Patent Number: 047724307
Section: description

This invention will be better understood by the following Examples with reference to the Figures. Referring now to FIG. 1, solid waste materials, for example, low-level radioactive miscellaneous solid waste materials, discharged from nuclear power plants or the like, are introduced through a hopper, a shredder or crusher where the waste materials are crushed, a pulverizer for pulverization if necessary, and a dispenser for dealing out the pulverized waste materials in fixed portions, into an extrusion molder where the pulverized waste materials are compacted and solidified thereby to produce rod-like, stand-like or like masses which are then cut into pellets if necessary and packed in containers such as drum cans for storage. In a case where supplementary thermoplastic resins are externally supplied, they are supplied through the dispenser to the extrusion molder where these resins are kneaded with the waste materials and then molded into said compacted and solidified masses. In the compaction and solidification step, it is possible to soften or melt the thermoplastic resins with friction heat by suitable selection of a ratio of compression of the waste materials in the extrusion molder. Thus, it is either unnecessary to externally heat the die and its neighboring portions except at the initial stage of operation of the extrusion molder, or only necessary to externally supply supplementary heat to said portions, thus being also preferable from the viewpoint of energy economy. The solidification in the extrusion molder is effected at approximately 120.degree.-260.degree. C. (about 100.degree.-190.degree. C. in cases where used ion exchange resins are solidified without evolution of SO.sub.x gases). The solid waste materials so solidified look as if they were buried in the thermoplastic resins, and they are extremely compact and stable when immersed in water. The solidified waste materials are remarkably reduced in volume as compared with the original. Since the amount of thermoplastic resins contained in solid waste materials is usually enough for the solidification, a synergistic volume reduction effect can be achieved. EXAMPLE 1 There were provided simulated solid waste materials having the composition indicated in the following Table 1 in which all numerical values are by weight. TABLE 1 ______________________________________ Composition of waste material Simulated waste material Example 1 ______________________________________ Cellulose Rag (cotton cloth) 22.1 Polyethylene Polyethylene sheet 39.7 Polyvinyl chloride Polyvinyl chloride sheet 2.1 Rubber Rubber gloves 1.1 Total amount of 65.0 combustibles Metal Aluminum sheet 9.0 (0.5 mm thick) Glass Asbestos Heat insulation material 5.0 (Pearlite) Concrete Concrete 6.0 Total amount of 20.0 incombustibles Moisture (Water) 15.0 Grand total 100.0 ______________________________________ The simulated waste materials (the water being previously absorbed in the rag) were crushed into pieces having a size of not larger than 4 mm square or cube by a cutter mill and then introduced into an extrusion molder as indicated in FIG. 2. In this Figure, symbol A indicates a hopper, symbol B a dispenser, numeral 3 a compression screw and numeral 5 a die. The forward portion (near the die 5) of the compression screw 3 is like a cutter in shape and functions as a mixer for sufficient mixing of the cut and pulverized waste materials. The simulated waste materials were passed through the hopper A and dispenser B to the compression screw 3 rotating at 150 r.p.m. where they were kneaded under compression to generate heat by friction with the barrel of the extrusion molder whereupon the thermoplastic resins in the waste materials were softened or melted, and the waste materials were pushed toward the open end of the compression screw 3, subjected to shearing force of said cutter-like portion and then passed through the die 4 to continuously produce 20 of rod-like or strand-like masses each having a 12-mm diameter which were intentionally broken off in a bundle when the length of the masses withdrawn from the die reached a suitable one. These broken masses were allowed to cool without being fusion-bonded to each other, thus obtaining satisfactory compacted and solidified masses. EXAMPLES 2-5 The simulated waste materials having the composition indicated in Table 2 were crushed into pieces having a size of not larger than 4 cm square or cube, passed through a 150 mm .phi. biaxial paddle screw-type dispenser C rotating at 16 r.p.m. as shown in FIG. 3 to an extrusion