WATERTUBE PANEL PORTION AND A METHOD OF MANUFACTURING A WATERTUBE PANEL PORTION IN A FLUIDIZED BED REACTOR

Abstract

A watertube panel portion for a fluidized bed reactor and a corresponding method. The watertube panel portion includes multiple parallel metal tubes having a tube length L1, an outer surface, an original outer diameter OD1, and an original wall thickness WT1, and a circumferentially extending recess formed in a central portion of each of the tubes, between first and second end portions. The recess has a constant depth D that is less than the wall thickness WT1. The recess encircles the outer surface of the central portion of the metal tube. A circumferentially extending metal coating has a constant thickness of at most the depth D of the recess to blanket the recess of each of the multiple metal tubes. A fin is continuously welded between each pair of adjacent tubes.

Claims

1. A method of manufacturing a watertube panel portion for a fluidized bed reactor, the method comprising the steps of: (a) providing multiple metal tubes comprising a first end portion, a second end portion, and a central portion between the first end portion and the second end portion, wherein each of the first end portion and the second end portion has an outer surface and a substantially constant outer diameter OD1, and the central portion has an outer surface and a substantially constant outer diameter OD2, that is less than the outer diameter OD1; (b) providing a circumferentially extending metal coating having a substantially constant thickness of at most D, wherein D is (OD1?OD2)/2, on the outer surface of the central portion to blanket the outer surface of the central portion; (c) arranging the multiple metal tubes in a plane in parallel to each other; and (d) forming the watertube panel portion by continuously welding a fin between each pair of adjacent in parallel arranged metal tubes.

2. The method according to claim 1, wherein each of the multiple metal tubes is formed by making the central portion the metal tube by forming a circumferentially extending recess having a constant depth equal to D between the first end portion and the second end portion of the metal tube, wherein the recess encircles the outer surface of the central portion of the metal tube so as to have the outer diameter OD2.

3. The method according to claim 1, wherein each of the multiple metal tubes is formed by connecting two ends of a first tube portion having the outer diameter OD2 to coaxially abut an end of a second tube portion and an end of a third tube portion, respectively, which second and third tube portions have the outer diameter OD1, whereby the first tube portion forms the central portion of the metal tube and the second and third tube portions form the first and second end portions of the metal tube, respectively.

4. The method according to claim 1, wherein the circumferentially extending metal coating is provided as a spiral weld overlay.

5. The method according to claim 1, wherein the step of providing a circumferentially extending metal coating is performed so that at least at one end of the coating is smoothly flush with the outer surface of the adjacent end portion of the respective metal tube.

6. The method according to claim 1, comprising further steps of forming a first bending at a first angle in a central region of the water tube panel portion by bending each of the multiple metal tubes and the fins between the metal tubes from the direction of the first end portions of the metal tubes around an axis perpendicular to both of the first end portions of the metal tubes and the normal of the plane to a bent direction, and a second bending at a second angle from the bent direction to a second direction.

7. The method according to claim 6, wherein the second angle is opposite to the first angle.

8. The method according to claim 7, wherein the second angle is equal to the first angle.

9. The method according to claim 7, wherein the second angle is greater than the first angle.

10. The method according to claim 6, wherein the metal coating of each of the metal tubes extends over the first and second bendings.

11. The method according to claim 10, wherein the metal coating of each of the metal tubes extends a longer distance from the first bending towards the first end portion of the metal tube than from the second bending towards the second end portion of the metal tube.

12. The method according to claim 6, wherein the metal coating of each of the metal tubes extends a distance of at least one meter from the first bending towards the first end portion of the metal tube.

13. A watertube panel portion for a fluidized bed reactor, the watertube panel portion comprising: multiple metal tubes comprising a first end portion, a second end portion, and a central portion between the first end portion and the second end portion, wherein each of the first end portion and the second end portion has an outer surface and a substantially constant outer diameter OD1; a circumferentially extending recess formed in the central portion of the multiple metal tubes to encircle the outer surface of the central portion, whereby the central portion has an outer surface and a substantially constant outer diameter OD2, that is less than the outer diameter OD1; a circumferentially extending metal coating having a constant thickness of at most D, wherein D is (OD1?OD2)/2, to blanket the recess of each of the multiple metal tubes, wherein the multiple metal tubes are arranged in a plane in parallel to each other; and a fin continuously welded between each pair of adjacent, in parallel arranged, metal tubes, so as form the watertube panel portion.

14. The watertube panel portion according to claim 13, wherein the circumferentially extending metal coating is provided as a spiral weld overlay.

15. The watertube panel portion according to claim 13, wherein the circumferentially extending metal coating is at least at one end of the recess smoothly flush with the outer surface of the adjacent end portion of the respective metal tube.

