JP4360273B2 - Catalytic combustor - Google Patents

Description

  The present invention relates to a catalytic combustor in which fuel is premixed with air to produce a premixed gas, which is burned by a catalyst at a downstream catalyst support.

In recent years, gas turbine engines have strict environmental standards regarding exhaust gas composition, and in particular, reduction of NOx (nitrogen oxide) emissions is desired. As a means for reducing NOx, a method of reducing the combustion flame temperature by injecting water or steam into the combustion chamber is generally adopted. However, in this method, the engine thermal efficiency is lowered, the turbine due to poor water quality, etc. There have been various drawbacks such as a decrease in engine life due to corrosion, and a rise in equipment and maintenance costs required for pretreatment for improving water quality. Further, as a method for reducing NOx without using such steam, it is well known that pre-evaporation and diluted pre-mixed combustion methods are effective. However, this method has a limit in reducing NOx and meets the regulation value of ₂ to 5 ppm (0 ₂ = 15% conversion value, for example, 2.5 ppm in Northern California) applied in a specific region of North America. It is necessary to use an exhaust gas denitration device together.

As a method for realizing low NOx of 2 to 5 ppm without using an exhaust gas denitration device, there is a method in which a preheated air-fuel mixture is burned with a catalyst as disclosed in Patent Document 1.

Japanese Patent No. 3364492

Hereinafter, the combustion catalyst will be described. FIG. 4 is a drawing of the partial oxidation catalyst supporting portion disclosed in Patent Document 1. FIG. 4 (A) is a cross-sectional view of the partial oxidation catalyst supporting portion cut at right angles to the flow direction, and FIG. FIG. 5 is a development view of FIG. As shown in FIG. 4 (A), the partial oxidation catalyst supporting part a has a honeycomb structure in which a thin metal flat plate b and corrugated plate c are attached and spirally wound to form a cylindrical shape. Is heat resistant stainless steel.

As described above, a plurality of substantially triangular flow paths are formed by the flat plate b and the corrugated plate c in the partial oxidation catalyst supporting portion a. However, as shown in FIG. 4B, the catalyst coating layer d is formed on the wall surface. The catalyst-coated flow path e having and the catalyst-free flow path f having no catalyst coating layer on the wall surface are alternately arranged adjacent to each other. As the catalyst, palladium or the like is usually used.

FIG. 5 is a cross-sectional view of the partial oxidation catalyst supporting portion cut in parallel to the flow direction, and is an explanatory view of the operation in the partial oxidation catalyst supporting portion a. FIG. 6 is a graph showing temperature changes in the combustor.

Catalytic combustion means that when a premixed gas in which fuel and air are premixed is passed through an elongated channel having a catalyst coating layer on the peripheral wall, the premixed gas reacts by the action of the catalyst and combustion is performed. Catalytic combustion is characterized by low NOx generation because the combustion temperature can be lowered. The inlet temperature of the partial oxidation catalyst supporting part a needs to be about 500 ° C. in order to stably ignite even with a lean fuel concentration. Further, if the catalyst temperature exceeds 1000 ° C., the catalyst is denatured or the metal wall is melted, so the outlet temperature needs to be kept at 1000 ° C. or lower. FIG. 6 is a graph of temperature calculated for the case where a catalytic combustor is used in a gas turbine for power generation of about 2000 KW. In this case, the outlet temperature of the compressor that compresses air to about 1.2 MPa is 385 ° C., which is too low for catalytic combustion, so the temperature is raised to 500 ° C. by a preburner (ignition burner). The premixed gas flows into the partial oxidation catalyst support part a at that temperature.

