A periodic check of pulverized coal fineness leaving the pulverizer should be made to determine if pulverizer is performing properly and to detect possible mechanical problems.
This should be done at approximately six month intervals but should be varied based on type of coal, abrasiveness of the coal, erosiveness of the coal and variations in the coal supply.
It must be noted that the fineness will vary with the grindability of the coal, the fraction of rated capacity that the pulverizer is operating at the coal air ratio, and classifier setting.
Therefore it is important to run the fineness tests at similiar mill loads, coal-air ratios and classifier settings each time to eliminate some of the variables which could effect the results.
The base rate of Babcock & Wilcox Pulverizer product fineness 200 mesh (74 micron) is 70% with 50 HGI and surface moisture 5% (correction factor is 1).
If coal 200 mesh 75% with 52 HGI and 8% surface moisture, we get 0.94 correction factor as picture above.
It means maximum capacity of pulverizer is reduce to 94%.
All above chart need Proximate analysis of coal sampling to get HGI (hard groove index) and surface moisture data. Coal fineness 200 mesh get 75% is from coal fineness taken sample at discharge Pulverizer coal pipe.
The ultimate task in pulverizer is the selection of size and number of mills for the proposed project.
The total boiler heat input and coal flow requirements are establish from combustion calculation and the specified boiler steam flow requirements.
The coal flow rate is then diveded by the capacity correction factor to establish the equivalent required pulverizer capacity.
For example if the unit at maximum load have each pulverizer handle 50T/h, so the capacity of each Pulverizer should be 50/0.94 = 53.2T/h
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