Published on: November 18, 2020|
Ben Green, Food and Water Division Manager of Alfa Laval UK and Ireland, discussed in depth why many plate heat exchangers (PHE) are not suitable for "on duty".
Ben Green discusses the problems surrounding plate heat exchangers and why they waste the profits of food manufacturers
As one of the fastest growing industries in the world, downtime and product damage are not options at all for food and beverage companies that aim to be efficient, responsible and competitive. However, advancing at this speed is not without challenges, which means that some basic principles are often overlooked.
It is estimated that the thousands of plate heat exchangers (all brands and sizes) in operation are not fully optimized, which may consume the energy of the enterprise unnecessarily. In addition, although the plate radiator is a precision-designed device that requires a well-thought-out active maintenance strategy, it is still often overlooked.
There are four main types of plate heat exchangers: gasketed, brazed, welded and semi-welded. The gasket plate heat exchanger (GPHE) is the most common compact heat exchanger used in food and beverage processing. In GPHE, the metal plates are equipped with elastic gaskets that seal and guide each fluid into alternating channels. Place the hot aisle and the cold aisle opposite to each other so that each fluid flows in the opposite direction or in parallel to promote heat transfer. GPHE is highly praised for its large surface area and high efficiency.
Ironically, the main cause of the problem is the solution. As the industry progresses and adopts more and more advanced technologies, this may bring unintended consequences. The fouling and cleaning of the plate heat exchanger is this way. In recent years, the heat exchanger industry has discovered a series of new challenges.
For example, the diversification of food and beverages has led to an increase in natural products, which has brought about changes in heat transfer challenges. Compared with sugar and other tried and tested ingredients, certain natural products are less tolerant of heat.
The pace of change and the rate of population growth mean that the food and beverage industry must expand factories to handle greater production capacity. At the same time, it must produce more products with as little downtime as possible-this inevitably increases the risk of failure and unintended consequences.
The fouling of GPHE is
. It is caused by particle sedimentation, biological material, decomposition and crystallization. The type of fouling depends on the process fluid, the design of the GPHE, and the frequency of cleaning.
The main cause of fouling depends on the flow pattern of the substance. However, if the GPHE is not specified correctly or is not regularly maintained, the flow rate of the substance may slow down or even sometimes not flow at all. This can cause major problems.
Over the years, there have been many researches aimed at helping to reduce fouling of plate heat exchangers used in food processing and technological development in the field of cleaning technology. For example, one study looked at scaling conditions that are common in the dairy industry, especially the pasteurization process. It further studies the joint chemicals that play a role in the accumulation of whey protein deposits.
Unfortunately, the relationship between the accumulation of protein fouling deposits and the chemical reactions that occur in the fouling solution remains unclear.
Corrosion is a big problem of plate heat exchangers, so the choice of materials is very important
Another study looked at the effects of the most relevant industrial operating parameters on the use of optical inspection methods and sudden expansion of the flow channel to remove the baked egg yolk layer.
Studies have shown that temperature is the most relevant parameter, but in particular sodium hydroxide at a concentration of 1.5 wt% shows an adverse effect. The combination of process parameters affects the type of removal.
Another paper attempted to link the mechanism of dairy product scaling with the chemical reaction of denaturation that occurs in bulk, to help propose innovative control measures to limit the formation of scale deposits.
It can be clearly seen from each study that once fouling occurs, it is very difficult to completely remove the fouling, which of course will increase the downtime. The best way is to reduce the possibility of scaling first.
The risk of GPHE failure will not stop due to scaling. Corrosion and gasket failure are also the main hazards of operation. Despite its sturdiness and durability, corrosion is still an inevitable result of metal use over time. GPHE requires extensive sealing along the edges of each board, so crevice corrosion may occur under the gasket. Chemicals released from the polymers used to make gaskets can exacerbate localized corrosion.
In addition to the above process, polymer gaskets will disappear over time. Whether it is due to ultraviolet light that affects performance, or heating incompatible fluids to the highest temperature or excessive pressure for a long time, no material can be completely invincible, which is why material selection is so important.
Harmful deposits discovered earlier can form an insulating layer, which reduces the efficiency of heat transfer between the two fluids, and corrosion can cause leakage and unintentional release of heavy metals into the environment. in
Opinions believe that keeping the plate heat exchanger (PHE) clean has many benefits for the company and should be regarded as the "low threshold" for achieving global sustainability goals. Most notably, a 2015 academic report pointed out that a large number of studies have shown that heat exchanger fouling may account for 1% to 2.5% of global CO2 emissions.
Passive maintenance (sometimes called "failure run") is a common strategy to reduce costs. Although useful in certain situations, its limitations ultimately make it a false economy for companies that want to gain a long-term competitive advantage. Effectively managing maintenance budgets can be difficult and can mean paying for a certain amount of maintenance
It may also be difficult to know what caused the problem, and fundamentally cause further problems, and pose a threat to the health and safety of personnel. Unplanned downtime is certainly an undesirable challenge in any industry-process engineers don't want to bear the brunt, especially if profits are affected by production losses.
Only through thoughtful maintenance strategies based on professional technology can higher output and effective energy consumption be achieved. However, perhaps one of the most eye-catching considerations is that if service evidence is not obvious, food and beverage companies may become victims of insurance companies, because insurance companies are unlikely to pay for bulk pollution caused by leaks.
Expert services can be regarded as "marginal benefits." When profit margins continue to fall and the market is easily commoditized, the ability to ensure uninterrupted service is crucial. However, unlike other incremental improvements, the impact of clean GPHE can be felt throughout the production process. Complacency will only lead to further problems.
Ben Green is the head of Alfa Laval's food and water sector in the UK and Ireland and has worked in the food and beverage industry for more than 20 years. Ben has a deep understanding of customer processes and challenges, and has spent many years providing customers with important business advice on servicing and repairing Alfa Laval's Fluid Handling, GPHE and Decanter products.
November 18, 2020
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