Next, the reaction and flow in the partial oxidation catalyst supporting part a will be described with reference to FIG. The premixed gas g heated to 500 ° C. flows into the partial oxidation catalyst supporting part a. The partial oxidation catalyst supporting portion a has a honeycomb structure partitioned by a wall i (a flat plate b or a corrugated plate c in FIG. 4), and has a catalyst coating layer d on one surface of the wall i as described above. The other surface is a bare surface that does not have a catalyst coating layer. Thus, the catalyst coating flow path e whose wall surface is the catalyst coating layer d and the catalyst-free flow path f whose wall surface is a bare surface are alternately arranged adjacent to each other. Metal or ceramic is used for the wall.

  The premixed gas g that has flowed into the catalyst coating flow path e in the partial oxidation catalyst support part a undergoes catalytic combustion by the action of the catalyst, and becomes a combustion gas h and flows out from the partial oxidation catalyst support part a. On the other hand, the premixed gas g flowing into the catalyst-free flow path f does not burn but flows out from the partial oxidation catalyst support part a.

  The gas flowing in the flow path is heated by heat generated by catalytic combustion in the catalyst coating flow path e, but part of the generated heat is expected to flow in the adjacent catalyst-free flow path f through the wall i. The mixed gas g is heated, and the temperature of the premixed gas g that does not burn is also raised. Therefore, both the combustion gas h and the premixed gas g are in a high temperature state at the outlet of the partial oxidation catalyst supporting portion a.

  There is an ignition delay downstream of the partial oxidation catalyst carrier a in accordance with conditions such as pressure, temperature, and fuel concentration, and the unburned premixed gas g is combusted by a gas phase reaction after the ignition delay.

  Returning again to FIG. As shown in the figure, the average temperature at the outlet of the partial oxidation catalyst supporting part a is 950 ° C., and the temperature is kept as it is during the vapor phase ignition delay, and the temperature is raised to 1350 ° C. by combustion by the gas phase reaction. . In this example, since there is a scroll portion (not shown) between the combustor outlet and the turbine inlet, the temperature is lowered by 200 ° C., and the temperature (TIT) at the turbine inlet is 1150 ° C.

  In this way, in the partial oxidation catalyst supporting part a, the catalyst coating flow path e and the catalyst-free flow path f are alternately arranged to exchange heat with each other through the wall i. The temperature of the catalyst coating layer d can be maintained at 1000 ° C. or lower at which the catalyst does not deteriorate, and the temperature of the premixed gas g flowing through the catalyst-free flow path f can be set to a high temperature at which gas phase reaction is likely to occur. Furthermore, since the premixed gas g passing through the catalyst-free flow path f is combusted by a gas phase reaction downstream of the partial oxidation catalyst support part a to increase the temperature of the entire gas, the thermal efficiency of the turbine can be maintained high.

  Combustion in the partial oxidation catalyst supporting part a is performed at a low temperature, so that the generation of NOx is small, and combustion by a gas phase reaction performed on the downstream side of the partial oxidation catalyst supporting part a is high temperature combustion, but premixed gas Since g is burned in a state where the fuel is lean when mixed with the combustion gas h, generation of NOx is small.

  The ignition performance of the premixed fuel gas in the partial oxidation catalyst support a is affected by the inlet temperature, pressure, gas type, flow rate, and the like. In the city gas containing methane as a main component, the ignition temperature at normal pressure is 350 to 400 ° C., but the temperature rises as the pressure rises, and when it exceeds 1 MPa, it becomes 400 ° C. or higher. Moreover, the ignition temperature tends to decrease as the fuel concentration increases.

  In a gas turbine combustor, the fuel concentration of the premixed fuel gas that flows in at low load or idling is reduced, making it difficult to ignite. In such a case, in order to ignite stably, as described above, It is necessary to raise the temperature of the premixed fuel gas flowing into the partial oxidation catalyst carrier by a preburner (ignition burner) to about 500 ° C. However, the use of a preburner leads to NOx emissions. Further, in order to make the preburner have a low NOx specification, it is necessary to prepare two or more fuel systems for diffusion combustion and premixed combustion using only the preburner.

