WO2011067400A1

WO2011067400A1 - Installation and method for processing molten material produced by a metallurgical plant, in particular for processing blast furnace slag

Info

Publication number: WO2011067400A1
Application number: PCT/EP2010/068898
Authority: WO
Inventors: Thomas Sgarbi; Marc Schweitzer; Bob Greiveldinger
Original assignee: Paul Wurth SA
Current assignee: Paul Wurth SA
Priority date: 2009-12-03
Filing date: 2010-12-03
Publication date: 2011-06-09
Anticipated expiration: 2012-06-03
Also published as: CN202626211U; LU91626B1

Abstract

An installation (100) for processing a metallurgical melt, in particular blast furnace slag, comprises at least one granulation unit (110; 120), which produces slurry of granulates and water, and a main dynamic dewatehng unit (130) connected downstream the granulation unit. The main dewatering unit (130) comprises a mobile component, in particular a rotary dewatering drum (132), for separating slurry into granulatesand water. According to the invention, the installation includes: - a slurry overflow (150) arranged upstream of or at the inlet of the main dewatering unit (130) and upstream of the water outlet (142), from which water is recovered from the main dewatering unit (130), this overflow being configured for draining slurry in excess of the unit's dewatering capacity; - a secondary dewatering unit (160) having an inlet (162) connected for receiving excess slurry from the overflow, a first outlet (164) for returning a secondary dewatered fraction to the main dewatering unit and a second outlet (166) for recovering water. The installation is configured to drain excess slurry so as to preclude excess slurry from reaching the water outlet (142) and to separate drained excess slurry into a secondary dewatered fraction returned to the main dewatering unit (130) and into a secondary water fraction recovered without passing through the main dynamic dewatering unit (130). A corresponding method of processing molten material, in particular for granulating blast furnace slag, is also proposed.

Description

INSTALLATION AND METHOD FOR PROCESSING MOLTEN MATERIAL PRODUCED BY A METALLURGICAL PLANT, IN PARTICULAR FOR

PROCESSING BLAST FURNACE SLAG

Technical field

[0001] The present invention generally relates to the field of processing molten material in metallurgical plants, and more specifically to granulation of molten slag such as blast furnace slag.

Background Art

[0002] In various metallurgical production processes, a flow of molten material has to be granulated in order to facilitate further use of this material, which is usually a byproduct such as blast furnace slag, or an intermediate product such as copper matte.

[0003] For the specific case of granulating blast furnace slag, various different types of installations are currently known. A now widely accepted practice, which constitutes a considerable improvement over traditional slag pit discharge, is granulation of the slag by water quenching. The resulting slurry i.e. mixture of granulated slag and water, which is an inevitable result of water quenching, must typically be dewatered before the granulated slag can be utilized further, e.g. in cement production.

[0004] A currently widespread system designed for granulation and dewatering, especially of blast furnace slag, is offered by PAUL WURTH S.A. under the commercial name ΝΒΑ®". Examples of this design are known e.g. from US patent no. 4,204,855, from international patent applications WO 96/1 1286 and WO 2006/005653, or from European patent no. EP 0 573 769. These systems typically comprise a granulation unit for granulating a stream of slag received from the skimmer by quenching the stream with water jets. The granulation unit usually comprises a runner tip from which the molten stream is poured into high-pressure water jets produced by one or more spray heads (usually called "blowing box"). The resulting slurry drops into a basin from where slurry is taken for dewatering. The granulation unit normally also comprises a condensation tower above the basin for condensation of produced water vapor. The slurry of granulated material and water produced by the granulation unit is fed to the inlet of a dynamic dewatering unit via a supply conduit, e.g. via a runner or a pipe conduit. As a key component of the ΊΝΒΑ®" system, the dewatering unit includes a rotary dewatering drum having a drum shell designed to have a sieving filter function and internal buckets for lifting the granulated slag upwards from where it drops onto a belt conveyor. By virtue of this design, the dewatering drum is configured to separate slurry into a granulated material fraction (phase) to be fed by the belt conveyor to a slurry outlet and into a water fraction (phase), discharged at the bottom of the sieving drum, to be fed to a water outlet for recovery as process water.

[0005] A design, in which the dewatering drum is arranged inside the granulation unit, i.e. in which granulation and dewatering are performed in a single unitary structure, is known from US patent no. 4,909,821 . Alternative dynamic dewatering units, which instead of a rotary drum suggest other kinds of mobile dewatering components are known e.g. from international patent applications WO 2006/108517, WO 2005/031008 or from Japanese patent application JP 01 079044, which suggest using a dewatering screw conveyor, or from German patent application DE 4 214 948, which proposes a dewatering scoop wheel with external dewatering scoops. A dewatering bucket elevator, as a further alternative, is known from US patent no. 3,615,329. Yet another type of dynamic dewatering unit is known from US patent no. 3,645,708 and from US patent no. 4,230,477, which both propose using a specially configured kind of endless conveyor belt as mobile dewatering component. A further different type of dynamic dewatering unit is known from US patent no. 3,912,487, which discloses a rotary horizontal dewatering disc configured to separate water from the granulated slag.

