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Coal Pulverisers--Performance and Safety

AUTHOR: David H. Scott
DATE: June 1995

This study reviews issues related to the efficient and safe operation of coal pulverising systems for large power station boilers. Commercial considerations and the need to comply with increasingly stringent environmental regulations are challenging existing design and performance specifications for pulveriser systems.

Pulverised fuel quality is critical in achieving clean and efficient combustion. Fuel quality is determined by the properties of the coal and by the design and operating specifications of the pulverising system. The term 'coal' covers a wide range of materials and coals of similar elementary analysis may have markedly different macro and micro structures. The size distribution of the pulverised fuel is a critical quality parameter. The need to lower NOx emissions while controlling the carbon content of the ash has implications for the required fineness of the fuel and hence for the design of the milling system. Accurate distribution of the fuel to the burners is also important and requires careful design, commissioning and operation of the fuel delivery system.

Safety hazards are associated with many of the coals used for power generation. In the finely powdered state, they may be prone to spontaneous combustion and may form potentially explosive mixtures with air. While it does not appear that the hazards associated with milling coal in air can be eliminated, the frequency of incident and the severity of the effects can be reduced by good practice and careful design.