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Hygienic Conveying How to Convey Hygienic Sensitive Bulk materials

| Author / Editor: Martin Stephan / Tobias Hüser

CIP–compliant rotary valves are especially required for pneumatic conveying in the food industry. Although the guidelines of EHEDG dictate how the systems should look like, at the end the requirements depend on the selected cleaning method. Read this article, how the implementation of these specifications can function.

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Fig. 1: Easily dismantled discharge valve type ZRD (hygienic version)
Fig. 1: Easily dismantled discharge valve type ZRD (hygienic version)
(Picture: Coperion)

When foods are processed, the individual products are subjected to a number of processes before the finished product is ready for distribution. When products are made by artisans, for example in a bakery, these processes are carried out in a small space and the ingredients are transported by hand from one stage to another. With the increase in industrial food production, the distances between the various process stages are becoming longer and the processes themselves are run continuously. This requires automated transport between the process steps.

Without Hygiene, No Enjoyment

There are a number of mechanical methods for handling this task such as conveying screws, transport belts, bucket conveyors and pneumatic conveying systems. Mechanical systems offer a high level of product conservation for the transport of fragile products, but require complex configurations and there is always the risk of product contamination caused by attrition generated by component wear. Hermetic sealing from the environment is also difficult.

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In contrast, a pneumatic conveying plant is a closed–circuit system with lower investment costs which only has mechanical components such as rotary valves at the supply or discharge points. The only disadvantage of pneumatic conveying is the often lower efficiency in comparison to a mechanical system. The advantages outweigh the disadvantages when non–fragile products are transported, which is why a pneumatic conveying system is often selected.

Cleaning Decides on Plant Design

However, several points must be observed for hygienic plant design when planning a pneumatic conveying system and these key components. First, the cleaning process that is to be used for this system section must be specified, as the selected cleaning method influences the design and construction. This aspect can best be described by using the flange connections as an example.

A centred flange connection with an O-ring seal is very suitable for dry cleaning, but not for wet cleaning. A flange connection that is suitable for wet cleaning must be equipped with a seal that is flush at the front to prevent penetration of capillary water into the metal to metal connection which occurs with an O–ring seal. This and other basic requirements for hygienic design are described in the guidelines of the EHEDG and illustrated with examples.

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