WO1996041991A1

WO1996041991A1 - Catalytic ignition burner for a gas turbine

Info

Publication number: WO1996041991A1
Application number: PCT/DE1996/001019
Authority: WO
Inventors: Erich Hums; Nicolas Vortmeyer
Original assignee: Siemens Aktiengesellschaft
Priority date: 1995-06-12
Filing date: 1996-06-11
Publication date: 1996-12-27
Also published as: JPH11509307A; RU2149317C1; ES2142588T3; JP4063871B2; EP0832399A1; IN191368B; EP0832399B1; DE59604180D1

Abstract

According to the invention a burner, especially for a gas turbine, is designed for the catalytically induced combustion of a fuel, in which the fuel outlet of a catalytic auxiliary burner (6) to stabilise the main burner (8) with the catalytic combustion of a pilot fuel flow is provided in the direction of flow of the fuel in a flow channel, in front of the fuel outlet of the main burner (8). The replacement of a diffusion pilot flame by a catalytic auxiliary burner substantially reduces the nitrogen oxide emission.

Description

description

CATALITIC BURNER OF A GAS TURBINE

The invention relates to a burner, in particular for a gas turbine, in which a catalytic auxiliary burner is provided for stabilizing a main burner. Natural gas, coal gas or some other gaseous hydrocarbon and / or hydrogen-containing mixture is provided as the fuel. Such a mixture or a fossil fuel in liquid form are also suitable.

When a named fuel is burned, nitrogen oxides NO _x are formed as particularly undesirable combustion products. In addition to sulfur dioxide, these nitrogen oxides are the main cause of the environmental problem of acid rain. One is therefore - also due to strict legal limit values for NO _x emissions - willing to keep the NO _x emissions of a burner in a gas turbine particularly low without significantly influencing the performance of the burner or the gas turbine.

For example, reducing the flame temperature in the burner reduces nitrogen oxide. In this case, water vapor is added to the fuel or compressed and preheated fresh air, or water is injected into the combustion chamber. Measures that reduce the burner's nitrogen oxide emissions per se are referred to as primary measures for nitrogen oxide reduction.

Accordingly, all measures are referred to as secondary measures in which nitrogen oxides contained in the exhaust gas of a combustion process are subsequently reduced.

For this purpose, the process of selective catalytic reduction (SCR) has established itself worldwide, in which the nitrogen oxides are contacted with a reducing agent, usually ammonia, on a catalyst and thereby form nitrogen and water. The use of this technology therefore inevitably involves the consumption of reducing agents. The catalysts for reducing nitrogen oxide arranged in the exhaust gas channel naturally cause a pressure drop in the exhaust gas channel. However, such a drop in pressure leads to a considerable drop in the power of the turbine when the burner is used in a gas turbine. Even a drop in output in the amount of a few per thousand, with an output of the gas turbine of, for example, 150 MW and an electricity sales price of approximately 0.15 DM / kWh of electricity, has a serious effect on the result which can be achieved with such a device.

More recent considerations regarding the design of the burner are that a diffusion burner or swirl-stabilized premix burner, which is usually used in a gas turbine, is replaced by a catalytic combustion chamber. With a catalytic combustion chamber, lower nitrogen oxide emissions are achieved than is possible with the above-mentioned burner types. In this way, the known disadvantages of the SCR process (large catalyst volumes, reducing agent consumption, high pressure loss) can be overcome.

It is usually used to stabilize a burner

(Diffusion burner, swirl-stabilized premix burner, catalytic burner) provided to use a pilot flame. This pilot flame is used to set a defined starting point for the combustion of the actual main fuel gas stream. A burner for generating such a pilot flame is usually a diffusion burner, which is a not insignificant source of nitrogen oxide. In view of the environmental problems caused by the nitrogen oxides and due to strict legal requirements for nitrogen oxide emissions, the aim is therefore to avoid any source of nitrogen oxide, however small, or at least to reduce its nitrogen oxide emission. The invention is therefore based on the object of specifying a burner, in particular for a gas turbine, in which the device for generating a pilot flame works particularly low in nitrogen oxide.

This object is achieved according to the invention in that a burner is provided for the combustion of a fuel, in which the fuel outlet of a catalytic auxiliary burner for stabilizing the main burner with catalytic combustion of a pilot fuel flow is provided in a flow channel in the flow direction of the fuel in a flow channel is.

The burner uses a catalytic combustion of the pilot fuel flow to stabilize or support the main burner.

