GB2073031A

GB2073031A - Depositing and mixing bulk materials

Info

Publication number: GB2073031A
Application number: GB8107010A
Authority: GB
Original assignee: PHB WESERHUETTE AG
Current assignee: PHB WESERHUETTE AG
Priority date: 1980-03-25
Filing date: 1981-03-05
Publication date: 1981-10-14
Also published as: ATA79181A; IT8120001A0; FR2479160B1; AU533645B2; GB2073031B; DE3011349A1; DE3011349C2; IT1138951B; AT372056B; AU6837081A; FR2479160A1; ZA811578B

Abstract

Bulk material is deposited in a substantially continuous part-annular dump which is triangular in cross- section, where the bulk material is deported as it is subjected to an oscillating angular movement through a constant central angle in a horizontal plane along the middle circumference of the part-annular dump between points of reversal which are advanced in one sense along said middle circumference, whereby the bulk material is deposited in layers and the bulk material mixed as it is stripped from the dump in a radial direction. The oscillating angular motion is effected at a substantially constant velocity except for the reversals so that the layers which are deposited have substantially the shape of a parabola in a section taken on the middle circumference of the annular dump, and the thickness of each layer increases from the crest of the dump to its base. <IMAGE>

Description

SPECIFICATION Process of depositing and homogenizing bulk material This invention relates to a process of depositing and homogenizing bulk material in a substantially continuous part-annular dump which is triangular in cross-section, wherein the bulk material is thrown off as it is subjected to an oscillating angular movement through a constant central angle in a horizontal plane along the middle circumference of the part-annular dump between points of reversal which are advanced in one sense along said middle circumference, whereby the bulk material is deposited in layers and the bulk material is stripped from the dump in a radial direction at the base of the end face of the partannular dump, which end face slopes at the natural angle of repose, and the bulk material is homogenized as it is thus stripped.

Such process has been disclosed by German Patent Specification 1,432,040. The plant which is disclosed in that patent specification for use in carrying out the process has a vertical axle, which is disposed at the center of a circular area, and a radially extending belt conveyor parforms the progressive oscillating angular motion in the horizontal plane about said axle. Bulk material is fed to the belt conveyor adjacent to the axle by another conveyor and is carried radially outwardly by the belt conveyor so that the discharge end of the latter defines the mean radius of the resulting part-annular dump. Because the oscillating angular motion of the belt conveyor proceeds in one sense and has constant central angle, the part-annular dump is gradually built up in successive layers.

The resulting dump is triangular in crosssection and at any stage of its formation is divided into two sections, namely, a full-height section and a transitional section in which the height of the dump and its base width gradually decrease to zero. The transitional section is defined by the angular range which has been swept last by the discharge and of the belt conveyor. The deposited layers are inclined from a horizontal plane and in a developed section extending along the middle circumference of the part-annular dump are straight; they are substantially paraliel to one another and are substantially equal in thickness and length. If the belt conveyor operates at a constant rate of conveyance, such layers can be formed only if the oscillating angular motion of the belt conveyor is performed at a varying angular velocity.Specifically, the highest angular velocity is required at the lowermost portion of the dump and the lowest angular velocity is required at the point where the transitional section merges into the section where the dump has its full height.

This is due to the fact that in order to obtain a layer of constant thickness the volume of material to be deposited per unit of length of the transitional section must increase as the height gradually increases linearly to the full height of the dump.

In accordance with German Patent Specification 1,432,040, the stripping of material from the base of the end face of the annular dump is effected by means of a radially extending stripping apparatus, which may consist of a screw conveyor, a scraper or another conveyor and moves the bulk material radially inwardly to a hollow discharge shaft, which leads downwardly and is provided at the center of the circular area which accommodates the annular dump. The stripping apparatus performs a circular movement about the vertical axle at the center of the circular area. That circular movement is always directed toward the end face of the dump and matches the progressive motion of the belt conveyor.The known homogenizing effect is produced because the layers left after the bulk material has thus been stripped include a predetermined, constant angle to the deposited layer as the direction of movement of the material being deposited and the direction of movement of the material being stripped are normal to each other.

The known process has various disadvantages.

In the first place, the dump area defined by the circular area is not optimally utilized so that the volume of bulk material that can be stored in the dump is relatively small. This is due to the fact that the crest of the dump declines linearly in the transitional portion so that the volume of the transitional portion is substantially as large as the volume of a curved three-sided pyramid. Besides, in the known process it is desired to oscillate the belt conveyor through an angle which is as large as possible so that the transitional portion will be as long as possible. As a result, the volume of bulk material which can be stored in the dump is only one-third of the volume of an annular dump having a constant height that is equal to the maximum height of the transitional portion. Another disadvantage is due to the varying angular velocity of the belt conveyor.Because the masses to be moved are relatively large, expensive driving and control means are required to impart such motion to the belt conveyor. Besides, the highest angular velocity is required just when the angular motion is to be reversed at the lower end of the dump so that difficulties arise owing to inertia.

It is an object of the invention so to improve the process described first hereinbefore that the disadvantages which have been explained are eliminated. This object is accomplished according to the invention in that the oscillating angular motion is effected at a substantially constant velocity except for the reversals so that the layers which are deposited have substantially the shape of a parabola in a section taken on the middle circumference of the annular dump, and the thickness of each layer increases from the crest of the dump to its base.

