Chlorine gas = 100% pure chlorine

[chiefwej]

I have a SWG pool, so my system generates chlorine gas.

I know that some large pool complexes and most water treatment plants use pure chlorine gas for chlorination. There is one pool service company here in Tucson that offers chlorine gas chlorination.

http://www.arizonapimachemical.com/100-pure-chlorine.html

What is the prevailing opinion on using pure chlorine AKA chlorine gas to chlorinate a residential pool?

 

[jblizzle]

Pretty sure the SWG does not produce chlorine gas, it produces hydrogen gas.

There is more than one company here that uses chlorine gas ... it is very easy and efficient to raise the FC levels. They just throw something that looks like a fire ring with a hose attached into the pool and then turn the gas on that bubbles up through the water. The problem is the danger, so a homeowner can not likely get the canisters of gas. Works well for the companies as it is "easy" to transport. The problem with the companies is they jack the CYA levels up so high (mine was over 300ppm) so that they can come every 1 to 2 weeks.

If somehow you were allowed to own the canister of gas and could inject it into the pool every day ... I would think it would be a great system. Just a BIG liability having a tank of chlorine gas sitting around.

 

[JasonLion]

Chlorine gas in a tank is very dangerous to handle, not at all recommended for residential situations. That is why the SWG makes sure it dissolves the chlorine gas it produces into the water inside the cell, before it can go anywhere else. After that it is disinfecting chlorine safely dissolved in the water.

jblizzle, chlorine gas is produced at one plate, while hydrogen gas is produced at the other place. Most of the hydrogen gas escapes as small bubbles, but the chlorine reacts with the water to produce disinfecting chlorine before it leaves the SWG cell.

 

[jblizzle]

Thanks for the clarification.

 

[duraleigh]

What is the prevailing opinion on using pure chlorine AKA chlorine gas to chlorinate a residential pool?

Kaboom!

 

[chem geek]

You have to have special certification to use chlorine gas because it must be handled very carefully. It's fine for a specialized pool service to use if they know what they are doing. Note that it is VERY acidic so one must add it in a way where the low pH does not become a problem (in an SWG, the hydrogen gas production is basic so completely counteracts the acidity from the chlorine gas dissolving into the water producing hypochlorous acid and hydrochloric acid). Usually, they put a diffuser at the bottom of the deep end and the chlorine gas rises up slowly and the rate of introduction is set so that the bubbles dissolve completely before reaching the surface. Oe also wants good circulation when this occurs. Usually such services use a combination of chlorine gas and chlorinating liquid (added separately) so as to reduce the amount of base they need to add to bring up the pH.

Pool Chlor is one company using chlorine gas and chlorinating liquid. The main advantage of chlorine gas is that is the the least expensive form of chlorine.

 

[jblizzle]

Interesting that you say they want good circulation, because Pool Chlor NEVER checked if the pump was running and I think I even recall them saying they preferred it off. They used to come to our house first thing in the morning before the pump turned on.

And they seemed to always be adding powder to the pool ... likely baking soda or soda ash, but I am not sure. They would also float tablets in the summer and I do not recall ever seeing them add bleach ... of course it has been a while and my memory is fuzzy

 

[chem geek]

I suppose the pump could be off during the dosing since the low pH and high chlorine would be in a "column" near the center of the pool, but after they dose it definitely should be circulated. If they were adding powder, it was probably either soda ash or perhaps borax or even lye to compensate for the acidity. Some gas shooters use some chlorinating liquid and some don't, so I guess they don't at least not in your area.

 

[Patrick_B]

I am honestly surprised to hear there are residential areas that allow it, not to mention a company willing to risk the liability of having it at someone's home. I love it for several reasons, and work around it every day, but it can be positively deadly.

EDIT: Nevermind, they handle all of it being administered so no problem with that. I like the idea, but doubt it would be cheaper than bleach.

 

[jblizzle]

Interesting quote from the link provided in the first post:

Gas chlorine is used as a deadly war gas.
No. Gas chlorine was briefly tried as a war weapon during World War I but was quickly replaced as such because it was ineffective for the use. It dissipated too fast, was neither toxic nor persistent enough to do the desired damage to troops, and its effects were too easily remedied. It was therefore quickly replaced by more toxic and effective compounds. In fact, pure pas chlorine was later used in training because troops exposed to it suffered no lasting damage…they recovered quickly and could learn from the experience of relatively benign gas exposure without suffering lasting damage from it.

 

[chiefwej]

I have some experience and training in HazMat. 40 Years as a firefighter. Chlorine is a very dangerous gas. It actually is more dangerous than it is actually classified and regulated. Because it is so commonly used in water treatment and both users and response teams are very familiar with its dangers, the regulations are relaxed when compared to other gases of similar toxicity.

Of course the size containers we were dealing with were one ton capacity. Our water treatment plant frequently had three containers on site at a time. I'm sure the tanks on a service truck are much smaller, but the vehicle should still have proper HazMat placards and observe safety procedures.

