JPH07318013A - Multi-stage lean premixing combustion method - Google Patents

Abstract

PURPOSE:To perform a complete combustion of lean premixed gas out of an ignitable limitation without discharging not-yet ignited substituent by a method wherein a lean premixed gas and a high temperature combustion gas are mixed and reacted in such a manner that a temperature within a combustion device may always become a value not less than a specified temperature after both gases are mixed and reacted with each other. CONSTITUTION:A lean secondary premixed gas Q2 out of an ignitable limitation is mixed with a high temperature combustion gas of a primary premixed gas generated within a primary combustion chamber 21 and reacted within a secondary combustion chamber 22. A thermocouple 40 and a sampling probe 50 are disposed at an outlet 24 of a combustion chamber 20 of the combustion device and then a temperature of the lean secondary premixed gas Q2 is measured by the thermocouple 40 after being mixed and reacted with the high temperature combustion gas. Then, during the actual operation, the lean premixed gas is mixed with the high temperature combustion gas and reacted with it in such a manner that the temperature within the combustion device after being mixed with and reacted with the high temperature mixture gas may always become a value not less than a specified temperature defined in response to the type of the combustion device and combustion constituents.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-stage lean premixed combustion method, and more particularly, to a multi-stage lean premixed gas which is out of the flammability limit, which has hitherto been impossible to completely burn it. Premix combustion method.

[0002]

And premixed combustion method has attracted attention as a low NO _x combustion method of the Related Art Various combustor, the development of practical combustor in various fields have been made. In the premixed combustion method, there is a trade-off relationship between suppression of deterioration of combustion efficiency due to emission of CO and unburned hydrocarbons at low load (so-called emission of unburned components) and reduction of NO _x emission at maximum load. In
How to balance these is a technical issue.

In order to overcome such problems, a method of bypassing air according to load fluctuations and controlling the air-fuel ratio in the combustion region within a certain range has been partially put to practical use in large gas turbine combustors. However, in this method, the system is very complicated, so space, safety,
In terms of cost, it is difficult to apply to medium and small gas turbine combustors.

As a solution to this problem, the applicant of the present invention dividedly supplies a premixed gas of fuel gas and air in two stages as shown in FIG. 1, and has high combustion efficiency and low NO _x over a wide load range only by fuel control. Has been developed and a patent has already been filed (see JP-A-5-296412 and JP-A-5-340508). That is, the premixed gas supply is divided into two stages, and the first stage supplies the low-air-ratio premixed gas for stable combustion as the primary combustion flame.
Fuel gas that is controlled according to the load is supplied to the stage. During that time, a constant amount of air is being supplied to the second stage, and as a result, in the region where the air ratio is about 1.3 to 3.5, the amount of unburned matter is kept low while maintaining low NO. _x
Burning takes place.

[0005]

When the present inventors further reduce the supply amount of the fuel gas in the second stage as the load decreases in the course of further continuing the experiment, the air ratio is about 20 (that is, It is possible to continue combustion until the fuel concentration is low and it is out of the combustion limit. However, unburned components (mainly composed of CO and hydrocarbons) are discharged in the process, and so-called incomplete It was found that it shows a combustion state. In other words, lean premixed combustion method of this type, although it significantly reduces NO _x emissions amount, especially the second stage is in the low load combustion at high air ratio, NO _x emissions reduction and unburned hydrocarbons, etc. The range in which the emission control of unburned components can be achieved at the same time is very narrow. Therefore, while monitoring the combustion state of the combustor, it is possible to perform continuous combustion in a state where the emission of unburned components is reduced. I learned that development is needed.

Therefore, the present inventors have examined a conventional control method for controlling combustion by monitoring the combustion state of the combustor of a known gas turbine. As an example,
In a gas turbine having first-stage and second-stage combustion chambers, a plurality of sensors that detect the concentration of unburned components in exhaust gas are arranged in the exhaust duct, and the concentrations of unburned components detected by these sensors are arranged. It is known that the combustion state of the second stage combustion chamber is determined based on a distribution pattern (see Japanese Patent Laid-Open No. 2-49933).

Although the concentration sensor is used in the above combustion state monitoring method, the concentration sensor is generally complicated,
There was a problem in practical application in terms of durability, compactness, and cost. Therefore, a method of measuring temperature instead of measuring concentration has been considered. In the method of measuring the temperature, in a gas turbine combustor having a head and a rear combustion chamber, a sensor for detecting the temperature is provided as a sensor for detecting a combustion flame in the combustion chamber, and a combustion state is detected by a signal from the sensor. There is also known one that is monitored (see Japanese Patent Laid-Open No. 3-102118).

