Reducing unburnt carbon

Paul Boughton

A fail-safe, high-precision fill-level and temperature measurement system helps produce the optimum combustion properties for your coal. Alexander Scholl reports.

Homogenous fuel is a key parameter for ensuring high levels of efficiency when burning coal. When the fineness of the coal is precisely suited to the particular combustion process and its homogeneity can be guaranteed, it is possible to keep the amounts of unburnt carbon to an absolute minimum.

In this regard, the quality of the grinding process is of exceptional importance. One of the most important factors that affects the efficiency of the grinding process is the fill-level of the ball mill.

An optimum fill-level ensures that the balls can grind the material in the most efficient manner possible. The grinding efficiency declines if the mill chamber is too empty or overly full. It also leads to increased wear and/or specific energy consumption.

The challenge, therefore, becomes how to measure the fill-level accurately and reliably for such grinding processes. The answer is SmartFill - a fail-safe, high-precision fill-level and temperature measurement system (Fig. 1).

Fields of application

The fill-level measuring device has been successfully used for a number of different types of ball mills in the power, cement and mining industry.

Over the past seven years, the system has been successfully sold for, and used in, more than 450 applications.

SmartFill is suitable for use in a variety of different types of ball mill, including (air-swept) tube mills, centre discharge mills and SAG mills. It can also be used irrespective of the type of lining (steel/rubber), grinding media (balls/cylpebs) or grinding process (wet/dry).

Once a measuring unit has been mounted on a mill for a while, it is also possible to obtain information about the wear to the ball charge by detecting incremental changes to the noise characteristics. However, this analysis must be carried out individually for each mill.


Microphones have had an important role to play in determining fill-level both from an historical and technological perspective.

Owing to their imprecision, however, it has not been possible to integrate them reliably into closed control loops.

SmartFill is claimed to 0the only measuring system worldwide that utilises the principle of structure-borne sound, combining it with intelligent technology, scientific methods of analysis and industry-standard interfaces.

Thanks to its high degree of precision and reliability, this fill-level measuring device can be used very efficiently with a closed control loop; in turn, this leads to considerable improvements in grinding process control.

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Alexander Scholl is with KIMA Echtzeitsysteme GmbH, Juelich, Germany.