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Heat Exchanger World Europe 2022 Conference Series
By choosing the correct BPHE high turbulence is enabled leading to increase shear stress , hence mitigating fouling . Cleaning in place ( CIP ) can be used to remove fouling and scaling . With high flow cleaning , turbulence is created to increase cleaning efficiency . Another CIP method is reversed flow , in which the dirt is moved in the opposite direction of the normal flow . The use of detergents , for particulate fouling , and weak acids , for scaling , can be used to dissolve and loosen the blockage . Indicators showing when CIP is required are when the temperature difference is smaller than specified or when higher pressure drop than expected are observed over the BPHE . A 30 % or higher increase than the nominal value is seen as a reference for conducting a CIP . Before deciding to clean the BPHE , it is crucial to make sure that filters are clean , and pumps are functional to rule out any other options for an increase pressure drop and decreased temperature difference . CIP does not require disassembly of the heat exchanger and can be made at the installation site . It results in a uniform removal and lower overall operating cost . It has no risk of mechanical damage to the plates or gaskets and if fluids can pass through the BPHE , it is possible to effectively clean it .
Corrosion Corrosion is the term for a chemical or electrochemical reaction between a material , usually a metal , and its environment , which produces a deterioration of the material and its properties . Pitting and crevice corrosion are essentially the same phenomenon . Pitting appears on exposed surfaces , for example attacking stainless steel if the passive layer is damaged . The passive layer is a protective surface film that is formed spontaneously when stainless steel is exposed to air . The attack can be sudden and quickly cause leakage . Crevices occur in welds that fail to penetrate , in flange joints and under deposits on the steel surface . General corrosion is a deterioration distributed uniformly over a surface . It is more predictable than pitting ; if a device has corroded 0.1 mm in one year , it will most likely corrode 0.2 mm in two years . This unwanted occurrence that leads to a decreased product efficiency is governed by the choice of material , media and operating conditions . The material of the plates play an important role in whether corrosion will occur . Stainless steel is for instance sensitive to high chloride content and copper is sensitive to both high sulphate content and high conductivity .
Leaching or metal migration Leaching or metal migration is the release of metal ions from heat transfer surface into the media . The focus is on the effect that the released ions have on the quality of the media , as certain applications are affected by media degradation . Drinking water applications requires extreme cleanliness and has a lot of health-related guidelines . For applications where pure or deionised water is used , the purity of the water should not be affected and leaching need to be avoided at all costs . Copper ions negatively affect the heat transfer and lubrication properties of oils . Media degradation caused by metal migration affect the efficiency of the BPHE .
Cut-out showing the deposit of inorganic salt , also called scaling , that occurs at high wall temperature when the media and operating conditions are not properly controlled .
A way to attenuate corrosion and leaching is to apply chemical or mechanical treatment to the heat transfer media . Corrosion inhibitors , oxygen binding chemicals and traditional filtration can be used . Avoiding stagnation for longer time periods and monitoring but also controlling the water quality is helpful . Ensuring that the selected product is made of correct material or is using surface treatment will further help reduce corrosion and leaching .
Product solutions Coating the product with thin-film technology to seal the inner surfaces of the BPHE with a protective layer of SiO 2 enhances the resistance to corrosion , scaling and leaching . The ceramic nature of SWEP ’ s SiO 2 based Sealix ® layer , for example , improves corrosion stability and there are indications that the organic functionalities improve the surface behavior in terms of scaling . The metal leaching is significantly reduced by sealing the surfaces in contact with water and oil . These benefits are achieved without affecting the thermal and hydraulic performance . Using coatings opens doors to new markets where a BPHE can contribute to improving a system ’ s efficiency . With tap water applications a coating serves as protection against nickel leaching and reducing scaling . In district water it reduces the tendencies for scaling . Having a protective layer can allow the product to withstand aggressive media with chlorides up to 1000 ppm at 60 ° C , reduce scaling tendency , and offer enhanced corrosion protection , allowing the technology to be used in cooling tower applications . All-Stainless is another SWEP product that can be used with corrosive heat transfer media such as ammonia , deionised water , or biogas . This is used to circumvent copper corrosion as it leads to system failure and shorter lifetime . All-Stainless is an enabler when using deionized water systems with conductivity below I µ S / cm . It also helps against media with high sulphury such as biogas and it can be used in different oil applications as it prevents copper leaching into the oil . The pharmaceutical process industry may require extreme cleanliness and that contamination of metals is kept to minimum , making the All-Stainless a product of choice . www . heat-exchanger-world . com Heat Exchanger World February 2023
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