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10.24 CHAPTER TEN

less steel balls (as required). Ball valves are preferred because it is easier to operate and
because the lever indicates the position of the valve at a glance. Piping systems should
be assembled by welding. Only diaphragm-type pressure gauges should be installed in
chlorine systems, and these should have silver diaphragms and Hastalloy-C housings.
Once a vacuum is created downstream of the vacuum regulator or once chlorine so-
lution is created downstream of the injector, carbon steel pipe is no longer appropriate for
chlorine service. If a leak occurs in piping in vacuum service, air and water will get into
the piping. The water will mix with the chlorine in the line to form hypochlorous acid,
which will rapidly destroy the steel. As stated earlier, rather than metallic piping, ther-
moplastic piping materials should be used. The thermoplastic material used most often is
Schedule 80 polyvinyl chloride (PVC). There are two types of PVC pipe available: type
I and type II. Type I is PVC without any components added for property control. Type II
PVC has other components present. These components are readily attacked by chlorine,
and this attack can result in premature pipe failure. The same argument applies to Chlo-
rinated PVC (CPVC) pipe. As such only PVC type I should be used for chlorine service:

Anhydrous Ammonia Systems
Ammonia is available on the commercial market in three useful forms: anhydrous am-
monia, aqueous ammonia, and ammonia sulfate. Aqueous ammonia and anhydrous am-
monia are the forms most commonly used.
Anhydrous ammonia is available as a compressed liquid in containers nearly identical
to those used for chlorine. Most of the equipment used in connection with chlorine can
also be used for feeding ammonia with minor modification. Chlorine gas feeders can be
used as ammonia gas feeders through the use of a simple modification kit. Ammonia has
a heat of vaporization of 328 cal/g and may be fed from the top of the cylinder in the
same manner as chlorine, although not at the same rate. The capacity of a 1-ton (1,016-
kg) ammonia cylinder by the evaporation method is about 84 lb (38 kg) per day. Like
chlorine, ammonia liquids should be transported in black iron pipe with welded steel fit-
tings. Note that the turndown for ammonia gas feeders is much less than for chlorine gas
feeders.
Although anhydrous ammonia can be fed by an injector system, it is highly soluble in
water, and simple direct feed ammonia gas feeder designs are common (pressure feed).
Although an ammonia injector-type system eliminates the need for transporting ammonia
under pressure to distant locations in the plant, ammonia is alkaline, unlike chlorine which
is acidic, and the ammonia will soften the water at the point of injection, producing a
precipitate of calcium carbonate. This can cause severe scale problems in the injection
system. Users of anhydrous ammonia report that carbonate precipitates also build up at
diffuser ports when anhydrous ammonia is fed directly.
These problems are particularly troublesome in hard water, so ammonia injector sys-
tems may require that soft water or a special self-cleaning diffuser with rubber sleeve be
used.

Aqueous Ammonia Systems
Aqueous ammonia is delivered in a solution that is 19% ammonia by weight. Aqueous
ammonia is often fed through PVC lines. Over time, resin formulations of PVC change.
The PVC pipe currently available is not compatible with aqueous ammonia. As such,
carbon or stainless steel pipe should be used in aqueous ammonia feed systems.
In concentrated form, ammonia reacts chemically with copper, so under no circum-
stances should any brass, bronze, or other copper alloy be used in any ammonia feed sys-