EP1334309B1 - Method for supplying fuel to a premix burner - Google Patents

Abstract

The invention relates to a method and device for supplying fuel to a premix burner, which has at least one burner shell (1, 2) that at least partially delimits an axially extending premix combustion chamber, in order to operate a gas turbine. According to the invention, premix gas is supplied into the premix combustion chamber via the burner shell (1, 2), whereby the premix gas (6) is mixed with combustion additional air and is ignited downstream at a location outside of the premix burner. The invention is characterized in that the premix gas is separately supplied via at least two areas (S1, S2), which are axially separated in a spatial manner, along the burner shell (1, 2), whereby one area (S1) is arranged upstream and at least one second area (s2) is arranged downstream. The invention is additionally characterized in that, for starting the gas turbine, more than 60 % of the entire premix gas is supplied over the first area (S1) and that, for the continued running up of the load of the gas turbine to full load, a gradual or continuous redistribution of the supply of premix gas to the second area (S2) ensues.

Description

Technical area

The invention relates to a method for supplying fuel to a premix burner having at least one burner shell at least partially delimiting an axially extending premix burner space for operating a gas turbine having a premix gas supply directed into the premix burner space above the burner cup, the premix gas being mixed with combustion air and downstream, is ignited outside the premix burner.

State of the art

Premix burners of the aforementioned type are well known for operating gas turbine plants and have different premix burner geometries. So is in the EP 0 321 809 B1 a cone-shaped premix burner consisting of several burner shells, a so-called double-cone burner, whose burner shells are composed in such a way that tangential air inlet slots for the combustion air are formed along the burner axis. At the inflow edges of the burner shells formed thereby are provided outlet openings for the premix gas, which are distributed in the direction of the burner axis. The injection of the Premixgases through the outlet openings along the inflow edges of the burner bowls leads due to the Brennerschalengeometrie in conjunction with the Brennungszuluft to a swirling mixing of the premixing gas and the combustion air supply.

Another premix burner geometry is in the WO 93/17279 shown, in which the premix burner is formed with an additional conical inner body. Also in this case, the premix gas is fed into the premix burner via respective exit openings arranged along the axially extending air inlet slots, where the premix gas is mixed with combustion air and ignited downstream within the combustion chamber.

Now it is possible to make optimizations by suitable choice of the arrangement, size, number of outlet openings and their mutual distance with regard to the quality of the combustion. In particular, the emission values, the extinguishing behavior of the flame forming in the combustion chamber, the flame backflow behavior and the flame stability can be decisively influenced by a suitable choice of the abovementioned parameters.

However, the optimization possibilities described above quickly reach their limits if measures are to be taken to optimize the burner behavior not only with a fixed burner geometry and with an ideal combustion state. Thus, it is almost impossible to keep the combustion behavior at a virtually constant optimum level with a structurally predetermined arrangement of outlet openings along certain areas of the burner shells, the combustion behavior under different load and ambient conditions. It has been found that an optimized arrangement of outlet openings for the premix gas supply within the premix burner, which has been optimally designed for the use of a particular type of machine, for example, for use in an annular combustion chamber, poor or even for the use of another type of machine, for example, for use in a silo combustion chamber, let übnern.

Also occur during the use of a burner creeping burner system changes that are caused by fatigue and lead, for example, to an increase in Lekage air currents. By the firm given arrangement of the Premixgasdurchtrittsöffnungen, which are themselves subject to no or only negligible aging phenomena, the aging-related changes can not be compensated jeodch, whereby a deterioration of the combustion process with increasing duration of the burner is unavoidable.

Existing premix gas supply systems are typically optimized for the medium and high load ranges of gas turbines in terms of low emissions and cushioned combustion oscillations. In order to start the combustion process and to reach the middle load range of the gas turbine, pilot stages are usually used. Usually, pilot gas is fed into the interior of the premix burner in the center of the premix burner axis via a burner lance, which mixture is mixed with combustion air and brought to ignition. Only after reaching a certain load range, the pilot gas supply is switched off and the Premixgaszufuhr be put into operation. In the same way, such switching occurs when the gas turbine is shut down, in which the premix gas supply is switched off and the pilot gas supply is switched on. In the switching processes, however, high combustion oscillations occur within the burner system, which are associated with strong pressure fluctuations, which in turn has an immediate and disturbing effect on the load behavior of the gas turbine, which is consequently subjected to large load oscillations.

If a gas supply system is switched off both when the gas turbine is raised and lowered, then it is necessary to clean the switched-off gas supply lines with inert gas in order to exclude re-ignitions into the supply line in order to avoid their damage. The amount of inert gases required to clean the gas supply takes on a considerable amount and not least also leads to high operating costs of such burner systems.

