Arrangement for a method of supporting a side wall of a vertical flue gas pass in a thermal power steam generator

Abstract

An arrangement for and a method of horizontally supporting a side wall of a top-supported flue gas pass. The side wall includes evaporative water tubes at a first temperature, and the flue gas pass includes a superheating tube at a temperature higher than the first temperature and having rigid, horizontal tube legs extending across the flue gas pass between the side wall and a second side wall of the flue gas pass and being supported from above by a hanger, which is in operation at a temperature higher than the first temperature. Rigidity of the side wall is increased by horizontally supporting the side wall by the horizontal tube legs including end sections attached to the side walls by attaching means allowing relative movements of the end sections with respect to the side wall to which the end section is attached, only in a direction of their relative thermal movement.

Claims

1. An arrangement for horizontally supporting a first side wall of a top-supported vertical flue gas pass in a thermal power steam generator, wherein the first side wall comprises evaporative water tubes for conveying a mixture of water and steam at a first temperature, and the top-supported vertical flue gas pass comprises a superheating tube for conveying steam at a second temperature higher than the first temperature, the superheating tube comprising multiple rigid, horizontally extending tube legs extending across the top-supported vertical flue gas pass from the proximity of the first side wall to the proximity of a second side wall opposite to the first side wall in the top-supported vertical flue gas pass, wherein the superheating tube is supported from above by a hanger that is, in operation, at a third temperature higher than the first temperature, and the rigidity of the first side wall is increased by each of the rigid, horizontally extending tube legs comprising a first end section and a second end section, each of the first and second end sections being attached to a proximate side wall by an attaching means, wherein the attaching means allows relative movement between a respective end section and the proximate side wall only in a direction slanted from a vertical direction towards the first side wall in downward direction of relative thermal movement between the respective end section and the proximate side wall, but does not allow purely horizontal movement between the respective end section and the proximate side wall.

2. The arrangement for horizontally supporting a first side wall of a top-supported vertical flue gas pass according to claim 1, wherein the attaching means is arranged to provide a sliding connection between the first and second end sections and the proximate side wall.

3. The arrangement for horizontally supporting a first side wall of a top-supported vertical flue gas pass according to claim 1, wherein the second side wall is externally supported by supporting means, making the second side wall more rigid than the first side wall, and the tube legs of the superheating tube provide means for transferring horizontal loads from the first side wall to the second side wall.

4. The arrangement for horizontally supporting a first side wall of a top-supported vertical flue gas pass according to claim 1, wherein the first side wall is a common wall of the top-supported vertical flue gas pass and an adjacent flue gas pass upstream of the top-supported vertical flue gas pass.

5. The arrangement for horizontally supporting a first side wall of a top-supported vertical flue gas pass according to claim 1, wherein the first side wall is a common wall of the top-supported vertical flue gas pass and a furnace of the thermal power steam generator.

6. The arrangement for horizontally supporting a first side wall of a top-supported vertical flue gas pass according to claim 1, wherein the first side wall is a common wall of the top-supported vertical flue gas pass and an empty pass downstream of a furnace of the thermal power steam generator.

7. The arrangement for horizontally supporting a first side wall of a top-supported vertical flue gas pass according to claim 1, wherein the second side wall comprises evaporative water tubes for conveying a mixture of water and steam at the first temperature, and the tube legs of the superheating tube provide an in horizontal direction rigid structure within the top-supported flue gas pass for increasing the rigidity of both the first side wall and the second side wall.

8. The arrangement for horizontally supporting a first side wall of a top-supported vertical flue gas pass according to claim 7, wherein the top-supported vertical flue gas pass comprises a third side wall and a fourth side wall comprising evaporative water tubes for conveying a mixture of water and steam at the first temperature, the third side wall and the fourth side wall being located in between and perpendicular to the first side wall and the second side wall, wherein the superheating tube comprises multiple, rigid, horizontally extending tube legs extending across the top-supported vertical flue gas pass between the third side wall and the fourth side wall, and the superheating tube comprises a first end section attached to the third side wall and a second end section attached to the fourth side wall by attaching means that allows relative movement of each of the first and second end sections with respect to the side wall to which the end section is attached only in a direction of relative thermal movement between the end section and the side wall to which the end section is attached, so as to provide a rigid structure within the top-supported vertical flue gas pass for increasing the rigidity of the third side wall and the fourth side wall.

