WO2006084682A1

WO2006084682A1 - Method and apparatus for fluidizing a fluidized bed

Info

Publication number: WO2006084682A1
Application number: PCT/EP2006/001113
Authority: WO
Inventors: Cornelis Klett; Michael STRÖDER; Werner Stockhausen; Roger Bligh
Original assignee: Outotec Oyj; Outokumpu Oyj; Outokumpu Technology Oyj
Current assignee: Outokumpu Oyj; Metso Corp
Priority date: 2005-02-11
Filing date: 2006-02-08
Publication date: 2006-08-17
Anticipated expiration: 2007-08-11
Also published as: DE102005006570B4; DE102005006570A1; BRPI0608239B8; MY146065A; CN101115552A; AU2006212416B2; BRPI0608239A2; BRPI0608239B1; AU2006212416A1; AU2006212416A2; AU2006212416A8; RU2410154C2; CN101115552B; RU2007133826A

Abstract

When fluidizing a fluidized bed, which forms a fluidized bed (3) of solid particles, in a vessel (1), the fluidizing gas is introduced into the fluidized bed via a pipeline (7) in the vicinity of the vessel base (9), the gas flow in the pipeline (7) being directed substantially continuously downwards. A flow resistance (10) which is arranged above the fluidized bed (3) is provided in the pipeline (7).

Description

Method and apparatus for flυidizing a fluidized bed

The invention relates to a method for fluidizing a fluidized bed, which forms a fluidized bed of solid particles, in a vessel with a base by feeding a fluidizing gas into the fluidized bed via at least one pipe, and to an apparatus for carrying out this method.

Hitherto, fluidized beds have been fluidized by gas being supplied from below via open vertical holes, nozzle tubes with lateral holes with or without caps or porous plates (cf. "Handbook of Fluidization and Fluid-Particle Systems", Chapter 6: Gas Distributor and Plenum Design in Fluidized Beds pages 155-176, Ed. W.C. Yang, Dekker, New York, 2003).

In the case of cap type nozzles, even fluidizing is achieved by virtue of the fact that each cap nozzle is equipped with a high pressure loss by virtue of small cross sections of flow. The high velocities and multiple diverting of the gas flow makes it difficult for solids to penetrate backwards into the gas supply. Nevertheless, when the gas supply is switched off, residual fluidization often causes solids to penetrate into the cap, and these solids are not generally flushed out again when the apparatus is started up again, which can even cause the cap to become blocked. Drainage measures then have to be undertaken, which represent an occupational safety problem in the case of processes carried out at a high temperature.

Porous plates or fabrics produce a very uniform fluidization but have the drawback that the porous medium becomes clogged over the course of time and cannot be fully cleaned again, or that the porous medium loses pressure loss over the course of time as a result of erosion. As in the case of the distributor equipped with caps or nozzles, it is necessary to provide for the possibility of emptying the space through which the gas flows at least for the eventuality of the fabric breaking. Moreover, the use temperature of the porous plates and in particular of the fabrics is limited.

It is known from DE 33 40 099 for gas to be introduced laterally upwards into the fluidized bed. However, in particular in this case the penetration of the solids occurs to an increased extent. Alternatively, the gas may be fed into the fluidized bed for example through pipes from the side (DE 40 07 835 C2). Even fluidizing requires a plurality of pipes, the ends of which are distributed evenly over the cross-sectional area. In addition, it is necessary to ensure that approximately the same volumetric flow of gas flows through each pipe. This is then achieved by each pipe being provided with a pressure loss which ensures that the gas is evenly distributed. In the case of nozzles which have hitherto been used for this purpose, the pressure loss is achieved by a significant narrowing in the nozzle tip. This has the drawback of high flow velocity in direct contact with solids, which generates turbulence, leads to erosion at the nozzle tip and mechanically stresses the particles in the fluidized bed.

It is also known to introduce a further medium with the aid of a gas stream de- signed as a jet nozzle (DE 102 37 124). In this case, however, the nozzle is not used for fluidization.

Therefore, it is an object of the invention to allow the uniform fluidizing of a fluidized bed without the possibility for parts of the gas feed to become blocked by the solids. In addition, it is intended to prevent erosion and/or particle fragmentation.

The invention achieved this object substantially by a method having the features of Claim 1 and an apparatus having the features of Claim 11.

Advantageous embodiments of the invention are evident form the dependent claims.