 

[chem geek]

The difference between a relatively small gas canister being released outdoors (as was done in wartime) vs. a chlorine tank leaking indoors is huge and largely explains the difference though the quantity also matters greatly as was already noted. There's no question it is nasty stuff and needs to be (and is) regulated. One can read of some chlorine gas release incidents in the following links:

http://www.cdc.gov/mmwr/preview/mmwrhtml/mm6148a1.htm
http://www.cdc.gov/mmwr/preview/mmwrhtml/mm6028a3.htm
http://www.cdc.gov/mmwr/preview/mmwrhtml/mm5403a2.htm

 

[onBalance]

When injecting chlorine gas into a residential pool via a diffuser (or dispenser device) at bottom of pool, the circulation system (filter) should be off. The rising of the bubbles (chlorine gas) from the bottom creates a lot of water movement by itself. Water is drawn into the rising column of chlorine. Even leaves nearby on the bottom of the pool will be drawn towards the diffuser device and then will rise with the chlorine bubbles.

The movement of the water will spread throughout the pool as the chlorine is diluted and neutralized. It generally takes about 20 minutes to be fully distributed throughout a pool. It is preferable to keep the filter system off until the dilution is achieved, rather than having a high chlorine content drawn into the pool equipment.

I believe most companies that use chlorine gas in the treatment of residential pools use canisters (actually cylinders) that contain about 15 to 20 lbs. of chlorine gas.

 

[dschlic1]

Ten years ago most municipal water plants used chlorine gas. However most have moved away from chlorine gas and are not using bleach. The main reason is safety. A water treatment plant close to where I work, and also one that I designed and installed the control system for, had a chlorine accident. A valve broke off of one of the canisters. Destroyed everything in the building.

 

[reynolds357]

Chlorine gas is an excellent way to maintain any pool in theory. The problem is that it is 100% un-forgiving. You can easily kill yourself with it or severely burn your lungs. Other than that, the only draw back to it is that it is extremely alkaline. It is mind blowing the amount of Muratic acid a Chlorine gas pool consumes.

 

[onBalance]

Many municipal water plants never had an accident, but changed away from chlorine gas to bleach because of the costly regulations that have been adopted in the past, and enforced by the local fire departments. Regulations in California are so severe and costly (the construction, size, and type of buildings, buffer zones, and required equipment) it doubles the operating cost and just isn't feasible to continue with gas.

And chlorine gas is not alkaline, just the opposite. The initial adding of one pound of chlorine gas to water adds the equivalent of about .65 quarts of 31.45% muriatic acid at first, then as the hypochlorous acid is used up, another .65 quartz of acid is generated for a total of about 1.3 quarts of 31.45% muriatic acid.
It requires about 1.45 lbs. of soda ash (or 2.3 lbs. of sodium bicarbonate) to neutralize the acid generated by 1 lb. of chlorine gas.

A CYA level of 100 ppm is sufficient for proper stabilization when using chlorine gas with weekly visits. No more is needed.
Chorine gas has been used in the treatment of residential pools since 1955.

 

[Patrick_B]

Really interesting posts balance. How do they get it in the pool? Is an eductor used to create vacuum which pulls it from a cylinder?

 

[onBalance]

Chlorine gas is stored as a liquid in a cylinder under pressure. The pressure is about 100 to 150 psi depending on the temperature. When the valve is opened, the pressure is released, and the liquid changes into a gas. The pressure forces the gas out of the cylinder and through the line to a disperser device.

Another interesting fact is that when the liquid becomes a gas, it does so at a freezing temperature of about a negative 35 degrees Celsius, which is known as its boiling point. When the liquid chlorine under pressure boils and becomes a gas, the temperature of the liquid lowers, and the discharge rate of the chlorine from the cylinder slows down significantly to a trickle and almost stops. After about two pounds of chlorine gas is released (or discharged) from a small 20 lb. cylinder, which takes about 4-5 minutes, the release rate of chlorine almost stops altogether. The cylinder and liquid chlorine then needs to warm up in order to be used again.

 

[Patrick_B]

Chlorine gas is stored as a liquid in a cylinder under pressure. The pressure is about 100 to 150 psi depending on the temperature. When the valve is opened, the pressure is released, and the liquid changes into a gas. The pressure forces the gas out of the cylinder and through the line to a disperser device.

Another interesting fact is that when the liquid becomes a gas, it does so at a freezing temperature of about a negative 35 degrees Celsius, which is known as its boiling point. When the liquid chlorine under pressure boils and becomes a gas, the temperature of the liquid lowers, and the discharge rate of the chlorine from the cylinder slows down significantly to a trickle and almost stops. After about two pounds of chlorine gas is released (or discharged) from a small 20 lb. cylinder, which takes about 4-5 minutes, the release rate of chlorine almost stops altogether. The cylinder and liquid chlorine then needs to warm up in order to be used again.

Intersting...I was just curious since we use a heated outlet and flow controller on the cylinders (2000#) in our industry. A water driven eductor creates a vacuum, pulling the gas into the drive water stream and then distributed into a system basin via that carrier stream. Interesting that they let it out that fast. We feed based on Pounds Per Day. One controller may be 0-50 range, but most are 0-100. I've had a few systems that could feed up to 500 PPD, but never needed quite that much, even in some fairly sized systems.

 

[Sandarsky]

U.S. Department of Homeland Security

I recently asked a company that produces chlorine gas about using it for swimming pools.

The representative indicated that if even one of the containers were stolen (in the U.S.), the U.S. Department of Homeland Security would likely get involved, probably for reasons related to fear of terrorist activity.

The representative made it clear to me that he thought that the use of chlorine gas in residential areas was a bad idea. He also mentioned that companies that do so have huge liability concerns.