The invention relates to a bulk material cooler having a cooling grate which carries the material to be cooled, such as hot cement clinker for example, and transports the material to be cooled, through which a cooling gas flows, from the charging end for the material to be cooled to the discharging end for the material to be cooled.
Grate coolers are used in the nonmetallic minerals and ores industry, in order to intensely cool the material previously burned in a furnace, for example cement clinker or other mineral materials, directly following the cooling grate. Apart from traveling grate coolers, widely used for the purpose of transporting the hot material to be cooled over the cooling zone are, in particular, pushing grate coolers, in which the grate system comprises a multiplicity of alternately fixed and movable grate plate supports on which a number of grate plates which are provided with cooling air openings and through which cooling air flows substantially from underneath upward are respectively secured. In this case, rows of fixed plates alternate, seen in the conveying direction, with rows of reciprocating grate plates, which are secured by means of their correspondingly reciprocating grate plate supports on one or more longitudinally movably mounted, driven pushing frames. The common oscillating motion of all the rows of movable grate plates has the effect that the hot material to be cooled is transported in batches and thereby cooled. In this respect, it is also known to prevent the grate plates from being subjected to thermal-mechanical overloading by providing the upper side of the plates with hollows or pockets for receiving and fixing material to be cooled, which then forms a layer providing protection against wear for the hot material to be cooled that slides over it (EP-B-0 634 619).
To avoid the problem of wear in the case of the pushing grate cooler, in the region where adjacent rows of moved and non-moved grate plates overlap, caused by cement clinker abrasion and material becoming lodged in the overlapping region of the grate plates, EP-B-1 021 692 and DE-A-100 18 142 disclose as an alternative to a conventional pushing grate cooler a type of grate cooler in which the cooling grate through which cooling air flows is not moved but stationary, a number of rows of adjacent reciprocating bar-shaped pushing elements, which are moved between a forward-travel position in the transporting direction of the material to be cooled and a return-travel position, being arranged above the stationary grate surface transversely in relation to the transporting direction of the material to be cooled, so that the reciprocating motion of these pushing elements in the bed of material to be cooled has the effect that the material is successively moved from the beginning of the cooler to the end of the cooler and is thereby cooled. As a result of the highly stressed pushing elements that are moved in the bed of bulk material, the bed of bulk material is intermixed, which has unfavorable effects on the thermal efficiency of this type of cooler. The bulk material conveying capacity is thereby decisively influenced by the difference between the volume of cement clinker that is moved with each forward travel in the conveying direction and the volume of clinker that is moved undesirably counter to the conveying direction in the return-travel movement. Furthermore, in the case of this known type of grate cooler, the pushing elements in the form of transverse bars are secured on the upper side of vertical drive plates, which are aligned in the longitudinal direction of the cooler, extend through corresponding longitudinal slits of the cooling grate and are driven from underneath the cooling grate. It goes without saying that it is arduous to seal the cooling grate loaded with material to be cooled in such a way as to prevent material falling through the grate at the locations where the drive plates pass through, and thereby keep the amount of material wear that occurs within limits.
Finally, DE-A-196 51 741 discloses a cooling tunnel for cooling and/or freezing material to be cooled by means of cold air by using the so-called “walking floor” conveying principle, in which a number of adjacently arranged bottom elements of the cooling tunnel are moved forward together in the transporting direction but are not moved back together but separately from one another. A high pile of bulk material is intended to form over the bottom elements, filling the entire cross section of the cooling tunnel, so that the cooling gas flows in countercurrent through the bulk material that is moved step by step. The bottom elements themselves remain uncooled by the cooling gas, so that for this reason alone the known cooling tunnel would not be suitable for cooling red hot cement clinker falling from the discharge end of a rotary kiln. The direct contact of the fresh hot cement clinker with the surface of the bottom elements would lead to high thermal-mechanical loading in terms of wear and therefore to an inadequate service life of such a cooling tunnel in the case of hot cement clinker.