8 replies to this topic

[aliadnan]

Hi

Different chemicals are added in the cooling tower basin for the following purposes.

CHLORINE:
It is added to remove algae, fungi and bacteria present in the water.

SULPHURIC ACID:
The pH of water is kept between 6.4-6.8. The reason for keeping pH in acidic ranger is that if the water becomes basic, dissolved impurities increases, which precipitates and cause scaling which reduces the rate of heat transfer. In order to keep the pH in acidic range sulphuric acid is added in the water.

ZNIC CHROMATE:
It is added as corrosion inhibitor. It forms protective layer on the inside of piping and exchangers and protects from corrosion.

I am still a young Graduate Engineer and have no Plant Experience but during my internship in a fertilizer plant I had chance to work on the utility unit of the plant and there I had spent sometime on the Cooling Towers.
I hope this helps.
Please correct me if I am wrong

Regards
Ali

[niallmacdowell]

Hi,
I have recently been involved in something like this. From what I have seen, there are usually three main treatments used for bio burden reduction: chlorine dioxide, ozone, UV treatment and barrier (membrane) treatment. You make a choice from this based on the level of bio burden reduction you require and the inlet bioburden of your water, the total size of your cooling loop, the number of cycles of concentration in your system, the destination of the bled off water with high concentration of dissolved solids (to an on-site treatment facility, to a municipal sewer etc) materials of construction of your cooling loop, the required persistance of your treatment (related to cooling loop size) and the hardness of your water. You will also need to consider anti fouling/scaling additions to the system as well.
Hope thats of some use-this is a large area worthy of long hours of discussion and consideration
Niall

[mbeychok]

Kenny:

As Aliadnan has said, cooling water treatment usually has three components:

(1) Chemical addition for preventing the growth of algae and fungi. Usually chlorine or some chlorine containing compound.
(2) Acid addition to control the pH of the water so as to limit the formation of scale. Usually sulfuric acid.
(3) Chemical addition to limit the amount of corrosion in the system. Chromate is only one option, there are others.

This is not something for "do-it-yourself". You should retain the services of an experienced water treatment company such as Nalco or GEWater:

http://www.nalco.com
http://www.gewater.com

[kumaqal.engr]

in my views there are a lot of chemicals, used in Cooling tower for water treatment, depends upon you, how much amount you want to spend, earlier days chlorine was used for the killing of bacteria and algae, but its toxic, so now a days other compounds are used like isothiazolene based, who has a broad spectrum against different bacteria and algae growth, so different types of scale inhibitors are available in the market, chromate phosphate and phosphonates, again depends upon you, which types of inhibitors you want to use,
in my opnion blends of phosphonates is the best because in phosphonates there CPO bonds which is more resistant than phosphate bonds that is COP (carbon oxygen phosphorus bond)
similarly corrosion inhibtor is added to safe your cooling tower, earlier days chromate is used, but this technology is not used in world wide these as they are envoirnmental hazards and few are carcenogenics. methy benzyl triazole and related corrosion inhibtors is use now a days suceesfully. acid and caustic dosing is totall depends upon the quality of water. one misconcept in our mind is that the pH range should be in b/w 6.8 - 7.0 but yet it's not so. actually its all depends upon the quality of water you used.
because its all depends upon the LSI Index, which depends upon four factors
1)Temperature
2) Alkalinity
3) Calcium Hardness
4) TDS
if you want to learn more
just go through this link

http://www.cheresour...?showtopic=1830



with best regards

[sdarone]

It is not too complicated to chemical treat the cooling water, as beychock mentioned, the best option is to contact one of the major companies involved in water treatment, one addition to the ones already mentioned is Kurita, a japanese company.
The chemical treatment will depend basically of the type of cooling tower, is it industrial type, large cooling tower, or is it small. It can be crossflow, or counterflow, forced draft or natural draft.
What is the quality of the make up water, is it filtered water, or it is desalinated water.
What are the concentration cycles to be kept.
What is the relationship between the water inventory and the circulating flowrate.
Are special parameters to be taken into account, i.e max level of chlorides in the cicurlating water, effluent parameters to be met if the blowdown is discharged to the sea... etc...etc...
Do not think about using cromates, the use is not allowed almost in the whole world.. due to the risk to human health.
Basically the function of the chemicals to be used are :
Oxydizing Biocide
Non Oxydizing Biocide
Corrosion inhibitor
Dispersant
PH control
Hardness control

The cost of the chemicals to be used for each one of the mentioned functions vary based on the above mentioned, as well as the flowrates to use, and special cares to take into account.

With all due respect to Milton and Ali,

I tend to agree that it is probably not something you want to do yourself. Several years ago I worked for Nalco, but don't feel any urge to try to sell their products. They are a good company for cooling water products. Betz was our biggest competitor, who is also quite competent with cooling water.

You don't want to use chromate products - in the U.S. they were outlawed about 15 years ago - carcinogenic (Probably the most effective corrosion treatment ever developed, but that's another story)

I don't think that you don't want to be acidic in the circulating cooling water - Being concentrating systems, all CW systems are always tending towards a compromise between corrosion (no scaling and low pH) and scaling (no corrosion but high pH)

Chlorine based products are the cheapest biocides. There are various types of phosphates for anti-scaling. Side stream filtration to try to reduce particulates is probably a good idea.

[Alzack]

VArious chemicals are those into the cooling towers as explained previously. But all those chemical dosing is merely "dose & hope for the best system"..... To further improve the water quality of you cooling tower, use Nalco 3D Trasar. It will further take care of your cooling tower more efficiently real time....

get the info from the link:

http://www.nalco.com...rasar/index.asp
http://www.3dtrasar.com