JPH06307259A - Fuel controlling method for two stage combustion type gas turbine combustor - Google Patents

Abstract

PURPOSE:To switch a combustion mode smoothly and surely by determining each stable combustion condition for both of the first stage combustion and the second stage combustion on the basis of humidity of the atmosphere, a discharge temperature and a discharge air flow rate of a compressor, and the nature of fuel and feeding fuel after correcting the predetermined fuel flow rate. CONSTITUTION:In a gas turbine, intake air 100 is compressed by a compressor 1, the compressed air 101 is burnt in a combustor 2, and the burnt high temperature gas 104 works in a turbine 3 so as to drive a generator 6, and then, an exhaust gas is exhausted from a chimney 5 via an exhaust heat recovery boiler 4. In this case, a humidity sensor 20, an air flow meter 21, and an air temperature sensor 22 are arranged in the compressor 1. On the other hand, a fuel nature measuring device 23, the first stage fuel flow meter 25, and the second stage fuel flow meter 27 are arranged in a fuel system. Each of output signals from each of meters 20-23, 25, 27 is inputted to a fuel flow rate setting device 35 respectively, and then, the openings of both of the first stage fuel flow rate regulating valve 24 and the second stage fuel flow rate regulating valve 26 are controlled so as to switch a combustion mode.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas turbine combustor, and more particularly to a fuel control method for a two-stage combustion type gas turbine combustor which produces less NOx (nitrogen oxide).

[0002]

2. Description of the Related Art In order to reduce NOx in exhaust gas of a gas turbine, a two-stage combustor combining premixed combustion and diffusion combustion has been developed. Although these combustor structures are different depending on the gas turbine manufacturing company and the NOx achievement level, Japanese Patent Publication No. 1-40246 discloses a can type two-stage combustor. Here, the first stage combustion diffusion burner of the sub-chamber structure is provided on the upstream side of the combustor, and the premix burner having the annular premixer of the second stage combustion is provided on the outer peripheral side of the downstream end thereof. It is shown that the first-stage combustion operates from the start of the gas turbine to the partial load zone, and the first-stage and second-stage combustion operates from the partial load zone to the rated load. Furthermore, here, regarding the switching of the combustion mode from the first stage to the second stage, a certain amount of fuel is supplied to the second stage in steps, and at the same time, the fuel supply amount to the first stage is increased. Is performed in the same amount stepwise. In such a two-stage combustor, the NOx is reduced after the combustion mode is changed, that is, by the second-stage premixed combustion, and it is required to reduce the gas turbine load that can be changed as much as possible. In addition, it is important to ensure that the combustion mode is switched and that the gas turbine output does not change during the switching.
However, since the flame stability of diffusion combustion and premixed combustion is affected by the operating conditions of the gas turbine, the atmospheric environment, etc., there is a problem in switching the combustion mode with high reliability in the conventional technology.

[0003]

As described above, the conventional two-stage combustion type gas turbine combustor has a problem that the combustion mode cannot be reliably and smoothly switched from the first stage to the second stage. .

An object of the present invention is to provide a fuel control method capable of reliably and smoothly switching combustion modes.

[0005]

[Means for Solving the Problems] In order to reliably and smoothly switch the combustion modes, the second-stage flame must be ignited reliably by the supply of the second-stage fuel, and stable combustion, It is necessary that the first-stage flame whose fuel flow rate is reduced by the amount corresponding to the second-stage fuel amount be connected for stable combustion. Therefore, in the combustion mode switching, the fuel flow rates of the first stage and the second stage after the completion of the combustion mode switching must be set within the stable combustion range of each flame. In particular, the second-stage premixed flame has a narrow stable combustion range and is strongly affected by various combustion conditions. Therefore, information on atmospheric humidity, compressor discharge air temperature, compressor discharge air flow rate, and fuel properties, which have a particularly strong effect on flame ignition and stable combustion, are taken in, and the degree of influence on these flames is evaluated and determined in advance. The planned fuel flow rate is corrected and supplied as necessary to enable reliable ignition and stable combustion of the second-stage flame and to maintain the stable combustion range of the first-stage flame.

