Revi sed: November 6, 2012
4.22.
Save this file before continuing.
4.23.
If you look at the Water stream leavi ng the reboiler, you will notice that this stream contains superheated water. We can potenti ally 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 sel ect a diff erent icon to display.
10
Dist-017H
4.24.
Revi sed: November 6, 2012
Double click on the heat exchanger (E-100). Select streamSour Water as the Tube Side Inlet, StripperFeed as the Tube Side Outlet, Water as the Shell Side Inlet, and create a stream called WaterCool 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.
11
Dist-017H
4.26.
Revi sed: November 6, 2012
We will now perform a case study to determine the optimal column feed temperature. In the Navigation Pane click the Case Studies folder and sele ct 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 begi n the calculations. To view results go to the Results or the Plots tab.
12
Dist-017H
4.29.
Revi sed: November 6, 2012
From the case study, you can se e that at higher fee d temperatures we have a lower reboil er 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 thi s lesson we le arned 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 separati on.
6. Copyright Copyright © 2012 by Aspen Technology, Inc. (“AspenTech”). All rights reserved. This work may not be
reproduced or distributed in any form or by any means without the prior written consent of AspenTech. ASPENTECH MAKES NO WARRANTY OR REPRESENTATION, EITHER EXPRESSED OR IMPLIED, WITH RESPECT TO THIS WORK and assumes no liabi lity for any errors or omissions. In no event will AspenTech be liable to you for damages, including any loss of profits, l ost savings, or other incidental or consequential damages arising out of the use of the information contained in, or the digital fi les supplied with or for use with, this work. This work and its contents are provided for educational purposes only.
AspenTech®, aspenONE®, and the Aspen leaf l ogo, are trademarks of Aspen Technology, Inc.. Brands and product names mentioned in thi s documentation are trademarks or service marks of thei r respective companies.
13