[0006] Other non-dynamic dewatering units are also known, i.e. systems that do not employ a mobile component for separation. German patent application DE 102 16 415 for instance suggests using a series of static dewatering bins complemented by a hydrocyclone to accelerate dewatering. Static systems, e.g. with dewatering bins or with settling basins usually require large-size equipment that takes up a much larger part of the plant ground floor and, more importantly, require more frequent and intense maintenance. Consequently, static systems are not frequently adopted in view of their higher investment and running cost.

[0007] As will be understood, despite their widely accepted advantages and advanced state of development, dynamic dewatering units still leave room for further improvement. A particular limitation of such dynamic dewatering units is their inherent processing capacity, i.e. the maximum incoming volume flow rate of slurry at which reliable separation is still warranted. The dewatering capacity is usually determined by the maximum operating speed (e.g. rotational speed of the drum / wheel / conveyor) and the dimensions of the mobile component, both setting an upper limit to capacity of reliable treatment. [0008] An attempt at enhancing an installation of the ΊΝΒΑ®" type in such a way that its dewatering capacity is increased without increasing the dimensions of the dewatering drum, or alternatively, for achieving a given capacity with a smaller dewatering drum, is proposed in Luxembourg patent no 86 943. The proposed solution essentially consists in providing an intermediate large-size buffer tank having considerable cubic capacity in between the granulation unit and the dynamic dewatering unit for accommodating an excess inflow of slurry. Drawbacks of this approach are however that it cannot readily be adopted to increase the capacity of an existing dewatering unit without considerable modifications to the existing plant and that it has comparatively high cost, in terms of additional ground floor space and of installation and especially maintenance cost.

[0009] Another approach, which is not primarily addressed to increasing dewatering capacity but may also serve this purpose is known from US patent no. 6'610'243. As one embodiment, this patent proposes an installation for processing molten material with a granulation unit for aqueous quenching of blast furnace slag, with a dewatering drum as a first dynamic dewatering unit and with a hydrocyclone as a second dynamic dewatering unit. US 6'610'243 suggests installing a distributor/separator downstream of the granulation tank and upstream of the dewatering units. This distributor has various hopper shaped concentration tanks, in which granules settle according to their specific weight. This distributor/separator is designed for separately feeding a slurry with coarser granules to the dewatering drum and separately feeding slurry with finer particles to the hydrocyclone. When used as a retrofit, this approach might allow increasing capacity. However, reliable operation of the specifically designed distributor/separator is difficult achieve among others because the slurry production is far from being constant. It may show peak values of more than four times the average rate during a cycle. Moreover, a suitable separator according to US 6'610'243 also requires considerable floor space.

Technical problem

[0010] It is a first object of the present invention to provide a method and installation for processing molten material produced by a metallurgical plant, in particular for granulating blast furnace slag, that allow operation at slurry input flow rates that exceed the dewatering capacity of the dynamic dewatering unit without requiring major changes to the existing dynamic dewatering unit and without requiring installation of a large-size high capacity buffer tank. General Description of the Invention

[001 1] The invention relates to an installation for processing molten material that is produced by a metallurgical plant, in particular for processing blast furnace slag. The installation comprises one or more granulation units for granulating a stream of molten material by quenching the stream with water, in particular with comparatively cold high- pressure water jets to produce a slurry of granulated material and water. It further has a main dynamic dewatering unit with a slurry inlet connected to the granulation unit(s) via a supply conduit, e.g. via an open runner or closed pipeline, for receiving slurry produced by the granulation unit(s). This unit has a material outlet from which granulated material can be recovered and a water outlet from which process water can be recovered, in particular for recycling the process water to the granulation unit(s). The main dynamic dewatering unit comprises a mobile component, preferably but not necessarily a rotary dewatering drum (e.g. as in an INBA® installation), that allows separating received slurry into a granulated material fraction that is fed, directly or indirectly, to the slurry outlet and into a water fraction that is fed, directly or indirectly, to the water outlet.

[0012] In order to achieve the above-mentioned first object, the installation comprises: a slurry overflow configured for draining excess slurry in excess of the dewatering capacity of the main dynamic dewatering unit before slurry cannot enter "clean water" portions of the installation. Depending on the type of main dynamic dewatering unit, the slurry overflow is arranged either upstream the slurry inlet, e.g. in the supply conduit or, alternatively, at (e.g. underneath) the slurry inlet, i.e. adjacent the slurry inlet.

A secondary dewatering unit that is also configured for separating slurry into a secondary dewatered fraction and a secondary water fraction. The secondary dewatering unit has an inlet connected for receiving excess slurry drained via the slurry overflow, a first outlet connected for feeding the secondary dewatered fraction back to the main dynamic dewatering unit, in particular onto or into its mobile component, and a second outlet connected to allow independent recovery of the secondary water fraction.

