[0001 ] The present invention relates to an expansion joint in a vertical channel for conducting hot particles and to a method of making an expansion joint in a vertical channel for conducting hot particles. The invention is especially directed for use in a channel for conducting high temperature particulate material in connection with a particle separator of a circulating fluidized bed reactor. [0002] It is commonly known that differential thermal expansions between components of a reactor have to be taken into account in order to avoid damages which may occur when the temperature of the reactor is changed. A common practice is to divide each channel connecting such components in separate upstream and downstream parts to allow relative movements of the components due to differential thermal expansion. In order to maintain the channel sealed, the upstream and downstream parts are connected by an air-tight flexible means, such as fabric or metal bellows. An expansion joint with fabric bellows is commonly used when relatively large movements or movements both in axial and lateral direction are expected.

[0003] High temperature expansion joints which are capable of handling relatively large thermal movements are often required in channels connecting to the particle separator of a circulating fluidized bed (CFB) boiler. A problem is that fabric bellows cannot withstand the high temperatures of the gas and particles flowing through the particle separator. Moreover, particles packing between the moving parts of the joint may prevent the movement and thereby cause breakage of the joint. [0004] U.S. Patent No. 5,366,255 discloses a high temperature expansion joint arranged between two portions of a channel. In the area of the joint, one of the channel portions telescopically overlaps the other channel portion in a spaced relationship to permit relative axial and lateral movements of the channel portions. Each channel portion comprises an outwardly extending extension, which outwardly extending extensions are sealingly connected with a composite fabric belt dimensioned to permit the relative movements. Thermal insulation is disposed between the outwardly extending extensions to inhibit heat flow to the fabric belt. A drawback in the joint is that the thermal insulation may be

irreversibly tightened in repeated compressions, and allow particulate material to pack into the joint and damage the fabric belt or prevent the movements of the joint.

[0005] Fl Patent No. 87271 discloses a high temperature expansion joint between an upstream portion and a downstream portion of a channel, which are sealingly connected by a flexible element connected on the outer side of the channel. The joint comprises intermediate elements which are connected in the downstream channel portion in a way that allows axial but not lateral movement of the intermediate elements. The intermediate elements are supported by a spring against a transverse plane of the upstream channel portion and comprise a downstream end arranged to slide on an inner circumference of the downstream channel portion. A drawback of this expansion joint is that at least when the system is used at a temperature lower than its highest operating temperature, the inner circumference of the downstream channel portion, on which the

intermediate element fits in a high temperature operation, is directly accessible to abrasive forces due to particles flowing in the channel. Therefore, the

construction has a risk of wearing of the sliding surface on the inner

circumference of the downstream channel portion in start-up and close-down phases of a fluidized bed boiler. Moreover, the maintenance of the expansion joint is complicated, while it can only be done inside the channel.

[0006] Fl Utility Model No. 201 10203 discloses a high temperature expansion joint which differs from that in Fl patent No. 87271 mainly in that axial extensions of the intermediate elements, which elements are movably connected to a first channel portion, are arranged to slide on an outer circumference of the first channel portion. Moreover, the intermediate elements are in case of a vertical channel supported against a transverse end plane of the second channel portion by gravitation only. A drawback of this expansion joint is that at least when the system is used at a temperature lower than its highest operating temperature, the sliding surface of the axial extensions of the intermediate elements, on which the first channel portion fits in high temperature operation, is directly accessible to abrasive forces due to particles flowing in the channel. Therefore, the

construction has a risk of wearing of the sliding surface on the axial extension of the intermediate elements in start-up and close-down phases of a fluidized bed boiler.

[0007] An object of the present invention is to provide a high temperature expansion joint and a method for making a high temperature expansion joint by which the above mentioned drawbacks of the prior art are minimized.

[0008] In order to obtain at least some of the above mentioned objects, an expansion joint in a vertical channel for conducting hot particles is provided, the channel comprising an upper channel portion and a lower channel portion sealingly connected by a flexible element connected on the outer side of the vertical channel, wherein the upper channel portion comprises a lower end portion with a lower edge and the lower channel portion comprises an upper channel portion with a horizontally extending upper plane. The expansion joint is specifically characterized in that in a predeternnined vertical level range the upper end portion telescopically overlaps the lower end portion in a spaced relationship to permit relative axial and lateral movements of the upper and lower channel portions, whereby the upper plane is at a higher level than the lower edge, and a sealing ring comprising mutually connected sealing blocks positioned on an outer circumference of the lower end portion is arranged on the upper plane.

