EP4023938B1 - Burner arrangement for a pre-mix burner - Google Patents

Description

The invention relates to a heater with a combustion chamber and a burner arrangement with a premix burner.

Modern heaters are operated with a mixture of air and fuel gas. For this purpose, air mixed with a suitable proportion of fuel gas is conveyed by a fan into a burner which has outlet openings for the mixture, which is burned in a combustion chamber after exiting the burner. The mixture is regulated very precisely to avoid the formation of pollutants so that combustion can take place as completely as possible. The resulting combustion gases contain only a little oxygen, but depending on the fuel gas, water vapor, carbon dioxide and mainly nitrogen. Small quantities of nitrogen oxides, hereinafter referred to as NOX, can also be formed during combustion, which is undesirable but not entirely avoidable, especially at high combustion temperatures. Particularly high combustion temperatures arise with certain fuel gases, including e.g. B. a large proportion of hydrogen in the fuel gas, as planned in the future, can increase the combustion temperature. The present invention is not just about large systems, but also about e.g. B. Wall devices for heating water and generally heating devices for heating buildings and/or providing warm water.

A burner typically used for such devices today has a burner body that is attached to or in a wall of a combustion chamber (usually in a door or maintenance hatch) and protrudes into the combustion chamber. Often, but not necessarily, such a burner body is designed to be rotationally symmetrical, in particular cylindrical, to a longitudinal axis. Its lateral surface is limited an interior. The mixture of air and fuel gas is fed to an inlet area of the interior of the burner body and blown from an outlet area with many outlet openings into the combustion chamber, where it burns and releases the resulting heat to heat exchanger surfaces. It is also known that flow-influencing elements can be arranged in the interior of the burner body, in particular in the inlet area. For example, guide vanes or similar elements for generating swirl and/or turbulence can be arranged there (see e.g. WO 2016/182778 A1 ) or a static mixer, such as B. a Venturi nozzle. The aim is to achieve an even distribution of the mixture across the outlet openings and thus ensure combustion with as few pollutants as possible. However, it is hardly possible to influence the combustion temperature in this way, as it essentially depends on the type of fuel gas and the mixing ratio with air.

From the DE 100 64 259 A1 It is also already known to influence the flame stability in a combustion chamber by recirculating combustion gases and in the WO2004/102071 A1 The reduction in the production of NOX through exhaust gas recirculation in a type of Venturi nozzle is also described. However, the arrangements mentioned require a relatively long installation space, which is often not available.

From the EP 0 970 327 A1 and the EP 0 867 659 A1 gas burners emerge in which a flame tube is arranged on a baffle plate, the baffle plate with a diaphragm insert forming openings and baffles through which air or a gas-air mixture can enter the flame tube. During operation, a negative pressure can be created downstream of the baffle plate, whereby exhaust gas can be sucked in via recirculation slots and openings formed on or in the flame tube in order to prevent sooting of the baffle plate or to heat the flame there. In contrast, in the heaters mentioned here, the gas is burned outside the burner body in the combustion chamber, so that the gas is burned The addressed problems of sooting and flame heating do not occur here. In addition, these concepts of the prior art require a coordinated installation situation towards the wall of the combustion chamber, so that increased expenditure on equipment is required.

The object of the present invention is to at least partially solve the problems described with reference to the prior art and, in particular, to reduce the generation of pollutants, in particular NOX, by making changes to the burner, without additional components or other significant changes to existing or new ones Investments. In particular, the combustion temperature should be reduced, which is particularly important for future fuels containing hydrogen or pure hydrogen.

A heater according to claim 1 is used to solve this problem. Advantageous refinements and developments of the invention are specified in the dependent claims. The description, especially in connection with the drawing, illustrates the invention and gives further exemplary embodiments.

The heater proposed here with a combustion chamber and a burner arrangement, comprising a premix burner, has a burner body to which a mixture of air and fuel gas can be supplied, which is attached to or in a wall of a combustion chamber, projects into it and has outlet openings in the combustion chamber for the mixture to exit having. The burner body has an interior with an inlet area and an outlet area, the interior in the inlet area having at least one element for generating swirl or turbulence, so that when the mixture flows through in the inlet area, a lower internal pressure is created than in the outlet area and than in the combustion chamber, and There are connection openings to the combustion chamber in the entry area.

The area in which an element for such a flow influence is located is included here and in the following as part of the entry area.

