Conveyors: power-driven – Conveyor section – Reciprocating conveying surface
Reexamination Certificate
2003-05-09
2004-08-03
Ridley, Richard (Department: 3651)
Conveyors: power-driven
Conveyor section
Reciprocating conveying surface
Reexamination Certificate
active
06769533
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a method of transporting bulk material, in particular cement clinker through a cement cooler, in which a plurality of grate bars that can move one behind another on a gas-permeable protective layer execute a forward stroke and a return stroke. Furthermore, the invention relates to an apparatus for implementing the method.
BACKGROUND OF THE INVENTION
The preferred application for equipment of this type is the conveyance of hot bulk material, in particular cement clinker, over a protective layer, the bulk material being cooled from below by means of a gas flowing in. Here, the grate bars are moved to and fro in the conveying direction and, during each operation, with their forward stroke face thus convey a volume of the bulk material through the cooler in the direction of an outlet end. In this case, the movement of the grate bars in the conveying direction is designated the forward stroke, the movement counter to the conveying direction the return stroke. If, in the following text, mention is specifically made of cement clinker, this is also intended to mean bulk material in general.
The conveying performance of the transport method is influenced critically by the difference between the volume of cement clinker moved during each forward stroke in the conveying direction and the volume undesirably moved counter to the conveying direction during the return stroke movement. The efficiency is therefore determined critically by the configuration of the grate bars.
Apparatuses are known which alternatively have fixed rows of grate plates and moveable rows of grate plates, which overlap one another in an imbricated manner. The rows of grate plates comprise grate plates arranged beside one another. By means of the moveable grate plates, a volume of the cement clinker is pushed in the direction of the outlet end during the forward stroke, while during the return stroke, the undesired backward transport of the cement clinker conveyed is restricted by the cement clinker being wiped off by the rear face of the moveable grate plates. In this case, the fixed grate plates prevent cement clinker being transported counter to the conveying direction. The imbricated arrangement makes it possible for the moveable grate plates to be pushed under the stationary grate plates during the return stroke. For the purpose of cooling, the cooling gas is led from below through the cement clinker layer to be cooled during the transport operation. In this case, the gas used for cooling is intended to be able to pass largely unhindered through the grate plates. For this purpose, passage openings, for example in the form of holes or slots, are provided on the rear face of the grate plate.
It has proven to be disadvantageous in practice that, depending on the abrasiveness of the cement clinker to be treated, a considerable material wear on the grate plates occurs in the movement gap between fixed and moveable grate plates. As a result of the movement gap becoming larger, an increasing proportion of the cement clinker trickles downward between the grate plates and has to be transported away with a great deal of effort. Cement clinker particles which are swirled up lead to removal of material and in this way to premature aging of the apparatus.
Furthermore, U.S. Pat. No. 2,904,323 discloses an apparatus in which, between the substantially wedge-like grate bars there is in each case arranged a likewise wedge-like scraper. Likewise, U.S. Pat. No. 3,010,218 shows the alternating arrangement of moveable grate bars which, in this case, have a very flat rear face and, in cooperation with a wedge-like shape of the area between the individual grate bars, prevent the undesired backward transport of the cement clinker. The grate bars are connected by means of a frame or a plurality of connecting elements and therefore, by means of a common drive, can be set into an oscillatory movement parallel to the conveying direction. The grate bars therefore have a cross section which is approximately triangular or wedge-like, the forward stroke face being inclined substantially more steeply with respect to the conveying direction than the rear face which, as a result, opposes a considerably lower resistance to the cement clinker slipping back during the return stroke. In this way, the intention is for more material to be conveyed in the forward stroke than in the return stroke, in order in this way to convey the cement clinker through the cooler.
Furthermore, WO98/48231A1 discloses a simplified cooling apparatus which has successive moveable grate bars, a stationary retention element arranged between them being dispensed with. In this case, according to a specific exemplary embodiment, individual ones of the bars can also have a symmetrical cross-sectional area.
In practice, it has proven to be disadvantageous in the known transport apparatuses that the efficiency of the transport performance can certainly be increased by suitable shaping of the grate bars but, nevertheless, considerable losses of performance occur. Even when use is made of retaining means which are arranged between the moveable grate bars, a considerable part of the backward transport reduced by the retaining means is canceled out again by the simultaneously increased resistance in the conveying direction. In addition, in this case mixing of the cement clinker to be conveyed occurs, as a result of which the efficiency of the cooling is disadvantageously reduced.
The grate bars are subjected to considerable wear. As a result, the shape of the cross section of the grate bar becomes increasingly rounded, which impairs the conveying performance. In order to compensate for the decreasing conveying performance, the stroke frequency has to be increased. As a result, with increasing wear, more and more strokes are required to convey the same quantity of cement clinker. As a result of the increasing stroke frequency, the wear progresses faster and faster, at the same time the required drive power increasing.
SUMMARY OF THE INVENTION
Against this background, the invention is based on the object of developing a method of the type cited at the beginning in such a way that the conveying performance can be increased substantially as a result. At the same time, the susceptibility to wear is to be reduced. Furthermore, an apparatus for implementing the method is to be provided.
According to the invention, the first-named object is achieved by a cavity closed off with respect to the cement clinker being formed by the forward stroke of the grate bar, into which cavity the grate bar moves during the subsequent return stroke movement without substantial material transport counter to the forward stroke movement. In this way, undesired backward transport of the cement clinker during the return stroke is prevented, by cement clinker being prevented from sliding into the return stroke area of the grate bar by the formation of the cavity. Accordingly, the engagement of the grate bar in the cement clinker during the return stroke is largely prevented, the cement clinker resting on the return face and, as a result, not being shifted or being shifted only insignificantly. It therefore becomes possible to dispense with the use of stationary, immovable grate bars entirely, so that in addition to the low outlay on manufacture, at the same time the efficiency is also increased. In particular, a movement gap between the stationary and the moving grate plates is dispensed with as a result. Here, the cement clinker is transported by the successive grate bars in the manner of steps over the rear face of the following grate bar into the forward stroke area of the latter, so that mutual impeding of the individual grate bars is also ruled out. In particular, the grate bars convey the cement clinker obliquely upward with respect to the conveying direction, as a result of which the frictional resistance of the cement clinker, caused by the forward stroke movement on the protective layer, is reduced by the partial lifting of the conveyed cement clinker volume.
Claudius Peters Technologies GmbH
Morrison & Foerster / LLP
Ridley Richard
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