JPH0245772B2 - - Google Patents

Description

Detailed Description of the Invention [Technical Field of the Invention] The present invention relates to a fuel-air combustion method in a gas turbine combustor used in a gas turbine power generation system, and more particularly, to a method for burning fuel-air in a gas turbine combustor used in a gas turbine power generation system. , NOx) generation is small, and
This invention relates to a long-life catalytic combustion method with good combustion efficiency.

[Technical background of the invention and its problems]

In recent years, with the depletion of petroleum resources and the like, various alternative energies have been required, and at the same time, efficient use of energy resources has also been required. Examples of systems that meet these demands include gas turbine/steam turbine combined cycle power generation systems that use natural gas as fuel, or coal gasification gas turbine/steam turbine combined cycle power generation systems. These power generation systems have higher power generation efficiency than conventional steam turbine power generation systems that use fossil fuels, so they can use fuels such as natural gas and coal gasified gas, whose usage is expected to increase in the future. It is expected to be a power generation system that can effectively convert into electricity.

Gas turbine combustors used in gas turbine power generation systems have conventionally adopted a homogeneous combustion method in which a mixture of fuel and air is ignited by a spark plug or the like. A conceptual cross-sectional view of one example of such a combustor is shown in FIG. In the combustor shown in FIG. 1, fuel injected from a combustion nozzle 1 is mixed with combustion air 3, and then ignited by a spark plug 2 and combusted. burned gas,
That is, cooling air 4 and dilution air 5 are added to the combustion gas, and after the combustion gas is cooled and diluted to a predetermined gas turbine inlet temperature, it is injected from the turbine nozzle 6 into the gas turbine. In the figure, 8 is a swirler.

One of the biggest problems with the exemplified conventional combustor is that a large amount of _NOx is produced during combustion, causing environmental pollution. The reason why this NO _x is generated is that during combustion, there is a high temperature area in the combustor that exceeds 1500°C.

In order to solve these problems, various combustion methods have been studied, and recently, a heterogeneous combustion method using a solid phase catalyst (hereinafter referred to as a catalytic combustion method) has been proposed.

This catalytic combustion method is a method in which a mixture of fuel and air is combusted using a catalyst. According to this method, combustion can be started at a relatively low temperature,
Furthermore, compared to the homogeneous combustion method shown in Figure 1, it is possible to mix a large amount of air with the fuel and combust it, resulting in a lower maximum temperature of combustion and little or no air for cooling and dilution. Not needed at all. Therefore, it becomes possible to extremely reduce the amount of NO _x generated.

FIG. 2 is a conceptual sectional view of an example of a combustor using the above-mentioned catalytic combustion method, and the numbers in the figure represent the same elements as in FIG. 1, respectively. A structural feature of this combustor is that it is equipped with a catalyst section 7.
This catalyst section 7 is normally filled with a catalyst having a honeycomb structure. The mixture of fuel and air is transferred to the catalyst section 7.
In order to preheat to the degree necessary for the reaction with the catalyst, in the case of this figure, the mixture consisting of the fuel injected from the fuel nozzle 1 and the combustion air 3 is ignited by the spark plug 2 and combusted to heat the catalyst. It is used as a preheat source to accelerate the reaction with Then, the fuel injected from the fuel nozzle 1' and the combustion air 3 are added to form a heated mixture, which then flows into the catalyst and is combusted.

FIG. 3 shows an example of the temperature rise of the mixture and catalyst in a combustor using the catalytic combustion method in relation to the flow direction of the mixture.

In the figure, the solid line shows the temperature change of the mixture,
The dotted line shows how the temperature of the catalyst changes. The solid line AB indicates the temperature in the region where fuel and air are mixed to form a mixture. The mixture then comes into contact with the catalyst and is combusted by a catalytic reaction. The dotted line B′C′ shows how the temperature of the catalyst increases due to the catalytic reaction, and the temperature of the mixture flowing through the catalyst increases due to heating from there. Each is represented by a solid line BC.
Then, when the temperature of the mixture reaches the ignition temperature, combustion occurs within the catalyst due to a gas phase reaction in addition to combustion due to a catalytic reaction. Here, the state in which most or all of the mixture burns and the temperature rises is represented by a solid line CD, and the rise in temperature of the catalyst at this time is represented by a dotted line C'D'. After this, the effluent flowing out from the catalyst burns a small amount of unburned fuel by a gas phase reaction, and the temperature further increases as shown by the solid line DE, and becomes combustion gas.

