The present invention relates to a grate cooler for cooling granular material, such as cement clinker or the like, which cooler is of the kind (hereinafter referred to as of the kind described) comprising a grate surface which is made up of a number of, preferably overlapping, rows of grate plates and the longitudinal edges of which are laterally bounded and overlapped by elongate edge guards of angular cross section which are fixed relatively to the side walls in such a way that a gap is provided between each edge guard and the grate plates at the respective edge of the grate surface.
EP-A-0378821 discloses such a grate cooler in which the gaps between the edge grate plates of the grate surface and the side walls of the cooler are sealed off by means of angular edge guards. This known grate cooler further comprises a tension arrangement which forces the grate surface in the direction towards the edge guards, thereby ensuring that the gap width is reduced as much as possible commensurate with varying operating conditions.
However, the disadvantage of this known grate cooler is that it has to be shut down for maintenance at relatively frequent intervals. This is owing to the fact that hot and fine clinker material will invariably enter the gap between the grate surface and the edge guards causing such abrasion of the grate plates at the edges of the grate surface as well as of the edge guards that regular replacement of the structural elements is necessary. Subject to wear exposure, there will be an undesirable increase in the gap width during cooler operation, without any possibility of equalizing the gap width by means of the tightening device, since the abrasion is not uniform.
It is the object of the present invention to provide a grate cooler by means of which the aforementioned disadvantage is remedied.
This is achieved by means of a grate cooler of the kind described which is characterised in that a hollow duct is provided extending along each side wall adjacent to the respective edge guard and is arranged to be connected to an air supply source; and in that each edge guard is formed with through-going passages which open at the gap and are connected to the interior of the duct so that air may be injected into the gaps between the edge guards and the adjacent grate plates.
It is thus ensured that the gaps between the edge guards and the edge grate plates are kept free from clinker material, hence minimizing the wear in this zone.
Preferably, each passage extends to a surface of its edge guard facing the duct where the passage is connected via a respective hole in the duct to the interior of the duct.
At least some of the passages may open at the underside of the overlapping part of the edge guard but at least some of the ducts may equally well open near to the top of a vertical part of the edge guard which bounds the grate surface.
In one embodiment of the invention, the hollow ducts may be built into the side walls of the cooler, in a second embodiment they may be mounted on the side walls between the latter and the edge guards, whereas in a third embodiment they may be mounted resting on transverse beams.
The invention will now be explained in further details with reference to the accompanying diagrammatical drawings, in which:
Fig. 1 shows a sectional view of a grate cooler 1 which comprises side walls 3 and a grate bottom or grate surface 5 upon which material 7, to be cooled, is conveyed.
The grate surface 5 is made up of rows of overlapping grate plates 9, each of which comprises through-going slits or holes, not shown, for injection of cooling air into the material 7 on the grate surface 5. The cooling air may, as shown on the drawing, be supplied to the grate plates 9 in groups via an underlying system of air supply ducts 11.
The grate surface 5 is bounded and overlapped at its longitudinal edges by angular edge guards 13 of L-shaped cross section, which, in the shown embodiment, are fixed directly to the side walls 3 of the cooler.
Grate coolers are typically designed with a number of rows of grate plates which are capable of reciprocating movement in the longitudinal direction of the cooler, hence providing for a material conveyance through the cooler, and, as a consequence hereof, the guards 13 do not fit closely against the grate plates 9 at the edges of the grate surface, but instead forming in conjunction with these plates fine gaps 15.
When conducting maintenance work on grate coolers, significant wear is, therefore, often observed on these movable, lateral grate plates and the appertaining edge guards, this being mainly ascribable to infiltration of hot and fine material into the gaps 15.
Figs. 2, 3 and 4 present examples showing how this problem may be resolved. In all the examples, a hollow duct 16, extending in the longitudinal direction of the cooler and being connected to an air supply source, not shown, is mounted at each of the side walls 3 of the cooler and at substantially the same level as the guards 13. The guards 13 are formed with throughgoing passages 17, each being connected via a hole 19 in the duct 16 to the interior of the duct and hence the air supply source, and terminating at the gap 15, either at the underside of the overlapping part 21 of the guard or adjacent to the top of the vertical part of the guard 13.
Hence the gaps 15 can be kept clean of material by injecting air through the passages 17.
In Fig. 2 the hollow ducts 16 are built into the side walls 3 of the cooler, in Fig. 3 they are mounted on the side walls 3 between the latter and the edge guards 13, and in Fig. 4 they are mounted resting on transverse beams 23 extending between the side walls 3 of the cooler.