Feeding processes: continuous or batch?
Customized feeding and weighing technology is essential to an efficient production process. Kubota Brabender Technologie’s substantial knowledge of processes and materials enables it to provide sound advice to customers when selecting a suitable system. They in turn will find the ideal solution to meet their solids and liquids feeding requirements.
Both batch and continuous processes are reliable industrial feeding technology methods. Selecting the correct system always depends on each individual situation and specific production targets. It is therefore advisable to conduct a
thorough and unbiased analysis before investing in a new production system.
Opting for the appropriate feeding method should factor in the following criteria:
- the materials to be fed and their properties
- recipe/formulation
- processing times
- production quantity
- required end-product quality
- process
- explosion prevention and occupational health and safety concepts
Two feeding systems, three approaches
1. Continuous processes
Continuous processes are generally more suitable for high throughputs or mass production with few recipe/formulation changes. The longer the production process is in operation, the more cost-effective it is. It is possible to reduce downtimes even with frequent recipe/formulation changes, if sufficient weigh-feeders are available to handle the different ingredients. In this case, any weigh-feeders which are not required are deleted from the recipe/formulation, and the production process can continue.
2. Discontinuous processes (batch)
Batch systems are generally suitable for processing limited production quantities involving multiple recipes/formulations. A distinction is also made between additive and subtractive weighing. In the case of additive or gain-in-weight weighing, all ingredients are sequentially fed into a weighed hopper and the weights are totaled up. In the case of subtractive or loss-in-weight feeding, each ingredient can be fed into the process in parallel, directly from a separate feeder.
3. Special case: batch with continuous feeding
As always, exceptions prove the rule. In addition to the three different feeding and weighing methods described above, a fourth method is sometimes applied. Bernhard Hüppmeier, Head of Business Development at Kubota Brabender Technologie, explains: “In this case, a batch is continuously fed into a process with precision control over a relatively long period. The focus here – as with a continuous process – is on short-time accuracy, but also on final batch metrics. Continuous process criteria then apply, as the switch-off point for final batch metrics is not as relevant compared to the batch size and can usually be disregarded."
Are you looking for the optimum method for your specific production process?
We help you find the right solution. Contact Bernhard Hüppmeier, Head of Business Development
Continuous feeding in detail
Gravimetric loss-in-weight feeders are used for continuous processes. High-resolution digital load cells deliver high feeding accuracy, and even micro quantities can be fed using micro feeders and do not require premixes. This process enables all ingredients to be fed in parallel. While premixes are possible, they require additional transportation and harbor a risk of ingredient segregation.
Due to the typical short-time accuracy requirement and the refilling phase, the level of control required for continuous processes is more complex and needs to be constant. This is needed to avoid system failures and ensure a high level of process reliability. Bernhard Hüppmeier puts it in more concrete terms: “Filling must be precision-controlled as the loss in weight is not checked during a refill.” Venting is another important factor: each weigh-feeder is vented separately to avoid dust mixtures. For higher throughputs, the weigh-feeders remain relatively small. Weigh-feeders which are not in use, can simply be deselected in the control system, which results in short downtimes. Easy ingredient change means that cleaning is also a simple procedure.
Advantages and disadvantages of the continuous method
High outputs are faster and easier to achieve with the continuous process, because the devices are smaller than for large batches. As the materials are fed directly within the processing machine, e.g. a mixer, extruder or kneader, and fewer operating staff are usually required, this feeding method can provide a high level of process reliability. Precise coordination is required only during the start-up and shut-down phase to avoid product losses.
Continuous systems require significant planning effort. In addition to precise layout design that takes material flows into account, we also have to consider environmental and system factors such as temperature, humidity, explosion prevention and working conditions. The relatively small footprint requirements, on the other hand, are an advantage here, especially the low height. Commissioning is simple for qualified and well-trained staff, as the weighing unit and the feeder form an integrated unit.
Generally speaking, there are increasingly more applications, where the switch from batch to continuous is being made or being planned.Bernhard Hüppmeier
Continuous or batch? Continuous or batch-based feeding:
Feeding processes compared on video
Overview: continuous method advantages and disadvantages
- substantial throughput
- high degree of process reliability
- smaller footprint and low height
- fewer operating staff required
- production of micro quantities feasible
- major planning effort required beforehand
Batch method featuring volumetric feeding (gain-in-weight feeding)
This process is based on individual, sequentially operating feeders and is characterized by a slow, time-consuming sequence of event involving premixes. Volumetric feeders feed the material into gain-in-weight hopper scales. As the hopper scales are usually configured for the largest batch, it is not possible to achieve a high level of accuracy for very small batches.
