3 Element Control for Boiler Drum


Thread Starter


I am an operating engineer in combined cycle power plant. I need any manuals or information on HRSG three element level control (tuning, how effective, problems, improvements).

my email is ([email protected])


Three Element control is used where load is dynamic in nature or continuously changing. where BFW Pump is used to feed multiple boiler and header pressure and flow changes according to demand three element is preferred.

1st Element is Steam Flow leaving the boiler, 2nd element is BFW flow, 3rd element is Steam drum Level.

I will provide you the logic used for three element.
Does it (three element control) help in compensating for false Level Readings due to swelling and shrinking phenomena? If yes, how?
Abrupt changes in boiler demand (steam demand) beyond boiler feed water pump capacity and burner design. Automation can't solve those sort of problems.
I suppose your concern is not the level readings itself but the resulting control action. If so: Three element control, which is nothing else but a feedback controller plus a feedforward, cannot compensate the shrink & swell effect, but can help indirectly. Since the feedforward adjusts the manipulated variable upon changes in the disturbance variable in a proactive way, practically all the needed action is already done and the feedback controller (= the level controller) has only to work on the remaining “imperfections”. As a consequence, it can be tuned now quite moderately and thus gives much less unwanted action in response to the shrink & swell effect.