How To: Controlling Biofilm in Cooling Towers
Controlling biofilm in cooling towers is the priority of any property owner. Biofilm robs your system of it’s efficiency and left unchecked can lead to the development of bacteria. Other than the specter of MIC eating on the metallic parts of your cooling system, aggregations of biofilms additionally repress heat transfer in the condenser tubes and can gather on cooling tower fill to the point where it can crumple the fill support and make serious damage to the cooling tower.
How To Control Biolfilm
The way to keep up control over microbiological populaces in power plant cooling water is to give a steady level of treatment consistently. That is, the treatment should be reliably powerful. The real convergences of biocide required to give this level of treatment may change essentially, contingent upon cooling water conditions and nature.
Some power plants find that they can stun treat the cooling water system for an hour daily amid the greater part of the year and slice back to a few times per week amid the winter while still appropriately controlling biofouling in their system. Other power plants do not just require every day or even consistent bolster of dye, yet additionally need to include extra nonoxidizing biocides amid the midyear months.
Oxidizing Biocide
The most widely recognized strategy for establishing that you are adding adequate oxidizing biocide to control microbiological fouling is the free chlorine test. This is a base and ought to be performed amid every chlorination cycle, or day by day for those that ceaselessly chlorinate. As conditions change the measure of blanch required to create the coveted free accessible chlorine leftover will change, and the plant ought to react by expanding or diminishing the biocide nourish rate likewise. Note that oxidation diminishment potential (ORP) isn’t a decent sign of microbiological control in cooling water. ORP is not a viable replacement for testing free accessible chlorine.
The Role of Chlorine
Getting the Full Benefit from Chlorine. A full exchange of the different sorts of biocides and advancing methodologies for their utilization is past the extent of this article. In any case, it is great to say a couple of words in regards to the most widely recognized biocide utilized as a part of energy plants: chlorine.
Already, the most widely recognized wellspring of chlorine was chlorine gas delivered to control plants as a dense fluid in 1-ton chambers. It was dissipated and cleared into the cooling water lines as a gas. At the point when chlorine gas broke down in water, it shaped hydrochloric corrosive and hypochlorous corrosive. The hydrochloric corrosive brought down the cooling water pH somewhat, which improved the impact of hypochlorous corrosive as a biocide. Evident worries about security were the essential reason that power plants moved far from the utilization of 1-ton chlorine barrels to sodium hypochlorite commercial bleach conveyance.
Commercial bleach can be commonly provided at 10% or 12.5% chlorine. 1 lb of chlorine gas will make 0.74 lb of hypochlorousacid, while 1 gallon of 12.5% bleach can possibly create 0.875 pounds of hypochlorous acid, if there is adequate hydrogen particle in the cooling water to shape the acid.
Commercial bleach is produced by gurgling chlorine gas into a scathing arrangement. Some additional scathing intentionally stays in the sanitizer to moderate the decay of hypochlorite to chlorates. The run of the mill pH of commercial bleach is near 11.5 and 13.5. Bleach arrangements that have a pH of 11 or less deteriorate quickly.
So the use of chlorine gas when compared to the use of bleach has the potential to increase the pH of cooling water. It has been stated that hypochlorous acid is more effective as a biocide than the hypochlorite ion. Thus, bleach loses its activity as a biocide in high pH cooling waters.
Sodium Hypochlorite Solutions
Sodium hypochlorite solutions will begin to decompose the minute they are created. They decompose along with 2 chemical pathways: by forming chlorate and by releasing oxygen. In quality hypochlorite solutions, the formation of chlorate is the main pathway. A variety of factors may accelerate the decomposition of bleach. The most critical are exposure to UV radiation, concentration, temperature, and time.
- Bleach will decompose over time. It is calculated that 90F storage, a 10% bleach solution will lose half of the effective hypochlorite concentration in 95 days. You may use a tank of bleach in a few weeks, you may want to ask the supplier how long it has been in storage before arriving at your facility.
- In just 60 days at 68F storage, bleach will lose 17% of the hypochlorite, where at 90F it will lose 55%. The temperature needs to be a consideration in placing a hypochlorite storage tank.
- UV Radiation. UV rays from sunlight can decompose bleach solutions. Your bleach tanks need to be made from UV resistant materials or coated in a way that it will exclude UV light or place them inside.
- The more concentrated the bleach solution is, the faster it will decompose. If your site is not a big bleach use, it may be best to stick with a 10% bleach solution instead of a higher concentration.
Other factors that will have an effect on the decomposition rate will include concentration of chlorides, and transition metals that may get into the bleach from caustic that was used in the manufacture or in the piping and tank materials where the bleach is stored. The nickel level in bleach needs to be less than 0.1 mg per 1 and copper needs to be less than 1 mg per 1.
Testing Bulk Chemicals
It is essential to test Bulk Chemicals. It becomes the chemistry personnel to check the hypochlorite concentration in every shipment of blanch before it is offloaded into their tank. One plant addressed why it was all of a sudden not accomplishing a free accessible chlorine remaining in its cooling water, as it had previously. A check of the detergent mass tank found that the fixation in the tank was just 2.5% dye. Clearly, the past dye conveyance was not the 10% dye the provider asserted it was. Basic hypochlorite test packs are accessible for this reason.
Avoid Bromine in Towers
Bromine Is Not a Biocide. At times I hear individuals alluding to their cooling water science as “bromine” science. Bromine is a rosy dark colored gas and exceptionally lethal (like its neighbor in the intermittent table—chlorine gas). Isn’t something that ought to ever be created at a power plant. The utilization of sodium bromide to improve the biocidal properties of blanch at higher cooling water pH esteems, in any case, is extremely normal.
It is vital to remember that sodium bromide isn’t a biocide. It is a simple salt that has no biocidal properties. It will only have them it has reacted with hypochlorous acid properly and not bleach that will form the hypobromous acid, which will be the desired biocide.
Stabilized hypobromous acid is also available at various chemical vendors. This helps to eliminate the need to mix sodium bromide and bleach on site. However,it will be more expensive to purchase the stabilized hypobromous acid than to make it.
Cooling Tower Maintenance & Repair
If you own or operate a facility in the Phoenix Valley that needs cooling tower maintenance or repair we can help! All Kote Lining, Inc. specializes in cooling tower repair and refurbishment. A big part of cooling tower maintenance is controlling and removing biofilm. If you’ve got a cooling tower that needs some attention, give us a call. We also provide chiller repair & maintenance and tank coating services.
Call today to schedule an appointment – 480-966-4446