The new form of fluidization is distinguished by the fact that the gas stream is guided continuously downwards from a distributor above the fluidized bed and emerges from the pipe in the vicinity of the vessel base. According to a preferred configuration of the invention the pipe does not have any narrowings in the direction of flow below the maximum height up to which the solids could rise in the pipe, i.e. the pipe has a cross section which remains constant or widens downwards below this height.

The pressure loss required to make the fluidizing more uniform is in each pipe brought about by a flow resistance (e.g. an orifice) which, however, in any event lies in a part of the individual pipe which remains free of solids. It is preferable for the flow resistance to be located outside the fluidizing space, so that it is readily accessible. According to the invention, the pressure loss in the flow resistance should amount to between 10 and 1500 mbar, preferably between 20 and 200 mbar.

The outlet velocity of the gas from the bottom end of the pipe depends on the sensitivity of the solids in the fluidized bed and its permissible stressing. If it is a sensitive, for example brittle, solid and fragmentation is undesirable, the velocity must be selected to be as low as possible. The outlet velocity should generally be between 2 and 50 m/s, preferably between 5 and 30 m/s.

To set the gas streams in all the pipes to be absolutely even, the pressure ratio across the orificecan be set to more than 2 to 1 , i.e. the absolute pressure up- stream of the orificeis at least double the absolute pressure downstream of the orifice. Consequently, sonic flow is reached in the narrowest cross section of the orifice. The sonic flow means that the volumetric flow in the pipe is accurately defined irrespective of the operating fluctuations and the outlet velocity at the bottom end of the pipe. The volumetric flows in the pipes may optionally also be determined in such a way that even a desired defined uneven distribution is achieved.

The pipes may be introduced vertically or at an angle to the horizontal. The angle is in this case more than 1 ° with respect to the horizontal, preferably more than 30° with respect to the horizontal. This makes it possible to prevent the pipes from becoming blocked, or else solids which have penetrated are easy to blow out again when the fluidizing is started up.

Irrespective of their introduction angle, the pipes are preferably cut off horizontally at the end, in order to enable the gas to flow out as far down as possible, i.e. close to the base of the fluidized bed, generally at a distance of less than 250 mm, preferably a distance of less than 150 mm, from it.

To further improve the flow at the pipe outlet, the pipe end can be provided with a "detachment lug" on the top side, which reduces the erosion to the pipe caused by the flow. To reduce wear to the pipes, it is possible to select a wear-resistant material, e.g. stainless steel. Furthermore, it is possible to prevent wear to the pipe end by means of a build-up weld.

This new design allows the gas distributor of the fluidized bed to be simple and inexpensive in form. Furthermore, the design prevents solids through-fall through the distributor.

To make it easy to optimize the operating performance of the fluidized bed, it is possible to configure the flow resistance as an exchangeable apertured orifice between two flanges. To further improve the ease of maintenance, it is addition- ally possible for the nozzle tubes themselves to be introduced into the vessel through connection pieces with flanges, in order to facilitate their replacement.

The method according to the invention is suitable for all fluidized beds, but in particular for those in which what is known as nozzle through-fall can very easily occur, for example if the particles are very small or remain in the fluidized state for a very long time after the fluidizing has been stopped.

The invention is explained in more detail below on the basis of exemplary embodiments and with reference to the drawing, in which all the features described and/or illustrated in figures form the subject matter of the invention, irrespective of the way in which they are combined in the claims or the way in which the claims are referred back. In the drawing:

Fig. 1 shows an apparatus according to the invention for fluidizing a fluidized bed,

Fig. 2a, b show alternative configurations of the pipe ends which open out above the vessel base, and

Fig. 3 shows another embodiment of an apparatus according to the invention.

The apparatus for fluidizing a fluidized bed which is diagrammatically depicted in Fig. 1 comprises a vessel 1 into which solid particles are introduced via a feed line 2. The solid particles are, for example, heat-treated in the vessel 1 in a fluidized bed 3 and then discharged again from the vessel 1 via a discharge line 4. The off-gas produced is discharged via an off-gas line 5. The fluidized bed 3 is flυidized by supplying a fluidizing gas, the composition and properties, in particular temperature, of which depend on the desired treatment of the solid particles. The fluidizing gas is supplied via a line system 14 which divides the fluidizing gas, via a gas distributor (header) 6, between a plurality of pipes 7 distributed for example in the shape of a circle. In the embodiment illustrated in Fig. 1 , the pipes 7 extend substantially vertically from above into the fluidized bed formed by the fluidized bed 3, and their respective outlet openings 8, which are cut off horizontally, open out into the fluidized bed 3 just above the base 9 of the vessel 1. The distance between the outlet openings 8 and the vessel base 9 is, for example, 100 or 200 mm.

