The unwanted accumulation of scale and detrimental impact of metallic corrosion can be significant issues that affect the operation and maintenance of open and closed cooling water systems. To ensure that such open and closed cooling systems are well maintained and operate at optimum efficiency it is essential that the correct water conditions are maintained at…
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The accumulation of microbiological slimes, biofilm and general bio-fouling in cooling water systems reduces system efficiency, increases operating and maintenance costs, and raises risks to safety and health. To ensure that such cooling systems are safe, well maintained and operate at optimum efficiency it is essential that the correct water conditions are maintained at all times.…
Cooling Tower Water Treatment Principles
Make-Up Water – Water added to the system to replace water lost through evaporation, bleed of and windage.
Recirculation – The rate at which water circulates in the cooling tower (in m3/hour litres/sec).
Bleed Off – Water deliberately bled from the system to prevent the cooling system water from becoming too concentrated.
Maximum acceptable concentration factor – An expression of how concentrated the cooling water can become if problems with scale formation and corrosion are to be avoided.
Windage – Water lost from the cooling tower through mechanical rather that evaporative losses.
Temporary calcium hardness – The lower of either the calcium hardness or the Alkalinity (M).
Typical Evaporation Rules
One tonne of refrigeration requires an evaporation rate of approximately 11.4L/hr.
One KW of cooling requires an evaporation rate of approximately 1.5L/hr.
1.8% of the recirculation rate evaporates for each 10oC temperature difference across a cooling tower (1% for each 10oF)
Cooling System Concentration Factors
Your cooling tower will at some stage reach a natural limit as it cannot cycle up in concentration indefinitely like a boiler. However, it may be possible that this natural limit will result in a control limit being exceeded, be on the lookout for:
- Systems with water chloride concentration exceeding 200pppm if stainless steel is present.
- System water contains temporary hardness exceeding the limit specified by your treatment.
- The system concentration factor exceeds the recommended maximum. As a general rule concentration factors should not exceed 5 but where the product is primarily inhibiting corrosion then this should be reduced to 3.5-4.0 to ensure sufficient inhibitor is added to maintain corrosion inhibiting film.