Power plants – Combustion products used as motive fluid – Combustion products generator
Reexamination Certificate
1999-08-13
2001-07-03
Freay, Charles G. (Department: 3746)
Power plants
Combustion products used as motive fluid
Combustion products generator
C060S733000, C060S742000, C060S746000, C060S748000, C060S751000
Reexamination Certificate
active
06253555
ABSTRACT:
The present invention relates generally to a combustion chamber, particularly to a gas turbine engine combustion chamber.
In order to meet the emission level requirements, for industrial low emission gas turbine engines, staged combustion is required in order to minimise the quantity of the oxide of nitrogen (NOx) produced. Currently the emission level requirement is for less than 25 volumetric parts per million of NOx for an industrial gas turbine exhaust. The fundamental way to reduce emissions of nitrogen oxides is to reduce the combustion reaction temperature, and this requires premixing of the fuel and most of the combustion air before combustion occurs. The oxides of nitrogen (NOx) are commonly reduced by a method which uses two stages of fuel injection. Our UK patent no. GB1489339 discloses two stages of fuel injection. Our International patent application no. WO92/07221 discloses two and three stages of fuel injection. In staged combustion, all the stages of combustion seek to provide lean combustion and hence the low combustion temperatures required to minimise NOx. The term lean combustion means combustion of fuel in air where the fuel to air ratio is low, i.e. less than the stoichiometric ratio. In order to achieve the required low emissions of NOx and CO it is essential to mix the fuel and air uniformly.
The industrial gas turbine engine disclosed in our International patent application no. WO92/07221 uses a plurality of tubular combustion chambers, whose axes are arranged in generally radial directions. The inlets of the tubular combustion chambers are at their radially outer ends, and transition ducts connect the outlets of the tubular combustion chambers with a row of nozzle guide vanes to discharge the hot gases axially into the turbine sections of the gas turbine engine. Each of the tubular combustion chambers has two coaxial radial flow swirlers which supply a mixture of fuel and air into a primary combustion zone. An annular secondary fuel and air mixing duct surrounds the primary combustion zone and supplies a mixture of fuel and air into a secondary combustion zone.
One problem associated with gas turbine engines is caused by pressure fluctuations in the air, or gas, flow through the gas turbine engine. Pressure fluctuations in the air, or gas, flow through the gas turbine engine may lead to severe damage, or failure, of components if the frequency of the pressure fluctuations coincides with the natural frequency of a vibration mode of one or more of the components. These pressure fluctuations may be amplified by the combustion process and under adverse conditions a resonant frequency may achieve sufficient amplitude to cause severe damage to the combustion chamber and the gas turbine engine.
It has been found that gas turbine engines which have lean combustion are particularly susceptible to this problem. Furthermore it has been found that as gas turbine engines which have lean combustion reduce emissions to lower levels by achieving more uniform mixing of the fuel and the air, the amplitude of the resonant frequency becomes greater. It is believed that the amplification of the pressure fluctuations in the combustion chamber occurs because the heat released by the burning of the fuel occurs at a position in the combustion chamber which is in phase with the pressure fluctuations.
Accordingly the present invention seeks to provide a combustion chamber which reduces or minimises the above mentioned problem.
Accordingly the present invention provides a combustion chamber comprising at least one combustion zone being defined by at least one peripheral wall and an upstream wall, a first fuel and air mixing duct being arranged to supply air into the at least one combustion zone to produce a first recirculating flow in the at least one combustion zone, a second fuel and air mixing duct being arranged to supply air into the at least one combustion zone to produce a second recirculating flow in the at least one combustion zone, the first and second fuel and air mixing ducts being arranged coaxially, fuel injector means being arranged to supply fuel into the first fuel and air mixing duct and fuel injector means being arranged to supply fuel into the second fuel and air mixing duct, the first and second fuel and air mixing ducts and the fuel injector means being arranged such that there is a predetermined difference in the amount, or proportion, of air and/or fuel supplied to the first and second fuel and air mixing ducts whereby the position of heat release in the first recirculating flow is downstream of the position of heat release in the second recirculating flow.
Preferably the first and second fuel and air mixing ducts and the fuel injector means are arranged such that the fuel to air ratio of the fuel and air flowing from the first fuel and air mixing duct into the at least one combustion zone is greater than the fuel to air ratio of the fuel and air flowing from the second fuel and air mixing duct into the at least one combustion zone.
Preferably the fuel injection apertures of the fuel injector means in the first fuel and air mixing duct have a greater cross-sectional area than the fuel injection apertures of the fuel injector means in the second fuel and air mixing duct.
Alternatively the fuel injector means in the first fuel and air mixing duct may have a greater number of fuel injection apertures than the fuel injector means in the second fuel and air mixing duct.
Alternatively the fuel injection means in the first fuel and air mixing duct comprises a greater number of fuel injectors than the fuel injection means in the second fuel and air mixing duct.
The inlet of the first fuel and air mixing duct may have a greater cross-sectional area than the inlet of the second fuel and air mixing duct.
The first and second fuel and air mixing ducts and the fuel injector means may be arranged such that the fuel to air ratio of the fuel and air flowing from the second fuel and air mixing duct into the at least one combustion zone is greater than the fuel to air ratio of the fuel and air flowing from the first fuel and air mixing duct into the at least one combustion zone.
Preferably the first fuel and air mixing duct comprises a first swirler, the second fuel and air mixing duct comprises a second swirler, the first and second swirlers being arranged to supply air into the at least one combustion chamber through an aperture in the upstream wall, the first fuel and air mixing duct having passages defined between vanes of the first swirler and the second fuel and air mixing duct having passages defined between vanes in the second swirler.
Preferably the fuel injection means and the first fuel and air mixing duct are arranged such that the fuel to air ratio of the fuel and air flowing from at least one of the passages of the first fuel and air mixing duct is different to the fuel to air ratio of the fuel and air flowing from the other passages of the first fuel and air mixing duct.
The vanes of the second swirler may have a greater cross-sectional area than the vanes of the first swirler.
Preferably the first swirler is a radial flow swirler and the second swirler is a radial flow swirler, the first swirler is axially downstream of the second swirler with respect to the axis of the combustion chamber.
Preferably the primary fuel injection means comprises a plurality of hollow members extending axially with respect to the first and second swirlers, each hollow member having a plurality of apertures spaced apart axially along the hollow member to inject fuel into one of the passages defined between the vanes.
Alternatively the primary fuel injection means may comprise passages extending axially in the vanes of the first and second swirlers, each vane having a plurality of apertures spaced apart axially along the vane to inject fuel into one of the passages defined between the vanes.
Preferably the combustion chamber comprises a primary combustion zone and a secondary combustion zone downstream of the primary combustion zone.
Preferably the combustion chamber comprises a
Freay Charles G.
Hayes Eric
Manelli Denison & Selter PLLC
Rolls-Royce plc
Taltavull W. Warren
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