GB2144717A

GB2144717A - Apparatus for dosing bulk materials

Info

Publication number: GB2144717A
Application number: GB08419052A
Authority: GB
Inventors: Wolfgang Krambrock
Original assignee: Waeschle Maschinenfabrik GmbH
Current assignee: Waeschle Maschinenfabrik GmbH
Priority date: 1983-08-12
Filing date: 1984-07-26
Publication date: 1985-03-13
Also published as: IT8422077A0; FR2550771A1; NL191484C; GB8419052D0; FR2550771B1; BE900318A; JPS60106736A; GB2144717B; NL8402343A; IT1218935B; NL191484B

Abstract

An apparatus for dosing bulk materials into at least one pneumatic conveying pipe comprises a cellular wheel (2) rotatable about a vertical axis, in a cylindrical housing (3) with an outlet pipe (9) from the housing for the conveying pipe, an air inlet pipe (7) entering the housing (3) from below and the top of the housing having an aperture for charging by gravity with the bulk material to be conveyed. The charging aperture takes up substantially the whole cross-section of the exposed end surface of the housing (3). The outlet pipe (9) for the conveying pipe extends radially from the housing (3) above the entry point of the pure air inlet pipe (7). The charging aperture is covered by a plate (5) above the entry point of the pure air inlet pipe (7); the plate covering at least the volume of one chamber of the cellular wheel (2). <IMAGE>

Description

SPECIFICATION Apparatus for dosing bulk materials This invention relates to an apparatus for dosing bulk material into at least one pneumatic conveying pipe, comprising a cellular wheel, rotatable about a vertical axis, in a cylindrical housing with an outlet pipe from the housing for the conveying pipe, an air inlet pipe entering the housing from below, and the housing containing an aperture at the top through which bulk material to be conveyed can be gravity charged.

So-called cellular wheel sluices are widely known as dosing means with which bulk materials can be sluiced continuously out of a chamber at any pressure into a pneumatic conveying pipe, against a higher or lower pressure prevailing therein. The cellular wheel seated non-rotatably on a horizontal shaft comprises a hub and radial fins, which accordingly bound wedge-shaped or trapezoidal chambers.

The buk material passes through the intake aperture in the top of the housing into one chamber of the cellular wheel at a time and, after rotating through about 1 8û C, possibly aided by compressed air, is fed through a outlet aperture into the conveying pipe.

The quantity of bulk material thus added in dosed quantities increases initially with the increasing speed of the cellular wheel, but diminishes again when there is a further increase in speed. The reason for this is centrifugal force. The maximum quantity of bulk material which can be added in metered quantities per unit of time is therefore reached at a speed of approximately 20 to 40 rpm. A further disadvantage is then observed if the pressure in the conveying pipe is higher than that at the intake side of the cellular wheel sluice. The filling of the chambers of the cellular wheel is impeded, particularly with fine grained bulk materials, by the gas flow directed counter to the stream of bulk material; this gas flow being caused by the gap between the cellular wheel and the housing resulting from the construction.Finally, there are also problems with bulk materials which do not flow readily, which are sticky and which form bridges, since the relatively narrow intake cross-sections resulting from this construction preclude continuous filling of the chambers of the wheel.

An apparatus of the above type, i.e. with a cellular wheel rotatable about a vertical axis, is already known. The bulk material is supplied through an eccentric aperture corresponding approximately to the cross-section of a chamber of the cellular wheel and, after being further transported through approximately 1800, is blown out of the wheel chamber in question into the inlet pipe to the conveying pipe, which outlet pipe is axially exactly opposite the entry point of the air inlet pipe to the housing. The disadvantage of this is that the narrow intake cross-section impedes continuous influx of the bulk material to be dosed, and with cohesive materials even makes it impossible.

There is thus a need for a generally improved dosing apparatus with a good dosing performance even for bulk materials which do not flow readily.

According to the present invention there is provided apparatus for dosing bulk material into at least one pneumatic conveying pipe, including a cellular wheel, rotatable about a vertical axis, in a cylindrical housing, at least one outlet pipe from the housing connectible to the pneumatic conveying pipe, at least one air inlet pipe opening into the housing from below parallel with the rotational axis of the cellular wheel, and with the housing containing an aperture at the top through which bulk material to be conveyed can be gravity charged into the housing, wherein the charging aperture is approximately equal in dimensions to the top end area of the housing, wherein the at least one outlet pipe extends radially from the housing from a point above the entry point of the at least one air inlet pipe, and wherein the charging aperture is covered by at least one plate above the entry point of the air inlet pipe, which plate covers at least the volume of a chamber of the cellular wheel.

With this construction neither centrifugal force nor any leakage flow have any disadvantageous effect on the filling of the chambers of the wheel. In addition, owing to the large cross-section of the intake aperture the bulk material flows to the chambers over a wide range of turning angles of the wheel, whereby the chambers of the wheel are filled completely. This is particularly so as the large cross-section of the intake aperture also prevents any bridge formation in the space above it, even if the bulk materials are cohesive.