In this way, the pilot flame required to stabilize the main burner or burners is generated by a catalytic combustion which is particularly low in nitrogen oxide.

In a preferred embodiment of the invention, it can be provided that, based on the cross section of the flow channel for the fuel, the catalytic auxiliary burner is central and the

Main burners are arranged coronally. This is particularly advantageous for a homogeneous distribution of the pilot flame in the radial direction, so that the combustion of the main fuel stream can also take place on a uniform front.

For the formation of the pilot flame, it is particularly preferred that the pilot fuel flow is led to the catalytic auxiliary burner via a preforming stage. In this way, a lowering of the catalytic ignition temperature of the pilot fuel flow is achieved, because in the preforming stage the fuel turns into easily igniting compounds is decomposed. In the case of natural gas, alcohols such as methanol, aldehydes and hydrogen are formed in the preforming stage, for example.

It can further be provided that the pilot fuel stream is mixed with ambient and / or compressor air. In this way, the NO _x emissions of the pilot burner can be further reduced by setting the volume ratios of fuel / preformed fuel to ambient and / or compressor air.

To stabilize the main flame in the main burner and to reliably prevent the main flame from reigniting, it is particularly preferred that the fuel outlet of the catalytic auxiliary burner is arranged between 0.5 and 5 m in front of the fuel outlet of the main burner, this distance preferably being about 0 , Can be 75 to 2 m.

In a further preferred embodiment of the invention it can be provided that the main burner is designed as a catalytic main burner. Such a burner, like the catalytic auxiliary burner, is distinguished by comparatively low nitrogen oxide emissions.

Embodiments of the invention are explained in more detail with reference to a drawing. Show:

1 and 3 each show a schematic representation of a longitudinal section through the burner part of a gas turbine; and

2 and 4 each show a top view of a cross section through the flow channel in the burner part according to FIG. 1 and FIG. 3.

In the figures, the same parts have the same reference numerals. The exemplary embodiment according to FIGS. 1 and 2 coincides with one feature with the exemplary embodiment according to FIGS. 3 and 4. The explanations which now follow therefore apply mutatis mutandis to FIGS. 3 and 4.

Figure 1 shows a schematic representation of the burner part 2 of a gas turbine not shown here. In the exemplary embodiment, the burner part 2 comprises a flow channel 4, into which a catalytic auxiliary burner 6 and a catalytic main burner 8 are installed. The catalytic support burner 6 and the main catalytic burner 8 are arranged rotationally symmetrically to the axis of symmetry 10 of the flow channel 4.

The arrangement of the catalytic auxiliary burner 6 in the center of the flow channel 4 creates an outer annular space 12 and an inner central space 14. A fuel mixture 16, consisting of fuel gas, here natural gas, is compressed in the annular space 12 by means of the compressor part of the gas turbine (not shown here) 18, and air 20. A pilot fuel flow 22 flowing into the annular space 12 originally consists of the same natural gas / air-gas mixture 18, 20 which, however, is preformed in a preforming stage 24. The preformed pilot fuel flow 22 flowing into the support burner 6 can also be referred to as an easily igniting pilot fuel flow. The natural gas / air mixture 18, 20 is preformed on a noble metal-containing catalyst which, for example, has a honeycomb shape, comprises titanium dioxide as the main component and platinum and rhodium as the catalytically active components. The catalyst is installed in the preforming stage 24 in a manner not shown here. Optionally, a heat exchanger can also be connected upstream of the catalyst in the preforming stage 24 in order to warm up the natural gas / air mixture 18, 20 entering the preforming stage and thus the effectiveness of the catalyst in the

Raise preformation level 24. When preforming, the substances which ignite comparatively easily from the natural gas 18, such as methanol, aldehyde and hydrogen.

In the exemplary embodiment, the fuel outlet of the catalytic auxiliary burner 6 is arranged in the flow direction of the fuel gas 16 at a distance d of approximately 1 m in front of the fuel outlet of the main catalytic burner 8. In the exemplary embodiment, the catalytic auxiliary burner 6 comprises a honeycomb catalyst which has at least one of the substances titanium dioxide, silicon dioxide and zirconium oxide as the basic constituent. In principle, all noble metals and metal oxides which have a strongly oxidizing effect on the fuels mentioned are suitable as catalytically active components. These are, for example, noble metals, such as platinum, rhodium, rhenium, iridium, and metal oxides, such as. B. the transition metal oxides vanadium oxide, tungsten oxide, molybdenum oxide, chromium oxide, copper oxide, manganese oxide and oxides of lanthanides, such as e.g. Cerium oxide. Metal ion exchanged zeolites and metal oxides of the spinel type can also be used.