16. The watertube panel portion according to claim 13, wherein the watertube panel portion comprises a first bending at a first angle in a central region of the water tube panel portion, wherein each of the multiple water tubes and the fins between the metal tubes are bent from the direction of the first end portions of the metal tubes around an axis perpendicular to both the first end portions of the metal tubes and the normal of the plane to a bent direction, and a second bending at a second angle from the bent direction to a second direction.

17. The watertube panel portion according to claim 16, wherein the second angle is opposite to the first angle.

18. The watertube panel portion according to claim 17, wherein the second angle is equal to the first angle.

19. The watertube panel portion according to claim 17, wherein the second angle is greater than the first angle.

20. The watertube panel portion according to claim 16, wherein the metal coating of each of the metal tubes extends over the first and second bendings.

21. The watertube panel portion according to claim 20, wherein the metal coating of each of the metal tubes extends a longer distance from the first bending towards the first end portion of the metal tube than from the second bending towards the second end portion of the metal tube.

22. The watertube panel portion according to claim 16, wherein the metal coating of each of the metal tubes extends a distance of at least one meter from the first bending towards the first end portion of the metal tube.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0030] FIG. 1 schematically shows a bottom portion of a circulating fluidized bed boiler.

[0031] FIG. 2 schematically shows a metal tube with a metal coating according to an embodiment of the present invention.

[0032] FIG. 3 schematically shows a plan view of a watertube panel portion according to an embodiment of the present invention.

[0033] FIG. 4 schematically shows a side view of an exemplary watertube panel portion, with a refractory coating, corresponding to the plan view shown in FIG. 3.

[0034] FIG. 5 schematically shows a side view of another exemplary watertube panel portion, with a refractory coating, corresponding to the plan view shown in FIG. 3.

DETAILED DESCRIPTION OF THE INVENTION

[0035] FIG. 1 schematically shows a bottom portion of a fluidized bed reactor 10 of a circulating fluidized bed boiler, the reactor 10 comprising waterwalls 12 formed of watertube panels 14 and a refractory coating 16 on the inwards tilted lower portions 18 of the waterwalls 12. The watertube panels 14 comprise a first bending 20 outwards and a second bending 22 inwards, the angle of the second bending 22 being greater than that of the first bending 20. The upper edge 24 of the refractory coating 16 is arranged in the area of the bendings 20, 22 so that the upper edge 24 is recessed from the fireside surface of the vertical watertube panel 14 above the refractory coated lower portion of the waterwall 12.

[0036] The fluidized bed reactor 10 comprises a conventional wind box 26 and fluidizing nozzles 28 for introducing fluidizing gas, usually air, for fluidizing fuel and other bed particles in the reactor 10. Fluidizing gas and bed particles flow mainly upwards in the reactor 10, but especially near the waterwalls 12 there is also a downwards directed flow of bed particles 30. The arrangement of having the upper edge of the refractory coating 16 in the area of the bendings 20, 22 minimizes erosion of the watertube panels 14 in the region 32 above the upper edge 24 of the refractory coating 16. When using especially eroding fuels or other bed materials, however, there is still a risk of erosion of the watertube panels 14 in this region due to turbulence eddies 34 of the downwards flowing bed particles caused by the discontinuity of the waterwall 12. Therefore, the present invention discloses an especially efficient method of making a metal coating 36 on the water tubes of the watertube panel 14.

[0037] FIG. 2 schematically shows a metal tube 40 of a length L1, having in its central portion, between a first end portion 42 and a second end portion 44 of the metal tube 40, a circumferentially extending recess 46 of depth D and length L2 formed on the outer surface of the metal tube 40. The metal tube 40 has originally an outer diameter OD1 and a wall thickness WT1. When the recess 46 is formed, the outer diameter OD1 is decreased in the central portion of the tube 40 to a value OD2, and the wall thickness to a value WT2. The ratio of the dimensions of the tube 40 shown in FIG. 2 differ clearly from what they usually are in practice. In reality, the tube 40 is usually much longer, and the wall thickness of the tube 40 and the depth of the recess 46 are much smaller than those shown in FIG. 2, when compared to the outer diameter OD1 of the tube 40.

[0038] In accordance with the present invention, a circumferentially extending metal coating 48 is provided in the recess 46. The recess 46 has a relatively smooth outer surface and a constant thickness, the thickness of the metal coating 48 being the same as the depth D of the circumferentially extending recess 46. The length of the metal coating 48 is correspondingly the same as the length L2 of the circumferentially extending recess 46. Thereby, the metal coating 48 blankets or fills the recess 46, and the thus formed outer diameter of the metal coated tube portion is the same as the original outer diameter OD1 of the metal tube 40.

[0039] Because the purpose of the metal coating 48 is to protect the metal tube 40 from erosion without causing any harmful turbulence eddies when installed into a fluidized bed reactor 10, the surface of the metal coating 48 is preferably at least at one end of the recess 46 smoothly flush with the outer surface of the adjacent end portion of the metal tube 40. To remove all surface texture, the surface may advantageously be lightly ground or polished flush with the tube surface above. In order to achieve the desired smoothness, the metal coating 48 is advantageously provided by a suitable spiral weld overlay method.

