Despite the fact that direct-cylinder mounted gas chlorinators have been available for over 50 years, there still remain many
misconceptions and out-dated "rules of thumb" regarding the rates at which chlorine can be withdrawn from 100 or 150
pound ( 45 or 68 kg) cylinders, using direct-cylinder mounted gas chlorinators.
One of these out-dated ideas that people still believe to be a fact, is the "rule of thumb" that you can only withdraw 40
to 50 pounds of chlorine per 24 hours from a single chlorine cylinder. The actual basis for this idea goes back manyyears to the time when the only type of gas chlorinator available was either mounted on a wall or in a floor cabinet. Theseunits were connected to either the chlorine cylinder or to a manifold by means of flexible connectors. Users of these gas
chlorinators were told to connect one (1) 100-pound or 150-pound ( 45 or 68 kg) cylinder of chlorine to the chlorinator orchlorinator manifold for each 40 or 50 pounds per 24 hours of chlorinator (800 or 1000 gr/hr) feed rate capacity.
At that time, all manufacturers of gas chlorinators had the same problems. Liquid chlorine could and would be formed in
the copper flexible connectors, and in the steel manifolds. There were already so many points of potential pressureleakage that it really didn't make much difference if one or more additional cylinders were hooked up. At the time when
the concept of mounting the chlorinator directly onto the chlorine cylinder valve was introduced, maximum withdrawal
rates suddenly became important. The idea that only 40 to 50 pounds per 24 hours (800 or 1000 gr/hr) could becontinuously withdrawn from a single cylinder was pushed very strongly by gas chlorinator manufacturers. At that time,those other manufacturers did not have a direct-cylinder mounted gas chlorinator to offer. Users were told that whenchlorine was withdrawn above these rates the chlorine would freeze; the valves would freeze up; the chlorinator wouldstop working; liquid would be formed in the chlorinator; etc. This issue was pushed very strongly in the 1960s andconsequently remains in the minds of many people today.
The primary facts stressed at that time seemed to indicate that the Chlorine Institute clearly states that only the low
withdrawal rates are possible. Many people today will still steadfastly maintain that the Chlorine Manual, published by
the Chlorine Institute, contains a statement to this effect. In reality, the Chlorine Manual clearly spells out the findings of theChlorine Institute with regard to chlorine withdrawal rates. It states, first, that the dependable continuous discharge rateof gas from a single 100 or 150 pound ( 45 or 68 kg) cylinder is about 1 3/4 pounds per hour, which is about 42 pounds
per day (840 gr/hr). This, however, is stated to be under the conditions of 70° F (21° C) when discharged against a backpressure of 35 psi (2.4 Bar) and without the cylinder sweating on the outside. These findings also indicate that if sweating
can be tolerated, these rates can be doubled. This takes us up to 84 pounds per day (1600 gr/hr). It makes little
difference to anyone whether or not the outside of the cylinder has sweat or condensation on it, and it certainly has noeffect on the operation of the chlorinator. The item that is most often overlooked is the fact that this data is given fordischarging against a 35 psi back pressure (2.4 Bar). With a vacuum operated, solution- feed gas chlorinator mounted
directly onto the chlorine cylinder valve, the discharge is not against a positive pressure, but is actually against acontrolled negative pressure of about 2 psi (0.14 Bar) below atmosphere.
To further verify this, data was obtained from tests made by one of the leading chlorine producers that showed acontinuous withdrawal rate of above 125 pounds per day (2500 gr/hr). They were discharging against 0(atmospheric) pressure. Additional tests were conducted during the winter and a 100-pound (40 kg) chlorine cylinder wasplaced out-of-doors at 20° F (-6.6° C) and left out-of-doors several days. At the time this test was conducted, theactual liquid chlorine temperature was 20°F (-6.6° C). A 100 PPD (2000 gr/hr) chlorinator was connected to the cylinder
valve and operated at above 100 PPD (2000 gr/hr) continuously. Higher than maximum capacity was withdrawn until
the liquid was almost exhausted, at which time the rate dropped to about 60 pounds per day (1200 gr/hr) for only a few
minutes until the chlorine cylinder was empty.
Figure 1 illustrates the rate of chlorine discharge in pounds per day from a 150-pound (68 kg) cylinder, at 70° F (21° C).
into the atmosphere (no back pressure) over a period of 20 hours. Curve "A" shows the rate of chlorine discharge overany given period of time when air is circulated by a fan blowing against the cylinder. Note that in this case maximum
chlorine discharge rates are continuously maintained at over 200 pounds per day (4 kg/hr) and that the entire cylinder
was exhausted in just 8 hours. However, more normal conditions are represented by Curve "B" where no air is circulated
past the cylinder by a fan. Curve "B" illustrates that fact that at least 100 pounds per day (2000 gr/hr) of chlorine can bedischarged continuously against atmospheric back pressure. In fact, the entire 150 pounds ( 68 kg) of chlorine contained in
the cylinder would be exhausted in just 20 hours at 70° F (21° C).

