Patent Number: 042809223
Section: summary

The invention relates to a method and device for removing radiant, pulverulent synthetic wastes and, more particularly such wastes which are mixed dry with a thermoplastic mass in a kneader and then delivered from a discharge opening of the kneader into a container capable of providing a final storage therefor, while gases and/or vapors are withdrawn from degassing domes of the kneader. Such synthetic wastes are, especially, filter materials which are introduced into nuclear facilities or installations for purifying radioactive liquids or gases and which can contain a varying fraction or portion of organic substance. According to the heretofore known method of the German Published Non-Prosecuted Application DE-OS 25 31 584, an effort is made to prevent decomposition of the synthetic wastes when intermixed in bitumin by keeping the bitumin temperature as low as possible. Limits are set, in this case, however, because the viscosity of the bitumin sharply increases with reducing temperature so that the embedding and mixing operations are rendered more difficult. The gases produced during decomposition of the synthetic wastes can be withdrawn, in fact, by means of the degassing domes, which lie between the end of the kneader at which the latter is supplied or charged and the discharge opening, and are connected to a degassing device. They create an impermissible danger there, however, due to their explosibility and concentration. It is accordingly an object of the invention to provide a method and device for removing radiant, pulverulent synthetic wastes wherein danger of decomposition and gas formation of the synthetic wastes is reduced without requiring the temperature of the bitumin to become undesirably low. Simultaneously, it is an object of the invention to provide such a method and device wherein a dangerous concentration of partly explosive gas in the degassing dome is prevented. In this regard, the dried filter residues are to be metered to the bitumin so that no blockages or obstructions occur. With the foregoing and other objects in view, there is provided, in accordance with the invention, a method of removing radiant, pulverulent synthetic wastes which are mixed dry with a thermoplastic mass in a kneader and then delivered from a discharge opening of the kneader into a container capable of providing a final storage therefor, while gases and/or vapors are withdrawn from degassing domes of the kneader, which comprises delivering fluidic dried wastes by mechanical movement through a metering tube into a degassing dome in the kneader disposed next to the discharge opening, and admitting scavenging gas into the metering tube at least temporarily in direction toward the kneader. Through this invention, the mixing time is considerably shortened and, accordingly, the thermal loading or stressing of the material being embedded is reduced because the transit time of the synthetic wastes is not provided any more by the movement of the wastes. through the entire kneader but rather only by the movement thereof through the short distance between the "last" degassing dome and the discharge opening of the kneader. In this manner, the mixing time can be shortened to one-third or even less. thus, the decomposition, which indeed, does not occur abruptly, is accordingly reduced. In this regard, due to the mechanical movement in the metering tube, the accuracy of the metering operation is improved so that it is actually possible to manage with such brief mixing times. Furthermore, due to the scavenging gas, the metering tube is kept free of contaminating vapors so that the removal of gases or vapors limited in essence to this degassing dome can effect no obstruction or blockage. In accordance with another feature of the invention, the method comprises applying vibratory motion to the metering tube as the mechanical movement, and in accordance with further features of the invention, the vibratory motion is applied transversely to the longitudinal axis of the metering tube. In accordance with an additional feature of the invention, the method comprises continuously admitting the scavenging gas into the metering tube in order to avoid the formation of clumps by the wastes. If necessary, by varying the amount of scavenging gas, obstructions in the metering tube can be removed. Besides, ordinary air as well as other gases can be introduced which, if need be, due to the content of inert components therein, can avoid danger of explosion even when disruptions occur in the feed of the scavenging air. In accordance with yet another feature of the invention, the method includes periodically heating the metering tube which preferably projects vertically into the degassing dome, with steam. Thereby, all at once, a given heating of the tube is achieved which facilitates expulsion of condensation products and possible bitumin splashes or spray along the short path to the discharge opening. In accordance with yet a further feature, the steam is passed through the metering tube, and is admitted from the metering tube into the degassing dome for scavenging synthetic powders adhering therein. For this purpose, a steam-conducting jacket disposed around the metering tube is provided with suitable discharge or exhaust openings. In accordance with yet an added feature of the invention, the method comprises mixing the wastes in a ratio of about 60:40 with bitumin which is at a temperature of from 110.degree. to 150.degree. C. and which is preferably distillation bitumin (B 15 or B 25). In accordance with the device of the invention, there is provided a kneader for embedding radiant synthetic wastes in bitumin comprising a plurality of degassing domes and formed with a discharge opening, one of the degassing domes being located adjacent the discharge opening and having a metering tube displaceable with respect to the one degassing dome. In accordance with another feature of the invention, the metering tube has a heating steam jacket. In accordance with a further feature of the invention, the kneader includes nozzles disposed on the metering tube and extending from the steam jacket into the one degassing dome. In accordance with an added feature of the invention, the kneader includes a vibrator disposed on the one degassing dome, the metering tube being connected to the vibrator. In accordance with a concomitant feature of the invention, the kneader includes a scavenging-gas union provided on the metering tube. Other features which are considered as characteristic for the invention are set forth in the appended claims. Although the invention is illustrated and described herein as embodied in method and device for removing radiant, pulverulent synthetic wastes, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.