[0006]

[Function] Both the first-stage flame and the second-stage flame have a stable combustion range determined by the burner characteristics and combustion conditions. That is, when the fuel flow rate is below a certain amount under a predetermined operating condition, the flame blows off, and above a certain amount, the burner becomes red hot and burns. In particular, flashback occurs in the second-stage flame of premixed combustion. Therefore, in order to maintain stable combustion, it is necessary to set the fuel flow rate within the range determined by the burner characteristics and combustion conditions. Especially, when switching the combustion mode of the second stage combustion, the second stage flame is ignited by the first stage flame and stabilized by the second stage burner, so the interaction between the first stage and the second stage The fuel control that takes into account the above is required, and the degree of influence of the influencing factors on combustion is evaluated, and by reflecting this in the fuel control, more reliable and
Smooth switching is possible.

Among the influential factors in the gas turbine combustor, those having a large effect are atmospheric humidity, compressor discharge air temperature, compressor discharge air flow rate, and fuel property. Of these, as the influence of atmospheric humidity becomes higher, the flow rate of ignition fuel and the flow rate of stable combustion fuel increase. When the compressor discharge air temperature is low, the ignition fuel flow rate and the stable combustion fuel flow rate increase. When the flow rate of air discharged from the compressor is large, the flow rate of ignition fuel and the flow rate of stable combustion fuel increase. Regarding the fuel properties, looking at the addition of liquefied natural gas,
As the methane component increases, it becomes difficult to ignite, and the fuel flow rate required for stable combustion increases. Therefore, the degree of influence of these influencing factors on ignition and stable combustion is experimentally evaluated in advance, and while this is converted into data, these quantities are measured during gas turbine operation, and these are compared and calculated.
By correcting the predetermined fuel control flow rate as necessary, reliable ignition and stable combustion of the second stage flame can be performed.

[0008]

FIG. 1 shows an embodiment of the present invention. The gas turbine comprises a compressor 1, a combustor 2 and a turbine 3,
Atmospheric intake air 100 is boosted by the compressor 1 and supplied to the combustor 2 as compressor discharge air 101, and fuel 200
The high temperature working gas 10 is burned with (natural gas in this embodiment).
4 is generated, the turbine works, and the exhaust gas is discharged from the chimney through the exhaust heat recovery boiler 4. The turbine output is converted into electricity by the generator 6.

The combustor is arranged between the compressor discharge casing 7 and the turbine casing 8 and is housed by the combustor casing 9 and the combustor cover 10. The combustor has a first-stage combustion nozzle 13 in the center on the upstream side, and a first-stage combustion flow path having a swirler 15 at the outer periphery of the downstream end of the combustor. The combustion air 103 is provided with a first-stage burner that burns while mixing in the combustion chamber of the first-stage fuel 201 that is ejected from the fuel injection hole 14 that is opened at the end of the first-stage fuel nozzle 13. A premixer 16 composed of an annular air flow path and a fuel supply nozzle is arranged on the outer peripheral side of, and its downstream end opens into the combustor on the outer peripheral side of the first stage burner. The second stage combustion air 102 flows in from the upstream side of the premixer 16, and the second stage fuel is injected from this air and the second stage fuel nozzle 18 attached to the second stage combustion supply flange 17. 202 is mixed in the premix and supplied as a combustible mixture into the combustion chamber. The combustion gas 104 generated in the combustion chamber is supplied to the turbine 3 via the combustor transition piece 12.

In the gas turbine combustor having this structure,
From the start of the gas turbine, the partial load is operated only by the first stage burner, and the partial load to the rated load zone is operated by operating the first stage burner and the second stage burner. Here, by setting the ratio of the fuel flow rate to the combustion air flow rate of each burner, that is, the fuel-air ratio to be smaller than the theoretical fuel-air ratio, the flame temperature can be suppressed to a low level, so that combustion with less NOx generation is achieved. In this case, the NOx reducing effect of the second-stage premixing burner, which can uniformly reduce the flame temperature, is great. Therefore low NO
As the x-combustor, it is important to burn a thin air-fuel mixture that has a large combustion amount of the premix burner and is close to the stable combustion limit.