[0013] As will be appreciated, the installation is configured to drain excess slurry upstream of the water outlet of the main dynamic dewatering unit and to separate drained excess slurry into a secondary dewatered fraction that returns to the main dynamic dewatering unit and into a secondary water fraction that is recovered without passing through the main dynamic dewatering unit. [0014] Accordingly, the proposed arrangement - especially of the overflow and connections to secondary dewatering - precludes slurry from "contaminating" the "clean water" portions of the installation. This is an incontestable benefit of the proposed configuration, when compared to the theoretical possibility of operating an existing installation with an excess of slurry over a certain time. The installation thereby enables continuous processing a flow of slurry that exceeds the dewatering capacity of the main dynamic dewatering unit.

[0015] Noting that slurry typically has a major water fraction and a minor solids fraction, a comparatively small-sized auxiliary (secondary) dewatering unit of comparatively lower dewatering capacity, in combination with the proposed overflow arrangement enables considerable increases of the combined dewatering capacity. By virtue of the proposed installation, only the minor secondary dewatered fraction is returned to the main dynamic dewatering unit whereas the major water fraction is directly available for further use without passing through the main dewatering unit. As will also be appreciated, the prior necessity for either large buffering capacities, e.g. according to Luxembourg patent no 86 943, or for replacement by a more expensive larger capacity main dewatering unit is overcome. To increase throughput and minimize footprint, the secondary dewatering unit is also preferably of the dynamic type, i.e. - as opposed to gravity-induced static dewatering tanks or settling basins - a device that dewaters by virtue of either motion of a driven dewatering component (e.g. a dewatering drum) or by motion of the slurry itself (e.g. in a hydrocyclone). As will be appreciated, the proposed installation, especially the proposed slurry overflow and secondary dewatering unit enable for cost-efficient upgrades (retrofitting) of existing installations that increase the overall dewatering capacity without major and costly constructional changes of the existing main components. On the other hand, the invention enables new installations to reliably process higher slurry input flow rates exceeding the nominal capacity of the main dewatering unit as such, i.e. the use of main dewatering units having reduced capacity compared to the prior art.

[0016] Further preferred features of an installation according to the invention are defined in the enclosed dependent claims 2-15. As will be understood, the installation is particularly suitable as retrofit or new equipment of a blast furnace plant.

[0017] The invention also relates to a method for processing molten material produced by a metallurgical plant, in particular for processing blast furnace slag.

[0018] The proposed method comprises: granulating a stream of molten material by quenching the stream to produce a slurry of granulated material and water;

feeding the produced slurry to a main dynamic dewatering unit that comprises a mobile component, in particular a rotary dewatering drum,

separating received slurry by the main dynamic dewatering unit into a granulated material fraction to be recovered at a slurry outlet and into a water fraction to be recovered at a water outlet.

[0019] In order to achieve the aforementioned first object, the method comprises:

feeding a flow of slurry that exceeds the dewatering capacity of the main dynamic dewatering unit via a supply conduit towards the main dynamic dewatering unit; draining excess slurry in excess of the dewatering capacity, upstream of the water outlet, via a slurry overflow arranged upstream of or, alternatively, adjacent the slurry inlet;

feeding drained excess slurry from the slurry overflow to a secondary dewatering unit;

separating drained excess slurry by the secondary dewatering unit into a secondary dewatered fraction and a secondary water fraction,

returning the secondary dewatered fraction to the main dynamic dewatering unit and recovering the secondary water fraction without passing the secondary water fraction through the main dynamic dewatering unit.

[0020] As will be appreciated, the proposed installation and method are particularly suitable for industrial application in the field of wet granulation of molten products and byproducts in metallurgical industry both ferrous, e.g. pig iron slag, and non-ferrous, e.g. copper matte.

Brief Description of the Drawings

[0021] Further details and advantages of the present invention will be apparent from the following detailed and not limiting description of several embodiments with reference to the attached drawings, wherein:

FIG.1 is a schematic layout and flow diagram of a first embodiment illustrating a main dynamic dewatering unit of the dewatering-drum type equipped with a secondary dynamic dewatering unit and with a first variant of a slurry overflow; FIG.2 is a schematic layout and flow diagram of the main dynamic dewatering unit of FIG.1 showing the rotatable dewatering drum in perspective view and illustrating recovery of granulated material from an outlet of the secondary dewatering unit into the dewatering drum;

FIG.3 is a schematic vertical cross-section through the main dynamic dewatering unit of FIG.1 illustrating a level sensor used as overflow detection device;

FIG.4 is a schematic perspective view of an exemplary collecting tank for use in the main dynamic dewatering unit of FIGS.1 -3;

FIG.5A&5B are schematic layout and flow diagrams of a second embodiment equipped with a second variant of a slurry overflow, FIG.5A illustrating a normal mode of operation and FIG.5B illustrating a higher-capacity mode of operation ("continuous overflow mode");

FIG.6 is a schematic layout and flow diagram of a third embodiment, in which a main dynamic dewatering unit of the scoop-wheel type is equipped with a secondary dynamic dewatering unit and with a third variant of a slurry overflow;

FIG. is a schematic layout and flow diagram of a fourth embodiment, in which a main dynamic dewatering unit of the dewatering-screw type is equipped with a secondary dynamic dewatering unit and with a slurry overflow as in FIG.6.

