Control the Drum Level with SLC-503 3

[Wolf2003]

I am using SLC-503 to control the Drum Level with 3 elements.
Can sommeone please:
1. Explain the relation of Steam Flow and Drum Level in the LIC? I understood that Steam vill be a feedforwarded, then what is the role of Drum level?
2. What is the Gain and Reset and/or rate I should start with?
thank you very much.

 

[FordPrefect]

Sounds dangerous!!! I would become very familiar with Control loops prior to trying to control a boiler drum!. Going empty at a high firing rate can be deadly!. & dumping too much feedwater in an empty tank can be even more explosive. I have 5 years experience in PLC programming and now I'm the controls specialist at a Power Plant. Boilers still make me nervous! 800 Lb steam (or greater) is not the right thing to learn with.

 

[Wolf2003]

Thank you for the advice, we do have some protections like Low Low level shutdown, and pressure controls firing etc..
What I would like to learn is how to integrate the Steam flow into the Drum Level controller PID. ALL I know is Steam flow will be a feed forward action...If you could please explain how it works.
thanks

 

[harkdog]

wolf2003

1. Stating the obvious, stream flow is the rate of material leaving the drum (plus blowdown). To maintain drum level you need to replace that with feedwater. At steady state and 3 element control all one needs to do is match steam flow with feedwater flow and you are done. This is the feedforward part. Likely you have the stream flow times a factor going into the bias of a loop that uses level as its process variable. That bias goes right into the output. So if the bias changes by 10% then the output is changed by 10% (until the level has time to interact). The level is the feedback portion of the control. Over time you want to adjust the feedwater because your feedforward is not perfect - and there are upsets to deal with. There is possibly a 2nd loop that gets set point from the loop just described and uses feedwater flow as the process variable. This is the 3rd element.
2. Gain in your PID algorythm is only part of a system. You have to look at drum size, steaming rate, valve characteristics - bunch of things. Experience, patience help a lot. Don't make it too radical - swell and shrinkage can be a pain. Sorry I can't help much in this area. 1st time might want to get help from someone who has done it a lot.

 

[Wolf2003]

Your explanation of how the feef forwrad in Level control works is very clear and easy to understand. Thank you vey much.
Yes, we have a second loop, flow control, using the LIC output as its remote setpoint.