Hepful hints and guidance in the field of process simulation using various commercial simulator packages like HYSYS, ASPEN Plus and PRO/II

drop-of-waterGeneration of physical property data is an important part of process simulation. It will invariably be the starting point of equipment design and as such any errors made here may have significant impact on project cost. In a worst case scenario equipment designed on erroneous properties may not even perform right. Now water is a strange animal when it comes to physical properties, especially when mixed with hydrocarbons. It is therefore important to understand the way in which your simulator handles water in determining physical properties.
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A modelling error that can catch you off guard is the pressure drop spiral. It may occur when a recycle loop is closed without paying attention to the pressure level of the recycle. Now as long as the recycle loop has a fixed pressure specification (preferably at its beginning), there will be no problem. It is also quite normal to “forget” about the modelling of (recycle) pumps in preliminary phases of simulation.

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Recently I was involved in answering an engineer’s query on physical property data. The initial request (access to the DIPPR database) suggested that pure component properties were required.

When challenging this request because PRO/II, HYSYS and ASPEN+ will provide access to this kind of data as well, it became clear that mixtures of polar components were in play. Subsequent discussion then moved in the direction of which simulator or property package could be used best.

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If you ever need to simulate a system that includes a big reactant or solvent recycle, a small high purity makeup stream and no purge, chances are you’ll encounter serious convergence issues. This will be especially true in case you are targeting a fixed recycle flowrate or feed/recycle ratio.

A typical example would be a hydrogen recycle in a hydrotreater via an existing – fixed volume – reciprocating compressor. However, also a liquid ring vacuum pump with seal liquid circulation and make-up would fit the bill.

If you know how to handle these systems in a process simulator, they realy don’t need to be a pain in the (you know where). If you don’t, you may be chasing your tail forever and a day… Read the rest of this entry »

FREE e-book

In case you need to model the performance of an existing plant, chances are that the flowing conditions for the flow instruments in the field will differ from those that they were originally designed and/or calibrated for.

To consolidate your test data, you’ll then need to correct the DCS readings.

The math involved to correct these readings is by no means rocket science, but because of the various possible units of measurement mistakes are easily made.

This FREE e-book aims to systematically approach the most common situations and provide in detail the derivations of the correction formulas involved for each of them.

An accompanying Excel workbook is provided that contains predefined worksheet functions (in Visual Basic) to apply these formulas in a reliable and easy fashion.

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