JPH0463963B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a low NOx combustor, and particularly to a low NOx combustor suitable for use in a gas turbine power generation system.

[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 can 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, which are currently being studied.
These gas turbine/steam turbine combined cycle power generation systems have higher power generation efficiency than conventional steam turbine power generation systems that use fossil fuels, so natural gas production is expected to increase in the future. It is expected to be a power generation system that can effectively convert fuels such as coal and gasified gas into electricity.

BACKGROUND ART Conventionally, in a gas turbine combustor used in a gas turbine power generation system, a mixture of fuel and air is ignited using a spark plug or the like to perform homogeneous combustion. An example of such a combustor is shown in FIG. In the combustor shown in FIG. 1, fuel injected from a fuel nozzle 1 is mixed with combustion air 3, ignited by a spark plug 2, and combusted. Cooling air 4 and dilution air 5 are added to the burned gas, that is, the combustion gas, and after cooling and diluting it to a predetermined turbine inlet temperature, it is injected into the gas turbine from the turbine nozzle 6. 8 is a swirler.
One of the serious problems with such conventional combustors is that a large amount of NOx gas is generated during fuel combustion, causing environmental pollution.

The reason why the above-mentioned NOx is generated is that when fuel is combusted, there is a part of the combustor that has a high temperature of over 2000°C.

In order to solve these problems with gas turbine combustors, various combustion systems are being studied.

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 uses a catalyst to combust lean fuel that would not burn in a normal combustor, so the combustion temperature is lower.
The temperature will not be high enough to generate NOx. Furthermore, the turbine inlet temperature can also be kept the same as in the conventional case.

FIG. 2 is a conceptual diagram of an example of a combustor used in the catalytic combustion method. Each number in the figure represents the same element as in FIG. A structural feature of this combustor is that it includes a catalyst filling section 7. Catalyst filling section 7
It is usually filled with a honeycomb-structured combustion catalyst, where a mixture of fuel and air is combusted.

This catalytic combustion method also has the following drawbacks. In other words, in the conventional catalytic combustion method, fuel is combusted by both catalytic reaction and gas phase reaction in the catalyst-filled part, so the temperature of the catalyst is high, which causes thermal deterioration of the catalyst and shortens its life. . Furthermore, it is difficult to cope with an increase in the gas turbine inlet temperature due to the heat resistance of the catalyst. Therefore, the present inventors
In the catalyst-filled section, only a portion of the fuel is combusted through catalytic reaction, and additional fuel is added downstream of the catalyst, allowing gas-phase combustion (non-catalytic thermal combustion) to occur in that portion.
We have already proposed a long-life catalytic combustion method that requires lower catalyst temperatures than conventional ones by generating . Furthermore, even in the conventional catalytic combustion system, it is easily presumed that adding fuel downstream of the catalyst is advantageous in increasing the gas turbine inlet temperature. Although it is important to add fuel downstream of the catalyst in this way, a new problem has arisen. First, adding fuel increases NOx production. This is thought to be due to the fact that the fuel burns before it is sufficiently mixed, resulting in localized high temperature areas.

[Purpose of the invention]

The present invention has been made in consideration of the above points, and
NOx when fuel is added downstream of the catalytic combustion section
The purpose is to provide a low NOx combustor that suppresses the generation of NOx.

[Summary of the invention]

The present invention includes: a mixing section that mixes fuel and air to form a fuel mixture; a catalytic combustion section that is provided downstream of the mixing section and combusts the fuel mixture with a catalyst; and a downstream side of the catalytic combustion section. a fuel supply section which is provided in the catalytic combustion section and adds fuel or a mixture mainly composed of fuel to the effluent from the catalytic combustion section; a gas phase combustion section which performs gas phase combustion of the effluent to which fuel has been added by the fuel supply section; A low NOx combustor comprising: a reverse fire prevention mechanism between the fuel supply section and the gas phase combustion section.

In other words, the present inventors have discovered that when fuel is added downstream of the catalytic combustion section, there is a mechanism to prevent reverse fire between the fuel addition section and the gas phase combustion section that performs gas phase combustion, that is, non-catalytic combustion. By installing a mechanism and making the flow velocity of the effluent higher than the fire propagation velocity,
It was discovered that NOx conversion is possible. It is believed that by providing the reverse fire prevention mechanism in this way, the charged fuel and the effluent that has passed through the catalytic combustion section are sufficiently mixed, and uniform gas phase combustion occurs.

This reverse fire prevention mechanism may have any configuration as long as it allows the flow velocity of the effluent to be higher than the fire propagation velocity. There are several possible methods (types).

As for the type, for example, a configuration in which the cross-sectional area of the flow path is made small can be considered. With such a configuration, the flow rate can be increased. Further, as for the type, a configuration can be considered that makes the effluent flow into a laminar flow. For example, by providing a filter with a honeycomb structure, if the cross-sectional area does not change, the flow velocity will not change, but the fire propagation speed will be slower in laminar flow than in turbulent flow. Therefore, the original purpose can be achieved.

