Sometimes circumstances dictate that you run your cooling tower system intermittently. This interval cooling, can be challenging — in part because it may be different from standard procedures and different from seasonal start-up and shut-down.
Potential Problems with Intermittent Cooling
At normal start-up, cooling systems are filled with water and chemistry. Initial adjustments are made, control parameters are set and feed rates are programmed into the controller. When a system is runs consistently – the properly functioning controller maintains consistent control.
When the cooling system is operating intermittently because of weather or demand, the control of scale, corrosion and microbiological growth becomes more challenging.
With on/off or intermittent operations some of these consequences may result:
- Chemical treatment levels might be high or low because the system has not caught up to the programmed controls because it shut down.
- Conductivity may be off for the same reason, the controller suddenly went to “no flow” and the bleed valve was interrupted.
- A drop-out of suspended impurities, because of no flow.
- Bacterial growth flourishes due to the presence of settled organic matter.
- Biocides aren’t fed because the addition schedule was interrupted, no flow.
- Corrosion potential increases from increased bacterial activity and no flow.
Consider running lower cycles of concentration in the tower. This will mean hardness solubility maximums are not exceeded and this will normally reduce suspended material is in the system.
If you know the system will be off for a time, be sure that biocide feed times are during anticipated run times. According to New York City guidelines, don’t shut down for more than five days without treatment and circulation. Remember that biocide feed is critical.
If you are facing the prospect of intermittent operation, use common sense. Failure to recognize potential problems associated with long intervals between “on” times may cause problems which can damage the system and be very difficult to correct.
Review and observe your existing start-up and shut-down procedures in order to minimize the potential for damage.
Biocide Feed is Critical
Have we emphasized biocide enough? Biocide feed is critical. The absence of biocide combined no flow and organic contaminants provides a perfect atmosphere for bacterial growth that may cause severe corrosion. Don’t let this happen! Be certain biocide is fed shortly before the condenser pumps turn off, ensuring that biocide is in the water for shut down.
You are always welcome to call us at Chemtex if you’re facing any questions needing expert answers.