Civil Engineering Reference
In-Depth Information
Fig. 24-22.
Sodium hypochlorite generator (Courtesy of USFilter / Wallace and Tiernan)
Piping
—Size discharge piping to have a velocity of at least 6 ft / sec at average
day feed rates to minimize gas production and pump binding. Another design
criterion is to limit the detention time in the discharge piping to 2 hours.
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Compatibility of chemicals is the key to having reliable systems. Chemical compati-
bility tables are included in Appendix G.
Manual and Low Flow Pacing for Chemical Feed Systems
There are three commonly used chemical feed systems: (1) dry feeders, (2) solution
feeders, and (3) gas feeders. Each type of feeder should have one or more means to
adjust the chemical feed rate (dosage) easily. The adjustment(s) may be manual or by
flow pacing, and must be accurate, repeatable, and easy to change. Also, they should
provide the broadest possible adjustment span from minimum to maximum feed rate.
Typical ranges are 10:1 to 20:1, but greater ranges are possible.
Dry Feeders
Most dry feeders are of the belt, screw, or oscillating plate type. The
feeding device (belt, screw, disc, etc.) is usually driven by an electric motor. Many
belt feeders, particularly gravimetric-type feeders, also contain a material flow control
device such as a movable gate or rotary inlet device for metering or controlling the
flow of chemical to the feed belt.
Volumetric Dry Feeders
Most volumetric dry feeders are of the rotating screw or
disc type, but the belt and rotary star valve types also are used. Generally, the screw
or disc type is driven by an electric motor through a gear reducer drive. In some cases
