OPERATION OF COMBUSTION FURNACE

PURPOSE:To reduce NOx originating from a burner by recirculating a part of exhaust gas via a burner throat, when a boiler is put in start-up or low-load operation, in the combustion furnace equipped with the burner, burner throat and the exhaust gas recirculating system. CONSTITUTION:A boiler 1 has its furnace 2 provided with a burner 3 and a burner throat 4 as well as its top with an exhaust gas flue 6. Recirculating gas is led to gas recirculating duct 7 which brances off from the exhaust gas flue 6 to a gas recirculating fan inlet damper 10A, a furnace bottom inlet damper 11 and finally to the furnace 2. When the boiler 1 is put in start-up or low-load operation, a part of the recirculating gas from the gas recirculating fan 9 is sent to branch duct 8 to be pressure-fed via a fan 10 into a wind box 5 and then into the furnace 2 via the burner throat 4. With this, the gas velocity necessary for the burner throat 4 is secured to enable reduction in NOx originating from the burner 3.