COOLING TOWER STARTUP
HIS TIME OF YEAR, cooling systems are being placed into service to provide comfort cooling and process cooling throughout the Midwest. Typically, the cooling towers are outside, and have been sitting idle, exposed to the elements over the past five to six months. During this time, while the cooling tower may have been off, the elements have been working on your cooling tower. You may find that your cooling tower has become full of dirt, sand, paper and flying debris, algae, birds, and other airborne particulate matter. Additionally, any debris left over from the last cooling season is still in the tower basin, distribution deck, and fill media. For the most optimal operation of your cooling tower, you should have all of these water and heat transfer surfaces cleaned.
In order for the cooling tower to be used, the first item that must be accomplished is a physical inspection of the tower. You will need to assess any physical damage to the structure, fill media, tower basin, distribution deck and covers, cooling tower piping, and make-up water piping. This is best done by the engineering staff at your facility, who know and understand your system. You may also want to contact a local cooling tower company that can provide onsite visual inspection, producing a condition report and recommendations for upgrades or repairs. These companies can also provide physical cleaning of the cooling tower at a negotiated rate. (Should you need a recommendation, please contact your Gehrke Technology Group representative, who will put you in touch with a local cooling tower service company).
The cooling tower needs to be physically cleaned before any water is applied. It is best to start by cleaning the cooling tower from the top down. Starting with the distribution deck, remove any debris or foreign material blocking the distribution tray/piping nozzles. If you have a Baltimore Air Coil (BAC) tower, the distribution piping should be opened, and any and all debris should be removed from the lower half of the header piping or branch piping. This will insure adequate water dispersion over the filled media.
The fill media can house old scale, microbiological fouling, and other airborne debris from normal operations. If your cooling tower has PVC honeycomb fill media, you will want to inspect the fill from top to bottom from both the internal and external sides of the cooling tower. You will want to look between the sheets of the fill as best you can, removing any debris that has lodged between any sheets of fill media. You can best clean this media with a stream of pressurized water, such as a spray washer or hose. Be cautious, however; a high pressure stream of water can cause the fill media to become physically damaged by cracking or breaking. While inspecting the fill media, you should take note that the sheets of PVC honeycomb media should be packed tightly together, hanging vertically in the cooling tower. Any shifting of fill, wide gaps, or missing sections of media should be repaired or replaced before the start of the cooling season.
The cooling tower has drift eliminators and louvers that are designed to prevent the cooling tower mist and water from leaving the cooling tower. Typically, the exterior louvers or drift eliminators are angled pieces of fiberglass or galvanized steel on the outside of the tower fill media. Cooling tower water is designed to splash on the surfaces, and debris and salts can foul the undersides or bottom edges of these louvers. This is typically cleaned up very easily by applying slight water pressure, i.e. through a hose, when directed to these surfaces. If significant accumulation has taken place over the years, you may need to perform a physical scraping and/or a chemical cleaning. This can be best determined by your staff, consulting with your water treatment vendor.
The internal drift eliminators are typically a PVC pipe material or a treated press paper. These are located on the inside of the cooling tower, along the interior edge of the cooling tower fill media. These surfaces should be inspected for any buildup of fouling, and physically cleaned. Typically, these areas experience a slight coating of a green, moss-like substance no thicker than 1/32 inch, and can be easily sterilized with an application of a biocide recommended by your water treatment vendor.
We are now at the bottom of the cooling tower, known as the tower basin. The tower basin holds the water reservoir and all other debris that the water collects during its recirculating process. In the tower basin, you will typically find sand-like dirt, muddy gray dirt, paper and debris, microbiological biomass, and other airborne particulates, based on tower location and local conditions. Any material on the bottom of the tower that has piled up over the season becomes detrimental to the operation of the cooling tower, the water treatment program, and the longevity of the cooling tower. This is why we need to clean this area.
Physically clean the tower basin from the outer edges into the center core or tower basin drain location. Begin the cleaning by shoveling, sweeping, or vacuuming the dry basin of any dirt or debris. Remember to clean the tower basin underneath the bottom edge of the cooling tower fill media. This area is best cleaned by dragging some type of straight-edge along the tower basin. The straight-edge acts as a scraper, gathering loose debris in this area. Depending on the design of your cooling tower, a vacuum hose attachment may aid in the removal of as much debris as possible.
Now, using a hose or pressurized stream of water, wash down the sides of the tower basin. Insure that the structural sides of the basin are hosed, and that the area underneath the fill receives attention. You will find that dirt and sand will flow towards the drain. Continue this operation until clear water without debris or dirt has been observed. Try to flush all of this material out of the cooling tower via the cooling tower drain. If you have any low depression in the cooling tower basin design, you may need to vacuum this dirty water and debris from those areas.
The cooling tower is now ready to receive the first fill of fresh make-up water. But before we begin filling, we recommend inspecting the piping for any cracks or leaks. As you begin to fill the cooling tower through the make-up water valve, you will want to observe and inspect the float valve assembly operation. All strainers and basket strainers should be removed and cleaned of any debris at this time, and should be replaced in proper working condition in the cooling tower. The float valve should fill the cooling tower up automatically to approximately one to two inches below the top of the overflow drain piping.
Once the tower has been filled with water, circulate water over the cooling tower fill for 24 to 48 hours. During this time, you should be physically inspecting the piping for any leaks or cracks. You will want to inspect the cooling tower distribution deck, removing any pipe chips or flakes that may block the distribution nozzles. If you have a BAC tower, inspect the spray nozzle dispersion patterns, so that the water spray is a conical shape over the fill media. Notice the cooling tower water basin level during water flow periods. Cooling tower water level in the basin should be maintained one or two inches below the top of the overflow drain piping. During periods of no flow, the cooling tower water in the basin should be approximately 1/2 inch below the top of the overflow drain piping. Cooling tower water should not overflow the drain during either of these two conditions. During idle periods of flow, there should be no water coming out of the make-up float valve. If any water flows, repair or adjust the float valve assembly.
After the first 48 hours, the cooling tower water may become dirty or discolored, and will need to be drained and refilled with fresh water. Also, at this time, the tower basin should be inspected again for any signs of dirt and debris that may have collected during the previous 48 hours. Once the tower has been refilled, this is a good time for your water treatment vendor to inspect and document the cooling tower condition. At this time, your water treatment vendor should be preparing you for the initial dosage of any sterilizing biocides that may be applied, and/or corrosion inhibitor application for threshold corrosion protection and metal preparation.
You now have a good start on a trouble-free cooling season as it relates to your critical component, the cooling tower. We suggest that you visually and physically inspect the cooling tower a minimum of once per week during the cooling season.