[0040] FIG. 3 is a schematic plan view of a planar watertube panel portion 50 formed of multiple metal tubes 40, 40 of the type shown in FIG. 2. Between each pair of adjacent metal tubes 40, 40 is welded a conventional fin 52 to form the water tube panel portion 50. The reference numbers used for the features in FIG. 2 are also used for the same or corresponding features in FIGS. 3-5.

[0041] Between the first end portion 42 and second end portion 44 of each of the metal tubes 40, 40 is arranged a circumferentially extending metal coating 48. As described above, the metal coatings 48 are made in circumferentially extending recesses (not shown in FIG. 3), so as to fill or blanket the recesses. If desired, a one-sided metal coating 48 can also be provided in the central portion of the fins 52.

[0042] If the watertube panel portion of FIG. 3 is to be installed in a waterwall 12 of a fluidized bed reactor 10 to minimize erosion in the area above the upper edge 24 of a refractory coated lower section of the waterwall 12, wherein the upper edge 24 of the refractory coating 16 is to be arranged in an outwardly bent portion of the waterwall 12, suitable bendings have to be formed in the watertube panel portion 50.

[0043] FIG. 4 schematically shows a side view of an exemplary watertube panel portion 50 corresponding to the plan view shown in FIG. 3. In a central portion of a metal tube 40 is seen a metal coating 48 that is provided circumferentially around the tube 40. The metal coating 48 is advantageously made as a spiral weld overlay. The surface of the metal coating 48 is flush with the outer surface of the upper and lower end portions 42, 44 of the metal tube 40. On the side of the first and second end portions 42, 44 of the tube 40 is schematically shown a fin 52, which is welded between a pair of adjacent tubes 40, 40.

[0044] In the lower section of the metal coated tube portion 48, there is a first bending 54 towards the side of the watertube panel portion 50, which will be an outer side of the panel portion when it is installed into a fluidized bed reactor 10. Further from the first bending 54, there is a second bending 56, which will be a lower bending when the panel portion 50 is installed into a fluidized bed reactor 10. As is seen in FIG. 4, the second bending 56 makes a larger angle than does the first bending 54, so as to form an inwards tapering waterwall 12 to the reactor 10.

[0045] Adjacent to the second end portion 44, which will be the lower end portion when the panel portion 50 is installed into a fluidized bed reactor 10, is seen a refractory coating 58. As is well-known to persons skilled in the art, the refractory coating 58 is conventionally applied to the fireside surface of the panel portion 50 only when the panel portion 50 is installed into a fluidized bed reactor 10. The refractory coating 58 conventionally has an upper edge 60 in the region of the second bending 56.

[0046] The discontinuity of the direction of the waterwall 12 tends to give rise to turbulence eddies above the upper edge 60 of the refractory coating 58, but the metal coating 48 of the metal tubes 40 provides efficient erosion protection to the tubes 40 in the region B shown in FIG. 4. The metal coating 48 advantageously extends clearly upwards, when installed into a fluidized bed reactor 10, from the first bending, preferably, by a distance of at least one meter, even more preferably, by a distance of at least two meters. The metal coating 48 also advantageously extends correspondingly to some distance downwards from the second bending 56, at least to a region that will be covered by the refractory coating 58.

[0047] In accordance with the present invention, the refractory coating 58 is formed circumferentially around the tubes 40, even if erosion protection is actually needed only on the fireside of the watertube panel portion 50. In many cases, it is enough to have erosion protection on the metal tubes 40 only. If needed, erosion protection can also be provided to the fins 52 welded between adjacent metal tubes 40. Erosion protection of the fins 52 is then advantageously made by providing a conventional one-sided metal coating to a one-sided recess formed to a desired portion of the fins 52. Erosion protection of the fins 52 is not shown in FIG. 4.

[0048] FIG. 5 schematically shows a side view of another exemplary watertube panel portion 50 corresponding to the plan view shown in FIG. 3. The watertube panel portion 50 of FIG. 5 differs from that shown in FIG. 4 only in that the angle formed by the second bending 56 is as large as the angle formed by the first bending 54. Thereby, the second end portion 44 is parallel with the first end portion 42, but to some extent shifted outwards from the fluidized bed reactor 10, when the panel portion is installed into the fluidized bed reactor 10. In some cases, there is a third bending (not shown in FIG. 5), at a level that will be below the second bending 56, to form an inwards tapering waterwall 12 to the lower section of the reactor 10.

[0049] While the invention has been described herein by way of examples in connection with what are at present considered to be the most preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but is intended to cover various combinations or modifications of its features and several other applications included within the scope of the invention as defined in the appended claims.