Finally, with the currently known premix burners, it is nearly impossible to use the premix burner with different types of fuel, such as liquid or gaseous fuel to operate, especially since the usually arranged centrally in the burner axis burner lance for supplying pilot gas, which is required as mentioned above for starting the gas turbine and for the lower load range, is located in close proximity to the central liquid fuel nozzle , Unintended ignition interactions between the two fuel outlets can not be excluded.

The two writings DE-A1-44 46 945 and EP-A1-0 592 717 disclose gas-powered premix burners in which combustion air is introduced at least approximately tangentially into the pre-mixing chamber of the burner. Fuel is injected via a plurality of nozzles arranged in the longitudinal direction of the premixing chamber and mixed with the combustion air. The nozzles are divided into at least two groups with different fuel supply.

Presentation of the invention

The object of the invention is to further develop a method and a device for supplying fuel to a premix burner according to the preamble of claim 1 in such a way that the above-mentioned disadvantages of the prior art are to be avoided. In particular, it is necessary to take measures on the premix burner, so that an optimized adaptation of the premix burner behavior in the entire load range of the gas turbine is possible. This should in particular be done without great technical and design effort and be feasible with only a small cost.

The solution of the problem underlying the invention is specified in claim 1. The concept of the invention advantageously further features are the subject of the dependent claims and the description, in particular with reference to the figures refer.

The idea underlying the invention is the axial stepped supply of premix gas along the flanks of the burner shells by the burner shells are divided into at least two axially successively arranged areas, which are each supplied via separated Premixgaszuleitungen. The separate areas along the burner shells are arranged axially one behind the other in the flow direction of the premix burner, wherein it has been recognized according to the invention that for starting the gas turbine more than 60% of the total premix gas supply over the upstream first area should be done and for the further start-up of the load Gas turbine to full load one step-wise or continuous redistribution of the Premixgaszuführung on the downstream of the first region adjacent areas.

Due to the axial subdivision of the Premixgaszuführung along the burner bowls of the premix burner and in particular the gradual supply of the individual areas with premix gas, it is possible to dispense completely with the supply of pilot gas, even in the case of starting and in lower load ranges of the gas turbine.

By dispensing with a pilot gas stage, a number of advantages are associated, resulting not least by eliminating the combustion chamber oscillations associated with the switching from pilot gas to premix gas supply.
With the mode of operation of a premix burner according to the invention, it is now possible to operate a gas turbine from startup to full load without a pilot gas stage. The continuous or step-by-step connection of individual areas, via which premix gas passes into the interior of the premix burner, takes place with the aid of control or regulation units provided in the individual supply lines, which in the simplest case are designed as controllable throttle valves.

Due to the advantageous omission of a pilot gas supply, it is in particular possible to atomize liquid fuel through a central injection nozzle protruding into the burner mouth, which in turn is suitably surrounded by a tubular combustion air flow.

An embodiment designed according to the invention for the targeted supply control of premix gas for the burner shells of the premix burner subdivided into different regions is referred to the following description with reference to the figures. Essential aspects of the method according to the invention is the separate, metered premix gas supply to the individual, axially successively arranged areas along the burner shells, through which the premix gas is injected into the interior of the premix burner.

Brief description of the invention

Figur 1

schematische Querschnittsdarstellung durch einen kegelförmig ausgebildeten Vormischbrenner,

Figur 2

Diagrammdarstellung zur Betriebsweise der in Figur 1 dargestellten Ausführungsform,

Figur 3

schematisierter Plan zum Verlauf von Zufuhrleitungen zur Versorgung des Vormischbrenners mit Premixgas, .

Figur 4

Ausführungsbeispiel eines Regelventils.

The invention will now be described by way of example without limitation of the general inventive idea by means of embodiments with reference to the drawing. Show it:

FIG. 1

schematic cross-sectional view through a cone-shaped premix burner,

FIG. 2

Diagram representation for the operation of the embodiment shown in Figure 1,

FIG. 3

schematic plan for the course of supply lines for supplying the premix burner with premix gas,.

FIG. 4

Embodiment of a control valve.

Ways to carry out the invention, industrial usability

FIG. 1 shows a schematic representation of a longitudinal section through a cone-shaped premix burner. The premix burner has cone-shaped burner shells 1, 2, along which are provided in the axial direction to the burner longitudinal axis A outlet openings 3, can be fed by the premix gas into the interior of the premix burner. The burner shells 1, 2 are subdivided into two differently separated regions S1, S2, which are supplied with premix gas by different premix gas supply lines 4, 5. As if tangentially in the direction of the conical shape, supply air is guided into the interior of the premix burner by air inlet slots, not shown in FIG. 1, which mixes with the premix gas 6 to form a fuel air mixture.

