Tubular flame burner and combustion control method

A multi-stage tubular flame burner apparatus comprising (i) a plurality of tubular flame burners including a first tubular flame burner and a second tubular flame burner and (ii) a combustion control means, each tubular flame burner comprising:

• (a) a tubular combustion chamber having an open front-end and a rear-end, the tubular combustion chamber having an inner circumferential wall, the tubular combustion chamber having rectangular slits at the rear-end thereof, the rectangular slits being long in an axial direction and narrow in a radial direction, wherein the inner circumferential wall of the tubular combustion chamber of the second tubular flame burner has a larger inner diameter than an inner diameter of the inner circumferential wall of the tubular combustion chamber of the first tubular flame burner;
• (b) a plurality of spraying nozzles for spraying a fuel gas and an oxygen-containing gas separately and individually, wherein a spraying direction of the fuel gas and a spraying direction of the oxygen-containing gas are the same, or spraying a premixed gas of the fuel gas and the oxygen-containing gas, the spraying nozzles having a flat shape and being connected to the slits, respective orifices of the respective nozzles facing toward the inner circumferential wall of the tubular combustion chamber, so as to spray the fuel gas and the oxygen-containing gas or the premixed gas in a tangential direction of the inner circumferential wall of the tubular combustion chamber to produce a swirl of the fuel gas and of the oxygen-containing gas or a swirl of the premixed gas in the tubular combustion chamber;
• (c) switching valves including first switching valves and second switching valves which are each in fluid communication with a fuel gas supply and an oxygen-containing gas supply, and are operable to permit or stop a flow of the fuel gas and to permit or stop a flow of the oxygen-containing gas, such that the first switching valves are for carrying out switching between using and stopping of the first tubular flame burner and the second switching valves are for carrying out switching between using and stopping of the second tubular flame burner,
• wherein the front-end of the first tubular flame burner and the rear-end of the second tubular flame burner are connected in series to form the multi-stage tubular burner, and the tubular combustion chamber of the second tubular flame burner has the larger inner diameter than the inner diameter of the tubular combustion chamber of the first tubular flame burner, and
• wherein the combustion control means controls combustion by selecting a tubular flame burner to be used from the plurality of tubular flame burners that form the multi-stage flame burner, such that a spraying speed of the fuel gas and the oxygen-containing gas or the premixed gas sprayed to the combustion chamber in accordance with a combustion load is controlled to within a range between a maximal permissive spraying speed dependent upon a pressure loss and a minimal spraying speed required for forming a tubular flame.