JPH0563687B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a method for supplying fuel and air to a gas turbine combustor, and particularly to a method for supplying fuel and air to a gas turbine combustor of a low NOx type two-stage combustion type gas turbine combustor. Regarding the combustor that obtains the performance.

[Background of the invention]

Air pollutants in gas turbines include nitrogen oxides (NOx), carbon monoxide (CO), soot, etc. contained in exhaust gas, and minimizing the emissions of these substances is as important as improving turbine performance. It is. In particular, NOx and CO are generated during the combustion process, and NOx is generated in a high-temperature combustion gas atmosphere, so methods are taken to lower the combustion gas temperature. Specifically, there are two methods: one is to add a refrigerant such as water or steam to the combustion gas, and the other is the lean low-temperature combustion method in which combustion is performed using excess air.The lean low-temperature combustion method is common in gas turbines because it reduces efficiency loss. It is carried out in However, supplying excessive air and performing low-temperature combustion also reduces combustibility due to supercooling, which causes an increase in the generation of CO, unburned components (HC), and the like. For this reason, in gas turbine combustors, NOx reduction and reduction of unburned substances such as CO and HC have contradictory characteristics, and the key to improving gas turbine combustors is to simultaneously eliminate these two factors.

Efficient, uniform, and low-temperature combustion with as little air as possible and avoiding the occurrence of supercooled areas will reduce NOx and will be very advantageous in preventing CO generation. As a specific method,
A head combustion chamber with a slight excess of air and a stable combustion flame is installed in the head, and air and fuel are supplied to its wake, resulting in uniform low-temperature combustion throughout. A two-stage combustion system is adopted in which the fuel is supplied to two stages. This method creates too much air when supplying fuel to the second stage, so unburned components and
It has the disadvantage that it generates a lot of CO, leading to a significant drop in combustion efficiency. This situation will be explained using FIG.

FIG. 1 is a cross-sectional view of a conventional two-stage combustion type combustor. A gas turbine consists of the following main components: an air compressor 1, a turbine 2, a combustor 3, and a load 4 (for example, a generator). Air 5 compressed by compressor 1
is led to the combustor 3. The combustor 3 includes an outer cylinder 6, an inner cylinder 7, and a side closed end. A primary fuel nozzle 11 that supplies primary fuel 10 to the head combustion chamber 9 is incorporated in the outer cylinder cover 8, and a fuel reservoir 1 is supplied to the rear combustion chamber 12 from a fuel supply section 13 attached to the cover 8.
4, secondary fuel is injected 17 from a plurality of fuel injection parts 15 to a secondary air supply hole (sometimes serving as a swirling vane) 16, and is supplied to the rear combustion chamber together with secondary air 18 to generate a premixed flame 22. Form. On the other hand, a turbulator 20 is attached around the primary fuel nozzle 11 to supply swirling air 19 to the head combustion chamber 9.
This promotes the stability of the diffusion flame 21 that is formed.

In this way, by forming the head diffusion flame by combustion of the primary fuel and further forming the premix combustion flame 22, the overall lean and low temperature combustion is realized, thereby reducing NOx. We are trying to

However, in the premixed combustion flame 22 of the secondary fuel 17 and the secondary excess air 18, the fuel 17 is added to the secondary air 18.
In the process of supplying fuel 17, at low loads when the supply of fuel 17 is very small, the fuel concentration becomes lighter than the air 18, resulting in supercooled combustion, inhibiting combustion, and leaving a large amount of unburned components such as HC and CO. There is a big drawback that it is discharged.

FIG. 2 shows an example of a fuel supply method using a two-stage combustion method. To supply fuel, first ignite with only the primary fuel, continue to increase the fuel, and when the turbine load reaches about 50%, stop increasing the fuel and form a flame in the head combustion chamber 9 to maintain a constant flow rate 21 do. At this point, start supplying secondary fuel 17, 50%
The turbine load increase from 100% to 100% is secondary fuel 1.
This is done by an increase of 7.

Figure 3 shows fuel 17 and air 18 after secondary fuel supply.
Indicates the state of The air flow rate 18 is always a constant flow rate because the compressor 1 is operating at its rated value. Fuel 17 will be supplied into this air, but in region A where the supply amount of fuel 17 is small, the fuel supply amount is small compared to the air flow rate, so the fuel becomes too dilute and combustion cannot occur. , it becomes a non-flammable range.

