PURPOSE:To stabilize a fuel line by controlling to stabilize combustion of a boiler, by previously controlling the coal rate by a corrected mill differential pressure in accordance with the changing rate of required value of coal feed rate, and by controlling the feeding rate of coal by adding a primary delay function to an operating signal to a coal feeder. CONSTITUTION:A preceding circuit 'H' is a driver to bring the rising of mill differential pressure in a mill near to a primary air differential pressure by previously controlling the differential pressure by adding a corrected value of mill ratio to it. A coal- feeder operating signal 31 calculated by a feeding coal arithmetic and adding circuit E-1 adds a primary delay circuit 'I' to a coal feeding rate command, that is a demanded value to the primary air differential pressure command for a primary air damper. Then the coal feeder is operated by a feed coal command. The delay time which appears as a mill differential pressure, that is, a delay time to pulverize coal is corrected by the primary delay circuit 'I'. A corrected value is added to the set signal of coal feeding rate, and a proper control is performed by a control circuit G-1 constituted of a proportional control and an integral control. The change caused by stoking of coal fuel is absorbed by the primary delay circuit 'I', and a feed coal controlling signal 28 which conducts a stabilized coal feeding can be output.
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