AU2007202566A1

AU2007202566A1 - Boiler tube wall and device for cleaning thereof

Info

Publication number: AU2007202566A1
Application number: AU2007202566A
Authority: AU
Inventors: Jorma Tuomaala
Original assignee: Alstom Technology AG
Current assignee: Arvos GmbH
Priority date: 2006-06-06
Filing date: 2007-06-05
Publication date: 2007-12-20
Anticipated expiration: 2027-06-05
Also published as: FI20070447A; CN101122451B; DE102007024286A1; DE102007024286B4; FI20070447A0; CN101122451A; FI122779B; AU2007202566B2

Description

001 Section 29 Regulation 3.2(2)

AUSTRALIA

INO

IC

Patents Act 1990 COMPLETE SPECIFICATION STANDARD PATENT Application Number: Lodged: Invention Title: Boiler tube wall and device for cleaning thereof The following statement is a full description of this invention, including the best method of performing it known to us:

DESCRIPTION

O

BOILER TUBE WALL AND DEVICE FOR CLEANING THEREOF ;The invention relates to a boiler tube wall which defines a gas duct through which hot, dust- or ash-laden gases flow and which is formed from a plurality of substantially vertically running finned tubes or a tube-web-tube combination carrying a working medium and a knocking or striking device is arranged on the outside of the boiler tube wall, which device imparts the knocking or impact energy to the boiler tube wall for cleaning dust or ash Swhich has accumulated on the inside of the boiler tube wall.

Boiler tube walls of the aforesaid species having one or more knocking or striking devices on their outwardly directed side, which are used to clean dust or ash which have accumulated on the boiler tube wall on the inside of the boiler or the side of the boiler tube wall facing the gas duct are generally known. Such devices are required to maintain efficient heat transfer from the hot gas flowing through the gas duct to the working medium flowing through the boiler tube which, however, is reduced by boiler tube walls covered with ash and dust.

US 3,835,817 has disclosed a device by which means boiler tubes or boiler tube walls whose tubes are not joined to one another, can be cleaned from outside. This is accomplished with a driven striking hammer which, being spring-mounted using a pair of spring disks, delivers an impact pulse to the end of a boiler-tube-wall division block. This impact pulse produces high accelerations which shake deposits or slag off the boiler tubes or the boiler tube wall. However, this device has proved rather impractical for use in boiler tube walls in which so-called ribbed walls or tube-web-tube combinations are used, i.e.

boiler tubes which are each interconnected and thus form a gastight tube wall. The problem lies in the fact that such boiler tube walls are substantially more rigid compared V:\PA\SHG310 C_engl.doc 2 with the first-mentioned tubes and thus an impact pulse at the end of a boiler-tube-wall division block exhibits an unsatisfactory cleaning effect.

Document DE 202 11 156 Ul has disclosed a device for removing baked-on dust on boiler walls, where at least one impact profile engages in an opening of the boiler wall on the outside of the boiler wall and wherein the impact profile is connected to at least one anvil profile which anvil device can be acted upon by at least one hammer, in particular a drop hammer. Thus, in this device the impact profile does not hit directly against the boiler wall but directly against the baked-on dust located on the inside of the boiler wall since the impact profile projects through an opening in the boiler wall and when an impact is initiated, comes in contact with the baked-on dust. A disadvantage with this device is that as a result of the openings in the boiler wall required for penetration of the impact profiles, the boiler itself is no longer gastight because of the openings to the atmosphere and must be sealed towards the external atmosphere by very complex sealing devices at each individual device. Another disadvantage is that the impact profile is directly exposed to gases and deposits in the boiler and is thus exposed to erosion and corrosion.

The object of the present invention is now to provide a boiler tube wall and device for cleaning thereof where the aforesaid disadvantages are avoided. In particular, the invention should provide a device by which means a boiler tube wall which defines a gas duct through which hot, dustor ash-laden gases flow and which is formed from a plurality of substantially vertically running finned tubes or a tube-web-tube combination carrying a working medium can be largely cleaned from dust or ash which has accumulated on the inside wall of the boiler tube wall.

The aforesaid object is achieved by the characterising features of claim 1. The solution provides that in order to make the knocking or impact energy on the boiler tube wall 3 more uniform, said boiler tube wall is provided with a horizontally running impact beam separated from the boiler tube wall by a distance X, which is connected to the boiler tube wall by a plurality of vertically arranged ribs, these ribs being configured elastically over their extension between the boiler tube wall and impact beam in the lateral direction in order to absorb different horizontal linear expansions of the boiler tube wall and the impact beam.

