Power plants – Combustion products used as motive fluid
Reexamination Certificate
2000-05-19
2001-12-04
Casaregola, Louis J. (Department: 3746)
Power plants
Combustion products used as motive fluid
C060S039230, C060S039250, C060S039240
Reexamination Certificate
active
06324828
ABSTRACT:
This invention relates to gas turbine engines and in particular relates to gas turbine engines for non-aero applications.
One main consideration for the operation of gas turbine engines is the specific fuel consumption value (SFC), measured in Kg/kWhrs. In general for certain gas turbine engine applications especially marine, automotive and even industrial, a significant proportion of operation is at low power. A gas turbine engine utilizes hot working fluid expanding through a given expansion ratio in the turbines which produces a power in excess of that required for the compressor to produce the corresponding pressure ratio. This is due to pressure and temperature ratios being proportional to one another during compression or expansion in the simple gas turbine engine cycle, which means that temperature change, and hence work, is proportional to the initial temperature level. Therefore reducing the amount of fuel available at part power results in reduced temperature levels and hence a reduced speed and pressure ratio thus resulting in a significant increase in specific fuel consumption (SFC).
Recuperated gas turbine engines use heat exchangers to return heat from the final turbine exhaust to pre-heat compressed air entering the combustor. This helps to conserve fuel by raising the combustor air temperature and therefore limiting the amount of fuel needed to achieve the turbine inlet temperature.
It is also known to provide a power turbine with variable area nozzles (VANs) to improve SFC at part power conditions. Such an arrangement of VANs is disclosed in GB2301868 and GB application No 9511269.4.
It is also known to provide a gas turbine compressor arrangement where the compressor vane angles are varied so as to alter the flow area. One such arrangement of variable compressor guide vanes is disclosed in GB2210108. Other arrangements for varying the mass flow through a gas turbine engine are disclosed in U.S. Pat. Nos. 3,138,923 and 3,025,688 and 4,145,875. These prior art patents disclose variable geometry arrangements in the form of angled vanes positioned to change the incident angle of gas flow with respect to either diffuser passages or nozzle passages.
As mentioned previously when the gas turbine engine is operated at low power the reduced levels of pressure ratio and temperature result in increased fuel consumption. It is desirable therefore that the gas turbine engine cycle is optimised at low power so that fuel consumption is reduced. In the prior art, for recuperated gas turbine engine cycles the variable area nozzle is closed as power is reduced maintaining the desired high temperature levels in the recuperator.
A small gas turbine engine is described in UK patent application no. 9800782.6 filed Jan. 15, 1998 and in a corresponding International patent application no PCT/GB99/00074 Jan. 8, 1999. This gas turbine engine comprises a centrifugal compressor, a diffuser, a heat exchanger, combustion apparatus, and at least one turbine. The compressor has variable inlet guide vanes, the diffuser has variable outlet guide vanes and the at least one turbine has variable inlet guide vanes so that the flow capacity of each component is independently variable while maintaining the temperature, pressure ratio and speed of rotation of the gas turbine engine substantially constant.
A combustion chamber is required for this gas turbine engine which produces low emissions of the oxides of nitrogen (NOx), carbon monoxide (CO) and unburned hydrocarbons (UHC) throughout the entire power range of the gas turbine engine, but especially at low powers.
The fundamental way to reduce the emissions of nitrogen oxides (NOx) 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. An annular tertiary fuel and air mixing duct surrounds the secondary combustion zone and supplies a mixture of fuel and air into a tertiary combustion zone.
It is an object of this invention to provide a gas turbine engine with improved fuel consumption over various power conditions and low emissions at low power levels.
According to the present invention there is provided a gas turbine engine comprising a centrifugal compressor, a diffuser, a heat exchanger, combustion apparatus and at least one turbine, wherein said centrifugal compressor, said diffuser, said combustion apparatus and said at least one turbine comprising means for varying the flow capacity at their inlets such that in operation the flow capacity of each component is independently variable so that over a predetermined power range the gas turbine engine mass flow is variable whilst maintaining the temperature, pressure ratio and speed of rotation of the gas turbine engine substantially constant.
Preferably the combustion apparatus comprises a primary combustion zone and a secondary combustion zone, the primary combustion zone being provided with a primary fuel and air mixing duct, the secondary combustion zone being provided with a secondary fuel and air mixing duct, said primary fuel and air mixing duct and said secondary fuel and air mixing duct comprising means for varying the flow capacity at their inlets.
Preferably the combustion apparatus comprises a primary combustion zone, a secondary combustion zone and a tertiary combustion zone, the primary combustion zone being provided with a primary fuel and air mixing duct, the secondary combustion zone being provided with a secondary fuel and air mixing duct, the tertiary combustion zone being provided with a tertiary fuel and air mixing duct, said primary fuel and air mixing duct and said secondary fuel and air mixing duct comprising means for varying the flow capacity at their inlets.
Preferably a first turbine is drivingly connected to the centrifugal compressor and a second turbine is drivingly connected to a load.
Preferably the second turbine is connected to the load via a gear unit.
Alternatively a first turbine is drivingly connected to the centrifugal compressor and is drivingly connected to an electrical generator.
Preferably the electrical generator is electrically connected to at least one electrical motor or an electric grid.
Preferably the electrical motor is drivingly connected to a load.
Preferably the load comprises a propeller of a marine vessel or a driving wheel of an automotive vehicle.
Preferably the means for varying the flow capacity of the compressor comprises variable inlet guide vanes.
Preferably the means for varying the flow capacity of the diffuser comprises moveable diffuser vanes pivotable such that their leading edges move in a tangential direction w
Fletcher Paul
Melville James
Walsh Phillip P.
Willis Jeffrey D.
Casaregola Louis J.
Gartenberg Ehud
Manelli Denison & Selter PLLC
Rolls-Royce plc
Taltavull W. Warren
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