In the operation of the gas turbine, it is necessary to switch the combustion mode from the first stage burner to the second stage burner. That is, the switching from the first-stage combustion to the first-stage and second-stage combustion modes is performed under a certain predetermined partial load condition in which the gas turbine reaches the rated operation. This is achieved by injecting a predetermined fixed amount of the second-stage fuel in steps while keeping the total fuel flow rate substantially constant, and reducing the first-stage fuel in steps almost simultaneously. When switching the combustion mode, the amount of fuel input must be the fuel flow rate required for reliable ignition and subsequent stable combustion for the second stage burner, and for the first stage burner it must be stepped. Even if the fuel is reduced, the fuel flow rate must be higher than the fuel flow rate to keep the flame stable.
These values are basically planned by a combustion experiment simulating the operating conditions of the gas turbine, and in detail, the fuel control plan is established by adjusting the gas turbine during operation.
Furthermore, in order to increase the reliability and operational margin of practical operation, stable combustion must be ensured so that it can sufficiently cope with changes in operating conditions of the gas turbine and changes in fuel composition due to seasons and weather.

[0012] To meet this requirement, specifically, it is investigated how the operating conditions of the gas turbine, atmospheric conditions, fuel properties, etc., which affect ignition and combustion stability, affect ignition and flame stability. The effects of the above and combined effects are compiled into a database, and various quantities are measured or predicted during gas turbine operation, the degree of their effects is evaluated, and the predetermined fuel control plan value is modified as necessary. It is realized by More specifically, the change in ignition and flame stability range due to atmospheric humidity as shown in FIG. 2 is experimentally investigated, and this is reflected in control. The three lines ((1), (2), (3)) connected by circles show changes in the ignition conditions of the second stage combustion when the atmospheric humidity is different, and the atmospheric humidity is (1 ) → (2) → (3). The ignition fuel flow rate of the second stage combustion tends to decrease as the fuel of the first stage combustion increases, but there is a minimum ignition fuel flow rate and the atmospheric humidity is (1). The first stage fuel is F ₂ *, and the first stage fuel at that time is F ₁ **. Also, there exists a stable fuel flow rate for the first stage combustion, which is F ₁ ** in the figure. Further, the ignition fuel flow rate in the second stage combustion at this time is F ₂ **. That is, in the case of atmospheric humidity (1), the flow rate conditions of the first-stage fuel and the second-stage fuel, which are marked with a circle, are the operable conditions. The combustion mode is switched by keeping the total fuel flow rate substantially constant and reducing the output change of the gas turbine. The condition of constant total fuel is shown by the chain line in the figure. Therefore, in the case of (1), from (a) (F ₁ *, F ₂ *) on this line
(b) Up to (F ₁ **, F ₂ **) is a switchable condition. When the atmospheric humidity is high (2), the second stage ignition fuel flow rate and the first stage combustion stability limit fuel flow rate shift in an increasing direction. In this case, (c) to (b) are switchable conditions. When the atmospheric humidity becomes higher (3), the ignition condition does not exist under the total fuel condition shown by the alternate long and short dash line. In this case, the combustion mode is switched under the gas turbine load condition in which the total fuel flow rate is increased. FIG. 3 shows changes in the ignition and flame stable ranges depending on the compressor discharge air temperature, and the compressor discharge air temperature is low in the order of (1) → (2) → (3). Similarly, FIG. 4 shows changes in the ignition and flame stability range depending on the compressor discharge air flow rate, and the compressor discharge air flow rate increases in the order of (1) → (2) → (3). The fuel flow rate required for ignition and stable combustion is correspondingly increased. Figure 5 shows the change in ignition and flame stability range for natural gas depending on the fuel composition, and the methane concentration in the fuel gas increases in the order of (1) → (2) → (3), and it corresponds to this. Then, the required fuel flow rate increases.

