Sequential combustion with dilution gas mixer

A method for operating a gas turbine with at least a compressor, a combustor arrangement comprising a first burner, a first combustion chamber, a mixer for admixing a dilution gas to the hot gases leaving the first combustion chamber during operation, a second burner connected to an outlet of the mixer at a downstream end for connection to the second burner, a second combustion chamber arranged sequentially in a fluid flow connection, a connection duct configured for cooling a liner of the combustor arrangement with dilution gas from a compressor, and a turbine, wherein the connection duct is inside a compressed air plenum formed by an outer casing of the combustor arrangement, wherein the mixer includes a plurality of injection pipes pointing inwards from the side walls of a duct, and wherein at least one of the plurality of injection pipes includes a pipe wall having cooling holes, the method comprising:

• guiding, via the mixer, combustion gases in a hot gas flow path extending between the first combustion chamber and the second combustion chamber;
• injecting the dilution gas from the connection duct via the plurality of injection pipes to cool hot flue gases leaving the first combustion chamber, wherein the dilution gas is admixed into different regions of the cross section of the mixer;
• and
• transferring heat from the pipe wall via a thermal barrier coating applied on an upstream side of the pipe wall and reducing a pressure drop in a hot gas flow via the cooling holes provided on a downstream side of the pipe wall.