If there is a drop in temperature, as little as one degree,
chlorine gas under pressure will start to go from the gas
phase back to the liquid phase. The ambient temperature has
no direct relationship drops, typically overnight, the chlorine
gas under pressure will go back to the liquid phase (reliquefy).
Likewise, if the ambient temperature is 10oC and temperature
drops, the chlorine gas under pressure will liquefy.
Ideally the chlorine supply system
should always be at a lower temperature than the chlorinator
when withdrawal is from the gas phase. This reduces the possibility
of reliquefaction of chlorine. The greatest difficulty in
operating such installations is caused by reliquefaction of
chlorine gas. This occurs mostly at the first point of pressure
reduction; when it occurs, impurities in the chlorine gas
are deposited at this point, which is the chlorine inlet pressure-reducing
valve of chlorinator. This phenomenon is a result of the hot
gas in the cylinder/container passing very slowly (inches
per hour) through the piping between the cylinder/container
and chlorinator and cooling during the night. This cooling
causes the gas to reliquefy. The amount and frequency of trouble
depends upon how much cooling takes place. This is a function
of the difference in ambient temperatures between day and
night, volume of gas between container/cylinder, and the velocity
of gas flow.
The lower the feed rate and the
greater the distance between container/cylinder and chlorinator,
the greater the chance of reliquefaction, other things being
equal. Reliquefaction will not occur if the container/cylinder
is kept cooler than the chlorinator.
As previously mentioned, chlorine
vapor leaving a container/cylinder will condense if the piping
temperature is significantly lower than the temperature of
container/cylinder. To minimize the condensation/reliquefying
in the manifold header and potential damage to the chlorine
gas handling equipment, it is required to install the outlet
drip legs, which the condensated liquid drops into, and install
the pad heater (25 watt, 120 or 240 VAC)onto the drip leg
for vaporizing the dripped liquid. The pad heater will give
sufficient heat to flash the chlorine liquid back into the
gas phase. If this pad heater is not installed, the liquid
drop can be entered to the chlorinator and can damage the
chlorinator (most cause of gas no feeding).
Also, to keep the temperature of
manifold header pipe slightly higher than the containers cylinders,
it is highly recommended to install the strip heater (40 watt,
120 or 240 VAC) on to the header pipe and flexible connectors
(connect the container/cylinders to the header pipe). For
best heat tracing results, this strip heater must be spiral
wrapped around the pressure header pipe.
These heaters must always remain
"ON" at all times and should be switched on prior
to introducing the chlorine gas into the piping.
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