GB2101980A

GB2101980A - Metered discharge of material from fluidized bed

Info

Publication number: GB2101980A
Application number: GB08216970A
Authority: GB
Inventors: Hermann Moller; Jurgen Pust
Original assignee: Moeller Hamburg Co KG GmbH
Current assignee: Moeller Hamburg Co KG GmbH
Priority date: 1981-06-12
Filing date: 1982-06-11
Publication date: 1983-01-26
Also published as: FR2507744B1; DE3123328C2; FR2507744A1; DE3123328A1; GB2101980B; NL8202380A

Abstract

In order to provide metered discharge of hot ash having a large particle spectrum, in apparatus which is not subjected to marked wear, even if the ash contains large foreign bodies, the ash is collected in a discharge container 6 and stands at its angle of repose beta . The lower portion of the heap 19 is carried off by an air stream over the base 8 of the discharge container 6. For this purpose, the base is provided with air outlet openings 10, and the lower portion of the delivery cone 19 is to be discharged via a lateral edge 20 of the base 8. In order to provide pressure compensation between the fluidized bed chamber 1 and the discharge container 6, these two components can be connected to each other by a pressure-compensating pipe 33. <IMAGE>

Description

SPECIFICATION Metered discharge of material from flu id- ized bed The invention relates to a process and apparatus for the metered discharge of particulate material, in particular hot ash, from fluidized bed reactors and fluidized bed furnaces.

Such processes and apparatus are used, for example, in power stations in which coal is burnt by the fluidized bed process and is discharged as ash at very high temperatures of about 800 to 900"C.

For the metered discharge of the ash, it is known to use a bucket wheel sluice or conveying screw whose speed can be varied.

Owing to the high temperature of the ash, marked thermal expansion occurs, so the conveyors have to be constructed with high tolerances. If the bulk product to be processed also has a broad particle spectrum, for example due to different furnace systems, the wear of the conveyors is relatively high. Marked wear also occurs if the conveyors are to be capable of also discharging foreign bodies such as slag, masonry, or iron particles embedded in the ash. As the conventional discharge devices such as bucket wheel sluices and screws are not particularly suitable for this purpose, different solutions in which the conveyed product is discharged pneumatically have already been sought.In one known discharge device of this type (German Offenlegungsschrift No. 28 1 9 184) it is proposed that the ash be collected in a trough and, after opening a check valve arranged on the base, be allowed to fall into a delivery pipe in which it is carried off by air blown into the conveyor tube through a nozzle beneath the valve.

However, this arrangement has the disadvantage that blockages can occur in the delivery pipe, for example due to sintered pieces of slag or other foreign bodies. Moreover, high operating costs are incurred in the necessary high compression of the conveying air needed for delivery purposes.

What is desired is a process and an apparatus for the metered discharge of hot ash, having a broad particle spectrum, which is not subjected to the conventional high wear owing to its design and which can be operated particularly economicaliy and with great reliability using simple mechanical parts, even assuming that the ash contains fairly large foreign bodies.

The present invention provides a process in which the material is collected in a discharge container standing at its natural delivery angle and the lower portion of the delivery cone is carried off by fluidization by an air stream over the base of the discharge container.

If a predetermined bed height is found to be exceeded when adopting this process, for example due to the foreign body content in the material, the discharge of the material can be further assisted by blowing conveying air into the delivery heap through a lateral wall of the discharge container. It is generally advantageous if the supply of conveying air for carrying off material from the heap is controlled as a function of the bed height.

To enable the process and its associated apparatus to be used optimally with variously constituted types of ash and other materials, e.g. with ash of differing particle size and also at differing temperatures, and to be able to utilize the angle of repose for this purpose, the inclination of the base of the discharge container is preferably adjusted as a function of the angle of repose.

