EP1690658B1 - Use of pellets based on clay minerals - Google Patents

Description

The invention relates to the use of pellets on a clay mineral basis, for sealing, for example, shafts, radioactive final deposits, heaps, landfills or the like, after which pre-compressed fine-grained starting material and then between at least two opposing and equipped with a respective profiling in the form of pellet forms on their surface rolls is finally pressed to the pellets that they have a grain density of more than 1.5 g / cm ³ .

The use described above is the subject of EP 0 568 430 A1 , which discloses the features of the preamble of claim 1, or DE 693 03 539 T2 , This is primarily a so-called clogging or sealing material, with the help of radioactive waste can be stored easily.

For this purpose, among other bentonite powder is compacted as a starting material in a Tangentialräderverdichter. This compressor is formed by a feed hopper, in the interior of which an Archimedean screw compacts the clay powder in question. The compacted clay powder flows between two tangential wheels whose outer surface is provided with honeycomb cells. In this way, the compacted clay powder is transferred by the pressure exerted by the wheels in lumpy clay platelets.

In addition, it is through the DE 689 12 138 T2 It is known that a mixture made paste-like by addition of water and extruded wet by using an inert material of the clay, bentonite, kaolin or mixtures thereof, and then dried to form pellets becomes. The mixture is discharged by means of rollers or a screw conveyor on a perforated plate and the product is passed through a stream of air for drying. As a result, a granular product is provided as a so-called soil correcting agent for agricultural applications in pellet form.

In addition, so-called green granules are known which are used to cover heaps, in particular salt heaps in accordance with the DE 199 37 270 C2 is used. The components of the granulate used are essentially settable ashes from incineration plants and other fillers. These fillers include clay alumina. The individual components are converted by mixing into the crumbly green granules of low cohesion at humidities of 10 to 30%.

By the DE 1 259 303 B a device for press-forming powdered material has become known. This device consists of a pair of rollers and a shaft arranged above this, which serves the task of the goods on the rollers. The roller pair is designed so that one shaft is held in conventional bearings while the other shaft is movably supported in known manner in bearings of special design. As a result, an automatic centering is to be achieved and can adjust the contact pressure between the press rollers.

As part of the JP 61133133 A It is about the processing of liquid radioactive waste, which is first dried and then processed into pellets. For this purpose, a device with a fixed roller and a spring-loaded floating roller is provided.

The state of the art can not satisfy in all respects. For one, the pellets are according to the DE 689 12 138 T2 due to their low clay mineral content hardly suitable to be able to provide covers or seals of heaps, deposits or the like. On the other hand, the handling of the green granules after the DE 199 37 270 C2 consuming or can be applied only to the dump contour. Stable and sealed floor seals can not be realized hereby. - In terms of DE 693 03 539 T2 It is noticeable that the clay tiles made with it can hardly be flexibly adapted to different requirements.

In addition, so-called sealing wall compounds are known which serve to seal landfills or below chemical factories and prevent the escape of pollutants, in particular in the groundwater. For this purpose, the respective landfills or contaminated soil areas are usually enclosed with vertical sealing walls, which extend to depths of impermeable soil layers. Self-hardening thixotropic suspensions of swellable clay materials are used as the sealing wall masses, as they are exemplified in US Pat DE 198 43 092 C2 to be discribed. In this regard, the suspension in question is generally filled into excavated vertical slot walls and solidifies therein.

Due to the initially liquid nature of the suspension, this procedure is not suitable for sealing shut-down shafts, for example. Because in such a case, the required impermeable bottom layer is missing in the shaft area, which prevents a vertical outflow of the suspension for producing the sealing wall mass into deeper layers. Here, the invention aims to provide a total remedy.

The invention is based on the technical problem of further developing such use so that the pellets produced are suitable in particular for horizontal pollutant sealing and can be manufactured flexibly in accordance with the various requirements.

To solve this technical problem, the invention is the use of pellets clay mineral base according to claim 1. In this case, the Loswalze is moved by means of the connected linear actuators or hydraulic cylinder relative to the fixed roller to the variation of the nip to adjust the grain density and the shape of the coarse grains. In this case, the grain density may in particular be more than 2.0 g / cm ³ , preferably more than 2.1 g / cm ³ .

According to the invention, pellets or coarse grains are thus produced which contain a clay mineral as the main constituent. That is, the clay mineral is present in a concentration of more than 50 wt .-%, in particular more than 70 wt .-% in each coarse grain. In addition, non-clay mineral-based fillers may additionally be added, for example gypsum and / or potassium sulfate and / or magnesium sulfate, optionally blast furnace slag, soda ash or other inert fillers which, like the main clay mineral-based component, are available as pulverulent to fine-grained product and dry can be added to the starting material.

