Page 204 - Water and wastewater engineering

CHEMICAL HANDLING AND STORAGE 5-7

Liquified Gases. Gases are normally stored in their shipping containers. The recommended
standards for chlorine are provided here in detail because of the extreme hazard of the gas and the
wide use of chlorine gas for disinfection (GLUMRB, 2003):

• Chlorine gas feed and storage shall be enclosed and separated from other operating areas.
The chlorine room shall be:
• Provided with a shatter resistant inspection window installed in an interior wall,
• Constructed in such a manner that all openings between the chlorine room and the
remainder of the plant are sealed, and
• Provided with doors equipped with panic hardware, assuring ready means of exit and
opening outward only to the building exterior.
• The room shall be constructed to provide the following:

• Each room shall have a ventilating fan with a capacity that provides one complete air
change per minute,
• The ventilating fan shall take suction near the fl oor as far as practical from the door and
air inlet,
• Air inlets should be through louvers near the ceiling,
• Separate switches for the fan and lights shall be located outside the chlorine room and at
the inspection window,
• Vents from the feeders and storage shall discharge to the outside atmosphere through
chlorine gas collection and neutralization systems,
• Floor drains are discouraged. Where provided, the floor drains shall discharge to the
outside of the building and shall not be connected to other internal or external drainage
systems.
• Chlorinator rooms should be heated to 15 C and be protected from excessive heat.
• Pressurized chlorine feed lines shall not carry chlorine gas beyond the chlorinator room.

• A continuous chlorine sensor and alarm is recommended.

5-4 CHEMICAL FEED AND METERING SYSTEMS
Figure 5-2 provides a diagrammatic system for the classification of chemical feed systems.

Dry Chemical Feed Systems
A typical dry chemical feed system consists of a storage silo or day hopper, a feeder, a dissolv-
ing tank, and a distribution system as shown in Figure 5-3 . Gravimetric feeders have an accuracy
range of 0.5 percent to 1 percent of the set feed rate. Volumetric feeders have an accuracy range
of 1 percent to 5 percent. Gravimetric feeders are preferred for chemicals with varying bulk
densities (Anderson, 2005).