Burner and Method for Forming a Flame in a Furnace by a Burner

A burner for forming a flame (F) into a furnace by means of gaseous fuel (G) and combustion air (I), simultaneously recirculating flue gases (S) in the furnace, wherein the burner comprises

• a burner frame and a combustion head connected by its cylindrical body to the burner frame, wherein an end portion of the combustion head facing the furnace extends at its first end to the furnace, and a second end of the end portion is connected to said cylindrical body,
• a primary gas pipe for supplying gaseous fuel (G;
• G1) to the furnace, wherein the primary gas pipe extends inside the combustion head in its longitudinal direction, particularly inside (T) of the end portion of the combustion head, and an orifice of the primary gas pipe opens into or close to the furnace, and a primary air supply pipe also extends inside the combustion head and surrounds said primary gas pipe, and an orifice of the supply pipe opens into the furnace or to the orifice of the end portion of the combustion head,
• a flow duct for main combustion air (Imain) extending inside the combustion head and surrounding said primary air supply pipe at least inside (T) of the end portion, and
• a set of main gas rods, comprising a set of elongated primary gas rods extending in the longitudinal direction of the combustion head, for supplying the furnace with fuel,
• wherein the main gas rods are arranged at least partly outside the cylindrical body of the combustion head, extending close to a joint (L) between the cylindrical body and the end portion so that they are surrounding said body at regular intervals around a circumference of the body,
• and
• wherein in connection with the main gas rods, at the end portion of the combustion head, several ejector ducts are provided for recirculating flue gas (S) from the furnace into the gaseous fuel (G, G2) coming from the main gas rods, and for conveying the produced flue gas-flue mixture (S+G2) further to the furnace,
• characterized in that the end portion of the combustion head has the shape of a truncated cone and comprises ejector ducts and air ducts alternating in a direction of a circumference of said end portion, free ends of the ducts opening in the direction of the furnace, and a top end of a duct groove of each ejector duct being also open in the direction of the furnace, and a lower end of the duct groove (of each air duct being also open in the direction of the central axis of the combustion head,
• wherein the end portion having the shape of the truncated cone expands at an angle of 3 to 30 degrees, seen from the direction of the joint (L) between the cylindrical body of the combustion head and the end portion of the combustion head.