WO1996041992A1 - Catalytic combustion chamber for a gas turbine - Google Patents

Abstract

The invention provides a burner with a catalytic combustion chamber. The combustion chamber is substantially cylindrically widened in the direction of flow of a fuel and has a catalytically active coating on the walls facing the fuel to oxidize the fuel. The catalytically induced combustion of a fuel results in a particularly low nitrogen oxide content in the burner's exhaust gases. At the same time, the coating of the walls does not raise the flow resistance in the burner, unlike prior art primary measures to reduce nitrogen oxides. The use of the burner in a gas turbine therefore provides particularly high efficiency with low nitrogen oxide emissions. The invention can be used in all gas turbines.

Description

Be honored

CATALYTIC GAS TURBINE COMBUSTION CHAMBER

The invention relates to a burner, in particular for a gas turbine, with a catalytic combustion chamber. A hydrocarbon and / or hydrogen-containing energy carrier is provided as a fuel both in liquid and in gaseous form. Such a fuel is, for example, natural gas, petroleum or methane. Such a burner can preferably be used in a gas turbine.

A gas turbine usually consists of a compressor part, a burner part and a turbine part. The compressor part and the turbine part are usually located on a common shaft which at the same time drives a generator for generating electricity. In the compressor part, preheated fresh air is burned with a fuel of the type mentioned. The hot burner exhaust gas is fed to the turbine section and expanded there.

Siemens AG, May 1994, Order No. A 96001-U 124-V 1-7600, provides detailed information on the construction and use of a gas turbine.

In the combustion of a fuel of the type mentioned, nitrogen oxides NO _x also arise as particularly undesirable combustion products. In addition to sulfur dioxide, these nitrogen oxides are the main cause of the environmental problem of acid rain. It is therefore - also due to strict legal limit values for NO _x emissions - willing to keep the NO _x emissions from a gas turbine particularly low and at the same time largely unaffected by the performance of the gas turbine. For example, reducing the flame temperature in the burner reduces nitrogen oxide. Here, water vapor is added to the fuel or the compressed and preheated fresh air or water is injected into the combustion chamber. Measures that reduce 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, for example, nitrogen oxides contained in a gas turbine or basically in a combustion process can be reduced by subsequent measures.

For this purpose, the process of selective catalytic reduction (SCR) has established itself worldwide, in which the nitrogen oxides are contacted together 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 nitrogen oxide reduction arranged in the exhaust duct naturally cause a pressure drop which, when the burner is used in a turbine, results in a drop in performance. Even a drop in output in the amount of a few parts per thousand has a serious impact on the result that can be achieved with such a device with an output of the gas turbine of, for example, 150 MW and an electricity sale price of approximately 0.15 DM / kWh of electricity.

As a primary measure for the reduction of nitrogen oxides, GB 2 268 694 A provides a catalytic combustion chamber, the ignition temperature of a fuel being lowered by a partial catalytic oxidation. The catalysts provided for this purpose are installed transversely to the flow direction of the fuel and extend over the entire flow cross section. This gives a high flow resistance. In the burners described above, there is therefore basically the problem that any nitrogen oxide reduction, primary or secondary, provided there, results in a loss of performance or a loss in the overall efficiency of the gas turbine system.

The invention is therefore based on the object of specifying a burner, in particular for a gas turbine, which is distinguished by particularly low nitrogen oxide emissions and, at the same time, a particularly high efficiency.

This object is achieved according to the invention with a burner in which a catalytic combustion chamber is provided, the combustion chamber having an essentially cylindrical expansion in the direction of flow of a fuel and the wall facing the fuel having a catalytically active coating for oxidizing the fuel. In this way, a particularly low nitrogen oxide content of the burner exhaust gas is achieved by the catalytically induced combustion of the fuel. At the same time, the coating of the wall of the combustion chamber does not increase the flow resistance, so that particularly high efficiencies can be achieved in a gas turbine with such a catalytic combustion chamber. The essentially cylindrical shape of the catalytic combustion chamber and the catalytically active coating of the wall contribute to the fuel igniting starting from the wall and a spreading of the flame front from the catalytically active surface of the wall into the free Flow of the fuel gas is possible. The cylindrical shape in particular contributes to an essentially concentric and thus homogeneous distribution of the flame front, which results in complete and uniform combustion of the fuel.

In order to achieve a particularly well rotationally symmetrical flame front, it is advantageous if a number concentrically catalytically actively coated rings are provided to the longitudinal axis of the combustion chamber.

The process of forming a largely rotationally symmetrical flame front in the combustion chamber is further supported if the ring or rings are arranged exclusively in the outer region of the essentially circular cross section of the combustion chamber.

