Patent Application
20090211255
This invention relates generally to a gas turbine combustor. More specifically, the invention relates to a flame stabilizer disposed at a fuel nozzle of the gas turbine combustor, whereby the combustor is operable with leaner premixed fuel air mixtures resulting in lower nitric oxide emissions.
Typically, a gas turbine combustor has both primary and secondary fuel nozzles. Such combustors have four modes of operation, which are primary, lean-lean, secondary, and premix. The primary mode is used for ignition of the combustor with fuel being delivered to the primary nozzles only. In the lean-lean mode the secondary nozzle is also ignited with fuel being delivered to both the primary and secondary nozzles. In the secondary mode fuel is only delivered to the secondary nozzle, thereby extinguishing the flame at the primary nozzles. Then in the premix mode fuel is delivered to both the primary and secondary nozzles, but the flame only exist at the secondary nozzle area, with the premixed fuel air mixture being optimized for desired performance including reduced nitric oxide emissions.
In seeking to lower the nitric oxide emissions of the combustors, they are often operated under lean conditions. However, operating under lean conditions runs the risk of lean blowout. Lean blowout occurs when operating under lean conditions and a change occurs, such as flow disturbance. Blowout results in the combustor transferring back to lean-lean mode or even shutting down, and respectively retransfer into premix or requiring re-ignition, as discussed above. To avoid lean blowout many combustors are run at richer conditions, but these conditions result in a higher flame temperature and greater nitric oxide emissions.
Government emissions regulations have become increasingly concerned with pollutant emission of gas turbines, such as nitric oxide.
U.S. Pat. No. 6,026,644 discloses a concaved cone shaped nozzle with turbulence promoters to promote a desired flame shape. The flame shape is disclosed as being more stable such that it is less susceptible to flow disturbances, thereby allowing leaner operation.
A gas turbine combustor is presented, which includes a premixing chamber and a combustion chamber. The premixing chamber includes at least one opening for ingesting air. At least one primary fuel nozzle is disposed to discharge fuel into the premixing chamber. The fuel discharged from the primary fuel nozzle mixes with the ingested air in the premixing chamber to provide a fuel air mix. The combustion chamber is positioned downstream of the premixing chamber. A secondary fuel nozzle is disposed proximate the combustion chamber to discharge fuel at the combustion chamber. A stabilizer is disposed at the secondary fuel nozzle so as to be positioned in close proximity of a flame when fuel at the secondary fuel nozzle is ignited. The stabilizer is composed of a material having the ability to absorb heat from a heat flux generated within the combustor and maintaining a temperature sufficient to sustain ignition of the flame.
A fuel nozzle for use in a gas turbine combustor is also presented, which includes a fuel nozzle and a stabilizer disposed at the fuel nozzle so as to be positioned in close proximity of a flame when the fuel nozzle is ignited. The stabilizer is composed of a material having the ability to absorb heat from a heat flux generated within the combustor and maintaining a temperature sufficient to sustain ignition of the flame.
A method of stabilizing a flame in a gas turbine combustor is presented. The method including discharging fuel at a combustion chamber of the gas turbine combustor and positioning a stabilizer in close proximity of a flame when the fuel at a combustion chamber is ignited. The stabilizer absorbing heat from a heat flux generated within the combustor and maintaining a temperature sufficient to sustain ignition of the flame.
Referring to
The gas turbine combustor 10 has four modes of operation, which are primary, lean-lean, secondary, and premix.
The primary mode is used for ignition of the combustor 10 with fuel 54 being delivered to the primary nozzles 14 only. Airflow is provided into the premixing chamber 18 through entry ports 50. It will be appreciated that primary fuel nozzle tip vanes and cooling circuits are not shown, in an effort to simplify the
In the lean-lean mode the secondary nozzle 16 is also ignited with fuel 54 being delivered to the primary and secondary nozzles, 14 and 16, respectively. About 60% of fuel 54 is supplied to the primary fuel nozzles 14 and about 40% percent of the fuel 54 is supplied to the secondary fuel nozzle 16. The secondary nozzle 16 ignites from the flame of the primary nozzles 14. This generates a desirable heat flux causing the flame stabilizer's 32 elongated member 34 to heat exponentially.
In the secondary mode fuel 54 is only delivered to the secondary nozzle 16, thereby extinguishing the flame at the primary nozzles. While combustion in the combustion chamber 12 continues at an even higher rate, nitric oxide emissions have not been reduced.
Then in the premix mode fuel 54 is delivered to both the primary and secondary nozzles, 14 and 16, respectively, but the flame only exist at the secondary nozzle 16. About 80% of the fuel 54 is then supplied in the primary fuel nozzle 14 and about 20% of the fuel is supplied to the secondary fuel nozzle 16. Fuel 54 from the primary fuel nozzles 14 is premixed with air induced from the entry ports 50 to create a fuel air mix within the premix chamber 18. This fuel air mix has not yet been ignited, and travels in a downstream direction, as indicated by arrows 58, toward combustion chamber 12. Where convergent/divergent walls, 60 and 62 of a venturi 20 constricts the flow of the fuel air mix. The flow constriction introduced by the venturi 20 will cause acceleration of the mix as it passes the convergent wall 60 based upon Bernoulli's Principle, whereby an increase in velocity comes with a decrease in pressure. Accordingly, this causes the fuel air mix to accelerate into the combustion chamber 12, while maintaining the flame in the combustion chamber 12. The fuel air mix is ignited in the combustion chamber 12 by the flame at the secondary fuel nozzle 16. Greatly enhancing the flame in the combustion chamber, 12 and, whereby increased heat flux is generated.
A flame stabilizer assembly 32 is mounted at the secondary fuel nozzle 16. The flame stabilizer assembly 16 takes advantage of heat flux generated in the combustion chamber 12.
Referring to
A generally cylindrical holder 36 supports member 34, with holder 36 being secured in the secondary nozzle 16. The holder 36 has an opening 38 therethrough with one end of the opening being threaded and the other end being tapered inwardly, as defined by a surface 39. Member 34 is inserted into the opening 38 of holder 36 such that surface 35 of member 34 interfaces or engages with surface 39 of the holder 36. A threaded member (e.g., a screw or bolt) 48 is treaded into the treaded opening securing the engagement of surface 35 of member 34 with surface 39 of the holder 36. The holder 36 further includes outwardly extending shoulder portion 46, which supports assembly 32 against the secondary fuel nozzle 16.
The combustor 10 may be operated under more lean conditions to further reduce nitric oxide emissions. Lean blowout will be significantly reduced, since the member 34 will provide continuous ignition to the fuel discharging from the secondary fuel nozzle 16. Accordingly, should there be an event such as, for example, flow disturbance, that may have otherwise caused a blowout; such a blowout will not occur as the member 34 will be providing a continuous ignition to the fuel discharging from the secondary fuel nozzle 16.
While preferred embodiments have been shown and described, various modifications and substitutions may be made thereto without departing from the spirit and scope of the invention. Accordingly, it is to be understood that the present invention has been described by way of illustrations and not limitation.