Only when the bulk materials are decidedly not of the readily flowing type it is desirable, in a further embodiment of the apparatus according to the invention, to provide an agitator, extending upwardly through the charging aperture, and non rotatably connected to the cellular wheel.

Particularly when the wheel has a large diameter, complete filling of its chambers can be further aided by having the hub of the wheel carry a deflecting cone.

The apparatus according to the invention further provides the possibility of dosing equal quantities of bulk material into a plurality of conveying pipes simultaneously. To this end the housing has, distributed around its periphery, a plurality of said air inlet pipes, a plurality of outlet pipes connectible to the conveying pipe and a plurality of said plates covering the corresponding spaces.

In another preferred embodiment a bearing for the cellular wheel which is dust-tight and accessible from outside can be provided by ensuring that the cellular wheel is seated on a drive shaft which is mounted rotatably in the housing in two spaced apart bearings, of which the upper bearing is sealed by a set of seals located above it and the lower bearing by a set of seals located below it, both being subject to action by scavenging air from compressed air passages in the housing connectible to a source of compressed air.

In a modification of this embodiment the tension of the upper set of seals and of the lower set can each be adjusted by a respective pressure ring which is adjustable from outside the apparatus.

A frequent requirement is that it should be possible for the quantity of bulk material dosed into the conveying pipe per unit time to be varied within broad limits. Instead of doing this by using a drive with an infinitely adjustable rotary speed for the cellular wheel in known manner, control ofthrough- put can be obtained at low cost, particularly in an apparatus of the type here proposed, if the or each air inlet pipe is connected to the or each conveying pipe by a bypass pipe, and if at least one of the pipes contains a valve for adjusting the quantity of air flowing through the bypass pipe.

In a preferred modification of this proposal the valve is a three-way valve, arranged either in the air inlet pipe or in the conveying pipe.

Apparatus according to the invention is illustrated in the accompanying drawings, in embodiments which have been chosen as examples and in diagrammatically simplified form. In the drawings; Figure lisa longitudinal sectional view through apparatus according to a first embodiment of the invention, Figure 2 is a cross-sectional view taken along the line I-I in Figure 1, Figure 3 is a longitudinal sectional view through a bearing of a cellularwheel forthe apparatus of Figures 1 and 2, Figures 4 and 5 are a diagrammatic side view and a plan view of apparatus according to a further embodiment of the invention for supplying a plurality of conveying pipes, and Figures Sto 11 show in longitudinal sectional views various embodiments of an apparatus of the invention with controllable throughput of bulk material.

The apparatus of the invention shown in Figures 1 and 2 has a cellular wheel with a hub 1 and radial fins 2, the wheel being seated non-rotatably on a drive shaft 4 in a cylindrical housing 3.

At the top the housing 3 has an intake aperture, extending over the entire cross-section of its end surface, for bulk material to be conveyed which may flow in by gravity, for example from a cone 12 at the bottom of a silo. Forthis purpose the housing 3 is screwed or bolted by means of a flange 10 to an opposing flange 11 at the outlet at the bottom of the silo. An agitator 13, joined non-rotatably to the cellular wheel 1,2 preferably projects into the bottom outlet of the silo.

The housing 3 has an eccentric aperture at the bottom, to which pure air 6 is supplied through an air inlet pipe 7. At the same radius as the entry point of the pure air inlet pipe 7 an aperture is provided in the wall of the housing 3, from which an outlet pipe 9 goes off radially. The outlet pipe 9 is connectible to a conveying pipe (not shown) leading to the place where the bulk material will be used. The region of the entry point of the air inlet pipe 7 and of the exit point of the outlet pipe 9 is covered by a plat 5 above the cellular wheel 1, 2. As shown in Figure 2, the plate 5 is shaped as a segment of a circle and is broader in the peripheral direction than a chamber of the wheel 1,2.

This construction enables the inlet cross-section to be almost of any desired size, thereby counteracting any bridging of the bulk material at the intake side.

The agitator 13 is therefore unnecessary for many bulk materials.

Nor is the influx of bulk material impeded by the leakage flow which takes place when the pressure in the pure air inlet pipe 7 is higher than that in the silo containing the bulk material. The flow of leaking air in fact runs approximately in the direction of the arrows 14, i.e. on the opposite side to the bulk material, flowing downwardly into the wheel chambers in the direction of the arrows 15, relative to the shaft 4.

Even when the cellular wheel 1,2 has a high rotary speed the influx of bulk material is not impeded by centrifugal force. On the contrary the centrifugal force aids in removing the bulk material from the wheel 1, 2, since the material is moved more rapidly towards the outlet pipe 9. It has been established by measuring that, with a sluice 300mm in diameter and a rotary speed of 50 rpm, the degree to which the chambers of the cellular wheel are filled is over 50%. Under comparable conditions the degree to which a cellular wheel sluice with a horizontal shaft is filled is only about 20%.

A preferred construction of the bearing for the shaft 4 is shown in section in Figure 3. The shaft 4 runs in two spaced apart ball bearings 15 and 16. To prevent dust from entering the bearings, seals 18 and 21 are located respectively above the ball bearing 15 and below the ball bearing 16. In addition the bearings may be impinged on with scavenging air via compressed air passages 23 to 27 in the housing, connectibleto a source of compressed air.

