Have you been maintaining water treatment diligently in your cooling tower all summer long?
That’s great. Summer heat places high demands on your cooling equipment, and conscientious maintenance is crucial to preserve the life of the equipment, keep the people and processes cool, and keep everyone safe from risks such as Legionnaire’s disease.
We’re here to remind you: Fall is coming and the weather may be cooling down, but it’s still important to stay disciplined with treatment, even if the cooling towers are only operated intermittently. Please don’t let all your summer maintenance go to waste by ignoring the water treatment program as the weather cools.
Fall Weather Means Cooling Tower Operations, Flow and Control May be Intermittent
As operations become less constant, here’s a quick summary of what it takes to ensure safe and efficient operation of your cooling tower.
Reducing conductivity prior to shut-down will minimize the sludge that settles on the bottom of the tubes, resulting in cleaner inspections, and continuing efficiency, for minimal cost.
Maintaining biocide feed is necessary to prevent bacteria from taking hold, which can cause damage to the system metallurgy. As operations become intermittent, normal biocide feed may be inadvertently bypassed by the controller program.
Adding lay-up chemicals prevents off-line corrosion. This will minimize spring iron throw, which means less maintenance and cleaning of distribution decks and strainers.
The Problems Caused by Poor Fall Shut-Down
Proper start-up is important to the integrity of the cooling system, and proper shut-down and lay-up are equally important.
Corrosion, fouling and scale may form if a cooling system is not properly taken off-line at the end of the cooling season. During intermittent fall operation, inadequate chemical treatment may occur during this time.
Suspended solids will begin to drop out during periods of off operation. High levels of scaling impurities may also result in precipitation. Lack of biocide addition will allow microbiological growth. When pipes are drained and then refilled, the corrosion process will begin, resulting in system metal loss. If piping is not properly taken care of after shut-down, out-of-service corrosion can cause a major problem.
Out-of-service corrosion normally shows up during the following cooling season when iron scale or so called pipe slag breaks loose and begins to plug distribution nozzles, pump strainers and even tube bundles. Pipe slag forms when non-continuous wetted pipe begins to rust and water impurities are left behind after evaporation. Pipe slag can be as thin as a piece of paper or as thick as a silver dollar. Pipe slag that is wedged in condenser tubes will result in lost flow and loss of cooling efficiency.
These problems can be avoided by taking appropriate steps when taking a system off-line for the season.
Fall Shut-Down and Lay-Up Protocols
The following procedures will help maintain the integrity of the cooling system during annual shut-down:
As the season winds down, decrease cycles of concentration. This will prevent high levels of dissolved and suspended solids from dropping out when the system is off-line.
Before shut-down, add a nonoxidizing biocide at maximum level to kill any biological growth that may be in the system. Remember stagnant water provides conditions that maximize biological growth.
A separate dispersant and/or biodispersant may be added to loosen and penetrate existing foulants.
To control out-of-service corrosion, a special post-film chemical should be added to the system and circulated. The use of Chemtex Chemfilm MXP will provide superior corrosion protection for the system metals. Use of this type of product will inhibit the formulation of pipe slag. This product should be added approximately three days before system shut-down
Once the system is brought off-line, drain all pipes and tower sump to prevent freezing. If possible, power wash or flush all mud and debris from the tower sump.
If the condenser is to be laid up wet, the unit should first be drained of all tower water. Add fresh make-up water along with a nonoxidizing biocide and a high level of corrosion inhibitor for corrosion protection.
Chemical feed and control systems should be taken off-line and cleaned. Conductivity and pH probes should be removed, cleaned and properly stored. Chemical feed pumps should be flushed with fresh water.
Follow these steps for cooling system start-up and shut-down to avert severe problems. These preventative steps will extend the life of cooling systems, provide more efficient chemical use and potentially save some serious energy dollars.
As always, we are here to help you make sense of this important information, as well as help resolve any problems caused by poor fall shut-down.