PURPOSE: To lower an unburnt component in an exhaust gas without raising the temperature of a furnace by setting an amount of air of a sub air port provided between main air ports based on a flow rate of a jet flow of a burner and a spiral force of the burner. ;CONSTITUTION: In an air port through which air for combustion is blown in on the downstream of a burner 2 which makes a burning below a theoretical air for making up for the shortage thereof, sub air ports 4 each with a smaller diameter thereof than main air ports 3 are provided between the main air ports or at least one or more thereof are provided between the main air ports and side walls or at both thereof to build a furnace 1. Then, the sub air ports 4 are provided with a flow rate adjusting function, an jetting direction adjusting function and moreover, a spiral generation function. The distribution or adjustment of the air ports is performed in correspondence to a flow rate distribution of a burner jet flow, a direction of turning the uppermost stage burner or a product of the direction of turning and a flow rate of the burner flow rate. This enables the lowering of an unburnt component in an exhaust gas without raising the temperature of a furnace.;COPYRIGHT: (C)1993,JPO&Japio
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