Pyrolysis plant for refuse and method for screening solid...

Classifying – separating – and assorting solids – Plural – diverse separating operations

Reexamination Certificate

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C209S044000, C209S044300, C209S270000, C209S654000, C209S669000, C201S025000, C201S021000, C110S235000

Reexamination Certificate

active

06786335

ABSTRACT:

BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a pyrolysis plant for refuse and a method for screening solid residues, through the use of which coarse solid fragments are separated from finer solid fragments.
In many industrial areas of use, it is necessary for solids which are contained, for example, in bulk material to be separated into a plurality of fractions. The fractions are, as a rule, subdivided according to different solid sizes, solid geometries or solid constitutions. Separation of solids is desirable whenever the different solid fractions are to be supplied for further treatment.
In the building industry, for example, building debris which occurs is separated from large and bulky debris constituents which are then sorted and reutilized. The separated finer building debris is disposed of, for example, at a dump provided for that purpose.
In the field of waste disposal, separation and sorting of the waste or of residues occurring during waste utilization are of ever-increasing importance with a view toward disposal which is as protective of the environment as possible. An essential factor therein is the separation of waste according to its size. Separation may be carried out before the waste is utilized. However, it may also be an essential method step in waste utilization itself.
Thermal methods are known for the elimination of waste, in which the waste is burned in refuse incineration plants or pyrolysed in pyrolysis plants, that is to say subjected to a temperature of about 400° C. to 700° C., with air being excluded. In both methods, it is expedient to separate the residue remaining after incineration or after pyrolysis, in order to either supply it for reutilization or dispose of it in a suitable way. The aim, in that case, is to keep the amount of residue to be ultimately stored at a dump as low as possible.
European Patent Application 0 302 310 A1, corresponding to U.S. Pat. No. 4,878,440, and a company publication entitled “Die Schwel-Brenn-Anlage, eine Verfahrensbeschreibung” [“The Low-Temperature Carbonization Incineration Plant, a Method Description”], published by Siemens AG, Berlin and Munich, 1996, disclose, as a pyrolysis plant, a so-called low-temperature carbonization incineration plant, in which essentially a two-stage method is carried out. In the first stage, the waste supplied is introduced into a low-temperature carbonization drum (pyrolysis reactor) and is carbonized there at low temperature (pyrolysed). During pyrolysis, low-temperature carbonization gas and pyrolysis residue occur in the low-temperature carbonization drum. The low-temperature carbonization gas is burned, together with combustible parts of the pyrolysis residue, in a high-temperature combustion chamber at temperatures of approximately 1200° C. The waste gases occurring at the same time are subsequently purified.
The pyrolysis residue also has non-combustible constituents in addition to the combustible parts. The non-combustible constituents are composed essentially of an inert fraction, such as glass, stones or ceramic, and of a metal fraction. The useful materials of the residue are sorted out and supplied for reutilization. It is necessary to have methods and components which ensure reliable and continuous operation for the sorting-out process.
In the case of screening devices, there is often the problem of screen surfaces becoming clogged. The screening device then breaks down, or at least it must be subjected to complicated and labor-intensive cleaning. The problem of the blockage of the screening device arises particularly when the solid to be separated has a highly inhomogeneous composition. Thus, for example, wires catch in perforated plates used as screen surfaces, so that the individual holes are first narrowed and, in time, become clogged.
The residue occurring during the pyrolysis is typically a highly inhomogeneous solid which has pronounced differences in terms of its material composition, its size and the geometry of its solid fragments. The residue contains not only stones, broken glass and larger metal fragments, but also elongate bars and entangled wires (wire pellets).
A device for discharging pyrolysis residue from a low-temperature carbonization drum is known, for example, from International Publication No. WO 97/26495, in order to provide for the separation of coarse pyrolysis residue. The discharge device includes a conveying device which has a separating bottom with a sawtooth-like profile as well as a downstream bar screen. The separating bottom is set in vibration, so that the fine constituents are separated from the coarse on the separating bottom. The fine constituents fall through the downstream bar screen, while the coarse constituents slide along on the latter. However, wire pellets may catch on the bars and lead to a blockage.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a pyrolysis plant for refuse and a method for screening solid residues, which overcome the hereinafore-mentioned disadvantages of the heretofore-known devices and methods of this general type and in which continuous operation is ensured by simple measures, without blockages occurring.
With the foregoing and other objects in view there is provided, in accordance with the invention, a pyrolysis plant for refuse, comprising a screening device having an interior for receiving solid residues, a rod wound along a helical line and bounding the interior, and a longitudinal axis, the screening device rotatable about the longitudinal axis.
The decisive advantage of a screening device constructed in this way is to be seen in that wire pellets or other solids cannot remain adhering to the rod. Thus, due to the rotation of the screening device and because of the turn of the rod, the wire pellets are thereby pushed down in the conveying direction. Blockages are therefore effectively avoided.
In accordance with another feature of the invention, the rod is constructed as a spiral with a plurality of turns, in particular with about four to ten turns.
In a screening device of this kind, which may also be referred to as a “spiral screen”, the solids to be screened are introduced into the interior formed by the three-dimensional spiral. Fine solids having smaller dimensions than the distance between two turns of the spiral fall through the spiral, while coarse solids are conveyed further in the interior. The maximum size of the screened finer solid constituent can be set by a suitable choice of the distances between the turns. The rotational movement of the spiral ensures that the coarser solid fragments are transported reliably and continuously in the conveying direction from the start to the end of the spiral.
An essential advantage of the spiral is that waste fragments possibly jammed between two turns are raised as a result of the rotational movement and, in particular, fall down due to their dead weight at an upper reversal point. The simple and robust construction of the screening device as a spiral therefore automatically avoids permanent blockages and allows continuous operation.
In accordance with a further feature of the invention, a number of rods are provided and the rod starts thereof are disposed so as to be offset in terms of rotation. In this case, each rod runs along a helical line. Such a screen having a plurality of rods is also referred to as a multi-flight screen.
In accordance with an added or alternative feature of the invention, the angle of rotation of the rods is smaller than 360°. In particular, the angle of rotation is smaller than or approximately equal to 180°. The screening device may be constructed with a plurality of rods which do not execute a complete revolution, so that it can be made more robust, as compared with a spiral screen having a plurality of turns.
In accordance with an additional feature of the invention, there is provided a rod element fixed relative to the rod, both in the spiral screen and in the multi-flight screen. The rod element runs essentially parallel to the outer sur

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