Heating – Tumbler-type rotary - drum furnace
Reexamination Certificate
2000-08-04
2001-06-12
Lu, Jiping (Department: 3749)
Heating
Tumbler-type rotary - drum furnace
C432S107000, C432S112000, C432S118000, C432S119000
Reexamination Certificate
active
06244859
ABSTRACT:
FIELD OF THE INVENTION
The invention refers to a rotary kiln with a horizontal kiln drum arranged rotatable and drivable in a furnace body, which kiln drum is closed on the charging and delivery side by end plates forming central charging and/or delivery openings, and which can be heated from outside via a heating chamber admitted with a heating medium, which heating chamber surrounds the drum shell.
DESCRIPTION OF THE PRIOR ART
Rotary kilns for various combustion and gasification processes have been made in manifold embodiments, with the kiln drum as yet forming a flat-walled cylinder jacket, which, at its inside, has been equipped with ribs and webs for rearrangement and longitudinal conveyance of the material charged to the kiln and subjected to the desired combustion or gasification process. Simultaneously, these ribs and webs serving as conveying and conducting facility have increased the heat transfer surface of the kiln drum heated from outside, however, due to the indirect heat admission of the webs and ribs via the drum shell, the thermal yield has remained unsatisfactory. To prevent a major deflection of the kiln drums, which are produced in relatively long lengths, these must be made accordingly solid and with substantial wall thickness, which does not only increase the expenditure of construction, but also adversely affect the heat transfer from the heating chamber admitted with the heating medium to the material to be treated in the kiln. Moreover, due to the very high operating temperatures of the rotary kilns and, consequently, the substantial thermal expansion, the kiln drum must be suitable for taking up heat-related deformations, which means a further increase of the expenditure of manufacture, as well as an increase of the related thermic drawbacks for heating of the drum and for executing the relevant combustion and gasification processes.
SUMMARY OF THE INVENTION
Therefore, the invention has the task to create a rotary kiln of the above mentioned kind, which is characterised by a solid design on the one hand, and, on the other hand, by a high thermal-energetic yield at a comparably inexpensive construction.
The invention solves this task by constructing a kiln drum that consists of U-sections arranged side by side along the drum circumference between the end plates, the open section sides of which U-sections point radially inward and are interconnected longitudinally in the touching end zones of the section limbs, and at the circumference via reinforcing elements axially distant to each other and bridging the remaining longitudinal gaps between the section webs.
By this cylindrical placement of U-sections side by side a kiln drum is created with a kind of internal toothing via the U-sections, with the touching limb ends of the U-sections being welded together and the U-sections supporting each other in the web zone by means of the provided reinforcing elements. Thus a very solid composite U-section structure is achieved, as the adjoining U-section limbs with the related reinforcing elements constitute high-strength triangular cross sections providing the kiln drum with the necessary stability. This high stability permits the use of U-sections of relatively thin wall thickness, so that both the own weight can be kept low and the heat transfer properties through the drum shell are improved. Even with long rotary kilns, there is no problem of sagging, the heat-related expansions can be taken up without major additional reinforcements, and it is possible to equip the end plates provided for closing the kiln drum with bearing races or similar for pivoting and/or for sealing the kiln drum, as this can be inferred, for example, from AT-B 397.861. Apart from the strength and stability properties of the kiln drum, extremely favorable thermal yield conditions are achieved via this special drum cross section with its internal toothing, since the spaces remaining between the adjoining U-section limbs, which are triangular in cross section, are accessible from outside and can be applied with the heating medium in the heating chamber, so that not only accordingly larger heat transfer surfaces are available, but, due to the inwardly projecting section limbs, heat can also be input directly to the material taken along and rearranged by the section limbs inside the drum. This leads to the most favorable results of the performed combustion and gasification process, since the inwardly projecting section limbs take up the material, when the drum is rotated, rearrange the material and pass it on from section to section, which implies an intensive contact between the section parts and the material to be treated, and thus an accordingly high heat yield.
As reinforcing elements single connection plates may be welded between the section webs, however, it is more expedient to provide as reinforcing elements rings embracing the U-sections, which can be applied efficiently and can also be used as bearing races for bearing of the drum or similar, if required.
In order to achieve, in case of horizontal drum position, a conveyance effect in longitudinal direction beside the rearrangement of the material inside the kiln, conducting walls, cocked against the drum axis, preferably axially offset against each other from section to section, can be arranged in the section profiles for longitudinal conveyance of the charged kiln content, so that the charged material steadily passes through the drum from the charging to the delivery side and is subjected to the desired heat treatment on its conveying route.
Since the kiln drum is usually borne in the furnace body at its ends in the area of the end plates, the drum ends project out of the heating chamber on both sides, which as yet has implied a cooler end zone of the rotary kiln in this border area of the drum compared with the heating chamber area, which may lead to disturbances in the proceeding combustion or gasification process, especially in these transitional areas at the charging and/or delivery side. To prevent this by simple means, a sealing collar coaxial to the kiln drum and enclosing the ends of the U-sections projecting out of the heating chamber is applied between each end plate of the kiln drum and the adjacent connecting wall of the heating chamber, which does not only serve for heat insulation of the drum ends, but which also constitutes a kind of double shell for the drum ends admitted with heating medium on part of the heating chamber, and provides for regular process temperatures even in the areas of the drum ends. Moreover, these sealing collars constitute a suitable sealing of the kiln drum against the penetration of the heating chamber.
REFERENCES:
patent: 2669444 (1954-02-01), Beetz
patent: 5033959 (1991-07-01), Bernt et al.
patent: 0 056 931 (1981-12-01), None
Collard & Roe P.C.
Lu Jiping
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