Important information about the new IO Flash in DWSIM 1.7

Friday, July 09. 2010

Important information about the new IO Flash in DWSIM 1.7

The original IO algorithm is intended to work only in the VLE region, that is, it was not meant to use in single-phase scenarios. That's why you'll see DWSIM slowing down when calculating PH/PS flashes in the single-phase region with the IO algorithm.

I'm still trying to find a way to tune the parameters and make the algorithm at least as fast as the nested loop one but, for now, be advised. If you would like to test it, try to run the Cavett simulation with the IO method and check the compressor calculation time - it is very slow because it is only gas, and there is a PS flash and a PH one right after.

Also, the critical point calculation is not behaving as expected. The problem is in the "triple sum" calculation, because the stability curve is being calculated correctly. I'll try to find another paper with the formulation for the PR EOS and check against the one I used to make the code. This only affects the phase envelope and critical point utilities, but it is important for you to know that this is a known bug.

Posted by Daniel Medeiros at 18:07 | Comments (3)

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Hi Daniel:

A couple more suggestions for the IO algorithm. If you're doing any broyden updates ... delay them for atleast 3-4 iterations. The acceleration works much better in this case.

The single phase problem is solveable. Lookup this paper "Efficient flash calculations for chemical process design — extension of the Boston–Britt “Inside–out” flash algorithm to extreme conditions and new flash types" - by Parekh and Mathias. You can also try introducing the pseudo-roots ... that the algorithm will converge most of the time except you'll get negative vapor fractions (or vapor fractions greater than one), indicating that you need to perform the calculation in the one phase region.

Hope this helps!
KP

#1 KP on 2010-07-10 02:29 (Reply)

Yes KP, I did what they suggested bu the algorithm gets a little lost in the R convergence loop when it finds a single phase solution and takes longer to converge.

It just needs some fine tuning, the rest is working well.

thanks again!

#1.1 Daniel on 2010-07-10 09:59 (Reply)

Hai Guys Daniel and KP,

You guys are rocking. Really setting a great example of how world should function.

Thanks for the Great work.

#2 Balaji on 2010-07-11 21:57 (Reply)

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About DWSIM

DWSIM is an open-source, steady-state chemical process simulator written in VB.NET. It has a HYSYS-like interface with many of the features present in commercial simulators:

- Thermodynamic models: Peng-Robinson, Peng-Robinson with Volume Translation and Immiscible Water, Soave-Redlich-Kwong, Lee-Kesler, Lee-Kesler-Plöcker, UNIFAC, Modified UNIFAC (Dortmund), UNIQUAC, NRTL, Chao-Seader, Grayson-Streed and Ideal Gas;

- Unit Operations: Mixer, Splitter, Separator, Pump, Compressor, Expander, Heater, Cooler, Valve, Pipe Segment, Shortcut Column, Heat Exchanger, Reactors, Component Separator, Orifice Plate, Distillation and Absorption Columns;

- Utilities: Phase Envelope, Hydrate Calculations, Pure Component Properties, Critical Point, PSV Sizing, Vessel Sizing, Spreadsheet and Petroleum Cold Flow Properties;

- Tools: Hypothetical Components Generator, Bulk C7+ and Distillation Curves Petroleum Characterization, Reactions Manager and
Component Creator.

- Process Analysis: Multivariate Constrained Optimization and Sensitivity Analysis utility.