JPH0261407A - Catalyst combustion - Google Patents

Abstract

PURPOSE: To prevent self-firing of fuel/air mixture by disposing a flame trap in the upstream of a combustion catalyst and constructing the flame trap of a catalyst-free honeycomb section or supporting the downstream side thereof on the catalyst-tree honeycomb section. CONSTITUTION: Fixed position rings 16, 18 are provided at the opposite ends of a cylinder casing 10. Two honeycomb units 20, 22 are disposed between the rings 16, 18 and a spacer ring 24 made of alpha-alumina is disposed between. The honeycomb 20 is made of an inert ceramic material having composition of low coefficient of thermal expansion and carries a combustion catalyst. The honeycomb 22 is composed similarly to the honeycomb 20 and since it is short and carries no combustion catalyst, it serves as a flame trap for preventing self-firing of fuel/air mixture in the upstream of the honeycomb 22. Since crack due to heat shock is eliminated, risk of separating from the catalyst carrying region is eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to catalytic combustion in which a gaseous or vaporized liquid fuel is combusted with an oxygen-containing gas (eg, air) in the presence of a combustion catalyst. For descriptive convenience, the oxygen-containing gas will be referred to as air, but it will be appreciated that oxygen itself or oxygen-enriched or oxygen-depleted air can be used.

Catalytic combustion can be used in a wide range of applications and has many advantages, such as tending to provide combustion products with lower nitrogen oxide content than conventional flame combustion.

One application of catalytic combustion is in gas turbines, where compressed gaseous or vaporized liquid fuel is mixed with compressed oxygen-containing gas (usually air) and this mixture is passed through a combustion catalyst. When catalytic combustion occurs, a hot gas stream is produced that is used to operate a turbine that in turn operates an air compressor and, if necessary, a fuel compressor. It produces a hot gas flow and also provides power that can be used, for example, for electricity generated by an AC power source operated by a turbine.

Other applications include industrial heaters and domestic heaters (eg water heaters). For example, catalytic combustion can be used in industrial combustion heater burners, domestic water boiler burners (eg, fully premixed burners), and pilot burners.

The above-mentioned catalyst for catalytic combustion usually includes materials such as platinum group metals such as platinum, palladium, and rhodium, or vanadium pentoxide, or mixtures thereof supported on an inert support. There is.

The support is usually a refractory material, especially alpha alumina. Conveniently, it is in the form of a monolithic nornicum structure (i.e., a single honeycomb unit) or an aggregate polygonal honeycomb unit grouped in parallel, each unit comprising a plurality of polygonal honeycomb units extending in the direction of gas flow. It has parallel passages. Examples of suitable supports are described in EP-A-206,535 and EP-A-226,306, and suitable manufacturing methods are described in EP-A-134N8.

During operation, the honeycomb becomes relatively hot. At least at the beginning of combustion, a fuel/air mixture is fed to the honeycomb at elevated temperatures and rapid combustion occurs upon contact with the combustion catalyst. Preheating of the fuel/air mixture may be carried out in various ways, for example by the heat generated during compression or by the addition of heated parast gas (eg steam). However, the temperature of the fuel/air mixture should be below the autoignition temperature. After the start-up time, the inlet temperature of the fuel/air mixture may be lowered, but the catalyst remains hot. During standard operation, the fuel/air mixture is fed at such a rate that the mixture enters the combustion catalyst before it is heated above its autoignition temperature by the heat released back from the combustion catalyst/nicum. However, during certain stages of operation, in particular when the flow rate is reduced, e.g. during part-load operation and/or during shutdown, the incoming fuel/air mixture heats up above its autoignition temperature due to the returned heat. There is a risk that it will be done. This will result in self-ignition of the fuel/air-empty mixture. There is then a risk that the flame from the ignition will return towards the fuel and/or air inlet and damage the container.

Also, during abrupt shutdown of the system, the catalyst temperature remains high, but the inlet gas velocity is reduced to the flame velocity (typically 6 m/s, with exceptions on the order of lOm/s). ), and the flame front accelerates away from the hot catalyst, potentially creating explosive or unstable combustion conditions upstream of the catalyst leading to thermal stress on the catalyst. .

The present invention seeks to overcome these problems and has particular use in applications such as gas turbines, or domestic water heaters, where combustion is often desired to stop and start. .

