A multi-component model for the vertical spindle mill

Abstract

Vertical spindle mills (VSMs) are widely utilised in coal power plants that account for more than 40% of the electrical energy generated worldwide. These mills can consume up to 1% of the gross power generated by the plant; and hence, present a good scope for optimisation. However, optimisation requires better understanding of the operation of these mills and reliable models to be used for investigating optimisation opportunities. A new model of VSMs has been developed which enabled interlinked simulation of comminution and classification operations that occur in the mill. The multi-component models incorporate the effects of size and ash distribution in coal feed, air and coal flow rate and power drawn by the mill. Both models utilise the size-by-size density distribution of the coal streams. An efficiency curve model based on settling velocity was used to describe and distinguish difference in behaviour due to variable density of the components and their composites in the three classification regions. The matrix comminution model works with a selection function that is only dependent on size and a three dimensional breakage function that is size, density and energy dependent to account for the differences in breakage of components and composite particles. It has been demonstrated that, the particle size distributions and flow rates corresponding to the streams in the mill and its product can be estimated with a very good accuracy. A reasonable prediction is also found for the density distributions in these streams.