Advantageous embodiments of the invention can be deduced from the dependent claims.

The solution according to the invention provides a boiler tube wall with a device for cleaning said wall, which has the following advantages: A single impact pulse can be transferred to the boiler tube wall over a large area, The boiler tube wall can expand independently and irrespective of the different thermally-induced linear expansions of the impact beam, as a result of the free and unhindered thermally induced linear expansion of the boiler tube wall and impact beam, cracks in these components and in the welded seams joining the two parts are avoided, since larger or broader impact beams can be used, only a small number of impact beams is required per boiler tube wall.

In an advantageous embodiment, the vertical ribs are connected to the fin located between the boiler tubes or to the web of the boiler tube wall located between the boiler tubes. As a result of this measure, the impact pulse is transferred to the rib or the web and not to the tube. No attenuation of the pulse occurs as a result of the fixed connection.

It is appropriate if the ribs are each arranged at a distance of two tube pitches (2 x t) over the length of the impact beam. The impact pulse is thereby introduced uniformly into the boiler tube wall.

4 In a particularly advantageous manner, the ribs are welded to the boiler tube wall and to the impact beam. As a result of this measure, the ribs are connected to the boiler tube wall and the impact beam by simple and effective means.

In an advantageous embodiment of the invention, the ribs each consist of two parts when viewed over their vertical extension. This measure ensures that the individual ribs are substantially more accessible to welding.

In an expedient manner, the impact beam is configured as a rectangular or other closed hollow profile or as a solid profile. It can also be configured as a double-T or Uprofile or another open profile. This ensures that firstly the impact beam has sufficient stiffness and secondly that it is simple to provide as a complete semi-finished product.

An advantageous embodiment of the invention provides that the impact beam is configured centrally with one or two horizontally arranged ribs for connection to the boiler tube wall. Axial forces which occur in the impact beam can be absorbed by introducing into the boiler tube wall.

In an advantageous embodiment of the invention, the impact beam extends over a length L of 0.5 to 5.0 m. This ensures that boiler tube walls of various width are covered.

The distance X between the boiler tube wall and the impact beam is appropriately between 10 and 1000 mm. As a result of this measure, the impact beam can then also remain free for a striking device if, for example, the outside of the boiler tube wall is insulated.

In order to achieve optimal cleaning of the boiler tube wall, it is advantageous if, when a plurality of impact beams are used, the distance of the impact beams from one another in the vertical direction is 2 to 5 m.

5 For direct transmission of the impact effect or the impact pulse from the impact beam to the boiler tube wall, the ribs in the front region, i.e. at the front or outwardly pointing side of the impact beam can be welded to said beam.

In order to transfer the impact energy most efficiently from the impact beam to the boiler tube wall, it is appropriate to arrange the ribs perpendicularly to the boiler tube wall and therefore also perpendicularly to the impact beam.

Exemplary embodiments of the invention are explained hereinafter in detail with reference to the drawings and the description.

In the figures: Fig. 1 is a schematic longitudinal section through a boiler tube which is exposed to an impact pulse (according to the prior art), Fig. 2 is a perspective view of the propagation of a shock wave triggered by an impact pulse within a plane for the example of a water surface, Fig. 3 is a perspective view of a boiler tube wall with a double-T support attached thereto as an impact beam according to the prior art, Fig. 4 is a perspective view of a boiler tube wall with a hollow-profile support attached thereto as an impact beam according to the prior art, Fig. 5 is a schematic cross-section through a boiler tube wall with impact beam according to the invention, where the cross-section shows the "cold state", i.e. the boiler tube wall of a boiler is out of operation, 6 Fig. 6 as Fig. 5 but with different linear expansions as a result of different heating of the boiler tube wall and the impact beam during operation of the boiler, Fig. 7 is a perspective view of an alternative embodiment of the boiler tube wall according to the invention and the device for its cleaning, Fig. 8 is a perspective view of another alternative embodiment of the boiler tube wall according to the invention and the device for its cleaning, Fig. 9 is a schematic view of a boiler tube wall according to the invention where finned tubes are used, Fig. 10 is a schematic view of a boiler tube wall according to the invention where a tube-web-tube combination is used.

