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CHAPTER TEN
10.22

tion is 5,000-1b/day, a 10,000-1b/day model would be selected and a 5,000-1b/day rotameter
would be installed within the unit. Thus the chlorine should be selected based on future
design capacities, and the rotameter installed at any particular time should be appropriate
for current demands. In addition, note that while the rotameter has a 20-to-1 turndown
capability, this is only in manual mode. In automatic mode, a chlorine feeder only has a
10-to-1 tumdown capability.
The driving force for the system comes from the vacuum, which is created by the chlo-
rine injector or gas induction unit. As the chlorine is dropped to a vacuum at the vacuum
regulator, the chlorine must be pulled through the vacuum regulator, piping, and chlorine
feeder. As a result, if the injector or gas induction unit is not operating correctly, the chlo-
rine feeder will not be able to operate. In extreme cases, there may be insufficient vac-
uum to open the vacuum regulator, in which case no chlorine would be fed at the feed
point. As such, proper design and selection of injectors and gas induction units is critical
to the application of a chlorine system.
Injectors rather than gas induction units are used predominantly to generate the vac-
uum required for chlorine systems. Injectors serve two purposes. First, they generate the
vacuum necessary for the system. Second, they put the gaseous chlorine into a liquid so-
lution so that it can be easily dispersed into the process flow. Injectors (eductors, ejec-
tors) operate on the Bernoulli principle wherein a volume of water is passed by a small
orifice generating a vacuum. The predominate variables that affect the proper operation
of an injector are the quantity of flow (gpm) and pressure (psig) of the source water, which
acts as the motive force for the injector and the backpressure of the generated chlorine
solution. If any of these parameters is insufficient for the selected injector, the injector
may generate only a light vacuum or may not function at all.
Gas induction units operate similarly to injectors but rather are immersed in the pro-
cess water and use a motorized impeller to pull water past the orifice to generate a vac-
uum. Gas induction units have the additional benefit of providing very efficient mixing
of the chlorine solution with the process water.
It should be mentioned that both injectors and gas induction units must be matched to
the capacity of the chlorine feeder. For instance, a chlorine feeder with a 10,000-1b/day
chassis and 5,000-1b/day rotameter would require a 5,000-1b/day injector or gas induction
unit. A 10,000-1b/day injector or gas induction unit could be used but would result in a
more expensive unit and a larger water or power demand.
A final issue in regard to injectors is location. Injectors can be positioned either local
to the chlorine gas feeders or remote of the chlorine feeders (local to the feed point). Both
have benefits and disadvantages. The advantages of injectors local to the gas feeders is
that if there are multiple feed points, only one water source is required and all the chlo-
rine equipment is in a single location (resulting in simplified operations and management
(O&M)). The disadvantages of injectors local to the gas feeders are that a pressurized
chlorine solution must be distributed throughout the plant and that backpressure on the
injectors may be excessive, resulting in large water demands. The advantages of injectors
remote of the chlorine feeders include the elimination of distribution of a pressurized chlo-
rine solution and less backpressure on the injectors. The disadvantages of injectors remote
of the chlorine feeders include distributed equipment (resulting in increased operations
and management) and the requirement of an extensive plant water system. The choice be-
tween remote and local installation should be made based on project requirements and
client preferences.

Chlorine Piping and Valving
There are six distinct areas of concern regarding piping and valving in a chlorine system:
ton container to the piping system (flexible connections), pressurized liquid chlorine pip-