AT404981B - BURNER - Google Patents

Description

AT 404 981 B

The invention relates to a burner according to the preamble of the independent claim.

Such a burner has become known from DE 2 733 552 A1. From this, a fully premixed burner has become known, in which the fuel mixture is fed to the catalyst body in the heated state. A secondary air supply is not available and fully premixing burners are at a disadvantage compared to partially premixing burners in their modulation range, while they are more advantageous in terms of Νθχ output.

The aim of the invention is to avoid this disadvantage and to propose a burner of the type mentioned at the outset, which can be operated as a partially premixing burner and which results in only a low NOx emission.

According to the invention this is achieved in a burner of the type mentioned by the characterizing features of claim 1.

The proposed measures ensure that only that part of the mixture is catalytically converted during operation for which the primary air is sufficient and only the rest of the mixture is burned in rams after it has mixed with secondary air. Since the remaining mixture, together with the exhaust gas generated during the catalytic conversion of the mixture, no longer has sufficient combustion air, secondary air is allowed to enter the rams through the channels between the burner chambers.

The formation of NOx is significantly reduced because a lean mixture flame is formed.

The premixing with primary air can be controlled so that the gas-air mixture is outside the ignition limits, thereby avoiding the risk of ram kickback.

In addition, a relatively long residence time of the mixture in the region of the catalytic surface of the honeycomb body can be achieved, so that a correspondingly large part of the mixture is converted catalytically. This is also due to the fact that guiding the mixture through the honeycomb body also ensures very intimate contact of the mixture with the catalytically coated surface.

Furthermore, it is also ensured that the lean mixture flames which form during the combustion of the remaining mixture form at a sufficient distance from the catalytically coated surface, so that there is only a small amount of heat input to the catalyst, which protects it from overheating and thus destruction. This effect is self-regulating, since secondary air must flow in before the fuel gas / air mixture is burned. Mixing with secondary air takes place along the outflow path of the fuel gas / exhaust gas mixture.

It can also be achieved by the proposed measures that the thermal buoyancy in the combustion chamber in which the burner is arranged can be used to overcome the pressure losses on the cover of the burner.

The catalytically coated surface can be designed so that the coupling of heat by radiation can be used to cool the catalyst. This is achieved in that a short length of the catalyst is catalytically coated on the side facing the combustion chamber.

With partially premixed burners there is also the advantage that they can be operated in a larger area compared to fully premixed burners. The proposed measures also eliminated the main disadvantage of the previous partially premixed burners, the increased NOx emissions compared to fully premixed systems.

The features of claim 2 provide the possibility of also producing larger burner arrangements, in which there are nevertheless essentially the same conditions over their entire surface, with sufficient access of secondary air also being possible in the central regions of such a burner arrangement.

If a continuous honeycomb body 7 is arranged over several burners, there is the advantage that heat is removed from the honeycomb body through the secondary air flowing through the spaces between the burners, thereby avoiding overheating of the catalytic coating 8. At the same time, the secondary air is preheated. The latter leads to better combustion of the non-catalytically converted mixture.

An embodiment of the invention is explained below with reference to Rg. 1 to 5 of the drawings.

Show:

1 shows a section through a burner according to the invention,

Rg. 2 a burner arrangement in plan view,

3 shows a cross section through the burner arrangement according to Rg. 2,

4 shows a plan view of a further burner arrangement and

5 shows a cross section through the burner arrangement according to Rg. 4. 2

Claims (3)

AT 404 981 B The same reference numerals denote the same details in all the figures. The burner according to FIG. 1 has a gas distribution pipe 1, into which nozzles 2 are screwed or which is provided with openings from which a gas jet 3 emerges. The momentum of the gas entrains air so that a sub-stoichiometric mixture is created. This flows through a diffuser 4 of an injector 5 into a gas collecting space 6. From there, the mixture flows into a honeycomb body 7 which has a catalytic coating 8. The gas distribution pipe 1 is shielded from the honeycomb body 7 by an angled plate 15 in order to avoid kickback on the nozzles 2. When the burner is in operation, the mixture flows into the gas collecting space 6 via the injector 5 and then flows through the honeycomb body 7. Part of the mixture 13 is converted catalytically. The resulting exhaust gases flow out together with the remaining mixture from the upper openings of the channels of the honeycomb body 7. The unreacted mixture 13 burns above the top of the honeycomb body 7 with flames 14. When the burner is started, the entire mixture flows through the honeycomb body 7 and burns with flames 14. The fuel gas / air mixture is ignited conventionally. The resulting rams 14 heat the honeycomb body 7 so that the catalytic coating 8 reaches its working temperature and part of the mixture is converted catalytically. The honeycomb body 7 is cooled by radiant heat coupling on the side facing the combustion chamber receiving the burner, which flows through the secondary air, through the channels not exposed to fuel gas, or through the spaces between the combustion chambers. It is not necessary to cool the mixture because the premix is outside the ignition limits. When the remaining mixture is burned, secondary air flows to the flames 14. As a result, the lean mixture flame stabilizes only at a further distance from the top of the honeycomb body 7, so that the heat input into it is reduced and overheating is prevented. Due to the lean mixed flames, it is also possible that the thermal buoyancy can be used to overcome the pressure. 2 and 3 show a burner arrangement in which the individual burners are arranged at a distance from one another, the injectors 5 being aligned with gas nozzles 2 and secondary air 12 being able to flow through the gaps 11 between the burners. The secondary air 12 can flow freely between the burners and thereby cool the walls of the burners. In a burner arrangement according to Rg. 4 and 5, the burner is covered by a continuous honeycomb body 7 ', so that the secondary air 12 rising through column 11 flows through the honeycomb body 7' and thereby dissipates heat from it. 1. Burner, which has a gas collection chamber (6), which is provided with a channel-forming outflow openings, at least partially covered with a catalyst (8) coated honeycomb body (7, T), characterized in that the burner is known per se Atmospheric partially premixing burner is formed which, in a manner known per se, has an injector (5) with a gas nozzle (2) which is essentially coaxial to its inlet, a secondary air supply being provided downstream of the honeycomb body (7, 7 '). 2. Burner arrangement with a plurality of burners according to claim 1, characterized in that the burners are arranged at a distance from one another, the distances being provided for the secondary air supply. 3. Burner arrangement with a plurality of burners according to claim 1, characterized in that the burners are arranged at a distance from one another and are covered by a common honeycomb body (7 ^), the distances being provided with the assigned channels of the honeycomb body (7 ') for the secondary air supply Sheet drawings 3