In this case, the starting material regularly has a bulk density below 1.5 g / cm ^3, preferably less than 1.3 g / cm ^3, and most preferably has a bulk density of less than 1.0 g / cm ³ . If predominantly bentonite is used as the fine-grained starting material, bulk densities of from 0.7 to 0.8 g / cm ³ are even observed. The grain density of the finished coarse grains can be derived as usual from the specific gravity, while the bulk density of the starting material follows from the specific gravity in bulk. In addition, reference is made to DIN 18124 with regard to the determination of the grain density.

The pre-compression of the starting material may result from the fact that the starting material passes by gravity into the nip between the two counter-rotating rollers. On the foot side of a mostly funnel-shaped supply device, a corresponding pressure (similar to a liquid column) is already achieved by this arrangement and due to gravity, and the desired precompression is made available. Additionally or alternatively, the starting material can also be pre-compressed by a plug screw in the feeder. This plug screw accesses one or more screw flights, which are arranged helically around a drive shaft.

Either way, the actual pressing process or final compression takes place after the pre-pressing, namely between the two counter-rotating rollers. For this purpose, the rollers are equipped with the profiled surface. The profiling, in conjunction with the nip, predetermines the shape of the coarse grains and their density. The profiling with corresponding formations is usually selected such that the coarse grains produced are spherical or ellipsoidal and have a diameter or a major axis length of more than approximately 10 mm, preferably more than approximately 15 mm and in particular more than approximately 20 mm, exhibit. The main axis is characterized according to the general language control the longest of the three half-axes of an ellipsoid. Of course, the inventive concept also includes coarse grains, the no have strictly spherical or ellipsoidal shape, but represent hybrids.

In contrast, the powdery to fine-grained starting material is present in a grain size with grain sizes below 10 mm, in particular less than 7 mm and preferably less than 5 mm. The starting material is dry compacted between the two counter-rotating rollers or in a compacting unit following the feeding device. In principle, the addition of a binder or a binder mixture is conceivable, at which point preference is given to using a bentonite suspension in water.

After compaction, the coarse grains are regularly subjected to pressure and / or impact for quality testing. In this way, faulty coarse grains can be easily separated. Such coarse grains occur, for example, when, as a result of a roll deflection, the required pressure in the nip is no longer produced in order to achieve the necessary grain density of the coarse grains of more than 1.5 g / cm ³ , in particular more than 2.0 g / cm ³ . preferably more than 2.1 g / cm ^{3 to} represent. The pressure or impact exposure can be realized by the compacted coarse grains are passed over a shaker plate. Alternatively, the coarse grains can be pressed against each other or beaten between two sheets. Either way, the pressure and / or impact ensures that insufficiently dense coarse grains with cavities, cracks, etc. are discharged inside.

For this purpose, the finished coarse grains are sieved, so that previously crushed coarse grains, chipped edges, etc. fall through the sieve and only suitable for the subsequent processing finished coarse grains with the desired grain density remain on the screen. This assumes that the screen is equipped with a mesh size which is smaller than the diameter or the major axis length of the coarse grains, that is below 10 mm.

As a result, a novel use is provided by which source coarse grains are prepared from a low bulk density starting material having a grain density of greater than 1.5 g / cm ³ , more preferably greater than 2.0 g / cm ³ , Coarse grains that do not have this grain density are identified by simple impact and / or pressure and can be easily screened out. As a result, source-shaped coarse grains, in particular pellets, are supplied, which can be used particularly advantageously when used as a shaft seal. Also final disposal sites for radioactive waste can be sealed hereby advantageous. Similarly heaps, landfills or the like.

Fig. 1

eine erfindungsgemäße Vorrichtung zur Herstellung quellfähiger Grobkörner und

Fig. 2

schematisch einen Schacht, der mit den erfindungsgemäßen Grobkörnern bzw. Pellets versiegelt worden ist.

In the following the invention will be explained in more detail with reference to a drawing showing only one exemplary embodiment; show it:

Fig. 1

an inventive device for producing swellable coarse grains and

Fig. 2

schematically a shaft which has been sealed with the coarse grains or pellets according to the invention.

In the figures, an apparatus for producing swellable coarse grains 1b is shown. These coarse grains 1b are not limited to spherical-to-ellipsoidal clay-mineral-based pellets 1b, namely those made from predominantly bentonite. This can happen to act calcium or sodium bentonite or a mixture. In any case, the bentonite is more than 70% by weight in the coarse grains 1b, it also being possible in principle for further additives such as stone meal, cement, gypsum, aluminum sulfate, quartz sand, etc. to be present.

