By Carlos Alberto Berrueta, Miller Technician, Advisor and Trainer in AOL
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| Image credit: Andrew on Flickr (CC BY 2.0) |
All of us who have been in charge of a Flour Mill have suffered inconveniences in the process of emptying the tanks or storage silos of the flours produced, mainly when their design was not ideal or correct, here we summarise some concepts and constructive characteristics to take into account when making decisions in this regard.
The best extractor is the one that covers practically the entire section of the cell, it is the ideal one, when this is not possible and we need to reduce the section in a lower hopper with a slope, we must look for asymmetry, since symmetrical hoppers favour formation of vaults or bridges. It should be taken in mind that for flour the slopes must be + 70º and as second important rule to take into account is to look for the good relationship "height-section", which should not be greater than five to one, the angles should be rounded and avoid building cells too high, since this avoids significant pressures on the material stored in the lower part of the cell.
If we have flour in the upper part of the cell with a density "d", the lower part will have a density "d1" greater than "d"; If we build the flour silo adjacent to the mill, its vibrations will favour compaction and, although they seem unimportant reasons or causes, they are factors to take into account. In the same way, the transit of heavy transport, rail, etc. they favour compaction.
Regarding the extractors themselves, there are mechanical extractors and extractors that we can qualify as pneumatic (fluidised bed); The extractors that offer the best performance are the Vibrating Cone type ('Rotoflow'), mainly due to their behaviour and singular simplicity. There are other mechanical unloader systems that have advantages over the previous one because a better dosage is achieved; although this can be achieved by placing a lock with a variable speed drive after the 'Rotoflow', obtaining an acceptable dosage.
However, if by volumetric dosing it is intended to add small proportions, this will lack precision. For this, the installation of integrating scales is ideal, otherwise you will have to stretch a certain product and then mix it by dosing, although this complicates and makes the operation of the system more expensive.
Regarding the maximum time that flour can be stored in silos or cells, this is directly related to the humidity it contains, and the temperature with which it enters the cell. Caution must be taken so that the cells where the freshly made flour enters do not have their walls exposed to the outside; if this is impossible, it is advisable to build a double wall to promote air circulation. If the relative humidity is reasonable (70 – 80 percent) and the flour at the entrance of the cell has 14 percent humidity, it can remain stored for up to a week, as long as we take the precaution of transferring it within 24 hours of elaboration.
When stored flour shows deterioration in the gluten, it´s because acidity has been developed in it, it is a chemical evolution, which causes the acidity of the flour to increase, resulting in a serious problem in baking that flour due to deterioration of the gluten, but the alteration is not due to the behaviour of the flour inside the silo, as has once been assumed, it is always, as in wheat, caused by a problem of poor storage.
In addition, care must be taken not to deliver the flour too quickly to the customer. It should be allowed to age a little and this is much more important in some years than others, the cause being not entirely known.
For more information visit the Agronomía Online website, HERE.
The Global Miller
This blog is maintained by The Global Miller staff and is supported by the magazine Milling and Grain
which is published by Perendale Publishers Limited.
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