Abstract:
A granulation plant for aqueous granulation of a product includes a granulation tank fitted for the injection of granulation water in order to granulate the product. The granulation plant further includes a sedimentation tank, separate from the granulation tank, in which the granulated product settles in the form of granules, as well as a distributor to transfer the water/granule mixture from the granulation tank into the sedimentation tank.

Description:
FIELD OF THE INVENTION 
     This invention relates to an aqueous granulation plant. 
     BACKGROUND OF THE INVENTION 
     In aqueous granulation, the product for granulation (for example, molten slag, a molten alloy, copper matte) is placed in a powerful flow of water. This flow of water granulates, solidifies and cools the product. The granules are then removed from the granulation water. 
     Such aqueous granulation plants comprise a granulation tank fitted for injection of granulation water and also a device for removing the granules from the granulation water. A conventional granule removal device comprises a sedimentation tank, separate from the granulation tank, in which the granules settle. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is the design of a simple granulation plant which facilitates granule removal. According to the invention this aim is attained by an aqueous granulation plant according to the present invention. 
     The aqueous granulation plant according to the invention comprises, in a recognised manner, a granulation tank fitted for injection of granulation water in order to granulate the molten product, a sedimentation tank separate from the granulation tank, in which the granulated product settles in granule form and a distributor to transfer the water/granule mixture from the granulation tank into the sedimentation tank. According to an important aspect of this invention, the sedimentation tank comprises a number of concentration tanks. It will be seen that when the water is fed into the sedimentation tank by the distributor, it is distributed among the various concentration tanks in which the granules settle according to their specific weight. Concentration of the granules in the concentration tanks according to their specific weight makes removal easier. Its modular design also enables the configuration of the sedimentation tank to be optimised for the product to be granulated. 
     In a preferred embodiment the sedimentation tank comprises a supporting structure and concentration tanks suspended from the supporting structure. 
     The concentration tanks are advantageously in the shape of a hopper with a horizontal top edge, allowing them to be suspended from the supporting structure. These edges are the only contact area between the supporting structure and the concentration tanks. 
     Two adjoining concentration tanks are advantageously arranged so that their top edges are adjacent. The water can then flow from one tank to the other over these adjacent top edges. 
     The sedimentation tank advantageously has a peripheral wall that rises above the top edges of the concentration tanks. This peripheral wall, however, comprises one or more overflow openings to allow the clarified granulation water to flow out of the sedimentation tank. 
     Partitions rising above the top edges can be erected between two concentration tanks. By means of such partitions, different paths can be defined for the water/granule mixture in the sedimentation tank. For example, a longer path can be arranged to favour settlement of fines. 
     The hopper-shaped concentration tanks advantageously discharge into a delivery pipe fitted with a sealing device. This enables either the material flow to be halted or the concentration tank to be emptied. 
     A water removal device may be fitted upstream of the sealing device. This water removal device comprises for example a filter sleeve separating a central duct from an annular water collecting chamber. The granulation water can thus be filtered by the filter sleeve and escape via the water collecting chamber, while the granules pass through the central duct after the sealing device opens. 
     In a first embodiment, the concentration tanks nearest to the distributor are connected to a draining drum. The granules that gather in these concentration tanks are discharged to the draining drum for separation of the granules from the granulation water. 
     The concentration tanks farthest from the distributor can then be connected to a hydrocyclone in order to extract the fines from the granulation water. 
     In a second embodiment, at least one conveyor is positioned underneath the concentration tanks to collect the said granules that gather in the said concentration tanks when the sealing devices are open, at least one said conveyor being for example fitted with a perforated belt to allow the granulation water to drain away. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     Further special features and characteristics of the invention will become clear from the detailed description of some advantageous embodiments which follows, by way of illustration, with reference to the drawings attached. These show: 
     FIG.  1 : synoptic illustration of an aqueous granulation plant with a draining drum and hydrocyclone; 
     FIG.  2 : sectional view of a concentration tank; 
     FIG.  3 : view of a supporting structure; 
     FIG.  4 : sectional view of a beam supporting two concentration tanks; 
     FIG. 5 sectional view of a beam sideways on; 
     FIG.  6 : synoptic illustration of an aqueous granulation plant with conveyor; 
     FIGS. 7,  8 ,  9  and  10 : views of different sedimentation tanks. 
     In the drawings the same reference numbers denote identical or similar components. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 shows a plant for aqueous granulation of slag. This principally comprises a granulation tank  10  and a sedimentation tank  12  which is separate from the granulation tank  10 . 
