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I have this boiler controlled manually at the moment, and I am wondering what would be the most proper approach to automate this process.

The boiler in this question basically burns fuel (saw dust, wood chips or coal dust) to produce high pressure steam that is consumed by other manufacturing processes.

This is the working principle of the boiler. boiler principle

Fuel is transferred to the Burning Chamber by a (VFD controlled) Conveyor belt. Here it will be burnt to produce heat to make steam. The desired level of heat in the chamber to be maintained is 800-1000 degree Celsius.

The Fresh Air Fan (also VFD controlled) works in harmony with the speed of the fuel Conveyor belt to provide sufficient oxygen for the combustion. Its speed is also dictated by the level of oxygen inside the burning chamber indicated by the Oxygen Sensor.

The Exhaust Fan (also VFD controlled) speed is only dictated by the vacuum level inside the burning chamber, indicated by the Vacuum Sensor. The speed of the Exhaust Fan is regulated to maintain a fixed level of vacuum inside the burning chamber.

As steam is consumed by the consuming manufacturing activities, the steam pressure measured by the Pressure Gauge will be lower, indicating the need to speed up the Conveyor to produce more steam.

Naturally, I would be thinking of applying several separate PID control loops for each sub-process of this system. However, the difficulty of this problem lies in the HETEROGENEOUS nature of the fuel. Incoming fuel varies in moisture content and calorific value (i.e. moist fuel will drop the heat inside the chamber and requires more time to produce heat, while fuel with a low calorific value produce less heat than that with a high calorific value.)

Maybe a machine-learning approach of some kind is best suited for this problem? Are there other control approaches that are best fit to this problem?

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  • $\begingroup$ Does the existing control perform adequately with dry fuel? Can you pull a little waste heat from it to dry the fuel as it is going up the conveyor? I agree with the answers below $\endgroup$
    – Pete W
    Commented Sep 20, 2021 at 13:41

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IMHO, you don't really need AI. PID (or even PI) would be sufficient in this problem. Arguably, you might need to add a cascade controllers (or two), but it should be sufficient.

Although AI is powerful, it still needs a lot of tailoring (probably training of the model), and at the end of the day you end up with a black box that could be difficult to debug.

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This is the exact control of a typical waste fuel boiler, nothing other than conveyor control is necessary. Steam pressure is controlled by the conveyor speed. Unless someone is standing on the conveyor with a fire hose, the moisture content should vary day to day, but not minute-to-minute.

What you may find is that is is difficult to control the flame at high moisture content and require an additional burner of fossil fuel to maintain a good flame condition. My experience with just such a boiler was the flame became unstable at very high moisture; the boiler at my plant had an oil burner for such instances.

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