[0022] Throughout these drawings, identical reference signs and reference signs with incremented hundreds digit identify identical or functionally similar components.

Description of Preferred Embodiments

[0023] In FIG.1 , an installation for processing molten material is generally identified by reference numeral 100. In particular, the installation 100 according to the first embodiment is designed to process pig iron slag into vitrified granulated slag ("slag sand"). Unprocessed pig iron slag is a low value by-product of pig iron produced in a blast furnace (not shown). Slag sand is a higher-value product suitable for further exploitation, e.g. in the cement industry. Whereas the entire plant including the furnace itself is not shown, the installation 100 is intended to be an integral part of a larger-scale metallurgical plant.

[0024] The installation 100 comprises two granulation units 1 10, 120 configured to quench a stream of molten slag with water, and more specifically, to inject a high-pressure jet of comparatively cold water, e.g. at <100°C, into a falling stream of liquid hot slag, e.g. >1200°C. To this effect, each granulation unit 1 10, 120 has a respective runner tip 1 12, 122 with an associated spray head 1 14, 124 (also called "blowing box") arranged below the runner tip 1 12, 122. Each spray head 1 14, 124 can provide a high-pressure water jet that impacts slag falling from the associated runner tip 1 12, 122 so as to achieve granulation. A suitable spray head is disclosed e.g. in EP 1 422 299. Molten slag is typically fed to the granulation units 1 10, 120 in intermittent manner, i.e. in more or less regular intervals at which the blast furnace (not shown) is tapped, via a respective slag runner (not shown) that originates at the skimmer (not shown). The runner tips 1 12, 122 are the downstream ends of the slag runners. Each granulation unit 1 10, 120 has a water- filled basin 1 16, 126 below its spray head 1 14, 124 for collecting the slurry (also called "pulp") resulting from water quenching of the molten slag and a hood for collecting fume and vapor emissions. The general configuration of a suitable granulation unit 1 10, 120 is well known. Hence for further details reference is made e.g. to US 4,758,260. A noteworthy unusual aspect however resides in that each granulation unit 1 10, 120 preferably comprises an auxiliary spray head 1 18, 128, which can be operated optionally in addition to the main spray head 1 14, 124. The auxiliary spray heads 1 18, 128 allow for granulating slag at higher input flow rates (above normal).

[0025] As further seen in FIG.1 , the installation 100 includes a main dynamic dewatering unit 130 equipped with a mobile dewatering component, more specifically with a cylindrical rotary dewatering drum 132 that is motor-driven and has a colander-like filtering function for dewatering slurry. A suitable general configuration of the dewatering unit 130 is well known from existing INBA® installations and described e.g. in US 4,204,855. Only features relevant to the present invention are thus discussed hereinafter. Main advantages of a dynamic dewatering unit 130, especially of the type with a rotary drum 132, lie in that it enables continuous dewatering, compact construction, high availability as well as low maintenance and operating costs.

[0026] The main dynamic dewatering unit 130 is connected downstream the granulation units 1 10, 120 for further treatment of slurry. In operation, the main dynamic dewatering unit 130 continuously separates the solid fraction of granulated material, i.e. coarse and fine slag sand, from the liquid fraction, i.e. process water, to facilitate separate recovery of each fraction. The preferred main dynamic dewatering unit 130 equipped with a dewatering drum 132 allows recovering granulated slag with comparatively low water content, e.g. <15% by volume, from slurry ("pulp") that has a much higher water proportion, e.g. >85% by volume.

[0027] The main dynamic dewatering unit 130 has a slurry inlet, generally identified by reference numeral 134. In the embodiment of FIG.1 , the upstream open front face of the rotary dewatering drum 132 forms the slurry inlet 134. The slurry inlet 134 is independently connected to each granulation unit 1 10, 120 by means of a respective supply conduit, e.g. a sloping gravity-feed open runner or a closed pipeline 136, 138 equipped with a respective pump as shown in FIG.1. The main dynamic dewatering unit 130 further has a material outlet 140 from which dewatered granulated material from the rotary dewatering drum 132 is recovered. As seen in FIG.1 , the material outlet 140 is formed by a delivery end, which is usually arranged above a stockyard, of a belt conveyor - a typical part of the main dynamic dewatering unit 130 - that has a receiving end inside the dewatering drum 132. Similarly, the main dynamic dewatering unit 130 has a water outlet 142 from which filtered process water that has a low or very low content of suspended fine (granulated) material particles can be recovered. In the installation 100, the water outlet 142 emanates from a collecting tank 144 (so called "hot water tank" - another typical part of an INBA® type main dynamic dewatering unit 130). More specifically, the water outlet 142 emerges from a clean water compartment 145 of or at the collecting tank 144. The clean water compartment 145 is connected, e.g. by means of a spillover weir, downstream a main settling compartment 146 of the collecting tank 144 (see below). As best seen in FIG.2, the main settling compartment 146 is arranged vertically underneath the rotary drum 132.

