Fouling of heat exchangers is a problem in the dairy industry and costs billions of dollars every year. It has been studied extensively by researchers around the world, and a large number of studies are reported in the literature. This review focuses on the mechanisms of milk fouling, investigating the role of protein denaturation and aggregation as well as mass transfer. We also endeavor to review the effect of a number of factors which have been classified into 5 categories: (1) milk quality, (2) operating conditions, (3) type and characteristics of heat exchangers, (4) presence of microorganisms, and (5) transfer of location where fouling takes place. Different aspects have been discussed with the view of possible industrial applications and future direction for research. It may not be possible to alter the properties of milk since they are dependent on the source, collection schedule, season, and many other factors. Lowering the surface temperature and increasing the flow velocity tend to reduce fouling. Reducing the heat transfer surface roughness and wettability is likely to lower the tendency of the proteins to adsorb onto the surface. The use of newer technologies like microwave heating and ohmic heating is gaining momentum because these result in lower fouling; however, further research is required to realize their full potential. The presence of microorganisms creates problem. The situation gets worse when the microorganisms get released into the process stream. The location where fouling takes place is of paramount importance because controlling fouling within the heat exchanger may yield little benefit in case fouling starts taking place elsewhere in the plant.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1541-4337.2006.tb00080.x

A Critical Review of Milk Fouling in Heat Exchangers

Modified stainless steel surfaces targeted to reduce fouling - Evaluation of fouling by milk components

Part 1 Risks: Range of microbial risks in food processing Biofilm risks Pathogen resistance to sanitisers Aerosols as a contamination risk Consumer perceptions of risks from food. Part 2 Improving design: Improving building design Improving zoning within food processing plants Improving the design of floors Improving design of walls Improving the hygienic design of closed equipment, heating equipment, equipment handling dry materials, packaging equipment, electrical equipment, valves, pipes, pumps, sensors. Part 3 Improving hygiene management and methods: Risk assessment in hygiene management Good Manufacturing Practice (GMP) in the food industry The use of Standard Operating Procedures (SOPs) Managing risks from allergenic residues Managing contamination risks from food packaging materials Improving hygiene in food transportation Improving control of insects in food processing Improving cleaning in place (CIP) Improving cleaning out of place (COP) Improving cleaning of heat exchangers Improving cleaning of tanks Ozone decontamination in hygiene management Enzymatic cleaning in food processing Contamination routes and analysis in food processing environments Testing surface cleanability in food processing Improving the monitoring of fouling, cleaning and disinfection in closed process plant Improving surface sampling and detection of contamination Improving air sampling Testing effectiveness of disinfectants and sanitisers Traceability of disinfectants and sanitisers Improving hygiene auditing.

Handbook of Hygiene Control in the Food Industry

Fouling of food process plant surfaces and the subsequent cleaning needed is a significant industrial problem, and as the cost of water and chemical disposal increases, the problem is becoming more significant. Current literature on water-based cleaning is reviewed here according to the classification of 3 types of cleaning problems. By doing this, it is hoped that new knowledge can be highlighted applicable to improving industrial cleaning. (i) For type 1 deposits (that can be cleaned with water alone)—Cleaning time appears related to Reynolds number and surface shear stress. An increase in Reynolds number seems to decrease cleaning time. Cleaning temperatures greater than 50 °C do not appear beneficial. (ii) For type 2 deposits (biofilms)—Removal behavior of biofilms seems to be dependent on the microbial aging time on the surface. Keeping a material hydrated on a surface enables easier removal of it with water. a. Water rinsing: Temperature and wall shear stress have varied effects on removal. b. Chemical rinsing: Flow and temperature were seen to have the biggest effect at the start of cleaning, but contact time was more important as cleaning progressed at a given sodium hydroxide solution flow and temperature. (iii) For type 3 deposits (that require a cleaning chemical)—For specifically, protein-based systems excessive chemical forms a deposit difficult to remove. Increasing wall shear stress and temperature was most beneficial to cleaning rather than concentration. The action of temperature can reduce the use of a chemical for type 2 and type 3 soils. The findings suggest that the right combination of flow characteristics at a given temperature and concentration is crucial to achieving fast cleaning in all cases. There are a number of cleaning monitoring methods at various stages of commercialization that may be capable of monitoring bulk cleaning and cleaning at the surface. To optimize cleaning will require integration of measurement methods into the cleaning process.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/1541-4337.12000