molder as indicated in FIG. 3 thereby to obtain the same secure and uniform solidified masses as obtained in Example 1. In this case, the heater temperature at the die (130 mm .phi..times.35 mm) portion having 62 holes or passages (each 8 mm .phi.) was set at 170.degree. C., however, such heating was not necessary except at the initial stage of operation of the extrusion molder. TABLE 2 ______________________________________ Simulated waste Example Example Example Example materials 2 3 4 5 ______________________________________ Polyethylene 37.7 9.4 30.8 43.4 Rag 20.8 49.1 16.9 23.9 Polyvinyl chloride 1.9 1.9 1.5 2.2 Rubber 0.9 0.9 0.8 1.1 Wood chips 5.7 5.7 4.6 6.5 Aluminum foil 8.5 8.5 6.9 9.9 Pearlite 4.7 4.7 3.9 5.4 Concrete 5.7 5.7 4.6 6.5 Copper wire 0.9 0.9 0.8 1.1 Moisture 13.2 13.2 29.2 0.0 Total 100.0 100.0 100.0 100.0 ______________________________________ As is mentioned above, it is possible according to this invention to compact and solidify solid waste materials for reduction of the volume thereof; this volume reduction effect is much improved as compared with the effect obtained by conventional baling treatment. This invention may conveniently apply to the compaction and solidification treatment of radioactive solid waste materials which are otherwise particularly difficult to treat so. The compaction and solidification according to this invention is conveniently effected by a specific extrusion molder. Miscellaneous solid waste materials containing thermoplastic resins such as PE and PVC are cut and crushed and then introduced into an extrusion molder where the waste materials are compression passed through die holes (or molding holes) while generating friction heat between the waste materials and the inner wall of the die holes, thereby to obtain rod-like moldings simultaneously with melting the thermoplastic plastics contained in the peripheral portions of the thus obtained rod-like moldings, thus forming a plastics impregnated layer in the peripheral portions. The extrusion molder used herein comprises a molder body case and extrusion screw which form a compression room together, a cutter for further crushing and agitating the waste materials compressed by said extrusion screw, and a die for molding the waste materials, which are compression inserted by said screw, into rod-like masses, the die having die holes which are large in diameter and long with an opening ratio enough to melt the thermoplastic resins contained in the peripheral portion of the rod-like moldings by the friction heat generated between the inner wall of the die holes and the waste materials. EXAMPLES 6-12 AND REFERENCE EXAMPLE In Examples 6-12, used ion exchange resins which had been drained (the moisture content of the drained resins: 42 wt.%) were mixed with simulated waste materials or polyvinyl chloride in varied mixing ratios to form mixtures which were then subjected to compaction and solidification treatment as indicated in Table 3. As is seen from Examples 6-12, the volume of the original waste materials was about 50 l on one hand, that of the post-treatment waste materials was 10 l on the other hand, the latter volume being about one-fifth (1/5) of the former. The treatment in Examples 6-12 was effected as follows. The waste materials indicated in Table 3 were crushed into pieces having a size of not more than 4 mm square or cube and then introduced through the hopper A and the dispenser B into the extrusion molder 1 as indicated in FIG. 2, in which molder the waste materials were passed under compression to the cutter-like forward end of the compression screw 3 rotating at 150 r.p.m. in order to crush TABLE 3 __________________________________________________________________________ Amounts of Waste Materials To Be Treated*.sup.4 Amounts of*.sup.4 Simulated*.sup.1 Polyvinyl*.sup.2 Used Ion*.sup.3 Post-Treatment Waste Materials Chloride Exchange Resins Total Waste Materials __________________________________________________________________________ Reference Example -- 50 (5.0) -- 50 (5.0) 8.3 (5.0) Example 1 -- 45 (4.5) 0.6 (0.5) 45.6 (5.0) 8.2 (4.9) Example 2 -- 40 (4.0) 1.2 (1.0) 41.2 (5.0) 7.8 (4.7) Example 3 -- 35 (3.5) 1.8 (1.5) 36.8 (5.0) 7.4 (4.5) Example 4 50 (5.0) -- 0.7 (0.56) 50.7 (5.56) 8.8 (5.3) Example 5 50 (5.0) -- 1.5 (1.25) 51.5 (6.25) 9.6 (5.7) Example 6 50 (5.0) -- 2.6 (2.14) 52.6 (7.14) 10.5 (6.3) Example 7 50 (5.0) -- 6.1 (5.0) 56.1 (10.0) 13.3 (8.0) __________________________________________________________________________ Note: *.sup.1 Polyethylene 49 wt. %, Polyvinyl chloride 18 wt. %, rubber 8 wt. %, rags 6 