CIRCULATING FLUIDIZED BED BOILER AND A METHOD OF ASSEMBLING A CIRCULATING FLUIDIZED BED BOILER

Abstract

A circulating fluidized bed boiler includes a rectangular furnace, which is horizontally enclosed by sidewalls, for combusting fuel and combustion gas and generating a stream of flue gas and particles. The sidewalls include first and second short sidewalls and first and second long sidewalls. Multiple particle separators are arranged on the side of each of the first and second long sidewalls for separating particles from the stream of flue gas and particles discharged from the furnace. Each of the particle separators includes a vertical gas outlet tube for discharging cleaned flue gas from the particle separator. A back pass arranged on the side of the second short sidewall of the furnace is horizontally enclosed by back pass walls. A horizontally extending cross over duct system is directly connected to the vertical gas outlet tubes of the particle separators for conducting the cleaned flue gas to the back pass.

Claims

1-15. (canceled)

16. A circulating fluidized bed boiler comprising: a rectangular furnace, which is horizontally enclosed by sidewalls, for combusting fuel and combustion gas therein and generating a stream of flue gas and particles, the sidewalls comprising first and second short sidewalls and first and second long sidewalls, wherein a common width of the first and second long sidewalls is greater than a common width of the first and second short sidewalls; multiple particle separators arranged on the side of each of the first and second long sidewalls, inlets of the multiple particle separators being connected to an upper portion of the adjacent long sidewalls, for separating particles from the stream of flue gas and particles discharged from the furnace, wherein each of the particle separators comprises a vertical gas outlet tube for discharging cleaned flue gas from the particle separator; a back pass arranged on the side of the second short sidewall of the furnace, the back pass being horizontally enclosed by back pass walls comprising a first back pass wall facing the second short sidewall of the furnace; and a horizontally extending cross over duct system directly connected to the vertical gas outlet tubes of the particle separators for conducting the cleaned flue gas to the back pass, wherein the cross over duct system provides a straight gas flow that is inclined to the sidewalls of the furnace from each of the vertical gas outlet tubes of the particle separators to openings in the first pack pass wall.

17. A circulating fluidized bed boiler according to claim 16, further comprising a supporting system for hanging the furnace from above, wherein the cross over duct system is arranged above the supporting system.

18. A circulating fluidized bed boiler according to claim 17, wherein the cross over duct system is supported from below by the supporting system.

19. A circulating fluidized bed boiler according to claim 16, wherein the cross over duct system comprises a first duct structure providing a straight gas flow path that is inclined to the sidewalls of the furnace from each of the gas outlet tubes of the particle separators arranged on the side of the first long sidewall of the furnace to first openings in the back pass wall, and a second duct structure providing a straight gas flow path that is inclined to the sidewalls of the furnace from each of the gas outlet tubes of the particle separators arranged on the side of the second long sidewall of the furnace to second openings in the first back pass wall.

20. A circulating fluidized bed boiler according to claim 19, wherein each of the first and second duct structures is constructed without a partition wall.

21. A circulating fluidized bed boiler according to claim 19, wherein the first duct structure provides a straight gas flow path that is inclined to the sidewalls of the furnace from each of the gas outlet tubes of the particle separators arranged on the side of the first long sidewall of the furnace to the first openings in the first back pass wall, and the second duct structure provides a second straight gas flow path that is inclined to the sidewalls of the furnace from each of the gas outlet tubes of the particle separators arranged on the side of the second long sidewall of the furnace to the second openings in the first back pass wall.

22. A circulating fluidized bed boiler according to claim 21, wherein the first and second gas flow paths are mirrored symmetrically inclined to the sidewalls of the furnace.

23. A circulating fluidized bed boiler according to claim 19, wherein each of the duct systems comprises at least one of water and steam tubes for transferring heat from the flue gas to water or steam.

24. A circulating fluidized bed boiler according to claim 23, wherein the duct systems are made of straight water tube panels.

25. A circulating fluidized bed boiler according to claim 21, wherein each of the first and second duct structures has a constant height.