     The granulation tank  10  is an oblong-shaped tank having a front wall  14 , a back wall  16  and two side walls  18  and  20 . The bottom of the granulation tank  10  is stepped with sloping steps, the lowest step being in contact with the back wall  16 . Slag is poured into the granulation tank  10  through a hot channel  22  located beside the front wall  14 . The granulation tank  10  is fitted with means of injecting granulation water (not shown). The granulation water is injected at a rate of approximately 10 m/s. The quantity of water required is around 15 to 25 kg per kg of slag poured. In the granulation tank  10  the molten slag is carried along by the granulation water and is then granulated and solidified. The more turbulent the flow of water in the granulation tank  10 , the less the risk of explosion due to release of hydrogen and superheated steam. 
     A pipe  24  carries the water/granule mixture from the granulation tank  10  to a distributor  26  which is arranged at one end  28  of the sedimentation tank  12 . In the configuration shown in FIG. 1, this sedimentation tank  12  comprises two rows of four concentration tanks  30 . These concentration tanks  30  are identical in dimensions and take the form of square-section hoppers. They discharge into a delivery pipe  32  fitted with a sealing device  33 . A peripheral wall  34  rises above the top edges of the concentration tanks  30  to hold the liquid inside the sedimentation tank  12 . Two overflow outlets  36  are provided in the shorter side farthest from the granulation tank  10 . 
     Let us assume a water/granule mixture comprising granules of different sizes and densities, therefore distinguished by different weights. On clarifying such a mixture, the heaviest granules have the fastest settling rate and the lightest granules (fines, for example) have a very slow settling rate, remaining in suspension in the granulation water for a long time. 
     The water/granule mixture is fed in via the distributor  26  and the granules therefore have a horizontal rate due to the flow current in the sedimentation tank  12  as well as a vertical settling rate. The composition of these two rates causes the granules to be distributed in the concentration tanks  30 . The granules with the fastest settling rate, in other words the heaviest, settle in the concentration tanks  30  nearest to the distributor  26 . The lightest granules, on the other hand, settle in the concentration tanks  30  farthest from the distributor  26 . The fines settle in the last of the concentration tanks. The clarified granulation water flows through the overflow holes  36  and is sent to a collecting tank  38 . The content of the concentration tanks  30  in fact depends on the distance between them and the distributor  26 . Likewise, the concentration tanks  30  that are the same distance from the distributor  26  will contain granules of similar particle size. 
     At this point it is interesting to take a closer look at the characteristics of a concentration tank  30 . FIG. 2 shows a sectional view of a concentration tank in the form of a square-section hopper through which the material flows into a delivery pipe  32 . It will be seen that the concentration tank has horizontal top edges  40  allowing it to rest on a supporting structure (see FIG.  3 ). The delivery pipe  32  is fitted with a sealing device  33  which halts the passage of material in the delivery pipe  32 . Upstream of this sealing device  33  the delivery pipe  32  is fitted with a water extraction device  42 , equipped with a filter sleeve  44  and an annular water collecting chamber  46 . The granulation water is filtered through the filter sleeve  44 , which holds back the granules, before being discharged via the water collecting chamber  46 . The granules can then flow through the delivery pipe  32  when the sealing device  33  is open. It will also be noted that a water injection device  48  is also included. This is a pipe discharging in two places in one of the walls of the concentration tank  30 . It sometimes happens that granules which have gathered do not flow through the delivery pipe  32  when the sealing device  33  is open. A movement has to be initiated in the heap of granules to set the flow in motion. This is the purpose of the water injection device  48 , which gets the heap of granules moving by injecting water into the concentration tank  30  in the direction of the arrow  50  to enable the concentration tank  30  to be emptied. 
     FIG. 3 shows a preferred embodiment of a supporting structure. The rows are delimited by three horizontal beams  52 ,  54  and  56 , the same distance apart, supported by pillars  58 . The concentration tanks  30 ′ and  30 ″ (similar to the concentration tank  30  in FIG. 3) can slide within a row defined by 2 beams ( 52 ,  54 ;  54 ,  56 ). This is an advantage of such a supporting structure, which readily allows the size of the sedimentation tank  12  to be altered. The presence of the peripheral wall  34  may also be noted. 
     FIG. 4 shows a preferred method of fastening the two concentration tanks  30 ′ and  30 ″ in FIG.  3 . The top flange of the beam  54  is covered by a thick rubber cushion  60 . The top edges  40  of the two concentration tanks  30 ′ and  30 ″ rest on the cushion  60 . Care has been taken to allow a space between the adjacent top edges  40 , which is filled with rubber. Holes  62 ,  64  serve to fasten the top edges  40  of the concentration tanks  30 ′ and  30 ″ firmly to the flange of the beam  54  by means of screws and bolts (not shown). 
