Power plants – Combustion products used as motive fluid – Process
Reexamination Certificate
2001-12-06
2003-12-23
Kim, Ted (Department: 3746)
Power plants
Combustion products used as motive fluid
Process
C060S737000, C060S742000, C060S748000
Reexamination Certificate
active
06666029
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to the field of gas turbine engines, and more particularly to a pilot burner for a gas fired combustor.
FIG. 1
is a schematic diagram of a typical prior art gas turbine engine
10
. A compressor
12
draws in ambient air
14
and delivers compressed air
16
to a combustor
18
. A fuel supply
20
delivers fuel
22
to combustor
18
where it is combined with the compressed air to produce high temperature combustion gas
24
. The combustion gas
24
is expanded through a turbine
26
to produce shaft horsepower for driving the compressor
12
and a load such as an electrical generator
28
. The expanded gas
30
is either exhausted to the atmosphere directly, or in a combined cycle plant, is exhausted to atmosphere through a heat recovery steam generator (not shown).
FIG. 2
illustrates one embodiment of combustor
18
where the compressed air
16
and fuel
22
are premixed in a premix section
32
of the combustor
18
upstream of a combustion zone
34
in order to promote a lean, clean-burning, efficient combustion process. Such lean combustion may become unstable, especially during transient conditions. To ensure stable combustion, a fuel-rich diffusion mixture flame
36
may be provided to the combustion zone by a pilot burner
38
. Fuel is injected through the pilot burner
38
directly into the combustion zone
34
without premixing with air. Combustion is initiated in the combustor
18
with a pilot flame by providing fuel through a fuel tube
40
that is centrally disposed within the combustor
18
. The fuel tube
40
is centrally located within a shell
41
. The shell
41
has an inlet end
43
for receiving compressed air
16
and an outlet end
45
. A swirl vane
47
may be located proximate the outlet end
45
. Fuel tube
40
has an outlet end
42
with a plurality of pilot fuel nozzle openings
44
formed therein for providing a flow of pilot fuel
46
for mixing with the compressed air
16
exiting swirl vane
47
. This fuel-air mixture supports the pilot diffusion flame
36
. A main fuel flow
22
is provided to the premix section
32
by main fuel nozzles
48
for combusting in the combustion zone
34
. The pre-mix combustion is supported by the pilot diffusion flame. Power is increased first by increasing the flow of pilot fuel
46
, and then by gradually increasing the main fuel flow
22
as the flow of pilot fuel
46
is decreased. Under full power conditions, the pilot fuel flow rate is decreased in order to reduce undesirable emissions into the atmosphere. Under low power and transient power conditions, the ratio of pilot fuel to total fuel flow may be as high as 50%. Thus, the pilot burner
38
must be designed to deliver enough fuel to produce as much as 30-40% of the rated power level of the engine
10
. Since the maximum supply pressure of fuel is fixed, the size of the pilot fuel nozzle openings
44
must be made sufficiently large to ensure that an adequate flow rate of pilot fuel
46
can be provided at the lower power conditions. This opening size then determines the pressure differential across the pilot fuel nozzles
44
. Once the pilot fuel flow
46
is decreased at full power conditions, the differential pressure across pilot fuel nozzle openings
44
may become unacceptably low, making the pilot flame susceptible to instability and even flame-out due to relatively minor fluctuations in fuel supply pressure. Since pressure drop is approximately proportional to the square of the mass flow (Mach number<0.8), a turndown of 20 to 1 means that the pressure drop at the low pilot flows typical of base load are approximately {fraction (1/400)}
th
of the pressure drop at the highest pilot flows typical of full power engine operation.
A pre-mix pilot burner design recently developed by Siemens Westinghouse Power Corporation provides a portion of the pilot fuel flow through premix pilot fuel outlet orifices
50
located on swirl vane members
52
upstream of the outlet end
42
of the pilot fuel tube
40
. Other geometries associating a premix fuel supply outlet and a swirl member may also be used. This innovation reduces the undesirable emissions produced by a pilot burner
38
by premixing all or a portion of the pilot fuel flow, however, as the diffusion portion of the pilot fuel flow is decreased, the pressure differential across the pilot burner diffusion nozzles
44
is further decreased.
U.S. Pat. No. 5,036,657 issued to Seto, et al., describes a dual manifold fuel system for a liquid-fueled turbofan engine for aircraft propulsion. Two sets of main fuel outlets are provided, with one set always fueled and the second set fueled along with the first set only at higher flow rates. A valve controlling the flow through the second set of outlets is computer controlled, using inputs such as fuel flow, air flow, weight on wheels, and other engine and flight parameters. U.S. Pat. No. 4,499,735 issued to Moore, et al., also describes a liquid fuel injection system for an aircraft gas turbine engine. The main fuel supply to the combustor is divided into a plurality of radially displaced zones and a plurality of circumferentially displaced segments. Fuel distribution is varied across the zones and across the segments during various conditions of operation of the engine in order to provide improved temperature control, fuel atomization, and ignition control. Such complicated fuel system designs are useful for addressing the unique problems presented by the main fuel supply of a liquid-fueled aviation engine, but they do not solve or even address the issue of inadequate pilot fuel nozzle differential pressure in a gas-fueled turbine engine.
U.S. Pat. No. 5,901,555 issued to Mandai, et al., does address the issue of inadequate pilot fuel nozzle differential pressure by dividing the pilot burner diffusion fuel flow into at least two independent systems. The fuel nozzle diameters of each system are different, and each system can be controlled independently. While such a system does provide improved control over the fuel nozzle differential pressure, it is costly to manufacture such redundant systems and more complex to operate an engine containing such independent systems.
SUMMARY OF THE INVENTION
Accordingly, a simple, less expensive approach is described herein to assure that adequate differential pressure is maintained across the pilot fuel nozzles of a gas turbine combustor, in particular, a gas turbine having an advanced premixed pilot design. The present inventor has discovered that improved gas-fueled pilot burner performance may be achieved by dividing the diffusion pilot fuel flow into two circuits. A first circuit delivers fuel to a first outlet nozzle, and a second circuit delivers fuel from the first circuit to a second outlet nozzle only when the fuel pressure in the first circuit exceeds a predetermined value. The second circuit may be connected to the first circuit through a spring-loaded relief valve.
In one embodiment, a fuel delivery arrangement for a gas-fueled combustor pilot burner is described as including: a first fuel delivery circuit having an inlet connected to a supply of gaseous fuel and having a first outlet opening disposed in a pilot fuel burner; and a second fuel delivery circuit having an inlet connected to the first fuel delivery circuit and having a second outlet opening disposed in the pilot burner. The fuel delivery arrangement may further include a pressure-regulated valve connected between the first fuel delivery circuit and the inlet of the second fuel delivery circuit for providing gaseous fuel to the second fuel delivery circuit only when a fuel pressure in the first fuel delivery circuit exceeds a predetermined fuel pressure. The pressure-regulated valve may be a spring-release valve.
A pilot burner for a gaseous fuel combustor is described herein as including: a first gaseous fuel delivery circuit having a first outlet disposed within a combustor, a flow of gaseous fuel through the first gaseous fuel delivery circuit being responsive to a fuel flow
Kim Ted
Siemens Westinghouse Power Corporation
LandOfFree
Gas turbine pilot burner and method does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Gas turbine pilot burner and method, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Gas turbine pilot burner and method will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3179767