Power plants – Combustion products used as motive fluid – Combustion products generator
Reexamination Certificate
1998-12-17
2001-11-06
Kim, Ted (Department: 3746)
Power plants
Combustion products used as motive fluid
Combustion products generator
C060S737000, C239S402000, C239S404000
Reexamination Certificate
active
06311496
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a fuel/air mixing arrangement of the radial inflow type for combustion apparatus such as burners in gas turbine engines. It has a particular applicability to gas-fueled gas turbines.
Both efficiency and environmental considerations mean that it has become essential to ensure that the levels of pollutant emission from combustion apparatus are kept as low as possible and various measures have been proposed with that aim in mind. For example, in the field of gas turbine engines, ‘lean-burn’ combustion systems are well-known. In such systems, the air/fuel ratio is at or near stochiometric and, specifically when the engine is running at or near full load, harmful exhaust pollutants, specifically CO, NO
x
and unburnt hydrocarbons are produced in relatively small amounts. However, at lower loads, known lean-burn configurations may not be so advantageous and, inter alia, difficulty may be experienced in maintaining flame stability to the extent that flame-out may occur due to the weak fuel content and the low velocity of the mixture.
Past proposals for overcoming such problems have generally utilized complicated arrangements for adjusting the operation of the engine to improve low-load performance. Inter alia, there have been proposed fuel staging arrangements whereby fuel is injected in stages depending on the load under which the engine is operating, with additional stages being brought into operation as the engine load increases. In other arrangements, a pilot flame is maintained by injecting fuel directly and axially into the center of a swirler to give a fuel-rich central zone with improved flame stability. However, pilot flame systems usually give higher levels of pollution when operating at low load. All these various arrangements can involve fairly complicated control systems for ensuring the right amount of fuel is being injected at the right time and to the right place.
SUMMARY OF THE INVENTION
The present invention aims to provide a simple, effective fuel/air mixing arrangement of the radial inflow type which adapts to the rate at which fuel is injected to ensure efficient combustion and low levels of harmful exhaust pollutants.
According to one aspect of the invention, there is provided a fuel/air mixing arrangement for a combustion apparatus comprising a mixing means wherein air and fuel are mixed to form a fuel/air mixture, a first conduit means whereby a first proportion of said fuel/air mixture is supplied from said mixing means to said combustion apparatus, a flow division means arranged to receive a second proportion of said fuel/air mixture from said mixing means, and a second conduit means to supply said second proportion from said flow division means to said combustion apparatus.
Preferably the mixing means comprises a primary swirler means. Preferably the flow division means comprises a secondary swirler means.
According to a further aspect the invention provides a fuel/air mixing arrangement for a combustion apparatus comprising a primary swirler means in which air and fuel are mixed to form a fuel/air mixture, a first conduit means to supply a first proportion of said mixture from said primary swirler means to said combustion apparatus, a secondary swirler means arranged to receive a second proportion of said mixture, and a second conduit means to supply said second proportion from said secondary swirler means to said combustion apparatus.
The primary swirler means preferably comprises a plurality of vanes defining passages there between arranged to produce a flow of said mixture there through, said flow having a radially directed component. The secondary swirler means preferably comprises a plurality of vanes defining passages there between arranged to produce a flow of said second proportion there through, said flow having a radially directed component.
Each passage of said primary swirler means preferably has at least one fuel injection orifice associated therewith for the supply of fuel to said passage. Shield means may be provided to shield the fuel injection orifice(s) from air flow entering the passages of the primary swirler means.
The arrangement may operate such that as the rate at which fuel enters the mixing means increases, the first proportion increases, or such that as the rate at which fuel enters the first swirler means increases, the first proportion increases.
The second conduit means may comprise a tube whose upstream end is integral with or attached to the secondary swirler means.
The secondary swirler means may be situated radially inward of the primary swirler means.
The secondary swirler means may have a smaller effective volume than that of the primary swirler means.
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Alstom Gas Turbines Limited
Kim Ted
Kirschstein et al.
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