Method of combustion with the aid of burners in industrial furnaces, and a burner to this end

A furnace heating gas burner, comprising:

• a burner head (1), an inner gas pipe (2) with an orifice (15), an outer protective pipe (3), an exhaust channel (5) leading to surroundings, the burner head placed at one end of the inner gas pipe (2) which inner pipe (2) is surrounded by the outer protective pipe (3), wherewith the fuel gases from the burner head (1) pass inside the inner pipe and also in the outer pipe and thereafter pass into the exhaust channel (5) which leads to the surroundings, the inner pipe (2) terminating short of the burner head (1);
• and
• a sleeve (10) provided downstream of the burner head, said sleeve (10) being inserted into and/or placed concentrically with the inner pipe (2) so that the sleeve orifice will be located within the inner pipe, the sleeve (10) having a terminal part (17) that co-acts with the inner pipe (2) to form a gap (14) therebetween, an exterior of the terminal part (17) co-acting with the inner pipe (2) being cylindrical in shape, wherein,
• the terminal part (17) of the sleeve (10), with the exterior cylindrical in shape, is inserted at a depth distance within the inner pipe (2) sufficient so the a size of the gap (14) formed between an inner surface of the inner pipe (2) and an exterior portion of the terminal part (17) of the sleeve (10) being cylindrical in shape is maintained cylindrical along the depth distance to maintain the size of said gap constant during thermal expansion and at full terminal expansion, and
• the size of the gap (10) is adapted so that the fuel and combustion air mixture coming from the burner head (1) and the recycled exhaust gases arriving through the gap (14) will be such as to cause the temperature of combustion to be lower than the temperature at which NOx is formed.

A furnace heating gas burner, comprising:

• a protective outer pipe (3);
• a burner head (1);
• an inner gas pipe (2) with an opening (15), the inner gas pipe (2) terminating short of the burner head (1), the inner gas pipe being separated from the outer pipe (3) by a space (16);
• a cylindrical sleeve (10) terminating with an orifice (13), the orifice located within a terminal part (17) of the sleeve (1), the sleeve (10) joined to a downstream end of the burner head (1) and the terminal part (17) of the sleeve (1) inserted into the opening (15) of the inner gas pipe (2) with the orifice (13) located within the inner pipe (2);
• an exterior portion of the terminal part (17) of the sleeve (10) co-acting with the inner tube to form only a single mixing gap (14) located between an inner surface of the opening (15) of the inner pipe (2) and an exterior portion on the terminal part (17) of the sleeve (10), the gap sized to mix fuel and a combustion-air mixture arriving from the burner head and an exhaust gas re-circulated through the gap (14) in a quantity such that the temperature of combustion will be lower than the temperature at which NOx is formed,
• wherein the exterior portion of the terminal part (17) of the sleeve (10) that co-acts with the inner tube to form said gap (14) is cylindrical and the terminal part (17) of the sleeve (10) is inserted at a depth distance within the inner pipe (2) sufficient so that the exterior portion of the terminal part (17) of the sleeve (10) that co-acts with the inner pipe to form said gap (14) is maintained cylindrical in shape along the depth distance to maintain the size of said gap constant during thermal expansion and at full thermal expansion,
• wherein, a ratio between a cross-sectional area (A1) of the sleeve outlet opening (13) and a cross-sectional area (A2) of the gap (14) is smaller than 0.10 but greater than 0.01,
• a ratio between the cross-sectional area (A4) of the space (16) present between the inner gas pipe (2) and the outer pipe (3) and the cross-sectional area (A2) of the gap (14) between the sleeve (10) and the inner pipe (2) lies in the range of 1.0-2.0,
• the ratio between the cross-sectional area (A4) of the space (16) between the inner pipe (2) and the outer pipe (3) and the cross-sectional area (A3) of the inner pipe (2) lies in the range of 0.75-1.75.