How to select the right blender for powder mixing plants
Whether you are just getting started, or are a seasoned professional, the choice of mixers is so extensive as to be just plain confusing. This article poses some questions to be considered when making that all-important selection.
One of the most significant functions and consequently one of the most important aspects in a powder processing system is blending. In most food applications, it is the major source of increasing value of the products that go into the process. This is the case whether you are manufacturing sports nutrition products or bakery and everything in between.
An increasing challenge in the powder handling industry is how to accommodate a wide portfolio of recipes and vast array of different ingredients, several of which pose an allergen risk. Some companies have been willing to spend significant amounts of capital installing highest speed mixers and packing lines in order to achieve high efficiency and throughput. But just because a mixer is high speed, does it necessarily mean that it provides the best process solution?
Batch or continuous processing?
Before we get started, the most important decision is whether to batch or continuously manufacture. Do you need to swap recipes on a regular basis or are you producing the same product day in day out? If there are no changes to be made, then it makes sense to consider continuous processing with large fixed mixers which are coupled to the upstream and downstream processes.
However, as most manufacturers are finding, consumers’ desire for more variety means more and more recipes being added to the ever-expanding product portfolio. The consequence of which is more recipe changes than ever before and means you need to take a close look at how you plan to conduct mixing. Here batch processing is the only way. The points raised in this article refer mainly to the case for batch processing as it is assumed this is an expanding area of consideration.
A free-flowing powder with similar ingredient particle sizes will mix easily. A more gentle blending approach will work well here, such as tumble blending or ribbon blending.
On the other hand, for cohesive, sticky powders to mix homogeneously, work needs to be applied to the material, forcing the particles to fold and join. In this case, blenders offering high shear in the form of knives or intensifiers are required. Applying the right amount of shear is vital to intermesh and blend the particles; however, if mismanaged, particle degradation and heat build-up may occur.
Big isn’t necessarily beautiful for blenders. It might be large enough to match the order amount and batch size, but watch out for loading times. Take into account how long it will take to fill by ripping and tipping 25 kg sacks of ingredients. Then think about how long it will take to empty the product to packing. During this time the mixer will stand idle and be unproductive, which is not lean. Companies often do not realise the cost of this lost time in filling and emptying the mixer. But it should be challenged for the waste that it clearly represents.
Also consider whether you will have different batch size demands. Do your customers always want the same size orders? Do you have to make small-sized batches of half or a quarter of the large batches? If you have wide variability consider using IBC (intermediate bulk container) systems for blending, whereby different-sized containers can be accommodated on the one blender.
Don’t be fooled by claims of only a four-minute blend time. It’s important to weigh up the full end-to-end process stage of blending, from filling the mixer to it being emptied and ready to go back into operation. It might well only take 4 minutes to blend, but it could take 2 hours to load and 3 hours for packing to call off. Giving a total blending time of 5 hours and 4 minutes!
In-bin/IBC blending might take a little longer for the blend cycle (often 10–15 minutes), but in the long run you save time as formulation of the recipe is done offline and the container is removed immediately from the blender and taken off to packing. The filling, mixing and packing process steps take place simultaneously. The blender itself doesn’t need cleaning so it is free to go back into service immediately. The only limiting factor is how quickly your operators can install and remove the bins from the blender.
If you are making several recipe changes throughout the day, using a fixed mixer can be inflexible. You will need to conduct a clean-down each time, thereby increasing the full end-to-end blending time even further.
In-bin blending, on the other hand, offers immediate changeover as there is no cleaning of the blender, enabling up to four batches/hour to be completed.
Ease of cleaning
It is important to ensure that the expensive, value-adding ingredients aren’t ‘lost’ during the mixing process. Have you ever considered what you might be leaving behind in the blender? All fixed mixers will have some residue left behind at the base of the mixer bowl or clinging to the sidewalls, shaft, paddles and bearings; this product is then washed away during cleaning. This is valuable product that costs money and shouldn’t be flushed down the drain.