In the combustion method described above, the temperature of the catalyst in the region B' ~ C' ~ D' is 815 ~ 1650 ° C.
This is disclosed in Japanese Patent Application Laid-Open No. 48-20766. Also,
JP-A-50-31210 describes combustion at temperatures where the operating temperature of the catalyst is substantially higher than the instantaneous auto-ignition temperature of the fuel-air mixture.

However, the problem with the above method is that the temperature of the catalyst in the area indicated by the dotted line C'D' where combustion by gas phase reaction is also occurring becomes considerably high. That is, it is necessary that the temperature of the catalyst be higher than the ignition temperature of the mixture in contact with the catalyst.

For example, when using a fuel that is difficult to burn in the gas phase, such as methane gas, the fuel will not burn completely completely unless the catalyst temperature is 1000° C. or higher. Therefore, the catalyst must have a heat resistance of 1000°C or 1100°C or higher.

However, at present, no catalyst has been developed that can withstand such high temperatures and can be used for long periods of time, making it extremely difficult to put the combustion method shown in FIG. 3 into practical use.

[Purpose of the invention]

The present invention aims to solve the problems of conventional catalytic combustion methods and to provide a catalytic combustion method for NO _x that is significantly more durable and stable.

[Summary of the invention]

The present inventors believe that the conditions for gas-phase combustion to occur in the effluent from the catalyst are that the temperature of the effluent is sufficiently high and the fuel concentration of the effluent is high; In the catalytic combustion method,
We focused on the fact that only the following conditions were satisfied: combustion by catalytic reaction and combustion by gas phase reaction occur simultaneously within the catalyst to increase the temperature of the effluent. Therefore, the inventors of the present invention changed the viewpoint from the conventional combustion method to increase the fuel concentration by adding more fuel to the effluent flowing out from the catalyst. We came up with the idea that combustion by gas phase reaction is possible even at low temperatures, and therefore complete combustion with low NO _x is possible without thermal deterioration of the catalyst due to high temperatures, and based on this idea we conducted intensive research. As a result of stacking,
The present invention has now been completed.

That is, the catalytic combustion method of the present invention includes a first step of mixing fuel and air, a mixture obtained in the first step, and a catalyst filled in a catalytic section, and the temperature of the catalyst is adjusted to ignite the mixture. a second step in which the mixture is combusted solely by catalytic reaction while being kept in contact with the mixture at a temperature lower than that of the catalytic converter; Add auxiliary fuel consisting of:
The present invention is characterized by comprising a third step of combusting the composite gas by a gas phase reaction. Further, in the above step, an oxidizing gas such as concentrated oxygen may be used as air, or nitrogen or other essentially inert gas may be used for further dilution.

FIG. 4 shows an example of the temperature rise of the mixture and catalyst in the combustor using the combustion method according to the present invention in relation to the flow direction of the mixture.

Similarly to FIG. 3, in FIG. 4, the solid line shows how the temperature of the mixture changes, and the dotted line shows how the temperature changes of the catalyst. A solid line ab indicates the temperature of the region where fuel and air are mixed, that is, the region where the first step proceeds. Next, the mixture created by the mixing comes into contact with the catalyst and burns due to the catalytic reaction.The dotted line b'c' shows how the catalyst temperature rises due to the catalytic reaction, and the mixture flowing through the catalyst due to heating from there. The rise in temperature is shown by the solid line bc.

In this region, only combustion occurs due to catalytic reactions, and no combustion occurs due to gas phase reactions. The combustion that takes place with the catalyst ends here, and this is one of the important features essential to the present invention. For example, in the second combustion step, approximately 30% of the fuel that has entered the catalyst is combusted by the catalytic reaction, and flows out of the catalyst along with the remaining 70% of unburned fuel to form an effluent. This is c
and c′. Supplementary fuel is then added to the effluent to form a composite gas which is combusted by a gas phase reaction downstream of the catalyst. The temperature rise at this time is shown by the solid line CD. This corresponds to the third step.

