Considerations Before Replacing Batch Mixing with Automated, Continuous MixingConsiderations Before Replacing Batch Mixing with Automated, Continuous Mixing
Continuous processes offer enticing throughput gains and labor savings but is it the smart approach for your process?
January 14, 2025

I was recently asked to tour the production facility of a major food and nutritional product manufacturer. Executives were putting pressure on the plant manager to increase throughput to meet rising demand yet also to cut costs - and staffing challenges had brought labor costs to the fore as a prime target for savings. Though the production line had already been optimized to meet previous throughput targets, quality control requirements, staffing levels, and cost structures, the plant manager realized the current line would no longer suffice and that significant changes were required to meet the new targets. He considered building a second production line, then investigated replacing batch mixers, fluid bed dryers, conveyors, and other equipment with new, larger versions to handle greater capacities at faster rates.
After further investigation, he concluded automating key parts of the process would likely solve all of the issues. For starters, replacing the batch mixing process and eliminating its labor-intensive requirements with an automated, continuous mixing process seemed an obvious and sensible place to begin. And it did make sense. But given my involvement in designing and installing a vast number of batch and continuous mixing systems all over the world for many years, I felt compelled to raise these considerations before agreeing it was time to sell off the batch mixer and go continuous.
Continuous Mixing Demands Continuous Feeding
In a typical batch mixing process, workers commonly carry bags of dry materials and ingredients to the mixer and empty them into a hopper, feeder, or directly into the mixer by hand. Then, any liquids and/or microingedients are manually added with careful timing to try to promote the desired amount of dispersion. Achieving a consistent level of homogeneity from one batch to another can be a challenge with this system and it's prone to human error and variability but ensuring the mixer is loaded with the proper ingredients before an operator presses start is not a major concern. However, when switching to a continuous mixing process, the proper care and feeding of each material becomes critical. The non-stop nature of the mixing action demands non-stop material feeding in the proper amounts, weights, and ratios per the recipe. Failure to keep any of the materials flowing from upstream may trigger a stoppage with costly, unplanned downtime. Since the latest continuous mixing and feeding control technology automatically monitors and meters the incoming ingredients into the mixer, in the event of a missing ingredient or shortfall, the system can alert an operator and/or shut down the process automatically. But stopping a continuous process that may need to operate 24/7 for the financial investment to make sense needs to be avoided.

A variety of nuts being mixed in a Gericke Multiflux GMS batch mixer (Gericke USA)
Ensuring dependable, non-stop feeding for continuous mixing often requires purchasing automated weigh feeders, and, in many cases, this means one feeder per ingredient. The fewer ingredients, the greater the efficiency and consistency benefits of an automated, continuous process. In recipes comprising a large number of ingredients, a pre-mixing stage may need to be performed upstream to minimize the number of feeders at the mixer infeed. Raisins, sunflower seeds, and coconut flakes for an energy bar, for example, may be pre-mixed upstream and then fed into the mixer via one feeder in the proper ratio while the primary base ingredient is fed via a second feeder. A liquid or viscous ingredient such as honey or a microingredient may be metered into the mix by a third feeder. In some cases, feeders used in the batch mixing process may be reused in the continuous process, but adjustments are typically needed that may nullify any cost savings. Many of the latest feeders and feeding control technologies are designed specifically for continuous processes to ensure an uninterrupted material flow. They can weigh, meter, and dose as needed in precise amounts at throughput rates of up to 54,000 liters/hour without clogging, even with non-free flowing powders, pellets, granules, and other bulk solids.
Keeping the feeders fed without workers emptying materials from bags into hoppers also needs to be addressed in a continuous processing environment. Though it is possible to manually load the materials in a 24/7 operation, loading a continuous mixer by hand conflicts with the very concept of automating the process. To fully realize the potential cost savings and efficiency improvements of continuous mixing while maintaining product quality, automating upstream operations needs to be considered, too.
Pneumatic conveying, vacuum conveying, or other approaches may be used to automatically transfer materials to the feeders for mixing without involving any significant human interaction. Depending on the scale of the operation, these conveyors may pick up the materials directly from a silo, from a bulk container, or sack tipping station, if bagged materials are to be used, and transfer them inside enclosed pipe or tubing. While any buffer hoppers and ancillary equipment needed for batch mixing can be removed and space opened when moving up to continuous processing, these automated bulk material handling systems will require a fair amount of space. However, even when conveying materials long distances of hundreds of feet, much of the space involved is overhead or otherwise out of the way and does not take up valuable floor space. In this type of automated approach, the materials never need to come into contact with workers or the workplace, and vice versa, safeguarding against both product contamination and worker exposure to dust or toxins.