9. The arrangement for horizontally supporting a first side wall of a top-supported vertical flue gas pass according to claim 1, wherein the attaching means includes first and second attaching means, the first and second attaching means allowing relative movement only in the direction slanted from the vertical direction.

10. The arrangement for horizontally supporting a first side wall of a top-supported vertical flue gas pass according to claim 9, wherein the first and second attaching means comprise a first part attached to one of an end section of one of the horizontally extending tube legs and the side wall to which the end section is attached, wherein the first part comprises a vertically extending metal plate having an oblong slot, and a second part comprising a transverse piece attached by a rod to the other one of the end section of the one of the horizontally extending tube legs and the side wall to which the end section is attached, and is arranged to be movable in the slot.

11. The arrangement for horizontally supporting a first side wall of a top-supported vertical flue gas pass according to claim 10, wherein the first part comprises two vertically extending metal plates arranged side by side, each of the metal plates having an oblong slot, and the transverse piece comprises a transverse metal pin or a transverse metal slab extending in the same direction as those of the oblong slots.

12. The arrangement for horizontally supporting a first side wall of a top-supported vertical flue gas pass according to claim 1, wherein the attaching means includes first and second attaching means, one of the first and second attaching means allowing relative movement only in a vertical direction and the other one of the first and second attaching means allowing relative movement only in the direction slanted from the vertical direction.

13. A method of horizontally supporting a first side wall of a top-supported vertical flue gas pass in a thermal power steam generator comprising an arrangement for horizontally supporting the first side wall according to claim 1, the method comprising the steps of: (a) providing a mixture of water and steam at a first temperature in evaporative water tubes of the first side wall; (b) conveying steam at a second temperature higher than the first temperature in the superheating tube arranged within the top-supported vertical flue gas pass, the superheating tube comprising multiple, rigid, horizontally extending tube legs extending across the top-supported flue gas pass between the first side wall and the second side wall of the top-supported flue gas pass opposite to the first side wall; (c) supporting the superheating tube from above by a hanger, which is at a third temperature, higher than the first temperature; and (d) increasing rigidity of the first side wall by horizontally supporting the first side wall by attaching the first end section and the second end section of each of the multiple, rigid, horizontally extending tube legs to the first side wall and to the second side wall, respectively, by an attaching means, wherein the attaching means is formed so as to allow relative movement of each of the first and second end sections with respect to the respective side wall to which the end section is attached, only in a direction of relative thermal movement slanted from the vertical direction towards the side wall in the downward direction between the end section and the side wall to which the end section is attached, but does not allow purely horizontal movements between the respective end section and the proximate side wall.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 schematically illustrates a fluidized bed boiler comprising an arrangement according to a first preferred embodiment of the present invention.

(2) FIG. 2 schematically illustrates another fluidized bed boiler comprising an arrangement according to a second preferred embodiment of the present invention.

(3) FIG. 3 schematically illustrates a still another fluidized bed boiler comprising an arrangement according to a third preferred embodiment of the present invention.

(4) FIG. 4 schematically illustrates a fluidized bed boiler comprising an arrangement according to a fourth preferred embodiment of the present invention.

(5) FIG. 5 schematically illustrates an arrangement according to a fifth preferred embodiment of the present invention.

