Bromine use in Cooling Towers

[mbridges]

We are considering using a bromine based system to control micorbial activity in our cooling towers. What options are available and how do they perform relative to other control methods? One person suggested BCDMH. Thanks in advance.

 

[waterexpert]

The most commonly used disinfectant agents are Bromine and Chlorine. They have common advantages as follows:

· being highly lethal to the vast majority of organisms

· being available in reasonably easy to handle forms

· being relatively inexpensive

· having a persistent residual disinfectant action, preventing growth of organisms throughout the system

Disinfection by means of bromine is favoured over chlorine, mainly because it is simpler to control, by virtue of its wider effective pH spectrum.

A side effect of the use of bromine is oxidation of organic contaminants and removal of ammonia from the system.

Bromine dosing is usually based on systems dissolving bromine containing solid tablets(such as BCDMH).

Manufacturers will be responsible for sizing the systems, but to allow for adequate feed pump capacity, one manufacturer recommends the provision of a flow to the brominator of 1 l.min-1 per 10,000 litres of system capacity. Brominator capacities of approximately 1 Kg of tablets per 7.5 m3 of capacity are usual, to give reasonable filling intervals.

Ultraviolet light is also used as a disinfection method. High rates of disinfection are possible with UV, but it leaves no residual disinfectant in the water, unlike chlorine or bromine.

Ozone is a highly reactive form of Oxygen that is gaining in popularity for water treatment.

Like UV, it leaves no residual disinfectant in the water, and therefore the possibility of growth of organisms within the body of the system is a concern. This is often overcome by being used in tandem with Chlorine dosing. Ozone is very toxic to humans, stringent and costly provision for avoidance of Ozone poisoning must therefore be incorporated within the design.


The above is an excerpt from an article on disinfection of water features which may be found on my website. If there are considerations in cooling tower applications which make the choices different, I would be happy to be informed of them.

http://www.expertise-limited.co.uk

Seán Moran

 

[lafroste]

Depending on your location and specifics of your application, I would consider ozone. Besides its microbial and algacide properties, it can also reduce fouling on the heat exchange surfaces, and tends to moderate pH towards a neutral value of ~7.4. It should be used with side stream filtration in addition to the normal blowdown.
Also, the previous poster's claim that it does not provide a residual disinfection capability is not entirely accurate. It is true that it is much less persistent than chlorine or bromine, however if correctly sized it can provide very adequate algal and microbial control while also providing an anti-fouling benefit.
Specifics that would affect the ozone requirement include your blowdown ratio, incoming TDS and calcium ion concentration. Existing scaling is also a factor, but you will find that existing scale will be gradually removed, and new scaling will be significantly less. Further, pH would be a factor if you ran your towers in an acid condition for some reason.
A reasonable starting point for budgetary estimate purposes would be to assume an ozone half life of 15 minutes in the sump and that all ozone would be stripped out in the tower itself. A reasonable target concentration would be in the neighborhood of 0.25 - 0.5 ppm in the sump. You should also pay attention to your selection of gasket materials and metal surfaces above the wetted areas.