3 Element control for boiler drum

Ben,

I appreciate your post and working in the Chemical industry, feedforward control (or single element) is completely insufficient to handle large swings in Fuel Gas specific gravity or steam pressure changes.

We operate two of three B&W boilers (450klb/hr, 600# steam capacity). We supply steam to an Olefins plant and several other derivative units. The olefins plant generates 1500# steam which drives turbines that have 600# extraction. Tail gas from the olefins unit feeds the plant fuel system which means that the boilers can see anything from H2 rich to fuel gas with ethane in it.

We have had numerous problems as you have noted from your paper plant experience with the boilers catching even with three element control before reaching the low level trip point. I'd be interested in talking with you regarding your experience.
 
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