WO2006005653A1

WO2006005653A1 - Process and apparatus for granulating a melt

Info

Publication number: WO2006005653A1
Application number: PCT/EP2005/052568
Authority: WO
Inventors: Patrick Leyser; Christian Cortina
Original assignee: Paul Wurth S.A.
Priority date: 2004-07-14
Filing date: 2005-06-03
Publication date: 2006-01-19
Also published as: TW200602121A; TWI339593B; CN1985009B; LU91088B1; CN1985009A

Abstract

In a process for granulating a melt, the melt is quenched by means of water, a mixture of granules and water being produced. In a dewatering apparatus, this mixture is dewatered, a solids-loaded wastewater being recovered and fed to a collection tank. In the collection tank, an inclined plate settler is disposed and is constantly immersed herein in the water. The solids-loaded wastewater is fed to the collection tank in such a manner that at least a portion of this solids-loaded wastewater flows through the inclined plate settler in the collection tank from bottom to top and at the top outlet of the inclined plate settler a substantially solids-free water stream flows off from the collection tank.

Description

PROCESS AND APPARATUS FOR GRANULATING A MELT

TECHNICAL FIELD

The present invention relates generally to a process and an apparatus for granulating a melt, in particular slag melt.

PRIOR ART

In granulation plants for blast-furnace slag, the molten slag flowing from the slag channel of a blast furnace is granulated by means of spray heads and nozzle systems and with the use of water. In this case what is termed slag sand is formed, a product predominantly of small granules solidified in the vitreous state. To produce a slag sand suitable for cement production, the chief field of application of slag sand, the heat of the molten slag must be removed by shock- like cooling. For this, depending on the amount of slag, relatively large amounts of process water are required. To dewater the slag sand and recover the water in the process circuit, the mixture of water and granules resulting from the spraying is fed to a dewatering plant. The wastewater removed from such dewatering plants still has a certain content of solids. This solids content can sediment in the plant components or lead to abrasive wear of the plant components in the further use of the wastewater. For this reason, it is known, for example, to use, downstream of the dewatering plant, a settling tank, from which, after settling of the solids, relatively pure process water is recovered. Such settling tanks, however, require considerable structural volume and need a relatively complex regular removal of the sedimented solids.

Alternatively, DE 102 16 415 proposed using a hydrocyclone for at least partially clarifying the wastewater from the dewatering plant. Although this process permits solids to be separated from the water and, in particular, to accelerate a static dewatering process having dewatering silos, it requires operation of the hydrocyclones which is complex in engineering terms and also additional energy consumption for operating the feed pump for the hydrocyclone. In addition, such a hydrocyclone appears to be particularly susceptible to blockages due to slag sand deposits.

A further problem is due to the latent hydraulic properties of the finely granulated slag sand present in the wastewater to be clarified. Wet slag sand actually has the property, on removal of water, to harden to form concrete-like deposits. In the clarification of the wastewater from the dewatering plant, hardening of slag sand deposits must therefore absolutely be avoided.

OBJECT OF THE INVENTION

An object of the present invention is to propose a process for granulating a slag, in particular slag melt, which makes it possible, by simple means, to recover a substantially solids-free water stream and which is of low susceptibility to blockages due to hardening slag sand deposits. This object is achieved according to the invention by a process for granulating a melt according to Claim 1. Likewise, an apparatus for carrying out the process is proposed.

