1. Field of the Invention
The invention relates to a rotary tubular kiln with a satellite cooler. In such a kiln and cooler combination, the cooling tubes are commonly held by support means that allow for thermal expansion of the cooling tubes. Such support means are located in the discharge region of the rotary tubular kiln at two fixing locations on the kiln casing spaced apart in the axial direction. Each of the cooling tubes communicates at its inlet end by way of an inlet pipe with the interior of the kiln.
Rotary tubular kilns of this type are used in the production of cement clinker. When such a rotary tubular kiln is in service, the kiln casing, cooling tubes and support means are subjected to highly variable stresses due, on the one hand, to their heating, which frequently exhibits extreme local variations, and, on the other hand, to the mechanical load cycling of the cooling tubes by the material being cooled owing to the revolution of the kiln.
2. Statement of Prior Art
Attempts were first made to prevent the expensive damage such as cracks and fractures of the support means and of the kiln casing which are caused by the co-operation of these effects, by use of intrinsically rigid retaining or bracing elements for the cooling tubes mounted so as to be tiltable in the axial direction on the kiln, casing and on the cooling tube, which permitted an unobstructed thermal expansion of the cooling tube only in the direction of the kiln's longitudinal axis.
In view of the unsatisfactory results, attempts were made to give the cooling tubes also a restricted radial thermal expansion by redesigning the support means.
In one known arrangement of this type annular support means are illustrated in West German OS 25 19 458. Such a support means comprises a sheet metal plate attached to the kiln casing, the sheet metal plate having an inner and an outer annular zone in the radial direction, using an interposed elastic bush, if desired. The two annular zones can be joined by slotted radial struts constructed integrally with them, or by plate rings.
The cooling tubes are accommodated in the plate rings or in the circular orifices formed by the arcuate radial struts so as to leave an annular gap, whilst they are screwed to the retaining elements, each by two lugs provided mutually opposite in the peripheral direction of the sheet metal plate on the radial struts, the plate rings, or the cooling tube shell itself. Where plate rings are used, they should be fixed, likewise by means of screws, to the inner and the outer annular zone of the sheet metal plate.
It is further possible for the inner and outer annular zones of the sheet metal plate to be composed of segment-like elements arranged in staggered relationship in the axial direction, whilst the segments overlap partly in the axial direction.
Lastly, a lamellar arrangement of the sheet metal plates is also possible.
The prior art support means described permit an unobstructed axial thermal expansion of the cooling tubes during service. However, their thermal expansion in the radial direction is restricted at the lugs, in which local stress concentrations occur, as they also do in the adjacent region of the cooling tube due to the turning of the latter. Having regard to the cyclic loads which act upon the cooling tubes during the revolution of the kiln and which are produced in constantly changing planes due to sagging of the cooling tubes, an increased danger of fracture occurs at these points of concentrated thermic stresses. The screw joints of the plate rings to the inner and outer annular zone of the sheet metal plate are threatened for similar reasons.