26. A circulating fluidized bed boiler according to claim 25, wherein each of the first and second duct structures has a width that increases stepwise in the respective flue gas flow.

27. A circulating fluidized bed boiler according to claim 21, wherein the first back pass wall is parallel to the second short sidewall of the furnace, and the first and second openings form a plane having a normal that is inclined to the first and second gas flow directions.

28. A circulating fluidized bed boiler according to claim 21, wherein the first back pass wall comprises a horizontally adjacent first connecting wall portion and a second connecting wall portion, each of the connecting wall portions having a central edge and an outermost edge and being inclined to the second short sidewall of the furnace so that the central edge of each of the first and second connecting wall portions is closer to the second short sidewall of the furnace than the outermost edge of the respective connecting wall portion, and the first openings and the second openings are located in the first connecting wall portion and in the second connecting wall portion, respectively.

29. A circulating fluidized bed boiler according to claim 19, wherein each of the first and second duct structures comprises at least one flow guide for directing flue gas flow from the gas outlet tube of a first particle separator to the side of a vertical extension of the gas outlet tube of a second particle separator, wherein the first and second particle separators are arranged subsequently on the same side of a long sidewall of the furnace so that the second particle separator is closer to the back pass than the second particle separator.

30. A method of assembling a circulating fluidized bed boiler according to claim 19, the method comprising lifting each of the first and second duct structures as a single piece above horizontal beams of a supporting structure of the boiler.

31. A method of assembling a circulating fluidized bed boiler according to claim 20, the method comprising lifting each of the first and second duct structures as a single piece above horizontal beams of a supporting structure of the boiler.

32. A method of assembling a circulating fluidized bed boiler according to claim 21, the method comprising lifting each of the first and second duct structures as a single piece above horizontal beams of a supporting structure of the boiler.

33. A method of assembling a circulating fluidized bed boiler according to claim 28, the method comprising lifting each of the first and second duct structures as a single piece above horizontal beams of a supporting structure of the boiler.

34. A method of assembling a circulating fluidized bed boiler according to claim 29, the method comprising lifting each of the first and second duct structures as a single piece above horizontal beams of a supporting structure of the boiler.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] FIG. 1 is a schematic side view of a circulating fluidized bed boiler in accordance with a preferred embodiment of the present invention.

[0028] FIG. 2 is a schematic horizontal cross section of the circulating fluidized bed boiler shown in FIG. 1.

[0029] FIG. 3 is a schematic horizontal cross section of a circulating fluidized bed boiler in accordance with another preferred embodiment of the present invention.

[0030] FIG. 4 is another schematic horizontal cross section of the circulating fluidized bed boiler shown in FIG. 1.

[0031] FIG. 5 is a schematic horizontal cross section of a detail of a circulating fluidized bed boiler in accordance with a preferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0032] FIG. 1 shows a schematic side view of a circulating fluidized bed (CFB) boiler 10 in accordance with a preferred embodiment of the present invention. The furnace 12 of the CFB boiler 10 has a rectangular cross section, having first and second short sidewalls 14, 14 and first and second long sidewalls 16, only one of which is seen in FIG. 1. Multiple particle separators 18 are connected to each of the long sidewalls 16 of the furnace 12. The number of particle separators 18 on each long sidewall 16 is, here, three, but it could also be, for example, two, or four. The particle separators 18 are in flow connection with a back pass 20 arranged on the second short sidewall 14 of the furnace 12 by a horizontally extending cross over duct system 22. In the following, the same reference numbers are generally used for the same elements in different Figures.

[0033] When fuel is combusted in the furnace 12, hot flue gas and particles entrained therewith are discharged through flue gas discharge channels 24, shown, e.g., in FIG. 2, to the particle separators 18. Particles separated from the flue gas in the particle separators 18, are returned back to the lower portion of the furnace 12 via return ducts 26. The return ducts 26 may advantageously comprise heat exchange surfaces, not shown in FIG. 1, to recover heat from the recycling hot particles.

