Patent Number: 046612904
Section: summary

BACKGROUND OF THE INVENTION The present invention relates to an apparatus for reducing the volume of various solid waste materials discharged from homes, factories, nuclear power plants, for example, to produce compacted solid masses for landfill or storage, to such an apparatus further comprising its accessory facilities and also to a method for cleaning said apparatus. Various solid waste materials are discharged from homes, factories, power plants, and other facilities of today. For example, solid wastes such as pieces of plastics, metal, glass, and other materials are discharged from homes and factories, and radioactive wastes such as rags, polyethylene sheets, paper, concrete pieces, steel members, high-performance filters, heat insulation are discharge from nuclear power plants. The aforesaid solid wastes discharged from homes and factories are processed in different ways, which raise their own problems. For example, the discharged pieces of plastics are burned in incinerators. However, the incinerators tend to be melted by heat generated by burning of plastics, clogged by the molten plastics and damaged by local overheating. Furthermore, the incinerators produce harmful gases such as chlorine and dioxin. Landfill of polystyrene foam pieces, polyethylene sheets, plastics bags is disadvantageous in that since these materials are bulky, the cost of transportation thereof is high, and they tend to be exposed onto the landfill surface after buried and then scattered due to winds, resulting in environmental pollution. Various methods have been proposed to recover and reuse waste plastics for effective exploitation of resources. However, since urban trash includes a wide variety of materials, it is more costly to classify the different trash materials than to recover the waste plastics. It has been proposed in Japanese Patent Publication No. 57-11273 to produce large solid masses containing inorganic particles fixed together with a melt of thermoplastic waste materials by adding a granular or particulate inorganic material such as sand, crushed stone, or ash to the thermoplastic waste materials under heat. This process is however not suitable to granulate metals, fabric pieces and the like, and hence is required to be effected after the metals, fabrics and the like have been separated from the other materials. The wastes contaminated by a radioactive material in nuclear power plants are normally packed in polyvinyl bags which are placed in drum cans for storage, sometimes after having been classified into combustible and noncombustible materials. Waste materials such as high-performance filters composed of a wood material, a filter aid (inorganic), a metal plate and the like which are joined together are required to be disassembled into individual parts which should then be sorted. This process is complicated and gives the workers a greater chance to get exposed to radiation. The drum cans are stored in storage houses. Since the available storage spaces in the storage houses are becoming smaller than expected these days, the combustible radioactive wastes are burned and the produced ash is stored in drum cans or mixed with cement and solidified as stable solid masses. The burning process is used for processing the bulky materials such as polyethylene sheets, polyvinyl bags, rags and paper wastes, and hence is capable of reducing the volumes of these waste materials. For this reason, the burning process is widely employed to process the waste materials discharged from nuclear power plants, facilities using radioisotopes, and other similar facilities. However, when a large quantity of plastic materials are burned in an incinerator, the incinerator is liable to get damaged, and the incinerator system is required to be equipped with an exhaust gas processing apparatus which itself produces a secondary waste material. In addition, the cost of installation of said apparatus is high. Another process of treating radioactive solid waste materials is to employ a press for compacting the wastes into smaller volumes. There is developed a high-pressure compacting apparatus for compacting waste materials under a pressure ranging from 1000 to 3000 kg/cm.sup.2. According to this compacting process, polyethylene sheets, polyvinyl bags, paper wastes, rags and similar waste materials can be compacted into masses free of free spaces or air pockets trapped therein. Although the compacting process is one of effective methods, produced compacted masses are combinations of heterogeneous materials that are not desired for a long-term storage. SUMMARY OF THE INVENTION It is an object of the present invention to provide an apparatus for compacting solid waste materials discharged from homes and factories or radioactive solid waste materials discharged from nuclear power plants and facilities using radioisotope, to solidify the waste materials into masses which can be pelletized, stuffed into drum cans, or shaped into prismatic forms for stable landfill or storage, without producing secondary waste materials. Another object of the present invention is to provide such an apparatus further comprising an accessory facility for stably controlling the operation of the foregoing compacting apparatus. Still another object of the present invention is to provide such an apparatus further comprising an accessory facility for shaping materials extruded from the foregoing compacting apparatus, cutting off the shaped materials, and charging the cut-off materials into containers. A still further object of the present invention is to provide such an apparatus further comprising an accessory facility for processing an exhaust gas from the foregoing compacting apparatus for use as effective cooling means without requiring extra equipment and producing unwanted secondary waste materials. A yet still further object of the present invention is to provide such an apparatus further comprising an accessory facility for cleaning the foregoing compacting apparatus without requiring extra equipment and producing unwanted secondary waste materials. According to the present invention, there is provided an apparatus for compacting a solid waste material, comprising a hollow cylindrical body having a charging inlet for charging the solid waste material therethrough into the hollow cylindrical body, a heating portion for heating the solid waste material in the hollow cylindrical body, and a