WO2004102071A1

WO2004102071A1 - Burner

Info

Publication number: WO2004102071A1
Application number: PCT/NL2004/000337
Authority: WO
Inventors: Albertus Van Der Weide; Willem Charles Mallon; Gjalt Christiaan Tiekstra
Original assignee: N.V. Nederlandse Gasunie
Priority date: 2003-05-16
Filing date: 2004-05-17
Publication date: 2004-11-25
Also published as: NL1023439C2

Abstract

The invention relates to a burner comprising an inlet side (3) for the supply of an air-fuel mixture (A) and a combustion side (4) where the air-fuel mixture can be burned. The two sides are connected by a feed-through channel (2) in which means are provided for preventing a flame from penetrating into the feed-through channel. In accordance with the invention the means are formed by a second feed-through channel (5) in the above-mentioned feed-through channel, having a first (6) end oriented toward the inlet side and a second end (7) oriented toward the combustion side, with the end at the second side taperingly widening toward the combustion side, with the widened portion being at least partly located in the feed-through channel.

Description

Burner

The present invention relates to a burner comprising a feed-through channel for an air-fuel mixture, which feed- through channel at an inlet side possesses a first end for the supply of an air-fuel mixture and at a combustion side a second end where the air-fuel mixture can be burned, wherein the feed-through channel connects the inlet side with the combustion side, and means are provided in the feed-through channel for preventing a flame from penetrating into the feed-through channel. In incinerators, combustion boilers and the like burners are employed that have a capacity of, for example, 10 kW to 10 MW. Such burners have to meet various requirements, both with respect to safety and environment. As far as safety is concerned, a flame is not allowed to penetrate into or at least not far, into the burner because if a flame reaches the first end, the consequence could be an explosion. Whether a flame is able to penetrate into the burner depends on a number of factors, in particular on the velocity with which the air-fuel mixture is supplied and on the flame propagation ve- locity. When the second is greater than the first, the danger alluded to arises. The flame temperature and flame stability need to be controlled strictly in order to keep the emission of noxious gasses, in particular nitrogen oxides, as low as possible. To this end the flame should be close to the burner. US 5,879,148 describes a burner., which makes it possible to meet the safety as well as the environmental requirements.

The known burner has indeed made it possible to comply with the environmental requirements that in the course of time have become increasingly demanding, but is relatively complex. Moreover, when the burner is operated under difficult circumstances, for example, in relatively narrow furnaces, its flame is insufficiently stable.

The present invention therefore provides a burner of the kind mentioned in the preamble, characterised in that the means are formed by a second feed-through channel in the above-mentioned feed-through channel, having a first end oriented toward the inlet side and a second end oriented toward the combustion side, with the end at the second side taper- ingly widening toward the combustion side, with the widened portion being at least partly located in the feed-through channel.

According to the invention, this provides a burner which, in addition to having a very simple construction, is operationally very safe. A cannot penetrate into the burner. The burner has a very low flow resistance, so that - in the unlikely event of flame break-through - there is no build-up of high pressure. The nitrogen oxide levels reached during operation are very low, even in narrow furnaces. In practice, the second feed channel will be disposed coaxially in the second feed channel.

The second end of the second feed-through channel preferably exits at the second end of the first feed-through channel.

This provides a burner with a stable central flame into which the outer gas-air mixture is injected.

According to a first preferred embodiment, the ratio Ri of i) the flow-through area of the first feed-through channel and ii) the flow-through area of the second feed-through channel at the combustion side is smaller than the ratio Rπ of i) the flow-through area of the first feed-through channel and ii) the flow-through area of the second feed-through channel at the inlet side.

This is an effective manner of creating zones in the burner, which have an increased air-fuel mixture gas veloc- ity, and which thus cannot be passed by a flame penetrating into the burner. The first and second ends of the first and second feed-through channels need not lie in the same plane. In other words, one end of a feed-through channel may extend beyond the end of the other feed-through channel. When in the present application reference is made to the (area) ratios of ends, these must be calculated at the position where both channels are still present, i.e. at the shortest end.

It is preferred for R_ to be. between 2.5 and 25 and Rn between 10 and 70, and more preferably between 7.5 and 15 and between 30 and 50, respectively.

In accordance with a preferred embodiment, the internal wall of the first feed-through channel is reduced be- tween the widening and the first end of the second feed channel, so that the ratio R_m of i) the flow-through area of the first feed-through channel and ii) the flow-through area of the second feed-through channel at the reduction is smaller than the ratio Ri of i) the flow-through area of the first feed-through channel and ii) the flow-through area of the second feed-through channel at the combustion side.

The reduction assists in preventing the flame from penetrating into the burner via the first feed channel.

It is preferred for Rm to be between 1.3 and 3 and Ri to be between 2.5 and 25, and more preferably between 1.4 and 1.7 and between 7.5 and 15, respectively.