In any case, the starting material 1a is fine-grained or has a fine grain and has a grain size with grain sizes below 10 mm, in particular less than 7 mm and preferably less than 5 mm. The starting material 1 a is dry compacted, in the device as in Fig. 1 is shown. In principle, however, the addition of a binder or a binder mixture, such as a cement suspension, conceivable and is encompassed by the spirit. In any case, the starting material is first filled into a funnel 2, which has a stuffing screw 3, 4 on the output side. The stuffing screw 3, 4 is composed in the embodiment of a substantially vertically arranged drive shaft 3 and a connected to the drive shaft 3 helical worm wing 4 or more screw flights 4 together. With the help of the plug screw 3, 4, the filled into the hopper 2 starting material 1a is pre-compressed. A further factor contributing to this is the fact that at the outlet 5 of the funnel 3 the starting material 1a already has an increased pressure due to gravity.

In any case, the fine-grained starting material 1 a is pressed together using high pressures to a lumpy good, namely the coarse grains 1 b or pellets 1 b. The pre-compression takes place by gravity as well as by the plug screw 3, 4. For final compression of the starting material 1 a two oppositely rotating rollers 6, 7 are realized. In this case, the precompressed starting material 1a is guided into a nip 8 between the two rollers 6, 7 and pressed in the nip 8.

The two rollers 6, 7 are rotatably supported in a press frame 9 and driven. In each case lateral abutments 10, 11 are used to absorb the pressing force. The right roller 7 in the embodiment according to Fig. 1 is movably mounted and consequently formed as a Loswalze 7 and can be laterally to the variation of the nip 8 with respect to the hard roller 6 back and forth, as the double arrow in Fig. 1 suggests. For this purpose, hydraulic cylinders 12 are provided or comparable linear positioning elements 12 can be realized which ensure the lateral movement of the roller 7 and the variation of the nip 8. Both rollers 6, 7 can be adjusted via eccentric in the axial direction, but this is not mandatory.

The linear actuators or hydraulic cylinders 12 and a related pressure generating device 13 are acted upon by a control device 14, which monitors and controls the entire process. In detail, the necessary hydraulic pressure in the pressure generating unit 13 is provided by means of a gear pump, wherein additionally a nitrogen-filled memory is provided to provide shock loads in the nip 8, the necessary flexibility of the rollers 6, 7 against each other.

Automatic regulation in the control device 14 influences the addition of the starting material 1a into the hopper 2 or its flow rate. In this way, changes in the properties of the starting material 1a can be taken into account in order to be able to keep the product quality of the coarse grains 1 b produced constant. In the simplest case, the speed of the plug screw 3, 4 is controlled by the control device 14 accordingly. The current consumption of a roller drive, not expressly shown, for the rollers 6, 7 serves as a setpoint.

If, for example, an increased power consumption of the roller drive indicates that the fine-grained starting material 1a reaches the nip 8 in a large amount and thus can hardly be processed into the coarse grains 1, then the control device 14 reduces the speed of the screw conveyor 3, 4 accordingly and vice versa , Overall, the hopper 2 forms with the plug screw 3, 4 and the outlet a feeding device 2, 3, 4, 5 for the fine-grained starting material 1a, while the rollers 7, 8 one of the feeding device 2, 3, 4, 5 following compacting unit 7, 8th represent, which compresses the starting material 1 a to the coarse grains 1 b.

In order to effect this compaction or final compaction in detail, the rollers 6, 7 have on their surface a profiling in the form of pellet molds 15, 16. With the aid of the control device 14 and the roller drive, the two rollers 6, 7 are controlled, that in the nip 8 in the compression each two pellet molds 15, 16 are opposite and so the starting material to the ellipsoidal coarse grains 1 b (dry) is compressed.

The rollers 6, 7 may be made in one piece or be constructed of interconnected in the axial direction of roller rings. In any case, the nip 8 is adjusted by means of the linear adjusting device 12 so that the coarse grains 1b thus produced have a particle density of more than 1.5 g / cm ^3, in particular more than 2.0 g / cm ^3, and preferably more than 2 , 1 g / cm ³ . In this case, the respective grain density can be checked with known methods for density determination, for example by determining the weight of the respective coarse grain 1b by means of an (electronic) balance and at the same time its displacement in a liquid. Here can also be combined on the weighing method with the so-called hydrostatic The respective coarse grain 1b is first weighed in air and then, for example, in water or another liquid (cf., in addition, the remarks in the book " Mineralogy "by Günter Strübel, Ferdinand Enke Verlag 1995, page 157 ff ).

