I was fortunate to be able to speak at the October dinner and meeting of the Houston Material Handling Society. This group has been in existence for many years and is an adjunct of ASME. It was a humbling experience for me to speak to a group of some 40 engineers and material handling specialists with nearly 1,000 years of total experience. Needless to say I was awed, but not speechless . I took the opportunity to quote Dr. Peter Martin of Invensys who stated, in the Executive Corner of the September issue of InTech magazine, that "engineers must step up and take a leadership role within their companies by helping drive new levels of business performance". This is a challenge and I set my goal to provide, in only one hour, one or two pieces of information and insight that could help these HMHS engineers do just that.

The topic of my talk was "Recent Directions in Bulk Solids Level Measurement & Monitoring" and I focused on two trends. First, the growing use of self-validation level monitors as high and low level bin level indicators. The second topic dealt with ensuring successful installation of the fastest growing and most popular level measurement technology for bulk solids applications, the guided wave radar level sensor.

Today, the cost of an overfilled silo is estimated to be about $5,000 each spill. This cost includes the cost of lost material, cleanup costs, damaged equipment such as baghouses and vents, fines for air quality violations and lost production due to downtime. Most spills seem to be caused by unknown level monitor failures. In other words, when your high bin level indicator fails you won't know about it until one day when you are filling the vessel you do not get the high level indication and, all-of-a-sudden, you have overfilled the silo. The amazing thing is that for about $100 more this can be eliminated. The #1 answer to preventing spills due to unknown level monitor failure is to use a self-validating device. These self-validating level monitors continuously check their health and ability to perform their intended function. If their is an internal failure an output indicates such and you are able to correct the failure before it costs you big time. The self-validating level monitor for bulk solids uses rotary paddle technology, which is low cost and very universal.

Guided wave radar level sensors are growing in popularity and use for bulk solids level measurement applications by more than 20% per year. The reason for this

includes their almost universal applicability in solids measuring applications. Granular materials, very dusty powders are no problem. Even many materials that might stick or cling can be handled. The only limitation of guided wave radar devices is low dielectric constant materials, and there is even a good solution for most of those. Guided wave radar devices are very affordable, accurate and reliable. To ensure successful installation however, there are a few tips worth mentioning:

The dielectric constant of the material will affect the maximum length or distance that can be measured using GWR and is therefore important. This only applies to the Direct measuring mode. This information will also determine if the TBF mode for low dielectric materials needs to be used.

The radar pulses generated by the instrument travel to the material surface guided by a probe, typically a very heavy duty stainless steel cable probe. It is important in these bulk solids applications to keep a clear 12" radius around the cable probe from top to bottom. In addition, this includes under the probe’s counterweight. And no, it is not recommended or desired for the cable probe to be secured to the bottom in these bulk solids level measurement applications.

The single biggest cause of problems in installations using GWR is the use of mounting nozzles. These should be avoided and installation should be done using a simple 1-1/2" NPT half-coupling mounted plumb on the roof of the vessel. If nozzles cannot be avoided then the diameter of the nozzle must be greater than the height.

Want more information about these subjects and the presentation at the October HMHS meeting? Contact Joe Lewis at jlewis@monitortech.com