This application is the US National Stage of International Application No. PCT/EP2008/050550, filed Jan. 18, 2008 and claims the benefit thereof. The International Application claims the benefits of German application No. 10 2007 030 766.9 DE filed Jul. 2, 2007, both of the applications are incorporated by reference herein in their entirety.
The following invention relates to a method for operating a burner, a burner and a gas turbine with reduced CO and NOx emissions.
A major requirement of modern burners, especially of burners used as part of a gas turbine, is to cover a greatest possible power range with the lowest emissions possible. The undesired emissions concerned are in particular carbon monoxide emissions (CO emissions) and nitric oxide emissions (NOx emissions). Basically the power of a burner is almost proportional to the flame temperature and to the air mass flow. Operation at low power means a low flame temperature, whereby CO emissions increase markedly. In addition the flame also becomes longer in such cases, which with cooled burner walls leads to quench effects, also resulting in increased CO emissions.
With a gas turbine the result can also be thermo acoustic instability over the entire operating range, which can jeopardize safe operation of the combustion system. Such thermo acoustic instability is frequently also referred to as “vibration” and can occur especially with the premix burners currently generally used.
As a rule the burners of a gas turbine must be switched off below a critical temperature limit at which the flame becomes unstable or the CO emissions become too high. If necessary other burner stages must be operated, as a rule diffusion burners, which however then create high NOx emissions.
An object of the present invention is to provide an advantageous method for operating a burner. Further objects of the invention consist of providing an advantageous burner and an advantageous gas turbine.
These objects are achieved by a method as claimed in the claims, a burner as claimed in the claims and a gas turbine as claimed in the claims. The independent claims contain further advantageous embodiments of the invention.
The inventive method relates to a burner comprising a burner output opening with at least two sectors, with each sector being assigned at least one fuel nozzle. The fuel nozzles of different sectors are supplied separately with fuel. This method of operating a burner is especially suitable for the operation of a gas turbine burner. The separate supply of fuel to the fuel nozzles of different sectors can be controlled with aid of valves for example.
The inventive method enables the a reduction of the CO and/or NOx emissions to be achieved in part-load operation of the burner. For example fuel can be supplied to the fuel nozzles of different sectors of the fuel outlet opening in an adjustable ratio of between 0:100 and 100:0, especially between 0:100 and 35:65.
Usually the burner is arranged in a combustion chamber. In such cases the combustion chamber has a central axis. The burner also has a radial direction and a tangential direction in relation to the central axis of the combustion chamber. The radial direction of the burner is characterized here in that it intersects with the central axis of the combustion chamber. The tangential direction of the burner is at right angles to the radial direction of the burner and runs tangentially to an imaginary circle applied around the central axis of the combustion chamber.
It has proved advantageous for the fuel nozzles which are assigned to a sector which is arranged along the tangential direction of the burner to be supplied with less fuel than the fuel nozzles which are assigned to a sector which is arranged along the radial direction of the burner. For example the fuel nozzles which are assigned to a sector which is arranged along the tangential direction of the burner can be supplied with 20% of the overall amount of fuel supplied to the burner. The fuel nozzles which are assigned to a sector which is arranged along the radial direction of the burner will be supplied in this case with 80% of the overall amount of fuel supplied to the burner.
It is known that separate control of the fuel supply to the individual sectors of the burner, typically with valves able to be regulated separately, will produce hotter and colder zones in the combustion chamber in part-load operation. Less carbon monoxide is produced in the hotter zones. The hotter zones can especially also be placed in those areas where the greatest quench effect would otherwise be expected. The colder zones can be placed where the longest time is available for full combustion so that here, despite a cooler temperature, no additional carbon monoxide or only insignificantly more carbon monoxide is produced. Overall, the total CO emissions generated are reduced with the total amount of fuel and thereby also the total power remaining the same.
In marginal cases individual sectors can also be switched off entirely, whereby no carbon monoxide can be produced in these sectors, since no fuel is present. During this time the other sectors are so hot that they barely produce any carbon monoxide. However there will always also be a transitional layer in this case between a hot and a cold zone in which CO emissions arise.
