Dual-fuel pre-mixing burner assembly

In a dual-fuel pre-mixing burner assembly for a turbine having a burner assembly body, a liquid fuel nozzle disposed substantially centrally of and adjacent an inlet to said body, a flow duct carried by said body, said duct including an upstream converging section, a throat section and a downstream diverging section, inner and outer generally concentric passages adjacent said body inlet, and at least one gaseous fuel nozzle carried by said body, a method of combustion comprising the steps of:

• flowing fuel from said liquid fuel injection nozzle into said flow duct for flow in a generally downstream direction;
• introducing air through said inner passage into said flow duct having flow components in a first generally tangential direction and said generally downstream direction for mixing in said flow duct with said liquid fuel and affording a swirl to the flow exhausting from said diverging section;
• establishing downstream of said burner body a recirculation zone resultant from expanding the swirling exhaust flow from the diverging section of the flow duct to afford flame stabilization;
• flowing air through said outer passage bypassing said flow duct into a flow region downstream of said burner body with a flow component in a second generally tangential direction opposite said first tangential direction to establish therewith a shear flow layer in said downstream flow region to further afford flame stabilization;
• and
• flowing gaseous fuel into said flow duct from said gaseous fuel nozzle for combining with the liquid fuel/air flow through said flow duct to obtain a lean pre-mixed fuel flow for reduced emissions.

A pre-mixing burner assembly for a turbine, comprising:

• a burner assembly body having an inlet for flowing fuel and air in a generally downstream direction and having a fuel nozzle disposed substantially centrally of and adjacent said inlet to said body for supplying fuel for flow in the generally downstream direction;
• a flow duct, carried by said body and having an upstream converging section, a throat section and a downstream diverging section, for receiving fuel from said central nozzle and air from said inlet;
• inner and outer generally concentric passages adjacent said body inlet for flowing air through said body;
• at least one gaseous fuel nozzle carried by said body and located to flow gaseous fuel through said duct in the generally downstream direction;
• said inner passage lying in communication with said flow duct to supply air thereto for pre-mixing, in said duct, air and fuel to form a lean air and fuel mixture from said at least one of said central liquid fuel nozzle and said gaseous fuel nozzle and for delivery of said pre-mixed air and fuel to a flow region downstream of said duct;
• an inner swirler in said inner passage for delivering to said duct air having a flow component in a first tangential direction such that the pre-mixed fuel and air delivered from said duct to said flow region has a flow component in said first tangential direction;
• said converging section of said duct and said pre-mixed fuel and air, exiting said converging section of said duct, comprising a means for establishing a centerline recirculation zone in said flow region therefore affording flame stabilization;
• and
• an outer swirler means in said outer passage for delivering to said flow region downstream of said duct air having a flow component in a second tangential direction generally opposite to said first tangential direction and for establishing, in combination with the flow having said first tangential component, a generally annular shear layer in said flow region, said centerline recirculation zone and said annular shear layer comprising a means for flame stabilization in said burner assembly.