Heating – With work cooling structure
Reexamination Certificate
2000-11-01
2001-11-06
Wilson, Gregory (Department: 3749)
Heating
With work cooling structure
C432S079000, C432S080000
Reexamination Certificate
active
06312252
ABSTRACT:
BACKGROUND OF THE INVENTION
It is known to cool combustion products (for example cement clinker) by a layer of the combustion products being conveyed on a grate, while cooling air is forced through the grate and the product layer. In a known type of such a cooler (EP-B-676031; EP-A-718578; WO-A-8401616), a stationary grate surface is used, over which the product bed is moved by means of a conveyor. The latter consists of a pair of endless conveyor chains which are arranged on both sides of the grate and between them carry drivers which lie transversely to the conveying direction and drive the products lying between and above them in the conveying direction, that is to say in the longitudinal direction of the cooler. The driver beams are surrounded by hot products and are therefore exposed to wear. This applies particularly to the initial region of the cooler, where the hot products to be cooled, emerging directly from the furnace, meet the drivers.
When the stream of products to be fed onto the grate meets the conveying grate and its drivers directly, high wear and high mechanical stress occur. In order to avoid this, there may be provision (EP-B-676031, EP-A-718578) for the combustion products first to fall onto a stationary surface which consists of grate plates with air throughflow and from which the products are moved, even without additional conveying means, towards the start of the conveying grate solely by virtue of an inclination of this surface. In order to ensure that the products have a dwell time sufficient for precooling, the surface is inclined only slightly and has a considerable length. This presents problems in terms of a uniform operation of the cooler, particularly in the case of difficult products which tend to cake on and cake together.
In another known cooler of the type just described (EP-A-726440) the grate and the drivers are protected in that, before the feed of the products to be cooled, a layer of already cooled products returned from the end of the grate to the start is fed. The grate and the drivers are protected, by the cool product layer enveloping them, from the hot product layer located above it. The outlay for returning the cooled products and for conveying double the quantity of products on the grate is high.
SUMMARY OF THE INVENTION
The object of which the invention is based is to reduce the thermal stress and the wear of the conveying grate in the initial region, in particularly at the drivers.
The solution according to the invention lies in the features of claim
1
and preferably in those of the subclaims.
According, there is provision for the drivers to run through a pre-space which is protected against the direct inflow of products and contains an intensively cooled slope of the product bed, before said drivers enter the feed region. As soon as a driver has entered this pre-space, it pushes forwards in the conveying direction part of the material which has accumulated in said pre-space. Other parts of the displaced products pour over it opposite to the conveying direction and settle behind it, together with products newly introduced to the slope, on the stationary grate surface, where, at a standstill, they are exposed to the influence of the cooling air until the next driver appears in order to drive them along. They have then already assumed a lower temperature, so that the driver comes into contact only with precooled products. This shields it on all sides against the fresh uncooled products. This applies not only as long as it is located in the pre-space upstream of the discharge limit of the products, but also downstream thereof, because it is located in the lower to medium height range of the product layer, this range being formed mainly by precooled products, while the newly arriving uncooled products come to rest on the top side of the layer. This sample measure affords effective protection of the drivers against thermal stress caused by uncooled products and against these products impinging directly on them. This also applies to the stationary grate surface.
In an apparatus for feeding bulk products onto the conveyor belt of a sintering plant (EP-A-359108), it is known for the product bed to be drawn off from a pile which is delimited, on the side opposite to the conveying direction, by a wall located at a distance from the conveyor belt. A slope is formed, opposite to the conveying direction, in the region of the orifice formed between the conveyor belt and the lower edge of this wall, the result of this being intended, in a way which is not easy to understand, to prevent the segregation of the material to be sintered. This has nothing to do with the present invention.
As regards travelling grates, it is known (U.S. Pat. No. 4,732,561, DE-A-1953415, DE-B-1108606) to delimit the feed region above the grate by means of a cooled oblique surface which terminates at a distance above the grate. No reference to the idea of the present invention is found on it.
The shape of the pre-space is not critical, insofar as it is covered on the top side in such a way that the conveying grate is not struck directly by the feed stream in the region of the pre-space. It may be expedient, however, to limit the height of the slope, in that the devices delimiting the feed stream on its side facing opposite to the conveying direction form an edge, from which the pre-space opens and from which the surface of the slope falls, opposite to the conveying direction, towards the conveying grate. In this case, it is advantageous, in general terms, if the height of the pre-space is dimensioned so as to be essentially sufficient for receiving the slope. In other words, its height is everywhere approximately at least the same as corresponds to the slope angle emanating from said edge. For example, the upper delimitation of the pre-space may be formed by an oblique surface descending opposite to the conveying direction. In some cases, it is expedient to make the height of the pre-space a little lower than corresponds to the height of the slope, so that no interspace, through which cooling air can escape, remains between the surface of the slope and the upper delimitation of the pre-space. The cooling air is thereby prevented from escaping through the regions of least height of the slope. It may be expedient, furthermore, if the length of the pre-space, as measured in the conveying direction of the grate, is a little shorter than the slope length, so that a region which is free of bulk products and through which air can escape, without combustion products being cooled, is not formed between the running-out end of the slope and the delimitation of the pre-space. However, this possibility may also be prevented by the air permeability of the grate surface being reduced or blocked on the far side of the region which is occupied in any event by the slope.
So that the length of the pre-space suffices for the products to have a dwell time sufficient for pre-cooling, said length is expediently equal to the speed of advance of the drivers, multiplied by the desired dwell time, and at the same time the latter should be at least of the order of magnitude of 0.5 to 3 min. In the case of a speed of advance of the drivers of 0.5 m/min, a length of the pre-space of 0.5 to 1 m has proved advisable. The longitudinal distance between the drivers is expediently of the same order of magnitude. It should be greater than 0.8 times the length of the pre-space.
In order to seal off the cooler space and, in particular, the pre-space sufficiently in relation to the surrounding atmosphere, it is expedient if, upstream of the pre-space, the drivers run through a closed-off duct, the length of which is at least equal to the distance between them. The delimitation of the conveying stream is expediently formed by an oblique surface descending in the conveying direction and terminates at said edge from which the pre-space and the slope emanate.
The descending oblique surface is expediently equipped with ventilated grate plates. In contrast to the prior art mentioned in the introduction, it do
Alix Yale & Ristas, LLP
BMH Claudius Peters GmbH
Wilson Gregory
LandOfFree
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