JPH0115775B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a combustion method and apparatus for a gas turbine combustor, and more particularly to a method and apparatus for performing premixed low NOx combustion.

[Conventional technology]

NOx when premixing fuel and air for combustion
The concentration has the characteristics shown in Figure 1, and the highest concentration occurs when the excess air ratio λ is around 1.1.
When it is 1.1 or more, the larger λ is, the lower the NOx concentration becomes. This characteristic is utilized to reduce NOx in gas turbine combustors, and an example is shown in Figure 2. In a gas turbine, the excess air ratio changes approximately four times from no load to rated load. On the other hand, the range in which NOx is low and stable combustion is possible is less than twice the excess air ratio. Therefore, the fuel nozzle is arranged in two stages in the axial direction of the combustor, and the excess air ratio at each stage is set so that NOx is low and NOx is low.
Moreover, it is specified within a range that allows stable combustion. Additionally, in order to more reliably reduce NOx, the combustion air is pressurized using a separate compressor, and a predetermined amount of air is supplied from the combustor head.
That is, in the conventional device of this type shown in FIG. 2, the air for lean combustion in the precombustion chamber 1 is diverted from the main compressor diffuser 6 through the bleed passage 7, and is pressurized by the compressor 18. The flow rate is controlled by the control valve 19 and guided to the fuel nozzle 3.
In the fuel nozzle 3, it is mixed with the primary fuel from the primary fuel pipe 8, and is supplied to the pre-combustion chamber 1 as a lean mixture capable of stable combustion. The secondary fuel from the secondary fuel pipe 9 and the secondary fuel header 12 is combined with the secondary air flowing directly from the compressor diffuser 6 and the secondary swirler 1.
1, and is supplied as a lean mixture to the main combustion chamber 2, where it is ignited by the flame in the pre-combustion chamber 1 and combusted. As a result, lean combustion occurs in both the pre-combustion chamber 1 and the main combustion chamber 2, resulting in low
NOx conversion becomes possible.

[Problems that the invention attempts to realize]

However, since the amount of air discharged from the compressor differential user 6 is approximately constant regardless of the load on the turbine, this type of device poses a problem when the load fluctuates. In other words, since the secondary air from the secondary swirler 11 always flows in a constant amount, when the secondary fuel starts to be injected, the air-fuel mixture becomes excessively thin and falls outside the flammable range, and most of the mixture becomes It will be discharged as unburned components. As a countermeasure to this, the amount of primary fuel and primary air supplied into the pre-combustion chamber 1 is increased, and even when the secondary air from the secondary swirler 11 flows in, the air-fuel mixture near the entrance of the main combustion chamber 2 is kept within the flammable range. It is also conceivable to configure the system so that the primary fuel is maintained at a constant temperature, but in this case, the turbine load handled by the primary fuel will increase, and there will be a switching point from the primary fuel to the primary and secondary fuels when the turbine load fluctuates. A problem arises in which load fluctuations cannot be performed smoothly. Furthermore, when the air for the pre-combustion chamber is pressurized by a compressor, the required power of the compressor increases.
Therefore, the drawback that the overall thermal efficiency is greatly reduced is unavoidable.

The object of the present invention is to provide a gas turbine combustor that can switch from primary fuel to primary and secondary fuels at a load lower than the normal load range of the gas turbine, and that can efficiently achieve low NOx without reducing thermal efficiency. An object of the present invention is to provide a combustion method using premixed combustion and an apparatus therefor.

[Means for solving problems]

The above-mentioned object of the present invention is to set the primary fuel amount of the gas turbine combustion device to a fuel amount corresponding to a load lower than the minimum normal load of the turbine, and to adjust the air introduced into the pre-combustion chamber to a ratio of the primary fuel to the above-mentioned primary fuel. excess air rate
The amount of secondary air to be mixed with the secondary fuel is set as a constant amount within the range of 1.2 to 1.6, and the excess air ratio is larger than the excess air ratio of the primary fuel, and the overall excess air ratio is This is achieved by controlling according to the turbine load so as not to exceed 4.

