PURPOSE:To permit the securing of the speed and amount of airflow without deteriorating a pulverized coal concentration by providing a circulating passageway for circulating air containing pulverized coal. CONSTITUTION:The rough particles of coal are separated from pulverized coal in the hopper 29 of a classifier by utilizing the centrifugal force of eddy current whereby air containing the rough particles of coal, air containing the pulverized coal and air diluted in the concentration of the pulverized coal, are present in a sequence from the outside of the eddy. The air diluted in the concentration of the pulverized coal is sucked into a bent tube 40 and circulates through a circulating passageway 41, then, blown up through the slits 42 of a throat 23 to blow up the pulverized coal together with usual primary air. In this case, the flow amount of the primary air, supplied from a primary air duct 12, the amount of coal, supplied by a coal supply tube 4, and the flow amount of air, circulating through the circulating passageway 41, can be measured respectively. The ventilating amount of a re-circulating fan 44 is controlled in accordance with the results of these measurements, whereby the concentration of the pulverized coal of a coal pulverizer 5 may be regulated freely. According to this method, the flow speed and the flow amount of the primary air in the throat 23 may be secured and the concentration of the pulverized coal may be increased simultaneously.
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