One structural example of the combustor of the present invention is shown in FIG. Numbers that are the same as in Figure 2 represent the same elements. In Fig. 3, the area of the part numbered 11 is smaller (reverse fire prevention mechanism). In the combustor shown in FIG. 3, the combustion air 3 and the fuel supplied from the fuel nozzle 9 are mixed (mixing section) and pass through the catalyst filling section 7 (catalytic combustion section). After some or most of the fuel is burned in the catalyst, fuel is added from the fuel nozzle 10 (fuel addition section). The added fuel is ignited as required by the downstream spark plug 2 (gas phase combustion section). The ignited flame propagates upstream of the flow, but does not propagate upstream of the reverse fire prevention mechanism. Therefore,
The distance between the fuel nozzle 10 (fuel supply section) and this section with a small cross-sectional area is set to an appropriate length to mix the fuel sufficiently and prevent local temperature rise to the extent that high concentration NOx is generated. Furthermore, instead of reducing the cross-sectional area of the section 11 in Fig. 3, a honeycomb structure with a cell diameter such that the flowing water in the cells becomes a laminar flow may be installed in that section. It is shown in Figure 4. The cell diameter may be arbitrarily set depending on the fuel type, operating conditions, etc.

Also, in Figure 3, pre-combustion is not performed upstream of the catalyst, but this is based on the assumption that a fuel and catalyst that can act even at low temperatures are used, so if pre-combustion is necessary, If so, it is also possible to provide a pre-combustion section as shown in FIG. Further, the fuel added downstream of the catalyst may be mainly composed of fuel, or may contain steam or other gas.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to obtain a low NOx combustor that generates less NOx even when fuel is added downstream of the catalytic combustion section.

[Embodiments of the invention]

Examples of the present invention will be described below.

Example 1 Figure 5 shows the inner diameter for demonstrating the effect of the present invention.
A simulated combustor with a diameter of 100 mm is shown. From the upstream side of the combustor
A mixture 12 of fuel (natural gas) and air heated to 450° C. was supplied to the catalyst filling section 7 (catalytic combustion section). Fuel (natural gas) is added from the fuel nozzle 10 (fuel supply section) downstream of the catalytic combustion section, passes through a reverse fire prevention mechanism 11 with a reduced cross-sectional area of 60 mmφ in diameter and 100 mm in length, and is then fed into the gas phase combustion section 13. It was burned with. Spark plug 2 was used for ignition. The flow velocity immediately before the catalyst filling section 7 was 20 m/sec. The fuel nozzle 10 had an inner diameter of 5 mmφ, and the nozzle tip also had a hole of 5 mmφ. The experiment was conducted by setting the adiabatic flame temperature of the mixer at the inlet of the catalytic combustion section to 1050° C. and adjusting the final adiabatic flame temperature by changing the fuel flow rate from the fuel nozzle 10. The experiment was conducted by measuring the combustion efficiency and NOx concentration with and without the reverse fire prevention mechanism 11 installed (comparative example).
Gas sampling was performed 30 cm downstream of the catalyst. Figure 6 shows the results of the experiment. In the figure, the horizontal axis is the adiabatic flame temperature after fuel addition. Curve a is the combustion efficiency in the case of the present invention, curve b is the combustion efficiency in the comparative example, curve c is the NOx concentration in the case of the present invention, curve d
is the NOx concentration of the comparative example. In the figure, the NOx in the comparative example increases rapidly as the adiabatic flame temperature rises because the additional fuel was burned before it was sufficiently mixed, resulting in local high temperatures.
This is thought to be due to a sudden increase in NOx. of the present invention
NOx concentration is lower than before, and combustion efficiency is also improved. The improvement in combustion efficiency is thought to be due to the enlargement of the diameter downstream of the portion shown by the reverse fire prevention mechanism 11, which created a reverse flow section and produced a flame-holding effect.

Example 2 Using the same device as in Example 1, the honeycomb cell diameter was 1 instead of the reverse fire prevention mechanism 11 in Example 1.
An experiment similar to that in Example 1 was conducted by installing a honeycomb structure measuring mm□ and having a length of 10 mm. The results are shown in Figure 7. In this example as well, good results were obtained regarding the NOx concentration.

[Brief explanation of drawings]

Figure 1 is a schematic diagram of a typical gas turbine combustor.
Fig. 2 is a conventional catalytic combustion type gas turbine combustor, Fig. 3 is a schematic diagram of a gas turbine combustor according to the present invention, Fig. 4 is a perspective view showing a honeycomb structure used in the present invention, and Fig. 5 is a schematic diagram of a gas turbine combustor according to the present invention. A schematic diagram of a combustor used in a simulation experiment of an embodiment of the present invention, and FIGS. 6 and 7 are characteristic curve diagrams. 1, 1', 9, 10... fuel nozzle, 2... spark plug, 3... combustion air, 4... cooling air, 5... dilution air, 6... turbine nozzle,
7...Catalyst filling part, 8...Swirler, 11...Reverse fire prevention mechanism, 12...Mixture of fuel and air, 1
3... Gas phase combustion section.

Claims (1)

[Scope of Claims] 1. A mixing section that mixes fuel and air to form a fuel mixture; A catalytic combustion section that is provided downstream of the mixing section and combusts the fuel mixture using a catalyst; The catalytic combustion section a fuel supply section which is provided on the downstream side of the catalytic combustion section and adds fuel or a fuel-based mixture to the effluent from the catalytic combustion section; A low NOx combustor, comprising: a combustion section, and a reverse fire prevention mechanism is provided between the fuel supply section and the gas phase combustion section. 2. The low NOx combustor according to claim 1, wherein the reverse fire prevention mechanism is a flow passage having a cross-sectional area smaller than the cross-sectional area of the flow passage in the fuel supply section and the gas phase combustion section. 3. The low NOx combustor according to claim 1, wherein the reverse fire prevention mechanism is a honeycomb structure that creates a laminar flow of the effluent to which fuel has been added by the fuel addition section. 4. Claim 1, wherein combustion occurs only by catalytic reaction in the catalytic combustion section.
Low NOx combustor as described in section.