GB2224346A

GB2224346A - Boilers

Info

Publication number: GB2224346A
Application number: GB8919949A
Authority: GB
Inventors: Otto Doemoek
Original assignee: STREBELWERK AG
Current assignee: STREBELWERK AG
Priority date: 1988-09-02
Filing date: 1989-09-04
Publication date: 1990-05-02
Anticipated expiration: 2009-09-04
Also published as: GB8919949D0; FR2636124A1; DE3904635A1; CH677965A5; ATA193389A; GB2224346B; AT400980B

Description

BOILERS The present invention relates to a boiler.

2224346 In the case of boilers, one is generally encouraged to keep the flue gas temperature at the feed pipe to the chimney in a range of 120' to 220C. For this purpose, so-called three-pass boilers have become known. Three- pass boilers of this type have a closed, central combustion chamber with a front and rear wall, a first turn adjacent the rear wall to the second passes. With the second passes, the flue gases are conducted outside the combustion chamber towards the front wall, where they are conducted at a second turn into third passes, latter behind the in order to be collected from the rear wall of the combustion chamber in an exhaust gas collecting box and conveyed by way of a smoke tube into the chimney.

At the back of the combustion chamber, the flue gases have a temperature of 800' to 10SO'C, at the second turn from the second to the third pass a temperature of 3000 to 4500C and at the waste gas collecting box a temperature of 120' to 220'C.

Due to the known environmental pollution by nitric oxides, ways have already been investigated for, at least, reducing the production of NOX-gases. For this purpose it has already been proposed to mix Part of the burnt waste gases with the flame and thus to increase the temperature at the root of the flame.

Hitherto, two methods have become known:

1. Sucking-out the waste gases at the end of the boiler after the waste gas collector with a fan, and 2. Sucking-out the waste gases in the combustion chamber internally by means of the flame pulse.

Both methods each have a drawback. In method 1, at excessively low exhaust gas temperatures (<180'C), one has to expect the condensation of acid, as a result of which the return lines and the fan are sulphurised, particularly when the boiler is oil fixed.

In method 2, the recirculating waste gases are too hot and must be added to the flame in a very large quantity, in order to be effective for NO Xreduction.

Accordingly it is an object of the invention to supply the exhaust gas at a better suited temperature over the shortest route to the flame.

I According to the invention there is provided a boiler with a horizontal, cylindrically or prismatically constructed combustion chamber with a burner for liquid or gaseous fuels fixed in a front end wall, a first turn located on the rear end wall, leading to at least one second pass returning the flue gases from the combustion chamber towards the front wall, a second turn close to or in the front wall, for conducting the flue gases to a third pass by way of a flue gas collecting box and a smoke tube into a chimney, characterised by at least one bleeder opening in the second turn, in order to supply waste gases from said second turn to the burner.

The pressure difference between the turning point can be produced as required by the injector effect of the combustion air, the flame or by an exhaust gas fan. The hot gases tapped off may also be supplied to the suction side of the burner.

Specific embodiments of the invention will now be described by way of example with reference to the accompanying drawings, in which:- Fig.1 is a sectional view through a three-pass boiler; 1 1 Fig.2 is a section on the line II-II through the front wall part of Fig.1; Fig.3 is a sectional view, similar to Fig.1, of a second embodiment of the invention; Fig.4 is a section on the line IV-IV of Fig.3; Fig.5 is a sectional view, similar to Fig.1, of a third embodiment of the invention; Fig.5a is a sectional view, similar to Fig-5, of a fourth embodiment of the invention; and Figs.6 to 8 are each section views of a boiler with second and third passes located at the top.

The three-pass boiler according to Fig.1 comprises a combustion chamber 1 with a front end wall 11, in which a burner 10 is installed. The rear end wall 12 is is connected to the cooling jacket 14 between the second and third passes 3, 5 respectively and forms a first turn 2 at the end of the first pass behind the jacket 13 of the combustion chamber 1. Provided beside the front end wall 11 at the ends of the second passes is a second turn 4 around the cooling jacket 14 and on the outside, a third jacket 15, which likewise 1 acts as a cooling jacket, surrounds the boiler.

According to the invention, waste gas is supplied from the second turn 4 to the combustion air, which thus has a temperature in excess of 3000C.

The point for the removal of the exhaust gas can be constructed in various ways, it is important that at least one bleeder opening 8 is provided in the second turn 4.

As shown by the sectional view according to Fig.2, an insert 17 may be provided between the front end wall 11 and the door 16, which insert 17 comprises two concentric annular channels, whereof the outer annular channel 8b lies below the bleeder openings 8 and the inner annular channel 9 lies below the openings 9a. The connection between the two annular channels 8b, 9 may be formed by a plurality of radial channels 8a. The outer annular channel 8b could also be constructed directly as the turn 4.

Thus, the pressure difference necessary for recirculation can be produced according to the boiler construction with the injector effect of the combustion air. Naturally, a fan may also be provided in order to return a greater proportion of the waste gases or by means of an additional regulation and control of the fan, a proportion adapted to the instantaneous conditions.

