Boiler & Cooling Tower Control Basics Series Installment 3

BEYOND OVERFEED / UNDERFEED There are other factors that can lead to constituent being out of range besides a chemical overfeed or underfeed, and these must be considered before a change to the feed rate is made. Perhaps a piece of equipment isn’t operation properly or process contamination is occurring. By knowing the system, equipment, and what each individual chemical constituent does, it shouldn’t take you long to figure out the cause and proper corrective action. Instead of going into a general vague discussion of this subtopic, I think it will be ore useful to describe several examples. Each of these examples assume that cycles have been corrected or considered already. SULFITE LEVEL TOO LOW Sulfite is added to a boiler system to remove oxygen from the water. When a deaerator is used, sulfite removes what oxygen is left after the deaerator mechanically scrubs the oxygen from the water. If the deaerator is not functioning properly, then more oxygen will be left in the water and more sulfite will be required to remove it. This easily explains why sulfite levels may be too low or why more sulfite than usual has to be fed to maintain levels. If the deaerator temperature is too low or if the deaerator isn’t being vented enough then not enough oxygen is being mechanically scrubbed from the water and the sulfite demand increases. Another source for the problem may be a mechanical failure in the deaerator itself such as bad spray nozzles or jumbled trays.