(6) FIGS. 6a and 6b schematically illustrate details of an arrangement according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

(7) The diagram of FIG. 1 schematically illustrates a thermal power steam generator, more specifically, a fluidized bed boiler 10, comprising an arrangement according to a first preferred embodiment of the present invention. FIG. 1 shows a conventional circulating fluidized bed boiler comprising a furnace 12, wherein a bed of particles is fluidized with a stream of air 14 so as to combust fuel introduced to the furnace with the air. In other applications of the present invention, there could be another type of a flue gas generating thermal power boiler than a fluidized bed boiler, such as a waste incinerator or a gas turbine power plant. In the application shown in FIG. 1, the combustion process generates flue gas, which is conveyed from the upper part of the furnace to a particle separator 16, wherein a portion of particles entrained by the flue gas is separated from the flue gas to be returned back to the furnace 12 via a return duct 18. Cleaned flue gas emanates from the particle separator 16 to a flue gas duct 20 comprising first a horizontal pass 22 extending over the top of the furnace 12 and then a down flow vertical flue gas pass 24, from where the flue gas is conveyed to further flue gas handling stages, not shown in FIG. 1.

(8) Vertical side walls 26, 28 of the furnace 12 are cooled in a conventional way by forming them as conventional tube walls, in which water is evaporated to steam. Thus, the water tubes in operation convey a mixture of water and steam from lower headers 30, 30 to upper headers 32, 32 and from there, in case of a natural circulation boiler, to circulate via a steam drum, not shown in FIG. 1. The side walls 26, 28 are thus in operation in the evaporation temperature, which depends on the pressure of the mixture. In view of the present invention, the boiler can alternatively be a supercritical once-through steam generator, in which water is gradually converted to steam, and there is no steam drum.

(9) The furnace 12 and the vertical flue gas pass 24 of the flue gas duct 20 are top-supported, i.e., they are hanging by suitable hanger rods 34 from a conventional support structure 36 extending above the furnace 12. External side walls 26 of the furnace 12 are supported against horizontal loads by conventional wall supporting structures, such as buckstays 38. As is well known to persons skilled in the art, such a fluidized bed boiler comprises also many other elements and features relating to, for example, fuel feeding, ash discharging, steam generation, and flue gas cleaning, which are, however, omitted from FIG. 1, because they are not important for the present invention.

(10) Because flue gas flows in operation of the boiler to the upper portion of the furnace 12, the furnace 12 can be called the first flue gas pass. Correspondingly, the down flow vertical flue gas pass 24 is in the following called the second flue gas pass. The second flue gas pass 24 is generally enclosed by four vertical side walls, of which a first side wall 40, the front wall of the second flue gas pass, and a second side wall 42, rear wall of the second flue gas pass, can be seen in FIG. 1. All the four vertical side walls are conventional evaporative tube walls, which in operation convey a mixture of water and steam from lower headers 30, 44 to upper headers 32, 46, and from there, in case of natural circulation, to the steam drum. The side walls of the second flue gas pass are thus in operation in the evaporation temperature, which depends on the pressure of the mixture.

(11) The front wall 40 is a common wall with the furnace 12, i.e., the front wall 40 of the second flue gas pass 24 is the same as the rear wall 28 of the furnace 12. Thus, according to the embodiment of the invention shown in FIG. 1, the flue gas flow direction is substantially opposite on different sides of the common wall 40. In the furnace side the flow is substantially upwards and in the down flow vertical flue gas pass 24, it is substantially downwards. The second side wall 42, as well as the third and fourth side walls, of the second pass, which are not seen in FIG. 1, are conventional external walls.

(12) The second flue gas pass 24 comprises a superheating tube 48 conveying steam to increase its temperature from that of a preceding stage, typically an earlier superheating stage, to a higher temperature. Thus, the superheating tube 48 is always at a higher temperature higher than the vertical side walls 40, 42 of the second flue gas pass 24. The superheating tube 48 is advantageously of a conventional sinuous type comprising multiple horizontally extending tube legs 50, which extend across the flue gas pass 24 between the first and second side walls 40, 42. The horizontally extending legs 50 are connected in series by first and second end sections 52, 54, on the sides of the first and second side walls 40, 42 of the second flue gas pass 24, respectively. The superheating tube 48 can alternatively be of another type having corresponding horizontally extending legs connected in series by end sections on the sides of the first and second side walls.