Figure 4 shows the emission characteristics of unburned components such as CO and HC contained in exhaust gas. Gas turbine output 50
% or less, the primary fuel 10 supplied to the head combustion chamber 9
Since the air temperature is almost the same as room temperature at the time of ignition, and the temperature of surrounding components is low, combustibility is inhibited. For this reason, CO emissions tend to increase. Further, the supply of fuel 17 to the main combustion chamber 12 is started from around 50% of the turbine output. In particular, at 50% to 70% output immediately after the start of secondary fuel supply, there is a large amount of secondary air 18, which corresponds to region A, where the amount of fuel supplied is small compared to air, as shown in FIG. For this reason, it remains unburned and is contained in the exhaust gas, increasing the CO concentration.

As described above, the two-stage combustion method has a major drawback in that it cannot suppress the generation of CO because the above-mentioned non-combustion range exists at the stage of supplying the secondary fuel. Therefore, attempts have been made to suppress the generation of unburned gas by changing the supply direction of the premixed fuel of secondary fuel and secondary air so that it faces the combustion flame 21 in the head combustion chamber. Since fuel is further supplied to the flame 21, the temperature of the combustor shaft center moves to a high temperature during rated operation of the gas turbine, which has the disadvantage of increasing NOx generation during rated operation.
In the case of secondary combustion, where secondary fuel is mixed with secondary air and premixed combustion is performed as a premixed fuel gas, this prevents the generation of large amounts of unburned components such as CO due to excess air at the beginning of fuel injection. I can't do that.

[Purpose of the invention]

The purpose of the present invention is to significantly reduce NOx in exhaust gas, and to reduce CO and CO within the operating range of the gas turbine.
The purpose of the present invention is to provide a combustor that suppresses the generation of HC and has good combustion performance.

[Summary of the invention]

The main point of the present invention is that the gas turbine two-stage combustor forms a stable flame in the head combustion chamber to reduce NOx through diffusion-lean low-temperature combustion, and furthermore, in the rear combustion chamber located downstream, fuel and air are formed. By performing premix combustion with a slight excess of air, a wide range of low
Aim to reduce NOx. Furthermore, the flow rate of premixed air supplied from the second stage is the flow rate ratio with the flow rate of fuel supplied to the second stage.
By controlling the fuel supply and the second stage air flow rate so that the flow rate ratio is always slightly excessive, even when the second stage fuel supply starts, the combustion range is always within the combustion range. The goal is to eliminate supercooling and suppress the generation of unburned components such as CO and HC.

In particular, the low NOx gas turbine combustor of the present invention
A head combustion chamber that performs diffusion combustion by introducing first-stage fuel and first-stage air into the head and forming a diffusion flame, and a second-stage combustion chamber located behind the head combustion chamber. It is equipped with a main combustion chamber that performs premix combustion by supplying a mixture of fuel and second stage air to form a premix combustion flame. In such a combustor, at startup of the turbine,
Both the first stage fuel and the first stage air are increased. Furthermore, when the output of the turbine is less than 50%, the first stage fuel is increased but the first stage air is kept constant.
Furthermore, when the output of the turbine is 50% or more, the first stage fuel is kept constant and the first stage air is increased,
It is characterized by providing an air flow regulator that increases both the second stage fuel and the second stage air.

[Embodiments of the invention]

Embodiments of the present invention will be described using FIGS. 5 to 8.

FIG. 5 is a cross-sectional view of one embodiment of a gas turbine combustor according to the present invention.

