Powder has always been one of the trickiest things for food and beverage plants to handle. It’s messy, intrusive, sometimes abrasive, prone to leak or escape—and, when it does, it often coats nearby surfaces and is hard to clean up.
Those challenges become many times harder when frequent changeovers are involved.
Many processors are called upon to switch between formulations quickly. The nature of powders and bulk solids makes this especially problematic, but it’s a situation that providers of equipment say their customers are increasingly facing.
“Cleanability is a frequent consideration for a large percentage of our customers. They’re very cognizant of the need to clean between changeovers,” says Mark Felts, sales director of Powder Process-Solutions.
This bag dumper from Powder Process-Solutions features a spray ball for cleaning in place.
Robert Meirick, sales and marketing manager for Material Transfer & Storage , agrees: “Many of our customers handle a wide variety of materials and have concerns about cross contamination when changing from one material to another.”
Cleaning is the most important, and most challenging, aspect of changing over between powders. They permeate like liquids but leave solid residue that can be very hard to clean. This is why cleaning methods are a fundamental concern facing every processor who uses powders, especially when cleaning has to be relatively frequent.
“There’s no question that more-sanitary equipment is being demanded all the time,” says Nick Hayes, CEO of Volkmann USA.
The most basic decision is whether cleaning will be done in-place or out-of-place – that is, whether the hoppers, mixers, and especially, the conveyors that handle the powder will be disassembled and manually cleaned. The latter is more thorough, and is often the only option in applications where powder is sticky or otherwise hard to remove. Such applications often need handling equipment to be cleaned often even without product changeover, as a sanitation measure.
Bag unloaders can be configured so that the neck of the bag is the only part that directly contacts the hopper below.
Photo: Vac-U-Max
If powder-handling equipment is to be manually cleaned, it has to be designed for quick disassembly and reassembly, preferably without tools.
“Complete disassembly without tools and internal/product contact surfaces without any edges or ledges will lead to the most effective cleanability,” says David Kennedy, business development manager at Vac-U-Max. “We also recommend using removable gaskets (no adhesives), and over-center clamps to hold components in place. These clamps are captive hardware so they can't be dropped into the process below or lost during the cleaning process.”
Heavy, static equipment can be designed for convenient access during cleaning. For example, Powder Process-Solutions provides sifters designed for easy disassembly and cleaning. Rotary valves with rotors on slide rails are suggested for systems that require frequent, seamless cleaning. Felts estimates that a wet cleaning of the rotor and interior of a rotary valve could take anywhere from 15 minutes to an hour depending on the application, installation, product and level of cleaning required.
Dry or wet?
Of course, some plants don’t have that kind of time to spend on changeovers. For those applications, cleaning in place is the only option.
Product changeovers are a challenge for conveyors that use physical objects to move product along.
Photo: Cablevey Conveyors
Cleaning in place can theoretically be done “dry” or “wet.” Dry methods involve blowing high-pressure air through conveyors or onto static equipment, removing residue and debris through physical impingement, or a combination of both.
For example, Cablevey Conveyors manufactures disk conveyors, which carry product through stainless steel tubes by means of disks strung on a cable. One common method to keep the tube clean is to include a flexible urethane disk, with a slightly larger diameter than the tube, that acts as a sort of internal squeegee, clearing fine particles from the interior surface of the tube.
Another alternative is a “brush box,” an enclosure with rotating brushes that knock large particles off the disks. For more thorough cleaning, a sponge can be saturated with cleaning chemicals and inserted onto the cable that drags the disks through the tube.
These dry methods, however, are usually more for ongoing sanitation than for cleaning between changeovers. The latter is more often done “wet,” with cleaning and/or sanitation chemicals and water. There are two basic ways to do wet cleaning: by forcing the cleaning solution through the system or by applying it with static devices like spray balls.
However it’s done, the biggest challenge in wet cleaning is getting everything ready to run again – in other words, drying it.
“When you introduce wet cleaning, you also have to also account for drying time,” Felts says.
