How to improve accuracy on your macro and midi ingredient weighing systems
by Benny Simonsen, Working Board Member, Jesma Vejeteknik A/S, Denmark
The production of terrestrial and aqua feeds is a typical example of a discontinuous production process that employs a process of batch and semi-continuous operations. The bottle neck in many feed mills is the macro- and midi- dosing cycle. This bottleneck can be avoided by employing a Jesma solution where you, at the same time, also optimise your batching operation as well as the dosing accuracy.
What is included in the typical feed mill?
At the centre of a typical feed mill process, you will find the batching, dosing, weighing and mixing processes. A batching system is typically based on an operating average of approximately 10-12 batches-per-hour, corresponding to between five-to-six minutes per batch. When calculating the total batching time, the emptying of scales and conveying systems need to be included.
The typical feed mill includes one macro, midi, micro and nano scale each
Calculating total batching time
When calculating the total batching time per cycle it is necessary to include the following operations:
- Dosing (each ingredient is dosed one by one)
- Stability of scale between each dosing
- Emptying of scale and transfer of ingredients to next process step
- Rest emptying of conveying line*
* To avoid cross contamination between different batches and production orders the scale and conveying lines should be cleaned by running the chain conveyors and bucket elevators for some time after the last product has discharged from the hopper scales.
As mentioned previously, a typical feed mill batching cycle is between five-to-six minutes and the bottleneck in many feed mills are the macro and midi dosing cycles. To eliminate this bottleneck, Jesma has developed solutions in which the batching operation, as well as, the dosing accuracy can be optimised.
Option one: Replacing the single macro-midi scale with a double hopper scale:
The single hopper macro and midi scale can be replaced by a double hopper scale.
The advantage of this solution is that you can run two operations at one time: dosing into the weighing bin (each ingredient dosed one by one) and at the same time empty the bin below the weighing hopper.
The time gained by this solution is approximately 40-70 seconds, the equivalent of the time it takes to empty the macro/midi scale and transfer the batch to the next step. This solution will, in most cases, also improve dosing accuracy.
Option two: Installing small scales on top of the single hopper scale:
In some instances, it will be possible to install one or several smaller scales on the top of a single hopper scale. This allows dosing of more than one ingredient at a time, thereby reducing the dosing time and, at the same time, improving the dosing accuracy of the given ingredient. The time gained in relation to this solution is approximately 10-15 seconds for each small single ingredient scale installed.
Other optionss for increasing speed of the batching system could be:
- Increasing the size and/or speed of dosing apparatus (dosing screw or similar dosing device)
- Increasing the capacity of the conveying lines used for transferring the batch from the scale to the next processing step.
The above-mentioned other options will not benefit from an increased weighing accuracy and are, therefore, not considered best practice.