wt. % and 19 wt. % *.sup.2 Herculite 80 equivalent *.sup.3 Moisture content 42 wt. % *.sup.4 Numerals are by volume (l) and parenthesized numerals by weight (Kg). them and thoroughly mix the crushed waste materials together and then passed through the die 5 to produce 20 of 12-mm diameter, rod-like or strand-like and solidified masses peripherally covered with a layer solidified with the thermoplastic resins. The solidified masses so produced were cut into pieces having a suitable length and then allowed to cool, thus obtaining satisfactory solidified pieces without fusion bonding to each other as those obtained in Reference Example. The solidified pieces thus obtained had a moisture content of 2 wt.% or less. Further, the surface of the solidified pieces was more satisfactory with the increase in resin mixing ratio. They were immersed in water at room temperature for 3 months with the result that, after the immersion, they exhibited no change in shape and weight, this proving that they had satisfactory water resistance. As is seen from the foregoing, the cost of disposal of solid waste materials according to this invention is in the range of from a half to less than one-tenth (from 1/2 to less than 1/10) of the conventional cost required for the use of HIC, decomposition and after treatment, and direct solidification. This invention enables the used ion exchange resins to be easily compacted for volume reduction at such a low cost. The reason for this is that according to this invention, the costs of initial installations, operations, decomposing agents, solidifying agents and the like are low. This invention may suitably apply to compacting and solidifying treatment of used radioactive or harmful heavy metals-containing ion exchange resins which will particularly be attended by economical difficulties when treated. The compacted and solidified masses produced according to this invention have satisfactory properties and substantially prevent the radioactive or harmful substances from exuding therefrom. EXAMPLE 13 The extrusion molder used herein will be explained hereunder in more detail by reference to FIGS. 4 to 7. With respect to FIG. 4, an extrusion molder 1 mainly comprises a molder body case 2, an extrusion screw 3, a cutter 4 and a die 5. The molder body case 2 has several projections 2a, whose cross-section is as shown in FIG. 5, extending longitudinally in the inner surface thereof. In the extrusion screw 3, the pitch of the screw gradually decreases from the right (waste material inlet side) to the left (waste material outlet side), and the screw axis 3a gradually increases in diameter towards the left (waste material outlet side). Thus, the volume of a compression chamber defined by the molder body case 2 and the extrusion screw 3 gradually decreases towards the left thereby enabling the waste material to be compressed. Further, the compression chamber 2b may also be decreased in volume towards the left side by a gradual decrease of the mold body case 2 in inner diameter towards the left in place of a gradual increase of the screw axis 3a in diameter towards the left. The cutter 4 is provided at the left tip, which is near the die 5, of the screw axis 3a and protrudes from around the left tip. The die 5 is fitted to the tip of the molder body case 2 by a clamping bolt 6, and the central part thereof constitutes a bearing for the screw axis 3a. As is apparent from FIG. 6(A), the die 5 has many holes or passages 5a for molding the waste materials. The ratio of total area of the holes to the whole area of the die 5 (the ratio being called herein "opening ratio") may preferably be increased as the content of thermoplastic resins such as PE and PVC increases. The suitable opening ratio is in the range of 10-20%. As indicated in FIG. 6(B), the molding holes 5a may be a combination of holes which are different in size (diameter). In this case, approximately uniform compression and friction forces will be obtained by using the die provides with small-diameter molding holes having a correspondingly small length and with large-diameter molding holes having a correspondingly large length. The molding holes or passages 5a may also be tapered such that they are large in diameter at their inlet and small in diameter at their outlet. In FIG. 4, numeral 7 indicates a thrust roller bearing and numeral 8 a coupling with the drive shaft of a motor. The method for extrusion molding solid waste materials using the above-mentioned extrusion molder, will be explained hereunder. At the initial stage of operation, the extrusion molder 1 is suitably heated to a die temperature of about 100.degree.