[Effect]

According to the configuration of the present invention, the excess air ratio of the primary fuel is almost constant regardless of the turbine load, and its value is in the range of 1.2 to 1.6, so the generation of NOx is small, and moreover, it is within the range for stable combustion. It is in. Furthermore, the amount of primary fuel is set to a fuel amount that corresponds to a load lower than the normal load zone of the turbine, so in the normal load zone, both primary and secondary fuel are always supplied, and the load due to fuel switching is reduced. No sudden changes occur. Furthermore, since λ of the secondary combustion is selected to be larger than the primary excess air ratio and the overall excess ratio does not exceed 4, there is no fear that unburned matter will increase.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. Similar to the conventional device, a part of the air for the pre-combustion chamber is diverted from the air bleed passage 7, boosted in pressure by the compressor 18, and guided to the fuel nozzle 3, but the flow rate control mechanism for controlling the flow rate of the primary air is The structure is such that the flow rate is determined to be a constant amount only by the primary swirler area at the outlet of the combustion nozzle 3. The primary fuel from the primary fuel pipe 8 is also adjusted to a certain amount and mixed with the primary air in the fuel nozzle 3,
It flows into the precombustion chamber 1 as a premixture. Therefore, the excess air ratio of the primary premixture is maintained at a constant value as described below. The flow rate of the secondary air is controlled according to the load by a control device 14 with a variable passage area provided in the air passage between the inner cylinder 4 and the outer cylinder 16, and the secondary air is supplied from the secondary fuel pipe 9. The fuel is premixed with the secondary fuel near the secondary swirler 11 or diffused and mixed at the outlet of the secondary swirler before being introduced into the main combustion chamber 2. This mixture is also leaner in fuel than the primary mixture in order to reduce NOx. The secondary air is controlled according to the turbine load by a control device 14 such as a guide vane in order to keep the air-fuel ratio in the main combustion chamber 2 constant, and is controlled by a device 20 that detects the fuel flow rate or fuel injection differential pressure. Air flow is controlled in response to the signal. Cooling air and dilution air in the main fuel chamber 2 are branched from the upstream side of the control device 14 and flow in through cooling air holes and dilution air holes 15 . Note that 13 is a partition wall, and only the air that has passed through the control device 14 is guided to the secondary swirler 11. 17 is a motor that drives the compressor 18.

In the gas turbine combustor configured as described above, the fuel distribution and excess air ratio that enable low NOx reduction and stable combustion without much structural difference from conventional combustors will be explained below.

First, the proportion of primary fuel burned in the preheating combustion chamber 1 is set in order to switch from primary to primary and secondary below the turbine's normal load range, and to reduce the power required to pressurize the air required for combustion of this primary fuel. The smaller the amount, the better, but it is necessary to ensure high combustion efficiency over the entire operating range by controlling the secondary air. As shown in Figure 4, the range in which a value close to the combustion efficiency near the rated load can be secured is when the overall excess air ratio, which is the sum of the primary and secondary, is 4 or less.
The range in which the secondary air should be controlled in order to ensure this excess air ratio is shown in FIG. Therefore, it is desirable to set the primary fuel ratio to 7% or more and 50% or less.

What Figure 5 means is that the higher the primary fuel ratio, the smaller the secondary air control range.
This shows that the flammable range λ<4 can be maintained.

By the way, in the present invention, the primary fuel amount and air amount are kept constant regardless of the turbine load, so the combustion amount must be set to a value that corresponds to a load lower than the load fluctuation range during normal operation of the turbine. Must be.

For turbines whose regular load is, for example, in the range of 50% to 100% of the rated load,
The primary fuel proportion can be set up to 50%. If the service load band is set to a lower load, the primary fuel proportion should be set to a correspondingly lower value.

Next, the excess air ratio is determined from the NOx characteristics shown in FIG. 1 and the precombustion chamber blowout characteristics shown in FIG. From the NOx characteristics, there is no NOx reduction effect even if the excess air ratio is set to 1.6 or more, and from the blow-off characteristics, when λ = 1.6, the blow-off flow rate is approximately 30% of the blow-off flow rate when λ = 1.2.
Since the combustor diameter is approximately doubled, it is desirable to set the upper limit and excess air ratio λ to 1.6. The lower limit is the low NOx effect due to lean combustion.
It is desirable to set λ = 1.2, which is 50%.

As is clear from the above explanation, the amount of primary fuel corresponds to a load lower than the normal load range of the turbine, and the primary fuel ratio is 7% to 50%.
The amount of air relative to the primary fuel is set so that the excess ratio λ falls within the range of 1.2 to 1.6. As an example, the overall excess air ratio is 2.9,
When the primary air excess ratio is set to 1.3, the relationship between the primary air ratio and the primary fuel ratio is shown in FIG. 7.

As is clear from Fig. 7, when λ = 1.3, when the primary fuel ratio is in the range of 7% to 50%,
The primary air proportion ranges from 3% to 22%.

