The steps involved in deciding the correct cooling
water treatment for a given application. In most cases there is no choice of
water available for cooling. It is therefore necessary to be able to use the
water given without any further external treatment and modify the internal
treatment to give acceptable cooling performance. The choice of treatment is
dictated by :
- The raw water quality
Whether it is hard or soft and what is value of other parameters like
TDS, Turbidity, Alkalinity, Chloride, Sulphate, Silica and Iron.
- The size of the system
Whether it is possible to justify expenditure on control equipment for
acid addition. Whether the system half life is short or long.
- The cooling duties
For example, water flow, metal skin temperatures and water temperature.
- Adjust the pH to make the recirculating water corrosive and
non-scaling in nature and then treat it with a strong corrosion
inhibitor. This is used for large systems where pH control can be
afforded and where high water or skin temperatures are involved, since
these can lead to local scaling problems. It is also use where the
incoming raw water can vary in quality.
- Allow the water to concentrate to make it scaling, but non-corrosive,
and then treat it with a good scale inhibitor. This is used for small
systems where there are no high temperatures, but pH control is
considered to be too expensive, and for harder make up waters.
- A third strategy is to make the recirculating water mildly corrosive
and non-scaling in nature by a combination of allowing it to concentrate
and/or adjusting the pH and then treating it with a mild corrosion
inhibitor plus a low concentration of scale inhibitor. This is used for
softer make-up.
It is essential that each case is viewed individually to ensure that the
correct balance between dosing and control costs, treatment costs and water
costs have been achieved.
Boiler water problem generally falls into classes:
deposit related and corrosion related. Because the two often interact, it is
very common to find a boiler experiencing both simultaneously. There are
many instances where deposit causes corrosion and corrosion causes deposits.
The other problem is of steam purity.
Therefore the aim of the boiler water treatment is
- To prevent the formation of scales and deposits on heating surface
- To prevent corrosion in the boiler and steam system.
- To maintain high level of steam purity.