As is known from fluid mechanics (and is used, for example, in suction jet pumps), the static pressure in a system with a flow is inversely related to the flow velocity, which in turn depends on the flow cross section while the volume flow remains the same, so that a higher static pressure is achieved in areas with slow flow There is more pressure than in areas with faster currents. The present invention makes use of this to suck combustion gases from the combustion chamber into the interior of the burner body during operation of the burner and add them to the mixture there. For various reasons, this leads to a lower combustion temperature and thus to a lower production of pollutants, especially NOX.

Studies have shown that e.g. B. a swirl generator or a similar element in the inlet area of a burner body, despite the short overall length, results in a significantly lower pressure in the inlet area, especially in the area of the swirl generator, than in the outlet area. This goes so far that the pressure is even lower than in the combustion chamber, where the pressure in turn must be lower than in the outlet area of the burner body so that mixture can escape from the outlet openings into the combustion chamber. These conditions allow combustion gases to be sucked in from the combustion chamber through connection openings according to the invention into the inlet chamber, where they mix with the mixture of air and fuel gas blown in there (or at least in the subsequent element), so that a mixture of air, Fuel gas and recirculated combustion gases arrive. Since combustion gases contain little oxygen and can therefore be viewed as almost inert, this lowers the combustion temperature and reduces the formation of pollutants, although the combustion gases remain after a certain cooling Due to heat exchange during recirculation, they still have a higher temperature than the rest of the mixture. One element for generating swirl or turbulence is sufficient to generate a sufficient pressure difference. The entry area in the axial direction is very short, namely 3 mm to 20 mm [millimeters], preferably 5 mm to 10 mm, whereby the area that the element occupies for influencing the flow is also included in the entry area.

In a special embodiment, the inlet area has a smaller flow cross section than the outlet area. This leads to a faster flow with the same volume flow as in the outlet area with a larger cross section and thus to a pressure difference that can be used for exhaust gas recirculation. Since the pressure in the combustion chamber, at least in most heaters, is close to atmospheric pressure (1 bar), small constrictions in the cross-section of the inlet area are sufficient for exhaust gas recirculation, in particular constrictions with 5 to 30% [percent] less cross-sectional area than that of the exit area. The proportion of recirculated combustion gases depends on the size of the restriction (and/or the design of elements for influencing flow) and an effective total cross-sectional area of the connecting openings. This can be between 2% and 20% [volume percent] of the mixture emerging from the outlet openings, preferably between 5% and 10%.

The entry area preferably forms approximately 2% to 20%, in particular 5% to 10%, of the axial length of the interior and has a lateral surface which is predominantly formed from connecting openings. Since only a small pressure difference can be utilized between the combustion chamber and the inlet area, it is important that the connecting openings have a sufficiently large effective cross-sectional area in order to suck in a quantity of exhaust gases that sufficiently influences the combustion temperature. This not only depends on the number of connection openings and their individual cross-sectional areas, but also their shape. The aim is therefore to provide as many and/or large connection openings as possible, as long as the size of the inlet area allows this and the stability of the burner body is not impaired.

The connection openings particularly preferably form a type of annular gap (at least one or, if necessary, several) which is interrupted by holding webs which carry the remaining burner body. Such an annular gap can have an axial width of 0.5 mm to 5 mm, in particular 1 mm to 3 mm.

It should be mentioned that when starting, such a burner may suck in additional air from the combustion chamber (which may then not yet contain any combustion gases), which means that the mixture intended for ignition is leaner than without recirculation. However, this can be compensated for by setting the mixture to be correspondingly richer during the ignition process or other measures with the same effect in order to ensure reliable ignition.

Fig. 1:

einen Brennerkörper mit Verbindungsöffnungen zur Verbrennungsgasrückführung in perspektivischer Ansicht und

Fig. 2:

einen zentralen axialen Längsschnitt durch den Brennerkörper von Fig. 1.

A schematic embodiment of the invention, to which it is not limited, and its mode of operation will now be explained in more detail with reference to the drawing. They represent:

Fig. 1:

a burner body with connection openings for combustion gas recirculation in a perspective view and

Fig. 2:

a central axial longitudinal section through the burner body Fig. 1 .

