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I recently helped upgrade an old (±20years) 4ton boiler (heavy fuel oil) with some monitoring instrumentation. I decided to have a look at the data and I'm not sure if these kind of oscillations are normal for an older boiler? I haven't really worked with boilers before.

Ignore the sudden drop (a topic for a different question), I'm referring to the oscillating behavior in the steady region. It seems to be rather...excessive? but follows a relatively consistent profile which leads me to believe its just a really barebones control system.

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SimpleJack
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2 Answers2

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Oscillations are normal. It's much harder to make a variable-output burner than a fixed-output burner, so the control systems for these are almost always "bang-bang": fully on, or fully off.

Are these oscillations normal for your boiler? It looks like the controller is doing a good job of keeping the pressure within a well-defined range, but you'll need to find someone who knows your particular system to know if it's an appropriate range.

Mark
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It is very difficult to cancel completely the oscillations in boiler pressure. I imagine that a boiler with an operating pressure between 8 ÷ 10 barg is small and most probably is heated with an on/off burner, in this case is impossible to eliminate the oscillations. But even when you can control the power of the burner and the feedwater flowrate you have to consider the shrink / swell effect that impacts the pressure oscillation.

Check https://controlguru.com/dynamic-shrinkswell-and-boiler-level-control/ for reference.

cactus-eng
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