40
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World Coal
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December 2015
DEWATERING
TECHNIQUES
John R. Casey II, Tabor Machine Co., USA,
looks at the process of removing surface moisture from
coal through vibrating and high-frequency screens.
T
abor Machine Co., an Elgin Separation Solutions company, was
founded in 1961 to meet the demands of the rising local coal
market. Since then, Tabor has been successful in supplying
vibrating screens all over the world to meet the ever changing
requirements of the coal preparation industry.
Dewatering uses
The dewatering application has many different uses pertaining to the
preparation of materials. One of the main uses is simply removing enough
of the water in order to produce a conveyable product in which gravity
will not overcome the friction of the material when transported by a
sloped belt. The material, whether it is a saleable product or reject, must be
able to be handled in a safe and efficient manner. Often, the easiest and
most economical way to remove the excess water is by mechanical means,
such as a dewatering screen.
The vast majority of coal preparation plants use a dewatering screen to
remove the water from the fine refuse so that the material can be
combined with the coarse refuse and transferred by belt or truck to the
refuse area. The fines may be delivered to the dewatering screen from the
cyclone and/or the spiral circuit for dewatering before being discharged
onto the refuse belt.
In many plants, even the ultra-fine refuse may be combined on the
dewatering screen after the material has formed a cake. This will help to
retain this ultra-fine material for disposal and reduce the amount of
material reporting to the thickener. The higher the volume of water that
can be removed from the refuse before the material reaches the dump , the
less likely problems associated with excessively wet material will arise.
The average moisture of the fine refuse after being screened on a
vibrating dewatering screen, and thus sent to the refuse area, is typically
between 12% – 20%. This percentage of moisture is based upon the type of
material being screened along with the average particle size of the feed.
Generally speaking, the smaller the average particle size, the higher the
surface moisture after screening due to its increased surface area.
Tabor Machine is now seeing a trend in the use of dewatering screens
underground for the same reason: efficiently and economically conveying