Returning to FIG. 1 again, the method of switching the combustion mode will be described. A humidity sensor 20 and an air flow meter 21 are attached to the intake duct of the compressor 1, and an air temperature sensor 22 is attached to the discharge portion of the compressor 1. These measurement signals are measured by a humidity data processor 29, respectively. The data is input to the air flow rate data processor 28 and the air temperature data processor 30. On the other hand, in the fuel system, the fuel property measuring device 23
Fuel flow rate measuring devices 25 and 27 are provided in the first-stage fuel system and the second-stage fuel system, respectively. These measurement signals are input to the fuel property data processor 32 and the first and second stage fuel flow rate data processors 31 and 32, respectively. Appropriate control signals are input from each data processor to the fuel flow rate / distribution calculator, where the first-stage fuel flow rate and the second-stage fuel flow rate required for combustion mode switching are calculated and set. This signal is input to the fuel flow rate setting device 35, and the opening degree of the first-stage fuel flow rate adjusting valve 24 and the second-stage fuel flow rate adjusting valve 26 is adjusted by the control signals uncovered from the signal, and the combustion is performed. Mode switching is performed. FIG. 6 shows the change over time in the fuel flow rate during the combustion mode switching process. At time t ₁ , the combustion mode is switched, and the appropriately set second-stage fuel gas is injected in a step-like manner, and the first-stage fuel is reduced in a step-like manner substantially corresponding to this fuel flow rate. _{At 2} , the mode switching is completed. FIG. 7 shows the time variation of the gas turbine output during the combustion mode switching process. According to the present invention, by switching the combustion mode, the change in the load of the gas turbine during this period is small as shown by the solid line, and smooth switching is possible. The dotted line shows the output change when the ignition of the second stage burner is delayed. Due to the ignition delay, the load is largely decreased, and after the ignition, the load is rapidly increased, and the combustion mode cannot be switched smoothly.

[0014]

According to the present invention, the following effects can be obtained.

(1) Even when the operating conditions of the gas turbine, the atmospheric humidity, and the fuel properties change, the combustion mode switching conditions are appropriately selected.

(2) As a result of proper selection of the combustion mode switching conditions, the ignition of the second stage burner is smoothed, the change in the gas turbine output during the combustion mode switching process is suppressed to a small level, and the reliability of the gas turbine is improved. It becomes higher and the drivability is improved.

[Brief description of drawings]

FIG. 1 is a fuel control system diagram of a gas turbine combustor.

FIG. 2 is a characteristic diagram showing changes in ignition and stable combustion ranges depending on atmospheric humidity.

FIG. 3 is a characteristic diagram showing changes in ignition and stable combustion ranges depending on compressor discharge air temperature.

FIG. 4 is a characteristic diagram showing changes in ignition and stable combustion ranges depending on the compressor discharge air flow rate.

FIG. 5 is a characteristic diagram showing changes in ignition and stable combustion ranges depending on fuel composition.

FIG. 6 is a characteristic diagram showing a change over time in the fuel flow rate during the combustion mode switching process.

FIG. 7 is a characteristic diagram showing a time change of a gas turbine output during a combustion mode switching process.

[Explanation of symbols]

2 ... Combustor, 13 ... First stage fuel nozzle, 17 ... Second stage fuel nozzle, 20 ... Humidity measuring sensor, 21 ... Air flow meter, 22 ... Air temperature measuring sensor, 23 ... Fuel property measuring device, 25 ... 1st stage fuel flow meter, 27 ... 2nd stage fuel flow meter, 34 ... Fuel flow rate / distribution calculator, 35 ... Fuel flow rate setter.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shohei Yoshida 502 Jinritsu-cho, Tsuchiura-shi, Ibaraki Hiritsu Seisakusho Co., Ltd.Mechanical Research Institute (72) Shigeyuki Akatsu 502 Jinre-cho, Tsuchiura-shi, Ibaraki Hiritsu Seisakusho Inside the Mechanical Research Institute (72) Inventor Tomoki Koganawa 502 Jinritsu-cho, Tsuchiura-shi, Ibaraki Prefecture Hiritsu Seisakusho Co., Ltd.

Claims (1)

[Claims] 1. A gas turbine combustor in which a diffusion burner for performing diffusion combustion and a premixing burner for performing premix combustion are combined, and the gas turbine combustor is operated by a diffusion burner for first-stage combustion during partial load operation from start of the gas turbine. However, the partial load to the rated load is operated by the premixed burner of the first stage combustion and the second stage combustion, and the switching of the combustion mode from the first stage combustion to the second stage combustion is performed by the first stage fuel. In a gas turbine combustor in which the second-stage fuel is charged to a predetermined amount while maintaining the constant flow rate or reducing the first-stage fuel, the atmospheric humidity, the compressor discharge temperature, the compressor discharge air flow rate, and the fuel properties Taking in one or more of these pieces of information, the stable combustion conditions for each of the first-stage combustion and the second-stage combustion in the combustion mode switching process are calculated and determined, and based on this, the planned fuel flow rate is calculated. Modified and supplied The fuel control method for a two-stage combustion type gas turbine combustor and performing combustion mode switching.