PURPOSE:To enable a stable flame to be obtained under a condition of wide combustion by a method wherein disturbance flow edges for applying disturbance flow to fine powder coal stream at a primary air port and the disturbance flow edges are provided at their sides with such tapered portions as causing the flow to be expanded. CONSTITUTION:Eight disturbance flow edges 16A are arranged in a primary air port 15 and both sides of the disturbance flow edges 16A are provided with tapered portions 18. With this construction, combustion air is pressurized with a forced blower, heat exchanged with a discharging gas with an air heater and heated thereby. An amount of air is adjusted with a damper, thereafter it is guided by a duct and supplied to an air box 1. A part of combustion air supplied to the air box 1 enters a secondary sleeve through a secondary air inlet port 5 adjusted by a secondary sliding damper 4, and the air is made as a circulation flow with a secondary vane 6 and then supplied into a furnace through a secondary air port 7.With this arrangement, the disturbance is increased by the disturbance flow edge 16A and thus a stable flame can be formed by this portion.
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