As shown in Figs.3 and 4, as already explained above, the outer annular channel 8b may also directly be the space for the front turn 4 in Figs.1 and 2. Instead of the direct supply of flue gases to the root of the flame, in this embodiment there is provision for the supply of the flue gases from the second turn 4 by means of a pipe 18 to suction box 20 of the burner 10.

A restrictor device 19 may be incorporated in the pipe 18, by which device the quantity of waste gases drawn off can be regulated independently of the pipe. Fig.4 is a sectional view through the front wall 11 which does not have the radial channels 8a of the embodiment of Figs.1 and 2. The burner 10 is thus inserted in a clearance-free manner in the wall 11.

Fig.5 shows a variation of the arrangement according to Fig.3. Disposed on the door 16, close to the bleeder opening 8, is a fan 21, by which flue gases can be supplied from the second turn 4 by way of the pipe 18 with the restrictor 19 to the suction box of the burner 10. Fig.5a shows a further variation, according to which flue gases are supplied from the second turn 4 to the burner 10 between the combustion fan 21 and pressure disc.

1 Z 1 7 - Whereas the embodiments of Figs.1, 3 and 5 comprise cylindrically and concentrically disposed jackets 13, 14, 15, Figs.6 to 8 show a boiler in which the second and third passes 3 and 5 are disposed above the combustion chamber 1, as shown clearly in Fig.7. However, even in a boiler of this type, first turns 2 are located at the rear and second turns 4 at the front close to the front end wall. The second passes 3 are thus four parallel channels, as illustrated in Figs.7 and 8. Since, on the one hand, the flue gases cool down and, therefore, take up a smaller volume and on the other hand, a quantity of flue gas is also discharged, two parallel channels, however, with somewhat greater width, are sufficient for the third passes 5.

According to this embodiment of the invention, flue gases are removed at the front wall 11 from the second turn 4, and, as shown in Fig-6, supplied by a pipe 18 to the suction box 20 of the burner 10. Here also a restrictor device 19 can be provided. The use of a fan similar to the above-described embodiments of Figs.5 and 5a is also possible.

The removal of the waste gases at the second turn, that is to say at the end of the second pass, also has the advantage that a pipe between the waste gas collector and the burner can be dispensed with, but the 1 1 Temperature of the recirculating waste gases is substantially lower than when returning the waste gases from the first pass, as is the case with internal recirculation. With a return rate of 10% of the waste gases and a bleeding temperature of the waste gases of 400'C, the temperature of the waste gas/air mixture in the burner housing amounts to approximately 580C. Both with oil as well as with gas-firing, the temperature lies above the water vapour dewpoint and for this reason no intensive formation of condensate is to be expected.

- 1

Claims

1. A boiler with a horizontal, cylindrically or prismatically constructed combustion chamber (1) with a burner (10) for liquid or gaseous fuels fixed in a front end wall (11), a first turn (2) located on the rear end wall (12), leading to at least one second pass (3) returning the flue gases chamber (1) towards the front wall from the combustion (11), a second turn (4) close to or in the front wall (11), for conducting the flue gases to a third pass (5) by way of a flue gas collecting box (6) and a smoke tube (7) into a chimney, characterised by at least one bleeder opening (8) in the second turn (4), in order to supply waste gases from said second turn to the burner.

2. A boiler according to Claim 1, characterised in that a plurality of bleeder openings (8) arranged in a circle are provided, which openings lead into a first annular channel (8b) behind the front end wall (11) and from there open by means of radial channels (8a) into a second annular channel (9) around the burner (10), and that a plurality of openings (9a) connect the second annular channel (9) to the burner (10).

3. A boiler according to Claim 2, characterised in that a first annular channel (8b), radial channels (8a) - 10 and second annular channel (9) are disposed in a door (16), on which the burner (10) is also flange-mounted.

4. A boiler according to Claim 1, characterised by a mechanical ventilation device (21), for supplying to flue gases from an annular channel (8b) to a mixing device by way of a suction connection (20) of the burner (10).

5. A boiler according to Claim 1, characterised by a mechanical ventilation device (21) with a connecting pipe (18) to a suction connection (20) of the burner (10), for supplying flue gases from an annularchannel (8b) to the burner (10) at said suction connection (20).

6. A boiler according to Claim 1, characterised by a bleeder pipe (18') between the turn (4) and a suction connection (20) of the burner (10), a restriction device (19) in the bleeder pipe (18'), for supplying flue gases directly and without mechanical ventilation device to the burner (10).

7. A boiler substantially as described herein with reference to the accompanying drawings.

Published 1990&tTheP&tentOMce.St&teHouEie.68'71 High Holborn. IoondonWClR4TP. Further copies maybe obtained from The Patent=ce Wes Branch, St Mary Cray. Orpington. Kent BR5 3RD- Printed by Multiplex tecb=ques ltd, St Mary Cray. Kent. Cor. 1187 1