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CHEMICALS AND CHEMICAL HANDLING 15.5

ulations for piping, loading, and unloading arrangements. The valves are similar to those
on tank cars, but the arrangement is not standard, and on some barges the valves are larger.
Tank trucks consist of cargo tanks for chlorine permanently attached to a motor vehi-
cle. U.S. Department of Transportation (DOT) regulations are explicit as to tank and ac-
cessories design and maintenance, marking, and emergency handling. Only a few chlo-
rine tank trucks are currently being operated in the United States. Railcar deliveries are
practical only for the largest plants and are subject to the economic feasibility of con-
structing a siding from the nearest rail line.
Ton containers of chlorine are authorized for rail shipment, but only on a special tank
car frame known as a multiunit tank car designed to hold 15 containers. The initial rail
shipment of these containers is unloaded from the car for use at the consumer's plant. In
subsequent shipments, the full containers are exchanged for empties, which are returned
for refilling. No freight is charged on the return carload of empty containers because tank
cars are entitled to free return movement.
It is impractical to ship less than 15 containers because the transportation fee is fig-
ured for 15 full containers at prevailing carload rates. Multiunit tank cars must be con-
signed for delivery and unloading on a private track. If a private track is not available,
containers may be removed from the car frame on carrier tracks with previous written
permission. Regulations provide that one or more ton containers may be transported on
trucks or semitrailers under special conditions.
If logistics show that purchase of chlorine by tank truck or railroad tank car is feasi-
ble, stationary storage facilities should be considered. The user can purchase chlorine for
a better price if the tank car or trailer is on-site only for the time it takes to unload it. On
the other hand, the use of tank truck trailers and railroad cars for on-site storage is also
common.
Stationary chlorine facilities should be designed in complete accordance with the rec-
ommendations of The Chlorine Institute as described in Facilities and Operating Proce-
dures for Chlorine Storage. Provision must also be made for a weighing device, either a
lever scale system or, more commonly, load cells.
An air padding system is recommended for unloading the tank car and removing gas
from the tank before inspection. The air should be dried with a heat-reactivated, desic-
cant-type air dryer. Facilities must be provided to vent chlorine gas or chlorine-and-air
mixtures from the storage tank to the consuming process or other disposal system. When
chlorine is transferred from the storage tank to the consuming process, air padding may
be necessary. The procedure is essentially the same as that required for emptying tank
cars.
Tank cars should be emptied through a suitable-metal flexible connection that ac-
commodates the rise of the car as its springs decompress. Tank cars are almost invariably
emptied by discharging liquid. Liquefied gases may be unloaded by their own vapor pres-
sure. Cold weather usually decreases the unloading rate. Sometimes it is desirable to place
an air pad over the chlorine vapor in the car to facilitate unloading. The air pad may be
provided by the chlorine supplier or at the point of use. Weight-measuring devices are
preferred to determine tank contents; gauge glasses should not be used. Adequate light-
ing, including auxiliary power sources, should be provided for night operations.
The location, design, maintenance, and operation of chlorine bulk storage tanks may
be subject to local or state regulations and to insurance requirements. The number and ca-
pacity of storage tanks should be consistent with the size of shipments received and the
rate of consumption. Receiving and unloading areas and safety precautions applicable to
the handling of single-unit cars, cargo trucks, and barges are subject to DOT, Coast Guard,
and other regulations.
Handling Chlorine Ton Containers and Cylinders. Cylinders should be stored up-
right and secured in a manner that permits ready access and removal. Ton containers