Power plants – Combustion products used as motive fluid – Combustion products generator
Patent
1995-10-23
1997-06-24
Freay, Charles G.
Power plants
Combustion products used as motive fluid
Combustion products generator
60746, F02G 300
Patent
active
056408510
DESCRIPTION:
BRIEF SUMMARY
This application claims benefit of international application PCT/GB 94/01135 filed May 24, 1994.
FIELD OF THE INVENTION
The present invention relates to a gas turbine engine combustion chamber.
BACKGROUND OF THE INVENTION
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 oxides 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 all the combustion air before combustion takes place. The oxides of nitrogen (NOx) are commonly reduced by a method which uses two stages of fuel injection. Our UK patent no. 1489339 discloses two stages of fuel injection to reduce NOx. 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 so that it has less than a 3.0% variation from the mean concentration before the combustion takes place.
The industrial gas turbine engine disclosed in our International patent application no. WO92/07221 uses a plurality of tubular combustion chambers, whose longitudinal 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 exhaust gases axially into the turbine sections of the gas turbine engine. Each of the tubular combustion chambers has an annular secondary fuel and air mixing duct which surrounds the primary combustion zone. A plurality of equi-spaced secondary fuel injectors are arranged to inject fuel into the upstream end of the annular secondary fuel and air mixing duct. The annular secondary fuel and air mixing duct has a plurality of equi-spaced outlet apertures to direct the fuel and air mixture into the secondary combustion zone. Each of the tubular combustion chambers of the three stage variant also has an annular tertiary fuel and air mixing duct which surrounds the secondary combustion zone. A plurality of equi-spaced tertiary fuel injectors are arranged to inject fuel into the upstream end of the annular tertiary fuel and air mixing duct. The annular tertiary fuel and air mixing duct has a plurality of outlet apertures to direct the fuel and air mixture into the tertiary fuel and air mixing zone.
Unfortunately the flow of air into the tubular combustion chambers is not uniform, this is because of an asymmetric flow of air from a diffuser at the downstream end of the gas turbine engine compressor to the tubular combustion chambers. Each of the secondary fuel injectors passes identical fuel flows and therefore a non uniform fuel and air mixture is created at the points of injection due to the non uniform air flow. The fuel and air mixture directed from the outlet apertures into the secondary combustion zone is non uniform. Similarly the fuel and air mixture directed from the outlet apertures of the tertiary mixing duct into the tertiary combustion zone will be non uniform. This increases the emissions of NOx to above the acceptable levels.
An initial solution for the problem was to redistribute the fuel to match the air mass flow distribution by adjusting the fuel hole sizes of the individual fuel injectors. This requires all of the fuel injectors to be unique in fuel hole diameters and position of the fuel holes to match the air mass flow to achieve the require
REFERENCES:
patent: 4455839 (1984-06-01), Wuchter
patent: 5319935 (1994-06-01), Toon et al.
patent: 5408825 (1995-04-01), Foss et al.
patent: 5469700 (1995-11-01), Corbet et al.
patent: 5475979 (1995-12-01), Oag et al.
Toon Ian J.
Willis Jeffrey D.
Freay Charles G.
Rolls-Royce plc
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