GENERAL DESCRIPTION OF THE INVENTION

In an inventive process, the melt is quenched in a known manner by means of water, a mixture of granules and water being produced. In a dewatering apparatus, this mixture is dewatered, a solids-loaded wastewater being recovered and fed to a collection tank. According to the present invention, in the collection tank an inclined plate settler is disposed and continuously immersed in water herein. Solids-loaded wastewater is fed to the collection tank in such a manner that at least a fraction of this solids-loaded wastewater flows from bottom to top through the inclined plate settler in the collection tank and, at the top outlet of the inclined plate settler, a substantially solids-free water stream flows off from the collection tank. This process makes it possible, by very simple means, to recover a substantially solids-free water stream and is in this case of little susceptibility to blockages due to hardening slag sand deposits. It has in fact been found that an inclined plate settler which is also termed lamellae plate settler or inclined plate separator is of low susceptibility to blockages due to hardening slag sand deposits, provided that it never dries out. In the inventive process, this is ensured by the fact that the inclined plate settler is disposed in the collection tank and is continuously immersed in water herein. Even in the event of interruptions of the process and relatively long idle times of the granulation plant, the inclined plate settler remains immersed in the water, so that the slag sand cannot harden. Owing to the arrangement of the inclined plate settler in the collection tank, in addition, no additional space is required for a secondary clarification plant. A further advantage is that an inclined plate settler is simple and reliable to operate, has no moving elements and requires no special repairs and virtually no expenditure on maintenance. In the collection tank, it is, in addition, very easy and inexpensive to exchange as required. A further advantage of the inventive process is that the secondary clarification in the inclined plate settler is a purely static process for which no additional energy is required.

The collection tank advantageously has a fϋFnnel-shaped outlet, a sediment sludge being taken off from this funnel-shaped outlet and being fed back again to the dewatering apparatus. This produces a constant solids concentration in the corresponding return circuit and the efficiency of the process may in fact further be improved.

The inclined plate settler is advantageously suspended in the collection tank on a support frame and can slide on this support frame. As a result, the inclined plate settler is particularly simply installed and removed in the collection tank.

In a preferred embodiment, the inclined plate settler consists of a plurality of modules which are individually suspended in the collection tank on a support frame and are brought into an operating position by sliding on this support frame. As a result the inclined plate settler is simply installed and removed even in the event of a restricted structural volume.

The dewatering apparatus advantageously comprises a rotatable dewatering drum which is provided on the inside with shovels. The inventive process can be operated continuously by means of such a dewatering drum. The dewatering drum is advantageously disposed directly over a first region of the collection tank, the inclined plate settler being disposed in an adjacent second region of the collection tank which is separated off laterally from the first region. With this design, the dewatering drum is combined with the collection tank and the inclined plate settler to form a particularly compact unit.

The dewatering apparatus, however, can likewise comprise one or more dewatering silos or else one dewatering screw, the wastewater of which is fed into the collection tank.

An apparatus for carrying out the inventive process comprises in a known manner an injection apparatus for injecting a water stream into the melt, a mixture of granules and water being produced, a dewatering apparatus for dewatering this mixture, a^''solids-loaded wastewater being recovered, and a collection tank to which the solids-loaded wastewater is fed. According to the invention, in the collection tank an inclined plate settler is disposed in such a manner that this is constantly immersed in the water, and that at least a portion of the solids-loaded wastewater which is fed to the collection tank flows through the inclined plate settler in the collection tank from bottom to top and can be taken off from the collection tank as substantially solids-free water stream at the top outlet of the inclined plate settler.

BRIEF DESCRIPTION OF THE FIGURES

Further details and advantages of the invention can be taken from the following extensive description of possible embodiments of the invention on the basis of the accompanying figures. In the figures: Fig. 1 shows a diagrammatic representation of a plant for granulating slag melts;

Fig. 2 shows a diagrammatic representation of a first installation step of an inclined plate settler into a collection tank;

Fig. 3 shows a diagrammatic representation of a second step for the installation of the inclined plate settler into the collection tank;

Fig. 4 shows a diagrammatic representation of a third step for the installation of the inclined plate settler into the collection tank;

Fig. 5 shows a diagrammatic representation of the inclined plate settler installed according to Figs. 2-4 in the operating state.

DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

In Fig. 1 , a granulation plant is designated generally with the reference 10. The granulation plant 10 has a granulation tower 11 of a type known per se. In the granulation tower 11 , to granulate blast-furnace slag, water is injected into a slag melt 14 which is discharging from a tapping channel 12. This shock-type quenching granulates the slag melt 14 to form slag sand. This granulation is performed in a known manner on the basis of a spray head 16 whiGh injects a bundle 18 of multiple water jets into the melt stream 14. The resultant mixture of water and slag granules is collected in a granulation tank 20 which is disposed in the lower region of the granulation tower 11. From the granulation tank 20 the mixture is then passed into a dewatering unit 24 via a distributor channel 22. The dewatering unit 24 is preferably an INBA® dewatering drum from Paul Wurth S.A., as is described, for example, in US 4 204855 or US 4289 519.

As shown in Fig. 1 , the slag sand 28 obtained from the dewatering unit 24 is transported off by means of a conveyor belt 26 to a suitable storage site 29. The solids-loaded water separated off in the dewatering unit 24, in contrast, descends as wastewater from the dewatering drum 24 into a collection tank 30 which is provided for this purpose and is also termed warm water tank. Owing to process conditions, despite the filtration function of the dewatering unit 24 which is formed by a slag sand layer (not shown in more detail) in the lower region of the dewatering drum, it cannot be avoided that this removed wastewater still has a relatively high proportion of solid fine particles, in particular slag sand residues.

The collection tank 30 is constructed in a funnel shape in its lower region and preferably has there an outlet connection 32. Via the outlet connection 32, the sediment sludge collecting in the lower region of the collection tank 30 is removed. This sediment sludge is transported back by means of pumps, preferably via abrasion-resistant pipelines 34, into the distributor channel 22, upstream of the dewatering unit 24. By this means the sediment sludge is again fed to the abovementioned filtration function. In the recirculation circuit according to reference 36, an equilibrium of the fine particle concentration is thus established.

From Fig. 1 it can further be seen that an inclined plate settler 40 is disposed directly within the collection tank 30. Such an inclined plate settler or lamellae separator 40 is a separation apparatus for separating the individual phases of ^different density of a disperse system. The inclined plate⁷ settler essentially consists of a bundle of parallel inclined lamellae or tubes through which the wastewater to be clarified flows generally upwards. As a result of gravity, the solid particles sediment and slide down the lamellae or tube bottoms downward out of the inclined plate settler 40.

The inclined plate settler 40 is mounted in the upper region of the collection tank 30, preferably on a straight outer wall. The inclined plate settler 40 has the function of substantially freeing from solids the solids-loaded water collected in the collection tank 30 for recovery to the water process circuit. Clarifying the solids-loaded wastewater from the dewatering plant 24 decreases, in particular, the abrasion, the sand depositions and hardening within all plant components which are fed with clarified water from the inclined plate settler 40. In this case, the illustrated arrangement of the inclined plate settler 40 within the collection tank 30 enables the plant sections over which solids-loaded wastewater is passed to be reduced to a minimum, in the ideal case to the section between dewatering unit 24 and collection tank 30. Furthermore, the length of the recirculation circuit 36 is likewise minimized as a result. The use of the inclined plate settler 40 further permits an efficient process water treatment with a minimum of monitoring, maintenance and processing expenditure. In addition, the inclined plate settler 40 may be integrated into a pre-existing collection tank 30, without additional requirement of structural volume. The inclined plate settler 40 is preferably used for clarifying the entire wastewater stream from the dewatering unit 24 which remains after removal of the sediment sludge. Alternatively, for example with a relatively small volume of the collection tank 30, a smaller design of an inclined plate settler can be used in a partial flow clarification process.

