Cleaning of powder handling equipment

Process plants operators may have to open and clean inside their equipment sometimes. It is particularly the case in food processing industry. This page is focusing in giving information for engineers working in such an environment and looking for best practices to clean equipment. It is assumed that the bulk materials handled are not hazardous (otherwise specific precautions for the health of the operators would have to be taken, which is outside of the scope of this webpage).

There are 2 different methods for cleaning powder handling equipment : dry and (controlled) wet cleaning. When operating a dry process, dry cleaning, which is inherently safer from a food safety point of view, should be prioritized. However wet cleaning may be required in some circumstances although it should be implemented with a lot of precautions.

1. Dry cleaning

Dry cleaning is a crucial process in maintaining powder-handling equipment such as mixers, hoppers, and bag tipping units. This method focuses on removing powder residues without the use of water or liquid cleaning agents, which can complicate the cleaning process and lead to extended drying times. Here’s an overview of dry cleaning, how to perform it, the tools required, and best practices.

1.1 What is Dry Cleaning ?

Dry cleaning involves using mechanical means to remove powder residues from equipment surfaces. This excludes the use of any liquid to clean (water of course, but also other kind of detergents). The absence of water will ensure that the risk of micro growth is minimized.

1.2 How to Perform Dry Cleaning

1. Preparation :

• Ensure that all personnel are equipped with appropriate personal protective equipment (PPE) such as gloves and masks.
• Lock out tag out the power source, and ensure equipment is safe to clean.

2. Removal of powder :

• Use a vacuum cleaner designed for powders to remove loose material from the equipment.
• For larger particles or stubborn residues, use brushes or scrapers to dislodge them, then vacuum clean the material dislodged. However when using tools, caution must be taken not to damage the equipment or the tools, which could create foreign bodies.

3. Final Inspection :

• Conduct a visual inspection of the equipment to ensure all residues have been removed.
• Consider swab testing if necessary to verify cleanliness, especially when handling allergenic powders.

1.3 Tools for Dry Cleaning

• Industrial Vacuum cleaners: Specialized vacuums designed for powders can effectively collect loose residues without creating dust.

• Brushes and Scrapers: Manual tools for dislodging stubborn residues from surfaces.

1.4 Best Practices for Dry Cleaning

1. Regular Cleaning Schedule : Establish a routine cleaning schedule based on usage frequency and type of powder handled. Immediate cleaning after use is ideal especially if the air conditions are not well controlled which could lead to powder pick up moisture and stick.

2. Design Considerations : Use equipment designed for easy access and minimal dead zones where powder can accumulate. Smooth surfaces and removable parts facilitate easier cleaning.

3. Have the right tools : industrial vacuum cleaners are very effective however they are costly which means that factories may not wish to buy them or minimize their number. This is not a good idea as the investment in good vacuum cleaners will pay by itself through quicker, safer, and more effective cleaning. (hence less prone to leading to cross contamination and product recall). It is also extremely important to define tools that are dedicated to the inside of the equipment, for example using a color code to make sure operators always use the tools dedicated for the inside for this purpose. This last recommendation is critical to avoid introducing microbial contamination inside the equipment.

4. Have the proper zoning in place : this is in general key in every facility producing food, but it is key to ensure the zone is declared dry and that nobody can bring water inside (including coming in with moist shoes for instance)

5. Training Personnel : Ensure that all operators are trained on proper dry cleaning techniques and understand the importance of maintaining hygiene standards, using the right tools, and that they can take action in the event of an issue during cleaning (for instance a tool that breaks) and avoid foreign body or microbial contamination during cleaning.

6. Documentation : Have the cleaning procedure written, with visual standards (references of what is clean or not). Keep records of cleaning procedures and inspections to ensure compliance with food safety regulations.

2. Controlled Wet Cleaning of Powder-Handling Equipment

Controlled wet cleaning is a method used to effectively remove sticky powders from processing equipment while minimizing water usage and preventing excessive moisture that could lead to contamination. This approach is particularly useful for equipment such as mixers, hoppers, and bag tipping units where residues are difficult to dislodge using dry cleaning methods alone. Here’s a detailed overview of how to perform controlled wet cleaning, the tools required, and best practices.

2.1 What is Controlled Wet Cleaning?

Controlled wet cleaning involves the careful application of water and cleaning agents to remove residues without completely washing down the equipment. This method allows for targeted cleaning of specific areas while maintaining the integrity of the equipment and preventing excess moisture accumulation.

2.2 How to Perform Controlled Wet Cleaning

1. Preparation:

• Equip personnel with appropriate personal protective equipment (PPE), including gloves, goggles, and masks.
• Lock out tag out the power source, and ensure that the equipment is safe to clean.

