Coal pulverisation with chaeng vertical roller mill

Vertical roller mill is the predominant equipment used for coal pulverisation in the power industry. The essential requirements of pulverisation are grinding, heating, classification and transport of the pulverised coal from the pulveriser.

The grinding elements coupled with proper alignment and compression are critical to coal pulverisation in the lower mill body (grinding zone) while the classification of the pulverised coal, discharge and recirculation, it is critical in the upper vertical mill body (classification zone).

The proper metering, distribution and control of air flow through the mill, this called primary air, it is critical throughout the pulveriser and it is the bridge between the lower grinding zone and the upper classification zone.

The coal pulveriser is the critical component of the fuel delivery system and it is a major influence of combustion efficiency in the burner zone as well as the performance and efficiency of the furnace itself. As such the coal pulveriser is truly the heart of the combustion process for a coal-fired power station.

In general, coal pulverisers are designed to achieve the maximum rated capacity grinding a design coal with a grindability of 55 HGI and 8-12% moisture and achieving a discharge fineness of 70 per cent passing a 200 mesh screen (74 micron) and 99.5 per cent passing a 50 mesh screen. Variation of the coal hardness or moisture content will effect, up or down, the discharge capacity or the discharge fineness.

To achieve these design considerations , it is essential that grinding elements are in good condition and they maintain a consistent profile. The loss of the grinding profile results in a loss of grinding efficiency, it means that the pulveriser must work harder to achieve an equal result.

Ultimately a point will be reached in which either a loss of capacity or a loss of fineness will result under uniform conditions. Longer lasting, more consistent grinding elements are crucial to pulveriser operation yielding longer operating campaigns, reduced maintenance and a lower overall invested cost.