Fluidized Bed Heat Exchanger

Abstract

A fluidized bed heat exchanger with a chamber (24) comprises a solid particles inlet port (22), a solid particles outlet port (30), arranged at a distance to the inlet port (22), means (46) for introducing a fluidizing gas from a bottom area into the chamber (24). The heat exchanger further comprises at least two heat transfer means (28) within the one chamber (24), each being provided with a heat transfer medium inlet port (42) and a heat transfer medium outlet port (44), wherein a first heat transfer means (28) is designed as a reheater and second heat transfer means (28) is designed as a superheater to achieve a heat transfer medium temperature and a heat transfer medium pressure above that of the reheater. At least one of the reheater or superheater is made of a multiplicity of heat transfer tubes arranged in a meandering fashion for conveying a heat transfer medium.

Claims

1. Fluidized bed heat exchanger with one chamber (24), comprising 1.1 at least one solid particles inlet port (22) 1.2 at least one solid particles outlet port (30), arranged at a distance to the at least one inlet port (22), 1.3 means (46) for introducing a fluidizing gas from a bottom area (24b) of said chamber (24) into said chamber (24), 1.4 at least two heat transfer means (28) within said one chamber (24), each being provided with a heat transfer medium inlet port (42) and a heat transfer medium outlet port (44), wherein 1.5 a first heat transfer means (28) is designed as a reheater and second heat transfer means (28) is designed as a superheater to achieve a heat transfer medium temperature and a heat transfer medium pressure above that of the reheater.

2. Fluidized bed heat exchanger according to claim 1, wherein the reheater is constructed to allow a heat transfer medium temperature of up to 600 C.

3. Fluidized bed heat exchanger according to claim 1, wherein the reheater is constructed to allow a heat transfer medium pressure of up to 50 bar.

4. Fluidized bed heat exchanger according to claim 1, wherein the superheater is constructed to allow a heat transfer medium temperature of up to 600 C.

5. Fluidized bed heat exchanger according to claim 1, wherein the superheater is constructed to allow a heat transfer medium pressure of up to 190 bar.

6. Fluidized bed heat exchanger according to claim 1, wherein at least one of said reheater or superheater is made of a multiplicity of heat transfer tubes for conveying a heat transfer medium and arranged in a meandering fashion.

7. Fluidized bed heat exchanger according to claim 1 with chamber walls (14w) being at least partially water-cooled.

8. Fluidized bed apparatus comprising a fluidized bed reactor (10) with an associated fluidized bed heat exchanger (24) according to claims 1, wherein the fluidized bed reactor (10) and the fluidized bed heat exchanger (24) have one common wall (14w).

9. Fluidized bed apparatus according to claim 8, wherein the common wall (14w) is water-cooled.

Description

[0156] The invention is now described with reference to the attached drawing, showingall in a very schematic wayin

[0157] FIG. 1

[0158] A general concept of a fluidized bed apparatus according to prior art

[0159] FIG. 2

[0160] A cross sectional view of a fluidized bed heat exchanger

[0161] FIG. 3

[0162] A top view on the FBHE 24 of FIG. 2 along line 3-3

[0163] FIG. 4

[0164] A cross sectional view of another embodiment of a fluidized bed heat exchanger

[0165] FIG. 5

[0166] A cross sectional view of further embodiment of a fluidized bed heat exchanger A with 2 groups of heat exchangers

[0167] FIG. 6

[0168] A top view on the FBHE of FIG. 5 along line 6-6

[0169] FIG. 7

[0170] A top view on a further example for a FBHE 24 with an amended inlet port

[0171] FIG. 8a

[0172] A cross sectional view of an FBHE with multiple nozzles sets in the bottom area

[0173] FIG. 8b

[0174] A cross sectional view of a syphon with multiple nozzles sets in the bottom area

[0175] FIG. 9

[0176] An general view of a fluidized bed apparatus mounted in a suspended manner

[0177] FIG. 10

[0178] A compact fluidized bed heat exchanger in a 3-dmensional view

[0179] In the Figures identical an similar acting construction parts are identified by same numerals.

[0180] FIG. 1 discloses the general concept of a fluidized bed apparatus and its main components according to the present invention.

