This instructable will guide you, step-by-step, through modeling an elementary distillation tower using the HYSYS software. Using HYSYS can drastically reduce the amount of time spent doing distillation tower calculations by hand. While it may take 1-2 hours to fully complete and understand the model, it is much faster and more reliable than doing numerous calculations by hand. HYSYS also allows the user to modify tower or stream conditions to see how the modifications affect other streams with a few clicks, rather than with numerous more pages of calculations! Please not that the following tutorial is designed for Chemical Engineering students who are familiar with separations and related terminology. It is also expected that the user has already downloaded and is using HYSYS version 8.0 on a Windows computer. 

Step 1: What You'll Need

Parts/Tools Required:

• Computer & Internet access

• HYSYS software downloaded

• License to run HYSYS (usually provided by university)

Step 2: Opening HYSYS

Once HYSYS is installed on your computer, the next step is to open the software. The HYSYS software can be found using the following path from the Windows start menu:

     1. Start > All Programs > AspenTech > Aspen HYSYS > Aspen HYSYS 

While you may have more or less programs in the "Aspen HYSYS" folder, the only one needed to model a distillation tower is the main "Aspen HYSYS" program (highlighted above). Again, please note that this tutorial is directed towards Windows users. If you are In order to run HYSYS on a Mac computer you must first install a Windows operating system.

Step 3: Create a New Case

After opening HYSYS, you will see the main screen (Figure 1). To begin modeling the distillation tower, open a new case.

       1. Click: file > new > new case.

If you prefer using keyboard shortcuts, 
       press: Control + n

This step is summarized in Figure 2.

The HYSYS main screen also displays software news, recent cases, and some helpful "getting started" links (these are labelled in Figure 2).

Step 4: Adding a Fluid Package

Before beginning a simulation, it is first necessary to define all of the necessary tower and stream parameters. The first parameter to define is the fluid package. The fluid package tells HYSYS which Equation of State to use for future sream calculations.

To select a fluid package:

       1. Click the fluid package tab on the left side of the screen (Figure 3a).
       2. Next, click "Add" on the bottom left of the fluid package screen (pictured in Figure 3b).

Once a fluid package is added, a new "basis" for calculations appears under the fluid packages tab (see Figure 4a). 

The most commonly used fluid package is Peng-Robinson. For this tutorial we will also use Peng-Robinson, however, if your system is known to better follow a different Equation of State, select the appropriate model.

       3. To set the desired fluid package, simply click the option from the "Property Package Selection" window.

Once a fluid package is selected it should be highlighted in blue as seen in Figure 4b.

Step 5: Adding Components

Next, we must define what chemical species are present in the system. For our purposes we will consider a debutanizer, which is designed to separate butane out of a stream containing many different hydrocarbons.

The HYSYS software has a list containing thousands of  known compounds to select from. There is also a search feature with several filters to help find certain compounds faster. If a species in your system is not in the HYSYS list, you can add a "user defined" compound.

To add compounds:

      1. From the fluids package screen, click "view" (located next to the Component List Selection).
      2. Pick a compound present in your system.
      3. Find the compound by searching or filtering the list of pre-loaded compounds on the right side of the screen. 
      4. Click to highlight the desired compound.
      5. Click "Add"
      6. Repeat for ALL compounds present in the system being modeled.
Compounds that have been successfully added are located in the list on the left hand side of the screen. In this case I have added several pure hydrocarbons.

       7. Close the Component List Window

Step 6: Beginning the Simulation

It is now time to enter the simulation environment.
      1. Click "Simulation" in the bottom left corner to enter the simulation environment (Figure 7a).

By default, when you enter the simulation environment, a palette appears. Many different unit operations can be chosen from the palette. For this tutorial we will utilize the distillation tower. 

     2. In the palette, click: Columns > Distillation Column Sub-Flowsheet (upper left corner, highlighted in Figure 7b).
     3. Click again anywhere in the simulation area to place the tower.

If you wish to get a less sophisticated tower to get rough estimates, you can select the Short Cut Distillation option from the palette. The embedded video below gives an overview of the short cut tower and how it is used to design a full-size tower. 

Step 7: Defining Tower Specifications I

The next steps are very important as they will define the conditions inside the tower.