The compressed air for combustion is divided into two systems, and the air discharged from the compressor 1 flows around the transition piece 23 and flows through the turbulator 20, which opens into the head combustion chamber 9, the air holes 24, and wall cooling, just as in the conventional combustor. air hole 25
and a system that is introduced into the combustor through the wall cooling air holes 25 and dilution air holes 26 that open into the main combustion chamber 12, and secondary air that branches air from the compressor and supplies it to the main combustor. Two systems leading to the swirl supply hole 27 are provided. That is, a valve 30 is provided that adjusts the flow rate of the air 29 so that the flow rate ratio of the fuel 28 and the air 29 supplied from the second stage to the main combustion chamber 12 is always slightly excessive. The air whose flow rate has been adjusted gathers in the air reservoir 31 and flows through the swirling air hole 27 into the main combustion chamber 1.
The fuel 32 is supplied into the swirling air flow into the swirling air flow, and is introduced into the main combustor 12 from the swirling hole 27 as premixed fuel with the air 29. The secondary air 29 is adjusted and supplied by a flow rate regulating valve 30 so that the flow rate ratio with the secondary fuel 32 is slightly excessive so that the excess air ratio: λ is 1.2 to 1.8. When λ is less than 1.2, the temperature of the combustion gas 33 becomes high, which increases the production of NOx. When λ≧1.8 or more, there is an excess of air relative to the fuel, inhibiting combustion, resulting in unstable combustion, CO, This reduces combustibility, such as increased emissions of unburned substances such as HC. in this way,
The flow rate ratio adjustment 33 is performed so that the secondary air flow rate always becomes the flow rate ratio with the fuel with a slight excess of air. The state of such control is shown in FIG. The air flow rate increases as the turbine load increases from the start of secondary fuel injection, and the flow rate regulator 34 increases as the turbine load increases.
Increase the air flow rate at , always ensuring that λ is between 1.2 and 1.8. Therefore, it is possible to maintain a state in which the fuel does not fall into the non-flammable range even immediately after the secondary fuel is introduced. Further, FIG. 7 shows how the air flow rate changes with respect to the gas turbine output. The total air flow rate and the changes in each air amount relative to this are shown. The secondary air is controlled so that it begins to flow when the turbine output reaches approximately 50%, and is controlled so that approximately 30% of the total air volume flows in at 100% load. If it exceeds 30%, the amount of secondary air flowing out increases, resulting in a decrease in flammability. Approximately 25% is good.

FIG. 8 shows the concentration characteristics of NOx, CO, and HC according to the present invention. Up to 50% gas turbine output, only the primary fuel is combusted, and when the gas turbine output is 0%
There is a tendency for a large amount of CO to be generated, but immediately after starting the supply of secondary fuel, which is the key point of this invention, CO
Its concentration is low and its production is almost non-existent. By controlling the secondary swirling air that mixes with the secondary fuel and continues combustion, it is possible to maintain a good combustion state by eliminating the supercooling state caused by excess air that was seen in conventional examples. This is because he became older. NOx generation is also the same as in the conventional method, which uses premixed combustion, and can be significantly reduced. On the other hand, the following methods can also be used. To change the flow rate of secondary air, the compressor discharge air system is divided into two systems, and a flow rate adjustment valve is installed in the middle.
A method to obtain a similar effect is to install a variable current plate in front of the secondary swirling air inlet, and by moving the current plate to change the air opening area, the same level of CO2 can be achieved. A reduction effect can be obtained.

〔Effect of the invention〕

According to the present invention, it is possible to significantly reduce NOx and suppress the generation of unburned components such as CO and HC within the operating range of the gas turbine.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of a conventional low NOx two-stage combustor.
Figure 2 is a fuel input diagram for a two-stage combustor;
The figure is a fuel-air condition characteristic diagram when fuel is input into the second stage of a conventional combustor, Figure 4 is an exhaust gas characteristic diagram of a conventional combustor, Figure 5 is a system diagram of an embodiment of the present invention, and Figure 6 7 is a diagram showing changes in the fuel-air state during second-stage fuel injection according to the present invention, FIG. 7 is a diagram showing changes in air according to the present invention, and FIG.
The figure is an exhaust gas characteristic diagram of the low NOx two-stage combustor according to the present invention. 3... Combustor, 16... Second stage air weight, 13
...Second stage fuel, 28...Second stage fuel, 29...
Second stage air, 9...Head combustion chamber, 12...Main combustion chamber, 30...Air control valve.

Claims (1)

[Scope of Claims] 1. A head combustion chamber that performs diffusion combustion by introducing first-stage fuel and first-stage air into the head and forming a diffusion flame, and said head combustion chamber. 2 behind
A low NOx gas turbine combustor comprising a main combustion chamber that performs premix combustion by supplying a mixture of stage fuel and second stage air to form a premix combustion flame, At startup of the turbine, both the first stage fuel and the first stage air are increased, and when the output of the turbine is 50% or less, the first stage fuel is increased and the first stage air is kept constant; When the output of the turbine is 50% or more, an air flow regulator is provided that increases the first stage air while keeping the first stage fuel constant and increases both the second stage fuel and second stage air. A NOx gas turbine combustor featuring: