Method for operating a premix burner

Abstract

In a method for operating a premix burner a water quantity is introduced into the burner and/or the reaction zone of the burner depending on at least one command variable formed from at least one measured value. The method in particular should also be used if a burner is operated in the actual sense dry, i.e., without water injection for nitrogen oxide injection, and the injected water quantity is less than 20% of the fuel quantity. The method can be used advantageously especially if a characteristic value derived from combustion pulsations or material temperatures is used as a command variable; such parameters are then kept below a permissible upper limit.

Description

FIELD OF TECHNOLOGY

[0001] The invention relates to the operation of a premix burner.

[0002] The invention also relates to a gas turbine operated with premix burners according to the method according to the invention.

STATE OF THE ART

[0003] The use of premix burners is widely applied in the operation of firing systems and, in particular, gas turbines. Such premix burners are known, for example from EP 321 809, EP 780 629, WO 93/17279, or EP 945 677. These burners are suitable for operation with liquid as well as gaseous fuels. A mutual characteristic of the burners disclosed in the cited documents is that combustion air is mixed in an inner chamber of the burner with a fuel as much as possible. The combustion air is hereby frequently fed into the inner chamber of the burner tangentially. The eddy current induced in this way bursts open when exiting the burner opening. This so-called “vortex breakdown” generates a recirculation zone where a flame can be stabilized in a purely aerodynamical manner without attaching thermally sensitive, mechanical flame holders. By premixing air and fuel, these burners can be operated principally while avoiding stoichiometric zones, which—at least during operation with gas—easily permits operation with very low emission values without any further measures.

[0004] When using liquid fuels, the premixing is relatively incomplete, so that in this case, a diffusion flame is actually present. Below, such burners are also called premix burners, however, since this term has become established for the cited burner types in the expert community. Premix burners operated with liquid fuel are frequently also operated additionally with steam or water injection so that here also relatively low emission values can be achieved, in particular with respect to nitrogen oxide emissions (these are values of less than 50 ppm). Hereby an inert medium is introduced into the flame, which reduces both the flame temperature and therefore the nitrogen oxide production. When used in gas turbine combustors and with an injection of water, the injected quantity of water is approximately in the same magnitude as the quantity of fuel; the ratio of the quantity of water to fuel is roughly in the range from 0.7 to 2 in order to achieve a corresponding nitrogen oxide reduction. The corresponding operating concepts are adjusted in measuring series, and the quantity of water or, respectively, the ratio of the quantity of water to fuel, is determined depending on the operating conditions of the machine. With such an operation, the cited quantities of water naturally result in a high consumption of correspondingly prepared, demineralized water.

[0005] In the same way, for example, in a gas turbine equipped with premix burners, emission values that are clearly below those of gas turbines with standard burners with a so-called dry operation, i.e., without targeted introduction of water for nitrogen oxide reduction, can also be achieved during operation without water injection. Especially in arid regions, where, for example, no infrastructure for gas is present, or oil is especially readily available, gas turbines with premix burners, for example, so-called EV or AEV burners are operated in “dry” oil operation, i.e., there is no nitrogen oxide reduction by injection of water.

[0006] The statements made for oil naturally also apply for operation with other liquid fuels.

[0007] The burners are generally also operated dry during premix operation with gas, whereby the dry operation of the burners within the framework of the present document should be understood to mean that no water or steam is introduced into the combustion zone in large quantities in a targeted manner for nitrogen oxide reduction.

[0008] In practice, it was now found that in the large operating range, whereby in addition to the greatly varying parameters of temperature and pressure of the combustion air, primarily the thermal power turnover of a burner and the impulse ratio of fuel and air, as well as the ratio of the axial impulse to the rotating impulse of the burner flow must be mentioned, combustion instabilities occur that may result in undesired combustion pulsations. The position of the flame also changes. If the flame is stabilized too close to the burner mouth, this may result in temperature increases and an associated reduction in life span.

