GB2245888A - Improvements in or relating to the discharge of discrete materials - Google Patents

Abstract

Equipment for the discharge of discrete materials from a storage vessel includes a housing 8 within which is disposed an inclined frame 14 having mounted therein a plurality of elements 12 spaced apart one from the other in echelon. Vibrating means 20 are provided for imparting vibrations to the frame and thus to the elements 12 to fluidise material thereon to regulate the discharge of material, which passes out via a wedge-shaped collection box 24. <IMAGE>

Description

IMPROVEMBIS IN OR RELATING TO THE DISCHARGE OF DISCREIsE MATERIALS This invention concerns improvements in or relating to the discharge of discrete materials.

In particular, the present invention has reference to the discharge of such materials from storage vessels, for example silos, hoppers or the like.

One of the problems attendant upon the operation of such vessels resides in the regulation of the discharge and the evenness of material flow thereform. The principal reason for this problem is the manner in which the material behaves within a vessel and when being conveyed after discharge. Essentially, this difference is one of mass flux velocity: this parameter is likely in practice to be three orders of magnitude greater during conveyance than when in storage. It is thus at the interface between the two that difficulties arise in flow regulation.

Various proposals have been made to assist in the solution of the problem highlighted above and one method of promoting discharge and hence flow at the outlet from a storage vessel of the kind indicated, involves effecting vibration of the region adjacent thereto. Equipment for this purpose is known in the art as a bin activator and may take a variety of forms, but is concerned with rendering the bulk material held in storage into a free flowing material amenable to control. Such equipment can be placed externally of the vessel and suspended below it on anti-vibration mountings, the object being to impart vibration to the material in the vessel thereby to promote mass flow. If a bin activator is vibrated continuously, the material within the vessel tends to compact and therefore its action becomes counter-productive.In reality, the activator operates to break material bridges within the vessel and is not able to regulate flow.

Intermittent operation of a bin activator is equivalent to an on-off valve which causes material compaction.

When flow is arrested in a mass flow bunker, there is a sharp change over between two states of the hydraulic pressure field from radial to axial. Upstream of an outlet or take-off point, the flow may be almost imperceptible and the contents of the bunker may be regarded as being in a state ofincipient flow maintained by a fully developed radial field. If this incipient flow is stopped, the hydraulic pressure field flips over into the stationary axial state.

However, for incipient flow to restart, the stationary state has to pass through a transient switch state responsible for the 'excess' silo-hip pressures.

The switch itself is a delta-shaped region of reorientating high pressure gradients, probably damaging to the material, for example coal. It is initiated by the off-take of material and moves therethrough to establish a flow stream ranging from the top of the charge down to the outlet. Below the switch, material is flowing, probably fast enough to produce cavitation. Above the switch, the material is stationary. Within the switch, material is being distorted.The time for the switch to pass through a silo, for example, may be substantial. In certain conditions, such as when a silo runs empty or at the top of the fill, the switch may be contained by hoop stresses and dissipate to produce funnel flow. With batch unloaders, the switch may be arrested to leave behind a perturbed bulk density region, and the incipient flow may never be established.In some unloaders, the switch state may be transient only with respect to location. Thus in a flat bottomed silo, emptied by a circling auger, the switch is tied to the up-take end of the auger and pushed or lashed around the periphery to generate a circulating hip-stress pressure wave on the silo wall.

Such a perception of flow suggests that irrespective of whether the material is being recovered from a mass flow or a funnel flow silo hopper, once incipient flow is established it should be maintained. Switching on and off causes some materials, for example, coal to compact and makes intractable coals impossible to handle. Currently, there is no activator capable of sustaining and regulating flow at the incipient level.

An object of the present invention is to provide equipment for regulating the discharge of materials from storage vessels which overcomes the problems associated with conventional equipment and their usage.

According to the invention there is provided equipment for the discharge of material from a storage vessel having an outlet sufficiently large such as in use to avoid bridging of material, the equipment including a housing having an inlet for registration with the said outlet of the vessel, a plurality of spaced elements arranged in echelon in an inclined plane internally across the housing, means for vibrating the elements, and an outlet means associated with the housing downstream of the elements.

The size of the inlet to the housing advantageously . matches the outlet from the storage vessel which may be a silo or hopper.

The elements may be mounted in a frame, and may be in the form of rungs or in the alternative in the form of platforms, capable of receiving material which upon vibration assumes a fluidised state.

The platforms may be constituted by flat and/or perforated plates which may be provided with an upstanding lip. The lip may be relieved; for example castellations may be formed therein such as in use to afford a varied discharge of material from the plate. The platforms may be of any suitable dimension and their spacing dictated by the manner of material flow required.