The discontinuous feeding control process is easier, because start weight and end weight can be achieved accurately. “Only the drop path from the volumetric feeder to the hopper scales can cause inaccuracies during filling,” Bernhard Hüppmeier explains. Ingredient changes are as complex and time-consuming
as cleaning, resulting in extended downtimes.
Advantages where smaller production quantities are involved
The many manual tasks involved reduce process reliability, more staff time is required and multiple processing steps cause product loss. It is therefore absolutely essential to have the correct calibration. Feeding first occurs in the hopper scales and then in the processing machine, the so-called batch mixer. The height of the equipment for this process is greater and requires considerably more space. The planning and commissioning workload is relatively high, because the scales and the feeder feature different technologies. Despite these limitations, the batch process involving volumetric feeding is ideal for small production quantities, even though product is lost through residues in the equipment.
An example of the gain-in-weight batch process is the manufacturing of powdered detergent. A transport container with hopper scales moves across a roller conveyor – manually or computer-controlled – and collects the required material volumes from the volumetric feeders installed overhead. At the end, the container is removed and placed onto a mixing system which mixes the fed products and discharges them (see gain-in-weight image).
Overview: discontinuous method (batch) advantages and disadvantages
- suitable for large batches
- different recipes/formulations feasible
- easy to control
- uncomplicated planning and installation
- larger footprint
- higher manpower requirements
Batch method involving gravimetric feeding (loss-in-weight weighing)
The third method also uses the batch process. In this case, however, loss-in-weight scales are used for gravimetric feeding purposes. This process enables all ingredients to be fed in parallel, saving time compared to gain-in-weight systems. Thanks to the high-resolution digital load cell, batch processing involving gravimetric feeding is a highly accurate process. It can also be used for micro quantities without premixes, if micro feeders are used. Premixes are basically feasible, but additional transportation means there is a risk of ingredient segregation.
Advantages of gravimetric feeding (loss-in-weight)
Control is easier, because the start weight and end weight can be achieved accurately. As far as filling is concerned, the product leaving the scales has always been weighed and is only fed after filling is completed. The only exception is multiple filling during a batch. As in the continuous process, separate venting is required on all scales, but this does not result in dust mixes. Bernhard Hüppmeier says: “Similarly to the continuous process, the workload involved in cleaning and ingredient changes is manageable: it only increases for large batch sizes, as the scales are much larger.”
Despite the manual work required by the batch process, gravimetric batch feeding provides a high level of process reliability without product losses, as the materials are fed directly to the batch mixer. Similarly to continuous feeding, a relatively small footprint is required. The exception being large batch sizes, where the scales are very large and consequently require more space. As with continuous feeding, commissioning is easy, as the scales and the feeder form an integrated unit.
Overview of batch method involving loss-in-weight weighing
- simple product changeovers
- high degree of process reliability
- no product losses
- smaller footprint
- uncomplicated commissioning
- greater effort involved with large batches
Uses of the batch method involving gravimetric feeding
This batch process is used, for example, to create a premix for masterbatch production purposes. Here, three loss-in-weight feeders simultaneously feed three different additive products into a container in batches (loss-in-weight), generating a premix effect. The masterbatch is then moved to the batch mixer and added to the main product there (see image).
Why the trend towards continuous systems?
Although there are good reasons for batch-based feeding being used in many industries, the trend in feeding is increasingly moving towards the continuous process, for example for applications in the pharmaceutical industry, in tire manufacturing or for powder coating. The continuous method is already being successfully used for feeding adhesives in hotmelt processes. A variety of other processes where continuous feeding can be applied to replace batching are under development.
Are you looking for the optimum method for your specific production process?
We help you find the right solution. Contact Bernhard Hüppmeier, Head of Business Development
Bernhard Hüppmeier draws a conclusion: “Generally speaking, there are increasingly more applications, where the switch from batch to continuous is being made or being planned. The mass production of batteries, for example, is currently changing over to the continuous process. In the food industry, this also applies to dry cereal mixing systems and granola bar systems, as well as baked goods, dough products and vegan meat substitute mixtures.” Basically, the significant planning work involved should not be underestimated, but even for smaller volumes, this should be balanced against the ease of automation, higher product quality and smaller equipment footprint.