2. Initial Dry Cleaning :

• Before applying any water, conduct an initial dry cleaning step using a vacuum system to remove loose powder residues.
• Use brushes or scrapers to dislodge any stubborn particles that may be present.
• See paragraph above for more details

3. Targeted Wet Application :

• Using a spray bottle, apply warm drinking water (ideally below 120°F) directly to the areas with sticky residues.
• Avoid soaking; instead, use just enough water to moisten the surfaces and loosen the residues.

4. Mechanical Action :

• Use brushes or cloths to scrub the wetted areas gently. Focus on corners, crevices, and other hard-to-reach spots where residues tend to accumulate.
• Be cautious not to damage any surfaces while scrubbing.

5. Rinsing :

• After scrubbing, use a damp cloth or sponge to wipe away loosened residues and detergent.
• Rinse the cloth or sponge frequently in clean water to avoid redepositing residues.

6. Drying :

• This step is extremely important, no moisture must remain in the equipment. Water must dry as soon as possible to prevent micro growth. Also any patch of water on which powder will come will lead to immediate sticking and process problems.
  

7. Final Inspection :

• Conduct a thorough visual inspection of the cleaned areas to ensure all residues have been removed. Make sure all water has dried.
• It is highly recommeded to perform swab tests to verify that no micro contamination has occured before returning equipment to service.

2.3 Tools for Controlled Wet Cleaning

- Spray Bottles : For precise application of water and detergents without oversaturation.
- Soft Brushes and Cloths: For gentle scrubbing of surfaces without causing damage.
- Vacuum Cleaner: To remove loose powders before wet cleaning begins.
- Buckets for Rinsing : To hold clean water for rinsing cloths or sponges during the process.

2.4 Best Practices for Controlled Wet Cleaning

1st rule : in a bulk handling process, only use wet cleaning when it is absolutely needed, otherwise use dry cleaning only.

1. Minimal Water Usage : Focus on using just enough water to moisten surfaces without creating puddles or excessive moisture that could lead to contamination.

2. Regular Cleaning Schedule : Establish a routine cleaning schedule based on usage frequency and type of powder handled. Immediate cleaning after use is ideal, especially for sticky powders.

3. Training Personnel : Ensure all operators are trained in controlled wet cleaning techniques and understand how to effectively manage moisture levels during cleaning, as well as the importance of a quick and complete drying.

4. Documentation : Keep detailed records of cleaning procedures performed, including any observations about residue types and quantities removed.

5. Equipment Design Considerations : Use equipment designed with smooth surfaces and minimal dead zones that facilitate easier cleaning while allowing for controlled wet applications.

3. Wet cleaning

Full wet cleaning is most of the time only applicable in dry processes for parts that can be dismantled and brought outside of the dry production area for cleaning. It could be for example the case of a piece of pipe with powder build up, it can be dismantled and cleaned outside. In this case a full drying and a swabbing for controlling there is no micro growth on the part is required before returning it to the production area. It can be advisable to have 2 identical parts (one in production, one in cleaning then back-up).

4. Other method : dry ice blasting

Dry ice blasting is a non-abrasive, moisture-free cleaning technique that uses compressed air to propel solid CO₂ pellets (dry ice) onto surfaces, where they sublimate on contact, causing residues to dislodge and fall away. This method is particularly advantageous in powder-handling environments because it removes stubborn residues without leaving moisture, reducing the risk of microbial growth and eliminating drying time. To be noted that this kind of cleaning method is not used in a routine manner but can be useful for example once a year for some applications. It requires very specific equipment, it may be required to contract a specialized company for this kind of cleaning.

Best Practices for Dry Ice Blasting: For optimal safety and effectiveness, operators should follow key best practices. Ensure that equipment surfaces are durable enough to withstand the CO₂ pellets, and maintain adequate ventilation in the cleaning area to prevent CO₂ buildup, which can displace oxygen. Always use appropriate personal protective equipment (PPE), such as gloves, goggles, and respiratory protection, as dry ice blasting generates noise and a cold atmosphere. Proper disposal of dislodged residues is crucial to prevent cross-contamination. Conduct thorough visual inspections afterward to ensure complete removal of residues before equipment returns to service.

Sources

https://www.profoodworld.com/food-safety/cleaning-and-sanitation/article/22578815/tetra-paks-clean-in-place-for-powder-handling-equipment
https://www.nsf.org/knowledge-library/clean-food-processing-facilities
https://www.foodprocessing.com/manufacturing-equipment/bulk-and-powder-handling/article/11304670/how-to-handle-powder-changeovers