-130.degree. C. by an external heating means (not shown) which is out of operation during the usual operation of the molder 1. Miscellaneous solid waste materials to be treated are cut and crushed and then mixed together by a mixing means as required before introduced into an extrusion molder. Such mixing is unnecessary in a case where the waste materials are composed wholly or almost wholly of thermoplastic resins. The waste materials supplied to the extrusion molder 1 are sent towards the die 5 while they are compressed by the extrusion screw 3. At this time, the waste materials generate heat due to their compression in the compression chamber 2b, their friction with the extrusion screw 3, shearing forces between the protrusions 2a and the extrusion screw 3, and the like, whereby PE and PVC contained in the waste materials start to be softened or melted. The waste materials sent to the forward end of the extrusion screw 3, are cut and agitated by the cutter 4 to be further finely divided and then sent under compression into the molding holes 5a of the die 5 while they are elevated in temperature. In the molding holes 5a, the waste materials so compressed cause friction with the inner wall of the holes 5a whereupon the portion of the waste materials which is near the inner wall, is further elevated in temperature. Thus, the PE and PVC contained in the peripheral portion of the waste materials which are being molded into rod-like masses, are further melted by said friction heat thereby securely solidifying the rod-like masses. The rod-like masses 10 in the peripheral portion of which the PE and PVC are melted to form a plastics-solidified layer 9 as shown in FIG. 7, are either forcibly cooled at the outlet of the die 5 by a cooler or the like or allowed to cool with the open air whereby the PE and PVC melted in the peripheral portion of the masses are shrunk and hardened to securely coat the masses 10, thus obtaining stable high-density rod-like masses 10 which are then pelletized if necessary. In a case where the die 5 is provided with molding holes 5a which are different in diameter, it is possible to obtain differently sized pellets at the same time and in a fixed mixed ratio. As is seen from the foregoing, the effects or advantages obtained by the specific extrusion molding are as follows. (1) The thermoplastic resins contained in the peripheral portion of the rod-like molded masses are surely melted by the friction heat generated between the masses and the inner wall of the molding holes of the die whereupon the rod-like masses are reinforced at their peripheral portion with the plastics-solidified layer as if they were covered with a crust, thus obtaining stable high-density moldings. (2) Secure plastics-solidified layers can be formed by selecting the size of diameter of molding holes of the die, the opening ratio of the die, the length of holes (passages), and the like depending on the composition of waste materials. (3) High-quality molded masses or moldings can be produced by very simple and inexpensive apparatuses such as extrusion screws and dies. EXAMPLE 14 An overall system for disposal of solid waste materials according to this invention will be illustrated as follows. Referring now to FIG. 8, numeral 11 indicates an easily openable and closable lid which is so fitted that it covers a feed opening 12a provided at the lower end of a lift device 12. The lift device 12 houses therein a lift 13 which is movable up and down. At the upper end of the lift device 12 is formed a preliminary feed chamber 14 in which a pusher 15 is laterally movable. At the left-hand outlet side of the preliminary feed chamber 14 is continuously provided a feed hopper 16 in which a first gate 17 and a second gate 18 are fitted. The gates 17 and 18 perform opening and enclosing operations alternately in sequence between the solid line and dotted line. As indicated in FIG. 9, a shredder 19 mainly comprises a casing 20, a rotary blade 21, a fixed blade 22 and a screen 23. The rotary blade 21 is fixed to a shaft 24 connected to a motor and can rotate in the direction of arrow symbol; further, as shown in FIG. 10, it is laterally divided and its blade tip 21a constitutes a so-called helical cutter which is slantwise arranged so that it retrogrades to the left and right. The fixed blade 22 is fitted to a casing 20 extending around the rotary blade 21 and cuts solid waste materials in cooperation with the blade tip 21a of the rotary blade 21. The screen 23 extends around the lower half of rotation orbit