discharging outlet for discharging the solid waste material from the hollow cylindrical body; a rotatable shaft disposed in the hollow cylindrical body and having a helical screw blade thereon, the screw blade and an inner wall surface of the hollow cylindrical body being spaced from each other with a clearance provided therebetween for allowing the solid waste material in the hollow cylindrical body to form a bridge therein; support means for radially movably supporting an end of the rotatable shaft; a prime mover coupled to the end of the rotatable shaft through the support means; and an outlet nozzle coupled to the discharging outlet for compressing the solid waste material discharged from the discharging outlet. The compacting apparatus can compact various solid waste materials including plastics discharged from homes, factories, nuclear power plants, and other facilities, and compacted solid waste materials can be solidified into solid masses or pelletized. The solidified masses produced by the compacting apparatus are coated with plastics, and can be buried directly if they are derived from urban trash. Harmful metals contained in dry cells and other discarded devices are confined in the solidified masses to guard against environmental pollution. Since the solid waste materials are processed in a confined spaced at a temperature below 280.degree. C., mercury contained in dry cells and the like and dioxin are not discharged from the compacting apparatus. The exhaust gas from the compacting apparatus can easily be processed as only the charging inlet is open. If radioactive solid waste materials are so small in quantity that they are negligible depending on the amount and type of the nuclide, they can be stuffed into a drum can or container which can be buried. The solid waste material as it is pelletized and stored in drum cans can finally be melted. The compacting apparatus of the invention can be carried on a truck or otherwise mobilized so that it can be moved to a desired processing location. If a chopper is disposed in or near the charging inlet such as a hopper of the hollow cylindrical body, then the conventional supply device composed of a chopper and a conveyor can be dispensed with, and the overall apparatus is compact in size. For processing radioactive solid waste materials, the compacting apparatus is useful in preventing environmental pollution. According to the present invention, the compacting apparatus may further comprise an accessory facility for controlling rotation of the rotatable shaft depending on a current flowing through the prime mover or a torque imposed on the prime mover. With this controlling method, the screw blade and the prime mover such as a motor can be prevented from being damaged or broken and can be continuously operated safely when the solid waste material is compacted. According to the present invention, the compacting apparatus may further comprise an accessory facility for producing a solid mass comprising a plurality of shaping tubes into each of which an extruded mass from the compacting apparatus can be forcibly charged; means for closing one of the shaping tubes at a time when the extruded mass is charged into said shaping tube; means for moving over the shaping tubes; and means for ejecting the extruded mass out of said one shaping tube. The method of producing a solid mass by the use of the accessory facility may comprise the steps of positioning a shaping tube with an end thereof opening toward the discharging outlet; closing an opposite end of the shaping tube with closing means; forcibly charging an extruded mass from the apparatus into the shaping tube; thereafter rotating the rotatable shaft in a reverse direction to cut off the extruded mass in the vicinity of the discharging outlet; moving over the shaping tube filled with the extruded mass to cool the same; and ejecting the shaped and cooled extruded mass out of the shaping tube. With the above producing facility and method, well shaped solid masses are successively produced at a constant rate, and can automatically be treated to thereby save labor power. For processing radioactive waste materials, the automatic treatment of the solid masses is effective in preventing workers from being exposed to radioactivity. The cost of the facility is low since it is not necessary to add a special cutter for cutting the extruded mass. According to the present invention, the compacting apparatus may further comprise an accessory facility for processing an exhaust gas discharged from the compacting apparatus, the processing method comprising the steps of filtering the exhaust gas produced by the apparatus to collect dust particles therefrom; thereafter discharging the exhaust gas through an exhaust gas line; and cooling a cooling medium for an induction heating coil for heating the heating portion, with the exhaust gas in a heat exchanger disposed on the exhaust gas line. According to this exhaust gas processing method, the exhaust gas produced when compacting the solid waste material is used for cooling the cooling medium for the induction heating coil, and hence no extra equipment such as conventional cooling tower and fan coil is not required. A fan used in the gas processing system is employed both to discharge the exhaust gas and to cool the cooling medium, and hence is an energy saver. The dust particles collected by the filter used in the gas processing system can be processed by the compacting apparatus without producing an undesired secondary waste material. According to the present invention, there is further provided a method for cleaning the compacting apparatus, the method comprising the step of charging a cleaning material into the hollow cylindrical body to force a remaining solid waste material out of the hollow cylindrical body. Since no other materials than the solid waste material and sand as the cleaning material, the remaining solid waste material can be cleared away without producing a secondary waste material and without requiring additional cleaning equipment. Therefore, the compacting apparatus is inexpensive and can easily be operated for cleaning. The cleaning process can prevent a reduction of the compacting efficiency due to melted plastics deposited in the apparatus. The above and other objects, features and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which preferred embodiments of the present invention are shown by way of illustrative example.