[0028] As seen in FIG.1 , in terms of process water, the installation 100 has a closed- circuit design. A process-water-recycling circuit 148 is connected to the water outlet 142 and equipped with pumps and a cooling tower 149. The water-recycling circuit 148 recirculates comparatively hot water recovered at the water outlet 142, after cooling to a suitable quenching temperature in the cooling tower 149, as needed to the spray heads 1 14, 1 18; 124, 128 of either or both granulation units 1 10, 120.

[0029] As shall be noted, the installation 100 has a slurry overflow with a first collecting gutter 150 that is arranged at the slurry inlet 134. In FIG.1 , the first collecting gutter 150 is arranged immediately at and underneath the open upstream front face of the dewatering drum 132. Furthermore, the slurry overflow may have a second collecting gutter 152 that is similarly arranged at the open downstream front face of the dewatering drum 132. The collecting gutters 150, 152 form a slurry overflow that enables draining any excess slurry, i.e. any proportion of the slurry received via the supply conduits 136, 138 that exceeds the dewatering capacity of the rotary dewatering drum 132 (i.e. its cubic capacity in FIG.1 ). In other words, any proportion of slurry fed into the dewatering drum 132 that cannot be properly processed spills at first into the slurry overflow 150, 152. As best seen in FIG.2, the slurry overflow may comprise respective upwardly open collecting troughs or gutters 150, 152 arranged below and along the width of the corresponding front face of the dewatering drum 132 so as to receive any spillover of slurry. As further seen in FIG.2, each gutter 150, 152 is connected to a drain conduit 154 that leads drained slurry into a separate dedicated slurry compartment or, preferably, into an integrated slurry compartment 147 that is arranged within the volume of the collecting tank 144 but separated from the main settling compartment 146 and from the clean water compartment 145, e.g. as will be detailed below in relation to FIG.4.

[0030] As will also be appreciated, the installation 100 further includes an auxiliary secondary dynamic dewatering unit 160 configured for separating slurry into a secondary dewatered fraction (sludge) and a secondary water fraction. The preferred dynamic secondary dynamic dewatering unit 160 includes a hydrocyclone (or a set of parallel hydrocyclones), which is of per se known configuration and connected in forward mode. In principle, any motion-induced continuously filtering (dynamic) dewatering device may be employed. Dynamic dewatering devices that have the benefit of comparatively high throughput (flow rate), even if not achieving optimal dehydration, i.e. very low moisture content in the dewatered fraction (dense fraction), are preferred. As an alternative or in addition to the hydrocyclone(s), the secondary dynamic dewatering unit 160 may comprise other dewatering devices e.g. one or more motor-driven true centrifuges of suitable type, e.g. a tubular bowl centrifuge, a chamber bowl centrifuge, an imperforate basket centrifuge, a disk stack separator or a decanter centrifuge (not illustrated).

[0031] As appears from FIGS.1 -2, the secondary dynamic dewatering unit 160 has an inlet 162 that is connected for receiving slurry from the collecting tank 144, especially excess slurry drained via the slurry overflow 150, 152 into the slurry compartment 147. The secondary dynamic dewatering unit 160 has a first outlet 164, e.g. the reject side of the hydrocyclone(s), that is connected with conduits for returning the secondary dewatered fraction (dense fraction / sludge) to the main dynamic dewatering unit 130, and a second outlet 166, e.g. the accept side of the hydrocyclone(s), that is connected with conduits for recovering the filtered secondary water fraction (light/fluid fraction). The secondary dewatered fraction, i.e. the sludge obtained at the first outlet 164, not necessarily but normally requires post-treatment in the main dewatering unit 130 to reach satisfying moisture content of the ultimately recovered granulated material.

[0032] Accordingly, as best seen in FIG.2, a recirculation conduit 172, e.g. an abrasion resistant piping, is connected to the inlet 162 to feed slurry from a bottom portion of the collecting tank 144, in particular excess slurry that has been drained via the slurry overflow 150, 152, to the secondary dynamic dewatering unit 160. The first outlet 164 in turn is connected to a first return conduit 174, e.g. an abrasion resistant piping, that feeds the dense secondary dewatered fraction, i.e. sludge with a considerably lower water content than the input slurry, from the secondary dynamic dewatering unit 160 back to the main dynamic dewatering unit 130. More specifically, as best seen in FIG.2, the first return conduit 174 preferably leads onto an inside surface of the dewatering drum 132. The return conduit 174 discharges onto the side at which concave blade-like filtering members, i.e. buckets 173 inside the dewatering drum 132 rotate upwards. Accordingly, the secondary dewatered fraction is fed onto a layer of granulated material on the filtering buckets 173 for additional dewatering and for discharge via the belt conveyor to the material outlet 140. Less preferably or with a different type of dewatering unit, the first return conduit 174 may also lead into either of the supply conduits 136, 138 or the basins 1 16, 126. As further seen in FIGS.1 -2, a bypass conduit 175 is provided to connect the recirculation conduit 172 directly to the first return conduit 174 without passing through the secondary dynamic dewatering unit 160, e.g. in the absence of excess slurry or for maintenance purposes. Suitable valves (not shown) in the bypass conduit 175 and the recirculation conduit 172 direct the flow as required through or in bypass of the secondary dynamic dewatering unit 160. The second outlet 166 in turn is connected via a second return conduit 176, e.g. a piping, to feed the secondary water fraction (light/fluid fraction), in a manner avoiding the solid-laden components of the main dynamic dewatering unit 130, into a reservoir with filtered "clean" process water, preferably directly upstream of the water outlet 142, e.g. into the clean water compartment 145 of the collecting tank 144.

