BOTTOM-SUPPORTED BOILER

Abstract

A bottom-supported boiler includes a boiler pressure body having a rectangular horizontal cross section formed by joining four planar water tube walls pairwise together so as to form four corner sections, and a support construction. The support construction includes four vertical columns vertically supported to the ground, the vertical columns being arranged outside of the boiler pressure body so that adjacent to each of the corner sections is arranged one of the four vertical columns. Each of the vertical columns is attached to the respective corner section so that vertical loads of the boiler pressure body are balanced by the four vertical columns.

Claims

1. A bottom-supported boiler comprising: a boiler pressure body having a rectangular horizontal cross section formed by joining four planar water tube walls pairwise together so as to form four corner sections; and a support construction wherein the support construction comprises four vertical columns vertically supported to the ground, the vertical columns being arranged outside of the boiler pressure body so that adjacent to each of the corner sections is arranged one of the four vertical columns, wherein each of the vertical columns is attached to the respective corner section so that vertical loads of the boiler pressure body are balanced by the four vertical columns.

2. A bottom-supported boiler in accordance with claim 1, wherein vertical loads of the boiler pressure body are balanced solely by the four vertical columns.

3. A bottom-supported boiler in accordance with claim 1, wherein each of the four vertical columns is attached to the respective corner section in a region having a height of at least 30% of the height of the boiler pressure body.

4. A bottom-supported boiler in accordance with claim 3, wherein each of the four vertical columns is attached to the respective corner section in a region having a height of at least 60% of the height of the boiler pressure body.

5. A bottom-supported boiler in accordance with claim 1, wherein each of the four vertical columns is attached to the respective corner section by a continuous metal strip so as to provide, in vertical direction, a rigid joint.

6. A bottom-supported boiler in accordance with claim 5, wherein the attaching is made with continuous welds.

7. A bottom-supported boiler in accordance with claim 6, wherein the attaching is made to a corner fin between outermost water tubes of the water tube walls forming the corner section.

8. A bottom-supported boiler in accordance with claim 1, wherein at least a portion of the four vertical columns is supported to the ground by using sliding elements so as to allow horizontal thermal expansion of the planar water tube walls.

9. A bottom-supported boiler in accordance with claim 8, wherein each of the vertical columns is supported to the ground by a support steel construction below the vertical column.

10. A bottom-supported boiler in accordance with claim 1, wherein the multiple vertical columns are supported to the ground by a support steel construction allowing bending of the support steel construction so as to allow horizontal thermal expansion of the planar water tube walls and a horizontal beam of the support steel construction.

11. A bottom-supported boiler in accordance with claim 10, wherein the support steel construction comprises a steel column below each of the four vertical columns.

12. A bottom-supported boiler in accordance with claim 1, wherein at least one of the multiple vertical columns is a boiler pipe.

13. A bottom-supported boiler in accordance with claim 12, wherein the boiler pipe is a downcomer pipe of the boiler.

14. A bottom-supported boiler in accordance with claim 1, wherein at least one of the four vertical columns is a column that is not a water pipe.

15. A bottom-supported boiler in accordance with claim wherein the at least one of the four vertical columns has a square cross section.

16. A bottom-supported boiler in accordance with claim 1, wherein each of the four vertical columns is arranged inside a common thermal insulation with the boiler pressure body.

17. A bottom-supported boiler in accordance with claim 1, wherein the boiler is a bubbling fluidized bed boiler.

18. A bottom-supported boiler in accordance with claim 1, wherein the boiler pressure body is a furnace, a convection cage in connection with a furnace, an empty pass in connection with a furnace, a solid separator in connection with a furnace or a horizontal pass in connection with a furnace.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] FIG. 1 schematically illustrates a side view of a boiler according to a first preferred embodiment of the present invention.

[0020] FIGS. 2a and 2b schematically illustrate two embodiments of a detail of a boiler according to the present invention.

[0021] FIG. 3 schematically illustrates a side view of a boiler according to a second preferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] The diagram of FIG. 1 schematically illustrates a side view of a bottom-supported bubbling bed boiler 10, representing an embodiment of the present invention. The bubbling bed boiler 10 is self-standing and supported to the ground 12 via a rigid support steel construction 14 arranged below the boiler. Thus, thermal expansion of the boiler takes place upwards from the support steel construction 14. However, in practice, there is also thermal expansion in horizontal direction, parallel to horizontal beams 16 of the support steel construction. The latter is taken into account by having the boiler at least partially supported on the support steel construction 14 by suitable sliding support elements 18. FIG. 1 shows one sliding support element 18 and one fixed support element 20, but it is also possible that the boiler is supported on the support steel construction solely by sliding support elements.

[0023] The boiler 10 comprises a boiler pressure body 22 made of four planar water tube walls 24, only one of which can be seen in FIG. 1. The water tube walls 24 are formed in a conventional manner of vertical water tubes 38 and fins welded between the water tubes. The water tube walls 24 are pairwise joined together so as to form a rectangular horizontal cross section, having four corner sections 26.

