If you are an engineer or facilities manager with a cooling tower, you will already be aware of the challenges of managing this type of system safely. Most of the info you need is here in a very usable format. www.hse.gov.uk/pubns/priced/hsg274part1.pdf
WHY IS CLEANING IMPORTANT?
From a compliance point of view, the most important reason is to reduce the risk of legionnaire’s disease. Failure to control this risk by having a dirty system can be a serious issue and can even result in a prosecution. But there are many other important factors which are often overlooked:
- Dirt, sediment and fouling in the water will reduce plant performance and heat exchange efficiency – ultimately this means the system works harder and uses more fuel – this means higher bills.
- Dirt in the water will also reduce the effectiveness of the expensive water treatment chemicals you are using – corrosion inhibitors, biocides etc will all work less well in a dirty system – which means you use more, which costs you more….
HOW OFTEN TO CLEAN?
Evaporative cooling systems are open to the air and so inevitably become contaminated by airbourne particles either from the site’s process, or even from a neighbouring site. So, at some point they always need cleaning – but how often?
This depends on how dirty the system gets, and how quickly. You need to clean the system if your inspection shows it to be needed, but as the cleaning process is disruptive its better to plan the cleaning in advance based on knowledge of the system.
HOW TO INSPECT THE SYSTEM
As most operators of evaporative cooling systems carry out regular planned cleaning, regular inspection is often overlooked. This causes several problems:
How do you know you are cleaning often enough? A good programme of thorough inspection could show that you need to clean more often – or less, which would be a saving in time, disruption, and money.
You may be limited how much of the system you can see when it is running but most systems will run ok with the fans and/or pumps off for a short time – long enough for a visual check inside the tower. Look at the quality of water in the sump – it should be clear. Is the pack clean and free from scale deposits? Are there signs of corrosion inside the tower? Can you see any biofilm? Can you access the drift eliminators – if possible, lift and/or remove in order to inspect.
A more detailed inspection should be possible during a period of shutdown. These are busy times for most sites but its worth spending the time so that you can be sure that your cleaning programme is right for you. For a better view of hard-to-reach areas, you could use a borescope.
HOW CLEAN IS CLEAN?
If you’re not sure how clean your systems have to be, take a look at page 33 of the HSE guidance where there are photos to guide you.
HOW TO CLEAN AND DISINFECT
So, you’ve inspected the system as much as possible and it seems dirty. You will need to clean and disinfect it.
It’s worth taking the time to look closely at the method you are going to use to clean the system (or are currently using). Its often the case that systems are cleaned the same way year after year just because ‘that’s the way it’s always been done’. Every system is different and needs its own planned approach.
Once the cleaning work is completed, a follow up inspection will tell you how quickly the system is becoming fouled again.
IDENTIFYING THE PROBLEM
Once you’ve cleaned the system, we would recommend inspecting immediately afterwards – otherwise how do you know whether the method you used was effective?
Following the cleaning – invest some time in understanding how the fouling happened:
- Once you know what’s causing the fouling, you can usually find a cost-effective solution:
- Install filtration – a simple side stream filter can make a huge difference to the water
- If scale is forming in the system – install a water softener. Low cost and very effective.
- Biofilm problems can be reduced by changing biocide dosing – are the chemicals you are using actually working?
- Is there contamination (usually oil/grease/product) coming from the process? If so, can this be reduced?
- Corrosion issues can be complicated but there are a number of strategies to help.
IN SUMMARY, OUR SUGGESTIONS ARE
- Find out whether you have dirt or fouling problems by inspecting the system.
- Review the guidance and decide whether your system needs cleaning (and how urgently)
- Plan the cleaning work carefully – and inspect the system afterwards
- Put a programme of regular cleaning in place
- Congratulate yourself and enjoy the peace of mind!