Optionally, a liquid fuel atomization direction 7 can be provided in the center of the premix burner, which allows mixing operation or switching from gaseous fuel to liquid fuel. The supply of liquid fuel takes place with the aid of a known atomizing nozzle, which is a conical spreading sputtering cloud generated within the premix burner. For protection against the Premixaustrittsöffnungen 3 and for purposes of shape stabilization, the spreading liquid fuel cloud is surrounded by a protective air jacket.

To start the gas turbine, that is to ignite the premix burner is not made as usual in the prior art, a pedestal, but in the embodiment illustrated two-stage Vormischbrennereinheit each area of the burner shell is supplied with a Premixgaszufuhr which is arranged upstream within the premix burner. In the exemplary embodiment, this is the area stage 1, which is operated for starting and for operating the premix burner in the low load range with more than 60% of the total Premixgaszuführung.

FIG. 2 shows an overview diagram from which the percentage distribution of the premix gas distribution between area S1 and area S2 can be seen. The fields entered in black correspond to the portion of the premix gas exiting via region 1, the brighter fields in each case to the premix gas fraction which reaches the interior of the burner via region S2 of the premix burner. As mentioned above, in the ignition (Egnition), the lion's share (ie, more than 90%) of the total premix gas supply flows over the region 1 into the interior of the premix burner. In the lower load range (idle), the proportion of premix gas exiting via region 2 increases slightly. In the case of the half-load state, both areas S1 and S2 are supplied with premix gas in approximately equal parts. In full load operation, slightly more premix gas enters the interior of the premix burner via region S2 than over region 1. The premix gas allocation to regions S1 and S2 shown in FIG. 2 is effected by means of a control unit which gradually or continuously distributes the premix gas allocation over the regions S1 and S2 can make. In the simplest case, these are coupled throttle valves, which are each provided in the individual supply lines 4 and 5.

A further possibility of controlled premix gas supply to the separate regions of the premix burner can be taken from the schematic representation according to FIG. Again, in the embodiment according to FIG. 3, a conical premix burner is provided, which has two regions S1 and S2, via which premix gas enters the interior of the premix burner separately. In a common supply line 8 is supplied via the premix to the premix burner, a main control valve 9 is provided. Via the main control valve 9, the direct inflow of premix gas to the area S1 of the premix burner can be regulated. In the supply line between the main control valve 9 and the outlet region S1 of the premix burner, a crossing point 10 is provided, at which a portion of the premix gas is discharged into a Zuführast 11. In Zuleitungsast 11 another control unit in the form of a spring-loaded pressure relief valve 12 is provided, which will be described in more detail below with reference to Figure 4. A bypass line 13, whose flow cross-section is small enough or in which a corresponding throttle element 14 is provided, ensures that when the control valve 12 is closed, a small premix gas flow can be supplied to the area S2 of the premix burner.

The feed system for premix gas, shown in FIG. 3, on the two regions S1 and S2 of the premix burner now has the following mode of operation. After opening the main control valve 9, the area S1 of the premix burner is supplied with premix gas. The gas pressure within the supply line which supplies the region S1 with premix gas, and also in the supply line 11, can not yet open the spring-loaded overpressure valve. Only a small proportion of premix gas passes via the bypass line 13 to the area S2 of the premix burner and exits there into the interior of the premix burner. This corresponds to the state when starting the gas turbine or when igniting the premix burner. After the start-up phase, the premix gas pressure prevailing in the feed line 11, which is able to open the spring-loaded throttle valve 12 continuously, causes an ever increasing proportion of the premix gas flowing through the main control valve 9 to flow through the pressure relief valve 12 into the region S2. If the supply gas pressure continues to increase, the pressure relief valve 12 opens completely, whereby a large proportion of the premix gas can reach the area S2 of the premix burner. By dimensioning the leads and adjusting the behavior of the pressure relief valve 13, it is possible to optimize the behavior of the premix burner in terms of emission and vibration behavior. Thus, it is possible, without the need for a pilot gas supply and using only a single control valve, namely the pressure relief valve 12 to realize a premix burner for operating a gas turbine over the entire load range.