(13) In the embodiment shown in FIG. 1, the superheating tube is vertically supported from above by a hanger tube 56, which is supported from above, preferably from the supporting structure 36, and is mainly located within the vertical flue gas pass 24. The hanger tube 56 is in steam flow connection with the lower most horizontally extending leg 50 of the superheating tube. More specifically, the hanger tube 56 is used to feed steam to the superheating tube 48, and thus functions also as a superheater. Thus, the temperature of the hanger tube 56 is always higher than that of the vertical side walls 40, 42 of the second flue gas pass 24. In other applications of the present invention, the superheating tube can alternatively be supported by another type of hanger, such as a separate from above hanging support construction, which is arranged within the flue gas pass so that it in operation heats up to a temperature higher than the temperature of the side walls of the second flue has duct.

(14) The second side wall 42, as well as the third and fourth side walls, of the second flue gas pass 24, are advantageously supported against horizontal loads by suitable wall support structures, such as conventional buckstays 58. Because the first side wall 40 is a common wall with the furnace, it cannot, due to intensive flow of hot flue gas on both sides of the wall, be supported against horizontal loads by buckstays. Therefore, in accordance with the present invention, rigidity of the first side wall 40 is increased by horizontally supporting the first side wall 40 by having the first and second end sections 52, 54 of each of the multiple horizontally extending tube legs 50 attached to the first and second side walls 40, 42, respectively, by suitable attaching means 60, 60. According to the present invention, the attaching means allow relative movement of each of the first and second end sections 52, 54 with respect to the first and second side walls 40, 42, respectively, only in a direction of relative thermal movement between the end section and the side wall into which the end section is attached. Examples of possible designs of the attaching means are explained below in connection with FIGS. 6a and 6b.

(15) Because the hanger tube 56 is heated to a higher temperature than the side walls 40, 42, the relative thermal movements between the end sections and the side walls into which the end sections are attached always have a vertical component. Therefore, as described above, the attaching means do not allow purely horizontal movements between the end sections 60, 60 and their adjacent side walls 40, 42, but allowed movements always have a vertical component. Thus, the arrangement of the horizontally extending legs 50 in the flue gas pass 24 is rigid in a horizontally direction. Therefore, the rigidity of the first side wall 40 is increased, according to the embodiment of the present invention shown in FIG. 1, by utilizing the horizontal legs 50 of the superheating tube 48 for transferring horizontal loads from the first side wall 40 to the second side wall 42.

(16) The diagram of FIG. 2 schematically illustrates a thermal power steam generator, more specifically, a fluidized bed boiler 10, comprising an arrangement according to a second preferred embodiment of the present invention. The embodiment of FIG. 2 differs from that of FIG. 1 in that the fluidized bed boiler 10 is a waste-to-energy boiler, in which flue gases emanating from the furnace 12 are first cooled in a down flow empty pass 62 before they enter to an up flow second flue gas pass 24. All elements in FIG. 2, which are in principle identical to corresponding elements in FIG. 1, are referenced by the same reference numbers as in FIG. 1. When there is a difference that is, however, not relevant in view of the present invention, the reference number used in FIG. 2, or correspondingly in the other FIGS. 3 to 6, is same as that in the previous figure, but added with an apostrophe.

(17) In the embodiment of FIG. 2, there is a common wall 40 between the empty pass 62 and the up flow flue gas pass 24. Thus, the empty pass 62 is in this case the first flue gas pass, and the up flow flue gas pass 24 is the second flue gas pass. The common wall 40 is a rear wall of the first flue gas pass 62 and a front wall of the second flue gas pass 24. In the second flue gas pass is arranged a superheating tube 48, which is principally identical with that shown in FIG. 1.