     FIG. 5 shows a preferred method of fastening a concentration tank  30  to the exterior beam  52 . One top edge  40  of a concentration tank  30  rests virtually on the whole surface of the top flange of the beam  52 . A rubber cushion  66  is inserted between the web of the beam  52  and the top edge  40 . Two holes  68 ,  70  are made to enable the concentration tank  30  to be fastened to the beam  52 . The peripheral wall  34  is welded perpendicular to the top flange of the beam  52 . Care has been taken to allow a space between the peripheral wall  34  and the top edge  40 . This space is filled with rubber. 
     In FIG. 1, the delivery pipes  32  are not fitted with water extraction devices  42 , but only with sealing devices  33 . Downstream of these sealing devices  33 , the first four concentration tanks  30 , in other words those arranged nearest to the distributor  26 , are connected to a draining drum  72 . The granulation water recovered from the draining drum  72  is sent to the collecting tank  38 ; the drained granules are sent to a pile  74 . The last four concentration tanks  30  are connected to a hydrocyclone  76 , to separate the finest granules from the granulation water. The water is sent to the collecting tank  38  and the granules are sent to the pile  74 . 
     Another possibility for draining the concentration tanks is illustrated in FIG. 6. A filtering belt conveyor  80 ,  82  has been arranged underneath each row of concentration tanks  30 . A water extraction device  42  with a filter sleeve  44  and water collecting chamber  46  is installed upstream of each sealing device  33 , according to FIG.  2 . The granulation water in the concentration tanks  30  is removed by the water extraction device  42 . The sealing device  33  is then opened to allow the granules to drop on to the conveyor  80 ,  82 . The granules removed are sent directly to the pile  74 . It will be noted that the granulation water flowing through the overflow holes  36  or filtered through the filter sleeves  44  is collected in the collecting tank  38 . 
     FIGS. 7,  8  and  9  show three embodiments of sedimentation tanks  12  which can readily be implemented in a supporting structure that has 3 beams, as shown in FIG.  3 . 
     FIG. 7 shows a sedimentation tank  12  similar to that in FIGS. 1 and 6. The peripheral wall  34  has two overflow holes  36 . The water/granule mixture is fed in via a distributor  26  across the whole width of the sedimentation tank  12  at one end, and the overflow holes  36  are located at the opposite end. The length of the path followed by the mixture in the sedimentation tank  12  is the same as the length of the tank. 
     In FIG. 8, the distributor  26  and the overflow hole  36  are diagonally opposite each other. Partitions  84  have been arranged to define a zigzag path through the sedimentation tank  12 . The length of the path followed by the mixture is twice the length of the sedimentation tank  12 . 
     In FIG. 9, the distributor  26  and the overflow hole  36  are in the upper part of the sedimentation tank  12 . The partitions  84  are arranged so as to define a U-shaped path through the sedimentation tank  12 . The distance covered by the mixture is likewise twice the length of the sedimentation tank  12 . 
     It can thus be seen that by means of the partitions  84  the distance travelled by the mixture in the sedimentation tank  12  can be increased, so facilitating the settling of small granules. 
     Obviously, the number of concentration tanks  30 , the number of rows and the number of partitions  84  can be altered to obtain various configurations. It will thus be understood that the modular design of the sedimentation tank  12  enables the path travelled by the water/granule mixture to be optimised according to the type of granules. The granules settle in the concentration tanks  30  according to their specific weight and are thus directly sorted during sedimentation, thereby saving on a subsequent sorting stage. Moreover, the use of identical concentration tanks  30 , which can be slotted anywhere into the supporting structure, allows the configuration of the sedimentation tank  12  to be changed easily and quickly. It is also to be noted that the latter can contain concentration tanks of different shapes. However, in order to preserve the modular properties of the sedimentation tank, it is preferable to use removable concentration tanks of standardised shape, which slot into an appropriate supporting structure. The concentration tanks will therefore preferably have simple exterior shapes (square or rectangular), allowing them to be fitted into the supporting structure. 
     It is even possible to operate with a sedimentation tank divided into two autonomous sedimentation units. This is the configuration shown in FIG.  10 . The tank comprises two rows of two concentration tanks  30  separated by a central partition  84 . There is a peripheral wall  34  and each row has an overflow hole  36 . By using a distributor  26  with a slewable duct, the water/granule mixture can be fed selectively into either row. 
     It will be noted that it is preferable to empty the concentration tanks  30  in sequence. This procedure has the advantage of enabling any concentration tanks  30  that are blocked to be located. The concentration tanks  30  nearest to the distributor  26  will generally have to be emptied most often.