chemical dosing schemes 1

[Nivrah]

Hi all,
I have been asked to undertake the preliminary design of a closed circuit cooling for our turbine room (turbines and compressors) cooling water. System flow is about 12 ML/day.
Could any of those experienced with closed circuit cooling thrown some ideas about how I go about establishing a chemical dosing scheme:
chemicals to use? i've been told sodium hypo or bromine
dosing amount?
frequency?

 

[bimr]

Contact the chemical treatment program provider that services your organization. The provider will survey your system, determine the metallurgy that will required protection, and the scope of the project.

Most likely, you will not be using sodium hypochlorite or bromine.

Makeup water to these systems varies from city water to deionized water. High purity water is usually within nuclear power plants. Other facilities use city water, or, if such water is of high hardness, then partially softened water is used.

The general approach to water treatment of these systems is to maintain a relatively alkaline pH and high inhibitor levels to control corrosion to as close to 100% as possible. Since most metals typically corrode much slower at pH levels of 8.0 to 10.0, the water treatments often buffer the pH to these levels, thus reducing the corrosion inhibitor demands.

Chromate or molybdate/nitrite/and other inhibitors are frequently used. Since the systems are closed, the dosage requirements are small.

 

[Nivrah]

bimr,
I know the current scheme in one of our many coolng towers use sodium hypo with a dosing rate based on the residual chlorine. all of our cooling towers are stainless steel/fibreglass built.

I infer from your comments that by contacting the company that currently services my company, the former should be able to give me estimated dosing rates for the new design!


Will update the thread once they reply back.

 

[bimr]

Open cooling tower have greater problems because of elevated levels of solids and organisms. The organisms are the reason for the feeding of the disinfectant, sodium hypo.

Closed systems have entirely different treatment schemes. You are not continuously introducing new microorganisms and solids like the open systems. The water chemistry is not constantly changing because of the evaporation of the water in the open systems.

You do have to worry about microbial induced corrosion because of anaerobic bacteria. But it is of much less concern than the problems that occur with an open cooling tower system.

 

[Nivrah]

Bimr,
you are right.
we do have one closed system but the make-up water is from untreated river water which implies the introduciton o new microorganisms and hence the use of sodium hypo.

 

[bimr]

You can chlorinate river water with hypochlorite such that the treated water has a 1-2 mg/l residual.

A better solution is probably to use a higher quality water. River water should be filtered in order to avoid the potential fouling of the cooling system with silt.

 

[Nivrah]

bimr,
i totally agree with our statement:"a better solution is to use high quality water".
This is why I am undertaking the cooling cirucit of the turbine room ( first post). currently, it is via river water but we want to change it to filtered water in a closed loop system. Make-up water will be filtered water as well.
would you still say that I won't need sodium hypo in this case?

 

[bimr]

Chlorinate as the water is being filtered. Not in the cooling tower system.

 

[Nivrah]

bimr,
what other biocides can you suggest that are less corrosive than Sodium hypo? i really do not want to run a cooling tower with high corrosivity water that can later stuff up our turbine room heat exchangers.
thanks,

 

[bimr]

Here is a listing of various biocides that can be used in closed systems:

http://www.coolingtowerchemicals.com/Cooling-Tower-Biocide-s/105.htm

Hypochlorite is not generally used in closed loop systems.