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Batch and continuous mixing comparison

Choice criteria in between batch mixing and continuous mixing of solids

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Section summary
1. Introduction
2. Comparison table batch and continuous mixing

1. Introduction

When a factory operator needs to invest in a new solid mixing system, be in pharmaceuticals, food or chemicals, the question of the technology of mixing will be asked. The process can either be batch or be based on a continuous dry-mix. Often, there is no direct answer and a rigorous comparison in between both options must be done, following different criteria, like capacity, space available, recipe formulation, competencies of local operators...etc...

This webpage is proposing a comparison table to help factory owners make their choice in between the 2 technologies.

2. Comparison table in between batch and continuous mixing of solids

What is the difference in between batch and continuous process for the mixing of solids ?

Batch mixing Continuous mixing Explanations
Recipe complexity From simple to complex Rather simple - if no preblend - Limited number of ingredients Max 4-6 Due to layout constraints, it is not possible to add a lot of ingredients in a continuous dry-mix, 4 appears to be often a maximum. Batch is more flexible. For both cases, preblending can be used but it is more complex to implement for continuous mixing
Flexibility - ease of changeover High Low For continuous mixing, there may be the need of diverting the 1st kg of mix until the equipment reach steady state
Capacity Wide range Wide range
Can reach higher capacity than batch
Continuous mixers can easily reach capacities of more than 10000 l/h with small mixers
Layout requirement (comparison at same capacity) Higher Lower Continuous mixers are much smaller than their batch equivalent for a same line capacity. The buffer capacities above and after the mixer can also be smaller. It must however be noted that LIWF for continuous mixing must be installed on very stable and vibration free supports
Segregation Higher Lower The continuous extraction of mixed powder from a continuous mixer allows the process to be less sensitive to segregation than batch (discharging the batch at the end of mixing creates segregation although it is often in acceptable limits)
Competency required for operation Low High For continuous mixing, operators must have a good understanding of the control of LIWF and be able to follow dosing graphs to troubleshoot the installation if required
Automation Simpler More complex The control of the feeders in continuous mixing must be elaborate in order to have an accurate dosing. As well, the start-up and stoppages procedures must be controlled. The ratio of the different ingredients must also be monitored in order to detect any deviation in the ratios of dosing.
Process validation May be every batch Per run In stringent applications like pharma, it may be required by authority to positively release each batch. A continuous mixer, for which a batch is a long run, may then have an advantage

In summary, continuous dry-mix are interesting to minimize layout requirement and investment for rather big lines with a simple set of recipes. They can also be interesting in pharma vs batches in order to have less release tests to perform.


Perry's, solids mixing
Manufacturers brochures
Experience of the author