(18) The front wall of the first flue gas pass 62 and the rear wall of the second flue gas pass 24 are external walls, which are externally supported by conventional buckstays 38, 58. Normally there are no large pressure differences between the sides of the common wall 40 but for a common wall having especially large width and/or height, there may be a need to enforce the wall against horizontal loads. The enforcing of the common wall 40 can advantageously be performed similarly as enforcing of the common wall 40 in the embodiment of FIG. 1, by attaching first and second end sections 52, 54 of the horizontally extending legs 50 of the superheating tube 48 by suitable attaching means 60, 60 to the first and second side walls, i.e., to the common wall 40 and the rear wall 42 of the second flue gas pass.

(19) The diagram of FIG. 3 schematically illustrates a fluidized bed boiler 10 comprising an arrangement according to a third preferred embodiment of the present invention. The embodiment in FIG. 3 differs from that in FIG. 2 in that the second flue gas pass 24 does not have a common wall with a preceding flue gas pass, and the superheating tube 48 within the second flue gas pass is used to horizontally support both the front wall 64 and the rear wall 42 of the second flue gas pass.

(20) Because of the horizontal support provided by the horizontally extending legs of the superheating tube 48 to a vertically central region of the second flue gas pass, external buckstays or other external supporting devices can be omitted or minimized in this region. However, vertical regions above and below the central region can still be provided by conventional buckstays 66, 58, or other suitable support structures.

(21) In the common wall comprising embodiments shown in FIGS. 1 and 2, the attaching means 60 at the common wall 40 advantageously differ from the attaching means 60 at the external wall 42 as will be explained in connection with FIGS. 6a and 6b. In the embodiment of FIG. 3, both the front wall 64 and the rear wall 42 of the second flue gas pass 24 are external walls, and therefore the attaching means 68 at the front wall 64 and the rear wall 42 are preferably identical with each other.

(22) The diagram of FIG. 4 schematically illustrates a fluidized bed boiler 10, comprising an arrangement according to a fourth preferred embodiment of the present invention. The embodiment in FIG. 4 differs from that in FIG. 3 only in that the superheating tube 48 is not supported from above by a hanger tube that feeds steam to the superheating tube 48, but by a separate hanger 56, for example, a from above hanging pipe or rod, that is arranged in the flue gas pass so that it in operation heats up to a temperature higher than the temperature of the side walls of the second flue has duct. A separate hanger 56 as shown in FIG. 4 can naturally also be used in many other embodiments, for example, in the embodiments shown in FIGS. 1 to 3, of the present invention.

(23) The diagram of FIG. 5 schematically illustrates an example of an arrangement of a superheating tube 70 in a flue gas pass 24, which can be used in different applications of the present invention, for example, in any of the embodiments shown in FIGS. 1, 2, and 3. The arrangement comprises two nested sinuous tubes 72, 72, each of which being vertically supported by a hanger tube 74, 74, which is in steam flow connection with the lower most horizontally extending leg 76, 76 of one of the sinuous tubes 72, 72. As is clear to a person skilled in the art, an arrangement of nested sinuous tubes can alternatively be supported from above by a separate hanger, as shown in FIG. 4.

(24) Each of the nested sinuous tubes 72, 72 comprises multiple horizontally extending legs 78, 78 that are pairwise attached together by suitable attaching pieces 80 to form combined, rigid horizontally extending legs 82. The combined, rigid horizontally extending legs 82 are attached to the side walls 64, 42 of the flue gas pass 24 in the same way as, for example, in the embodiment of FIG. 3 to provide horizontal support to the side walls 64, 42. In practice the superheating tube 70 can comprise even more than two nested sinuous tubes, such as three or four sinuous tubes. In each end section of such a combined superheating tube, the outermost tube is attached to an adjacent side wall by a suitable attaching means, but all the tubes form combined, rigid horizontally extending legs as described above, so as to provide horizontal support to the adjacent side walls.