Bear in mind what ‘hold up’ areas there might be in the mixer you are choosing.
- Can operators safely and easily access all the corners and joints?
- Are the paddles/shafts removable?
- Are there easy-access doors? What safety locking systems are incorporated?
On a fixed mixer, clean-down time between recipes can vary from as little as half an hour for a dry clean between non-allergen recipes up to taking a full 8-hour shift for a full wet clean and dry. This represents a significant amount of not only waste but manpower costs as this is usually a labour-intensive activity.
With in-bin blending, only the container is cleaned, which is conducted offline. Even if the IBC has a complicated split butterfly valve which needs to be removed for cleaning, this won’t affect the OEE (overall equipment effectiveness) rate of the blender as other previously cleaned IBCs will be returned to the manufacturing process to maintain the optimum flow.
Risk of cross-contamination
With an increasing number of products containing allergens, it can be challenging to manage changeovers and clean-downs. Particularly tricky are the fixed mixers and inline conveying systems because the system is coupled, so it can take a long time to clean down between recipes and to validate that it really is clean.
If different recipes are to be mixed on the same mixer then you need to consider the risk of cross-contamination if cleaning is not done properly. To mitigate the risk, some companies dedicate a blender to any allergen recipes. This is acceptable if only one additional fixed mixer is needed, but is it really practical to consider half a dozen?
For allergen handling, in-bin blending offers a simple, safe solution. Containers can be used one time for allergens then cleaned and used next time for a non-allergen product. A common blender can be used as there are no product contact points on the blender.
After mixing — segregation risk
Even though the fixed mixer may be providing well-blended material, this does not guarantee production of a quality product as it needs to be transferred out of the mixer. This is when segregation of the mix might occur as air displaced by powder leaving the mixer carries the ‘fines’ back up through the powder. This is further exacerbated if large product transfer heights are involved. Here the particles have more chance to move apart and de-mix the blend as some will move faster than others depending on their particle density and characteristics.
You also need to consider the ease of discharge from the fixed mixer. Ensure the mixer empties fully with no residual product held up. Consider the opening size of the discharge point, as some powders might be sticky and will have poor flow properties so are likely to become stuck. Then again, the free-flowing products could suffer from a core flow through these discharge points, which will cause segregation.
IBCs help to reduce the issue of segregation. Not only is the product mixed within the container, but it is then transported to feed to packing where it is coupled to the infeed hopper reducing the drop height. A note of caution, not all IBCs are equal. Those with butterfly valves can still get product segregation issues due to core flow and rolling of particles. Where this is a high risk, it is worth using ‘cone valve’ IBCs, which offer the best protection against segregation due to product flowing under mass-flow discharge with all particles moving down through the bin in unison.
Don’t just consider the size of the mixer itself — take into account what space you need around the mixer for loading and unloading product and cleaning. Also check on what ceiling height is necessary for access above and below.
IBC blenders tend to have a small footprint and head height, so if space is an issue, then it is worth exploring these further. The IBC blenders can be located in open areas with low hygiene control as they provide a closed process.
When selecting a mixer, it pays to do some research. If you choose the right one you also have the added benefits of:
- By reducing the downtime of the mixer for non-value-add functions greater efficiency can be obtained and production capacity increased.
- Quick product changeovers due to no cleaning of the IBC blender provide increased production capacity.
- Multiple batch sizes can be mixed in one IBC blender therefore eliminating the need for multiple mixers.
- Through reducing the amount of idle time wastage.
- Incorporating more efficiency in the blending process can reduce the number of shifts required.
- Lower manpower costs for cleaning.
- Minimised lost product via residue or scrap due to it becoming de-mixed.
- Eliminating inventory or WIP.
Improved product quality
- Prevent segregation for a better final product that is of high quality every time.
- Removal of the risk of cross-contamination.
- Closed hygienic system.
Don’t just be swayed by choosing the cheapest option just to get started or using ‘what everyone else has got’ (they may not have done as good research as you have). Think differently and see where it may take you.
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