  The present invention was devised in view of such problems of the prior art, and paying attention to the fact that a preburner can use a high concentration premixed fuel gas regardless of the load of the gas turbine, and adopting catalytic combustion in the preburner. An object of the present invention is to provide a catalytic combustor that can achieve low NOx.

  Patent Document 2 discloses a catalytic combustor that uses a fuel-rich air-fuel mixture. However, the technique disclosed in Patent Document 2 relates to (1) the main burner, not the pre-burner, and (2) the fuel concentration of the premixed fuel gas is not less than the stoichiometric ratio but exceeds the stoichiometric ratio. This is different from the present invention in that it is a concentration, and (3) the gas passing through the catalyst-free flow path of the catalyst support portion is not premixed fuel gas but air. In catalytic combustion, the calorific value is greatest when the fuel concentration of the premixed fuel gas is close to the stoichiometric ratio, but the catalytic combustor disclosed in Patent Document 2 operates at a concentration exceeding the stoichiometric ratio. When starting, the fuel concentration passes through a state close to the stoichiometric ratio. At this time, the combustion catalyst may change in quality or the metal wall may melt.

Special table 2003-528283

  In order to achieve the above object, a catalyst combustor according to the present invention is a catalyst having an ignition catalyst burner that is provided in an air inlet passage of the catalyst combustor and raises the air flowing into the main catalyst carrier to the catalyst ignition temperature. The combustor, the ignition catalyst burner having a partial oxidation catalyst support, and the fuel concentration of the premixed gas flowing into the partial oxidation catalyst support is less than the stoichiometric ratio, and the partial oxidation catalyst support The temperature is higher than the concentration that can be ignited under the temperature and pressure conditions of the air flowing into the section.

  You may provide a mixer and a whole quantity oxidation catalyst support part in the downstream of the said partial oxidation catalyst support part.

  Next, the operation of the present invention will be described. The catalyst burner for ignition of the catalytic combustor of the present invention has a partial oxidation catalyst support. As described above with reference to FIGS. 4 and 5, the partial oxidation catalyst supporting portion is alternately adjacent to the catalyst coating flow path whose wall surface is a catalyst coating layer and the non-catalyst flow path whose wall surface is a bare surface. A structure that is arranged together. The fuel concentration of the premixed gas flowing into the partial oxidation catalyst supporting portion is less than the stoichiometric ratio, and is maintained at a level that can be ignited under the temperature and pressure conditions of the air flowing into the partial oxidation catalyst supporting portion. Therefore, it is possible to stably ignite, generate heat in the partial oxidation catalyst support, and raise the air flowing into the main partial oxidation catalyst support to the catalyst ignition temperature (for example, 500 ° C.). The temperature of the air flowing into the partial oxidation catalyst supporting part of the ignition catalyst burner and the fuel concentration that can be ignited under pressure conditions can be determined by experiment. For example, the air pressure is 1.2 MPa, the temperature Was 385 ° C. and the equivalence ratio was 0.3 to 0.5, ignition was possible. The equivalent ratio is the ratio of the actual fuel / air ratio to the stoichiometric fuel / air ratio.

  Since gas phase combustion does not occur downstream of the partial oxidation catalyst supporting portion of the ignition catalyst burner, unburned fuel is mixed in the gas. Therefore, a mixer and a whole amount oxidation catalyst support part are provided downstream of the partial oxidation catalyst support part to oxidize unburned fuel in the gas. When the entire amount of air heated by the pre-burner flows into the main partial oxidation catalyst carrier, unburned fuel in the air is oxidized by combustion by the main partial oxidation catalyst carrier and the subsequent gas phase reaction. Therefore, the mixer on the downstream side and the total amount oxidation catalyst supporting portion may be omitted, but are necessary when there is a case where the bypass is sometimes used.