The arrangement described above is advantageous if the fluidized bed in the fluidized bed chamber is subjected to a normal atmospheric pressure and consequently also the discharge container, In practice, however, a higher pressure usually prevails in the fluidized bed. In such cases, there is a danger of the ash being carried off more rapidly from the discharge container than is suitable. With the device described above, a pressure difference can exist between the fluidized bed chamber and the delivery pipe of the discharge container owing to the pressure of the gases introduced into the fluidized bed chamber for fluidizing and due to the higher static pressure of the material in the feed tube of the discharge container. This causes gas to flow continuously from the fluidized bed chamber through the feed tube of the discharge container onto the heap.Bulk material is continuously entrained in the process, particularly at the outer upper edge of the heap in the region of a lateral wall of the discharge container. However this, should be avoided as far as possible as it results in irregular discharge of the bulk product.

It is therefore advantageous to use an apparatus which permits the controlled discharge of the material from the discharge container without pressure differences between the fluidized bed chamber and the discharge container. For this reason, the discharge container is preferably arranged in a pressure chamber defined by a pressure vessel so that there is no significant reduced pressure in the discharge container which would lead to an undesirable gas stream from the fluidized bed chamber into the discharge container.

The increased pressure in the additional pressure vessel can optionally be built up by itself from the heat of the material to be carried off or as a result of the higher pressure exerted by the fluidized bed chamber. However, it is advantageous if the pressure vessel is additionally connected by a pressure compensating pipe to the fluidized bed chamber, which compensates the pressure between the fluidized bed chamber and the interior of the discharge container.

For the precise metering of the quantity of material to be discharged, taking into consideration the differing particle sizes, it is also beneficial to arrange in the feed tube of the discharge container a metering valve with blocking members preferably positioned as a function of the pivoted position of the container so that, in one or other pivoted position of the container, the container can receive a larger or smaller quantity of material. For this purpose, the blocking members of the metering value can be connected by adjusting levers to the container to permit adjustment of the blocking members via a mechanical coupling during a pivoting movement of the container. However, it is also possible to adjust the blocking members hydraulically or electrically, preferably as a function of the oblique position of the base of the container.

As the preferred discharge container has a swivel joint to permit it to pivot, it is possible to design the metering valve itself as a swivel joint for the discharge container.

The metering valve has an inlet opening at its top and an outlet opening at its bottom.

Using the blocking members, it is basically possible to seal the lower outlet opening and to clear it for the passage of the material using the blocking members. In this case, however, the ash would collect above the outlet opening and would have to be penetrated by the blocking members (preferably designed as flaps) as the metering valve is opened. On the other hand, it is preferable if the blocking members block the upper inlet opening of the metering valve so as to form below them a cavity which makes it easier to adjust them as the metering valve is opened.

The invention will be described further, by way of example, with reference to the accompanying drawings, in which: Figure 1 schematically shows a first embodiment of apparatus for the metered discharge of ash from a fluidized bed; Figure 2 shows a second embodiment of the apparatus, with a pressure chamber; Figure 3 shows a metering valve with blocking members which are mechanically coupled to the discharge container, in the closed position; Figure 4 shows the arrangement from Fig.

3 in the opening position; Figure 5 shows a metering valve with blocking members for blocking the inlet opening, in the closed position; and Figure 6 shows the arrangement from Fig.

5 with blocking members in the open position.

In the apparatus reproduced in Fig. 1 for the combustion of coal by the fluidized bed process, there is in the fluidized bed chamber 1 a layer of bulk product of height H which rests on a base 2 penetrated by air supply pipes 3 through which combustion air is introduced in the direction of the arrows.

The ash produced is introduced via a feed tube 4 and an intermediate duct 5 into a discharge container 6 which is connected by a swivel joint 7 to the intermediate duct 5. The discharge container 6 has a base 8 provided with steps 9 beneath which there are located respective air chambers 9'. The air chambers 9' are provided with slit-shaped air outlet openings 10 in the lower edges of the risers (front faces) of the steps 9, which openings are preferably designed with variable crosssections. The air chambers 9' are supplied by air pipes 11 and check valves 1 2 from an air manifold in which there is a valve 1 3 connected via a control pipe 1 4 to a regulator 15.

