Mixer Cleaning “It’s Important to Limit Cross Contamination” – Interview on Dry Mixer Cleaning

Editor: Dominik Stephan

When mixing sticky bulk solids, residues can be quite a challenge. They pose the threat of cross contamination or product impurities. Since rinsing mixer and screw with water and liquid cleaning agents bring unwanted moisture into the machine, dry cleaning methods can be an attrcative alternative. But also this approach poses several challenges – in a short interview with PROCESS Worldwide, Hendrik Freije, application engineer of Hosokawa Micron’s Food & Pharma team, talks about the Do’s and Dont’s of dry cleaning.

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Hendrik Freije of Hosokawa Micron BV, application Engineer of the company's Food & Pharma team: “Dry cleaning in between different batches has the advantage, that the user is certain that no water will be present during the mixing process.” (Picture: Hosokawa Micron)
Hendrik Freije of Hosokawa Micron BV, application Engineer of the company's Food & Pharma team: “Dry cleaning in between different batches has the advantage, that the user is certain that no water will be present during the mixing process.” (Picture: Hosokawa Micron)

Hendrik Freije, application engineer of Hosokawa Micron’s Food & Pharma team, talks about the Do’s and Dont’s of dry cleaning.

PROCESS: Mr. Freije, for what mixing applications do dry cleaning methods work best?

Freije: Dry cleaning is widely appreciated where many recipes are produced during the week, and also where it is important to limit cross contamination between batches to very low ppm levels.

PROCESS: What are the advantages of dry compared to wet cleaning?

Freije:Dry cleaning in between different batches has the advantage, that the user is certain that no water will be present during the mixing process. So creation of lumps in the product by water droplets can be avoided, as well as wet spots behind o-rings or gaskets. Another advantage is that wet cleaning creates large volumes of contaminated water (or other cleaning liquids) that have to be taken care of.

PROCESS: Do you consider an automatic dry “cleaning in place” (CIP) application possible?

Freije:Sometimes dry cleaning by means of air nozzles is employed, e.g. to blow away dust from the orbit arm or the mixing screw. But in general CIP by dry cleaning methods is extremely difficult, because deposits can show strong adherence bonds. It is also limited because a dust cloud will always be dispersed by the air nozzles that can not be removed to the full 100%. The majority of dry cleaning operations therefore involves manual labour.

PROCESS: Can dry cleaning methods be used for wet bulk products or moist residues, or does the presence of moisture eliminate the advantages of dry cleaning?

Freije:When a mixture contains free liquid, it is not advised to use dry cleaning. On the other hand, mixtures containing a small percentage of liquid can very well be dry cleaned.

More about dry cleaning? Read a profesional article on How to Optimize Dry Cleaning Methods for Bulk Residues in Mixers.

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