Increasing adoption of automation and smart technology solutions means that preventative maintenance is growing in popularity in the UK. Yet though it is a precision-engineered piece of equipment, the humble plate heat exchanger (PHE) still tends to be overlooked, despite needing a proactive and considered maintenance strategy to operate at the best possible level (see also report, www.is.gd/laxihe).
Indeed, numerous problems can arise if such a strategy is not in place. Leakage, fouling and corrosion, can in turn lead to further problems, such as poorly-sealed units, clogged or cracked plates. Failures like these, together with unwanted deposits, can negatively affect heat transfer efficiency, meaning more energy is required for processing applications. The added power required may also lead to company operations impacting the environment in a way that would be easily avoidable if not for poor or infrequent PHE maintenance.
Reactive maintenance is often seen as an effective method of keeping costs down. Sometimes known as ‘run-to-failure,’ the immediate savings such a strategy can help realise are ultimately illusory, and can hamper a business’s efforts to be competitive. A primary reason for this is that it is difficult to anticipate unplanned downtime resulting from equipment failure.
There are four main types of PHE: gasketed, brazed, welded, and semi-welded. As far as compact heat exchangers are concerned, gasketed plate heat exchangers (GPHEs) are the most popular model due to their large surface areas, which allow for high efficiency rates. They are used in chemical production, heat and cooling applications, and food and drink processing.
Elastometric gaskets are fitted to a GPHE’s the metal plates, sealing and directing each fluid into alternate channels. Hot channels are placed against cool channels with each fluid flowing counter or co-currently to facilitate thermal transfer.
Though GPHEs are reliable and resilient, they can still suffer issues caused by the intensity of the heat transfer process. Without regular maintenance, the exchanger’s performance, lifetime and output will decrease, and could negatively impact other connected assets.
For example, despite being made of durable metal, a GPHE will naturally corrode over time, most commonly along the edges of each plate. This crevice corrosion, which occurs under the exchanger’s gaskets due to extensive sealing requirements, could be exacerbated by chemicals released from the polymers used to make gaskets.
It is also important to point out that these polymer gaskets deteriorate over time too. A number of factors can be responsible for this, including incompatible fluids being heated to maximum temperatures for prolonged periods, overly high pressure and exposure to UV light, and all of which can negatively impact performance.
An additional concern is fouling, which is caused by the settlement of particulates, biological matter, formation of scale, decomposition and crystallisation. The type of fouling experienced hinges on the GPHE’s design, process fluid used and how often the exchanger is cleaned. Without a proactive maintenance programme, even a basic water exchange can be hampered by this issue.
The insulating layer created by these unwanted, settled deposits can disrupt heat transfer efficiency between two fluids. In turn, this will impact pumps and essential equipment connected to the unit, causing either under-or-over performance in processes elsewhere, resulting in added costs. The leakages caused by corrosion may also lead to potentially harmful heavy metals being unintentionally released into the environment.
Concerns like these make it clear that keeping a plate exchanger clean should not just be desirable – it should be necessary. Doing so is highly beneficial and should be seen as ‘low-hanging fruit’ for companies looking to improve overall sustainability. In fact, a 2015 academic report (www.is.gd/qexoxi) highlighted numerous studies identifying that heat exchanger fouling may be responsible for 1-2.5% of global CO2 emissions.
It is only through a considered maintenance strategy, informed by technical expertise, that engineers can help realise higher yields and more efficient energy consumption.