(25) The diagram of FIG. 6a schematically illustrates a vertical cross section of an exemplary attaching means 60 to be used for attaching an end section 52 of a horizontally extending tube leg of a superheating tube to a side wall 40 of a flue gas pass, in accordance with the present invention. The attaching means comprises a wall part 84 attached by a suitable method, such as welding, to the side wall 40 and a tube part 86 attached by a suitable method, such as welding, to the end section 52. The wall part comprises advantageously two vertically extending metal plates 88 arranged side by side, one of which is seen in FIG. 6a, each of the plates having an oblong slot 90, which is to some extent slanted from the vertical direction. The tube part 86 advantageously comprises a transverse metal slab 92 attached by a rod 94 to the end section 52 of the tube. The transverse metal slab 92 extends in the same direction as the slots and is arranged to be movable in the slots.

(26) FIG. 6a shows the attaching means 60 in ambient temperature, i.e., when the horizontal and vertical dimensions of the superheating tube, as well as those of the side wall 40 of the flue gas pass, have their low temperature lengths. When the steam generator is heated up to its operation temperature, the superheating tube and its hanger, which is not seen in FIG. 6a, are thermally expanded more than the flue gas pass, whereby the end section 52 moves in the flue gas pass downwards and towards the sidewall 40. This relative thermal movement is possible thanks to the oblong slots 90, which are slanted outwards in the downward direction.

(27) As discussed above, the direction of the slots 90 and the slab 92 are arranged to correspond to the relative thermal movement between the wall 40 and the end section 52 of the superheating tube taking place in the location of the attaching means. Therefore, the attaching means 60 allows relative movement of the end section 52 with respect to the side wall 40 only in a direction slanted from the vertical direction, and more specifically, only in a direction of their relative thermal movement. The connection is thus sliding in the direction of the relative thermal movement, but rigid in other directions, and provides horizontal support to the side wall 40.

(28) The diagram FIG. 6b schematically illustrates a vertical cross section of another exemplary attaching means 60 to be used for attaching an end section 54 of a horizontally extending tube leg of a superheating tube to a side wall 42 of a flue gas pass. The attaching means 60 differs from the attaching means 60 in FIG. 6a only in that the slots 90 in the wall part 84 and the slab 92 in the tube part 86 are vertical instead of slanted. Thus, the attaching means 60 allows only vertical relative thermal movement, mainly caused, as explained above, by a hanger, not shown in FIG. 6b, between the wall 42 and the end section 54 of the superheating tube. Relative horizontal thermal movement is thus prevented by the attaching means 60, and has to be in full enabled in the other end of the respective horizontally extending tube leg, by an attaching means, for example, as shown in FIG. 6a. The attaching means 60 is used to provide a thermal movement reference line in a horizontal direction. Preferably, such an attaching means with vertical slots and slabs are used when connecting a superheating tube to an externally supported side wall, such as side walls 42 in FIGS. 1 and 2, to provide a horizontal thermal reference line therein. Because of horizontal thermal expansion, an attaching means allowing purely vertical movement can only be used in at most one of opposite side walls of a vertical flue gas pass.

(29) As is clear to a person skilled in the art, attaching means allowing relative movement of an end section of a superheating tube with respect to a side wall only in a single, predefined direction, the direction of their relative thermal movement, can be achieved also by other designs than those shown in FIGS. 6a and 6b. For example, the designs of the wall part and the tube part can be switched. Thereby, the part comprising a metal plate with a slot can generally be called a first part, that can be connected either to an end section of a horizontally extending tube leg or to a side wall. Correspondingly, the part comprising a transverse piece attached by a rod to an end section of a horizontally extending tube leg or to a side wall, can generally be called a second part.

(30) According to an alternative design, the first part of the attaching means comprises two vertically extending metal plates with oblong slots, as described above, and the second part comprises a strong, transverse metal pin attached by a rod to the side wall or to the end section of a horizontally extending tube. Also, it is possible that the first part of the attaching means comprises only one vertically extending metal plate with an oblong slot with a definite direction, and the second part comprises a transverse metal slab extending in the same direction as the slot or a strong, transverse metal pin, which slab or pin is arranged between two rods attached to the side wall or to the end section of a horizontally extending tube.

(31) 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.