[0034] Streams of cleaned flue gas are conducted from the particle separators 18 through vertical gas outlet tubes 28 to the cross over duct system 22, to be conducted through the cross over duct system to the back pass 20. The flue gas enters from the cross over duct system 22 to the back pass 20 through openings 30 arranged in a first back pass wall 32 facing the second short sidewall 14 of the furnace 12. According to the present invention, the cross over duct system 22 has a form that provides a straight gas flow path, that is inclined to the sidewalls of the furnace 12, from each of the vertical gas outlet tubes 28 of the particle separators 18 to the openings 30 in the first back pass wall 32.

[0035] The back pass 20 usually comprises heat exchange surfaces 34 for transferring heat from the flue gas to a heat transfer medium. In FIG. 1, there is symbolically shown only one heat exchange surface 34, but, in practice, there are usually several heat exchange surfaces 34, such as superheaters, reheaters, economizers, and air heaters.

[0036] Cooled flue gas is conducted from the back pass 20 further to gas cleaning stages, such as a dust collector and a sulfur dioxide scrubber, not shown in FIG. 1. The cleaned flue gas is finally released to the environment through a stack, or it is, in oxyfuel combustion, conducted further to carbon dioxide sequestration.

[0037] The circulating fluidized bed boiler 10 shown in FIG. 1 is of a conventional top-supported type, i.e., it comprises a supporting system 36 comprising vertical pillars 38, horizontal beams 40, and hanger rods 42, for hanging at least the furnace 12 from above. The back pass 20 is conventionally also of a top-supporting type and comprises a similar supporting system, not shown in FIG. 1. The cross over duct system 22 is advantageously arranged at a higher level than the supporting system 36 of the furnace 12, at least partially above the supporting system 36 of the furnace 12. Thereby, the cross over duct system 22 is advantageously bottom supported, i.e., it is supported from below by the supporting system 36.

[0038] Due to differential thermal expansions of the particle separators, 18, the cross over duct system 22 and the back pass 20, there are advantageously suitable bellows 44, 46, or other movement allowing structures, between the particle separators 18 and the cross over duct system 22, and between the cross over duct system 22 and the back pass 20, respectively. Due to differential thermal movements between the supporting system 36 and the cross over duct system 22, the cross over duct system 22 is advantageously supported on the supporting system 36 by using sliding support devices 48 arranged on the supporting system 36 of the furnace 12.

[0039] FIG. 2 schematically shows a horizontal cross section A-A of the embodiment shown in FIG. 1. For the sake of simplicity, the support construction, feature 36 in FIG. 1, is not shown in FIG. 2. As can be seen in FIG. 2, the cross over duct system 22 comprises two mirror symmetrically arranged portions 50, 50. Thus, the cross over duct system 22 comprises a first duct structure 50 providing a straight gas flow path from the outlet tubes 28 of each of the particle separators 18 arranged on the side of the first long sidewall 16 of the furnace 12 to the first back pass wall 32, and a second duct structure 50 providing a straight gas flow path from the outlet tubes 28 of each of the particle separators 18 arranged on the side of the second long sidewall 16 of the furnace 12 to the first back pass wall 32.

[0040] The duct structures 50, 50 provide a straight, i.e., shortest possible, gas flow path from each of the particle separators 18, 18 to openings 30 in the first back pass wall 32. Because the particle separators 18, 18 are arranged on the two long sidewalls 16, 16 and the back pass 20 on a short side wall 14 of the furnace 12, the straight gas flow paths are naturally mirror symmetrically inclined to all sidewalls of the furnace 12.