[0181] It comprises: [0182] A circulating fluidized bed reactor (CFBR) 10. Its lower part comprises a grate-like structure 12 through which air (arrow A1) is blown into a reactor chamber 14 via (not shown) nozzles, thus providing a fluidized bed (denseboardDB) above said grate 12, wherein said denseboard comprises a particulate material like coal, wood etc. to be burnt. [0183] The CFBR has two outlet ports 16 at opposite sides of its upper part, allowing a mixture of gas and solid particles exhausted from the CFBR to flow into associated separators 18, namely cyclone separators. The separators serve to separate solid particles from the gas. [0184] Transfer means 20, designed as ducts, extend from the lower end of each separator 18 downwardly and into an inlet port 22 along the ceiling 24c of a fluidized bed heat exchanger (FBHE) 24. [0185] A syphon-like tube construction 26 (U-shaped) extends from the lower end of each separator 18 into reactor chamber 14 and enters into chamber 14 shortly above grate 12 of said CFBR. [0186] The FBHE is equipped with (plate-like) heat transfer means 28 and an outlet port 30 merging into reactor chamber 14 at the same vertical height as tube construction 26.

[0187] This concept belongs to prior art. Insofar details are not further illustrated as known to the skilled person.

[0188] The invention includes one or more of the following features:

[0189] According to FIG. 2 the fluidized bed heat exchanger 24 displays an inlet port 22 at its upper end (in FIG. 2: top left) and an outlet port 30 at its upper end (in FIG. 2: top right), i. e. opposite to each other. Said outlet port 30 provides return means for solid particles transported along transfer duct 20 into said FBHE and is provided within a common wall 14w of chamber 14 and FBHE 24.

[0190] Outlet port 30 comprises multiple flow through openings, arranged in a horizontal row with a distance to each other along a corresponding wall section of said wall 14w.

[0191] Said wall 14w is water-cooled, namely constructed of vertically extending tubes with fins running between adjacent tubes. The tubes are cooled by water fed through said tubes.

[0192] The through holes having the function of discrete outlet ports are shown in FIG. 2 in a slightly inclined orientation, with a lower end towards the fluidized bed heat exchanger 24 and a higher end towards the fluidized bed reactor chamber 14.

[0193] This inclined orientation (sloped outlet port 30) can be provided as part of a 3-dimensional profile (for example as a convexity 14w) of said wall 14w towards the inner space/chamber of the fluidized bed heat exchanger 24 as shown in dotted lines in FIG. 2 and characterized by numeral 30.

[0194] FIG. 2 further shows the design and construction of heat transfer means 28 within the fluidized bed heat exchanger 24. In the Figure only one of said heat transfer means is shown. Further heat transfer means of equal design are placed at a distance to each other within FBHE 24 (perpendicular to the plane of projection).

[0195] Steam is fed into said means 28 via a central feeding line 42, then flowing through the meandering tube (as shown), providing said means 28, and escaping via a common outlet line 44, allowing to take heat from the particulate material (symbolized by dots P) moving through FBHE 24 between inlet port 22 and outlet port 30.

[0196] It is important that each of said means 28 is designed in a wall-like pattern and extending substantially parallel to the main flow direction of the solid particles on their way to and through the outlet port 30, symbolized in FIG. 2 by arrow S.

[0197] All tubes 28 are connected to the same feeding line 42 and outlet line 44.

[0198] The meandering tubes not only give the heat transfer means 28 a wall-like pattern but as well a grid-like structure to allow the particulate material to pass through as well in a horizontal direction.

[0199] The horizontally extending sections of said tubes are about three times longer than the vertically extending sections (FIG. 2 is not drawn to scale). Adjacent horizontal sections extent to a distance to each other being about the tube diameter.

[0200] As shown in FIG. 2 the heat transfer means 28 extent about more than 60% of the chamber height, being the distance between a chamber bottom 24b and a chamber sealing 24c. In the embodiment each of said wall-like heat transfer means 28 extends from slightly above bottom 24b to slightly below inlet port 22 and from slightly off wall 14w to slightly off opposite wall 24w.

[0201] This allows to avoid any structural means within FBHE 24 which could otherwise urge the solid particles to meander within FBHE. In particular the new design allows to avoid any entrance chamber and/or return chamber for the particulate material to homogenize.

[0202] In prior art devices a separate entrance chamber EC with a discrete partition wall is constructed between wall 24w and adjacent part of heat transfer means 28 as well as a separate return chamber RC between wall 14w and parts 28. These walls and chambers caused the stream of solid particles to flow up and down, which is now avoided with the new design without any partition walls.