The frame may be suspended or supported on anti-vibration mountings capable of being vibrated in its own plane or a vertical plane or in an elliptical path. The degree of vibration must in use be sufficient to produce fluidisation of the material received upon the elements. The vertical component of acceleration has to be in excess of 1g.

The outlet means associated with the housing may be in the form of a wedge-shaped collection box which may be attached to the frame or may be independent thereof. The outlet means may meter directly into a transport system, for example a screw trough, or a belt conveyor or into a surge hopper fitted with a flow regulator such as a rotary valve.

All the parts of the equipment may be coated with ultra high molecular weight plastics.

By way of example only, one form of equipment for the discharge of material from a storage vessel is described below with reference to the accompanying drawing which is a diagrammatic vertical section.

In the drawing, a storage vessel is depicted at 1 and includes a frusto-conical discharge section 2 having an outlet 4 which registers with an inlet 6 of equipment 8 for the discharge of material according to the invention. The equipment 8 includes a housing 10 having disposed therein in an inclined plane a plurality of elements 12 mounted in a frame 14.

The elements 12 comprise a series of rungs 16 supporting plates 18 arranged in spaced relation one to the other and in echelon. A vibrating mechanism 20 is provided for the frame 14 and may be disposed in the most suitable position to yield the optimum vibration of the plates 18. An alternative position for the mechanism is shown at 20'.

Outlet means 22 are associated with the housing 10 and in this embodiment of the invention are attached to the frame 14. The means are in the form of a wedge-shaped trough 24 provided with a discharge chute 26 at its lower end.

In operation, material, for example coal, is held within the vessel 1 and outflows through the discharge section 2 and the outlet 4 and through the inlet 6 of the housing 10. The material encounters the elements 12. Vibration of the elements causes the material to fluidise on the plates 18, which have upstanding lips 19, and transport of the material is thereby effected at a controlled rate into the outlet means 22 whence the material is discharged into the chute 26 for further conveyance to its point of intended use.

For a given bulk material and its granularity, density and cohesion, the equipment can be designed having regard to the maximum throughput required. One of the criteria which will apply in the design of the equipment is the balance of the weight of the frame, or individual elements, against the centrifugal or electrodynamic forces used to generate vibration and fluidisation. The spacing, size, shape and orientation of the elements will also be preset having regard to the specification of material and the performance requirements. The regulation of the material flow will be effected in the final analysis by the frequency of vibration which may be varied in response to a control signal from downstream of the equipment, for example the line conveyor feeder which may be a rotary valve, a screw conveyor, a belt conveyor, a venturi or a surge hopper.For example, a turndown of 3:1 may be achieved.

In an alternative embodiment to that shown, the housing 10 of the equipment 8 is incorporated in the storage vessel 1 per se; thus, for example the equipment 8 may be an integral part of the discharge section 2 of the vessel.

In a further alternative embodiment, the elements are formed of blades which upon vibration pare the material for discharge.

The advantage of the present invention resides in the ability of the equipment to handle difficult materials, particularly smalls coals, and to enable washed singles coals to be stored in silos without deterioration.

Furthermore, with the degree of control upon the discharge rate, it may well be possible to reduce or obviate the need for intermediate storage facilities, such as day bunkers inthe case of coal feed to boilers, the coal being discharged directly from the equipment of the present invention to the boiler.

Claims (11)

CLAIMS:

1. Equipment for the discharge of material from a storage vessel having an outlet sufficiently large such as in use to avoid bridging of material, the equipment including a housing having an inlet for registration with the said outlet of the vessel, a plurality of spaced elements arranged in echelon in an inclined plane internally across the housing, means for vibrating the elements, and an outlet means associated with the housing downstream of the elements.

2. Equipment according to claim 1 in which the elements are mounted in a frame.

3. Equipment according to claim 1 or 2 in which the elements are in the form of rungs bearing platforms.

4. Equipment according to claim 1 or 2 in which the elements are in the form of plates.

5. Equipment according to claim 4 in which the plates have upstanding lips.

6. Equipment according to claim 5 in which the lips are relieved to provide castellations.

7. Equipment according to any one of the preceding claims 2 to 6 in which the frame is suspended or supported on anti-vibration mountings.

8. Equipment according to any one of the preceding claims in which the outlet means are in the form of a wedge-shaped collection box.

9. Equipment according to any one of the preceding claims 2 to 8 in which the outlet means are attached to the frame.

10. Equipment according to any one of the preceding claims 2 to 8 in which the outlet means are independent of the frame.

11. Equipment for the discharge of material from a storage vessel substantially as hereinbefore described with reference to the accompanying drawing.