The Pros and Cons of Continuous vs Batch Processing
An accurate feeding and weighing system specifically designed for your application is essential for an efficient and reliable production process. Our detailed knowledge of production processes and feeding of both solid and liquid ingredients, helps our customers select the best system for their production lines.
The video above gives you an overview of the main pros and cons of the different approaches, batch production or continuous production.
Batch and continuous processes are both reliable methods for industrial feeding technology. Selecting the correct system always depends on the individual situation and the specific production targets. It is therefore advisable to conduct a thorough and unbiased analysis before investing in any new production system. The decision is typically based on several criteria including:
- the ingredients being fed and their properties
- the recipe
- the processing times
- the target production volume
- end product quality requirements
- the production process conditions
- any requirements explosion protection and health and safety constraints
Two feeding systems, three approaches
Continuous processes are generally more suitable for higher throughputs or mass production with only a few recipe changes. The longer the production process runs, the higher the economic efficiency and the better your ROI. Downtime can be reduced, even with frequent recipe changes, as long as enough weigh-feeders are available to handle the different ingredients. In this case, any weigh-feeders which are not required are excluded from the recipe and the production process can continue.
Batch systems are generally suitable for processing smaller production volumes with multiple recipes. Batch systems can weigh the ingredients either by addition (gain-in-weight) or subtraction (loss-in-weight) techniques. For gain-in-weight (GIW) weighing, all components are sequentially fed into a single weighing hopper and the weights are totalized. For loss-in-weight feeding (LIW), each ingredient can be fed into the process in parallel, directly from a separate feeder. The video above explains this well.
Continuous feeding in detail
Gravimetric loss-in-weight or belt feeders are used for continuous processes. High-resolution digital load cells provide high feeding accuracy and when used with our micro feeders for smaller ingredients, extremely low rates can be achieved without the need for premixes. All ingredients can be fed in parallel and while premixes are possible, they require additional transportation and there is a risk of ingredient segregation.
Continuous processes typically demand a high short-time accuracy and as they need refilling while continuing to run, their control is more complex.
Filling must be precisely controlled as the weight of material fed out at this point in the cycle cannot be checked. Correct hopper venting is another important factor and each weigh-feeder is vented separately to avoid cross contamination of ingredients . 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 with easy ingredient changes and a simplified cleaning process.
High outputs are faster and easier to achieve with a continuous process because the devices are smaller than for larger batches. Since the materials are fed directly into the downstream processing machine, e.g. a mixer, extruder or kneader, and fewer personnel 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.
The relatively small footprint requirements, are an advantage, especially the lower height requirements. Commissioning is simple for qualified and well-trained personnel, as the weighing unit and the feeding device are one unit.
Batch processing with volumetric feeding
This process is based on individual, sequential volumetric feeders and is characterized by a slow, time-consuming sequence often with premixes. Volumetric feeders meter the material into a gain-in-weight hopper scale. Since the weighing system is usually configured for the largest batch, it is not possible to achieve a high level of accuracy for very small batches.
The control process is easier for discontinuous feeding because the start weight and end weight can be accurately calculated. Caution should be taken over the drop distance from the volumetric feeder to the weigh scale as this can cause inaccuracies during filling. An ingredient change can be complex and time-consuming as the feeder may need cleaning and refilling with the new product, resulting in extended downtimes.
The many manual tasks reduces process reliability, more personnel time is required and the many processing steps can cause product losses. It is therefore absolutely essential to have the correct calibration. The material is first metered into the hopper scale and then transported to the batch mixer. The equipment for this process is generally taller and requires considerably more space. Despite these limitations, this batch process using volumetric feeders is ideal for small production volumes.
An example of the gain-in-weight batch process is in the manufacturing of powdered laundry detergent. A transport container with hopper scale moves across a roller conveyor – manually or computer-controlled – and collects the required material volumes from the volumetric feeders installed above. At the end, the container is removed and placed onto a mixing system which mixes the fed products and discharges them.
Batch processing with gravimetric feeding
In this batch process loss in weight scales are used for gravimetric feeding of each ingredient. This allows all ingredients to be fed in parallel, saving time compared to gain-in-weight batch systems. Thanks to the high-resolution digital load cell, batch processing with gravimetric feeding is a highly accurate process. It can also be used for ultra low amounts without premixes if micro feeders are used. Premixes are possible, but there is a risk of ingredient segregation when transferred.
Control is easier because the start weight and end weight can be achieved accurately. When it comes to filling: The product leaving the scale has always been weighed and is only fed after filling is completed. The only exception would be multiple refills during a batch. As in the continuous process, separate venting is required on each scale, but this produces no ingredient mixing. As with the continuous process, the workload for cleaning and ingredient changes is manageable and 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. Similar to continuous feeding, a relatively small footprint is required. The exception being large batch sizes, where the scales become very large and consequently require more space.
An example application is when batch processing with loss-in-weight weighing is used for generating a premix for masterbatch production. Multiple loss-in-weight feeders simultaneously feed different additive products into a container in batches (LIW), generating a premix effect. The masterbatch is then moved to the batch mixer and added to the main product there.
Trend to continuous systems
Although there are good reasons for batch-based feeding processes in many industries, the trend in feeding is increasingly moving towards the continuous processes, for example for applications in the pharmaceutical industry, in tire manufacturing or for powder coating. The continuous concept 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 in development.
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