The reduction is preferably provided with inlet openings for the supply of a gas.

Gasses to be considered are in particular an inert gas or a substantially inert gas, especially flue gas produced during combustion. This allows the temperature of the flame to be decreased to a desirable value, which further limits the emission of nitrogen oxides. The inlet openings are preferably provided slightly downstream from the narrow- est portion of the reduction.

The present invention will now be further elucidated by way of an exemplary embodiment and a drawing, in which

Fig. 1 shows a burner according to the invention; and Fig. 2 shows an alternative embodiment of a burner according to the invention.

Fig. 1 shows a burner 1 according to the invention with a feed-through channel 2 for an air-fuel mixture A. The feed-through channel 2 has a first end 3 oriented toward the inlet side for air-fuel mixture A and a second end 4 at a side, the combustion side, where the air-fuel mixture A can be burned. The feed-through channel connects the inlet side with the combustion side. In the feed-through channel 2 a second feed-through channel 5 is provided. This second feed- through channel 5 also has a first end 6 and a second end 7. According to the invention, the second feed-through channel 5 widens taperingly at a second end 7. The widening may be re- alised in any manner, step-wise or conical, but is preferably cup-shaped as shown. The widening is in the feed-through channel 2. In the embodiment shown, the second end 7 of the second feed-through channel 5 is located in the first feed- through channel 2, but this is not obligatory, as long as the widening is located inside the first feed-through channel 2. Advantageously, the burner 1 of Fig. 1 is provided with a reduction 8 in the first feed-through channel 5. This reduction is preferably located between the widening of the second feed-through channel 5 and the first end of the second feed-through channel 5. The reduction 8 is preferably provided with inlet openings 9, via which a part of the flue gas B that stems from the combustion of the air-gas mixture A at the combustion side, can be admixed to the air-gas mixture A in the feed-through channel 2. In this way the concentration of nitrogen oxides in the flue gas B can be reduced to well below 10 ppm.

Fig. 1 shows by means of dotted lines cross-sections indicated with roman numerals, which are used above for the definition of Ri, Rπ, R_ra. Fig. 1 indicates velocities V for the first and the second feed-through channel 2, 5 at different positions over the length of the burner 1 and compares velocities inside a feed-through channel 2, 5.

Fig. 2 shows an alternative burner 1, the various reference numerals of course relating to the matters discussed in Fig. 1. Fig. 2 shows a conical widening of the second feed-through channel 5. Furthermore, between the interior wall of the feed-through channel 2 of the external wall and the second feed-through channel 5, fins 10 are provided to prevent turbulence in the air-gas mixture A. To this end the fins 10 are arranged parallel to the central axis of the feed-through channel 2. While it is possible to arrange them, for example, tangentially, radial positioning is preferred.

Claims

1. A burner comprising a feed-through channel for an air-fuel mixture, which feed-through channel at an inlet side possesses a first end for the supply of an air-fuel mixture and at a combustion side a second end where the air-fuel mix- ture can be burned, wherein the feed-through channel connects the inlet side with the combustion side, and means are provided in the feed-through channel for preventing a flame from penetrating into the feed-through channel, characterised in that the means are formed by a second feed-through channel in the above-mentioned feed-through channel, having a first end oriented toward the inlet side and a second end oriented toward the combustion side, with the end at the second side ta- peringly widening toward the combustion side, with the widened portion being at least partly located in the feed- through channel.

2. A burner according to claim 1, characterised in that the second end of the second feed-through channel exits at the second end of the first feed-through channel.

3. A burner according to claim 1 or 2, characterised in that the ratio R_ of i) the flow-through area of the second feed-through channel and ii) the flow-through area of the second feed-through channel at the combustion side is smaller than the ratio Rπ of i) the flow-through area of the first feed-through channel and ii) the flow-through area of the second feed-through channel at the inlet side.

4. A burner according to claim 3, characterised in that Ri is preferably between 2.5 and 25 and Rπ between 10 and 70, and more preferably between 7.5 and 15 and between 30 and 50, respectively.

5. A burner according to one of the preceding claims, characterised in that the internal wall of the first feed-through channel is reduced between the widening and the first end of the second feed channel, so that the ratio R_m of i) the flow-through area of the first feed-through channel and ii) the flow-through area of the second feed-through channel at the reduction is smaller than the ratio R of i) the flow-through area of the first feed-through channel and ii) the flow-through area of the second feed-through channel at the combustion side.

6. A burner according to claim 5, characterised in that Rm is preferably between 1.3 and 3 and Ri between 2.5 and 25, and more preferably between 1.4 and 1.7 and between 7.5 and 15, respectively.

7. A burner according to claim 5 or 6, characterised in that the reduction is provided with inlet openings for the supply of a gas.