Femke Schaefer discusses what can be done to tackle the issues of capacity, noise, energy consumption, plot space, pollution and cross-winds in coolers
Many oil and gas applications rely on air-cooled coolers, particularly in areas where water-cooling is either not available or no longer allowed. In air-cooled coolers, the ambient air is used to cool (part of a) process. That is why coolers are always positioned outside. However, this also makes them more sensitive to factors that affect their capacity, such as cross-winds, pollution by dust and pollen, and air pollution. Furthermore, because they are situated outside, the noise of the fans result in coolers often being one of the greatest causes of noise in a process. Besides that, they take up a lot of space and consume a lot of energy. However, there are a number of solutions to these three problems – and even for all three problems at the same time.
Capacity problems due to pollution
Pollution of the bundles of tubes is a well-known problem that occurs everywhere where bundles are located close to trees, roads, agricultural land and cities – in other words, practically everywhere on land. And what if your bundle looks like the one in the photo? Well, you’ve probably long-since resigned yourself to the fact that your cooling capacity is limited or that it has become a bottleneck in your process, yet you need to find a solution fast because you have very little cooling capacity left! There are solutions, but they’re often temporary or they only clean the bundles on the outside (because deep cleaning is difficult), which means that your cooling capacity will still not be optimal and is likely to deteriorate again in the course of time anyway. But suppose there were some as yet unknown solutions that might yield unprecedented benefits? And suppose you could take them just that little bit further?
So then, let’s say you are the proud owner of some polluted bundles, as shown in the photo. This bundle evidently needs cleaning, and the most obvious way to do that would be to use water. However, if you don’t choose the right method (high-pressure water or foam on the inside of the machine), there is a good chance that you’ll only manage to clean the first row and not the rows behind. Added to that, the fins often get sprayed flat, and this actually reduces heat transfer. Other solutions are also possible, but many of them require the equipment to be switched off as it cannot be cleaned while the fans are still running. This could cost you a lot and is therefore an unappealing prospect for oil and gas projects, where downtimes can be considerably more costly than in other sectors.
Alternative solution
The alternative here is dry cleaning, which is ideal for induced and forced-draft cooling bundles. A special (non-toxic, biologically degradable) powder is sprayed on the bundles using low air pressure (5-6 bar), and in effect this blows the dirt off the fins. With this method, you no longer need to walk over the bundles, the fins remain undamaged, all the rows of fins are actually cleaned, and, if you use induced draft, you don’t even have to switch off the fans. Bronswerk recently managed and supervised a project whereby bundles were cleaned using this method. The result was a very satisfied and enthusiastic customer thanks to the efficient maintenance solution and the ultimate result, as shown in the second photo. The lower costs and increased effectiveness of the process added up to efficiency in terms of minimal downtime, greater reliability and availability and maximum output of the asset.
One step further
After dry cleaning, the cooling capacity returns to the desired level – that is, if you don’t take into account cross-winds or wind in general. The maximum wind speed at which an A-frame cooler is tested and which it must withstand to officially achieve the required capacity is 3m/s, which is almost no wind at all. Wind plays a major role in an A-frame as the pressure drop over the bundle – and therefore the air speeds – are relatively low. Many coolers (whether A-frames or not) are situated in areas where, during the summer months, capacity problems are caused by the high temperatures of the ambient air. Or they must comply with the stricter European regulations for noise and energy consumption that will come into effect in Germany, for example, in 2017. A number of Bronswerk’s customers are encountering these problems or combinations of these problems. A refinery in Germany even had to close its plant because it was unable to comply with the permitted noise levels with the equipment it was using at that time!
In these cases, the situation involves an existing plant, with existing coolers and usually limited plot space, and sometimes also limited capacity and cable diameters, all of which need to be taken into account to implement the desired or required improvements. Despite the considerable challenges, solutions do exist for situations of this kind. Using high efficiency cooling with the Whizz-Wheel fan, an existing plant can be retrofitted. The existing fan and part of the housing are replaced with the highly efficient Whizz-Wheel fans and specially designed inlet and control systems. With a retrofit, Bronswerk leaves the existing plant as it is, but the adjustment still brings about the desired or required changes. In terms of results achieved via such projects, at the abovementioned refinery, where the plant had to close temporarily due to noise restrictions, the company not only returned production to 100% but also realised unprecedented energy savings of 53%. In addition to this, in Bronswerk’s experience thus far, bundles under which a Whizz-Wheel is suspended are less sensitive to pollution and also cost less to maintain.
In summary
If you have capacity problems with your cooling equipment, the logical first step is to check the condition of the bundles. If there is dirt on the bundles (and this is often the cause, even if the dirt is not visible on the outside of the bundle), you can now safely and efficiently clean the bundles using Bronswerk’s dry cleaning method. This will be a vast improvement in itself, but if you aim to keep increasing the cooling capacity and want even less dirt in the future, the company also offers various retrofit options. Even more importantly, given the forthcoming regulations: if you are facing possible noise constraints and restrictions in your energy consumption, Bronswerk recommend checking your cooling equipment as an urgent priority.
Femke Schaefer is with Bronswerk.
For more information, visit www.engineerlive.com/iog