The inclined plate settler 40 has a top outlet 42 via which a clarified, substantially solids-free, water fraction is removed from the collection tank 30. The top outlet 42 is situated at a lower level, compared with the remaining water level in the collection tank 30, and is sealed laterally against this level by corresponding partition walls 44. This ensures that solids-loaded water flows into the inclined plate settler 40, and in the top outlet 42, only purified water is present which cannot return from there to the collection tank 30. The inflow according to arrow 46 takes place in this case spontaneously, in the case of a suitable filling level of the collection tank 30, owing to the difference in level. This produces a stream of solids-loaded wastewater which flows spontaneously through the inclined plate settler 40 from bottom to top and is there progressively freed from solids by sedimentation. Thus no further measure for operating the inclined plate settler 40 is necessary. The solids and fine particles which settle out in the inclined plate settler 40 fall back into the lower region of the collection tank 30 according to arrow 48 solely by the action of gravity. As described above, the solids in the sediment sludge are recirculated to the dewatering unit 24 according to arrow 36 and are there at least partially filtered out. Separate removal and disposal of the separated solids are thus unnecessary. It should be noted here that the removal rate via outlet connection 32 and piping 34 is always less than the feed rate from the dewatering unit 24. Advantageously, this removal rate is chosen in such a manner that the inclined plate settler 40 is always optimally loaded.

To cool the water which is heated by the melt waste heat, this water is transported, for example by pumps, to the cooling towers and water storage 52, 52', from a storage vessel 50 connected to the top outlet 42. The water fraction purified by the inclined plate settler 40 is thus directly suitable for further use as process water, in particular in the spray head 16. It remains to be pointed out that the simply maintained constant filling level of the collection tank 30 ensures in a simple manner that the inclined plate settler 40 always remains immersed in water. This ensures, in particular, that no hardening can occur due to drying out of slag sand deposits in the inclined plate settler 40. The described integration into circuits according to arrow 36 and arrow 54 additionally ensures, without further measures, automatic circulation of the tank contents with constant water level of the collection tank 30.

Fig. 2 shows a first step for introduction into a collection tank 30' of an inclined plate settler 40' which is designed in two parts. A first module 401 of the inclined plate settler 40' is let down, for example, by means of a crane, into the collection tank 30' lying against the side. The first module 401 comprises a top¬ side frame 411 , for example made of steel, to which the lamellae or tubes of the inclined plate settler are attached as a package. On the frame 411 are mounted rollers 421, by means of which the module 401 is suspended in the collection tank 30' so as to be able to slide on a corresponding support frame 300 which is equipped with rails. Advantageously, the moveable elements, or else the entire support frame 411, are disposed above the water level of the collection tank 30'.

From Fig. 3, it can be seen how the first module 401 of the inclined plate settler 40' can be pushed laterally into the tank 30' via the rollers 421 and the rails of the support frame 300. In the stop, when the first module 401 is situated approximately in the centre of the tank 30', it can be detained there by suitable means.

Fig. 4 shows a third step for the installation of a second module 402 of the inclined plate settler 40' that corresponds to the first module 401. This second module 402 is introduced, in a similar manner to the step in Fig. 2, flush against the first module 401. The second module 402 is likewise mounted via a support frame 412 on rollers 422 on which it is suspended into the tank 30'. Finally, top¬ side outlet channels 431 , 432 of the two modules 401 , 402 are connected to form one or more outlet channels 440.

Fig. 5 shows the inclined plate settler 40' in the state ready for operations. In Fig. 5, there can be seen a first region 301, over which the dewatering unit (which is not shown) is disposed for feeding the wastewater into the collection tank 30'. The inclined plate settler 40' which is composed of the modules 401 and 402 is situated within a second region 302 which is separated off from the first region 301 by partition walls 44' which are disposed laterally at the start. The described construction and the described installation process according to Figs. 2-5 permit the inclined plate settler 40^s" to be mounted in the collection tank 30', even in the event of restricted space conditions. Furthermore, rapid installation or removal are made possible, should, for example, maintenance work be necessary. The modules 401 and 402 are removed in this case in a manner corresponding to the installation.