     1. Double-click on the tower that was just placed in the simulation area.

This will open the Column Input window which consists of five pages. These five steps will vary greatly from process to process (i.e. different projects will call for different tower specs). However certain aspects are relevant to all projects.
    2. If desired, change the Column Name by clicking and typing a new name.
    3. Select the appropriate condenser type (total, partial, or full reflux) as stated by your tower design.

For this example a total condenser will be used.

    4. Click each input and output stream and type a distinct name for each (all required streams that need names are highlighted in yellow above).
    5. For the inlet stream, select the stage or tray where it will enter by clicking the "Inlet Stage" drop-down menu
If the number of tower stages is known, type in the "# stages" box.
    7. Click "Next" once all streams are named.

If your tower design includes a side draw, simply name that stream as well before proceeding. 


Step 8: Defining Tower Specifications II

Pages 2 through 5 of the Column Input also vary from tower to tower. 

      1. Select the type of reboiler to be used (Figure 8), and click "Next."
      2. Input the specified condenser, reboiler, and pressure drop (Figure 9), and click "Next."
      3. Inputting condenser, reboiler, and top stream temperature is optional, if you chose, input these (Figure 10) and click "Next."
      4. On the final Column Input page, enter the desired top stream flow rate and condenser reflux ratio (Figure 11), click "Done."

If you had side streams or other side operations, click "Side Ops" rather than "Done."

Step 9: Specifying the Inlet Stream

To proceed to running a simulation on the tower, the feed stream conditions need to be specified.

The necessary specifications are:

• Temperature
• Pressure
• Inlet Flow
• Composition 

      1. Expand the "Streams" folder and click "Feed" or the name you assigned to the inlet stream.
      2. Click the "<empty>" box and type the designated values based on given information (Figure 13a).

While units are typically set to SI, they can be changed via the drop-down menu when entering the value.

      3. Next, under worksheet, click "Composition" (Figure 13b).
      4. Enter the inlet stream compositions based on your specific project (Figure 14a).

Inlet stream compositions can be entered on many different bases (e.g. Mole Fractions, Mass Fractions).

      5. Select what basis your composition is based on by simply clicking the appropriate bullet (Figure 14b).

Note: Ensure that under the "Home" tab, the "Solver" is set to active so that the calculations can be run in the next step.

Step 10:

The tower is now fully specified and can be run to simulate how well the separation will occur.

To run the calculations:

    1. Double-click on the tower to open the tower menu.
    2. Click "Reset" to ensure all settings are current (Figure 15a). 
    3. Click "Run" to run the calculations and simulation (Figure 15b).

Caution: make sure that the conditions have "converged" and display a green box to the right of the "Reset" button. If this box is red and says "unconverged" then the simulator will run continuously without finding any answers.  

Step 11: Viewing Results

After the simulation has run, the results do not display spontaneously. Below are two methods for viewing results. 

       1. Individual Streams

              a.) To view an individual stream, double-click the stream and you can click through stream conditions, composition, etc.

A menu much like the one used to specify the feed stream will appear and can be sorted through to find certain desired values.

       2. Complete Report

              a.) On the top toolbar/ribbon, Click: Home > Reports 
              b.) To view a text file of the full report, Click: Full Report > Create.

The report will save as a text file and report every possible calculation/specification imaginable. The full report is usually includes way more information than necessary.

             c.) To create a custom report, in the Custom Report box Click "Create" (Figure 16a).

This will open a "Report Builder" window.

             d.) Click "Insert Datasheet"
             e.) Select (by clicking the check marks) which information you want in the report and click "Add" (Figure 16b).
              f.) Save and Print the report.


Step 12: Finishing Touches

• A useful tool is the workbook function, you can select certain criteria you want to track as you vary other conditions. This data can also be graphed and included in a report. For instance if you were varying inlet temperature in an effort to attain a larger amount of butane in the product, you can graph inlet temperature vs. butane in product.

• Under the economics tab, you can determine the economic impact of the condenser/reboiler and distillation tower as a whole if you wish to investigate cost further.

You now have a basic working model of your desired distillation project. With this HYSYS model, you can alter any specification (pressure, temperature, reflux ratio, compositions, etc.) in order to see how it affects the separation. As long as the specifications are fully defined, the simulation will run. If you are having trouble getting the simulation to run, double-click each stream and see if HYSYS says a variable is undefined (at the bottom of the stream window). If this does not solve your problem, you may want to contact HYSYS support at support.aspentech.com, or refer to the tutorials and tips presented on the home screen (discussed in step 3).

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