[0033] As further seen in FIGS.1 -2, the recirculation conduit 172 is equipped with a first pump 177 dimensioned for normal load and a second pump 178 dimensioned for excess load. The pumps 177, 178 are connected in parallel for alternating operation and have their respective intake connected to the bottom of the collecting tank 144 at the side of the slurry compartment 147. Alternating operation of the pumps 177, 178 by suitable process control is based on the operating condition determined by an overflow detection device as described below in relation to FIG.3, for delivering slurry either to the secondary dynamic dewatering unit 160 or through the bypass conduit 175 as required.

[0034] As will be understood from the foregoing, by virtue of the arrangement of the slurry overflow 150,152, the installation 100 is capable of draining any excess of slurry received by the main dynamic dewatering unit 130 upstream of the water outlet 142 and upstream of its clean water carrying components (such as the clean water compartment 145) to thereby avoid contamination of recovered "clean" process water. Moreover, by virtue of the secondary dynamic dewatering unit 160 and its conduit connections, the installation 100 can continuously separate drained excess slurry into a dense fraction that returns to the main dynamic dewatering unit 130 and into a water that is recovered without passing through the main dynamic dewatering unit 130 and its solids-laden components (such as the main settling compartment 146).

[0035] Accordingly, it will be noted that the installation 100 enables operation in two modes, namely a normal mode of operation at which the input flow rate of slurry fed to the main dynamic dewatering unit 130 does not exceed its maximum dewatering capacity and, - as will be noted - a novel "continuous overflow" mode of operation, in which slurry at an input flow rate that exceeds the maximum dewatering capacity is fed to the main dynamic dewatering unit 130 over a comparatively long period (i.e. quasi-continuously).

[0036] EXAMPLES:

maximum dewatering capacity of the main dynamic dewatering unit 130: 2400m³/h

A) normal mode of operation (see FIG.5A):

only one granulation unit 1 10, 120 operating and producing 2000m³/h slurry;

normal load pump 177: on; excess load pump 178: off;

bypass 175: open; inlet 162: closed;

slurry flow rate via either of the supply conduits 136, 138: 2000m³/h; recirculation flow rate via recirculation conduit 172: 200m³/h;

input slurry flow rate at slurry inlet: 2200m³/h.

B) "continuous overflow" mode of operation (see FIG.5B)

both granulation units 1 10, 120 operating, producing in total 3000m³/h slurry (» dewatering capacity)

normal load pump 177: off; excess load pump 178: on;

bypass 175: closed; inlet 162: open;

slurry flow rate via 1 ^st supply conduit 136: 1500m³/h;

slurry flow rate via 2^nd supply conduit 138: 1500m³/h;

excess slurry flow rate: 600m³/h (+100m³/h returned sludge);

recirculation flow rate via recirculation conduit 172: 700m³/h;

sludge/fluid ratio of secondary dynamic dewatering unit 160: 1 :6;

flow rate of returned secondary dewatered fraction (sludge): 100 m³/h; flow rate of recovered secondary water fraction (fluid): 600 m³/h;

input slurry flow rate at slurry inlet: 3100m³/h.

[0037] As will be appreciated, the proposed installation allows operation at flow rates that considerably exceed (e.g. >125%) the nominal maximum capacity for which the main dynamic dewatering unit 130 is designed, the actual increase in total capacity being dependent mainly on the capacity of the secondary dynamic dewatering unit 160.

[0038] Turning to FIG.3, an exemplary overflow detection device 180 is illustrated for detecting whether the flow rate of slurry received via the slurry inlet 134 (see arrows 181 in FIG.3) exceeds the dewatering capacity of the main dynamic dewatering unit 130, i.e. whether "excess slurry" is fed. A preferred overflow detection device 180 is e.g. a level transmitter, as seen in FIG.3, which is connected to a signal line 182 of the plant process control system and arranged inside the lowermost portion of the dewatering drum 132. The overflow detection device 180 of FIG.3 determines whether the level of slurry inside the drum 132 remains within upper and lower limits 183, 184. Alternative or complementary overflow detection devices are also possible, e.g. devices including a radar probe measuring the slurry level inside the dewatering drum 132 or inside the supply conduit(s) 136, 138, or including an unbalance-sensor for measuring the imbalance (unbalanced mass), or a torque-meter for measuring the moment of inertia, of the slurry- containing drum 132. The choice of overflow detection device 180 depends mainly on the type of the main dynamic dewatering unit 130. Irrespectively of its configuration the overflow detection device 180 provides data, e.g. via the signal line 182, based on which process control switches the operating state between the normal mode and the continuous overflow mode (see above), among others by correspondingly activating or deactivating the normal load and excess load pumps 177, 178, valves at the bypass conduit 175 and, if motor-driven, the secondary dynamic dewatering unit 160.

