Changing from Sodium Hypochlorite to Chlorine Dioxide

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Appreciate your view and comment based on your experience after changing from sodium hypochlorite to chlorine dioxide as oxidizing biocide in cooling water treatment program.

My concerns as follows:-

1. The current issue is mainly on the reaction of sodium hypochlorite with ammonia and caused the sodium hypo strength become lesser and required additional consumption. At the same time, it will create another issue in term of high chloride in cooling water and potential of stress corrosion cracking at the stainless steel cooling water heat exchangers.

2. Another concern in term of algae formation at the cooling tower wall. Is chlorine dioxide able to resolve or need to injection other chemical as back up?

3. Loose of chlorine dioxide via evaporation process and required huge consumption  

your experience much appreciated

  

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8 Answers

  1. Choosing a biocide for a recirculating cooling or process water is almost always difficult.  When oxidizers can be used, they are often the most economical solution.  But EVERY biocide program has its Pros and its Cons.  Choosing the correct program requires evaluation of many variables, including but not limited to: water chemistry, system metallurgy, contamination levels (suspended solids or dissolved species), etc. etc. One also must evaluate the logistics of the operation: is the system needing treatment on the roof of a tall building, is the only good feed point located 325 yards away from the nearest electrical source, etc.?  And of course, unlike many other treatment chemicals biocides are heavily regulated in most countries, both on the application side AND on the discharge side.  If you are still interested in this question, please feel free to email me at cbaron@chemtreat.com and I will be happy to help you evaluate your options.

  2. Sounds like your concerns are driven by conflicting information.

    1st some municipalities add ammonia with chlorine to create chloroamines to get extended distances of oxidant in the service lines of their potable water. At least one water treatment company is promoting adding ammonia to create chloroamines in the recirculating water. Chloroamines are very toxic. The issue in cooling towers is centered around copper alloy corrosion due to the ammonium ion. Adding Bromine creates a more toxic bromoamine but the copper issue remains.

    Chlorine dioxide is easily consumed by all forms of other materials decreasing its availability to kill biological materials. You do not want to add it as you would in a typical replacement of chlorine gas or bleach.

    There are a number of ways in which you can generate ClO2. Some will really increase Cl levels and other will not. Both methods will lower pH so if you use acid for pH control going the Purate route will be the most economical and will have the lowest chloride production in the water.

    Do not expect miracles from ClO2. It can do an excellent job on algal materials but not if you do not have contact with a sufficient concentration.  

    Loss thru the cooling tower is well overrated. What usually happens is the ClO2 goes after a bunch of organic material that has built up in the CT fill. This is actually a good thing. The bad thing is you get no residual in the basin where you want to kill the alga. 

    There are great benefits to ClO2 but it is not a cure-all.

    The greatest mistake made is not identifying what "your" problem is and what are the best solutions for "your" problem specifically.

    Hope it helps.

    1 Comment

    1. I disagree that bromamines are corrosive to copper.  In any case many treatment programs contain copper inhibitors.  I have worked with a number of bromine treated systems, which contained copper and alloys, copper corrosion was not an issue being

  3. Chlorine dioxide does a job.  It is volatile because it is a gas dissolved in water and is driven off by the fans of cooling towers so it is possible to have a clean system and a fouled pack.  Chorine reacts with ammonia to form chloramines which are also volatile.  If you have it available, I would use bromine which reacts with ammonia and forms bromamine, which is much less volatile and does control algae with much lower chloride.

  4. Maybe you should consider a chlorine free alternative. Check out EcoClearProx, combined with UV for extra oxidation force. 100% biodegradable, safe, economically easy to apply, little to no pH problems, no toxic by products.

  5. My first question is why are you having ammonia in cooling water?  Is this an ammonia chiller plant?  Ammonia in air around the cooling tower?  Ammonia in source water??

    Sodium hypochlorite goes stale (meaning it has its own fugitive emission) so it loses strength, mainly from solar heating of the tank.  Some places install a chiller on the hypochlorite tank to attempt to (mostly unsuccessfully) mitigate the issue.  In my humble opinion sodium hypochlorite use in a large industrial setting is a waste of money.

    If your stainless steel is undergoing SCC failure, you installed the wrong metal, sorry, but true.

    Chloride dioxide is ideal for cooling tower use, and will provide better control of algal growth at walls and wet/dry areas than any other oxidant program other than "mixed oxidant", although I myself prefer to use chlorine gas with N,N-dibromo sulfamic acid salt.  Mixed oxidant is produced is a specific electrode arrangement using DC (sometimes AC) current, in a high strength sodium chloride brine.

    Chlorine dioxide is not nearly as volatile (gaseous nature) as chlorine water solution, so I would not be as concerned with tower losses due to air exchange.

    Phosphate in the treatment program is not the limiting factor in algal growth.

    1 Comment

  6. Before providing a formal answer, a few questions.  1) What industry? 2) How large is the tower? 3) Ammonia levels?  4) Phosphate in treatment program?

     

    1 Comment

    1. Ammonia Fertilizer Plant. 23000m3/hr circulation rate. Ammonia 10ppm. Phosphate treatment program

      1 Comment reply

      1. then you have no chance to avoid ammonia, or the production of chloramine from any chlorine oxidant you add.  You might try hydrogen peroxide, although I would not expect great results.  Perhaps you should consider high efficiency water softeners, run cycles of concentration higher than 20, almost no bleed-off water, and have a high system pH, such as > 9 to assist with ammonia rejection from the cooling water.

  8. Chlorine dioxide is more effective biocide with better control. Chlorine dioxide has a higher residual compared to chlorine/hypo in the cooling tower resulting in reduction in consumption of chlorine dioxide. For most microbiological species in cooling water chlorine dioxide is effective. Maintain ORP of > 450 mV under normal conditions and occasionally raise it > 600 mV. Dose chlorine dioxide at the suction of cw pumps (at the suction level of cw pumps).

     

    1 Comment

    1. My experience using chlorine (12% bleach) is that water with a pH above 8.4 it loses its effectiveness.  Storage of liquid chlorine also tends to reduce the strength due to de-gassing of the solution. Use of a solid slow dissolving tablet form may be desirable.

      Bromine/chlorine tablets or a stabilized liquid bromine may be preferable at higher pH conditions. Continuous feed will be more effective than shock feed; generally 0.5 to 2.0 ppm of using a DPD test kit should provide good control. It also will reduce potential addition of chlorides. Weekly "shock" addition of a non-oxidizing biocide will improve algae control as well.

      Chlorine dioxide is a very effective biocide in penetrating biofilm which is the foundation for algae growth. However it has be very short shelf life ater production which means it is best to make it on site. It is best to be fed within hours of its generation. My experience is that it degasses very easily. Control levels are in the ppb range but testing in the field is difficult. It will not contribute cosiderable levels of Cl. 

      Regarding stainless steel tubes, if they are SS 316 or higher, many metalurgist feel chlorides are not a concern unless the metal has been stressed due to poor quality welding or bending. However SS 304 can be penetrated by Cl at >50 ppm.

      1 Comment reply

      1. SS 316 can tolerate chloride upto 1000 ppm (and some time in running seawater) however; these are when SS 316 is in an oxidizing atmosphere but under reducing conditions such as biofouling/fouling etc chloride tolerance is lower. Most of the cases are those where water has remained stagnant and biofouling has taken place.