Power plants – Combustion products used as motive fluid – With variable oxidizer control
Reexamination Certificate
2000-02-16
2001-06-26
Casaregola, Louis J. (Department: 3746)
Power plants
Combustion products used as motive fluid
With variable oxidizer control
C060S737000
Reexamination Certificate
active
06250066
ABSTRACT:
TECHNICAL FIELD
This invention relates generally to low NOx combustion systems for a gas turbine engine. More particularly, the present invention relates to a venturi for mixing fuel and air and injecting the mixture into a combustion chamber of such a system.
BACKGROUND OF THE INVENTION
Gas turbine engines of the type used for industrial applications may employ combustor systems designed to minimize nitrogen oxide emissions. One such combustor system, disclosed in U.S. Pat. No. 5,481,866, entitled Single Stage Premixed Constant Fuel/Air Ratio Combustor, issued to Mowill on Jan. 9, 1996, is incorporated herein by reference to the extent necessary for a full understanding of such a combustor. The '866 patent discloses a combustor having an externally cooled non-perforated combustor liner that receives all combustion air from a venturi shaped premixer. Excess air that does not enter the combustor through the premixer is ducted so as to externally cool the combustor liner, and eventually re-enters the flowpath downstream of the combustion region through dilution ports. An air valve is used to directly control the amount of air supplied to the premixer so as to minimize nitrous oxide emissions at all power settings. The air valve has the effect of indirectly controlling the amount of air routed to the dilution ports.
A problem occurs when combustors of the type disclosed in the '866 patent are used in conjunction with an engine having a compressor with a relatively high compression ratio. At low engine power settings, the valve used to control air to the premixer is mostly closed forcing most of the compressed air through the dilution ports. Although engine power is reduced, the total volume of air being pumped by the compressor at low power or idle settings remains high, resulting in a substantial increase in dilution airflow at reduced power. However, the dilution ports are necessarily sized to provide adequate backflow margin at the lower flow, higher power settings. Thus at reduced power, higher dilution flow conditions, the dilution ports overly restrict the dilution airflow causing a larger than desired pressure drop across the combustor and a loss of engine efficiency.
One solution has been to provide a separate apparatus for varying the flow area of the dilution ports at different power settings in addition to a valve for controlling air to the premixer. A disadvantage is that such apparatus are typically very complex, adding significantly to the total cost of the combustor system.
Another solution is disclosed in the copending U.S. patent application Ser. No. 08/966,393, filed Nov. 7, 1997. This application discloses a combustor dilution bypass system that includes a valve and a low pressure drop combustor bypass duct. The valve simultaneously controls both the supply of air to the premixer, and the amount of air directed into a large bypass duct. Air entering the bypass duct is reintroduced into the gas flowpath as dilution air downstream of the primary combustion zone. At low power settings the valve directs most of the air to the bypass duct, in effect adding dilution flow to that provided through the fixed area dilution ports, whereby the pressure drop across the combustor may be controlled at an optimal level. This combustor dilution bypass system is illustrated in
FIGS. 1-11
of this application.
Referring to
FIGS. 1 and 3
there are two premix injectors
64
on each side of the combustor spaced about 180° apart. Each premixer injector
64
injects tangentially a mixture of fuel and air into the combustion chamber
60
.
FIG. 12
shows the results from testing of this combustor and reveals two spikes in carbon monoxide generation as a function of angular distance around the combustion chamber
60
. These spikes occurred just downstream of the venturis
70
and indicate areas of unburned fuel. This unburned fuel is believed to be caused by some of the mixture exiting the venturis flowing directly to the dilution zone
36
instead of being mixed and combusted in the combustion chamber. To see how this could happen, viewing
FIG. 2
, the fuel air mixture flowing from the premixer injectors
64
enters the combustion chamber tangentially and sprays outward upon entering the combustion chamber. Therefore some the mixture flows directly to the dilution zone
36
located at the exit of the combustor and does not mix in with the gas in the combustion chamber.
Accordingly, a need exists in a venturi to be used in these premixer injectors that would direct the flow of gas away from the combustor exit.
SUMMARY OF THE INVENTION
In view of the above it is the object of the present invention to provide a venturi that directs the flow of gas away from the combustor exit.
Another object of the present inventions is to combine this venturi in a combustor system designed for low nitrous oxide emissions for a simplified method of reintroducing excess air not used for combustion, back into the flowpath downstream of the combustion zone without the complexity and expense associated with variable area dilution ports.
The present invention achieves these objects by providing a valve and a low pressure drop combustor bypass duct. The valve simultaneously controls both the supply of air to the premixer, and the amount of air directed into a large bypass duct. Air entering the bypass duct is reintroduced into the gas flowpath as dilution air downstream of the primary combustion zone. At low power settings the valve directs most of the air to the bypass duct, in effect adding dilution flow to that provided through the fixed area dilution ports, whereby the pressure drop across the combustor may be controlled at an optimal level.
The premixer includes a premix injector in which air and fuel are mixed. The premix injector includes an air blast fuel nozzle, a venturi, and a premix chamber. The venturi extends from an inlet to an exit which is in fluid communication with a combustion chamber. Importantly, the venturi has a jet deflector along its interior wall near its exit and on the side of the venturi nearest the exit of the combustor.
These and other objects, features and advantages of the present invention are specifically set forth in or will become apparent from the following detailed description of a preferred embodiment of the invention when read in conjunction with the accompanying drawings.
REFERENCES:
patent: 2552851 (1951-05-01), Gist, Jr.
patent: 2620626 (1952-12-01), Lysholm
patent: 2628475 (1953-02-01), Heath
patent: 3531937 (1970-10-01), Sneeden
patent: 3633361 (1972-01-01), Bauger et al.
patent: 3739576 (1973-06-01), Chamberlain
patent: 3851466 (1974-12-01), Verdouw
patent: 4193260 (1980-03-01), Carlise et al.
patent: 4215535 (1980-08-01), Lewis
patent: 4356698 (1982-11-01), Chamberlain
patent: 5377483 (1995-01-01), Mowill
patent: 5628182 (1997-05-01), Mowill
patent: 5638674 (1997-06-01), Mowill
patent: 5669218 (1997-09-01), Greninger
patent: 5685156 (1997-11-01), Willis et al.
patent: 5797267 (1998-08-01), Richards
Publication: Development of a Dry Low Emission Combustor for the AS1042 Industrial Gas Turbine Engine, P. Samuel and J.E. Lenertz; D.B. Bain and R.J. Mowill (06/97).
Lawrence Kyle
Lenertz James E.
Casaregola Louis J.
Desmond, Esq. Robert
Honeywell International , Inc.
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