[0041] Each of the duct structures 50, 50 is advantageously constructed without partition walls, and, therefore, the flue gas streams from the particle separators 18, 18 arranged on the same long sidewall 16, 16 form a combined flue gas stream. The combined flue gas streams in the first and second duct structures 50, 50 have first and second gas flow directions 52, 52, respectively, which are mirror symmetrically inclined to the sidewalls of the furnace 12. In order to keep the flue gas flow velocity at a substantially constant value throughout the duct structures 50, 50, the duct structures have a width W that increases stepwise at the locations of the outlet tubes 28 of the particle separators 18, 18, in the respective flue gas flow direction. Such a constant flue gas velocity renders possible a smooth flow of the gas without excessive turbulence and minimized erosion caused by fine particles remaining entrained with the gas.

[0042] The flue gas enters from each of the duct structures 50, 50 to the back pass 20 through openings 30 in the first back pass wall 32. It is possible that there is one large opening for the flue gas from each of the duct structures 50, 50, but advantageously, there are multiple substantially evenly distributed openings in first and second opening areas 54, 54, located symmetrically on opposite sides of a vertical center line of the first back pass wall 32.

[0043] The duct structures 50, 50 are advantageously made of straight tube panels, which are typically used for heating steam. The duct structures 50, 50 are advantageously constructed so as to have a planar bottom and top, and a sidewall 56 having a constant height 58, as shown in FIG. 1. In the embodiment shown in FIG. 2, the first back pass wall 32 is planar and parallel to the second short sidewall 14 of the furnace. Thereby, the first and second opening areas 54, 54 are on a common plane having a normal direction that is inclined to the first and second gas flow directions 52, 52.

[0044] FIG. 3 schematically shows a horizontal cross section of another embodiment of the present invention, which differs from that in FIG. 2 in that the first back pass wall 32 is not fully planar, but it comprises in its upper portion a section, a so-called connecting section 60, having a central portion 62 that protrudes towards the furnace 12. The connecting section 60 preferably has a height that is only slightly greater than the height 58, shown in FIG. 1, of the cross over duct system 22, or the duct structures 50, 50, while the lower portion 32 of the first back pass wall 32 is planar, and therein, the back pass 20 has a conventional rectangular cross section. Such a towards the furnace protruding connection section 60 provides the advantage of enabling horizontally wider gas flow paths from the particle separators 18, 18 to the back pass 20, while having a certain distance between the furnace 12 and the rectangular lower portion of the back pass 20.

[0045] The connecting section 60 comprises horizontally adjacent first and second connecting wall portions 64, 64, comprising first and second opening areas 66, 66, respectively, each of the connecting wall portions 64, 64 being inclined to the second short sidewall 14 of the furnace 12. Preferably, the connecting wall portions 64, 64 are planar, and have normal directions that are advantageously substantially parallel to the first and second gas flow directions 52, 52, respectively.

[0046] Each of the connecting wall portions 64, 64 has a central edge 68, 68 and an outermost edge 70, 70, wherein the central edges are closer to the second short sidewall 14 of the furnace than the outermost edges. According to FIG. 3, the central edges 68, 68 of the connecting walls portions 64, 64 are connected together at the center portion 62, but it is also possible that they are separated from each other. Thus, there can be between the central edges, for example, a free space for a vertical column of a supporting structure.

[0047] FIG. 4 schematically shows a horizontal cross section B-B of the embodiment shown in FIG. 1. The cross section B-B is taken just above horizontal beams 40, 72 of the supporting structure 36, and shows an example of locations of sliding support devices 48 of the duct systems 50, 50, on the horizontal beams.

[0048] FIG. 5 schematically shows an example of a flow guide 74 arranged in the duct system 50 adjacent to a vertical outlet tube 28 of a particle separator 18. The flow guide 74 directs flue gas flow 76 from the gas outlet tube of an in-gas flow direction earlier particle separator to the side of the vertical extension of the gas outlet tube 28 of the in-gas flow direction later particle separator 18 for minimizing interference between the flue gas flows from the succeeding particle separators. The flow guide 74 is formed by bending the sidewall 78 of the duct structure 50 so as to form a suitable gas-directing device. The flow guide can alternatively be constructed as a separate member formed within a duct system having a simple stepwise bent sidewall 56, as shown, for example, in FIG. 2.

[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 embodiment, 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.