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HEAT TRANSFER RETHINK YOUR MAINTENANCE STRATEGY
Andrew Peacock, from Alfa Laval, explains the consequences of ‘run to failure’ and the steps you can take to avoid them
he notion of doing more with less has never been so prevalent across industry. As such, it’s easy to see why many process engineers might think they have no other choice than to run equipment to failure. However, the consequences of taking such an approach could be catastrophic for businesses at such a critical time, particularly as the crisis appears to have been a catalyst for improving sustainability.
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While uptake of preventative maintenance has appeared to be slower in the UK, advancing automation and smart technology is beginning to curb that trend. Nevertheless, the humble plate heat exchanger is still often overlooked despite being a precision-engineered piece of equipment requiring a considered and proactive maintenance strategy. There are a number of issues that can originate from poor or infrequent maintenance of plate heat exchangers, including fouling, corrosion and leakage, which can lead to clogged or cracked plates, or poorly sealed units. All such failures and unwanted deposits can impact efficiency of heat transfer, increasing energy requirements for processing..
Reactive maintenance, sometimes known as ‘run to failure’, is a common strategy for driving down costs. While useful in some cases, its limitations often make it a false economy for businesses in the long-term. This is for a number of reasons. First of all, it can be difficult to manage maintenance budgets effectively, resulting in businesses
paying a premium for repairs. It can also be difficult to know what is causing issues and essentially lead to further problems, endangering staff health and safety. Additionally, unplanned downtime remains an unwanted challenge in any industry. There are four main types of PHE: gasketed,
brazed, welded, and semi-welded. Gasketed plate heat exchangers (GPHEs) are the most common. In a GPHE, the metal plates are fitted with elastomeric gaskets which seal and direct each fluid into alternate channels. Hot channels are placed against cool channels with each fluid flowing counter or co-currently to facilitate thermal transfer. GPHEs are efficient and offer a large surface area. GPHEs are durable, but they still encounter difficulties. For instance, the intensive nature of the heat transfer process means that, if it is left unchecked, it will eventually affect an asset’s performance, output and expected lifetime, and may have knock-on effects to other connected assets.
As referenced earlier, fouling is caused by the settlement of particulates, biological matter, formation of scale, decomposition and crystallisation. The type of fouling that occurs will depend on the process fluid, design of GPHE and how often cleaning takes place, with even the most basic water exchange presenting issues.
Despite the robustness of metals used on GPHEs, corrosion is also an inevitable concern over time. Indeed, because they require extensive sealing along the edges of each plate crevice, corrosion may eventually
Andrew Peacock, service manager, Energy Division UK & Ireland at Alfa Laval: ‘The impact of a clean GPHE can be felt throughout the entire production process, but complacency will only lead to further problems
appear under the exchanger’s gaskets. In addition, polymer gaskets can also perish over time for various reasons. No materials are entirely invincible, which is why material choice is crucial.
The unwanted deposits mentioned earlier can also create an insulating layer that lowers the efficiency of heat transfer between two fluids. This can have an impact on pumps and other essential equipment connected to the unit. In turn this will cause other elements to over or under perform and ultimately increase costs.
Additionally, corrosion can cause leakages and the unintentional release of heavy metals into the environment. In Alfa Laval’s opinion, keeping a plate heat exchanger (PHE) clean has a wealth of benefits for companies including those pursuing sustainability goals. Most notably, an academic report from 2015 stated that numerous studies have shown that heat exchanger fouling may be responsible for 1- 2.5% of global CO2 emissions. Higher yields and efficient energy consumption are only possible with a considered maintenance strategy that is underpinned by technical expertise. Expert servicing should be treated as a ‘marginal gain’ for companies looking to boost the sustainability and efficiency of their operations. Uninterrupted service is vital in a time when margins continue to recede and markets fall foul of commoditisation.
Alfa Laval
www.alfalaval.co.uk/fitforduty
DECEMBER 2020/JANUARY 2021 | PROCESS & CONTROL 47
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