The inside 6 of a boiler tube wall 1 which defines a gas duct 7 through which hot, dust- or ash-laden gases flow and which is formed from a plurality of substantially vertically running finned tubes 2 (Fig. 9) or a tube-webtube combination 3, 4 (Fig. 10) carrying a working medium can be cleaned of dust or ash using a knocking or striking device which is arranged on the outside 5 of the boiler tube wall 1 and in which the knocking or impact energy is imparted to a point on the boiler tube wall 1. In this case, a pair of spring disks 13 which imparts the impact or the impulse to the object, i.e. the boiler tube wall 1 can be adapted so that the generated impulse corresponds to a sine half-wave of about 1000 Hz. If the impulse receiver is a boiler tube 2, 3, the impulse is divided into two sine waves which propagate further on both sides of the impulse point 14. In the case of a frequently used 38 x 4.5 boiler tube (outside diameter 38 mm, wall thickness 4.5 mm), the length of the sine half-wave is about 300 mm. If the boiler tube 2, 3 is freely suspended, the impulse propagates very far almost free from losses. Figure 1 shows a boiler tube 2, 3 schematically in longitudinal section with an impulse point 14 at which an impact pulse 15 is supplied to the 7 boiler tube 2, 3 and thus generates a shock wave 16 on both sides of the impulse point 14. In the immediate proximity of the impulse point 14, the boiler tube 2,3 is already at rest.

In a thin, flat wall such as a boiler tube wall 1, the distribution of a punctiform impact pulse 15 is more difficult. The shock wave 16 propagates circularly and the length of the shock wave 16 becomes increasingly larger, thereby losing its effect and magnitude. Such a phenomenon is observed, for example, in water when an impulse is triggered by a falling object, see Fig. 2.

In order to transmit a sufficient impulse strength, for example, to a sufficient region of a thin wall, the impact pulse 15 directed to the impulse point 14 must be very strong. This however causes much too high stressing or tension at the impact or impulse point 14. In order to prevent such high stresses, the impact pulse 15 can be propagated for example by means of a welded-on beam, for example, a profile support. In the beam the half-wavelength of the impact pulse 15 is about 400 to 500 mm. If the wall consists of a flat steel sheet of 8 mm, the half-wavelength of the impact pulse 15 is only 137 mm. In this case, the shock wave 16 acquires an elliptical shape equivalent to a more linear pulse front and thus much stronger pulse power than from a punctiform impulse point 14.

Compared to the application of an impact pulse 15 to a flat steel sheet, the application of an impact pulse 15 to a boiler tube wall 1 formed of finned tubes 2 or from a tubeweb-tube combination 3, 4 is even more difficult. This is because the fins 11 or webs 4 between the boiler tubes 2, 3 are only 6 to 8 mm thick but the boiler tubes 2, 3 themselves are much stiffer than the fins 11 or webs 4. The boiler tube wall 1 consisting of finned tubes 2 is, for example, approximately 25 times stiffer about its horizontal axis than about its vertical axis. It is therefore difficult to bring about a shock wave 16 in flat 8 elliptical form with an impact pulse 15 on such a boiler tube wall 1.

Figure 3 shows prior art which uses a 140 mm double-T support as the impact beam 8. At the finned tubes 2 of the boiler tube wall 1 filled with water as the working medium, a shock wave 16 having a half-wavelength of 280 mm is generated following an impact pulse 15. The double-T beam itself is partially loaded with the weight of the tube wall and following the impact pulse 15, exhibits a shock wave 16 having a half-wavelength of 424 mm. The front profile of the shock wave 16 is only slightly elliptical. Figure 4 shows prior art in which a 250 x 150 x 10 mm box profile is used as the impact beam 8. When an impact pulse 15 is applied to this impact beam 8, a shock wave 16 having a half-wavelength of 743 mm is generated. The front profile of this shock wave 16 is clearly better than the front profile of the shock wave 16 shown in Figure 3, i.e. the impact pulse 15 is transmitted to the boiler tube wall 1 by the box profile with higher effect or efficiency.

The main problem with using an impact beam 8 is seen in the transmission of the impact pulse 15 from the impact beam 8 into the boiler tube wall 1. Attempts have been made to press the impact beam 8 onto the boiler tube wall 1. During pressing, the impulse is only transmitted to the wall in an attenuated form. Instead of merely pressing-on the impact beam 8, joining the impact beam 8 to the boiler tube wall 1 by welding can be seen as a single useful method for cleaning the boiler tube wall 1.

