Inboard radial dump venturi for combustion chamber of a gas turbine

A double wall venturi chamber having a converging section, a diverging section and a cylindrical section wherein said chamber defines a venturi zone in which compressed air, fuel and combustion products flow downstream through converging section, diverging section and cylindrical section, and has a cooling gas passage between the walls of the venturi chamber, a least one cooling gas inlet in an outlet wall of the venturi chamber, and at least one cooling gas outlet in an inner wall of the venturi chamber, wherein said cooling gas outlet is in at least one of the diverging and the cylindrical section, and the outlet is downstream of the at least one cooling gas inlet and upstream of an axial end of the chamber.

BACKGROUND OF THE INVENTION

This invention relates to gas turbine combustors and, in particular, to combustors having primary and secondary combustion chambers divided by a venturi.

A combustor in an industrial gas turbine typically has dual combustion chambers. A venturi typically divides the combustor into primary and secondary combustion chambers. Combustion gases generated in the primary chamber flow through the venturi to the secondary combustion chamber. The conventional venturi chamber generally has dual-walls with cooling gas passages between the walls. Cooling air enters an upstream inlet to the passage between the walls of the venturi. The cooling air flows out from an axial end of the venturi. A conventional venturi chamber is disclosed in U.S. Pat. No. 5,575,146.

Conventional dual-wall venturi chambers exhausts cooling air from the annular passage between the walls of the venturi. The air from the venturi chamber is discharged from the axial end of the venturi chamber adjacent the combustor liner wall in the secondary combustion chamber. The combustion air is discharged from the venturi in an axial direction paralleling the centerline of the combustion chamber. The air from the discharge end of the venturi flows into the secondary combustion chamber along the liner wall of the combustor and flows in a direction generally parallel to the centerline of the chamber. The air discharged from the axial end of the venturi generally flows along the surface of the liner wall and does not quickly mix with the combustion gases in the combustion chamber.

There is a long felt need for combustors having robust mixing of compressor air and combustion products. This need also exists with the gas flow through a venturi. Robust mixing of air and combustion products tends to reduce emissions, such as reduced nitrogen oxides (NOx).

BRIEF DESCRIPTION OF THE INVENTION

The invention may be embodied as a venturi for a gas turbine combustor comprising: a double wall venturi chamber having a converging section, a diverging section and a cylindrical section wherein said chamber defines a venturi zone in which compressed air, fuel and combustion products flow downstream through converging section, diverging section and cylindrical section; a cooling gas passage between the walls of the venturi chamber; at least one cooling gas inlet in an outlet wall of the venturi chamber, and at least one cooling gas outlet in an inner wall of the venturi chamber, wherein said cooling gas outlet is in at least one of the diverging and the cylindrical section, and the outlet is downstream of at least one cooling gas inlet and upstream of an axial end of the chamber. The venturi chamber is adapted to be positioned between a primary combustion chamber and a secondary combustion chamber of the combustor. The cooling gas outlet may comprise a plurality of cooling gas outlets arranged circumferentially around the inner wall of the venturi chamber such that cooling gas projects radially inward to the venturi zone or at some angle less than 90 degrees from a radial line through the venturi zone.

The invention may also be embodied as a venturi for a gas turbine combustor comprising: a double wall venturi chamber having a converging section, a diverging section and a cylindrical section wherein said chamber defines a venturi zone in which combustion products flow downstream through converging section, diverging section and cylindrical section; a cooling gas passage between the walls of the venturi chamber; a cooling gas inlet in an outlet wall of the venturi chamber, and at least one cooling gas outlet in an inner wall of the venturi chamber, wherein said cooling gas outlet is in at least one of the diverging and the cylindrical section, and the outlet projects cooling gas radially inward into the venturi zone.

Further, the invention may be embodied as a method for injecting cooling gas into a combustor having a double wall venturi chamber having a converging section, a diverging section and a cylindrical section wherein said chamber defines a venturi zone in the combustor, said method comprising: providing cooling gas to an outer wall of the venturi chamber such that the cooling gas enters inlets in the outer wall; cooling the chamber with the cooling gas flowing through a passage between the outer and an inner wall of the venturi chamber, and discharging the cooling gas from the chamber and radially inward into the combustor through an outlet in the inner wall of the venturi chamber, wherein said cooling gas outlet is upstream of an axial end of the chamber. The cooling gas may be compressed air from an axial compressor of a gas turbine and the compressed air is also directed into the combustor upstream of the converging section.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1illustrates a conventional gas turbine12that includes a compressor14(represented by a section of a compressor casing), a combustor16and a turbine represented by a single blade18. The turbine is drivingly connected to a compressor along a common axis. The compressor14pressurizes inlet air which is turned in a reverse direction (see arrow33) towards the combustor16. The compressed air cools the combustor and provides air for the combustion process ongoing in the combustor. The gas turbine includes a plurality of the generally cylindrical combustors16(only one shown) which are located about the periphery of the gas turbine. In one exemplary gas turbine model, there are fourteen such combustors. A transition duct20connects the outlet end of the combustor with the inlet end of the turbine to deliver the hot combustion gases process to the turbine.

