Civil Engineering Reference
In-Depth Information
Storage areas should be clean, cool, well ventilated, and protected from corrosive
vapors and dampness. Cylinders and ton containers stored indoors should be in a fire-
resistant building, away from heat sources (such as radiators, steam pipes, etc.), flam-
mable substances, and other compressed gases. Subsurface storage areas should be
avoided, especially for chlorine and sulfur dioxide. If natural ventilation is inadequate,
as would be the case for chlorine or sulfur dioxide, storage and use areas should be
equipped with suitable mechanical ventilators. Cylinders and ton containers stored
outdoors should be shielded from direct sunlight and protected from accumulations of
rain, ice, and snow.
All storage, handling, and use areas should be of such design that personnel can
quickly escape in emergencies. It is generally desirable to provide at least two ways
to exit. Doors should open out and lead to outside galleries or platforms, fire escapes,
or other unobstructed areas. Storage areas for ton cylinders should include a means
for moving the cylinders to active use, and loading and unloading the delivery vehicle.
Typically this is accomplished using a monorail system with a hoist. For larger facil-
ities, a bridge crane may be more appropriate.
Feeding Systems
Feeding systems for chemicals involve conveying the chemicals from storage to the
application point(s), and include pumps, conveyors, dry or liquid chemical feeders,
eductors, and vacuum and pressure gas systems. This section discusses liquid chemical
feeding, dry or solid chemical feeders, and gas feeding systems.
It is sometimes preferable to plan the feeding equipment for the first few years of
flow in the plant and replace or add on equipment in later years. This will allow a
more accurate feed range to be selected. The capacity of the feeding equipment must
meet the maximum dosage required on a maximum day demand, and it must be able
to feed that dosage while maintaining reserve units. It is generally accepted practice
to install 50 percent more than the maximum dose. For chemicals that are of primary
importance in the plant, such as coagulants and disinfectants, backup units or reserve
units should be provided for periods of time when the feeding equipment may be out
of service. The feeding equipment's construction materials should be compatible with
the chemicals that may be used.
Feeding systems should also be designed so that an accurate inventory of chemicals
can be maintained at all times. The feed rate should be checked often, as well as the
total amount of chemical fed. The change in tank level should be recorded daily and
possibly at more frequent intervals, depending upon feed rate and the cost of the
chemical.
Chemical feeder control can be manual, automatically proportioned to flow, depen-
dent on some form of process feedback, or a combination of any two of these methods.
More sophisticated control systems are feasible, if proper sensors are available. If
manual control systems are specified with the possibility of future automation, the
feeders selected should be able to be converted with a minimum of expense. An
example would be a feeder with an external motor that could easily be replaced with
a variable-speed motor or drive when automation is installed.
Standby or backup units should be included for each type of feeder used. Points
of chemical addition and piping to them should be capable of handling all possible
changes in dosing patterns in order to have proper flexibility of operation. Designed
flexibility in hoppers, tanks, chemical feeders, and solution lines is the key to maxi-
