GAS FUEL FIRING BURNER

PROBLEM TO BE SOLVED: To provide a gas fuel firing burner capable of decreasing the generation of NOx with high combustion efficiency. SOLUTION: A gas fuel nozzle 15 arranged in a secondary air passage 6 for supplying gas fuel 19 to a furnace is formed with a double pipe having an inner pipe 152 and an outer pipe 153. To a fuel passage 155 for thick flame formed in the inner pipe 152 is supplied gas fuel 191 for thick flame separated from the gas fuel which is supplied to primary air 016 supplied to a furnace 022 from a primary air passage 05 and forms the diffusion flame of high fuel concentration in the furnace 022. Further, to a fuel paste 156 for thin flame formed between the outer pipe 153 and the inner pipe 152 is supplied gas fule 192 for thin flame composed of remaining gas fuel 19 which is supplied to tertiary air 017 flowing in a tertiary air passage 07, mixed with the tertiary air and supplied to the furnace 022 to form a premix flame of low fuel concentration in the furnace 022.