The cooling tower manufacturer’s operation and maintenance instructions should be followed whenever possible. The guide below provides for a reasonable cooling tower maintenance program. This is only a basic guide. Larger, more complicated cooling towers with special filters or controls will demand a more comprehensive maintenance program.

X Scale products are based on the use of a foaming chlorine dioxide (stabilised) system and our Clean in Place (CIP) range has been introduced to offer a practical alternative to removal of the pack. Although removal of the tower pack for cleaning is regarded as best practice by the HSE, alternative methods of cleaning the tower may be considered where there are practical difficulties in doing so (see paragraph 138 of the UK Health and Safety Executives Approved Code of Practice L8)


What is a Cooling Tower?

A cooling tower extracts heat from water by evaporation. When water is reused in the process, it is pumped to the top of the cooling tower and will then flow down through plastic or wood shells, much like a honeycomb found in a bee’s nest.  The water will emit heat as it is downward flowing which mixes with the above air flow, which in turn cools the water.  Part of this water will also evaporate, causing it to lose even more heat.



Cooling Tower Pack


Types of Cooling Towers

One way to distinguish between cooling towers is how the air and water interact, open cooling towers or closed cooling towers.  Open cooling towers, also called direct cooling towers, allow the water to come into contact with outside air.  If cooled water is returned from the cooling tower to be used again, some water must be added to replace the water that has been lost.  Pollutants are able to enter into the water used in these processes and must be filtered out.  Some open water cooling towers are designed with sand and gravel filters to help combat this issue.  Another method of combating the excess minerals and pollutants is some means of a dissolved solid control, such as a blow down.  With this, you drain off a small percentage of the flow to aid in the removal of these contaminants. This is fairly effective, but not as efficient as filtration.  
Closed loop (or closed circuit) cooling tower systems, also called indirect cooling tower systems, do not allow the water to come into contact with any outside substance, therefore keeping the water more pure due to the lack of foreign particles introduced. 

Another classification of cooling towers is made between field assembled towers and factory assembled towers.  Field assembled towers are shipped in pieces and assembled on site by a highly qualified and certified installation team.  Factory assembled towers typically only require the fan motor to be mounted. 

In an evaporative cooling tower, a small portion of the water being cooled is allowed to evaporate into a moving air stream to provide significant cooling to the rest of that water stream.  Evaporative Cooling towers are relatively inexpensive and very dependable means of removing low grade heat from your process. 

Cooling Towers are commonly used to provide lower than ambient water temperatures and are more cost effective and energy efficient than most other alternatives.  The smallest cooling towers are structured for only a few gallons of water per minute while the largest cooling towers may handle upwards of thousands of gallons per minute.  The pipes are obviously much larger to accommodate this much water in the larger towers and can range up to 12 inches in diameter.

Cleaning Procedures

HSE Removal of pack from cooling towers

Appendix 1- Assessment led approach to tower fill pack removal
Appendix 2- Risk assessment led approach to cooling tower fill pack removal

The cleaning procedure is based on the use of the X Scale CIP Tower Pack Cleaning products and is intended for the routine cleaning of cooling towers. It is not to be used for the descaling of badly fouled towers, however X Scale has an excellent solution to any descaling requirement. Where a tower is heavily fouled an assessment of the nature and degree of fouling must be made, and then an appropriate remedial procedure must be carried out.

Pipe descaling within the Cooling Tower



The HSE’s Approved Code of Practice, L8, requires the following steps:-

1) Pre-clean and disinfection
2) Pack removal and manual clean of the system
3) Post clean and disinfection

The basic steps in this alternative procedure are as follows:

1) Pre-clean and disinfection.
2) Foam the pack.
3) Rinse the pack thoroughly with defoamer and neutraliser.
4) Inspect the packing to verify the process has been effective.
5) Manually clean the tower to remove all debris etc.
6) Post clean disinfection.

Foaming the Pack

X Scale will select the correct chemicals depending on the scale build up and these chemicals will vary especially where there are components vulnerable to acidic attack. The activation procedure takes 15 – 20 minutes, so this will be done towards the end of the pre-clean disinfection step

Chlorine dioxide is present to assist in the removal of biofilms and to provide additional protection to the engineers. It is not present to eliminate the necessity for either of the usual disinfection stages.

The foam is generated and applied through a suitable pressure jet washer fitted with a venture device and foam lance. The venturi must be fitted between the pump and the lance, not before the pump, as this cause damage to the pump. The venturi must be capable of mixing 10% detergent into the water. At 10% dilution the detergent will contain 50ppm chlorine dioxide, this can be confirmed using a photometer always carried by X Scale engineers. The foam lance should be capable of generating wet clingy foam. Dry dense foam is not suitable as it does not penetrate the pack and takes a long time to travel through the pack.

