Method for premixing air with a gaseous fuel and burner arrangement for conducting said method

A method for premixing air (33) with a gaseous fuel for being burned in a combustion chamber (12) comprises the steps of: guiding said air (33) in an air stream along a burner axis (13) through a coaxial air tube (11) into a combustion chamber (12) arranged at an end of said air tube (11); impressing a swirl on said air stream by passing it through a first swirl device (14) concentrically arranged within said air tube (11) and comprising a plurality of radially oriented first blades (29); injecting gaseous fuel into said air stream at said first swirl device (14); and mixing said air in said air stream with the injected gaseous fuel in a first mixing zone (15) arranged just after said first swirl device (29) An improved fuel/air premixing and low pressure drop is achieved by taking the further steps of: sending the mixed fuel/air stream leaving said first mixing zone (15) through at least one second swirl device (16) concentrically arranged within said air tube (11) and comprising a plurality of radially oriented second blades (30) to reduce the swirl of the mixed fuel/air stream; injecting gaseous fuel into said mixed fuel/air stream at said second swirl device (16); and further mixing said mixed fuel/air stream with the injected gaseous fuel in a second mixing zone (17) arranged just between said second swirl device (30) and said combustion chamber (19).