[0024] FIG. 1 also shows a steam drum 42, from where circulating water is conveyed in a conventional manner through downcomer pipes 44, 46 and lower headers 28, only one of which is seen in FIG. 1, to the water tubes 38 of the water tube walls 24. The steam drum is advantageously arranged on top of downcomer pipes 44 so as to be supported by the downcomer pipes 44. Water is evaporated in the water tubes 38, and a mixture of steam and water is conveyed through an upper header 48 and steam pipes 50 back to the steam drum 42 in order to provide steam for further use. Due to the circulating water, thermal expansion of the downcomer pipes 44, 46 is nearly as large as that of the tube walls 24 of the boiler pressure body 22.

[0025] In accordance with the present invention, the boiler pressure body 22 is not supported on the support steel construction 14 in a conventional manner at multiple points of the lower headers 28 of the water tube walls 24, but by using four vertical columns 30 arranged outside the boiler pressure body 22. In the embodiment shown in FIG. 1, the vertical columns are defined by the downcomer pipes 44, 46. In other possible embodiments, the vertical columns can be other boiler pipes than downcomer pipes, such as steam pipes. In still other embodiments, the vertical columns may be other columns than boiler pipes, for example hollow vertical beams.

[0026] Because the water tube walls 24 are not supported from below but from their sides, by the four vertical columns 30, the risk for bulging of the water tube walls is minimized. Thereby, conventional horizontal buckstays 56 can be arranged even at the lower portion of the water tube walls 24 with such mutual distances that there is enough space for arranging fuel feeders 58, and other desired equipment, on the water tube walls.

[0027] According to the present invention, adjacent to each of the corner sections 26 is arranged one of the four vertical columns 30. Each of the vertical columns 30 is in vertical direction rigidly attached to the respective corner section 24 by a vertically extending metal strip 32. The metal strips are advantageously dimensioned so as to provide sufficient thermal conductivity between the corner sections 26 and the respective vertical columns 30. The temperature difference between corner sections 26 and the vertical columns 30 has to be in any operating condition relatively small in order to avoid unnecessary thermal fatigue.

[0028] FIGS. 2a and 2b show, in more detail, two examples of attaching a vertical column 30, 30 to the corner section 26 of two water tube walls 24. In FIG. 2a, the vertical column 30 is a downcomer pipe, or another relatively thick walled boiler pipe. In FIG. 2b, the vertical column 30 is a hollow vertical beam with a square cross sectional shape. As shown in FIGS. 2a and 2b, the metal strips 32 are preferably attached by continuous welds 34 to the vertical columns 30, 30 and to a corner fin 36, 36 between outermost water tubes 38, 38 of the water tube walls 24 forming the corner section 26. In the embodiment of FIG. 2a the corner fin 36 makes a corner, whereas the corner fin 36 in FIG. 2b is beveled.

[0029] In FIGS. 2a and 2b the metal strip 32 is in forty-five degrees angle to the water tube walls 24, but in practice the metal strip can alternatively be parallel to a water tube wall, or in other suitable angle to the walls. FIG. 2b schematically shows also insulation 40 surrounding both the water tube walls 24 and the vertical column 30, which is necessary to maintain the vertical column and the water tube walls 24 at a uniform temperature. It should be understood that corresponding insulation is to be used also in the embodiment of FIG. 2a.

[0030] As mentioned above, in the embodiment of FIG. 1 the support steel construction 14 below the boiler pressure body is rigid, and horizontal thermal expansion is taken into account by slidingly supporting at least a portion of the vertical columns 30 to the support steel construction 14. FIG. 3 shows another embodiment of the present invention that differs from the embodiment of FIG. 1 only in that instead of being rigid, the support steel construction 14 arranged below the boiler pressure body 22 is designed flexible. Thereby, the flexible support steel construction 14 renders sufficient bending of the support steel construction possible, to allow horizontal thermal expansion of the planar water tube walls without using sliding elements between the vertical columns and the support steel construction. The support steel construction comprises second vertical columns 52 below each of the above described vertical columns 30 adjacent to the corner sections 26. The flexible support steel construction may also comprise diagonal braces 54 from the bottom portion of the second vertical columns 52 to a central section of a horizontal beam 16 in the upper portion of the support steel construction 14. It should be noted that in the embodiment of FIG. 3 the second vertical columns 52 and diagonal braces 54 are connected to the insulated, hot vertical columns 30 and horizontal beams 16, respectively, whereas in the embodiment of FIG. 1, the support steel construction 14 comprises an upper horizontal 16 beam that is nearly at the ambient temperature.

[0031] As becomes clear from above, different embodiments of a bubbling fluidized bed boiler with a simple and reliable supporting construction of a bottom-supported boiler are provided. It should be understood that the elements described in connection with an embodiment can be used also in other embodiments, when possible. Corresponding supporting constructions are applicable also in a number of other applications, such as a furnace, a convection cage in connection with a furnace, an empty pass in connection with a furnace, a solid separator in connection with a furnace or a horizontal pass in connection with a furnace and purposes.

[0032] 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.