Additional air nozzles 1 7 and 1 8 having valves 1 2 also connected to the regulator 1 5 by the control pipe 14, are arranged in a lateral wall 1 6 of the discharge container 6, for the introduction of air for conveying bulk product inside the container 6.

A delivery pipe 21, which is adjustable in length and is designed (for example) as a flexible coupling 26 for this purpose, is open next to a free lateral edge 20 of the base 8 of the discharge container 6. The ash to be discharged passes through this delivery pipe 21 onto a conveyor 22 which is provided with an exhaust pipe 24 in the same way as the discharge container 6 is provided with an exhaust pipe 23.

During operation of the apparatus, the ash falls through the feed tube 4 and the intermediate duct 5 on to the base 8 of the discharge container 6. A natural slope angle is thus formed at the free upper conical surface of the delivery heap 1 9 as a so-called angle of repose, p, whose value depends on the composition and temperature of the ash. If air is blown through the air outlet openings 10 of the steps 9 into the chamber of the discharge container 6 in this state, the lower layer of the heap 1 9 is fluidized and carried off by the effect of the air over the lateral edge 20 into the delivery pipe 21, further ash falling on to the base from above at the same time owing to the weight of the ash. If the height H of the layer of bulk product is found to exceed a predetermined value in the course of the process, additional conveying air can be blown into the delivery cone 1 9 via the air nozzles 1 7 and 1 8 after the triggering of signals by sensors (not shown) and the regulator 15, until the height of the layer of bulk product has dropped to a desired value. This occurs, for example, if the ash contains foreign bodies which obstruct the natural flow.

On the other hand, if the height of the layer H falls below a predetermined value, the air supply which issues through the nozzles 10 on the base 8 of the discharge container 6 can be throttled under the control of the regulator 15.

As the natural angle of repose, ss, to be employed for the operation of the apparatus is dependent on the particular composition of the ash and the temperature thereof, it is advantageous if the angle between the free surface and the base can be influenced. This is effected by suitable adjustment of the inclination of the base 8, which, together with the other components of the discharge container 6, can be adjusted by an adjusting device 25 through an angle 2 or an angle + a relative to the horizontal as indicated in Fig. 1. Owing to the possibility of adjusting the angle of inclination of the base 8 of the discharge container 6, it is possible to take into consideration varying characteristics specific to the bulk product, of the type resulting for example from the composition of the fuels used.In addition, the discharge capacity can also be influenced by changing the angle of inclination and can be increased significantly by a large angle. However, it has been found advantageous to select the angle of inclination in such a way that the angle of repose p specific to the material is formed within the discharge device and mass flow of the bulk product is obstructed.

In the arrangement reproduced in Fig. 2, the same parts as in Fig. 1 are provided with identical reference numerals.

Unlike the embodiment according to Fig. 1, the discharge container 6 in the embodiment in Fig. 2 is arranged in a pressure vessel 31.

The pressure vessel 31 is stationary. The discharge container 6 is pivotal.

To compensate the pressure between the pressure chamber 29 inside the pressure vessel 31 on the one hand and the fluidized bed chamber 1, there is provided a pressure-compensating pipe 33 which is joined via a flexible 34 to the pressure vessel 31.

On the base of the pressure vessel 31 there is a hopper 32 into which the delivery pipe 21 of the discharge container 6 extends to ensure that the ash is discharges from the pressure vessel 31 in every pivoted position of the discharge container 6.

The ability of the discharge container 6 to pivot relative to the feed tube 4 with its intermediate duct 5 is due to a swivel joint 7, which is further developed in design according to Fig. 2 as a metering valve 30 having a cylinderical chamber in which there are two check flaps 37 and 38 (Figs. 3 and 4) or, in the design according to Figs. 5 and 6, two check flaps 39 and 40. These check flaps 37, 38 or 39, 40 are mounted pivotally about the rotational axis of the discharge container 6. They lie in a cylindrical chamber of the metering valve 30, about whose centrai axis the feed tube of the discharge container 6 is pivotal.