In order to be able to discharge coarse grains 1b which do not have the desired grain density, the compacting unit 6, 7 is followed by a pressure / impact device 17, 18. In the exemplary embodiment, this is an optional conveyor belt 17, which transfers the finished coarse grains 1b to a vibrating plate 18, which performs movements in the direction indicated by a double arrow. As a result, the coarse grains 1b on the vibrating plate 18 are subjected to a combined pressure and impact action, which leads directly to the fact that insufficiently compressed coarse grains 1b with crumbs or voids inside, for example, crumble or disintegrate. At the same time protruding edges of the coarse grains 1 b are ground down.

Subsequent to the pressure / impact device 17, 18, the coarse grains 1 b are then still sieved, resorting to a conventional screening device 19, which is merely indicated. The sieve device 19 has one or more sieves whose mesh size is adapted to the size of the coarse grains 1 b so that they can be discharged without difficulty. In fact, one will work here with mesh sizes of about 10 to 15 mm.

Not shown is the possibility to realize lateral Ausschleusbleche or discharge devices in the axial direction of the rollers 6, 7. These can take into account the fact that any bending of the rollers 6, 7 as a result of the generated pressing force and, consequently, too low a grain density of the pressed coarse grains 1 b in such a case is directly encountered by these coarse grains 1b are discharged. As a rule, however, attempts are made to apply and adjust the rolls 6, 7 and consequently the nip 8 in the axial direction in such a way that matching pressure conditions in the axial direction are present when the coarse grains 1b are pressed. For this purpose may optionally also the crowning of the rollers 6, 7 are changed by means of the control device 14, which is not shown.

In the Fig. 2 Finally, one recognizes a preferred field of application of the coarse grains 1b produced. This is to seal a shaft 20 after its decommissioning. For this purpose, a horizontal layer of the coarse grains 1 b is introduced into the shaft 20 approximately at a height in which water-impermeable layers 21 are found, so that the groundwater level adjusts to comparable values after the shaft closure, as is the case without shaft 20. Overall, a water-conducting layer 22 located above the water-impermeable layers 21 results in the swellable coarse grains 1 changing their size as desired and providing the watertight horizontal termination of the shaft 20.

In fact, on a clay-mineral basis, the coarse grains 1 b are known to be able to carry out a so-called intracrystalline swelling, which is associated with a corresponding material expansion. As a result, the initially loose bulk composite of the individual coarse grains 1 b in the shaft 20 after swelling forms a continuous, water-impermeable layer which directly adjoins the natural, water-impermeable layers 21.

Claims (5)

1. Use of mineral clay-based pellets (1) to seal for example shafts, radioactive disposal sites, dumps, landfills or the like, according to which

   - fine-grained starter material (1) undergoes preliminary compaction and is then finally compacted between two counter-rotating rollers (6, 7), the surface of each of which is furnished with a corresponding profile in the form of pellet shapes (15, 16), to produce the pellets (1b) in such manner that said pellets have a grain density greater than 1.5 g/cm³, according to which both rollers (6, 7) are retained and driven freely rotatably in a press frame (9),
   characterised in that

   - one roller (6) is designed as a fixed roller (6), and the other roller (7) is designed as a movable roller (7) that is adjustable relative to fixed roller (6),

   - the two rollers (6, 7) are retained rotatably and driven in a press frame (9), wherein

   - lateral thrust bearings (10, 11) are provided on either side to absorb the pressing force, wherein further

   - the movable roller (7) is moved relative to the fixed roller (6) by means of connected hydraulic cylinders (12) in order to vary a roller gap (8), thereby adjusting the grain density of and shape of the pellets (1b), and wherein

   - the hydraulic cylinders (12) and an associated pressure generating device (13) are subjected to load by a control device (14), which monitors and controls the entire process.
2. Use according to claim 1, characterised in that the starting material (1a) has a bulk density lower than 1.5 g/m³, particularly lower than 1.3 g/m³, preferably lower than 1.0 g/m³.
3. Use according to either of claims 1 or 2, characterised in that the pellets (1b) are spherical to elliptical in shape and have a diameter or major axis length of more than 10 mm, particularly more than 20 mm.
4. Use according to any one of claims 1 to 3, characterised in that the pellets (1b) are subjected to pressure and/or impact loading after compacting in order to test the quality thereof.
5. Use according to any one of claims 1 to 4, characterised in that the completed pellets (1b) are sifted.

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