Figure 2 illustrates the same data as above but it is expressed in terms of the total pounds of chlorine that are discharged
over a given elapsed time, with the same conditions as stated for Figure 1. It should be noted that in the case where air is
not circulated against the cylinder by a fan, as in Curve "B", 100 pounds (45 kg) of chlorine will be discharged in lessthan 9 hours.
Another misconception that has managed to survive after all of these years is the story that if chlorine is withdrawn at
too high a rate from a single cylinder, the chlorine will freeze. This is impossible. Chlorine freezes at approximately

-150° F (-101° C). The pressure in the cylinder changes only with the temperature change and has nothing to do withthe amount of liquid left in the cylinder. A certain lack of understanding on this point has led many people to believe thata chlorine pressure gauge installed in the system will somehow let them know how much chlorine remains in thecylinder. The vapor pressure presented in the Chlorine Manual shows that the cylinder pressure at 80°F (26° C) is 102 psi.
(7 Bar). At 60° F (15.5° C) the pressure is 71 psi (4.9 Bar) and at -30° F (-34° C) the pressure in the cylinder finally drops
to 0 psi (0 Bar).

A direct-cylinder mounted gas chlorinator will actually draw about a 2 psi (0.14 Bar) vacuum in the cylinder. As gas istaken out of the cylinder the pressure in the cylinder is reduced which causes the liquid in the cylinder to boil. This boiling
obviously requires heat that is supplied by the temperature of the air around the cylinder. At high withdrawal rates thetemperature of the outside of the cylinder adjacent to the chlorine liquid surface is lowered and this will eventually causecondensation of moisture to form on the outside of the cylinder. At very high withdrawal rates the temperature at thissurface may drop below 32° F (0° C) and the condensation will freeze to form a frost layer. This is the same thingthat can happen in valves, flexible connectors or manifolds where the chlorine gas has gone back to liquid state and isthen rapidly re-evaporated. Obviously there is no freezing on the inside and the frost is merely an indication of theoutside surface temperature and high humidity. This is no different than frost forming on refrigerator coils andcertainly the refrigerant inside the coils is not frozen. An examination of the chlorine vapor pressure curve, showsthat as the temperature of the liquid--and consequently, the pressure--becomes lower and lower you finally reach anequilibrium condition. At this point, the amount of gas that can be withdrawn from the cylinder is strictly a function

of how much heat can be supplied from the atmosphere. Since the withdrawal rate is now limited, the cooling effect due
to evaporation remains constant.
Let us examine for a minute the condition that exists when a gas chlorinator is hooked up to a cylinder by means of aflexible connector. The pressure inside the chlorine cylinder, the flexible connector, and in the gas manifold is constantsince the cylinder valve is open and there are no points of pressure reduction. The cylinder itself is essentially a boiler
with a very heavy steel wall. The flexible connector is comparable to a condenser tube with the surrounding air being
the cooling medium. Since this system contains both liquid and gas phase, any decrease in temperature will cause someof the gas to go back to liquid. What often occurs is that a door or window is opened to cool off the room, or athunderstorm or other change in weather causes the room to cool. Even sun through a window hitting the cylinder, but
not hitting the flexible connector, can cause the connector to be at a lower temperature. Any slight differential intemperature that occurs will cause gas in the flexible connector and manifold to change to liquid. This liquid passing
through the lines will actually tend to scrub the copper and steel so that when the liquid re-evaporates, dirt will bedeposited. This remains the greatest single source of chlorinator failure and maintenance in non-cylinder mounted gas
chlorinators. All chlorinator systems having flexible connectors and manifolds should either be in a temperature
controlled room or have special heaters on the connectors and manifold to make sure that they are at all times at a higher
temperature than the cylinder. A direct-cylinder mounted gas chlorinator is not susceptible to this problem since
cylinder pressure is immediately reduced to a vacuum as the gas leaves the cylinder valve and enters the chlorinator,
imparting what is known as "superheat" to the gas, making condensation of the gas back into a liquid a physicalimpossibility.

A WORD ABOUT CHLORINE TON CONTAINERS AND WITHDRAWAL RATESAll of the information discussed, above, regarding evaporation of chlorine, “Freezing”, etc., is equally applicable toChlorine ton Containers. Since ton containers have a much larger exterior surface area, a larger volume of chlorine
liquid is in contact with the heat exchanging surface. The same type of withdrawal testing has been done using direct
Ton Container Mounting Adaptors which allow the chlorine vacuum regulator t o be mounted directly on the gas outletvalve. The continuous allowable chlorine gas withdrawal rate from a Ton Cylinder, at 70°F (21° C) is approximately
500 PPD (10 kg/hr), under all of the same conditions used in the chlorine cylinder withdrawal tests.

Chemical Injectiion Technologies, Inc.
835 Edwards Rd., Ft. Pierce, FL 34982
Ph: 772-461-0666 Fax: 772-460-1847
E-Mail: SUPERIOR @chlorinator.com
www.chlorinators.com