However, welding the impact beam 8 to the boiler tube wall 1 brings new problems with it since the two parts experience different temperatures during operation and thus are subjected to very different expansion. The temperature of the boiler tube wall 1 can vary very rapidly during operation, particularly in the fins 11 or webs 4 between the boiler tubes 2, 3. The large temperature differences cause large stresses and ultimately fatigue cracks between the impact beam 8 and the boiler tube wall 1. These cracks 9 rarely cause leaks in the boiler tube wall 1 but the impact pulses 15 provided for cleaning cannot be transmitted further as a result of the cracked locations.

The present invention solves the aforesaid problems whereby, in order to make the knocking or impact energy on the boiler tube wall 1 more uniform, said boiler tube wall is provided with a horizontally running impact beam 8 as shown in Figure 5, which is separated from the boiler tube wall 1 by a distance X and which is connected to the boiler tube wall 1 by a plurality of vertically arranged ribs 9, these ribs 9 being configured elastically over their extension between the boiler tube wall 1 and impact beam 8 in the lateral direction in order to absorb different horizontal linear expansions of the boiler tube wall 1 and the impact beam 8, and wherein for the ribs 9 according to their elastic formation in the lateral direction a lateral deflection E can be absorbed in accordance with the relationship "lateral deflection E 0.001 to 0.1 times the distance X between the boiler tube wall 1 and the impact beam Different horizontal linear expansions means on the one hand the horizontal linear expansion of the boiler tube wall 1 over its width and on the other hand, the horizontal linear expansion of the impact beam 8 over its length L. The impact pulse 15 is applied by means of the knocking or striking device in the middle of the rigid and heavy impact beam 8. This beam 8 preferably has a length of to about 5 m and can keep equally wide boiler tube wall zones clean. Each horizontal impact beam 8 on the boiler tube wall 1 comprises a preferable height of action of about 2 to 5 m of the boiler tube wall 1. The impact beam 8 transmits the impact pulse 15 to both ends of the impact beam 8. The impact beam 8 can be coupled or connected to every other fin 11 or every other web 4 of the boiler tube wall 1. This coupling or connection is made with the vertically arranged ribs 9 described in detail above, the ribs 9 being welded at their respective ends to the impact beam 8 as well as the boiler tube wall 1 by means of weld seam 12.

10 A plurality of vertically arranged ribs 9 means that the impact beam 8 is configured over its length L with at least three, but usually with more than three ribs 9. In theory, one rib 9 can be arranged between the boiler tube wall 1 and impact beam 8 after each pipe pitch t. Figures 5 to show an advantageous arrangement in which one rib 9 is arranged after every other tube pitch, i.e. 2 x t. A triple or multiple tube pitch is also feasible for arranging a rib 9.The height of the respective rib 9 or its vertical extension is restricted to the region of the impact beam 8.

It will protrude or project above and below the impact beam 8 with a sufficient excess so that the respective rib 9 can be welded to the boiler tube wall 1 as well as to the impact beam 8 and can reliably transmit the knocking or impact energy from the beam 8 into the boiler tube wall 1.

In this case, the ribs 9 are advantageously arranged perpendicular to the boiler tube wall 1. Hammers or the like, not shown, are used as the knocking or striking device, for example, which can be driven mechanically, hydraulically, pneumatically or also electrically.

Figure 6 shows the device according to the invention for cleaning a boiler tube wall 1 during operation, in the hot state of the boiler tube wall 1. In this case, as a result of the high wall temperatures (up to above 400 0

C),

the boiler tube wall 1 expands considerably more substantially than the impact beam 8. The difference in expansion formed in the horizontal direction and when viewed parallel to the boiler tube wall 1 between the two parts 1 and 8 is compensated by the elastic ribs 9. For better illustration this is shown highly disproportionately in Figure 6. In this case, the elastic ribs 9 absorb different lateral deflections E between the impact beam 8 and boiler tube wall 1 over the extension or length L of the impact beam 8. Whilst the ribs 9 arranged centrally on the impact beam 8 must absorb virtually no deflection E, the elastic ribs 9 arranged at the respective outer end of the impact beam 8 absorb the greatest deflection E.

11 With this device, it is possible to keep clean very broad 0 panels or zones of the boiler tube wall 1 using a knocking

O

Sor striking device. As a result of the size and weight of the impact beam 8, larger hammers can be used for knocking or striking and the number of required hammers or knocking devices can thus be substantially reduced.