In the pipes 7, an apertured orifice 10 is in each case provided as a flow resistance above the region which can be reached by the solid particles of the fluidized bed 3. The apertured orifice 10 is, for example, secured between two flanges 11, so that it can easily be replaced in order to optimize the operating properties and/or for maintenance or repair work. The passage opening of the apertured orifice 10 may be variable, in order to set the pressure loss and therefore the quality of even distribution of the gas. Given a sufficiently high admission pres- sure, the diameter of the apertured orifice 10 can alternatively be set in such a way that a pressure ratio of at least 2:1 is produced at the orifice, and sonic flow is achieved at the smallest cross section.

In the embodiment illustrated, the apertured orifices 10 lie outside the vessel 1. However, they may also be arranged inside it, provided that it is ensured that the solid particles cannot rise up as far as the flow resistance and block it and/or cause wear to it.

Instead of the vertical arrangement of the pipes 7 illustrated in Fig. 1 , the pipes 7 may also be inclined. Fig. 2a and 2b illustrate examples of an inclined pipe arrangement of this type, in which the pipes 7a and 7b are at an angle of approx. 30° (25°-35°) with respect to the horizontal.

To increase the resistance to erosion with regard to the gas flow, the pipe cross section is thickened in the region of the outlet opening 8a or 8b. In the embodiment shown in Fig. 2a, in this case a material thickening produced for example by a build-up weld 12 is provided around the opening region of the pipe 7a. By contrast, in the variant shown in Fig. 2b, there is merely a "detachment lug" 13 provided at the top side, since the gas in any case rises upwards and is guided away from the pipe 7b by the detachment lug 13.

When using the apparatus shown in Fig. 1 (or the variants shown in Fig. 2a or 2b), fluidizing gas is introduced into the fluidized bed 3 through the pipes 7 and fluid- izes the solid particles. The pressure loss brought about by the flow resistance produces even fluidizing, while it is ensured that the solid particles cannot rise up as far as the flow resistance and block the pipe 7.

Fig. 3 shows another example of the use of the fluidizing method according to the invention for solid conveying in what are known as "airlift sending pots". An airlift system is used for the pneumatic conveying of 100 t/h of aluminium hydrate with grain diameters of between 30 and 170 μm over a height of approx. 60m. The airlift sending pot 20 shown in Fig. 3 is for this purpose used to feed the conveying. The vessel 21 has a diameter of 1200 mm with a centrally arranged conveying pipe 22 with a diameter of 400 mm. A conveying air stream of approx. 6000 m³/h (s.t.p.) is passed through the central nozzle 23 and carries the solids with it. To achieve even conveying, the surrounding solids have to be fluidized, so that they can always flow sufficiently into the region of the central nozzle 23. This requires a fluidizing gas flow of 300 m³/h (s.t.p.). The vessel is fluidized via 30 pipe nozzles 24 (nominal width 1"), the bottom ends of which are arranged in two concentric rings of different diameters, so that the annular space between convey- ing pipe 22 and vessel wall 25 is uniformly supplied with air. The fluidizing pipes 24 are supplied with air from a common distributor 26 which lies above the region which can be loaded with solids. In each pipe 24, there is an orifice 27 just below the distributor 26, which with a pressure loss of 150 mbar is designed in such a way that each pipe 24 receives virtually the same volumetric flow of air.

Surprisingly, it has been found that this form of fluidizing is superior to standard bottom fluidization with a porous fabric in terms of the evenness of solids conveying. It is virtually impossible for the fluidizing pipes to become blocked. There is no need for the standard emptying measures. List of reference numbers

1 Vessel

2 Introduction line for solids

3 Fluidized bed

4 Discharge line for solids

5 Off-gas line

6 Gas distributor

7 Pipe

8 Outlet opening

9 Vessel base

10 Apertured orifice

11 Flange

12 Build-up weld

13 Detachment lug

14 Line system

20 Airlift sending pot

21 Vessel

22 Conveying pipe

23 Central nozzle

24 Fluidizing pipe

25 Vessel wall

26 Distributor

27 Orifice

Claims

1. Method for fluidizing a fluidized bed (3) of solid particles, in a vessel (1) with a base (9) by feeding a fluidizing gas into the fluidized bed via at least one pipeline (7), characterized in that the fluidizing gas is introduced into the vessel (1) via the pipeline (7) in the vicinity of the vessel base (9), the gas flow in the pipeline (7) being directed substantially continuously downwards.