Owing to these measures, the belt conveyor or other means for distributing the bulk material may be driven and controlled by simple means.

Besides, serious problems due to the mass forces are no longer encountered in the region in which the angular motion is reversed at the lower end of the dump because it is no longer required to brake the motion abruptly from a maximum velocity to a standstill and then to accelerate to said maximum velocity.Because the angular velocity is constant, the thickness of each layer in the transitional portion decreases gradually from the base of the dump to the full height of the dump since when the bulk material is conveyed at a constant rate the volume of bulk material which is deposited per unit of length will remain constant so that the cross-sectional area of the layer will remain constant too whereas the cross-sectional shape of the layer will become increasingly elongated as the height of the transition portion increases. (The cross-section of the layer consists of two strips which lie on the outside of the legs of the triangular cross-section of the previously deposited triangular section.) As a result, the layers are substantially parabolic in a developed sectional view taken on the middle circumference of the part-annuiar dump.This means that in a dump having a given maximum height and a transitional portion having a given length, the volume of a transitional portion deposited according to the invention is higher than the volume of the bulk material that has been deposited in accordance with the known process because in accordance with the invention the crest of the dump declines in the transitional portion substantially along a parabola whereas it slopes to the base along a straight line in a dump formed according to the known process. The volume of the transitional portion obtained in accordance with the invention is 50% larger than the volume of the transitional portion obtained by the known process. It is apparent that the use of the invention will increase the volume of bulk material which can be stored in a dump that it accommodated on a given circular area and has a given height.

Another advantage afforded by the invention is due to the fact when the bulk material is conveyed at a constant rate the volume of bulk material deposited per unit of length of the layer will always be constant so that the bulk material will be subjected to substantially constant trickling conditions throughout the length of each layer and the time required to deposit the material in a given unit of length of the layer is substantially the same everywhere. This is favorable for the preservation of the quality of the bulk material for the homogenization which is effected as the dump is subsequently stripped.The preservation of the quality of the bulk material can be further improved if the oscillating pivotal motion performed at a substantially constant velocity is combined with a lifting and lowering motion which is performed at a variable velocity and matches the parabolic shape of the layers. In this way the distances over which the bulk material trickles and the trickling times can be minimized because the distance from the point at which bulk material is thrown off to the crest of the previously deposited dump will remain substantially constant.

The invention will now be explained with reference to the accompanying drawing, in which Figure 1 is a perspective view showing an entire part-annular dump deposited in accordance with the invention, Figure 2 is a developed sectional view taken on the middle circumference of the annular dump shown in Figure 1, and Figure 3 is an enlarged view showing a portion of Figure 2.

The part-annular dump shown in Figure 1 has a portion A-B having the full height and a transitional portion B-C having a crest which slopes along a parabola to the base of the dump (Figure 2). As is particularly apparent from Figure 2, the end face of the dump slopes at the natural angle of response of the bulk material. In Figure 1, some layers are diagrammatically shown at the end face. It is apparent that the cross-sectional areas of the layers are the same and that the layers decrease in thickness from bottom to top (or from the inside outwardly).

Figure 2 shows the several parabolic layers which increase in thickness toward the base of the dump. The length increment of the dump per deposited layer is designated AL.

Figure 3 serves to explain another advantage afforded by the process according to the invention over the process known from German Patent Specification 1,432,040. The length of the angular motion, measured at the middle circumference of the part-annular dump, is designated L and is equal to the base length of the transitional portion B-C at the base of the dump.

It is apparent that the dump can be deposited to its full height in accordance with the invention in that, e.g., six parabolic layers are deposited, which are numbered 1 to 6. If parallel layers which slope along straight lines and have a constant thickness equal to the thickness of the lowermost parabolic layer obtained in accordance with the invention were deposited in accordance with the known process, only three of such layers could be accommodated in a transitional portion having the same base length and rising to the same dump height. These layers sloping along straight lines are shown in Figure 3 and numbered 1 to 3. This shows that under given geometric conditions the process according to the invention permits a deposition of about twice as many layers than can be deposited in the known process. This result will permit an improved homogenization.

It is also directly apparent from Figure 3 that the transition portion deposited in accordance with the invention is larger in volume that the transitional portion obtained by the known process as the parabolic crest extending from point B to point C is above the straight crest extending from point B to point C.

Claims

1. A process of depositing and homogenizing bulk material in a substantially continuous partannular dump, which is triangular in cross-section wherein the bulk material is thrown off as it is subjected to an oscillating angular movement through a constant central angle in a horizontal plane along the middle circumference of the partannular dump between points of reversal which are advanced in one sense along said middle circumference, whereby the bulk material is deposited in layers and the bulk material is stripped from the dump in a radial direction at the base of the end face of the part-annular dump, which end face slopes at the natural angle of repose, and the bulk material is homogenized as it is thus stripped, characterized in that the oscillating angular motion is effected at a substantially constant velocity except for the reversals so that the layers which are deposited have substantially the shape of a parabola in a section taken on the middle circumference of the annular dump, and the thickness of each layer increases from the crest of the dump to its base.

2. The process according to claim 1, characterized in that the oscillating pivotal motion performed at a substantially constant velocity is combined with a lifting and lowering motion which is performed at a variable velocity and matches the parabolic shape of the layers.

3. A process substantially as hereinbefore described and as illustrated by the figures of the accompanying drawing.