The multi-stage premixed combustion in the conventional gas turbine combustor is to burn a premixed gas having an air ratio within a combustible limit at each stage. The judgment is the judgment of the state of ignition, misfire or non-ignition. Therefore, for example, when detecting the concentration of the unburned component, it is possible to determine the combustion state by utilizing the fact that the concentration change to be detected is large and abrupt. In addition, even if a sensor that detects the temperature is provided as a sensor that detects the combustion flame to monitor the combustion state, the temperature may drop sharply due to misfire or misfire and reach the same level as the temperature of the combustion air. From this, it is possible to easily determine misfire or misfire.

However, by using the multi-stage lean premixed combustion apparatus as shown in FIG. 1, the high temperature combustion gas generated by the combustion in the preceding stage has a high air ratio and is outside the flammability limit as described above. When the premixed gas is mixed and reacted, the lean premixed gas absorbs heat and reacts while mixing with the high temperature combustion gas. Therefore, when the amount of heat generated by the reaction of the lean premixed gas is small, the temperature in the combustor may drop during the mixing with the high temperature combustion gas, and the reaction of the lean premixed gas may stop. The phenomenon of ignition or misfire does not appear. That is, when the high-temperature combustion gas is mixed with the ultra-lean premixed gas that is outside the flammability limit, phenomena such as a sudden increase in the emission of unburned components and a decrease in temperature do not appear.
As a result, it has been found that it is impossible to directly apply the above-described conventionally known combustion state monitoring means for a gas turbine.

Therefore, an object of the present invention is to provide a multi-stage lean premixed combustion method in which a high temperature combustion gas generated by combustion in the preceding stage is mixed with a lean premixed gas outside the flammability limit to react with the hot combustion gas. It is an object of the present invention to provide a multi-stage lean premixed combustion method in which a lean premixed gas is completely burned without discharging unburned components.

[0011]

In order to solve the above problems and achieve the object, the present inventors have conducted various combustion tests using a two-stage lean premixed combustor of the type shown in FIG. It was The combustor used for the combustion test was a primary swirl flow burner 10
Is composed of a combustion chamber 20. The air A ₁ and the primary premix gas Q ₁ in the street combustible range fuel gas G ₁ is swirler 13 from the primary fuel inlet 12 from the primary air inlet 11 in the primary swirl flow burner 10 Next, a stable premixed flame is formed in the primary combustion chamber 21, and complete combustion is performed to form high temperature combustion gas. A secondary premixed gas (lean premixed gas) supply nozzle 30 is provided downstream of the primary combustion chamber 21, and a lean secondary premixed gas Q ₂ outside the flammability limit is supplied from the nozzle 30. The supplied secondary premixed gas Q ₂ is supplied to the primary combustion chamber 2
The primary premixed gas produced in 1 is mixed with the high temperature combustion gas and reacted in the secondary combustion chamber 22.

At the outlet 24 of the combustion chamber 20 of the combustor, a thermocouple 40 and a sampling probe 50 are arranged,
The temperature T after the lean secondary premixed gas Q ₂ is mixed and reacted with the high temperature combustion gas is measured by the thermocouple 40, and the exhaust gas at the combustor outlet 24 is collected by the sampling probe 50 to analyze its components. Then, the presence or absence of unburned components was measured. In addition, 23 is a heat insulating material.

In the combustion test, the primary premixed gas Q ₁
Air ratio lambda ₁ of the air ratio lambda ₂ of the secondary lean premixed gas Q _2,
Various combinations of the flow rates of the primary premixed gas Q ₁ and the secondary premixed gas Q ₂ were performed, and the exhaust gas temperature T was measured and the components were analyzed for each. Through the combustion test, even if the combustion conditions are different, the temperature of the combustion exhaust gas, that is, the temperature T after the lean premixed gas is mixed and reacted with the high temperature combustion gas is higher than the specific temperature determined by the combustion equipment and the fuel component. If it is higher, the combustion exhaust gas contains no unburned components and is completely combusted, and if it is lower than the specific temperature, it is known that the combustion exhaust gas contains unburned components. It was

The multi-stage lean premixed combustion method of the present invention is based on the above findings. Basically, the high temperature combustion gas produced by the combustion in the preceding stage is mixed with the lean premixed gas outside the flammability limit. A multi-stage lean premixed combustion method for reacting,
The temperature after the lean premixed gas in the combustor is mixed and reacted with the high temperature combustion gas before and after the start of the discharge of unburned components from the combustor outlet for the combustor is measured in advance in actual operation. , The lean premixed gas is mixed and reacted with the high temperature combustion gas so that the temperature in the combustor after the lean premixed gas is mixed with the high temperature mixed gas and reacted is always higher than the measured temperature. .