The metering valve 30 has an upper inlet opening 41 and a lower outlet opening 42. In the design according to Figs. 3 and 4, the outlet opening 42 can be blocked by the check flaps 37 and 38. This takes place as a function of the pivoted position of the discharge container 6. A lever connection is provided for this purpose between the discharge container 6 and the check flaps 37 and 38, which consists of lever rods 35 and 36 of which the lever rod 36 is adjustable in length for the preliminary adjustment of the pivoting flaps 37 and 38.

In contrast, inthe embodiment according to Figs. 5 and 6, the upper inlet opening 41 of the metering valve 30 is to be blocked so that the chamber lying beneath it is free from ash after being blocked and the check flaps 39 and 40 are to be pivoted into the open position against a relatively slight resistance.

Claims

1. A process for the metered discharge of particulate material from a fluidized bed, in which the material is collected in a discharge container having a base on which the material stands as a heap having a free surface sloping at the angle of repose of the material, and the lower portion of the heap is removed by an air stream over the base of the discharge container.

2. A process as claimed in claim 1, in which conveying air is blown into the heap through a lateral wall of the discharge container.

3. A process as claimed in claim 1 or 2, in which the supply of air is controlled as a function of the height of the fluidized bed.

4. A process as claimed in any preceding claim, in which the inclination of the base of the discharge container is adjusted as a function of the angle of repose of the material.

5. Apparatus for the metered discharge of particulate material from a fluidized bed, comprising a discharge container connected to the bottom of a fluidized bed chamber by a feed tube through which the material falls, the discharge container having a base on which the material is to stand as a heap having a free surface sloping at the angle of repose of the material, and a delivery pipe into which the material is to flow from the edge of the heap, the base of the container having air outlet openings for providing an air stream over the base.

6. Apparatus as claimed in claim 5, in which the base of the container rises in steps from the delivery pipe and the air outlet openings are arranged on the risers of the steps.

7. Apparatus as claimed in claim 6, in which the individual steps are pivoted with their own air chambers which are to be charged separately with air.

8. Apparatus as claimed in any of claims 5 to 7, including air nozzle arranged in a lateral wall of the discharge container above its base.

9. Apparatus as claimed in any one of claims 5 to 8, in which the inclination of the base of the container is adjustable.

10. Apparatus as claimed in any one of claims 5 to 9, in which the discharge containeris connected by a swivel joint to the feed tube.

11. Apparatus as claimed in any one of claims 5 to 10, in which the delivery pipe is connected via a flexible coupling to a conveyor.

1 2. Apparatus as claimed in any one of claims 5 to 10, in which a collecting hopper is arranged beneath the delivery pipe.

1 3. Apparatus as claimed in any one of claims 5 to 12, in which the air outlet openings have variable cross-sections.

14. Apparatus as claimed in any one of claims 5 to 13, in which the discharge container is arranged in a pressure chamber defined by a pressure vessel.

15. Apparatus as claimed in claim 14, in which the pressure vessel is connected by a pressure compensating pipe to the fluidized bed chamber.

16. Apparatus as claimed in any one of claims 5 to 15, in which a metering valve is arranged between the fluidized bed chamber and the discharge container.

1 7. Apparatus as claimed in claim 16, in which the discharge container is pivotable and the metering valve has blocking members which are positioned as a function of the pivot position of the container.

1 8. Apparatus as claimed in claim 17, in which the blocking members are connected by adjusting levers to the container.

1 9. Apparatus as claimed in any of claims 1 6 to 18, in which the upper inlet opening of the metering valve is to be blocked by the blocking members.

20. Apparatus as claimed in any of claims 1 6 to 19, in which the discharge container is pivotable and the metering valve is designed as a swivel joint for the container.

21. A process for the metered discharge of particulate material from a fluidized bed, substantially as described with reference to Fig. 1 or Fig. 2 of the accompanying drawings.

22. Apparatus for the metered discharge of particulate material from a fluidized bed, substantially as described with reference to, and as shown in, Fig. 1 or Fig. 2 of the accompanying drawings.