[0039] FIG.4 illustrates an exemplary configuration of a collecting tank 144 for collecting filtered water dripping from the rotary dewatering drum 132. The collecting tank 144 has an upper portion 190, which is arranged underneath the rotary dewatering drum 132 and is adapted to the dimensions of the drum 132, i.e. has an upper surface sufficiently large to collect all water that drips down through the barrel of the dewatering drum 132. The collecting tank 144 further has a generally downwardly tapering, e.g. conical, lower portion 192, in which solid slag particles can settle to densely accumulate at the bottom tip. As will be noted, the collecting tank 144 of FIG.4 has an internal partition 194, e.g. an inclined plate, which reaches from the top downward and terminates above the bottom of the tank 144. The partition 194 divides the internal volume of the collecting tank 144 into the main settling compartment 146 and into the slurry compartment 147 arranged laterally to the shorter side of the main settling compartment 146. Since the partition does not entirely divide the lower portion 192, the compartments 146, 147 communicate via in the lowermost region of the lower portion 192. Integrating the slurry compartment 147 into the collecting tank 144 has the benefit of easily allowing retrofitting an existing installation with a priming volume for secondary dewatering without major modifications of an existing concrete collecting tank 144 and also simplifies connection of the collecting gutters 150, 152 of the slurry overflow. In other words, the existing "hot water tank" serves as a priming volume with sufficient suction head for the pumps 177, 178. Moreover, solids settled during normal operation (see above) in the main settling compartment 146 can also easily be recovered via the secondary dynamic dewatering unit 160 by operating the normal load pump 177.

[0040] In the embodiment of FIG.4, the clean water compartment 145 is arranged as a separate tank or by means of a partition, laterally of the collecting tank 144, e.g. on the long side. The clean water compartment 145 communicates with the main settling compartment 146, and optionally with the slurry compartment 147, only via an uppermost edge, e.g. via a spillover weir or spillover runners, so that due to gravity little if any solids spill over.

[0041] As best seen in FIGS.1 -2, the slurry overflow 150, 152 are connected to feed drained excess slurry directly into the slurry compartment 147, according to arrow 193 of FIG.4. Accordingly, all slurry i.e. settled solids from the main settling compartment 146 and mainly, in case of excess slurry ("continuous overflow" mode), drained excess slurry from the slurry compartment 147 is pumped off, according to arrow 195, from the lowermost tip of the main settling tank 144 into the recirculation conduit 172 for recirculation into the process. In order to prevent excessive wear due to abrasive slurry, the side-wall portions of the collecting tank 144 and the side of the partition 194 that face the internal volume of the slurry compartment 147 are covered with abrasion-resistant layers 196, e.g. with a coating of abrasion-resistant concrete. Substantially clean water on the other hand spills over, according to arrows 197, from the main settling compartment 146 into the clean water compartment 145, from which it is pumped, according to arrow 199, via the water outlet 142 into the water-recycling circuit 148.

[0042] In FIGS.5A&5B, which partially illustrate a second embodiment of an installation 200 according to the invention, reference sings that identify identical or functionally similar parts are incremented by one hundred. The installation 200 mainly differs from that of FIGS.1 -4 by the configuration of the slurry overflow 250. The installation 200 has one slurry overflow 250 arranged upstream of the slurry inlet 234 of the main dynamic dewatering unit 230 in a single supply conduit 236, e.g. an upwardly open sloping runner or a pipeline. Upstream of the supply conduit 236, one granulation unit (not shown) or a pair of granulation units (not shown) are connected directly or by means of a Y-piece respectively.

[0043] The second variant of slurry overflow 250 comprises a spillway 251 arranged within the supply conduit 236 to draw off excess slurry. More specifically, the slurry overflow 250 comprises a skimmer-like spillway 251 configured so that any amount of inflowing slurry above the lip or crest of the spillway 251 flows out off the supply conduit 236, as best illustrated by arrows 255 in FIG.5B. The limit at which slurry flows over, i.e. the maximum rate of slurry inflow into the main dynamic dewatering unit 230, as illustrated by arrows 257, is chosen by properly setting the level (height) of the crest of the spillway 251 within the cross-section of the conduit 236. Hence, the slurry overflow 250 of FIGS.5A&5B carries off any proportion of excess slurry that exceeds the maximum dewatering capacity even before such excess slurry can enter the dewatering drum 232. Downstream the spillway 251 , a diversion conduit 253, in particular a piping or a runner, is connected to lead excess slurry directly into the slurry compartment 247 of the collecting tank 244. The diversion conduit 251 , similar to the drain conduit 154 of FIG.2, thus indirectly connects the spillway 251 to the inlet 262 of the secondary dynamic dewatering unit 260, e.g. a (set of) hydrocyclone(s).