To explain specifically using the schematic diagram shown in FIG. 5, air 13 whose pressure and temperature have been raised by a compressor etc. and fuel 11 supplied by a fuel nozzle etc. are mixed to form a mixture. The mixture is fed to the catalyst. Here, fuel is combusted only by catalytic reaction, and the temperature of the catalyst reaches a maximum of approximately 900°C.
Increase the temperature to a certain level. At this temperature, flame-retardant fuel such as methane gas does not undergo gas phase combustion within the catalyst. A supplementary fuel is then supplied to the effluent from the catalyst to produce a composite gas. In FIG. 5, the supplementary fuel is heated by passing the supplementary fuel 19 made of fuel and steam through the fuel supply pipe 21 that has passed through the catalyst, as shown in the figure.
Combustion in the process is becoming more likely to occur. Further, the composite gas is mixed and homogenized by the flow expanding portion 15, and is then easily combusted in a gas phase by using an igniter stick 17 or the like as an ignition source or by spontaneous ignition. At this time, the temperature of the catalyst needs to be lower than the ignition temperature of the mixture. If this temperature is higher than the ignition temperature, in addition to the combustion due to the catalytic reaction described above, combustion due to a gas phase reaction will also occur in the catalyst. Heat deterioration progresses. Normally, the temperature of the catalyst is preferably in the range of 300 to 900°C, although it depends on the type of fuel. The temperature of such a catalyst can be determined by appropriately selecting the type of catalyst used, the shape of the catalyst, the flow rate of the mixture, the fuel concentration, etc.

As an example, a preferable example of the catalyst is a honeycomb-shaped catalyst containing palladium oxide as a main component. This will be explained in detail below. The present inventor has revealed that the activity of palladium as a catalyst is mainly due to palladium oxide. Palladium has an equilibrium relationship as shown in the following equation.

PdOPd + 1/2O ₂ This equilibrium is controlled by temperature and oxygen partial pressure, and the higher the temperature and the lower the oxygen concentration, the more the reaction of PdO → Pd + 1/2O ₂ progresses, and the amount of PdO decreases. catalytic activity decreases. Therefore, if a catalyst containing palladium oxide as a main component is used, the temperature of the catalyst will not exceed a certain level. This temperature is considered to be about 900°C under the conditions of a gas turbine combustor, for example. This makes it difficult for the temperature of the catalyst to rise more than necessary, which is preferable since there is less deterioration of the catalyst due to heat. In addition, depending on the type of fuel, catalysts containing palladium oxide as a main component can initiate a catalytic reaction even at the temperature of combustion air heated by a compressor, etc., so there is no need to preheat the mixture and pre-combustion It is also possible to omit such heating depending on the case.

Then, in the third step, a predetermined amount of auxiliary fuel is further added to the effluent flowing out from the catalyst and heated to a predetermined temperature, and combustion is caused by a gas phase reaction.
It is necessary to control the adiabatic flame temperature at this time to a temperature of 1500° C. or less, which is substantially lower than the NO _x generation temperature. If the temperature exceeds 1500°C, a large amount of NO _x will be generated and the object of the present invention will not be achieved. This control can be easily achieved by appropriately selecting the amount of fuel, the flow rate of the effluent or composite gas, the amount and method of injection of the additional auxiliary fuel, the combustor structure, etc.

Furthermore, if a region where the flow of the effluent or composite gas is retarded or reversed is provided at the location where the third step is carried out, such as the region 15 where the flow expands in FIG. This is advantageous because combustion proceeds easily. Furthermore, if an ignition source such as the igniter stick 17 shown in FIG. 5 described above is installed, it is effective because it facilitates the initiation of gas phase combustion of the composite gas.