Figure 7 shows a boiler tube wall 1 according to the N invention with a device for its cleaning, where a hollow profile is used as the impact beam 8. Each of the ribs 9 Sarranged vertically between the boiler tube wall 1 and the s impact beam 8 are configured in two parts 9a, 9b and joined Sto the boiler tube wall 1 and to the impact beam 8 by means of a welded seam 12. As a result of the slender and therefore very elastic configuration of the ribs 9a, 9b with thin wall thicknesses, the impact beam 8 can be positioned right in the vicinity of the boiler tube wall 1, i.e. the distance X between the boiler tube wall 1 and impact beam 8 can be kept small. The impact pulse 15 is transmitted to the impulse point or the anvil 14 arranged centrally on the impact beam 8. The impact pulse 15 formed by the hammer strike at around 1000 Hz is transmitted by means of the disk or plate spring 13.

The impact pulse 15 can possibly also be caused by axial vibrations of the impact beam 8. In order to prevent this, it is possible to insert one or two horizontally arranged ribs 10 at the centre of the impact beam 8 between this and the boiler tube wall 1 and thereby replace the rib 9 or ribs 9a, 9b otherwise located at this point according to Figure 8.

For optimum introduction of the impact pulse 15 from the impact beam 8 into the boiler tube wall 1, the ribs 9a, 9b according to Figures 7, 8 are welded to the impact beam 8 in its front region. That is, the ribs 9a, 9b sit predominantly on the front edge of the impact beam 8 and not at the rear edge which lies closer to the boiler tube wall 1.

12 REFERENCE LIST 1 Boiler tube wall 2 Finned tube or boiler tube 3 Tube or boiler tube 4 Web Boiler outside 6 Boiler inside 7 Gas duct 8 Impact beam 9 Rib, vertical 9a Rib, vertical, divided into two 9b Rib, vertical, divided into two Rib, horizontal 11 Fin 12 Welded seam 13 Disk or plate spring 14 Impulse point Impact pulse 16 Shock wave

Claims

1. A boiler tube wall which defines a gas duct (7) through which hot, dust- or ash-laden gases flow and which is formed from a plurality of substantially vertically running finned tubes or a tube-web-tube combination 4) carrying a working medium and a knocking or striking device is arranged on the outside of the boiler tube wall which device imparts the knocking or impact energy to the boiler tube wall for cleaning dust or ash which has accumulated on the inside of the boiler tube wall characterised in that in order to make the knocking or impact energy on the boiler tube wall more uniform, said boiler tube wall is provided with a horizontally running impact beam separated from the boiler tube wall by a distance which is connected to the boiler tube wall by a plurality of vertically arranged ribs these ribs being configured elastically over their extension between the boiler tube wall and impact beam in the lateral direction in order to absorb different horizontal linear expansions of the boiler tube wall and the impact beam and wherein for the ribs 9 according to their elastic formation in the lateral direction a lateral deflection can be absorbed in accordance with the relationship lateral deflection 0.001 to 0.1 times the distance between the boiler tube wall and the impact beam

2. The boiler tube wall according to claim 1, characterised in that the ribs are connected to the fin (11) or to the web of the boiler tube wall

3. The boiler tube wall according to claim 1, characterised in that the ribs are each arranged at a distance of two tube pitches (2 x t) of rhe boiler tube wall over the length of the impact beam V:\PA\SHG310_Cengl.doc 2

4. The boiler tube wall according to claim 1 or 2, characterised in that the ribs are each connected to the boiler tube wall and the impact beam by means of welded seams (12) The boiler tube wall according to claim 1, characterised in that the respective ribs each consist of two parts (9a, 9b) when viewed over their vertical extension.

6. The boiler tube wall according to claim 1, characterised in that the impact beam is configured as a rectangular or other closed hollow profile or as a solid profile.

7. The boiler tube wall according to claim 1, characterised in that the impact beam is configured as a double-T or U-profile or another open profile.

8. The boiler tube wall according to claim i, characterised in that the impact beam is configured centrally with one or two horizontally arranged ribs (10) for connection to the boiler tube wall (1)

9. The boiler tube wall according to claim 1, 6 or 7, characterised in that the impact beam extends over a length of 0.5 to 5.0 m. The boiler tube wall according to claim 1, characterised in that the distance between the boiler tube wall and the impact beam is between 10 and 1000 mm.

11. The boiler tube wall according to claim 1, characterised in that when a plurality of impact beams are used, the distance of the impact beams (8) from one another in the vertical direction is 2 to m. 3

12. The boiler tube wall according to claim 1, characterised in that in the front region of the impact beam the ribs are welded to said beam.

13. The boiler tube wall according to claim 1, characterised in that the ribs are arranged perpendicularly to the boiler tube wall IND IND