Such a pressure relief valve is shown as an advantageous embodiment in Figure 4. The pressure relief valve 12 has a conically shaped piston 15, the spring-loaded by a spring 16 gas-tight a counter-contour 17 rests. Now, if the piston 15 by means of gas pressure (see arrow on the left side of the throttle valve) pressurized, so the pressure acting on the piston 15 gas pressure, the spring 16 against a stop 18 can push together. This opens a gap between the piston 15 and the mating contour 17, whereby gas can pass through the pressure relief valve to the right. Depending on the choice of the spring force of the spring element 16 and the dimensioning of the piston size, the gas pressure-dependent flow rate of the premix gas by the pressure relief valve 12 is set individually. With the help of suitable dimensioning of the pressure relief valve 12 and the supply lines 11 and 14 involved in the premix gas supply, it is possible to optimize the combustion process in a conventional manner. Even with the exemplary embodiment illustrated in FIG. 3, it is possible to obtain a targeted premix gas allocation to the stages S1 and S2 of the burner shells of the premix burner according to the diagram in FIG.

A number of disadvantages are associated with the method according to the invention for supplying fuel to a premix burner: The graduated premix gas feed into the premix burner allows it to be used in significantly larger range limits than just single-stage premix burners.

With the help of the embodiment shown in Figure 3, only a single Premixgaszuleitung is required.

By using a control unit designed as a pressure relief valve only a single control unit is required to operate the premix burner.

The retrofitting of the inventive method to existing Vormischbrennersysteme is easy to carry out, especially since the use of two or more separate Premixgaszuleitungssysteme is not required.

The targeted supply of a minimum proportion of premix gas in the second area of the premix burner via the bypass line, it is not necessary to clean this supply line with natural gas. Experiments have shown that the system according to the invention only cause low pulsations in the starting behavior. With the individual Premixgaszuteilung on the different areas of the premix burner, it is possible to make corresponding optimizations even when occurring aging phenomena.

Due to the possible omission of a pilot gas supply, any pulsations that occur when switching between pilot gas to Premixgaszufuhr can be avoided.

The entire device is structurally simple and inexpensive to produce.

LIST OF REFERENCE NUMBERS

1, 2

burner shells

3

Premixgasaustrittsöffnungen

4, 5

leads

6

premix gas

7

Flüssigbrennstoffzerstäubungseinrichtung

8th

supply line

9

Main control unit

10

intersection

11

branch line

12

Pressure relief valve

13

bypass line

14

throttle element

15

piston

16

feather

17

mating contour

18

attack

S1, S2

Areas 1, 2 for the staged Premixgasaustritt

Claims (7)

1. Method for supplying fuel to a premixing burner for operating a gas turbine, the premixing burner having at least one burner shell (1, 2) which at least partially bounds an axially extending premixing space, and a premixing gas supply (3) directed into the premixing space via the burner shell (1, 2),

   - the premixing gas (6) being mixed with combustion inlet air in the premixing space and

   - being ignited downstream, external to the premixing burner, and

   - the premixing gas supply being carried out separately by means of at least two spatially axially separated regions (S1, S2) along the burner shell (1, 2), having a region (S1), which is arranged upstream, and at least a second region (S2), which is arranged downstream,

   characterized in that
   more than 60% of the total premixing gas supply takes place via the first region (S1) in order to start the gas turbine, and in that a stepwise or continuous redistribution of the premixing gas supply to the second region (S2) takes place for the further run-up of the load on the gas turbine to full load.
2. Method according to Claim 1, characterized in that the supply of the premixing gas to the first region (S1) and the second region (S2) takes place mutually independently.
3. Method according to Claim 1 or 2, characterized in that, under full-load conditions, at least 50% of the total premixing gas supplied to the premixing burner is supplied via the second region (S2) or the regions located downstream.
4. Method according to one of Claims 1 to 3, characterized in that the premixing burner is conically configured and has at least two burner shells (1, 2), which are arranged relative to one another in such a way that they respectively bound two air inlet slots through which the combustion air enters the conically widening premixing burner space, in that the first region (S1) of the burner shells (1, 2), via which at least part of the premixing gas is fed into the premixing burner space, is arranged in the region of the narrowest conical cross section and extends into the premixing burner region which is widening in cross section.
5. Method according to one of Claims 1 to 4, characterized in that the regions (S1, S2), which are axially separated from one another, for the supply of premixing gas are supplied with premixing gas via separate supply lines.
6. Method according to one of Claims 1 to 5, characterized in that the premixing gas supply to the individual regions (S1, S2) takes place mutually independently.
7. Method according to one of Claims 1 to 5, characterized in that the premixing gas supply to the individual regions (S1, S2) is carried out by means of a single control unit (12).

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