Fig. 1 and Fig. 2 show schematically a section of a combustion chamber 1 with a wall 2 in which there is a door 3 (or flap) on one Burner assembly is attached. A premix burner 4, which can be supplied with a mixture of air and fuel from a system not shown, has a burner body 5 which projects into the combustion chamber 1 in an axial direction (see arrow). The burner body 5 has an interior 6, which is composed of an entry area 7 and an exit area 8. In the outlet area 8 there are numerous outlet openings 9 through which the mixture can flow into the combustion chamber 1, where it is burned to form combustion gases. In the entry area 7 there is an element 11 for influencing the flow, in the present example a swirl generator. This causes a lower pressure to develop in the inlet area 7 during operation than in the outlet area 8 and also than in the combustion chamber 1. This results from the flow velocities in the inlet area 7, in particular in the area of the element 11, or in the outlet area 8. Through connection openings 10 in a lateral surface 12 of the inlet area 7, combustion gases are therefore sucked in from the combustion chamber 1 into the inlet area 7 during operation and mixed there with the remaining mixture, which is supported by a swirl generator or a swirling element.

Since generally only a small pressure difference between the inlet area 7 and the combustion chamber 1 can be used, the connecting openings 10 preferably have the largest possible cross-sectional area overall in order to be able to recirculate as much combustion gases as possible. Since the inlet area 7 is usually only a few millimeters long in the axial direction, there is not much lateral surface 12 available, so that the connecting openings 10 take up a large part of it, although the stability of the burner body 5 must be maintained. A type of annular gap 13 is advantageous as a connecting opening 10, which is interrupted by (as narrow and/or as few as possible) retaining webs 14 due to the stability of the burner body. Depending on the attachment of the element 11 for influencing the flow, this annular gap 13 can lie approximately in the same axial position as the element 11. He can run around the Burner body 5 may be designed with a width (in the axial direction) of 0.5 mm to 5 mm, preferably 1 mm to 3 mm, being interrupted by three to ten holding webs 14, which have a width (in the circumferential direction) of 1 mm to have 10 mm. Not shown, but applicable individually or together with the system described, is a cross-sectional narrowing of the inlet area 7, which leads to an (additionally) reduced pressure and enables or supports the described recirculation of combustion gases. Depending on their proportion, adding combustion gases to the mixture of air and fuel gas reduces the production of pollutants, especially NOX.

The present invention enables a reduction in the combustion temperature and thus a reduction in pollutant emissions in heaters, in particular those that are operated with hydrogen or hydrogen-containing fuel gases, through simple design changes to the burner of a heater.

Reference symbol list

1

combustion chamber

2

Wall

3

door (flap)

4

Premix burner

5

burner body

6

inner space

7

Entry area

8th

Exit area

9

Exit openings

10

Connection openings

11

Element for influencing flow

12

Lateral surface

13

Annular gap

14

retaining bars

Claims (4)

1. Heating device with a combustion chamber (1) and a burner arrangement, comprising a premix burner (4), which has a burner body (5) with an inner chamber (6), which burner body is attached to or in a wall (2) of the combustion chamber (1) and projects into this combustion chamber (1), to which a mixture of air and fuel gas can be supplied, and towards the combustion chamber (1) has a plurality of outlet openings (9) for the outlet of the mixture and for combustion outside the inner space (6) in the combustion chamber (1), wherein the inner space (6) is composed of an inlet region (7) starting from the wall (2) of the combustion chamber (1) in a region of up to 20 mm in an axial direction of the burner body (5) and an outlet region (8) with the plurality of outlet openings (9), wherein the inlet region (7) of the inner space (6) has at least one element (11) at least for swirl generation or turbulence, so that when the mixture flows through it a lower internal pressure is produced in the inlet region (7) than in the outlet region (8) and than in the combustion chamber (1), and wherein in the inlet region (7) connecting openings (10) are provided to the combustion chamber (1) through which the combustion gases are drawn in from the combustion chamber (1) and are mixed in the inlet region (7) with the remaining mixture.
2. Heating device according to claim 1, wherein the inner space (6) has a smaller flow cross-section in the inlet region (7) than in the outlet region (8).
3. Heating device according to any one of claims 1 or 2, wherein the inlet region (7) forms 1% to 20% of the inner space (6) and has a casing surface (12) which is predominantly formed by the connecting openings (10).
4. Heating device, according to any one of the preceding claims, wherein the connecting openings (10) form a kind of annular gap (13) interrupted by retaining webs (14), which annular gap has an axial width of 0.5 to 5 mm.

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