To lower the catalytic ignition temperature of the fuel in the combustion chamber, it is particularly advantageous if a fuel comprising a main fuel stream, a preformed partial fuel stream and air can be fed to the combustion chamber. The main fuel flow consists mostly of natural gas and / or coal gas and / or hydrogen. The preformed partial fuel stream is a partial stream which is separated from the main fuel stream and passed through a preforming stage. In this catalyst-based preforming stage, for example, natural gas ignites catalytically easier than natural gas, such as e.g. Alcohols, aldehydes and hydrogen. A fuel gas mixed with such a preformed partial fuel flow therefore has excellent catalytic ignitability.

A particularly advantageous embodiment with respect to

The ignitability of the fuel introduced into the catalytic combustion chamber can provide that a preformed partial fuel stream, optionally premixed with air, enters the combustion chamber through bores in the wall. In this way, the comparatively easily igniting gas mixture of the preformed partial fuel stream is brought into direct contact with the catalytically active coating and ignites spontaneously, so that a reliable, spatially standing ignition is formed in the form of a hollow cylinder in the catalytic combustion chamber is. In order to protect the catalytically active coating which is located on the wall of the catalytic combustion chamber which can be turned towards the fuel gas, the wall can be cooled. Here, the wall can be cooled, for example, with air, at the same time preheating the air. This preheated air can, for example, be subsequently compressed in the compressor part to the combustion chamber inlet pressure.

The catalytic effect of the catalytically active coating occurs particularly advantageously when the catalytically active coating titanium dioxide, which is preferably flame and plasma sprayed, and a noble metal component selected from platinum, rhodium, palladium, iridium, rhenium and / or a metal oxide component , consisting of one or more transition metal oxides. Suitable transition metal oxides are those oxides which have a strongly oxidizing catalytic effect, e.g. Copper oxide, chromium oxide, iron oxide, molybdenum oxide, tungsten oxide, vanadium oxide, manganese oxide, cerium oxide and other oxides of lanthanides.

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

1 shows a schematic representation of the burner of a gas turbine with a catalytic combustion chamber;

2 shows a schematic representation of the burner of a gas turbine according to FIG. 1 with a slight difference

Figure 1 modified catalytic combustion chamber; and

3 shows a catalytic combustion chamber in cross section.

In FIGS. 1 to 3, the same parts have the same reference numbers. 1 shows a gas turbine 2 which comprises a compressor part 4, a burner part 6 and a turbine part 7. The burner part 6 comprises a catalytic combustion chamber 8, the wall 10 of which has a catalytically active coating 12.

In the exemplary embodiment, the catalytic combustion chamber 8 has a circular cross section. A fuel gas flows into the catalytic combustion chamber 8 as fuel 14, which in the exemplary embodiment consists of air 16 compressed in the compressor part 4, a main fuel stream 18 and a preformed partial fuel stream 20. This preformed partial fuel stream 20 is separated from an original fuel stream 22 and passed through a preforming stage 24. In the exemplary embodiment, the fuel stream 22 consists of natural gas, from which in the preforming stage 24 substances which ignite catalytically more easily than natural gas, such as e.g. Alko¬ hole, aldehydes and hydrogen are formed. To perform its function, the preforming stage 24 comprises a ceramic honeycomb catalyst based on titanium dioxide, which is not shown any further and which additionally comprises a noble metal component consisting of platinum and palladium applied superficially to the honeycomb catalyst.

The catalytically active coating 12 on the wall 10 of the catalytic combustion chamber 8 consists of a flame-sprayed titanium dioxide layer with a thickness of approximately 500 μm, on which are additionally deposited noble metal particles of platinum, rhodium and palladium as well as particles of transition metal oxides, such as cerium oxide. Vanadium oxide and chromium oxide are applied. As an alternative to a flame-sprayed titanium dioxide, a plasma-sprayed titanium dioxide layer can also be provided. Both layers are distinguished by their great strength on the wall 10 of the catalytic combustion chamber 8, which is usually made of an austenitic steel. When the gas turbine 2 is operating, the fuel 14 now flows into the catalytic combustion chamber 8 and ignites on the catalytically active coating 12 of the wall 10. The upstream flame front 26 formed in this way, like the downstream flame front 28, is largely rotationally symmetrical, so that the temperature distribution in the catalytic combustion chamber 8 along the main flow direction has approximately circular isotherms with respect to the cross section. This is advantageous for a uniform and low-pollutant combustion of the fuel 14.

