In all of these methods, you must check how the sight glass or sample connects to the vessel. Stilling wells inside the vessel can confuse the observations, because they prevent foam from getting to the sight-glass connections or the sampling taps.
If appropriate connections are unavailable, you may require the high-tech approach — radio-scanning. Essentially, a gamma-ray source and detector determine the average mass density across the vessel. A plot of relative mass density versus elevation results. Properly done, this can identify foaming.
Foaming is a major cause of tower problems. Proving that foam is present (or absent) is one of the more challenging field jobs in process engineering. The techniques here are a start to finding out if you have foam or not.
By Andrew Sloley, contributing editor
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