[0203] The particulate material may take a direct way from the inlet port 22 to the outlet port 30 (see arrow S) along the channels/gaps C formed between adjacent tubes (heat transfer means), as may be seen in FIG. 3.

[0204] Fluidization of the particulate material within FBHE 24 is achieved by air nozzles 46 in the bottom area 24b. The particulate material is circulated by said purging means within FBHE 24 in order to optimize heat transfer from the hot solid particles P onto the steam flowing within tube like heat transfer means 28.

[0205] The embodiment of FIG. 4 differs from that of FIGS. 2,3 insofar as two baffles 50, 52 extent from sealing 24c downwardly, ending shortly above heat transfer means 28. These baffles 50, 52 extend substantially perpendicular to a straight line between inlet port 22 and outlet port 30 (dotted line L).

[0206] Both baffles 50, 52 extend between opposite walls of FBHE 24 (only one, namely 24s is shown), being the walls bridging said walls 14w, 24w. The baffles 50, 52 are arranged at a distance to each other.

[0207] Each of said baffles 50, 52 comprise one opening symbolized by dotted line O to allow pressure adjustment (equalization) within the inner space of FBHE 24.

[0208] The said baffle(s) 50, 52 may as well be designed like a curtain, fulfilling the same function as a continuous board, namely to urge the particulate material to flow through said channels C (FIG. 3) between adjacent heat transfer means 28 on their way between inlet port 22 and outlet port 30.

[0209] In FIG. 4 outlet port 30 is extended, namely protruding into circulating fluidized bed reactor 10.

[0210] In the embodiment according to FIG. 5 the multiplicity of heat transfer means 28 is split into two groups.

[0211] A first group G1 is made of a number of heat transfer means 28 as shown in FIGS. 2, 3 with the exception that the horizontal extension between walls 24w, 14w is much shorter and ending about half the way between said walls 14w, 24w.

[0212] This group G1 of multiple heat transfer tubes 28 connected to a common feeding line 42 and a common outlet line 44 is characterized by a feeding temperature of 480 C. and an outlet temperature of 560 C. of the heat transfer medium (steam) and an average steam pressure of 32 bar, thus fulfilling the function of a so called reheater.

[0213] The second group G2 of several heat transfer means 28 is constructed the same way as group G1 but connected so separate inlet lines 42 and outlet lines 44 for said steam and designed to achieve a heat transfer medium temperature of between 510 C. (inlet temperature) and 565 C. (outlet temperature) as well as an average 170 bar pressure. This allows to use the tubes of group G2 as a so called superheater.

[0214] As shown in FIG. 5 tubes of group G2 are arranged closer to the outlet port 30 and adjacent to wall 14w while tubes of group G1 are arranged adjacent to wall 24w with a distance between groups G1 and G2.

[0215] FIG. 6 is a top view of FIG. 5 along line 6-6 in FIG. 5.

[0216] The fluidized bed heat exchanger 24 according to FIG. 7 displays a different design around inlet port 22, which widens towards the inner space of chamber 24, wherein said widened section 22w is further inclined towards the bottom area 24b of FBHE 24 to provide a distributor means allowing the entering stream of solid particles to spread over substantially the full width of said inner space of chamber 24, wherein the width is defined by the distance of side wall 24s.

[0217] This distributor means (section 22s) are arranged in a transition region defined by end section of inlet port 22 and the adjacent section of chamber 24, extending upstream of said heat transfer means 28 and extending over about of the chamber width.

[0218] Ribs 22r protrude from the surface of said distributor 22s and are arranged in a star-like pattern.

[0219] Again all walls 14w, 24w and 24s of said FBHE are made of water-cooled tubes with fins between adjacent tubes, symbolized in the right part of FIG. 7.

[0220] FIG. 8a displays an FBHE 24 characterized by a modified bottom area 24b.

[0221] Numerous air nozzles 46 are mounted within bottom 24b. Each nozzle comprises an outer end 460, protruding downwardly from the outer surface of bottom 24b and an inner end 46i, protruding into the hollow space of FHBE 24 equipped with groups G1, G2 of heat exchange tubes 28.

