Measuring Coal Powder Levels
When Nothing Else Will Work
Coal-fired power plants are commonplace around the
world. In order for these power generating stations
to create huge amounts of electricity the turbines
need to be feed with steam and the steam created by
boilers that are fired by … yep, coal. But
coal as it comes from the mining operations is not
what is fed to the burners. First it is ground
or pulverized into powder. It is not unusual
for the coal powder to be stored in silos awaiting
the demand for it to be fed to the burners. The
inventory of coal powder in these silos needs to be
monitored to allow for efficient operation of the power
plant.
So, how do we monitor the inventory of coal powder
in a silo? Not easily. In one typical application
the power plant personnel found that the only technology
that would work reliably is the modern smart weight & cable
system fro Monitor Technologies LLC, the SiloPatrol® SE.
Anhui
Tongling power plant in Anhui province in China had
tried almost ever technology possible to get a reliable
level measurement in their 5 coal powder silos. Radar,
ultrasonic and others were tried, but none worked reliably. It
wasn’t until Beijing Conasen walked in and proposed
that the Tongling plant use the SiloPatrol SE smart
cable-based inventory monitoring system that the power
plant personnel found a reliable solution.
Mr. William Yuan, sales manager for Beijing Conasen
indicates that the power plant tried many major brands
of ultrasonic, radar, and other technologies but that
due to good relations with the Tongling plant personnel
he was able to sell three SiloPatrol SE model SMU sensors
and an HMI operator interface to them. The units
were installed by plant personnel. Because of
the heavy amount of coal dust in the silos an air purge
using dry compressed air was used. The SiloPatrol
sensor incorporates the patent-pending use of Hall-effect
sensor technology, a split-compartment enclosure, microcontroller,
redundant optics and many other valuable features and
technology to ensure reliable measurement even in challenging
dust applications like coal powder.
The SiloPatrol SE system has been working reliably
and the plant has since purchased two additional sensors
and connected them into the same HMI operator interface. This
same sensor technology is working reliably at other
coal-fired power stations in China as well.
Monitor Technologies LLC is a pioneering supplier of level measurement instrumentation,
solids flow monitors, particle emission monitors and aeration devices for the
worldwide powder and bulk solids markets. The experience and market knowledge
gained over 50 years of business has earned Monitor a reputation for providing
high quality and reliable product solutions backed with trusted customer service.
Monitor is located in Elburn Illinois.
The TrueCap® Model MK-2
RF Capacitance point level probe is designed to provide a superior
and stable sensitivity threshold making it suitable for a variety
of powder / bulk solids and some liquid or slurry applications.
Advanced features of the Model MK-2 include: > Automatic immunity to material build-up on
the probe by its driven shield design > Push-button calibration > Enhanced temperature compensation > Maximized reliability via smart sensing algorithms
like “self-validating” fail-safe protection > Visible status LED on ordinary location units > Versatility through a variety of configuration
options including: hazardous location version, split architecture
design, quick-connect process connection, stub probe, cable extensions,
solid extensions, Nylon® probes, Ryton® - equiv. probes,
etc.
A practical application for the TrueCap would be to use this level sensor where
a residual material build-up on a different sensor would cause a false material
level indication.
Principle of Operation for the TrueCap RF Capacitance Level
Probe:
The vessel wall and the active probe element establish an impedance reference
between each other when exposed to air which has a dielectric constant of 1.
When materials with a dielectric constant greater than 1 are in close proximity
to the probe, the impedance of the sensing field between the sensor and the vessel
wall will change. Once the amount of change exceeds a threshold that was electronically
determined during the calibration process, an output relay will either be energized
or de-energized depending upon the position of the fail-safe selector on the
probe’s electronic circuit board. A change of as little as .5 pico-farad
is all that is necessary for the probe to sense the presence of material.