The modified temperature field produced by using the inventive method and the simultaneously modified time needed by the fuel to travel from the nozzle outlet to the flame front also influences the thermo acoustic behavior of the combustion chamber used. The separate supply of fuel to the sectors can thus also be used to explicitly exert a positive influence on the thermo acoustic behavior.
In full-load operation the aim as a rule is to achieve a homogeneous temperature distribution, since this means the least stress on components and the lowest NOx emissions. All sectors are again preferably supplied evenly with fuel here.
The inventive burner comprises a burner outlet opening with at least two sectors, with each sector being assigned at least one fuel nozzle. The inventive burner is characterized by having at least two separate fuel supply lines leading to the fuel nozzles of different sectors and a facility for setting the fuel mass flow passing through the respective fuel supply line. Each fuel supply line thus supplies the fuel nozzles of other sectors with fuel.
The burner outlet opening can in particular have a circular cross-sectional surface. The fuel nozzles of the inventive burner can then be arranged for example in the form of a ring in relation to the central point of the burner outlet opening. In addition fuel nozzles lying opposite each other in each case can be assigned to the same fuel supply line. Furthermore the different sectors can form segments of the circular surface of the burner outlet opening with angles of between 70° and 110°. If for example four equal-size segments are present, these each have an angle of 90°. The fuel nozzles of segments lying opposite one another can then especially also be assigned the same fuel supply line.
Basically the facility for adjusting the fuel flowing through the respective fuel line can involve valves able to be regulated arranged in the respective fuel line.
The inventive method can be carried out with the inventive burner so that the advantages described in relation to the inventive method can be achieved.
The inventive gas turbine comprises at least one inventive burner.
Overall the present invention makes it possible to adhere to predetermined emission limits over a wide operational range. In addition a thermo acoustically stable operation of the burner over a wide operational range is possible or, with the operational range remaining the same, operation with reduced NOx emissions. The effect of the invention is thus to produce an overall expansion of the operational range of a burner. Over and above this the invention opens up expanded regulation options for operation of a burner by creating an additional measure of freedom in distribution of the fuel. Thus for example, with the overall amount of fuel remaining the same, the fuel proportion of the additional operating stage can be used as an manipulated variable in a closed-loop control circuit for regulating the thereto acoustic behavior or the emissions.
Further features, characteristics and advantages of the present invention will be described below on the basis of exemplary embodiments which refer to the enclosed figures.
The gas turbine 100 features a rotor 103 inside in supported to allow its rotation around an axis of rotation 102 with a shaft, which is also referred to as the turbine rotor.
Following each other along the rotor 103 are an induction housing 104, a compressor 105, a typically toroidal combustion chamber 110, especially an annular combustion chamber, with a number of coaxially arranged burners 107, a turbine 108 and the exhaust housing 109.
The annular combustion chamber 110 communicates with a typically annular hot gas duct 111. In this duct four turbine stages 112 connected one behind the other form the turbine 108 for example.
Each turbine stage 112 is formed from two rings of blades. In the hot gas duct 111, seen in the flow direction of a working medium 113, a series of guide blades 115 is followed by a series 125 composed of rotor blades 120.
The guide blades 130 are attached in this case to an inner housing 138 of a stator 143, whereas the rotor blades 120 of a series 125 are attached for example by means of a turbine disk 133 to the rotor 103.
Coupled to the rotor 103 is a generator or work machine (not shown).
During the operation of the gas turbine 100 air 135 is sucked by the compressor 105 through the induction housing 104 and compressed. The compressed air provided at the turbine-side end of the compressor 105 is directed to the burners 107 and mixed there with a combustion agent. The mixture is burned to form a working medium 113 in the combustion chamber 110. From there the working medium 113 flows along the hot gas duct 111 past the guide blades 130 and the rotor blades 120. At the rotor blades 120 the working medium 113 expands and imparts a pulse so that the rotor blades 120 drive the rotor 103 and this drives the working machine coupled to it.
The components subjected to the hot working medium 113 are subject to thermal stresses during the operation of the gas turbine 100. The guide blades 130 and rotor blades 120 of the first turbine stage seen in the direction of flow of the working medium 113 are subject to the greatest thermal stress, along with the heat shield elements 106 cladding the annular combustion chamber 110. In order to withstand the temperatures prevailing there, these can be cooled by means of a coolant.
