At ECEX, we’re always looking for ways to improve plant efficiency and ensure the longest possible life out of any equipment we supply. This interesting article was posted by Randy Simmons, Vice President of Air Solution Company; a company that specialise in air filtration from across the pond. It’s longer than the articles we usually post, but definitely worth it!
How a Legionella Tragedy Can Happen
Interestingly, when someone becomes ill from an unsafe cooling tower it most often is not the result of a company’s blatant negligence. You might be surprised to hear that typically, the cause usually originates from a company having not understood the need for their water treatment program to be in alignment with an effective debris management and cooling tower maintenance program.
If the amount of debris inside a cooling tower exceeds the established biocide dosage, the demand placed upon the dosage will quickly be consumed, having little impact on the bioactivity.
Remember: Cooling towers are highly efficient air scrubbers; anything drifting past a cooling tower is likely to get caught in its draft and be sucked-in. When organic debris such as seed, leaves, insects, pollen, grass, birds and their droppings, etc. get into the water and decompose, they create a nutrient rich environment for bacterial growth, including Legionella.
It’s important to recognise that if the volume of decomposing debris exceeds the chemical dosage’s ability to provide control, the cooling tower will silently grow dangerous, even while chemical dosing continues. It is easy for companies to develop a false sense of security that their cooling towers are safe either because they are treating the water themselves or because they’ve hired water treatment services to establish dosage levels that should ensure the tower is safe. In either case, if organic debris management isn’t in alignment with water treatment dosage levels and made integral to the maintenance process, there is an increased probability of the tower becoming a health and safety hazard. It doesn’t matter how large or small the company or cooling tower is; bacteria, including Legionella, doesn’t discriminate; it thrives in any poorly managed cooling tower!
An Obvious Question
“What is the required ratio of water treatment chemicals to debris load inside the cooling tower in order to ensure cooling tower safety?”
The answer isn’t as clear as the question might suggest. Organic debris is drawn into cooling towers in different concentrations depending upon location and time of year. Every type of debris places a different demand upon the biocides and scale inhibitors being dosed into the water; therefore, there is no known ratio that will hold constant for every cooling tower. However, it is safe to say that if you don’t deploy diligent maintenance procedures that specifically call for the prevention of organic debris from getting into the cooling tower or its periodic removal, more water treatment chemicals will be required to keep it safe.
Adding chemicals to offset poor maintenance practices however is a shortcut that will do little to prevent fouling and clogging of the fill, strainers, blow-down valves, chiller and heat exchangers. This will ultimately lead to health and safety issues, along with a reduction in equipment performance. Although the answer to the chemical ratio to debris question isn’t apparent, the answer to how to keep a safe cooling tower is crystal clear:
Keep the cooling tower free from debris and deploy a good water treatment program and your cooling tower will operate safely and efficiently.
This may sound like over simplification, but if you keep the debris out of the cooling tower, you will break the bacteria-supporting food chain. Additionally, when you chemically treat the water you create an environment non-conducive to bacteria habitation. In short, when you eliminate food and shelter for bacteria, it won’t take-up residence in your cooling tower!
How to Keep a Safe Cooling Tower
Although L8 ACOP and associated guidelines are excellent, companies must ultimately weigh the operational and economic realities of any maintenance procedure they deploy. As the old saying goes “There’s more than one way to skin a cat”. If on the one hand maintenance procedures are too frequent, cumbersome or complex, it commonly results in more downtime, lost productivity and higher maintenance costs. Conversely, if the intervals between maintenance are too long, it may be more cost effective, but the condition of the cooling tower at each interval may be less than desirable and potentially place maintenance workers, employees, tenants and the public at risk. So the answer lies somewhere in the middle, at the point where water treatment and debris management in the tower come together.
Companies have many options available to them for managing debris; including a variety of water-based filtration technologies and air intake filtration technology. Water filtration can help manage water-borne and other debris after it gets into the cooling water while Air intake filtration technology is highly effective at stopping airborne debris from getting into the tower by filtering the air as it enters the system. Furthermore, air intake filtration can be used in glycol based cooling systems and on other air-cooled condenser systems to keep airborne debris out of the coils enabling optimal cooling efficiency.
When determining what maintenance and debris management technology to use, it is important to first determine what the source of debris is. If the source is water-borne, water filtration in combination with a good water treatment programme is typically the best solution to protect the chiller and heat exchanger from scaling and fouling. If on the other hand, the source of debris is airborne, then water filtration systems will not stop the debris from getting into the cooling tower (especially the fill). As such, the best solution for prevention debris from getting into the system by using air intake filtration technology to filter the air as it enters the system. Air intake filtration in combination with a good water treatment program is highly effective in stopping the debris that clogs strainers, blow-down valves, fill, chillers and heat exchangers.
In short, air intake filtration effectively protects the entire system. In extreme cases where both waterborne and airborne debris is problematic, both air intake filtration and water filtration in combination with a good water treatment program may be required in order to keep the cooling tower safe and operating efficiently.
Consider the costs of a sick tower
Companies that don’t take appropriate precautions and insist upon diligent cooling tower maintenance procedures not only place their employees’ health and safety at risk, but also their business and reputation. Consider the cost of a single cooling tower related Legionella incident:
In comparison to the cost of a proactive maintenance initiative, the incidents listed above when considered individually or collectively carry staggering cost.
It Doesn’t Take Rocket Science
It simply requires that companies using cooling towers initiate proactive and on-going maintenance procedures that align effective debris management technology with effective water testing and treatment techniques. When these elements are in alignment, the result is a safe, healthy and efficient operation.
Randy Simmons is VP at Air Solution Company, Commerce Township, MI. a manufacturer of air intake filtration solutions. Visit their website at www.airsolutioncompany.com.
For the ecex web page and case studies please see
http://www.ecex.co.uk/ladders.asp
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