[0009] An advantage of the present invention is that, because the sealing ring is arranged on the horizontally extending upper plane of the upper end portion, which is at a higher level than the lower edge of the upper channel portion, the sealing blocks are not directly accessible to abrasive forces due to particles flowing in the channel. Thereby, the lower end portion protects in all circumstances the sealing ring from wearing due to the particle flow in the channel.

[0010] The sealing blocks are preferably made of a suitable ceramic material. The sealing blocks preferably have a flat bottom surface, and the sealing ring is arranged to be held on the horizontally extending upper plane of the upper end portion by gravitation. The sealing ring is formed of sealing blocks to seal the upper plane so as to prevent particles from entering from the channel to the space behind the sealing ring.

[001 1 ] Correspondingly, the sealing blocks preferably have a smooth side face to be mounted against an outer circumference at the lower end portion. The inner circumference of the sealing ring is advantageously made to relatively closely fit on an outer circumference of the lower end portion. Thereby, the sealing ring also seals the lower end portion so as to prevent particles from escaping from the channel upwards to the space outside the sealing ring.

[0012] Thereby, between each sealing block of the sealing ring and the horizontally extending upper plane is arranged a horizontal sliding surface so as to allow relative horizontal movement between the sealing ring and the

horizontally extending upper plane. In practice, when differential thermal expansions cause relative horizontal movement between the upper and lower channel portions, the sealing ring moves together with the lower end portion of the upper channel portion, and slides on the upper plane of the upper end portion of the lower channel portion.

[0013] Correspondingly, when differential thermal expansions cause relative vertical movement between the upper and lower channel portions, the sealing ring moves together with the upper end portion of the lower channel portion, and slides on an outer circumference of the lower end portion of the upper channel portion. Therefore, between each sealing block of the sealing ring and the outer circumference of the lower end portion of the upper channel portion there is a vertical sliding surface which allows relative vertical movement between the sealing ring and the lower end portion of the upper channel portion.

[0014] As another aspect, the present invention provides a method for forming an expansion joint in a vertical channel for conducting hot particles comprising an upper channel portion and a lower channel portion, wherein the upper channel portion comprises a lower end portion with a lower edge and the lower channel portion comprises an upper channel portion with a horizontally extending upper plane. The method is specifically characterized by the steps of arranging the upper and lower channel portions so that in a predetermined vertical level range the upper end portion telescopically overlaps the lower end portion in a spaced relationship to permit relative axial and lateral movements of the upper and lower channel portions, whereby the upper plane is at a higher level than the lower edge, forming a sealing ring on the horizontally extending upper plane by arranging mutually connected sealing blocks on an outer circumference of the lower end portion, and thereafter sealingly connecting the upper channel portion and the lower channel portion by connecting a flexible element on the outer side of the vertical channel. [0015] Advantageously, a space limited at least by the horizontally extending extensions and the ring of mutually connected sealing blocks, so-called sealing space, is at least partially filled by insulating material before the step of connecting the upper channel portion and the lower channel portion by the flexible element.

[0016] An advantage of the method according to the present invention is that the expansion joint, especially the sealing ring thereof, can be made and maintained at the outside of the channel. [0017] Preferably, the seal between the upper and lower channel portions is made so that the upper and lower channel portions comprise an outwardly extending extension, which outwardly extending extensions are sealingly connected by the flexible element, such as a fabric bellows. Advantageously, the space limited at least by the fabric bellows, the horizontally extending extensions and the sealing ring, the sealing space, is at least partially filled by insulating material, such as insulating wool. [0018] Advantageously, the space limited at least by the fabric bellows, the horizontally extending extensions and the ring of mutually connected sealing blocks, the sealing space, is pressurized by a gas. Thereby, the pressurizing gas causes a continuous, relatively small flow of gas from the sealing space towards the channel, and thus further minimizes the risk of particles packing into the sealing space. The pressurizing gas can be, for example, air or exhaust gas.