DESCRIPTION OF THE INVENTION

[0009] It is the objective of the invention to avoid the disadvantages of the state of the art for a method of the initially described type.

[0010] This objective is realized within the entirety of the characteristics of claim 1.

[0011] The core of the invention consists of introducing, in a targeted manner, a quantity of water depending on at least one measured command variable. In particular, this has the effect of varying the axial impulse of the burner flow in a targeted manner and independently from other operating parameters, such as the fuel quantity, and in this manner to be able to independently shift the location of the flame stabilization within certain limits.

[0012] Within the framework of this disclosure of the invention, the term command variable means a dimension, depending on which the quantity of water that is introduced is adjusted.

[0013] In a preferred variation of the process, the burner is operated dry, i.e., without water injection for nitrogen oxide reduction. The introduced quantity of water is hereby kept as low as possible, if at all possible at less than 20% of the quantity of the fuel. Preferably, it is attempted to limit the quantity of water to less than 10%, in particular to less than 5%, of the quantity of the fuel.

[0014] During “wet” operation of a premix burner according to the method according to the invention, i.e., during operation with water injection for reducing the nitrogen oxide, the process-specific variation of the quantity of the water is analogously kept in an advantageous manner to less than 20% of the fuel quantity. Preferably, it is attempted to limit the process-specific variation of the quantity of water to less than 10%, in particular to less than 5%, of the quantity of the fuel.

[0015] This method can be used advantageously for operating the burner with liquid fuel.

[0016] In a preferred embodiment of the invention, the combustion pulsations present at least one measured value. As a command variable, for example, a summation value can be formed from this, or an amplitude peak of a frequency spectrum of the pulsations can be used as a command variable. Furthermore, one or more frequency ranges of the spectrum of the combustion pulsations also can be used to form the command variable.

[0017] In another preferred variation, at least one temperature is measured, in particular a material temperature of the premix burner, in order to form a command variable. In the same way, a signal of an optical sensor can be used. This would make it possible, for example, to obtain an indication of the flame position, which would be used as a command variable.

[0018] The water quantity adjustment introduced into the burner advantageously can be operated in a closed control circuit in order to adjust a command variable to a desired value, maintain it within a desired interval, or limit it to an upper or lower limit.

[0019] The quantity of water on the one hand can be added via nozzles of the burner; it is furthermore also possible to mix the quantity of water prior to the injection of a liquid fuel into the combustor with the latter and in this way to operate the burner with a water-in-fuel emulsion.

[0020] The quantity of water either can be easily controlled simply depending on the command variable. On the other hand, the quantity of water also can be operated in a closed control circuit with the command variable as a regulating variable, in order to keep, for example, pulsations or material temperatures below an upper limit or in order to achieve a desired value of the flame position.

[0021] The invention is explained in more detail below with the help of exemplary embodiments in reference to the drawing.

BRIEF DESCRIPTION OF DRAWING

[0022] The only FIGURE shows a simplified gas turbine system prepared for performing the method according to the invention.

