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:
||Know the dielectric constant
of the target material.
||Respect the energy field surrounding
the probe element from the top to the bottom
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 email@example.com