In actual operation, the temperature in the combustor after the lean premixed gas is mixed with the hot combustion gas and reacted may be measured at one measurement point, preferably the same cross section across the flow of the combustion gas. The measurement may be performed at a plurality of measurement points at a plurality of points. In the latter case, the unburned components can be surely avoided by mixing and reacting the lean premixed gas with the high temperature combustion gas so that the lowest temperature of the latter is equal to or higher than the measured temperature.

In the combustion method according to the present invention, as the first stage, the premixed gas in the flammable range is burned, and the lean premixed gas which is outside the flammable limit with respect to the combustion gas is treated under the above conditions. It may be a two-stage premixed combustion method in which the combustion gas produced by the above two-stage premixed combustion is referred to as "high temperature combustion gas burned in the preceding stage", and the flammability limit is set there. A mode may be adopted in which the lean premixed gas outside is mixed so as to satisfy the above conditions. The number of repeating stages is arbitrary, whereby a multi-stage lean premixed combustion method can be obtained.

[0017]

[Operation] According to the present invention, even when a clear flame does not appear and an unburned component is generated, neither a sudden change in temperature in the combustion region nor a sudden change in component occurs. Even in a multi-stage lean premixed combustion in which a certain lean premixed gas is mixed and reacted, the temperature in the combustion chamber outlet, that is, after the lean premixed gas is mixed with the high temperature combustion gas and reacted, is measured, and the temperature is measured. Combustion is performed by maintaining a complete combustion state without the generation of unburned components by mixing the lean premixed gas with the high-temperature combustion gas and reacting them so that the temperature becomes higher than the specific temperature value obtained in advance. It is possible to continue.

[0018]

EXAMPLES The present invention will be described in more detail below based on experimental examples using the combustion apparatus shown in FIG. 1 and using a fuel containing methane as a main component as a lean premixed gas. In the experiment, the air ratio lambda ₁ of the primary premix gas Q ₁ is 1.2 to 1.
8. Various cases where the air ratio λ 2 of the secondary lean premixed gas is ₂ to 12, and the ratio of the supply amount of the primary premixed gas Q ₁ to the secondary lean premixed gas Q ₂ is 5: 5 and 6: 4. Experiments were conducted under the combination of, and the temperature T in the combustor after the combustion chamber outlet, that is, the lean premixed gas was mixed and reacted with the high temperature combustion gas by the thermocouple 40, was measured by the sampling probe 50. The components of the collected exhaust gas were analyzed by gas chromatography. Then, the combustion efficiency 2nd.CE (%) of the secondary lean premixed gas was obtained by the following formula.

[0019]

[Equation 1]

The results of the combustion test are shown in FIGS.
Incidentally, in the figure, the air ratio lambda ₂ on the horizontal axis secondary premixed gas Q _2, the left vertical axis combustion efficiency of the secondary premixed gas Q ₂ 2nd.C.
E. (%), the right vertical axis is the combustion chamber outlet temperature. 2 to 4
Is an air ratio λ ₁ = 1.2, 1.4 of the primary premixed gas Q ₁ under the condition that the ratio of the supply amounts of the primary premixed gas Q ₁ and the secondary lean premixed gas Q ₂ is 5: 5. , 1.6, and the air ratio λ ₂ of the secondary lean premixed gas Q ₂ is changed to ₂ for each.
It is the case when changing from 1 to 12.

That is, FIG. 2 shows the primary premixed gas Q.₁of
Air ratio λ₁Is 1.2, the secondary lean premixed gas Q
₂Combustion efficiency of 2nd.C.E. is the air ratio λ₂Change of
However, all are 100%,
Combustion after a thin premixed gas mixes and reacts with the hot combustion gas
The temperature T in the vessel is the secondary lean premixed gas Q₂Air ratio λ ₂
As the temperature rises, it drops to about 1200 ℃ -950 ℃
There is.

