How do you measure your glass level in your production hall?
How much is important a stable glass level for furnace operation?
Which is the overall performance increase due to a very stable glass level?
Within this technical paper we discuss about 3 measuring technologies and make a confrontation on their capabilities and characteristics regarding:
The three model chosen for this test are:
A standard probe (contact) type with platinum tip, encoder and analog output
An optical (no-contact) measuring system with emitter/receiver both in light or laser technology
Glass Service brand new interferometric radar technology (no-contact)
How do you measure glass level in your production hall?
What kind of system would you choose to do the following measurement?
What are the main characteristics that you have to verify for proper measuring?
The measuring precision/repeatability of your instrument must be higher than the value that you are going to detect. The instrument precision and repeatability is done from:
Precision of the measuring sensor and relative measuring process
Precision/stability of the sensors support
For a correct measure the precision of the support must be at least 10 times higher than the measure precision/repeatability required.
In glass industry the glass level precision required is 0,1 mm.
It means the sensor support precision/stability must be at least 0,01 mm.
Which are the parameter that influence the correct measure precision in glass furnaces?
The main are:
Environment temperature, and furnace radiation
Water temperature and water pressure for water cooled probe
Environment temperature, and furnace radiation in optical measure system
The optical measure system based on the light emitter and the light receiver are installed on a metallic support.
Because the long distance between emitter and receiver a few deformations of the support have a high error in light beam receiver position.
e.g.
for emitter-receiver distance of 3000 mm inclined an angle of 15 Deg from horizontal plane, a supporting deformation of 0,01 deg have a variation of 0,5 mm.
Environment temperature, and furnace radiation in standard probe type with platinum tip
In this model the installation could be with water cooled probe or ceramic probe.
In booth case the thermal deformation of the machine and his support have two main direction:
This value are not negligible.
e.g.
a supporting column in carbon steel + the machine body with a total length of 1500 mm have a thermal extension with 10 °C variation of 0,18 mm, more than the instrument precision to measure.
Including the bending of supporting probe (2 in picture) this value is quite bigger than the measure precision required.
For the water cooled machine the thermal deformation of the probe (2 in picture) change also with the water-cooled temperature and the water pressure.
Who’s controlling the controller?
You should always remember that your actual glass level is controlled by your furnace level control so if it’s introducing an error on his own you are not detecting it because the batch charger will follow exactly its signal THUS meaning that you may are reading a continuous signal which is only a continuously wrong signal with an oscillating glass level.
What is the advantage of radar technology?
In radar Glass level the probe deformation is controlled by the radar software and compensate. The software knows the length of the probe and the shape of the probe at ambient temperature. In case of dimension variation, it can calculate the probe deformation and compensate for a correct reading.
How much is important a stable glass level for furnace operation?
It’s clear enough that a very stable furnace level could be achieved only when the glass level control it’s very precise
AND
It’s coupled to a well dimensioned speed controlled batch charger: without this necessary condition nothing of what is following would be true.
But in that case a stable glass level in your melting process determines:
Stable charging process = stable quantity of cold materials introduced in the basin = stable melting conditions = gas savings
Stable glass flow and more homogenous (through time) temperature in the distributor and feeders = gas savings
Stable conditioning conditions = less variation in gob weight = increased production efficiency
More scientific and accurate approach to furnace conduction it means less need of changings or adjustments in furnace control (i.e.: between day and night shifts settings).
Which is the overall performance increase due to a very stable glass level?
It is not easy to determine how much a very stable glass level could help increase your production efficiency but in such a competitive scenery like the one you’re acting on nowadays even a 0.001% efficiency increase would be able to grant you, on a standard 100 Tons per day furnace, an yearly advantage of more than 36 tons against your competitors.
On a provisional (minimum) equipment life time of 6 years how worth is the investment to have back more than 215 Tons of glass produced? (…and this values increases to 430 Tons for a 200 Tons per day melting furnace…).
In this page we will follow with a resuming table that gives you and in-depth analysis and confrontation on 3 different level control technologies.
Comparison of 3 different glass level control technologies
very poor poor standard good outstanding
Control Technology
Evaluated Field | Probe type | Optycal | Interferometric Radar |
Reading Accuracy |
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Reading Repeatability |
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Temperature Effect on Accuracy |
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Time Effect on Accuracy |
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“Mechanical” error introduced by the chassis |
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Tolerance to environment “climate” changes |
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Reading precision |
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Maintenance demand |
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Maintenance interval |
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Maintenance costs |
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Maintenance skills required |
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Life expectation |
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Cooling demand |
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Melting basin level stability with proper batch charger connection |
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Cost |
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Average Evaluation |
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