In the present invention, a flame trap is provided upstream of the combustion catalyst so that in the event of self-ignition, the flame cannot return towards the fuel/air inlet.

Accordingly, the present invention provides that, by passage of a fuel/air mixture over a combustion catalyst supported on a monolithic honeycomb structure,
In a catalytic fuel system in which combustion of a fuel/air mixture is achieved, a flame trap is placed upstream of the combustion catalyst;
An improved catalytic combustion system is provided, characterized in that the flame trap is comprised of a honeycomb section without a combustion catalyst or is supported on its downstream side by a honeycomb section without a combustion catalyst.

The combustion catalyst-free section may itself be a flame trap, or it may be a support for a conventional gauze seven frame trap. The part without combustion catalyst is cooler than the catalyst-containing honeycomb and is therefore less likely to self-ignite the fuel/air mixture upstream of the honeycomb without combustion catalyst as a result of heating by the heat released from the combustion catalyst.

The passages through the honeycomb generally have a hydraulic dixmeter of less than 5 mm, in particular less than 2.5 mm, and generally greater than 0.1 mm. The term fluid diameter means four times the cross-sectional area of the passage divided by the circumference of the cross-section of the passage. (For passages with a circular cross-section, the fluid diameter is therefore the diameter of the cross-section of the passage, whereas for passages with a cross-section of regular polygonal features, the fluid diameter is the diameter of the inscribed circle.) The cross-sectional shape of the passage is preferably a rectangle, particularly a square, or a triangle, specifically an isosceles triangle (e.g., an equilateral triangle, a right isosceles triangle obtained by dividing a square diagonally). . Preferably, the honeycomb has a pore area of at least 30%, in particular 40-90%, and in the case of polygonal cross-section channels the walls between adjacent channels preferably have a
It has a thickness of mm. Preferably there are 10 to 1110 passages, particularly 15 to 50 passages per unit cross section cm2.

In one version of the invention, the catalyst-free honeycomb portion may be integrated with the catalyst-loaded honeycomb, for example as a result of coating only the downstream portion of the honeycomb with combustion catalyst. The configuration of this feature is simple, however, due to the temperature difference that tends to occur between the uncatalyzed area and the catalyst-loaded area, cracking due to thermal shock may occur as a result of the catalyst being coated. The drawback is that there is a possibility that the non-containing region may separate from the catalyst-supporting region. This risk can be minimized by limiting the length of the catalyst-uncoated region to less than about 10Q times, preferably less than about 50 times, the fluid diameter of the passage. The non-catalyst-coated region is at least as large as the fluid diameter of the passageway, particularly when the non-catalyst-coated region acts as a flame trap itself, rather than simply as a support for a conventional flame trap. It should be 1 times longer, preferably at least 5 times longer.

Also, separate catalyst-free honeycomb units or collections of such units can likewise be used upstream of the combustion catalyst-carrying honeycomb, either as a seven-frame trap or as a support for a fine wire frame trap. in this case,
The disadvantage of the risk of separation as a result of cracking due to thermal shock, as mentioned above, of course does not occur. It will be appreciated that in this embodiment, the dimensions of the passages in the catalyst-free honeycomb may differ from those in the combustion catalyst-supported honeycomb. However, the dimensions are preferably within the ranges described above.

If the honeycomb itself without combustion catalyst acts as a flame trap, the fluid diameter of the passages is preferably 0.
．． In the range 5-2.5 mm, the passage length is typically up to 100 mm, preferably less than 50 mm.

Whether or not the catalyst-free honeycomb itself acts as a flame trap, its minimum length is dictated by the need to provide sufficient strength to be self-supporting. The length required to support itself is typically greater than the length required for the catalyst-free honeycomb to function as a flame trap, and is typically at least as long as the channel hydraulic pressure. It will be such that it is 1 times longer, in particular at least 5 times longer.

It will be appreciated that if the honeycomb is used to support a conventional frame trap, the fluid diameter of the passageways can be larger than would be useful for a frame trap. The use of larger fluid diameter passageways can reduce the pressure drop that occurs as the fuel/air mixture passes through the passageways.

The use of catalyst-free honeycomb as a support for conventional flame traps overcomes the difficulties associated with supporting conventional flame traps during extreme conditions of temperature and gas velocity encountered in feed facilities.

The invention will be illustrated with reference to the accompanying drawings, which are line cross-sectional views of the combustion zone of a gas turbine.