[0222] The nozzles 46 are assembled into five nozzle sets N1, N2, N3, N4 and N5, one behind the other in a row between walls 24w and 14w. All nozzles 46 of a nozzle set are commonly connected to a respective common gas channel 48. If air is fed along one of these channels all corresponding nozzles 46 will be activated to allow air to enter into FBHE 24.

[0223] The arrangements of discrete nozzle sets N1 . . . N5 with discrete channels 48 make it possible to set different air pressure in different channels and accordingly to introduce air into the fluidized bed of solid particles within FBHE under different pressure at different areas to optimize homogenisation of the particles within the fluidized bed.

[0224] A similar design may be used to improve the syphon-type seal 26 between separator 18 and FBHE 24 or reactor 10 respectively, as illustrated in FIG. 8b.

[0225] A mixture of gas and solid particles like ash coming from separator 18 [0226] enters the inlet tube of the U-shaped syphon 26 in a downward direction, [0227] is then fluidized by a fluidized bed construction in a bottom area 26b of said inlet tube via nozzles 27, [0228] turns about 90 degrees, [0229] flows along an intermediate chamber section 26i, where further fluidization takes place, [0230] then turns up into an outlet tube of the U-shaped syphon 26, where further fluidization by nozzles 27 at the bottom area of said outlet tube may take place, before [0231] flowing along another U-shaped tube section and entering the CFBR 10 via a corresponding return line.

[0232] Similar to the embodiment of FIG. 8a, the multiplicity of air nozzles 27 is split into three nozzles sets SN1, SN2 and SN3, each with a certain number of nozzles 27, and each coupled to a respective air duct D1, D2 and D3, feeding air to the respective nozzles 27 under same or different pressure.

[0233] Similar to FIG. 8a the air ducts D1 . . . D3 have a funnel shape at their upper ends.

[0234] FIG. 9 represents a fluidized bed apparatus wherein its main components, namely the CFBR 10, the FBHE 24 as well as corresponding separators 18 are mounted in a suspended manner to a central supporting structure, namely a frame 60. The frame 60 has the shape of an inverted U with its legs 601 fixed within ground GR.

[0235] While the CFBR 10 and the separator 18 are each directly suspended from base 60b of frame structure 60 (by posts 62), the FBHE 24 is mounted in a suspended manner from separator 18.

[0236] Mechanical stability of FBHE 24 is further achieved by said common, water-cooled wall 14w with CFBR 10.

[0237] Because of the hanging structure thermal expansion and constriction take place at all components in the same direction and avoids mechanical as well as thermo-mechanical tensions between adjacent construction parts at most.

[0238] To make the construction wear resistant, the fluidized bed heat exchanger has no refractory lining; all walls are water cooled metal walls.

[0239] The hanging structure allows an integration of a syphon 26 with its return duct 26r without transferring mechanical forces or moments between the respective construction parts.

[0240] According to FIG. 9 the lowermost point LP1 of outlet port 30 of fluidized bed heat exchanger 24 enters the circulating fluidized bed reactor 10 at a height of >0.15 L, calculated from the lowermost end of the axial length L of CFBR 10. The lowermost end is defined by grate 12 of the fluidized bed. The minimum distance of >0.1 L, better >0.2 L, allows to place the return means 30 out of the so called denseboard DB and avoids the risk of any backflow of solid particles from the fluidized bed within reactor 10 into the associated construction elements like FBHE 24. This feature may be combined with sloped outlet ports 30 as disclosed in FIG. 2 or sloped return ducts 26r.

[0241] The lowermost point of return duct 26r of syphon 26 enters the CFBR at a height of the denseboard DB, close to grate 12 and below outlet port 30.

[0242] This positioning of the two outlet ports/return means 30,26r to each other is an important combined feature valid for various applications.

[0243] In case of an apparatus comprising more than one separator 18, for example 3 separators, FIG. 10 discloses an embodiment with three corresponding fluidized bed heat exchangers 24.1, 24.2, 24.3 which are mechanically connected to provide one common fluidized bed heat exchanger 24 of corresponding, suitable size, with water-cooled intermediate walls 24i. Again: all three wall sections 14w of the common heat exchanger 24 are part of the reactor wall 14, i.e. a common water-cooled wall with integrated outlet openings 30.

[0244] Walls 14i, 14w are made of metal tubes, welded to each other and connected with a fluid source to feed cooling water through said tubes.