The tension of both the seal 18 and the seal 21 can be readjusted. To enable that of the seal 18 to be readjusted from outside, the hub 1 of the cellular wheel is made hollow and surrounds a pressure ring 19, which presses the seal 18 against an annular shoulder on the housing 3 and can be readjusted from outside by means of screws 20. A further pressure ring 22 interacts with the lower seal 21. This ring 22 is constructed as a union nut and is therefore also easy to readjust.

Figures 4 and 5 show, in a diagrammatically simplified form, an embodiment of the apparatus with which a plurality of consumers can be supplied with equal, controllable quantities of bulk material.

For example, the apparatus might supply a plurality of burners in a furnace with coal dust. For this purpose it is flange mounted at the outlet of a silo 412 and contains a cellular wheel with a hub 41 of relatively large diameter and with short fins or cellular wheel webs 42. The hub 41 is covered by a deflecting cone 428 provided with stirring members 413. Six outlet pipes 49a to 49f are equally distributed over the periphery of the housing. Air inlet pipes 47a to 47f have their entry points below them, while above the cellularwheel an equal number of plates 45a to 45f are mounted in those positions.

Figure 6 shows a form of the apparatus where the pure air inlet pipe 7 is connected to the outlet pipe 9 to the conveying pipe by a bypass pipe 50 with a throttle valve 51 arranged in it. Given a constant rotary driving speed for the cellular wheel, the quantity of bulk material fed into the conveying pipe from the outlet pipe 9 can be varied over a wide range by adjusting the valve 51. As shown in Figure 7, a further throttle valve 52 may be arranged in the pure air inlet pipe 7, downstream of the place where the bypass pipe 50 branches off, thus enabling the division of the quantities of air to be set still more accurately.

More desirable than the use of two throttle valves 51 and 52 as shown in Figure 7, however, is the use of a three-way valve, which can then be arranged either as in Figure 8, at reference 53 in the pure air inlet pipe 7 or, as shown in Figure 9, at reference 54 in the outlet pipe 9 to the conveying pipe.

In Figure 10 of a three-way valve 53 of this type is shown in the form of a displaceable shutter. Figure 11 shows a three-way valve 54 constructed as a pivotable flap.

The possibility of continuously controlling throughout by means of a bypass pipe, as shown in Figures 6 to 11, is particularly advantages in the embodiment of the apparatus shown in Figures 4 and 5, for in contrast to control through the rotary driving speed of the cellular wheel, the quantities of bulk material dosed into the individual outgoing conveying pipes can here be set and varied independently of one another. This may be necessary, for example, when the apparatus is used to supply coal dust burners.

Claims

1. Apparatus for dosing bulk material into at least one pneumatic conveying pipe, including a cellular wheel, rotatable about a vertical axis, in a cylindrical housing, at least one outlet pipe from the housing connectible to the pneumatic conveying pipe, at least one air inlet pipe opening into the housing from below parallel with the rotational axis of the cellular wheel, and with the housing containing an aperture at the top through which bulk material to be conveyed can be gravity charged into the housing, wherein the charging aperture is approximately equal in dimensions to the top end area of the housing, wherein the at least one outlet pipe extends radially from the housing from a point above the entry point of the at least one air inlet pipe, and wherein the charging aperture is covered by at least one plate above the entry point of the air inlet pipe, which plate covers at least the volume of a chamber of the cellular wheel.

2. Apparatus according to claim 1, including an agitator extending upwardly through the charging aperture, which agitator is non-rotatably joined to the cellular wheel.

3. Apparatus according to claim 1 or claim 2, characterised wherein the hub of the cellular wheel carries a deflecting cone.

4. Apparatus according to any one of claims 1 to 3, wherein the housing has, distributed around its periphery, a plurality of said air inlet pipes, a plurality of outlet pipes connectible to the conveying pipe and a plurality of said plates covering the corresponding spaces.

5. Apparatus according to any one of claims 1 to 4, wherein the cellular wheel is seated on a drive shaft which is mounted rotatably in the housing in two spaced apart bearings, of which the upper bearing is sealed by a set of seals located above it and the lower bearing by a set of seals located below it, both being subject to action by scavenging air from compressed air passages in the housing connectible to a source of compressed air.

6. Apparatus according to claim 5, wherein the tension of the upper set of seals and of the lower set can be adjusted by means of a pressure ring which can be readjusted from outside the apparatus.

7. Apparatus according to any one of claims 1 to 6, wherein the or each air inlet pipe is connected to the or each conveying pipe by a bypass pipe, at least one of the pipes containing a valve for adjusting the quantity of air flowing through the bypass pipe.

8. Apparatus according to claim 7, wherein the valve is a three-way valve arranged either in the air inlet pipe or in the conveying pipe.

9. Apparatus for dosing bulk material into at least one pneumatic conveying pipe, substantially as hereinbefore described with reference to Figures 1 to 3, Figures 4 and 5, or Figures 6 to 11 of the accompanying drawings.