Trends in Food Science & Technology 20 (2009) S57eS59

Review

* Corresponding author.

0924-2244/$ - see front matter � 2009 Published by Elsevier Ltd.doi:10.1016/j.tifs.2009.01.017

Cleaning of dry

material handling

installations

Johan Roelsa,* and

Martin Stephanb

aJ-Tec Material Handling, Lieven Gevaertstraat 11,

2950 Kapellen, Belgium (Tel.: D32 2 6 60 53 43;

e-mail: johan.roels@j-tec.com)bCoperion GmbH, Niederbieger Str. 9, 88250

Weingarten, Germany (Tel.: +49 751 4 08 3 98; e-mail:

martin.stephan@coperion.com)

The food industry is constantly changing. On one hand,customers are getting more assertive and demanding, and thenumber of products on offer keeps growing. In practice, thismeans that companies have to find a way to deal with shorter‘change-over’ times and a need for increased flexibility.

On the other hand, there is a continual evolution in thefield of legislation and microbiological requirements.Food companies and their staff can be held responsible(because of new legislation) for inadmissible productsthat are sold to the consumer.

For these reasons, there is a tendency towards cleaningsystems that can be validated.

By this we mean a cleaning system that is verifiable,automatic and operator-independent.

It is crucial to take the decision whether to opt for a wetor dry cleaning procedure during the design phase. Experi-ence has shown that installations that were originally meantto be dry cleaned can cause problems (e.g. microbiologicalcontamination) when a wet cleaning procedure is applied.This is often because they do not meet the requirementsof hygienic design.

It is still highly recommended to focus on the possibilityof only using dry cleaning procedures. Introducing water inthe dry material handling area is a hazard from a foodsafety point of view. Wet spots in the process lines for pow-ders might be the source of microbiological proliferationand the possibility of product contamination.

However, depending on the products wet cleaning can-not always be avoided, e.g. the complete removal of aller-gens often requires a wet cleaning protocol.

Dry cleaningIf dry cleaning is chosen during the design phase, the

installation as a whole should never be cleaned with anaqueous solution. However, it is possible to disassemblethe components and subsequently have them wet cleanedat a different location.

If the choice has been made to clean the installationusing both dry and wet techniques, the dryewet boundaryhas to be established during the design phase. The designalso has to include the potential to effectively disconnectthe dry part from the wet part, so as to prevent dropletsor vapours from entering the dry zone.

Dry cleaning is hard to validate and a particular diffi-culty lies in the fact that dry cleaning is very operator-dependent. Most components that are dry cleaned cannotget an EHEDG certificate based on test protocols, asopposed to components that are used in the liquids industry.Adequate test methods on dry cleaning procedures do notexist (the components mentioned below are certified byEHEDG based on wet cleaning procedures).

Wet cleaningIn general, installations designed for liquids can be

cleaned in place (CIP). However, this is not true for mostdry material handling installations. Currently, most of thecomponents that are used do not meet the requirements(in terms of hygienic design) to be cleaned in place. Atpresent, there is little experience with cleaning in placeamong the manufacturers of dry material plants.

That is why the following practice has to be kept inmind when a powder needs to be dissolved into a liquid:‘‘Bring the liquid to the powder and not the other wayround.’’ In this way all the powder gets dissolved. If youbring powder to the liquid, powder residues might stay be-hind in the dry part of the system, rendering the cleaningmore difficult.

The development of CIP cleaning of equipment in thepowder industry is in its infancy, but progress is beingmade.

The components shown below demonstrate that a numberof steps have already been taken to perform a wet cleaningprocedure on equipment that is used for dry materials. A)

Fig. 1. A) CIP cleanable discharge station for FIBCs and bags (J-TEC Material Handling). B) Special attention has been given.

S58 J. Roels, M. Stephan / Trends in Food Science & Technology 20 (2009) S57eS59

shows a CIP cleanable discharge station for FIBCs (Flexi-ble Intermediate Bulk Containers) and bags (Fig. 1), B)

deals with a diverter in CIP execution (Fig. 2)and C) isa example of a rotary valve in CIP execution (Fig. 3).

Fig. 3. Rotary valve ZRD in CIP execution. The CIP execution of the valve is different from a standard ZRD rotary valve. A special sealing designbetween housing and side plate and at the inlet and outlet flange is installed. The shaft sealing also has a special air purged design. During cleaningthe purge air for the shaft sealing must be switched on, and supplied with a pressure higher than the pressure of the washing liquid in the rotary valveto prevent the washing liquid from entering into the sealing arrangement. The speed of the valve is adjusted according to the required flow of thecleaning liquid through the system. Both components, WYK in CIP execution and ZRD in CIP execution, were tested by the EHEDG. The suitability

for CIP cleaning is confirmed and certified by the EHEDG.

Fig. 2. Two-way diverter WYK in CIP execution (COPERION). Pulling back the conical rotor enlarges the narrow gap between rotor and housing, sothat the washing liquid reaches the whole rotor and inner area of the housing. The used washing liquid is drained on the backside of the rotor. Thisensures that the washing liquid together with the rinsed off product is conveyed out of the diverter valve. During the cleaning process, the diverter isswitched several times from straight through to divert and back. The rotor remains in the lifted position. After wet cleaning the whole plant includingthe diverter is dried with hot air (rotor remains in the lifted position). After drying, the rotor is pushed forward into the operating position and the plant

is ready for restart.

S59J. Roels, M. Stephan / Trends in Food Science & Technology 20 (2009) S57eS59

Johan Roels: Technical Sales Manager, J-Tec Material Handling. J-Tec is

specialized in the design and installation of equipment for the handling of

solids and liquids as well as turnkey projects, www.j-tec.com. Member of

EHEDG subgroup Dry Material Handling (Chairman: Karel Mager).

Martin Stephan: Senior product manager components, Coperion

Waeschle. Coperion Waeschle is the specialist for bulk materials plants

and components, www.coperion.com. Member of EHEDG subgroup Dry

Material Handling (Chairman: Karel Mager).