[0019] According to a preferred embodiment of the present invention, adjacent sealing blocks of the sealing ring are mutually connected by steel plates. The seal blocks may advantageously comprise upright pins, and the steel plates, with corresponding holes, can be mounted by laying them to be connected by the pins. Advantageously, adjacent sealing blocks of the sealing ring are partially overlapping so as to prevent or at least minimize the possibility of escaping of particles from the channel upwards between the sealing blocks to the sealing space.

[0020] An expansion joint according to the present invention can

advantageously be used in a circulating fluidized bed (CFB) boiler, especially in vertical connecting channels of the particle separator of a CFB boiler. The lower end of such a particle separator is connected to a return duct leading an intense stream of separated particles to the lower portion of the furnace of the CFB boiler. Due to the constructions of the particle separator and the return duct, differential thermal expansions may cause relatively large horizontal and vertical relative movements between the particle separator and the return duct. An expansion joint according to the present invention is therefore advantageously arranged in a channel leading from the particle separator to the return duct. Correspondingly, the upper end of the particle separator is connected to an exhaust gas channel, which still carries also some fly ash. Thus, an expansions joint according to the present invention can advantageously be arranged also in a vertical channel leading flue gas and fly ash from the particle separator to the exhaust gas channel. [0021 ] The above brief description, as well as further objects, features, and advantages of the present invention will be more fully appreciated by reference to the following detailed description of the presently preferred, but nonetheless illustrative, embodiments in accordance with the present invention, when taken in conjunction with the accompanying drawings, wherein:

[0022] Fig. 1 is a schematic vertical cross section of a part of a vertical channel comprising an expansion joint according to the present invention.

[0023] Fig. 2 is another schematic vertical cross section of a part of a vertical channel comprising an expansion joint according to the present invention.

[0024] Fig. 3 is a schematic plan view of a sealing ring of an expansion joint according to the present invention. [0025] Figs. 4a and 4b are a schematic vertical cross section and a schematic plan view of two adjacent sealing blocks of an expansion joint according to the present invention.

[0026] Fig. 1 shows schematically an expansion joint 10 arranged in the wall 12 of a channel 14. The channel comprises an upper channel portion 16 and a lower channel portion 18, which are sealed to be airtight by a fabric bellows 20 attached to outwardly extending extensions 22, 22' of the upper and lower channel portions. The channel of Fig. 1 is water cooled as can be seen of the horizontal water distributors 24, 24', but in other embodiments the channel can also be uncooled. The upper and lower channel portions are advantageously covered by a layer of refractory 26. [0027] The upper channel portion 16 comprises a lower end portion 28 with a lower edge 30 and the lower channel portion 18 comprises an upper end portion 32 with a horizontally extending upper plane 34. A sealing ring 36 formed of mutually connected sealing blocks 38 is arranged on the horizontally extending upper plane 34. The sealing ring 36 is held by gravitation against the upper plane 34. The sealing ring 36 is also arranged to relatively closely fit on an outer circumference 40 of the lower end portion 28 of the upper channel portion 16.

[0028] The upper end portion 32 of the lower channel portion 18

telescopically partially overlaps the lower end portion 28 of the upper channel 16 portion in a spaced relationship. The upper and lower channel portions are arranged relative to each other so as to permit the relative axial and lateral movements due to possible differential thermal expansions. The amount of overlapping 42 between the upper and lower channel portions depends on temperature, but the channel portions are arranged so that in all conditions the upper plane 34 is at a higher level than the lower edge 30.

[0029] The space limited by the lower end portion 28, the sealing ring 36, the upper plane 34, the outwardly extending extensions 22, 22' and the fabric bellows 20, so-called sealing space 46, is advantageously at least partially filled with insulating wool 44. The insulation wool enables to keep the fabric bellows 20 at a temperature below its maximum operating temperature. It also prevents hot particulate material which may penetrate between the sealing blocks 38 or between the sealing blocks and the lower end portion 28 from entering further into the sealing space 46. The space filled with the insulating wool may be further limited by suitable means, such as plates or nests 48, 48' attached to the outwardly extending extensions 22, 22'. The plates 48, 48' are preferably connected to the extensions 22, 22' by bolts or by another easily removable way. Thereby the insulating wool and sealing blocks can be checked and possibly changed at the outside of the channel 14.