Fouling and Cleaning Studies in the Food and Beverage Industry Classified by Cleaning Type

The effect of temperature and shear rate upon the aggregation of whey protein and its implications for milk fouling

Modified stainless steel surfaces targeted to reduce fouling––surface characterization

/pdf/on-the-respective-effect-of-the-surface-energy-and-micro-305ckd13ue.pdf

On the respective effect of the surface energy and micro-geometry in the cleaning ability of bare and coated steels

Cleaning of bare or coated stainless steel surfaces is investigated using some specific techniques for both particulate soil and oil removal. Particulate soil is removed from the surface by a water drop sliding, whereas oil is eliminated by shear flow of a commercial detergent. The cleanability performance is found to depend both on surface energy and topography. In general, the water contact angle hysteresis, which itself is related to the advancing contact angle and the surface roughness, is found to be an appropriate criterion for characterizing the cleaning performance. This finding is discussed in terms of retention and removal forces during the cleaning process and could provide in the future a criterion for material selection for industrial use of stainless steel surfaces.

Relation between the cleanability of bare or polysiloxane-coated stainless steels and their water contact angle hysteresis


 Renewables in the offshore space are integrated with technologies to deliver at-scale solutions for offshore green Hydrogen production and sustainable renewable energy. The system in the frame of the Deep Purple project consists of offshore wind turbines and offshore Hydrogen technologies for the production, storage and transportation of energy in the form of pressurized green Hydrogen. It can also be used to supply off-grid energy in remote locations, and to provide green Hydrogen for decarbonizing industrial processes.
 Within this context, subsea pipelines are needed to transport gaseous Hydrogen. Nevertheless, Hydrogen is well known for its ability to cause steel embrittlement and is also a non-usual gas within standard offshore Oil & Gas sector. For these reasons, caution has to be taken and suited qualification testing needs to be conducted to propose a reliable transportation solution.
 Flexible pipes represent an effective and versatile solution for conveying gaseous Hydrogen subsea from fixed or floating turbines or systems, in particular under dynamic conditions. Their intrinsic low allowable minimum bending radius, and tolerance to accommodate large relative motions, make this field proven solution in Oil & Gas infrastructures a perfect choice for floating offshore systems in shallow water areas targeted for deployment of offshore wind turbines with Hydrogen technologies. Furthermore, the efficient installation time and cost enable to envisage an extended use for the offshore green Hydrogen transportation systems. Finally, by construction, flexible pipes have their high strength steel wires in between two polymer sheathes, in a less severe, so-called annulus, environment. With this kind of solution, a very low part (< 1% of the flow) of the carried Hydrogen will permeate through the external polymer sheath but the high strength steels will be submitted to lowered Hydrogen pressures compared to bore, and might be used without any embrittlement risk.
 Within the frame of the present study, many materials used in flexible pipes for Oil & Gas application have been tested in presence of gaseous Hydrogen, in annulus (a few tens of bar) or in bore (a few hundred bar) conditions: different carbon steel grades, used as wires and connexion parts, 316L austenitic stainless steel and several polymer materials (polyethylene, thermoplastic elastomer, polyamide). It includes the following tests: Slow Strain Rate Tensile (SSRT), toughness, fatigue, crack propagation, four points bending, Rapid Gas Decompression (RGD) and ageing.
 Results allow to select materials compliant with the Hydrogen transport application and to acquire the data needed to perform the detailed engineering of the flexible pipe. Furthermore, they enable to establish the flexible pipe as a qualified and reliable solution for Hydrogen transportation, tolerating advantageously elevated hydrogen pressure.
 This work is likely one of the first to be discussing about the influence of Hydrogen on materials used in flexible pipes for subsea transportation and to highlight a qualified solution for such an Hydrogen carrier application.

Christelle Gabet

Papers

Modified stainless steel surfaces targeted to reduce fouling––surface characterization

On the respective effect of the surface energy and micro-geometry in the cleaning ability of bare and coated steels

Relation between the cleanability of bare or polysiloxane-coated stainless steels and their water contact angle hysteresis

Qualification of Flexible Pipes for Gaseous Hydrogen Transportation