The fuel 14 catalytically burned in this way enters the turbine part 7 of the gas turbine 2 at a temperature of approximately 1100 ° C. and is expanded there. The thermal energy transmitted in the turbine part is used to drive a generator for generating electricity, which is not shown here. This generator is arranged on the same shaft (not shown further here) as the gas turbine 2. The burner exhaust gas 30 leaving the turbine part 7 is particularly low in nitrogen oxide due to the catalytic combustion of the fuel gas 14 and has a nitrogen oxide content of approximately 70 ppm. The burner exhaust gas 30 can be used in a waste heat steam generator (not shown here) for steam generation.

FIG. 2 shows a schematic representation of a gas turbine 2 'slightly modified compared to FIG. 1. The modifications are limited to the design of the catalytic combustion chamber 8. The catalytic combustion chamber 8 'shown in FIG. 2 differs from FIG. 1 in that 10 bores 32 are provided in the wall through which the preformed fuel - partial flow 20 and air 16 enter the combustion chamber 8 '.

This measure has two advantages over the configuration according to FIG. 1. The first advantage is that the fuel mixture with the lowest catalytic ignition temperature temperature enters the combustion chamber 8 'directly at the catalytically active coating 12 and therefore ignites comparatively spontaneously. This measure therefore contributes particularly to the stabilization of the upstream flame front 26. The second advantage is that the walls 10 are cooled by the flowing mixture of preformed partial fuel flow 20 and air 16. This cooling also reduces the thermal load on the catalytically active coating 12, which has a favorable effect on the durability of this coating 12. Cooling of the wall 10 can alternatively also be achieved in a manner not shown here by means of a flow of air 16 which enters the compressor part 4.

FIG. 3 shows a schematic representation of the cross section of a catalytic combustion chamber 34 modified compared to FIGS. 1 and 2. The wall 10 and the catalytically active coating 12 for the oxidation of the fuel 14 can again be seen. The oxidation of the fuel is understood to mean, of course, that the fuel 14, 22 is oxidized and the oxygen which is brought in via the air 16 and is required for combustion is reduced. The catalytically active coating 12 for the oxidation of the fuel gas 14 therefore means the coating which induces the entire combustion process with oxidized and reduced combustion products.

The combustion chamber 34 has three rings 36 arranged concentrically. These concentric rings 36 are thin strips of sheet metal, consisting of the material of the wall 10. The rings 36 have the same catalytically active coating 12 with which the wall 10 of the combustion chamber 34 is also coated. For the sake of clarity of the illustration, the catalytically active coating 12 is only shown in a selected quadrant. The webs 38 holding the rings 36 also have this catalytically active coating 12. The rings 36 are exclusively in the outer Region of the substantially circular cross-section of the combustion chamber 34 is arranged to restrict the initial ignition of the fuel 14 to the outer region of the cross-section of the combustion chamber 34. The flame front then extends automatically into the free flow of the fuel gas 14. The rings 36 with the catalytically active coating 12 thus contribute to stabilizing the flame front and ensuring complete and therefore particularly low-emission combustion.

Claims

claims 1. Burner with a catalytic combustion chamber (8, 8 ', 34), the combustion chamber (8, 8', 34) in the flow direction of a fuel (14) having an essentially cylindrical expansion, and the fuel (14 ) facing wall (10) of the combustion chamber has a catalytically active coating (12) for the oxidation of the fuel (14). 2. Burner according to claim 1, so that a number of rings (36) concentrically arranged and catalytically actively coated with the cylinder longitudinal axis of the combustion chamber (8, 8 ', 34) is provided. 3. Burner according to claim 2, so that the ring or rings (36) are arranged exclusively in the outer region of the essentially circular cross section of the combustion chamber (8, 8 ', 34). 4. Burner according to one of claims 1 to 3, characterized in that the Brenn¬ chamber (8, 8 ', 34) a fuel (14) comprising a main fuel stream (18), a preformed partial fuel stream (20) and Air (16) can be supplied. 5. Burner according to one of claims 1 to 4, characterized in that a preformed partial fuel flow (20), optionally premixed with air (16), through bores (32) in the wall (10) in the combustion chamber (8 ' ) can be introduced. 6. Burner according to one of claims 1 to 5, d a d u r c h g e k e n n z e i c h n e t that the wall (10) is coolable. 7. Burner according to one of claims 1 to 6, characterized in that the catalytically active coating (12) titanium dioxide, preferably flame or plasma sprayed, and a noble metal content, selected from one or more of the noble metals platinum, rhodium, Palladium, iridium, rhenium, and / or a metal oxide portion selected from one or more transition metal oxides. 8. A gas turbine comprising a burner according to one of claims 1 to 7.