[Embodiments of the invention]

Example 1 A simulated combustor shown schematically in FIG. 6 was manufactured, and a honeycomb-shaped catalyst 10 mainly made of palladium oxide was provided in the combustion tube 9. The diameter of the catalyst is
The length is 30mm and the length is 9cm. Fuel 11 and air 13 are injected into the combustion pipe 9 from their respective systems and mixed,
The mixture flowed into catalyst 10. A supplementary fuel 19 consisting of fuel 12 and steam 22 was added to the effluent from the catalyst 10, and the combustion gas 14 was sampled to measure the gas composition. In addition, air 13 is 400℃
Then, steam 22 was preheated to 750°C. air 13
Flow rate of 450/min, flow rate of fuel 11 9/min,
Fuel 12 flow rate 4/min, steam 5g/min
It was hot. Natural gas was used as fuel.

For comparison, the same device as above, catalyst diameter 30 mm, length 17 cm, fuel 11 flow rate 13/min,
Flow rate of air 13 450/min and auxiliary fuel 19
A conventional catalytic combustion method was used without adding .
The preheating temperature of the air was 500°C.

Changes in combustion efficiency, catalyst temperature, and catalyst pressure loss over time in both cases were measured and are shown in Figure 7. In FIG. 7, ' is the combustion efficiency of the present invention and the conventional example, , ' is the catalyst temperature of the present invention and the conventional example, respectively, and ' is the pressure loss of the catalyst of the present invention and the conventional example, respectively. As is clear from the figure, according to the combustion method according to the present invention, there is almost no deterioration in long-term combustion efficiency, and the catalyst temperature is maintained at a lower temperature than in the conventional method, thus extending the life of the catalyst. Since the length of the catalyst can be significantly extended and the length of the catalyst can be shortened, pressure loss can be reduced, contributing to improved performance of the combustor.

In addition, the amount of NO _x generated during combustion is 2 to 2 in the conventional example.
In the present invention, it was 1 ppm or less. In addition, in the embodiment of the present invention, an experiment was conducted in which only fuel was added without adding steam from the fuel supply pipe 21, and other conditions remained unchanged _.
The amount generated was 2 to 3 ppm. These experiments confirmed that the addition of steam stabilizes combustion and reduces NO _x more than conventional combustion methods using catalysts.

Example 2 A test was conducted to determine the maximum amount of combustion gas that could be obtained using the simulated combustor according to the present invention shown in FIG. Fuel 11, 92/min and air preheated to 420°C, 13, 4.8 m ³ /min are mixed in the first step, and in the second step, a honeycomb with a diameter of 100 mm and a length of 9 cm containing palladium oxide as the main component is mixed. shaped catalyst 10
supplied to. Furthermore, in the third step, supplementary fuel consisting of fuel and steam was added little by little through the fuel supply pipe 21 that had passed through the catalyst to raise the temperature of the combustion gas. The amount of steam added at this time ranged from 5 to 50 g/min. Natural gas was used as fuel.

Furthermore, as a comparative example, a test was conducted using a conventional simulated combustor shown in FIG. Mainly made of palladium oxide, diameter 100mm, length 9cm
A honeycomb-shaped catalyst is first filled in the upstream side of the catalyst section 7 that comes into contact with the mixture, and then
A honeycomb-shaped catalyst with a diameter of 100 mm and a length of 9 cm, mainly composed of platinum, is filled in the rear stage side, and the fuel 11
as natural gas, and air preheated to 500°C13,
4.8m ³ /min was supplied. Here, the temperature of the combustion gas was increased by gradually increasing the amount of fuel 11.

As a result of the experiment, in the case of the present invention, it was possible to raise the temperature of the combustion gas to a maximum of 1450℃, but in the case of the conventional example, the catalyst melted and was damaged when the combustion gas reached 1300℃. .