The secondary fuel then varies from zero percent to the remaining percent of the primary fuel proportion. When the primary fuel ratio is 30%, the secondary fuel changes from 0 to 70%, the fuel flow rate at that time is detected by the fuel flow rate detection device 20, and the flow rate passes through the control device 14 according to the detection signal. Since the amount of air changes, the mixing ratio of secondary fuel and air remains approximately constant even if the amount of fuel changes. And the excess air ratio is 1.2 or more due to low NOx.
It is as below.

Therefore, under any conditions, the secondary air-fuel mixture is within the flammable range, the emissions of unburned components are small, and the concentration of NOx is also low.

Reduces the power required to boost the pressure of primary air.
It is desirable to reduce the amount of air to NOx, and as a limit, it is also possible to supply primary air to the pre-combustion chamber using only the pressure difference between the inside and outside of the inner cylinder 4 without providing the boosting compressor 18. In this case, the pressure difference between the pre-combustion chamber and the outside is small due to the pressure balance of the total pressure.
It is difficult to supply a large amount of primary air, and this can be achieved by reducing the amount of primary air compared to the conventional method. In the present invention, the primary fuel proportion is 7%
Since the primary air ratio at that time can be reduced to a minimum of 3%, it is possible to omit the compressor. Even in this case, the secondary air is controlled so that the overall excess air ratio including the secondary air is 4 or less. As a result, the air hole area changes depending on the load, and the combustor pressure loss increases, resulting in a slight decrease in thermal efficiency, but there is an advantage that a separate compressor is not required.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to switch from primary fuel to primary and secondary fuels at a load lower than the normal load range of the gas turbine, and moreover, it is possible to reduce the emission of unburned components. The effect is that NOx can be reduced without reducing the thermal efficiency of the system.

[Brief explanation of drawings]

Figure 1 is a diagram showing the NOx characteristics of a premixed flame, Figure 2 is a diagram showing the structure of a conventional premixed combustor, and Figure 3 is a diagram showing the NOx characteristics of a premixed flame.
Figure 4 is a diagram showing the structure of an embodiment of the premix combustor of the present invention, Figure 4 is a data diagram showing the range in which combustion efficiency does not decrease, Figure 5 is a diagram showing the control ratio of secondary air, Figure 6 is a diagram showing the blow-out characteristics of the precombustion chamber, and Figure 7 is a diagram showing the primary air amount ratio when the precombustion chamber excess air ratio is 1.3 in a combustor with an overall excess air ratio of 2.9. be. DESCRIPTION OF SYMBOLS 1... Pre-combustion chamber, 2... Main combustion chamber, 3... Fuel nozzle, 4... Inner cylinder, 14... Flow rate control device, 1
6...Outer cylinder, 18...Compressor, 20...Fuel flow rate detection device.

Claims (1)

[Claims] 1. A pre-combustion chamber is provided in the head and a main combustion chamber is provided in the rear, primary fuel and primary air are premixed and supplied to the pre-combustion chamber for combustion, and secondary fuel and air are mixed. In a gas turbine premix combustion method in which a generated air-fuel mixture is ignited and combusted in a main combustion chamber by a flame in a pre-combustion chamber, the amount of primary fuel is kept constant at a value corresponding to a load smaller than a normal load band of the gas turbine. kept,
The excess air ratio of the premixture to be generated is set to a substantially constant value within the range of 1.2 to 1.6, and the excess air ratio of the mixture generated by the secondary fuel and secondary air is equal to the excess air ratio of the premixture. so that the overall excess air ratio is greater than the excess air ratio and does not exceed 4.
A gas turbine premix combustion method, characterized in that the amount of secondary air is controlled according to a gas turbine load. 2 One end is connected to a fuel nozzle that injects a premixture of primary air and primary fuel, and the other end is connected to an open pre-combustion chamber and the secondary air is connected to the pre-combustion chamber near the connection. an inner cylinder that forms an air passageway between the inner cylinder and the outer peripheral surface of the inner cylinder, and an outer cylinder that surrounds the inner cylinder and forms an air passage between the inner cylinder and the outer peripheral surface of the inner cylinder; a booster device that boosts the pressure of a certain amount of air and supplies it to the fuel nozzle; a primary fuel pipe that supplies a constant amount of primary fuel regardless of the turbine load; A gas turbine premix combustion device comprising: a flow rate control device that controls the flow rate according to the flow rate.