Industrial burner and related combustion process for heat treatment furnaces

#The present invention relates to a high speed burner with lean and compact flame capable of obtaining very low NOx emissions while keeping the flame stable at any chamber temperature. The burner implements combustion techniques such as dividing the main combustion into three stages (air and fuel staging), recirculating flue gases and further diluting some reagents.

#Over the last years, the market demand concerning a reduction in gas consumption has forced industrial furnace manufacturers to develop their products by taking advantage of the heat of the combustion flue gases for heating the combustion air by means of exchangers. Therefore, the need has been created to develop burners which operate with comburent air pre-heated at a temperature of about 400-550° C. At the same time, the laws on nitrogen monoxide and dioxide emissions have established increasingly restrictive limitations and have forced manufacturers to make burners capable of falling within the limitations set.

#However, it is known that the formation of the NOx also increases according to the temperature of the combustion air. The higher the temperature of the air, the more the temperature of the flame increases thus generating the formation of thermal NOx. To keep the emissions low, low NOx burners use techniques for decreasing the temperature of the flame such as flame staging, flue gas dilution and flameless combustion.

#Further features and advantages of the invention will be more apparent in light of the detailed description of a preferred, but not exclusive, embodiment of a burner, shown by way of non-limiting example, with the aid of the accompanying drawings in which:

#FIG. 1 shows a first perspective view of a burner according to the invention;

#FIG. 2 shows a second perspective view of the burner in FIG. 1;

#With reference to the figures, a preferred embodiment is shown of a burner, globally indicated by numeral 1, adapted to achieve a very low NOx emission combustion with high speed flame by using the simultaneous combination of the techniques of “fuel staging”, recirculating flue gases and diluting the flame.

#The burner 1, object of the present invention, defines a longitudinal axis X and comprises: a main metal holly body, in essence of cylindrical shape, comprising a first longitudinal hollow element 2 connected to and communicating with a second longitudinal tubular element 5 or flame guide tube; a pipe for feeding the comburent air 3; a pipe for feeding the combustible gas 4; a connection flange 6 of the burner to the furnace armour plate; a connection flange 10 of the first longitudinal hollow element 2 on the connection flange 6; a cylindrical tubular element 7, preferably made with silicon carbide or other suitable material, accommodated within the flame guide tube 5 at the front end thereof (FIGS. 4 and 5); a combustion head or diffuser 13, in essence of flat and round shape, for passing the combustible gas and the comburent air into the combustion chamber of the furnace, said diffuser 13 being accommodated within said cylindrical tubular element 7 so as in essence to define a cup whose bottom is the diffuser 13 (FIG. 5); a feeding lance 14 for the combustible gas; a housing for the ignition device 11 with electrode 16 or pilot burner, obtained in the first longitudinal hollow element 2; a guide tube 12 for accommodating a flame detection device.

#The pipe for feeding the comburent air 3 is connected with the tubes of the feeding system by means of the flange 8 which may have, for example, circular or square shape. The air passing through the pipe 3 passes through the volume 26 within the hollow element 2 of cylindrical shape and through the volume 27 within the flame guide tube 5, before being injected into the combustion chamber.