Example 3 A simulated combustor as shown in FIG. 9 was manufactured having a honeycomb-shaped catalyst mainly made of palladium oxide and having a diameter of 100 mm and a length of 10 cm. In this combustor, a region 15 is provided downstream of the catalyst 10 in which the flow of the composite gas expands. This part 1
5 is a reverse region or slow zone of the composite gas flow. An igniter stick 17 is installed at the portion 15 to constitute an ignition source. Prior to the experiment, the catalyst was heated in an electric furnace at 800°C for 5000 hours before use. Flow rate of fuel 11 100/min, fuel 40/min and steam 40 preheated to 750℃
The flow rate of air 13 preheated to 350°C is 4.8 m ³ /min, and the auxiliary fuel 19
was dispersed and added from three locations. Natural gas was used as fuel. After the fuel and air have flowed in, a spark is emitted from the igniter stem 17 to completely burn the composite gas, and then the igniter stem 1
I pulled out 7. Combustion efficiency after 1 hour of ignition is 99.9%
As mentioned above, the amount of NO _x generated was 1 ppm or less. Also, the maximum temperature of the catalyst in the flow direction did not rise above 780°C. This is lower than the temperature forced to heat for 5000 hours in an electric furnace, so even in actual combustion,
It was estimated that it could last for over 500 hours.

〔Effect of the invention〕

As is clear from the above explanation, compared to the conventional method, the catalytic combustion method of the present invention can omit the region where combustion by catalytic reaction and combustion by gas phase reaction occur simultaneously in the conventional method. The length of the catalyst can be shortened, thus reducing pressure losses. There is no region where combustion by catalytic reaction and combustion by gas phase reaction occur simultaneously. In other words, since there is no high-temperature part of the catalyst, thermal deterioration of the catalyst can be eliminated and its durability can be significantly improved.
Since the proportion of combustion due to gas phase reactions is large, it is possible to easily follow fluctuations in the output of turbines, etc. And since the thermal combustion temperature of the effluent can be controlled to be lower than the NO _x generation temperature,
It is possible to reduce the amount of NO _x generated. It has the following advantages and its industrial value is extremely large.

[Brief explanation of the drawing]

FIG. 1 is a conceptual sectional view of a conventional gas turbine combustor, and FIG. 2 is a conceptual sectional view of a conventional catalytic combustion type gas turbine combustor. FIG. 3 is a characteristic diagram showing how the temperature of the catalyst and mixture increases in the conventional catalytic combustion method, and FIG. 4 is a characteristic diagram showing how the temperature of the catalyst and mixture increases in the catalytic combustion method of the present invention. Fig. 5 is a conceptual schematic diagram representing one embodiment of the present invention, Fig. 6 is a conceptual schematic diagram of a combustor used in Example 1 of the present invention, and Fig. 7 is a characteristic diagram representing the results of Example 1. 8 is a conceptual diagram of a combustor used in a comparative example of Example 2, and FIG. 9 is a conceptual diagram of a combustor used in Example 3. 1, 1'...Fuel nozzle, 2...Spark plug, 3...Combustion air, 4...Cooling air, 5...
... Dilution air, 6... Turbine nozzle, 7... Catalyst section, 8... Swirler, 9... Combustion pipe, 10...
Catalyst, 11, 12...Fuel, 13...Air, 14
...Combustion gas, 17...Igniter stick,
19...Auxiliary fuel, 21...Fuel supply pipe, 22
……steam.

Claims (1)

[Claims] 1. A first step of mixing fuel and air, and a step in which the mixture obtained in the first step is placed in a catalyst filled in a catalyst section, and the temperature of the catalyst is lower than the ignition temperature of the mixture. a second step in which the mixture is brought into contact while being maintained at a temperature and the mixture is combusted only by a catalytic reaction;
A third step of further adding auxiliary fuel mainly consisting of fuel and steam to the effluent flowing out from the catalyst after the step of step 1 to form a composite gas, and combusting the composite gas by a gas phase reaction. A catalytic combustion method characterized by: 2. The catalytic combustion method according to claim 1, wherein the temperature of the catalyst is 300 to 900°C. 3. The catalytic combustion method according to claim 1, wherein a portion where the third step is performed is provided with a portion where the flow of the mixed gas is delayed or reversed. 4 Claim 1 characterized in that an ignition source is provided at the location where the third step is performed.
Catalytic combustion method described in section. 5. The catalytic combustion method according to claim 1, characterized in that a catalyst containing palladium oxide as a main component is used. 6. A catalytic combustion method according to claim 1, characterized in that the supplementary fuel added in the third step is added to the effluent through a pipe passing through the catalyst.