Name: What is the best way to manage process variables in Aspen Plus
Uploaded: 2024-12-26T14:30:41.000Z
Duration: 5 min 43 s
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What is the best way to manage process variables in Aspen Plus and how custom tables can help you do it?

When you design your processes in Aspen Plus, you do have to make quite a lot of assumptions and you need to input design specifications.

So you can do that either in the streams data, right, so you do that in stream data directly or in the process unit operations block options, blocks, you would specify that directly as well.

So this is okay when you've got a very simple model where you can realize where your data is and where you have to take your data from in order to analyze it later on.

When you have more complex models like refinery models, it might get pretty complex in terms of the number of data assumptions, the data that you have to collect, but also in terms of how much design specifications you have to make.

Then when you want to change something, you need to find the exact location where that specification was made.

So that's where custom tables come in handy and they can definitely save you time doing your design sensitivity analysis.

So when you look at your flow diagram, you can go into the customize tab and basically we can create custom tables.

So custom tables, you create that as any other option in Aspen Plus, you just press new, create an ID, random ID, so that if you use more than one custom table, make sure that it's easy to understand what it is, right?

So when you open a new custom table, create a new custom table, it will show you a new empty table.

It's not populated yet because you haven't implemented any independent and dependent variables.

So I like to attach it to the side so that I can see my flow diagram, mostly because you can drag and drop data to the custom table from your flow diagram.

So I want to have a look at the effect of some of the process variables, so my assumptions on the net power output, which is the key performance indicator in this case.

So I want to, for example, look at the airflow rate.

I just drag and drop it and name it airflow rate so that I know what that variable represents.

And I'll also include one of the block specifications.

So for example, the combustor, I fix the temperature over here, 950.

So just do combustor temperature, for example.

Now it is a good practice to separate inputs and outputs.

So I'll add a new row that will be empty.

I can also add a new row over here, so that it's specified as inputs.

Probably doesn't let you bold it, but anyway, it doesn't matter.

So I can go to my net power output now, so that's the net power output from my generator.

And what I have to do is I have to mark this and drag it over here, so you can see this is my net power.

And I can also look at the composition, right?

So I can go to my stream, results, mole fractions, for example, and I can have a look at CO2 composition and water content, sorry, oxygen, because oxygen indicates whether we've got a full combustion or not.

And then you can see if I leave it like this, we will not know exactly what parameter that is.

Well, we know, but it's a little bit difficult.

So I'll just name it as CO2 molar content or mole fraction.

So now the good thing about custom tables is that you can basically change something in the table and it will be reflected in the final design, right?

So I changed this to 900 in my table, it changes that in the block.

When I run the model, it will be reflected in my results as well.

So let me change that back and I will see, say, if I have much less fuel than necessary, you'll be able to see that I will have no oxygen or yeah, sorry, much less air.

So I have no oxygen, I have very low CO2, mostly because I will have incomplete combustion and I will have a majority of my carbon as a CO, right?

So I might want to add CO to the table as well.

So you can see that data tables can be a useful tool in order to manage the simulation and process variables.

 And hopefully, I hope that you'll find them useful and I hope that they will save you time when doing your process designs.