The combustion chamber 110 is typically embodied as a so-called annular combustion chamber, in which a plurality of burners 107 which generate flames are arranged in a circumferential direction around an axis of rotation 102 and open out into a common combustion chamber space. To this end the combustion chamber 110 is designed overall as an annular structure which is positioned around the axis of rotation 102.
To achieve a comparatively high level of efficiency the combustion chamber 110 is designed for a comparatively high temperature of the working medium M of around 1000° C. to 1600° C. In order, even with these operating parameters unfavorable for the materials, to make a long operational life possible, the combustion chamber wall 153 is provided on its side facing towards the working medium M with an inner cladding formed from heat shield elements 155.
The burner 107 depicted in
In the example shown in
With reference to a longitudinal axis through the annular combustion chamber 1 not shown in
In
The burner 107, of which the burner outlet 4 is depicted in
For each output level an optimum fuel ratio can be set between the sectors 8a and 8b on the one hand and the sectors 9a and 9b on the other hand, which brings about a greatest possible reduction in the quench effect. In full-load operation the aim is to have an even supply of fuel to sectors 8a, 8b and 9a, 9b. With sectors of equal size this corresponds to a distribution of the fuel in the ratio of 50:50 to sectors 8a and 8b on the one hand and sectors 9a and 9b on the other hand.
In part-load operation the total amount of fuel supplied is reduced compared to full-load operation, which can, as mentioned above, lead to higher emissions and reduced thermo acoustic stability. A slight shift in the ratio in the distribution of the fuel to the sectors 8a, 8b and 9a, 9b can have a positive effect on the thermo acoustic stability of the burner 107 in part-load operation and also already have a positive effect on the emissions.
Basically a number of burners or all burners 107 of the annular combustion chamber 1 can be embodied according to the invention, i.e. comprise a number of sectors with separate fuel supply lines.
On the X axis of the diagram shown in
Curve 12 shows the NOx emissions of the burner 107 for an oxygen content of 15% within the fuel-air mixture as a function of the distribution of the fuel to the sectors A and B. The units for the NOx emissions are again selected arbitrarily. Curve 12 has a dished shape. The nitric oxide emissions are accordingly minimal when the proportion of fuel supplied to the sectors A lies at around 30% and 60% of the overall fuel supplied to the burner 107. Below 30% and above 60% the nitric oxide emissions occurring increase continuously, with the maximum of nitric oxide emissions being reached when fuel is being supplied exclusively to the sectors A.
When both the carbon monoxide and also the nitric oxide emissions are to be minimized, it emerges from curves 11 and 12 in
Plotted as a percentage on the X axis of the diagram shown in
Curve 15 shows the dependence of the carbon monoxide emissions on the flame temperature for an inventive burner, in which the individual sectors are arranged as described in conjunction with
The measurement points indicated in
Curves 15, 16, 17 are all characterized in that the carbon monoxide emissions occurring fall continuously as the flame temperature rises. However, for a specific flame temperature, the CO emission values of the curve 15 lie below the CO emission values of the curve 16 and below the CO emission values of the curve 17. The CO emission values of the curve 16 also lie below the CO emission values of the curve 17. The form of operation of an inventive burner represented in the curve 15 accordingly makes it possible to operate the burner at a lower flame temperature with simultaneously reduced carbon monoxide emissions compared to the burners or forms of operation represented by curves 16 and 17.
Overall the arrangement of the sectors A and B in an inventive burner 107 described in conjunction with
Number | Date | Country | Kind |
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10 2007 030 766 | Jul 2007 | DE | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
---|---|---|---|---|
PCT/EP2008/050550 | 1/18/2008 | WO | 00 | 12/17/2009 |
Publishing Document | Publishing Date | Country | Kind |
---|---|---|---|
WO2009/003729 | 1/8/2009 | WO | A |
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Entry |
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Communication from Yamaguchi International Patent Office, Aug. 17, 2011, pp. 1-2, 1-5. |
Number | Date | Country | |
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20100180598 A1 | Jul 2010 | US |