  As described above, the catalytic combustor of the present invention uses a catalytic burner as a pre-burner. Therefore, unlike the conventional pre-burner, there is no need to use a diffusion combustion or lean premixed combustion type burner, and there is one fuel system. Moreover, ultra-low NOx can be realized.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a sectional view of an ignition catalyst burner of the catalytic combustor of the present invention, and FIG. 2 is a sectional view of the catalytic combustor of the present invention. The catalytic combustor 1 has an outer cylinder 2 and an inner cylinder 4, and a passage (air inlet passage) 3 for compressed air 20 is formed between the outer cylinder 2 and the inner cylinder 4. One end of the outer cylinder 2 is sealed with a mirror plate 2a. A fuel injection pipe 5 is provided on the upstream side of the inner cylinder 4, and fuel 22 is injected into the inner cylinder 4. A mixer 6 is provided downstream thereof, and a main partial oxidation catalyst carrier 7 is further provided downstream thereof. The partial oxidation catalyst carrier 7 has the same structure as the partial oxidation catalyst carrier a described above with reference to FIGS. The partial oxidation catalyst support 7 is divided into two stages, an upstream side 7a and a downstream side 7b. Reference numeral 8 denotes a flame generated on the downstream side of the main partial oxidation catalyst supporting portion 7, which is slightly separated from the downstream end of the partial oxidation catalyst supporting portion 7 due to ignition delay. Reference numeral 4 a denotes a stop at the downstream end of the inner cylinder 4.

  An ignition catalyst burner 9 is provided in the air inlet passage 3 and raises the compressed air 20 flowing into the main partial oxidation catalyst support 7 to the catalyst ignition temperature. The ignition catalyst burner 9 has an outer casing 10 and an inner casing 12, and a bypass passage 21 for compressed air 20 is formed between the outer casing 10 and the inner casing 12. The upstream side of the inner casing 12 is a diameter-enlarged portion 12a whose diameter increases toward the downstream, where the flow rate of the compressed air 20 is reduced. A fuel injection pipe 11 is provided on the downstream side of the enlarged diameter portion 12 a and injects fuel 22 into the inner casing 12. A mixer 13 is provided downstream thereof, and a partial oxidation catalyst carrier 14 is further provided downstream thereof. The partial oxidation catalyst carrier 14 has the same structure as the partial oxidation catalyst carrier a described above with reference to FIGS.

  A throttle 15 is provided downstream of the inner casing 12. The throttle 15 is for improving the mixing of the gas 23 exiting the partial oxidation catalyst support 14 and the compressed air 20 passing through the bypass passage 21 and suppressing combustion due to the gas phase reaction. Reference numeral 16 denotes a mixer provided downstream of the diaphragm 15. Reference numeral 17 denotes a total amount oxidation catalyst support. The total amount oxidation catalyst supporting part 17 is such that all the flow paths in the partial oxidation catalyst supporting part a described with reference to FIGS. 4 and 5 are the catalyst coating flow paths e.

  Next, the operation of this embodiment will be described. In this example, the pressure of the compressed air 20 compressed by a compressor (not shown) and flowing into the air inlet passage 3 of the catalytic combustor 1 is 1.2 MPa, and the temperature is 385 ° C. A part of the compressed air 20 flows into the ignition catalyst burner 9, and the remaining part is bypassed. Part of the compressed air 20 that has flowed into the ignition catalyst burner 9 flows into the inner casing 12, and the remaining part flows through the bypass passage 21. The compressed air 20 that has flowed into the inner casing 12 is decelerated at the enlarged diameter portion 12a in order to improve ignition at the downstream partial oxidation catalyst support portion 14.

  The fuel 22 is injected into the inner casing 12 from the fuel injection pipe 11 on the downstream side of the enlarged diameter portion 12a. The injection amount of the fuel 22 is set so that the fuel concentration of the premixed gas 24 after the mixer 13 is equal to or higher than the concentration that can be ignited by the partial oxidation catalyst support unit 14. The lower limit of the ignitable fuel concentration can be determined by experiment. FIG. 3 is a graph showing the results of such an experiment. The horizontal axis represents the catalyst inlet gas temperature (° C.), and the vertical axis represents the catalyst outlet gas temperature (° C.). In this graph, a straight line A indicates a state in which the catalyst inlet gas temperature and the catalyst outlet gas temperature are the same, and curves C, D, and E indicate states in which the fuel concentration is sequentially increased. The temperature at which the portions where the curves C, D, and E rise apart from the straight line B are ignited. As can be seen from this figure, the ignition temperature decreases as the fuel concentration increases. According to experiments, if the pressure of compressed air is 1.2 MPa and the temperature is 385 ° C., the fuel concentration can be ignited if the equivalent ratio is 0.3 to 0.5.