The pilot fuel flow 22 entering the catalytic auxiliary burner 6 is oxidized due to the catalytically active substances and burns with a pilot flame 26. Because the fuel outlet of the auxiliary burner 6 is arranged in the flow direction of the fuel gas 16 the distance d in front of the fuel outlet of the main burner 8, it is guaranteed that the main flame 28 cannot strike back into the main catalytic burner 8 or even into the areas in front of the catalytic burner 6, 8. The distance d is approximately 1 m in the selected exemplary embodiment.

The catalyst material in the main burner 8 does not differ from the catalyst material of the auxiliary burner 6. As a catalytically particularly active substance with regard to the oxidation of the hydrocarbons contained in the fuel 16, 1% by weight of platinum and rhodium and 2% by weight of vanadium are in each case ¬ oxide, chromium oxide and tungsten oxide provided. The burner exhaust gas emerging from the burner part 2 has a particularly low nitrogen oxide content because, on the one hand, the fuel 16 is burned catalytically in the main burner 8 and because the pilot flame 26 is also generated by catalytic combustion of the pilot fuel stream 22 in the auxiliary burner 6. In a variation of the main catalytic burner 8, diffusion burners or spin-stabilized premix burners known from the prior art can also be used as main burners.

FIG. 2 shows a top view of the flow channel 4, in which the arrangement of the main burner 8 as a catalytically active honeycomb catalyst can be seen in a schematic representation. Such honeycomb catalysts usually have a cell number of 4 to 100 cells per inch ^ and have a wall thickness of the webs of 0.5 to 5 mm. As an alternative to the honeycomb catalysts used in the exemplary embodiment, it is also possible to use metallic plate catalysts or, in principle, plate catalysts. In terms of the geometry of the channels, the catalytic auxiliary burner 6 arranged centrally in the top view according to FIG. 2 is usually identical to the geometry of the catalytic main burner 8.

FIGS. 3 and 4 show an exemplary embodiment of the invention, in which the main catalytic burner 8 recognizable from FIG. 1 and FIG. 2 is replaced by a non-catalytic main burner which has guide blades 31 as important distinguishing features. These guide vanes 31 impart a swirl to the fuel-air mixture flowing through, which stabilizes the combustion that starts in this mixture. The non-catalytic main burner is characterized by a particularly low operational pressure drop and by a particular simplicity of construction, which particularly recommends this main burner for use in a gas turbine. In any case, the fact that the main burner causes premix combustion is a comparatively small one NO _x emissions guaranteed. Since the pilot burner 6 is also designed as a catalytic auxiliary burner 6 in the exemplary embodiment according to FIGS. 3 and 4, it is in any case not an essential source of nitrogen oxides; accordingly, the burner according to FIG. 3 and FIG. 4 is also qualified as a burner with particularly low NO _x emissions.

Claims

claims

1. Burner for the combustion of a fuel (16), in which the fuel outlet of a catalytic auxiliary burner (6) for stabilizing the main burner (8) in a flow channel (4) in the flow direction of the fuel (16) in front of the fuel outlet of a main burner (8) ) is provided with catalytic combustion of a pilot fuel stream (22).

2. Burner according to claim 1, d a d u r c h g e k e n n z e i c h n e t that based on the cross section of the flow channel (4) for the Brenn¬ fuel (16) the catalytic support burner (6) centrally and the main burner (8) are arranged coronally.

3. Burner according to claim 1 or 2, so that the pilot fuel flow (22) is guided via a preforming stage (24) to the catalytic auxiliary burner (6).

4. Burner according to claim 3, so that a premixing of the pilot fuel stream (22) with ambient and / or compressor air (20) is provided.

5. Burner according to one of claims 1 to 4, so that the fuel outlet of the catalytic auxiliary burner (6) is arranged between 0.5 and 5 m in front of the fuel outlet of the main burner (8).

6. Burner according to claim 5, characterized in that the fuel outlet of the catalytic auxiliary burner (6) is arranged about 0.75 to 2 m before the fuel outlet of the main burner (8).

7. Burner according to one of claims 1 to 6, g e k e n n z e i c h n e t d u r c h a main catalytic burner (8).

8. Gas turbine comprising a burner according to one of claims 1 to 7.