It remains to be noted that the described process and the described apparatus can also comprise, as dewatering apparatus, a dewatering screw, a shovel wheel or other dynamic dewatering apparatuses, and also static dewatering apparatuses, for example a filtration bed or dewatering silo.

Claims

1. Process for granulating a melt comprising:

quenching the melt by means of water, a mixture of granules and water being produced;

dewatering this mixture in a dewatering apparatus, a solids-loaded wastewater being recovered and being fed to a collection tank; and

secondary clarification of the solids-loaded wastewater from the collection tank, a substantially solids-free water stream being recovered;

characterized in that an inclined plate settler is disposed in the collection tank and is constantly immersed herein in the water, and the solids-loaded wastewater is fed to the collection tank in such a manner that at least a portion of this solids-loaded wastewater flows through the inclined plate settler in the collection tank from bottom to top and flows off from the collection tank at the top outlet of the inclined plate settler as substantially solids-free water stream.

2. Process according to Claim 1 , characterized in that the collection tank has a funnel-shaped outlet, a sediment sludge being taken off from this funnel- shaped outlet and fed again to the dewatering apparatus.

3. Process according to one of Claims 1 to 2, characterized in that the inclined plate settler in the collection tank is suspended on a support frame and can slide on this support frame.

4. Process according to one of Claims 1 to 3, characterized in that the inclined plate settler consists of a plurality of modules which are individually suspended in the collection tank on a support frame and are brought into an operating position by sliding on this support frame.

5. Process according to one of Claims 1 to 4, characterized in that the dewatering apparatus comprises a rotatable dewatering drum which is provided on the inside with shovels.

6. Process according to Claim 5, characterized in that the dewatering drum is disposed directly over a first region of the collection tank, and the inclined plate settler is disposed in an adjacent second region of the collection tank, which region is separated off laterally from the first region.

7. Process according to one of Claims 1 to 4, characterized in that the dewatering apparatus comprises at least one dewatering silo.

8. Process according to one of Claims 1 to 4, characterized in that the dewatering apparatus comprises a dewatering screw.

9. Process according to one of Claims 1 to 8, characterized in that the melt is a blast-furnace slag melt.

10. Apparatus for granulating a melt comprising: an injection apparatus for injecting a water stream into the melt, a mixture of granules and water being produced; a dewatering apparatus for dewatering this mixture, a solids-loaded wastewater being recovered; and a collection tank to which the solids-loaded wastewater is fed; characterized in that an inclined plate settler is disposed in the collection tank in such a manner that this inclined plate settler is constantly immersed in the water, and in that at least a portion of the solids-loaded wastewater which is fed to the collection tank flows through the inclined plate settler in the collection tank from bottom to top and can be taken off from the collection tank at the top outlet of the inclined plate settler as substantially solids-free water stream.

11. Apparatus according to Claim 10, characterized in that the collection tank has a funnel-shaped outlet, the apparatus comprising circulation means which take off a sediment sludge from the funnel-shaped outlet and feed it again to the dewatering apparatus.

12. Apparatus according to Claim 10 or 11 , characterized in that the inclined plate settler in the collection tank is suspended on a support frame and can slide on this support frame.

13. Apparatus according to Claim 10 or 11 , characterized in that the inclined plate settler consists of a plurality of modules which are individually suspended in the collection tank on a support frame and, by sliding on this support frame, can be brought into an operating position.

14. Apparatus according to one of Claims 10 to 13, characterized in that the dewatering apparatus comprises a rotatable dewatering drum which is provided on the inside with shovels.

15. Apparatus according to Claim 14, characterized in that the dewatering drum is disposed directly over a first region of the collection tank, and the inclined plate settler is disposed in an adjacent second region of the collection tank which is separated off laterally from the first region.

16. Apparatus according to one of Claims 10 to 13, characterized in that the dewatering apparatus comprises at least one dewatering silo.

17. Apparatus according to one of Claims 10 to 13, characterized in that the dewatering apparatus comprises a dewatering screw.