  The gas 22 exiting the partial oxidation catalyst carrier 14 and the compressed air 20 passing through the bypass channel 21 are mixed well by the throttle 15 and uncombusted in the gas 23 through the mixer 16 and the total oxidation catalyst carrier 17. The fuel is oxidized and flows out from the ignition catalyst burner 9. Here, the ignition catalyst burner 9 is mixed with the compressed air 20 bypassed, and the temperature of the compressed air 20 flowing into the inner cylinder 4 is increased to 500 ° C. Fuel is further blown into the inner cylinder 4 and flows into the main partial oxidation catalyst support 7 through the mixer 6. The partial oxidation catalyst supporting portion 7 is divided into two stages, an upstream side 7a and a downstream side 7b. 1/2 is oxidized on the upstream side 7a, and the rest is further oxidized on the downstream side 7b, so that the whole is oxidized. 3/4 is oxidized. The gas that exits the main catalyst carrier 7 is completely ignited by a gas phase reaction after an ignition delay and generates a flame 8.

As described above, since the catalytic combustor 1 of the present invention uses the ignition catalyst burner as the preburner, there is no need to use a diffusion burner or lean premixed combustion type burner unlike the conventional preburner. Also, one system is sufficient, and ultra-low NOx can be realized.

The present invention is not limited to the embodiments described above, and various modifications can be made without departing from the scope of the invention. For example, the structure of the main catalytic combustion in the inner cylinder 4 is not limited to that shown in FIG.

It is sectional drawing of the catalyst burner for ignition of the catalytic combustor of this invention. It is sectional drawing of the catalytic combustor of this invention. It is a graph which shows the experimental result of the relationship between a fuel concentration and ignition temperature. (A) is sectional drawing which cut | disconnected the partial oxidation catalyst support part at right angles with respect to the flow direction, FIG.4 (B) is a development view of FIG.4 (A). It is sectional drawing which cut | disconnected the partial oxidation catalyst support part in parallel with the flow direction. It is the graph of the temperature calculated about the case where a catalytic combustor is used for the gas turbine for about 2000KW electric power generation.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Catalytic combustor 3 Air inlet flow path 7 Main partial oxidation catalyst carrying part 9 Ignition catalyst burner 13 Mixer 14 Partial oxidation catalyst carrying part 17 Total oxidation catalyst carrying part 20 Air 24 Premixed gas

Claims (2)

The main partial oxidation in the inner cylinder provided in the annular air inlet channel between the outer cylinder and the inner cylinder of the catalyst combustor having the outer cylinder and the inner cylinder provided concentrically with the outer cylinder. A catalytic combustor having a cylindrical ignition catalyst burner that raises the air flowing into the catalyst carrier to the catalyst ignition temperature, the ignition catalyst burner comprising: an inner cylinder provided concentrically with the outer cylinder and the outer cylinder; And having a partial oxidation catalyst supporting portion in the inner cylinder, the fuel concentration of the premixed gas flowing into the partial oxidation catalyst supporting portion is less than the stoichiometric ratio, and the partial oxidation catalyst supporting portion A catalytic combustor characterized in that it is kept at a concentration that can be ignited under the temperature and pressure conditions of the air flowing into it. The catalytic combustor according to claim 1, wherein a mixer and a total amount of oxidation catalyst support are provided downstream of the partial oxidation catalyst support of the ignition catalyst burner.

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