Each combustor16comprises a primary or upstream combustion chamber24and a secondary or downstream combustion chamber26separated by a venturi zone28. The combustor16is surrounded by a combustor flow sleeve30which channels compressor discharge air to the combustor. Arrows33show the flow of compressed air flow in a reverse direction to the combustion gas flow within the combustor. The combustor is further surrounded by an outer casing31which is bolted to the turbine casing32.

Primary nozzles36deliver fuel to the upstream combustion chamber24and are arranged in an annular array around a central secondary nozzle38. In an exemplary gas turbine, each combustor may include six primary nozzles36and one secondary nozzle38. Each of the primary nozzles36protrudes into the primary combustion chamber24through a rear combustor wall40. Secondary nozzle38extends from the rear wall40to the throat region28to introduce fuel into the secondary combustion chamber26. Fuel is delivered to the nozzles36through fuel lines, which are not shown. Ignition in the primary combustion chamber is caused by a spark plug and associated cross fire tubes, which are not shown.

Combustion air is introduced into the fuel stage through air swirlers42positioned adjacent the outlet ends of nozzles36. The swirlers42introduce swirling combustion air which mixes with the fuel from primary nozzles36to provide an ignitable mixture for combustion, on start-up, in the primary chamber24. Combustion air for the swirlers42is derived from the compressor14and from the routing of air33between the combustion flow sleeve30and the wall44of the combustion chamber.

The cylindrical liner wall44of the combustor is provided with slots or louvers48in the primary combustion chamber24, and similar slots or louvers48downstream of the secondary combustion chamber26. The compressor discharge air flow through the slots or louvers cools the liner and introduces dilution air into the combustion zones24,26to prevent substantial rises in flame temperature. The secondary nozzle38is located within a centerbody50and extends through a liner52provided with a swirler54through which compressor discharge air is introduced for mixing with fuel from the secondary nozzle.

FIG. 2is an enlarged cross-sectional view of a combustor16showing in greater detail a venturi zone which is defined by an improved venturi chamber60. The venturi chamber defines a throat70between the primary and secondary combustion chambers. The venturi chamber60includes an upstream converging portion56, a diverging portion58and a downstream cylindrical portion59. The double-walled venturi chamber60has an inner wall62and an outer parallel wall63both of which generally follow the contours of the converging and diverging portions of the venturi chamber but in radially spaced relation thereto.

A cooling passage64between the walls62,63of the venturi cools the walls of the venturi. The walls62,63may be held apart by a lattice of longitudinal internal struts65. The outer wall is provided with a plurality of cooling inlet apertures72through which compressor discharge cooling air enters the venturi passage64. The cooling air is air33from the compressor that flows through the sleeve30and through slots and louvers46,48in the liner wall44. The cooling air flows downstream and parallel to the direction of combustion gases through the passage64between the walls of the venturi.

Cooling air from the venturi passage64is discharged from an annular outlets74arranged on the inner wall62of the venturi. The annular outlets may be arranged in one or more circular arrays around the circumference of the inner wall62. The outlets are down stream of the cooling air inlets72in the venturi and upstream of the axial end76of the venturi chamber. The relatively low pressure in the combustion chamber26draws air into the venturi air passage64from the relatively high-pressure air33flowing outside of the outer wall63of the venturi. The cooling air outlets74exhaust cooling air into the combustion chamber26in a radial direction that is substantially perpendicular to the centerline of the combustor. Alternatively, the exhaust cooling air may project from the outlets74into the combustion chamber at an acute angle (i.e., less than 90 degrees) from a radial line through the venturi.

The throat of the venturi chamber60accelerates the core combustion premixed reactants immediately upstream of the flame zone. Gas velocities in the venturi are maintained above the flame speed of the mixture to ensure that the flame front does not propagate upstream into the premixing section24of the combustor. Air that is used to cool the venturi travels downstream through the venturi's internal annular passage, and is discharged into the combustor reaction zone26in an axial direction on the outboard surface of the combustion liner. Air that has been used to cool the venturi is injected into the core combustion flow through a plurality of injection sites74, such as slots, orifices and scoops. Injection of cooling air into the core flow is achieved by producing a series of penetrating jets, oriented in a orthogonal direction relative to the axial core flow.

The radial discharge of cooling gases from the outlets74of the venturi is expected to improve NOx and CO emission levels from the combustor. The radial injection of cooling air from the venturi walls should enhanced mixing of venturi cooling air with core combustor reacting gas flow and thereby reduce NOx and/or CO emissions.