Difference between revisions of "DWSIM-3.4/C2/Sensitivity-Analysis-and-Adjust/English"

In this tutorial, we will learn how to do sensitivity analysis and adjust.

My name is Kannan Moudgalya.

• We will determine the exact Reflux Ratio for a separation

• We will first do this through Sensitivity Analysis

• We will repeat this through the Adjust operation

• How to open a simulation file in DWSIM
• How to carry out rigorous distillation simulation
• How to add components to a flowsheet

You can access these tutorials and also all the associated files from this site.

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This was solved using Rigorous distillation.

The purity achieved was less than what was desired.

How do we improve the purity?

We need to increase the reflux ratio.

Let us open the corresponding file in DWSIM - the file name is in the heading.

I have already opened the file rigorous dot dwxml

This file is available to you for download from our website spoken tutorial dot org.

In the Properties section, let us locate Molar Composition, item 2.

Let us click the arrow next to Mixture.

The Benzene mole fraction is 0.945.

We would like to increase this to 0.95.

Let us attempt this by increasing the reflux ratio.

This is what we saw in the slide a little while ago.

Let me click it.

Let me click the option Sensitivity Analysis.

We can see five menus in the menu bar of sensitivity analysis.

Locate Sensitivity Studies.

If it is not already selected, click it.

Click on New option.

This will help in creating a new Sensitivity Analysis case.

We see the name SACase0.

We want to increase the reflux ratio so as to get better purity.

Thus, reflux ratio is the independent variable.

Let me click on empty space besides the Object button.

Click on DC-000, the name of our distillation column.

Let me bring this inside.

Let me click the down arrow.

Now scroll down and identify Condenser_Specification_Value.

It comes at the bottom of this menu.

It plays the role of reflux ratio.

Click and select it.

You can see it selected here.

So, we will enter the Lower limit as 2.

Change the Upper limit to 2.5.

Change the number of points to 6.

On the left hand side, see a column called Variables.

Below that, see a plus button in green to Add variables.

Click it.

Click the down arrow below Object.

You may have to click it twice.

Click on the option named Distillate.

Let me click the down arrow below Property.

You may have to click this also twice, to open a drop down menu.

Locate Molar Fraction (Mixture) – Benzene.

You have to scroll down to reach it.

There are also other options that sound very similar to it.

Make sure that you choose this.

Click it.

It gets selected and appears on the tab.

We can see the option called Start Sensitivity Analysis.

Let me click it.

At the end of the simulation, we get the message Done.

We also see the corresponding benzene compositions.

Change the number of points to 11.

Return to Results.

Click Start Sensitivity Analysis once again.

You can see that eleven runs get completed.

Type 2.05, 2.1

See that the desired purity of 0.95 will be achieved between 2.05 and 2.1.

You may choose these as the lower and upper limits in

Independent Variables and repeat.

But, I will not do that now.

Continuing in this manner, we can determine the exact reflux ratio required for 0.95 purity.

Can you find out the reflux ratio required for 0.95 purity?

Follow the procedure I explained just now.

I will give you the answer: it is approximately 2.067.

Click on Chart option.

Click on Draw option.

You can see the chart here.

Distillate composition versus the condenser specification value.

That is, the reflux ratio.

Let me close this pop up.

Let me save this simulation as sensitivity.

In the previous assignment, include a second dependent variable:

benzene mole fraction in the bottoms.

Observe both distillate and bottoms compositions.

Find out how to plot two profiles using Chart.

Verify whether the reflux ratio of 2.067 that we saw in assignment 1 will work.

For this, start with rigorous.dwxml once again.

Change the reflux ratio to 2.067.

Simulate.

What distillate composition do you get?

DWSIM has a powerful method to directly calculate this.

It is called Adjust.

Locate Adjust from the object palette on the right hand side.

Drag it to flowsheet and drop it outside the column, below the distillate.

Let me click and choose it.

This corresponds to the dependent variable, namely, distillate composition.

If it is not already opened, let us click the arrow to the left of Controlled Variable.

And, this will open up.

Click where it says Click to Select.

Click the button that comes at the right end.

It has three columns.

Below Type, click on Material Stream, if it is not already selected.

In the Object column, that is, the middle column, choose

Distillate.

This produces a lot of variables on the right most column.

Locate Molar Fraction (Mixture) – Benzene

It comes after Solid Phase entries end

Click it.

Once again, be careful, as there are many similar sounding options.

Click OK.

Verify that this gets reflected in the properties menu.

Click the button on the right.

In the pop up, scroll down and locate Distillation column.

Click on it.

Then click DC-000.

Then locate Condenser_Specification_Value.

Click it and then OK.

Scroll down to see it.

We can see an option called Adjust Property Value.

This value is generally 1.

Delete 1 and enter 0.95.

I shall enter a slightly larger number 0.95001.

I want you to think about why I have entered a slightly larger number.

A few lines below this, see an option called

Simultaneous Adjust.

Following the usual way, change its value to True.

Press Play and then Recalculate All.

In my case, it calculated automatically.

So, I shall not click those.

In a short time, calculations get completed.

Choose Distillate.

Check Mixture under Molar Composition.

We can see that the benzene composition is 0.95.

For this, click on the Distillation column.

Check the value under Condenser Specification.

We see a value of 2.067.

It is the same as what we obtained in the Sensitivity Analysis.

Let me save this simulation as adjust.

Supposing that I want 0.96 benzene mole fraction in the distillate.

What reflux ratio is required?

As in the problems we solved, you may change only the reflux ratio.

Solve this first by Sensitivity Analysis.

Check your calculations with Adjust.

Find the highest distillate purity you can get in this column.

You may vary the reflux ratio only, as in the earlier assignments.

I could go up to a mole fraction of 0.99, by proceeding gradually.

• how to do Sensitivity Analysis
• how to narrow the solution range
• how to directly achieve the same results using Adjust
• how to use Adjust to push a plant to deliver more

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