Complex Recipes Require Testing
As the number of ingredients in a recipe increases, and as the properties of each new ingredient differ from the others in particle size, moisture content, flow characteristics, and viscosity, for example, the difficulty in consistently repeating a batch mixing process and achieving the required quality specifications increases accordingly. For recipes with few ingredients and/or common ingredients with a well-known history of their behavior in a mixer, switching to continuous mixing and achieving the same homogeneity is often a seamless process. The existing recipe may simply be programmed into the new HMI, and after a brief testing period, the mixer may be commissioned for startup. But recipes for more complex products involving multiple dry and liquid ingredients with a diverse range of properties may not translate to continuous as seamlessly. Recipes like these may require more extensive testing. Similarly, sequential recipes where ingredients need to be added in a specific order typically need more extensive testing to determine the ideal position for each feeder on the mixer and ensure the proper residence time for each ingredient. Recipes that need uncommonly long residence times do not fully capitalize on the speed and throughput advantages of continuous mixing and may be better served remaining as a batch process. Once the recipes are fully tested and perfected, however, today's continuous mixers are proven to effectively reproduce complex products with comparable and sometimes superior homogeneity to batch mixers, automatically at the press of a button.
Beware Downstream Bottlenecks
Automating key processes such as feeding, mixing, and bulk material transfer typically achieves the faster production anticipated, and, sometimes, the faster production outpaces the capabilities of downstream equipment. Switching to continuous mixing for higher throughput rates only to create a backup below at the infeed of a dryer, conveyor, or filling machine can trigger costly line downtime and product loss, as well as a costly cleanup given the regulatory nature of a sanitary process. The few workers on-site would certainly not enjoy managing this situation. In any processing, filling, or packaging line, it's vital for all of the machinery and equipment to work together at the same speed to achieve the targeted, overall throughput rate. One machine that operates at a far slower pace than the others can create serious problems but the reverse – when one machine operates at a far faster pace – can also create similar, serious problems.
When automating mixing with a continuous mixer, it is common to automate companion steps in the process to ensure each step matches the same speed, such as automating material transfer and feeding upstream, and drying, filling, and packaging downstream. This may involve switching from an oven to a continuous, vibrating fluid bed dryer, for example, replacing manual loading of a vertical form fill seal machine with a pneumatic conveyor, or switching from manually collecting excess ingredients or spillage to capturing, conveying, and returning excess ingredients to the process upstream automatically.
Flexibility at Scale
When a continuous mixer is designed to produce a given product that meets specific quality requirements at a given throughput rate, it will typically excel at that task and deliver the speed, efficiency, and cost savings exactly as projected. Payback periods are often met within a few months. But this high volume of production at scale often comes with a tradeoff in flexibility and versatility. If demand for the product declines, or if it fluctuates seasonally, operating a continuous process in short runs is possible but may not be a viable choice. Similarly, if major changes to the recipe are needed, or if the material properties differ over time then pivoting with a continuous mixer is possible but may require involving the manufacturing team to adjust the mixer based on the new parameters and expectations. When developing new formulations, a lab-sized, tabletop batch mixer still ranks as the ideal solution for nearly any new food, chemical, pharmaceutical or other product.
While transitioning from batch to continuous mixing offers substantial benefits in terms of efficiency, throughput, and labor savings, it is not a decision to be taken lightly. Plant managers and owners need to weigh these tangible benefits against the upfront investment and calculate the potential ROI. Then other issues such as future flexibility need to be considered. Thorough testing, proper integration with upstream and downstream processes, and alignment with overall production goals are critical for a seamless transition to harnessing the advantages of continuous mixing.
Rene Meira Medina is executive vice president of Gericke USA (Somerset, NJ). Founded in 1894, the company designs and manufactures a range of pneumatic conveying systems, feeders, mixers, lump breakers, and other powder processing equipment. For more information, call 855-888-0088 x 805, email [email protected], or visit www.gerickegroup.com.
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