of the rotary blade 21 and the ends thereof are fitted respectively to the fixed blades 22 and 22 (FIG. 9). In FIG. 8, a screw feeder 25 composed of two parallel screw axes is provided below, or downstream of, the shredder 19. The feed outlet of the screw feeder is connected to the feed inlet of lower end of a swing turn lift 26 composed of many buckets pin-supported by a chain. A stock tank 27 is provided below the feed outlet located at the upper end of the swing turn lift 26 and stores the waste materials temporarily. A paddle mixer 28 is provided below, or downstream of, the stock tank 27. As is shown in FIGS. 11 and 12, in the paddle mixer 28, two screw axes 30 fitted with many vanes 29 are arranged in parallel with each other and can be rotated respectively in the directions indicated by arrow symbols. In this case, the vanes 29 are fitted to the screw axes 30 in such a manner that they are slant with respect to the axial line of the screw axis 30 and the vanes 29 fitted to one screw axis 30 overlap with those 29 fitted to the other 30 (FIG. 11). Now turning back to FIG. 8, an extrusion molder 1 is provided below, or downstream of, the paddle mixer 28. The extrusion molder used in this overall system for disposal of solid waste materials is the same as shown in FIG. 4. The structure, function and the like of the extrusion molder 1 have previously been mentioned in detail with reference to FIG. 4. With further reference to FIG. 8, downstream of the molder 1 are arranged a cooler 40 and then a cutter 41 having cutting blades 42. Downstream of the cutter 41 is arranged a conveyor 43. The conveyor 43 may be of a horizontal type as shown or may be of a vertical type such as a vertical screw conveyor or bucket elevator. Numeral 44 indicates a discharge gate downstream of which is arranged a drum 46 mounted on a vibropacker 45. The vibropacker 45 is intended to give vibrations to the drum 46. The air located around the feed hopper 16, cutter 41 and discharge gate 44 are suctioned by a fan 48 and filtered by a filter 47 thereby to be purified for discharge to the open air. The above-mentioned various apparatuses and units are operated and controlled by a control panel 50 provided in a control room 49. These apparatuses and units are arranged in an enclosed space which is isolated from the outside and are movable in a body in the precinct of buildings such as nuclear power plants. The overall system for disposal according to this invention is of such an enclosed type as mentioned above and will therefore prevent the dusts and the like from scattering to the outside of the system. Further, since the system is movable in a body, it can be used at desired sites or places. With particular reference to FIGS. 8 and 4, the disposal operation using the above-mentioned overall system will be illustrated as follows. Such miscellaneous solid waste materials as previously mentioned are packed in a suitable amount in a thermoplastic resin bag P. In this case, too long electric cords, stone, concrete masses and metallic articles such as bolts and nuts, are removed from the waste materials if they are contained therein for efficient use of the disposal system. The waste materials to be fed are controlled in their kinds, sizes, mixing ratios and the like and, further, the waste materials are adjusted so that they contain about 10-20 wt.% of thermoplastic resins by external supply thereof if necessary. The waste materials so controlled can stably be compacted and solidified. The resin bag P so packed is fed at the opening 12a onto the lift 13 and, thereafter, the lid 11 is closed. The lift 13 is then elevated to send the bag P into the preliminary feed chamber 14 wherein the bag P is pushed as far as the second gate 18 located at the solid line by the pusher 15. Upon the bag P reaching the second gate 18, the pusher 15 returns to its original position and then the first gate 17 is pivotally moved from the solid line position to the dotted line position thereby to intercept the preliminary feed chamber 14 from the feed hopper 16. When the first gate 17 is closed, the second gate 18 is pivotally moved to the dotted line whereupon it opens to drop and feed the resin bag P to the shredder 19. When the bag P is so withdrawn, the second gate 18 returns to its original solid line position and then the first gate 17 opens at the solid line position for subsequent feeding. The operations of the gates 17 and 18 in sequence are automatically performed under control of limit switches and the like and, the lift 13, in turn, descends accordingly. The resin bag P fed