Hayes of Volkmann agrees: “The issue isn’t clean in place. We can clean in place with today’s technology, spray nozzles, whatever you need to do to clean in place. Your issue is dry in place.” The biggest challenge, he says, is filters, which are nearly impossible to dry while they’re installed. “Your question becomes, can you dry them, and the answer is no, you can’t dry them when they’re inside a conveyor.” The filters must be removed and dried separately, which makes the cleaning system a hybrid of clean-in-place and clean-out-of-place.
Conveying cleanliness
Other factors that affect the decision about cleaning methods include the nature and size of the equipment to be cleaned. For instance, there are several alternatives for conveying powder. The kind of powder being conveyed, and its handling characteristics, will be by far the most important factor in specifying a conveyor type – but the different types of conveyors vary in ease of cleaning.
“At a very high level, I would characterize pneumatic (vacuum) conveying as the most cleanable, the flexible (or centerless) screw conveyor in second place, and the aeromechanical conveyor in third place,” says Vac-U-Max’s Kennedy. He explains that ease of cleaning in pneumatic conveyors depends on the length of the segments; short ones can be disassembled relatively easily, while longer ones may have to be “pigged” by running a cleaning block through.
With flexible screw conveyors, even though they don’t have a lot of parts, cleaning the helix and the inside of the tube still will take time. As for the third alternative, “We generally don't recommend aeromechanical conveyors if you frequently change products unless you have a lot of time in between runs, and that would be for non-sanitary applications,” he says.
Hayes agrees that with conveyors, the longer the line, the harder it is to clean. “That’s where life gets more difficult,” he says. “It’s easy to take a filter receiver and take it apart to clean, but what about the 30, 40, 50, 100 feet of conveying line that gets to the component?”
Conveyors that physically push product along, such as disk or screw conveyors, can be designed so that the disks or augers extend past the point of discharge. This pushes out some of the residual powder.
Wet or dry cleaning accessories can be attached to a cable conveyor between changeovers.
Photo: Flexicon
“Flexi-Disc tubular cable conveying systems are driven beyond the point of final discharge, preventing material contact with seals or bearings,” says David Boger, executive vice president for Flexicon Corp. “By evacuating material at the end of a production run, these conveying systems can eliminate waste and residual material, minimizing downtime for cleaning and sanitizing.”
Conveyors present different changeover challenges from processing equipment like mixers, blenders and bag unloaders. Simplicity, as in few moving parts, is an important aspect of cleanability for such equipment.
“Above all, food processors looking to reduce changeover times while eliminating cross-contamination should specify mixing and blending equipment that lacks internal shafts and other internal moving parts,” says Steve Knauth, marketing manager for Munson Machinery Co. “Regardless of whether the shaft rotates a vessel or an agitator within a stationary vessel, material contact with shaft seals poses an inherent drawback that adds time, complexity and, in some cases, uncertainty to cleaning and sanitizing protocols.”
Knauth notes that Munson makes rotary batch and V-cone blenders that are optimal for dry powder blending with quick changeover because they lack internal moving parts and have unobstructed interiors.
Cleanliness is a constant concern with bag unloaders, which have to switch bags on a regular basis, even when the contents stay the same. The powder in the bag enters a transition hopper, which releases it downstream; that hopper has to be accessible for cleaning. Volkmann and others make unloaders with hoppers that can be wheeled out for cleaning.
“One of the biggest problems with bulk bags is not when they’re full, it’s when they’re empty,” Hayes says. Taking down the bag and folding it up drives out the air trapped inside – and the residual powder along with it. Volkmann offers a dust collector that sits to the side of the point where the bulk bag unloads, drawing a vacuum that picks up any dust generated by the powder flow. When the bag is finished unloading, the vacuum redirects to the bag itself, drawing out the remaining powder residue.
If cleaning powder out of equipment becomes too difficult, at some point a processor may have to consider the alternative: avoiding changeover by dedicating separate lines and equipment to different products.