FIG. 3 is an air ratio lambda ₁ of the primary premix gas Q ₁ is
In the case of 1.4, in this case, the primary premixed gas Q ₁
Due to the decrease in the fuel gas inside, the temperature T at the outlet of the combustion chamber is lower than in the case of FIG. The secondary lean air ratio lambda ₂ of the premixed gas Q ₂ combustion efficiency 2nd.CE secondary lean premixed gas Q ₂ at the 6 before and after shows that unburned components no longer 100% occurs . At that time, the temperature T at the outlet of the combustion chamber is approximately 900 ° C.

FIG. 4 shows the air ratio λ ₁ of the primary premixed gas Q _1.
In the case of a more dilute case of 1.6, the temperature T at the outlet of the combustion chamber is lower than that in the case of FIG. 2 due to the influence of the decrease in the fuel gas in the primary premixed gas Q ₁ . Then, the air ratio lambda ₂ of second lean premixed gas Q ₂ is 3 combustion efficiency 2nd.CE secondary lean premixed gas Q ₂ at the front and rear are no longer 100%, the temperature of the combustion chamber outlet at the time T is almost 9
It is 00 ° C.

5 to 7 show that under the condition that the ratio of the supply amounts of the primary premixed gas Q ₁ and the secondary lean premixed gas Q ₂ is 6: 4,
Changing the air ratio λ ₁ = 1.4,1.6,1.8 primary premixed gas Q _1, for each further change the air ratio of the secondary lean premixed gas Q ₂ lambda ₂ from 2 to 12 It is the case when it is made to. Also in this case, when the air ratio lambda ₁ in the case of FIG. 5 or primary premix gas Q ₁ is 1.4, the 2
The combustion efficiency 2nd.CE of the next lean premixed gas Q ₂ is 100% irrespective of the change in the air ratio λ ₂ , and the combustion chamber outlet, that is, after the lean premixed gas is mixed with the high temperature combustion gas and reacted. The temperature T in the combustor is about 1100 ° C. to 920 as the air ratio λ ₂ of the secondary lean premixed gas Q ₂ increases.
It has dropped to ℃.

[0025] Figure 6 is an air ratio lambda ₁ of the primary premix gas Q ₁
In the case of 1.6, in this case, the primary premixed gas Q ₁
The temperature T of the combustion chamber outlet than in Figure 5 under the influence of reduction in the fuel gas has fallen in, and the secondary lean secondary lean premixed air ratio lambda ₂ gas Q ₂ is at the 6 before and after The combustion efficiency 2nd.CE of the premixed gas Q ₂ was not 100%, indicating that unburned components were generated. At that time, the temperature T at the outlet of the combustion chamber is still about 900 ° C.

FIG. 7 shows the air ratio λ ₁ of the primary premixed gas Q _1.
In this case, the combustion chamber outlet temperature T is lower than that in the case of FIG. 5 due to the decrease in the fuel gas in the primary premixed gas Q ₁ . cage, and an air ratio lambda ₂ of second lean premixed gas Q ₂ combustion efficiency 2nd.CE secondary lean premixed gas Q ₂ at the 3 before and after are no longer 100%. At that time, the temperature T at the outlet of the combustion chamber is also about 900 ° C.

The results of FIGS. 5 to 7 also show that the primary premixed gas Q ₁
When the ratio of the secondary lean supply amount of the premixed gas Q ₂ is unchanged, in the case of changing the air ratio lambda ₁ of the primary premix gas Q _1, a combustion chamber outlet That lean premixed gas and hot combustion gases mix If the temperature T in the combustor after the reaction is about 900 ° C. or higher, the combustion efficiency of the secondary lean premixed gas Q ₂ is always 100%, which is the air ratio of the secondary lean premixed gas Q ₂ . It shows that it has nothing to do with λ ₂ .

Next, FIG. 3 and Comparing FIG. 5, when the air ratio lambda ₁ = 1.4 primary premixed gas Q _1, the primary premix gas Q ₁ and the secondary lean premixed gas Although the temperature T at the combustion chamber outlet changes differently as the ratio of the supply amount of Q ₂ changes, if the temperature T is about 900 ° C. or higher, the combustion efficiency of the secondary lean premixed gas Q ₂ is always It shows 100%. This is the same in comparison between FIG. 4 and FIG. 6. From the above results, the multi-stage lean reaction in which the high temperature combustion gas generated by the combustion in the previous stage is mixed with the lean premixed gas outside the flammability limit In the above premixing type combustion apparatus, when a fuel containing methane as a main component is used as the lean premixed gas, the temperature in the combustor after the lean premixed gas is mixed with the high temperature combustion gas and reacted is always It is understood that the combustion can be performed without the generation of unburned components by continuing the combustion while controlling the temperature to be about 900 ° C. or higher.

