Ozone/bromine vs. chlorine dioxide 1

[ProjectEng]

Hello all,

Our water treatment company is touting the benefits of a chlorine dioxide generator (from sodium hypochlorite, chlorine, and sulfuric acid). I think it's because they're going to make more money off of it rather than what's good for us necessarily.

I'm also considering the ozone/bromine system but I don't have much experience with it. I would like some input from you on the pros/cons of these two systems.

I'm aware that the initial capital investment is bigger with ozone/bromine.

Thanks!

 

[Gungadin]

Hi ProjEng,

I work for a medium sized utility department, and we are currently reviewing alternatives to liquid (pressurized) chlorine for our water treatment plant. We currently peak at about 90mgd. Our biggest concern with liquid chlorine is safety issues - functionally, it does a great job. If we opted for an alternative, we may still use chlorine at the tail end to maintain a residual in the treated water. Space requirements for liquid chlorine are much less than for other alternatives also. Another issue is disinfection byproducts (DBPs) resulting from the use of various disinfectants and your particular water quality (very site specific).

 

[ProjectEng]

This cooling tower is for a Cogeneration plant. Make-up water would be RO reject water. Max recirc rate would be 140,000gpm.

We went to chlorine dioxide to get away from chlorine gas. Now we're being told (not by our water treatment folks) that ozone and bromine can do the same job as chlorine for a lot less money. That is the statement that I'd like to evaluate.

 

[af7k]

I found that each application has appropriate disinfection so that a blanket commentary is inappropriate.

One caution with bromine has to do with disinfection byproducts if this is for drinking water. Ozone does not give a measurable residual.

 

[BobPE]

ProjectEng:

I would doubt the statement that chlorine is more expensive that ozone and bromine too. Gas chlorine is the cheapest out there. The problem with it is safety, not cost. Sodium Hypo is cheap too, but costs get up there with capital equipment needed to feed it.
I would probably use hypo in your cooling tower if it were me.

BobPE

 

[smile1]

A couple of thoughts....using reject water from the RO system by itself means high chemical costs for corrosion and scale control. If you are trying to squeeze more use out of your water, there are better approaches. Gas Chlorine is the best biocide for high alkalinity and high volume water, even with the safety issues. Liquid chlorine, bleach, is the next, but one must use acid. Bromine is very expensive. Chlorine dioxide has use in extremely high organic systems, which is unlikely in a cogen plant.

The best bet is to rethink your overall water treatment system, starting with the RO.

 

[ajw160]

An extremely effective and cost effective option for "cycled" water with relatively high pH, say above 8.5, (where you are operating), is to manufacture hypobromous acid on site--that is a ratio of a chlorine source and Sodium Bromide. The chlorine source can be liquid or gas with Bromide:Chlorine molar ratios from 1:1 on down to like 7.5:100. Ratios closer to 50/50 provide the fastest kill and most conversion; lower ratios are, of course, more economical.

Ozone is great killer but is maint. prone and is so unstable it will never penetrate any deposits or areas with build-up, ie...good bulk water treatment and that's it.

CTI (cooling tower institute) reccomends 2 biocides, oxidizing and non. Check it out, CTI.org

(everyone reccomending liquid bleach should check out the disassociation of sodium hypochlorite relative to pH)

 

[oxilume]

Dear ProjectEng,

I was the first person to apply the two chemical chlorine dioxide generator to a cooling tower. This application was at Texaco's Henry Hub Gas Processing Plant in Erath, Louisiana.

NOTE: Natural Gas prices are quoted via Henry Hub.

As a former water treatment chemical salesman I can go into every detail with respect to the Pros and Cons for disinfecting cooling tower water with chlorine dioxide.

Please keep in mind that ClO2 is not a very good disinfectant for algae. You will foul and plug your main condenser and other heat exchanger systems if you do not use an effective algaeicide!

This is from experience and not simply a guess.

The goal of Texaco Henry Hub was to eliminate one ton chlorine cyclinders + reduce water treatemnt chemicals.

In order to get around the issue of adding biocides and algaecides, I simply suggested covering the cooling tower with a deck. This would reduce the growth of algae, due to blocking sunlight.

If you can prevent the formation of algae by covering your deck, then all you need is an excellent high power UV light system.

I can suggest an excellent high-power UV light source that will irradiate through an oopaque fluid!

Sincerely,
Todd Foret
toddforet@usa.net

 

[Aldream]

ajw160, you mentioned this statment (everyone reccomending liquid bleach should check out the disassociation of sodium hypochlorite relative to pH). What do you mean?

 

[ProjectEng]

Sodium hypochlorite decomposes at high ambient temps (~110F) but I'm not aware of the pH correlation.

 

[GarySCWSVI]

ProjectEng,

Suppliers of services are always looking to upgrade their customers. Sometimes for the $ benefit to the supplier and sometimes for the $ benefit plus other benefits to the customer. You seem to lean toward the former as far as your supplier goes. That would indicate a "distrust" in that supplier and maybe you have good reason then to look for another.

It sounds like you are currently satisified with the results you get with what you are currently using. I know of many who say "If it ain't broke, don't fix it.". I would suggest that you ask the current supplier and maybe some other supplier to justify economically their various recommendations. AND there will be many recommendations for the result you want. There are any number of ways to get the result you want. Just as you see the replies here you may also become more confused. Again, I repeat: "If it aint broke, don't fix it.". Maybe change that to "why fix it.". Good luck.

 

[ajw160]

Aldream and ProjectEng, Dissociation probably wasn't the best choice of words in that post. What I was getting-at is the percentage of product available as Active, which does the killing. I tried to paste a graph in here...but anyway...here is roughly how things work-out.

----------Chlorine---------Bromine
pH--------%Active----------%Active

5----------100%--------------100%
7-----------65%--------------100%
8-----------20%---------------82%
8.5---------10%---------------60%
9------------2%---------------40%
9.5----------0%---------------30%

Sorry GarySCWSVI, but I have to comment on the "ain't broke don't fix it" mentality because it's dangerous. Here's one example of a good "why to fix it": ASHRAE, CTI, and OSHA (the WHO too, or soon I think) all have recently authored position papers regarding guidelines for safely operating cooling towers--particularly with respect to biological control and Legionellosis risk/liability containment. Unrelated to system heat exchange performance-- Does anyone here think that if they performed a swab test on their cooling towers or other water systems that they wouldn't find Legionella? And here's the kicker, what if you did find it? Even worse yet, what if some people who were on-site got sick (maybe from someplace else) and the CDC came back and tested? Would they find it? Yes, undoubtedly. Then the question becomes: What have YOU actively done to minimize the risk?

 

[GarySCWSVI]

ajw160,

There was no mention of any "broken problem". I agree with you on your "why to fix it". That situation would indicate that the system is "broke" and needs fixing. You are exactly right. May be that is why they are considering a change. If not, then someone is looking to reduce cost or increase income.

 

[ProjectEng]

Actually we're putting in a new cooling tower and I didn't want to depend on our water treatment company to tell me whether or not ozone/bromine system would work well for us.

We're probably going to go with chlorine dioxide. I think it will be cheaper on the 60000gpm tower, it won't have pH dependence, quite effective, don't have to worry as much about keeping a residual, no chlorine gas cylinders, and a significantly smaller initial capital investment.