Appropriate health and safety measures will be taken working at heights on slippery surfaces and when using hazardous chemicals.

X Scale will foam the top of the tower generously. As the product penetrates it will be reapplied as required to maintain a steady stream through the pack. As the foam exits the pack the acidity and chlorine dioxide levels will be tested. The results will indicate the extent of scaling and fouling with organic matter. Foaming and testing will continue until the foam exiting the pack has an acidity and chlorine dioxide level close to that of the original detergent. The remaining foam will be left in the pack for a further 45 minutes to an hour.

The spent detergent in the tower sump will be treated with defoamer and neutraliser and the pack rinsed with clean low pressure water. The interior of the pack will be inspected using an endoscope.

If the condition of the pack is satisfactory, cleaning of the remaining parts of the tower will continue and the post-clean disinfection procedure will be followed. If necessary and if considered beneficial by X Scale, the foaming procedure will be repeated and then the cleaning and disinfection process continued as normal.

If the product procedure has not achieved a satisfactory level of cleanliness within the pack the strategy for cleaning the tower must be reviewed.


Major components of a Cooling Tower

Cooling Tower Hot Water Distribution System:  An open basin above each fill bank receives the hot water that is piped to each cell in the tower. 

Cooling Tower Hot Water Basin:  This basin receives the hot water that is piped into each cell in the tower and has removable covers to restrict the influx of debris.  Water enters through a removable wave suppressor splash box.

Cooling Tower Fan:  Fans are individually adjustable propeller type and driven through v-belts and protected with a belt guard, or with drive shafts and gear boxes.

Cooling Tower Fill, Louvers, and Drift Eliminators:  Each fill sheet has louvers and drift eliminators formed by thermoformed PVC.  The fills are suspended by hot dip galvanized structural tubing and are elevated above the floor of the cold water basin.

Cooling Tower Cold Water Basin:  In a cooling tower, water is supplied from the discharge of the circulating water system to a distribution basin, from which the cooling tower pump takes suction.  Accessories include both a side suction connection OR a hole and bolt circle in the basin floor suitable for gravity flow, which have debris screens and anti-cavitation devices. 

Cooling Tower Pump:  Pumps of a variety of sizes may be used, depending upon the size of cooling tower and the demands of your process.   




General Cooling Tower Maintenance routines

Weekly

• Test water sample for proper concentration of dissolved solids. Adjust bleed water flow as needed.

• Measure the water treatment chemical residual in the circulating water.

• Maintain the residual recommended by your water treatment specialist.

• Check the strainer on the bottom of the collection basin and clean it if necessary.

• Operate the make-up water float switch manually to ensure proper operation. Inspect all moving parts such as drive shafts, pulleys and belts.

• Check for excessive vibration in motors, fans, and pumps.

• Manually test the vibration limit switch by jarring it.

• Look for oil leaks in gear boxes.

• Check for structural deterioration, loose connectors, water leaks, and openings in the casing.

• During periods of cold weather, check winterization equipment. Make sure any ice accumulation is within acceptable limits.

• Check the distribution spray nozzles to ensure even distribution over the fill.

• Check the distribution basin for corrosion, leaks, and sediment.

• Operate flow control valves through their range of travel and re-set for even water flow through the fill.

• Remove any sludge from the collection basin and check for corrosion that could develop into leaks.

• Check the drift eliminators, air intake louvers, and fill for scale build-up. Clean as needed.

• Look for damaged or out-of-place fill elements.

• Inspect motor supports, fan blades, and other mechanical parts for excessive wear or cracks.

• Lubricate bearings and bushings. Check the level of oil in the gear box. Add oil as needed.

• Adjust belts and pulleys.

• Make sure there is proper clearance between the fan blades and the shroud.

• Check for excessive vertical or rotational free play in the gear box output shaft to the fan.

• Check the casing, basin, and piping for corrosion and decay. Without proper maintenance, cooling towers may suffer from corrosion and wood decay. Welded repairs are especially susceptible to corrosion. The protective zinc coating on galvanized steel towers is burned off during the welding process. Prime and paint any welded repairs with a corrosion-resistant coating.

• Leaks in the cooling tower casing may allow air to bypass the fill. All cracks, holes, gaps, and door access panels should be properly sealed.

• Remove dust, scale, and algae from the fill, basin, and distribution spray nozzles to maintain proper water flow

Maintenance of a Cooling Tower

X Scale Limited recommends your cooling tower be cleaned bi-annually.  To learn more about our maintenance packages please contact us with your water treatment needs.