WAY OF EXECUTING THE INVENTION

[0023] The single FIGURE is a very schematic drawing showing a simple gas turbo-set 1 consisting of a compressor 4, a combustor 5, and a turbine 6. The gas turbo-set drives a generator 3 via a shaft 2. Naturally, the gas turbo-set also could have several turbines and/or partial compressors arranged consecutively on one or several shafts. In the same way, a further combustor could be arranged between two each turbines or an intermediate cooler between partial compressors, without this influencing the basic concept of the invention. The combustor 5 constructed as a ring combustor is provided with a plurality of premix burners 7 distributed over the circumference, of which premix burners only the burner lance is shown in the drawing. The burners are connected via the fuel lances with one or more ring lines 8, through which the operating media, in particular fuel, are supplied. On the one hand, a burner hereby may have several supply lines, and individual ring lines also may selectively supply individual burner groups. The performance of the gas turbo-set is determined in a first approximation by the quantity of fuel added. An adjustable advance guide row 41 of the compressor is used to vary the air mass flow over the entire load range to be covered. The gas turbine system is provided with a plurality of measuring points that enable the monitoring of the operating states and regulation of the gas turbo-set during operation. The measuring signals are gathered in a central control module 50. The drawing shows example of signal lines 51, 52, 53, 54, 55. From these signals, physical values are calculated in the control module, and from them, command variables for controlling the gas turbo-set are formed. In the FIGURE, a signal line 56 extends, as an example, from the control module 50 to a fuel quantity adjusting element 9, so that, for example, depending on a control variance of the generator performance or speed, the fuel mass flow is reduced or increased via this adjusting element. The lances of the burners 7 are connected in the FIGURE with another ring line 11. Through this ring line, water is fed to the burners. The water quantity is set through the water quantity adjusting element 10. The water quantity adjusting element is controlled by the control module 50 via a signal line 57. The water quantity can be injected via nozzles of the burners directly into the burners; on the other hand, the water can be mixed via mixers with the liquid fuel and the burners can be operated with a water-in-liquid fuel emulsion. The opening and closing instructions are hereby generated depending on the current operating states inside the control module. From the plurality of measured values combined in the control module, selected values are calculated with each other to form a command variable for the water quantity to be injected. Within the framework of the injection it is hereby possible to control the water quantity simply depending on a command variable in an open control chain. For example, the water quantity can be specified simply as a function of the current, relative performance of the gas turbo-set. On the other hand, and in an advantageous manner, the control of the water quantity can be performed in a closed control circuit in order to keep pulsations or burner temperatures below a permissible maximum value. In another embodiment, optical sensors detect the location of the combustion zone before the burner opening. The water injection then can be used to adjust the flame position to a desired value.

[0024] This enumeration of possible operating modes of the method according to the invention is not complete; one skilled in the art will be able to implement a number of variations of the method according to the invention without difficulty.

LIST OF REFERENCE NUMERALS

[0025] 1 Gas turbo-set

[0026] 2 Shaft

[0027] 3 Generator

[0028] 4 Compressor

[0029] 5 Combustor

[0030] 6 Turbine

[0031] 7 Burner

[0032] 8 Ring line

[0033] 9 Fuel quantity adjusting element

[0034] 10 Water quantity adjusting element

[0035] 11 Ring line

[0036] 41 Adjustable advance guide row

[0037] 50 Control module

[0038] 51 , 52, 53,

[0039] 54 , 55 Measuring signals, signal lines

[0040] 56 , 57 Control signal, signal line

Claims

1. Method for operating a premix burner, characterized in that depending on at least one command variable formed from at least one measured value a water quantity is introduced into the burner and/or the reaction zone.

2. Method according to claim 1, characterized in that the introduced water quantity is less than 20%, preferably less than 10%, and in particular less than 5% of the fuel quantity fed into the burner.

3. Method according to claim 1 or 2, characterized in that the burner is operated with liquid fuel.

4. Method according to one of the previous claims, characterized in that at least one measured value constitutes combustion pulsations.

5. Method according to one of the previous claims, characterized in that at least one summation value of combustion pulsations is used as a command variable.

6. Method according to one of the previous claims, characterized in that at least one amplitude of a frequency spectrum of combustion pulsations is used as a command variable.

7. Method according to one of the previous claims, characterized in that combustion pulsations are used within at least one specific frequency range in order to form the command variable.

8. Method according to one of the previous claims, characterized in that at least one measured value is at least one temperature.

9. Method according to one of the previous claims, characterized in that at least one measured value is a material temperature of the premix burner.

10. Method according to one of the previous claims, characterized in that at least one measured value is a signal of an optical sensor.

11. Method according to one of the previous claims, characterized in that the water quantity is introduced via nozzles of the burner.

12. Method according to one of the previous claims, characterized in that the water quantity is mixed prior to the injection of a liquid fuel with a liquid fuel in such a way that the burner is operated with a water-in-fuel emulsion.

13. Gas turbine operated with premix burners in accordance with a method according to one of the previous claims.