[0030] The sealing space 46 may advantageously be equipped by means 50 for pressurizing the sealing space, for example, by air or flue gas. The sealing space 46 is usually not airtight in respect of the channel 14, and the

pressurization gives rise to a flow of gas from the sealing space to the channel 14. This relatively small flow of gas guarantees that particulate matter does not pack from the channel 14 to the sealing space 46. The use of pressurizing gas also helps to keep the fabric bellows at a relatively low temperature.

[0031 ] Fig. 2 shows the same expansion joint 10 as Fig. 1 , but in another temperature. The upper channel portion 16 is supported, for example, so that at a higher temperature, shown in Fig. 2, it moves vertically closer to the lower channel portion 18. Thus, the overlap 42' between the upper channel portion and the lower channel portion shown in Fig. 2 is larger than the corresponding overlap 42 shown in Fig. 1 .

[0032] At the same time, there may be relative horizontal movement between the upper channel portion 16 and the lower channel portion 18. In Fig. 2, the upper channel portion 16 is moved left relative to the lower channel portion 18, as compared to the situation shown in Fig. 1 . Thus, the gap 52 between the lower end 28 and upper end 32 is smaller than the corresponding gap in Fig. 1 . Because of the relative movements shown in Fig. 2, the fabric bellows 20 is bent outwards, and the insulating wool 44 is compressed, as compared to Fig. 1 .

[0033] In the situation of Fig. 2, the sealing blocks 38 have slid horizontally on the horizontal sliding surface 54 of the upper plane 34 and vertically on the vertical sliding surface 56 on the inner circumference 40 of the lower channel portion 28. While the sealing blocks 38 remain in all temperatures in contact with the upper plane 34 and the lower end portion 28, particulate matter cannot enter from the channel 12 to the sealing space 46.

[0034] Fig. 3 shows a plan view of the sealing ring 36 formed of mutually connected ceramic sealing blocks 38. As described in connection with Figs. 1 and 2, the sealing ring is arranged on the upper plane of the upper end portion of the lower channel portion and on an outer circumference of the lower end portion of the upper channel portion. The upper and lower channel portions are, however, not shown in Fig. 3. As indicated by the form of the sealing ring in Fig. 3, the upper and lower channel portions preferably have a rectangular cross section. However, it is also possible to have upper and lower channel portions with another type of a cross section, such as a circular cross section. In such cases, the sealing blocks are modified to form a sealing ring corresponding to the cross section of the upper channel portion.

[0035] The size of the sealing blocks can be varied. The sealing ring can be formed of only a small number, such as four, sealing blocks. However, preferably the sealing blocks are made relatively small to keep the handling of the blocks easier. Therefore, the sealing ring is preferably formed of at least 10 - 20 sealing blocks. Typically the sealing blocks have a height of about 5 cm to about 10 cm, and horizontal dimensions from about 10 cm to about 50 cm. [0036] Figs. 4a and 4b show a vertical cross section and a plan view on two adjacent sealing blocks 38 of a sealing ring. According to this embodiment, adjacent sealing blocks are formed to partially overlap so as to prevent particle flow upwards between the blocks.

[0037] Adjacent sealing blocks 38 are preferably mutually connected together to maintain the form of the sealing ring when relative movements between the components of the system take place. Figs. 4a and 4b show an advantageous method to connect adjacent sealing blocks 38. According to this method, each sealing block includes metal pins 58 cast into the block. Steel plates 60 with corresponding holes are then placed in the pins to form a rigid sealing ring. [0038] An advantage of the present expansion joint is that it can stay in good operating conditions in the start-up, operating and close-down phases of a circulating fluidized bed boiler. More particularly, this means that at most a small amount of particulate material penetrates into the sealing space 46, and wearing of the sealing ring 36 and sliding surfaces 54, 56 are minimized. Therefore, the need for frequent replacing and cleaning of parts of the expansion joint is avoided. Moreover, when cleaning or replacing parts of the expansion joint is desired, it can easily be made from the outside of the vertical channel 14. This can be done by first removing the fabric bellows 20 and possible insulation holding means 48, 48', whereafter the insulation wool and sealing blocks can be maintained and, if needed, replaced.

[0039] While the invention has been described herein by way of examples in connection with what are at present considered to be the most preferred embodinnents, 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.