A combustion zone consisting of a cylinder casing 10 is shown in the drawing. The cylinder casing 10 is provided at one end with an inlet area 12 for supplying compressed air and into which fuel can be injected and vaporized (if not gaseous), for example by conventional means not shown. casing 10
is provided at its other end with an outlet region 14 for the combusted combustion gases to be supplied to the turbine region. At each end of the cylinder casing 10 there is a localization ring 16.18 (
The target is made of alpha alumina). Between the rings 16.18 two honeycomb units 20.22
are arranged therebetween, with a spacer ring 24 made of alpha alumina (i.e., an insulating material) provided therebetween. A ceramic fiber packing (not shown) was placed in a ring +6. It may be provided between Ill, 24 and the casing IO as well as between the casing IO and the honeycomb unit 20.22.

Honeycomb 20 is typically made from alpha alumina or other inert ceramic material with a low coefficient of thermal expansion composition by extrusion and then firing;
Combustion catalysts consisting of platinum or vanadium pentoxide deposited by impregnation, precipitation or dipping, typically from 0.05 to 50%, based on the honeycomb. Carrying 0%. Honeycomb 22 has a similar configuration to honeycomb 20, but is shorter in length and does not have a combustion catalyst. It then acts as a flame trap to prevent self-ignition of the fuel/air mixture upstream of the honeycomb 22.

In a typical example, honeycombs 20 and 22 are 4511 mm
with a diameter of 33 cm per cross section of the unit
It has a passageway for books. The passage has an isosceles triangular shape with a fluid diameter of approximately 1.2 mm, and the dirt floor of the adjacent passage is approximately 0.0 mm.
It has a wall thickness of 25 mm. The pore area of the honeycomb is approximately 66
%. The length of the catalyst-supported honeycomb 2o is 150 mm, but the length of the honeycomb 22 without catalyst is only 25 mm. The distance between honeycomb units 20 and 22 is 5m
It is m.

[Brief explanation of the drawing]

The drawing is a line sectional view of the combustion zone of a gas turbine. In the figure, 1G... cylinder casing 12... inlet area, 14... outlet area, +6. +g...Localization link, 20.22...Honeycomb unit, 24...Spacer ring.

Claims (1)

Claims: 1. A catalytic fuel system that achieves combustion of a fuel/air mixture by passage of the fuel/air mixture over a combustion catalyst supported on a monolithic honeycomb structure, comprising: a flame trap; is installed upstream of the combustion catalyst, and the flame trap is composed of a honeycomb part without a combustion catalyst, or is supported on its downstream side by a honeycomb part without a combustion catalyst. Catalytic combustion system. 2. The honeycomb supporting structure has a coating made of a combustion catalyst, and the honeycomb portion without the catalyst is the non-coated portion of the honeycomb supporting structure, and the diameter of the fluid is 100 times or less than the fluid diameter of the passage extending through the honeycomb. A catalytic combustion system according to claim 1, wherein the catalytic combustion system is of a length. 3. The catalytic combustion system according to claim 1, wherein the honeycomb portion without catalyst is separated from the honeycomb structure supporting the combustion catalyst. 4. Claim 1, wherein the catalyst-free honeycomb portion is at least five times the length of the fluid diameter of the passageway extending through the honeycomb.
3. The catalytic combustion system according to any one of 3 to 3. 5. A catalytic combustion system according to any preceding claim, wherein the passages extending through the honeycomb section or honeycomb sections have a fluid diameter of less than 5 mm. 6. The catalytic combustion system according to any one of claims 1 to 5, wherein the cross section of the honeycomb part or plurality of honeycomb parts has a pore area of at least 30%. 7. Claim 1 in which the honeycomb portion or a plurality of honeycomb portions have 10 to 100 passages per cm^2 of the honeycomb cross section.
7. The catalytic combustion system according to any one of . 8. The uncatalyzed honeycomb section itself forms a flame trap, and the fluid diameter of the passages in the uncatalyzed honeycomb section is 0.
．． Within the range of 5 to 2.5 mm, and the passage length is 100 mm.
The catalytic combustion system according to any one of claims 1 to 7, which has a diameter of less than mm. 9. A gas turbine incorporating the catalytic combustion system according to any one of claims 1 to 8. 10. A domestic water heater incorporating the catalytic combustion system according to any one of claims 1 to 8.