UFC 3-240-13FN
25 May 2005
CHAPTER 7
WATER TREATMENT CHEMICAL FEED AND CONTROL
7-1
CHEMICAL FEED AND CONTROL SYSTEMS. Chemical feed and
control systems are designed primarily for dynamic industrial water systems that require
regular use of chemicals and control of makeup water and blowdown. These systems
consist of integrated components, including sensors, automatic valves, and chemical
pumps. Some of the ancillary components include drum level sensors, alarms, and
telecommunications for remote monitoring. Normally, a mechanical design engineer will
develop the specifications for a chemical control and feed system.
7-1.1
Controller Types. Water quality controllers are of two types. For cooling
towers or boilers, a stand-alone type controller is the most commonly used and can be
obtained from the manufacturer or from a water treatment service company. The other
type of controller is an integrated component of a building management system. In
many instances both types of controllers will be used for a given system, with one
controller being used to augment the monitoring of the water system performance. This
Chapter focuses on the stand-alone type controllers.
7-1.1.1
Cooling Tower Water Controllers. Cooling tower water controllers
control blowdown and chemical inhibitor feed, as a minimum. Inhibitor feed can be tied
into blowdown; however, it is preferable to have inhibitor feed independent of blowdown
to allow for adequate feed in cases in which excessive drift (uncontrolled blowdown)
results in no requirement for controlled blowdown. Remote monitoring can also control
biocide feed and pH control. The most desirable cooling water inhibitor feed control
strategy incorporates real-time, continuous measurement of the inhibitor concentration
in the recirculating system water. The controller should then make precise chemical
feed adjustments based on the real-time measurement, so that treatment levels can be
reliably maintained. The typical controllers used in cooling systems are listed in Table
7-1.
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