It is presumed that the value of the temperature T = 900 ° C. varies depending on the type of the combustion device and the type of the main component of the fuel used as the lean premixed gas. Therefore, in the operation using an actual machine, after the lean premixed gas in the combustor before and after the start of the discharge of unburned components from the combustor outlet of the combustor is completely mixed and reacted with the high temperature combustion gas, Temperature is measured in advance, and in actual operation, the lean premixed gas is diluted with the high temperature combustion gas so that the temperature in the combustor after mixing and reacting with the high temperature combustion gas is always above the measured temperature. It is desirable to mix and react the premixed gas.

At this time, due to external factors such as the type of combustion chamber of the combustor or the supply form of the secondary lean premixed gas,
It is expected that the temperature distribution in the combustor after mixing the hot combustion gas and the lean premixed gas will produce a distribution characteristic of the equipment. Therefore, in actual operation, the temperature of the lean premixed gas after mixing and reaction with the high temperature combustion gas, preferably at a plurality of points in the same cross section across the flow of the combustion gas in the combustor is measured, and the lowest temperature among them is measured. It is also a very desirable mode to mix the lean premixed gas with the high-temperature combustion gas and to react them so that the above temperature is always above the measured temperature.

[0031]

According to the present invention, a premixed gas which has been considered to be incombustible in the past, that is, an extremely lean premixed gas which theoretically cannot burn by itself (for example, in the case of methane, the preheating temperature is At 25 ° C., it is possible to completely burn a premixed gas having an air ratio of 2 or more. As a result, low NO _x that enables combustion with a very high air ratio in total
A combustor can also be realized.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an example of a multi-stage lean premixed combustion device.

FIG. 2 is a graph showing the results of a combustion test.

FIG. 3 is a graph showing the results of a combustion test.

FIG. 4 is a graph showing the results of a combustion test.

FIG. 5 is a graph showing the results of a combustion test.

FIG. 6 is a graph showing the results of a combustion test.

FIG. 7 is a graph showing the results of a combustion test.

[Explanation of symbols]

Q ₁ … Primary premixed gas, Q ₂ … Secondary lean premixed gas, 1
0 ... Primary swirl flow burner, 20 ... Combustion chamber, 21 ... Primary combustion chamber, 22 ... Secondary combustion chamber

Claims (4)

[Claims] 1. A multi-stage lean premixed combustion method in which a high temperature combustion gas generated by combustion in a first stage is mixed with a lean premixed gas outside a flammability limit to react, and the combustor outlet is provided in advance for the combustor. The temperature after the lean premixed gas in the combustor is mixed and reacted with the high temperature combustion gas before and after the start of the discharge of unburned components from the A multi-stage lean premixed combustion method, characterized in that a lean premixed gas is mixed with a high temperature combustion gas and reacted so that the temperature in the combustor after mixing and reacting with is always above the measurement temperature. 2. A multi-stage lean premixed combustion method in which a high temperature combustion gas produced by combustion in a first stage is mixed with a lean premixed gas outside a flammability limit to react, and the combustor outlet is provided in advance for the combustor. The temperature after the lean premixed gas in the combustor is mixed and reacted with the high temperature combustion gas before and after the start of the discharge of unburned components from the After mixing and reacting with, measure the temperature at multiple points in the same cross section in the combustor, and mix the lean premixed gas with the high temperature combustion gas so that the lowest temperature among them is always above the measured temperature. A multistage lean premixed combustion method characterized by reacting. 3. In a multi-stage lean premixed combustion method in which a high temperature combustion gas produced by combustion in the preceding stage is mixed with a lean premixed gas outside a flammability limit and reacted, methane is the main component as the lean premixed gas. Using the fuel, the lean premixed gas is mixed and reacted with the high temperature combustion gas so that the temperature in the combustor after the lean premixed gas is mixed with the high temperature combustion gas and reacted is always around 900 ° C. or higher. A multi-stage lean premixed combustion method characterized by the above. 4. In a multi-stage lean premixed combustion method in which a high temperature combustion gas generated by combustion in a first stage is mixed with a lean premixed gas outside a flammability limit to react with each other, methane is a main component of the lean premixed gas. Measure the temperature at multiple points in the same cross section in the combustor after using the fuel and reacting the lean premixed gas with the high temperature combustion gas, and make sure that the minimum temperature is always around 900 ° C or higher. In addition, a multistage lean premixed combustion method is characterized in that a high temperature combustion gas is mixed with a lean premixed gas and reacted.