By Allen D. Houtz 1

My objective is to continue the discussion we began in the article Cascade, Feed Forward and Boiler Level Control. Here we explore the causes and cures of the dynamic shrink/swell phenomena in boilers.

Boiler Start-up
As high pressure boilers ramp up to operating temperature and pressure, the volume of a given amount of saturated water in the drum can expand by as much as 30%. This natural expansion of the water volume during start-up is not dynamic shrink/swell as discussed later in this article, though it does provide its own unique control challenges.

The expansion (or