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Frequently Asked Questions

Why would I use ChemSep?

ChemSep is a program for modeling distillation columns as well as other, similar, separation processes with a state of the art, nonequilibrium (rate-based) column model that includes validated performance models of commercially available trays and packings. The program is easy to learn; many users are solving problems within 15 minutes, starting with classic equilibrium stage models, before moving on to more advanced rate-based models. ChemSep column models can be inserted into any CAPE-OPEN compliant flowsheeting package (such as COCO ); one can, therefore, easily switch between solving a specific separation problem to simulating an entire chemical plant!

What makes ChemSep unique?

ChemSep was one of the first packages to make available a nonequilibrium (also referred to as rate-based) column model. Now, most major flowsheet simulation programs can boast a nonequilibrium model so that isn't something unique anymore. However, what we can say with complete truthfulness is that our nonequilibrium model was the one that inspired all of the others and that it currently boasts many features not available elsewhere!

Key to nonequilibrium modeling is having a state of the art design-mode allowing the user to specify only the number and type of trays, or the packed bed height and type of packing. Then the mass transfer and hydraulic models for the column internal at hand are selected automatically. By using design methods and tools of equipment vendors ChemSep allows you to combine simulation and column design into one process, with significant benefits over the common two step approach.

Along with many other programs ChemSep has the ability to estimate physical properties of the mixtures you are dealing with. However, to the best of our knowledge ChemSep is the only program that can let you visualize multicomponent diffusion coefficients. These properties are used in the nonequilibrium model to compute mass transfer rates in the column. Another unique aspect to ChemSep is the nonequilibrium model for simulating liquid-liquid extraction columns.

Can I take ChemSep for "test drive" to see if I like it?

You may indeed. We suggest that you download ChemSep-LITE. It is completely free to use but LITE does not include the nonequilibrium column model (although you can inspect case files created with that model).

That's the third of fourth time that this page mentions a nonequilibrium model. What is this model anyway?

We are delighted that you asked, and we hope that you plenty of time to read, because there is no short and simple answer. Nonequilibrium - often named rate-based - models consider distillation and related operations as the mass transfer rated-based processes that really they are. This model differs from the traditional model of distillation operations that chemical engineers have been using for over 100 years that is based on the assumption that the streams leaving any given stage are in equilibrium with each other. They aren't and, what's more, chemical engineers have known this for almost as long as they have been using the equilibrium stage model!

How have engineers dealt with this problem?

The conventional way around the problem that real distillation operations don't reach equilibrium is to employ efficiencies. There are several kinds of efficiency that are or have been used in distillation column design/modelling:

  • Overall
  • Murphree
  • Hausen
  • Vaporization
For packed columns chemical engineers use something analogous to the stage efficiency called the HETP (Height Equivalent to a Theoretical Plate).

Efficiencies (usually of the Murphree variety) and HETPs often are estimated simply from past experience with similar processes, and a new one might be expected to have approximately the same efficiency (or HETP). However, for new processes that have not been built this approach is of no use whatsoever (and sometimes fails even for old ones).

There are many other pitfalls connected with the use of efficiencies but we don't have the space to go into details here. We suggest that you consult our extensive reading list .

OK, I get that; so what?

Well, the nonequilibrium model dispenses completely with efficiencies of all kinds and goes back to first principles and combines the equations that model mass transport between two phases with the material and energy balances. We solve all of these equations all at once. In this way we avoid having to introduce efficiencies at all. There is a great deal more that we could say about these models; for a basic technical introduction to nonequilibrium modeling as well as material with all of the gory details we again suggest that you consult our extensive reading list .

How may I obtain ChemSep?

As we said above, you can download the LITE version free of charge. But you won't be able to try the nonequilibrium model with that version.

An academic site licenses for the full unrestricted version of ChemSep may be obtained from the CACHE Corporation.

For corporate use of ChemSep your company needs to join the ChemSep Consortium .

OK, so I get ChemSep. How do I install it?

Simple, just run the "install" program. ChemSep is a rather compact program and does not take up a hige amount of disk space.

What do I do if I need help?

ChemSep has a built in "help" system. This includes technical material.

There is a great deal of material available online as well as in the program help (although the lite version omits some of the more detailed technical help). Several tutorials are available online as well.

Then there is the ChemSep Book for the most words about ChemSep ever written!

If you can't find what you need in any of these resources then please write to us! We are happy to help (to the extent possible).

If you find a bug we will fix it, but please note that it is very difficult for us to find and fix problems that we cannot reproduce; carefully document any problems that you encounter. The best approach is to send us a "sep-file" that demonstrates the problem (along with some description of how you created it).

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