2. Method according to Claim 1, characterized in that a pressure loss is generated in the pipeline (7) above the fluidized bed (3) in which the solid is fluidized in the vessel (1).

3. Method according to Claim 2, characterized in that the pressure loss can be selected according to the demands imposed on the quality of even distribution of the gas between the pipelines (7).

4. Method according to Claim 2 or 3, characterized in that the pressure loss in the pipeline (7) amounts to between 10 and 1500 mbar.

5. Method according to Claim 4, characterized in that the pressure loss in the pipeline (7) is between 20 and 200 mbar.

6. Method according to one of Claims 2 to 5, characterized in that the pressure loss in the pipeline (7) is generated by a flow resistance (10), and in that the flow velocity in the narrowest cross section of the pipeline is equal to the speed of sound.

7. Method according to one of Claims 2 to 6, characterized in that the pressure loss in the pipeline (7) is generated by a flow resistance (10), and in that the pressure ratio at the flow resistance (10) is > 2:1, based on the absolute pressures upstream and downstream of the flow resistance (10).

8. Method according to one of the preceding claims, characterized in that the volumetric flows in the pipes (7) are set in such a way that a defined uneven distribution of the fluidizing gas introduced into the vessel (1) is produced.

9. Method according to one of the preceding claims, characterized in that the outlet velocity of the fluidizing gas from the pipeline (7) is between 2 and 50 m/s.

10. Method according to Claim 9, characterized in that the outlet velocity of the fluidizing gas from the pipeline (7) is between 5 and 30 m/s.

11. Apparatus for fluidizing a fluidized bed (3), having a vessel (1), to which solids are fed via a feed line (2) and from which solids are removed via a discharge line (4), having a line system (14) for feeding a fluidizing gas into the fluidized bed, and having an off-gas line (5) for discharging the off-gas, in particular for carrying out a method according to one of the preceding claims, characterized in that at least one pipeline (7) for supplying the fluidizing gas is introduced substantially continuously downwards into the vessel (1) and in the vicinity of the vessel base (9) has an opening (8) for the outlet of the fluidizing gas, and in that a flow resistance (10) which is arranged above the fluidized bed (3) is provided in the at least one pipeline (7).

12. Apparatus according to Claim 11 , characterized in that the flow resistance (10) is attached by means of a flanged connection (11) in the pipeline (7).

13. Apparatus according to Claim 11 or 12, characterized in that the flow resistance is formed by an orifice (10).

14. Apparatus according to one of Claims 11 to 13, characterized in that the pipeline (7a, 7b) has an angle of inclination with respect to the horizontal of from 1° to 90°, preferably > approx. 30°.

15. Apparatus according to one of Claims 11 to 14, characterized in that the pipeline (7) does not have any narrowing below the region which can be reached by the solids.

16. Apparatus according to one of Claims 11 to 15, characterized in that the pipeline (7) has a horizontal outlet opening (8) at its open end.

17. Apparatus according to one of Claims 11 to 16, characterized in that the outlet opening (8) of the pipeline (7) is arranged < 250 mm, preferably < 150 mm, above the vessel base (9).

18. Apparatus according to one of Claims 11 to 17, characterized in that the pipeline (7a), in the region of its outlet opening (8a), has an outer material thickening, in particular a build-up weld (12).

19. Apparatus according to one of Claims 11 to 18, characterized in that in the region of its outlet opening (8b) the pipeline (7b) has an in particular upwardly directed detachment lug (13).

20. Apparatus according to one of Claims 11 to 19, characterized in that the pipeline (7) is attached to the vessel (1) by means of flange connection pieces (11) provided on the vessel (1).

21. Apparatus according to one of Claims 11 to 20, characterized in that a plurality of pipelines (7) are provided in the vessel (1), distributed in the shape of a circle.

22. Apparatus according to Claim 21 , characterized in that the pipelines (7) are provided distributed on a plurality of preferably concentric circles within the vessel (1).