It is pretty amazing the many types of goodies that you can create with flour. These creations require various types of flour and some of these flours, because of their composition, are tougher than others to accurately measure their levels in a silo.
To the flour mill producer, the characteristics of each type of flour allows for the right recipe blend. In the milling process, production goes hand-in-hand with inventory. It happens that the various characteristics that flour exhibits from crop-to-crop, season-to-season or environment-to-environment can create some challenges in terms of level measurement. Thus, to accurately monitor the flour level in a silo, it requires us to take a closer look.
What causes variances in flour, and what should you watch for when deciding if a technology will perform as desired to meet your level measurement needs?
Claims are often made that one technology or instrument can be suitable to all your flour level application needs; however, this is not entirely accurate. In general, non-contacting level technologies are more favorable than other technologies, but sometimes the type of flour may call for a contacting one whereas in other applications it may not be applicable.
Remember, not all flours are created equal. The season, harvest, mesh, bleaching and maturing agents play a role in the flour’s make-up. Because flour composition varies greatly, how the flour settles or flows out of the silo can differ from one type to another. Also, the filling method, which is typically pneumatic, creates lots of dust and the aeration tends to lower the bulk density on some flours more than others. The level of humidity of the product or the environment can also be good or bad. Good because humidity increases the bulk density of the product, and bad because it increases the potential for buildup on the measuring device.
To minimize fussing with accurate level measurements, watch for some of the tell-tale signs that can be problematic. This will help you make better educated choices as to what types of instruments would be more in line with the process conditions that you are dealing with.
What should you consider when picking your level device?
Chances are that you are handling more than one type of flour, and the more that you know about the flour properties that you are dealing with, the better solution you can find for your applications.
To help identify whether or not you need more than one type of technology, take a look at the list below to see if any of these conditions exist.
• Does the flour pack easily into shapes?
• Does it exhibit a high angle of repose?
• Does the material bridge or rat hole?
• Does it build up on the silo walls?
• Is the space very dusty when filling?
• Does the inside of hatch show excessive buildup?
• Past level experiences, does it behave differently according to the season?
Choosing your level technology? Here are some tips that might help in the process!
In a nutshell, dusty environments these days are easily handled with high frequency non-contact radar transmitters, i.e. 78 GHz. An easy way to remember this is:
• If the flour tends to build up too much, contacting technologies will require more maintenance.
• If the bulk density of the flour drops too much due to aeration, guided wave radar can be a suitable alternative. This, of course, is valid as long as the pull forces exerted by instrument cables on the roof and material contacting the instrument are not a concern.
• Anything operating off of laser or acoustic energy can be challenged under very dusty conditions, which makes these technologies less favorable.
I would be remiss if I don’t mention one key factor that has to with solid bulk powders like flour. Bulk powders exhibiting some of the characteristics mentioned above, will not flow properly out the silo if the silo is not designed for mass flow. In other words, in the silo is designed for a channel flow pattern. Contacting and non-contacting technologies will struggle giving you a reliable measurement. This is not because of the instrument, but because the material becomes stagnant in some areas in the silo and favoring flow in areas not seen by the level instruments. i.e. the material is channel flowing or rat holing.
It is wonderful that there are many kinds of flours to create the myriad of recipes we all enjoy directly and indirectly. As you know, these flours flow, disperse, compact and/or stick to surfaces differently. Trying to measure the level in a silo with one technology can be a daunting task. To help you solve your problem, not only you need to use a silo designed for mass flow, which should be used with cohesive materials but also, understanding the flour behavior and using suitable process instrumentation can lead not only to better automation and control, but also to better recipes.