into the shredder 19 is cut and crushed into suitably sized pieces between the rotary blade 21 and fixed blade 22, and the pieces are passed through the screen 23 to the screw feeder 25. The rotary blade 21 is a helical cutter and it can therefore handle a wide range of waste materials ranging from soft materials such as paper and cloths to hard materials such as metals and concrete. The waste materials so cut and crushed are sent in the lateral direction to the feed opening located at the lower end of the swing turn lift 26 and then they are conveyed upward by the lift 26 for temporary storage in the stock tank 27. The waste materials temporarily stored in the stock tank 17 are suitably dosed or dispensed to the paddle mixer 28 where the cut and crushed waste materials are mixed together particularly to mix the PE and PVC with the rest of the waste materials while they are sent under agitation towards the outlet by the vanes 29 for feeding into the extrusion molder 1. If the waste materials are composed wholly or mostly of thermoplastic resins such as PE and PVC, the mixing operation of the paddle mixer 28 may be omitted. The extrusion molder 1 is heated to about 100.degree.-130.degree. C. by a suitable external heating means (not shown) at the initial stage of operation of the molder. The heating is suspended during usual operation except the operation at said initial stage. The waste materials fed to the molder 1 are passed under compression to the die 5 by the extrusion screw 3. At this time, the waste materials generate heat due to said compression force, friction with the extrusion screw 3 and shearing force produced between the protrusions 2a and extrusion screw 3, and the like, whereby the PE and PVC in the waste material start to be softened or melted. The waste materials containing the softened or melted thermoplastic resins, which have been sent to the forward end of the extrusion screw 3, are further cut and crushed by agitating action by the cutter 4 and then sent under compression to the molding holes 5a of the die 5 while being elevated in temperature. By the agitation, mixing, crushing, heat generation and melting effected in said manner by the cutter 4, high-density molded masses are obtained from the waste materials. In the molding holes or passages 5a, the waste materials under compression cause friction with the inner wall of the holes 5a to produce friction heat whereby the portion of the waste materials near said wall is further elevated in temperature, and the PE and PVC contained particularly in the peripheral portion of the waste materials being molded into rod-like masses by the molding holes 5a surely melt function as a coking or bonding agent for the waste materials being molded. The selection of opening ratio of the molding holes 5a will enable high-density molded masses to be obtained and this invention to be applied to the disposal of a wide variety of waste materials. The rod-like molded masses so obtained, particularly those covered at their peripheral portion with the melted PE, PVC, etc., are soon cooled by the cooler 40 provided at the outlet of the die 5 thereby to shrink and harden said resins, thus obtaining stable high-density rod-like moldings which are then sent into the cutter 41. The water vapor together with the rod-like molded masses, withdrawn from the molder 1 was subjected to dew condensation and collected as water in a container. The rod-like molded masses are passed to the cutter 41 where they are cut into pellets having a length of, for example, about 15-25 mm by the cutting blade 42 and then withdrawn onto the conveyor 43. The pellets so withdrawn onto the conveyor 43 are packed under control of the discharge gate 44 into drums 46 and then subjected to longitudinal vibration by the vibropacker 45 for compaction to achieve high density. On this occasion, not only the ratio of gap between the pellets will decrease but also the efficiency of packing will increase in a case where differently sized pellets are mixed in suitable ratios and packed as compared with a case in which identically sized pellets are packed. For this purpose, as indicated in FIG. 6(B), it is necessary that the die 5 be provided with molding holes 5a having different diameters. There can thus be obtained differently sized pellets in a desired mixing ratio. In the above Example the solidified molded masses withdrawn from the extrusion molder are soon forcibly cooled, however, such forcible cooling is not always necessary but such molded masses may be allowed to cool at ambient temperature according to this invention.