Patent Application
20130167541
The present invention relates to gas turbines and, in particular, to an air-fuel premixer for a gas turbine combustor with a variable swirler.
Gas turbine engines generally include a compressor for compressing an incoming airflow. The airflow is mixed with fuel and ignited in a combustor for generating hot combustion gases. The combustion gases in turn flow to a turbine. The turbine extracts energy from the gases for driving a shaft. The shaft powers the compressor and generally another element such as an electrical generator.
Gas turbine output varies based on many factors, one of which is fuel type. Lower reactivity fuels typically have lower flame speed, and as a consequence, the flow rate of the fuel and compressed working mixture from the primary nozzles is sufficiently high so that combustion in the upstream chamber occurs at a sufficient distance from the primary nozzles to prevent the combustion from excessively heating and/or melting the primary nozzles. Higher reactivity fuels, however, have higher flame speeds. Increased flame speeds can move the combustion in the upstream chamber closer to the primary nozzles. Local flame temperature in the upstream chamber using higher reactivity fuels could result in premature or catastrophic failure of the component.
In the current swirler or swozzle set up, at base load or any given load condition, average axial velocities in the burner tube exit remain constant. The axial and tangential velocity components depend on swirler vane angle. The desired axial velocities at the burner tube exit are determined from flame speeds of a particular fuel composition (e.g., 30 ft/s safety margin at the burner tube exit).
It would be desirable to control axial velocities in the burner tube to aid in operating the machine over an extended operating range for various fuel compositions.
In an exemplary embodiment, a swirler assembly in a gas turbine combustor includes a hub, a shroud, and a plurality of vanes connected between the hub and the shroud. A vane angle of the plurality of vanes is adjustable.
In another exemplary embodiment, a burner for use in a combustion system of a gas turbine includes a fuel/air premixer having an air inlet, a fuel inlet, and an annular mixing passage. The fuel/air premixer mixes fuel and air in the annular mixing passage into a uniform mixture for injection into a combustor reaction zone. The fuel/air premixer includes a swirler assembly downstream of the air inlet. The swirler assembly includes a hub, a shroud, and a plurality of vanes connected between the hub and the shroud that impart swirl to the incoming air. A vane angle of the plurality of vanes is adjustable. The burner also includes an inlet flow conditioner disposed at the air inlet of the fuel/air premixer upstream of the fuel inlet.
In yet another exemplary embodiment, a swirler assembly in a gas turbine combustor includes a hub, a shroud, and a plurality of vanes connected between the hub and the shroud. A vane angle of the plurality of vanes is adjustable. Each of the plurality of vanes includes a fixed section secured between the hub and the shroud and a movable section movably secured to the fixed section. At least one of the plurality of vanes includes a fuel passage.
Air enters the burner from a high pressure plenum 6, which surrounds the entire assembly except the discharge end, which enters the combustor reaction zone 5. Most of the air for combustion enters the premixer via the inlet flow conditioner (IFC) 1. The IFC includes an annular flow passage 15 that is bounded by a solid cylindrical inner wall 13 at the inside diameter, a perforated cylindrical outer wall 12 at the outside diameter, and a perforated end cap 11 at the upstream end. In the center of the flow passage 15 is one or more annular turning vanes 14. Premixer air enters the IFC 1 via the perforations in the end cap and cylindrical outer wall.
The perforated walls 11, 12 perform the function of backpressuring the system and evenly distributing the flow circumferentially around the IFC annulus 15, whereas the turning vane(s) 14 work in conjunction with the perforated walls to produce proper radial distribution of incoming air in the IFC annulus 15. Depending on the desired flow distribution within the premixer as well as flow splits among individual premixers for a multiple burner combustor, appropriate hole patterns for the perforated walls are selected in conjunction with axial position of the turning vane(s) 14.
To eliminate low velocity regions near the shroud wall 202 at the inlet to the swozzle 2, a bell-mouth shaped transition 26 may be used between the IFC and the swozzle.
After combustion air exits the IFC 1, it enters the swozzle assembly 2. The swozzle assembly includes a hub 201 (
The swirler assembly according to exemplary embodiments serves to control the axial velocities in the burner tube to aid in operating gas turbines over an extended operating range for various fuels. The swirler assembly serves to enhance fuel flexibility and extended operability. With reference to
With a straight vane, a tangential component of the velocity is almost negligible, while axial velocity represents the bulk of the velocity magnitude. As the vane angle increases, axial velocity decreases and tangential velocity increases.
With reference to
With reference to
Preferably, the vane angle is set to the same angle for each of the plurality of vanes 23. Vane angle can be set using conventional structure such as the structure used for controlling inlet guide vanes (IGVs) of a gas turbine. See, for example, U.S. Pat. No. 7,985,053, FIGS. 1 and 2. Preferably, the vane angle is determined according to a type of fuel input to the gas turbine. That is, based on the fuel composition, an optimum angle for the swirler vanes can be set before turbine start up to give enough safety margin for reliable operation. The vane angle may also be determined according to ambient conditions in which the gas turbine is operating. Still further, the vane angle may be changed while the system is running.
In an alternative embodiment, with reference to
The variable swirler angle addresses flame holding issues (inside the premixer) and serves to stabilize the flame in the combustion zone for a wide range of fuel compositions by suitably varying axial velocities.
While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiments, it is to be understood that the invention is not to be limited to the disclosed embodiments, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.