[0044] FIG5A further illustrates a normal mode of operation without excess slurry, in which the secondary dynamic dewatering unit 260 is not operating. Hence, a typical load of solids settled in the main settling compartment 246 is re-circulated via the recirculation conduit 272 and via the bypass 275 back inside the dewatering drum 232. Conversely, FIG.5B illustrates a "continuous overflow" mode of operation, in which secondary dynamic dewatering unit 260 is operating. Hence, in "continuous overflow" mode, excess slurry is drained by virtue of the slurry overflow 250 and fed into the slurry compartment 247. Thus a considerably higher excess load of slurry is pumped from the slurry compartment 247 to the inlet 262 and dewatered by the secondary dynamic dewatering unit 260. Accordingly, in the "continuous overflow" mode, sludge with comparatively low water content and at relatively low flow rate (a smaller fraction of total excess slurry) is returned via the first return conduit 274 onto the buckets of the dewatering drum 232 whereas comparatively clean water, at relatively high flow rate (a larger fraction of total excess slurry), is returned via the second return conduit 276 directly into the clean water compartment 245 to be recycled as process water. [0045] FIG.6 illustrates an installation 300 for processing molten material according to a third embodiment. The installation 300 differs from the preceding embodiments mainly by a different type of main dynamic dewatering unit 330 and by a third variant of a slurry overflow 350. Other components in FIG.6, which are substantially identical in function are not repeatedly described and have reference signs based on FIGS.1 -4 incremented to three hundred.

[0046] The main dynamic dewatering unit 330 in FIG.6 is of the scoop-wheel type. Accordingly, its mobile dewatering component is a vertical rotary scoop wheel 332 with colander-like external dewatering scoops (shovels) 373. During rotation of the scoop wheel 332, the dewatering scoops 373 shovel slurry out of a slurry tank 343, dewater the slurry and feed dewatered material onto a feeder such as a conveyor belt toward the material outlet 340. Due to a colander-like configuration of the dewatering scoops 373 and possibly the wheel 332 itself, water drips out of the dewatering scoops 373 downwardly, e.g. into the scoop wheel 332. Filtered process water may then be recovered from inside the scoop wheel 332 and fed via a suitable conduit to a separate clean water tank 345 as seen in FIG.6. The outlet of the clean water tank 345 also forms the water outlet 342 of the main dynamic dewatering unit 330. A suitable scoop-wheel 332 is detailed e.g. in German patent DE 4 214 948 C1 and thus not further discussed.

[0047] The slurry overflow 350 in the installation 300 of FIG.6 comprises an overflow bin or overflow surge tank 353 that is arranged immediately upstream the slurry tank 343 of the main dynamic dewatering unit 330. Both supply conduits 336, 338 are arranged to feed slurry from the granulation units 310, 320 at first into the overflow surge tank 353. As seen in FIG.6, the overflow surge tank 353 is provided with a drain in the form of an overfall 355, e.g. a lowered overflow edge, via which excess slurry naturally drains from the overflow surge tank 353 into an overflow collector 357. In a bottom portion, the overflow surge tank 353 has an outlet opening 359 leading into the slurry tank 343. The outlet opening 359 hence forms the slurry inlet 334 of the main dynamic dewatering unit 330. The cross-section of the outlet opening 359 is dimensioned to have a maximum throughput that corresponds to the maximum admissible slurry inflow, i.e. to the dewatering capacity of the main dynamic dewatering unit 330. Accordingly, excess slurry cannot enter the slurry tank 343. No more than the admissible maximum inflow is received into the slurry tank 343 while any excess slurry necessarily spills via the overfall 355 into the overflow collector 357. Optionally, the outlet opening 359 may have a valve-like configuration in order to control the flow rate of slurry overflow into the overflow collector 357 in function of the processing capacity of the dynamic dewatering units 330, 360. Suitable configurations of the schematically illustrated secondary dynamic dewatering unit 360 have been described above. As will be noted and as equally applicable to the preceding embodiments, the secondary dynamic dewatering unit 360 may also include other types of motion-based i.e. dynamic dewatering units, preferably of reduced capacity, e.g. a dewatering capacity in the range of 20-50% of the dewatering capacity of the main dynamic dewatering unit 330.

[0048] As further seen in FIG.6, the overflow collector 357 is connected via the recirculation conduit 372 with pumps 377 to the inlet 362 of the secondary dynamic dewatering unit 360. Similar to FIGS.1 -5B, the first outlet 364 is connected via a first return conduit 374 to return dewatered slurry (sludge) back to the main dynamic dewatering unit 330 and more specifically directly onto the dewatering scoops 373 of the scoop wheel 332 upstream their point of discharge onto the belt conveyor. The second outlet 366 is also connected to a second return conduit 376 for returning water recovered by the secondary dynamic dewatering unit 360 immediately into the clean water tank 345.

[0049] FIG.7 illustrates a fourth embodiment of an installation 400, which essentially corresponds to that of FIG.6 except for the use of yet another different type of main dynamic dewatering unit 430. In FIG.7, the main dynamic dewatering unit 430 comprises a dewatering screw conveyor 433, e.g. according to WO 2006/108517 or WO 2005/031008. The dewatering screw conveyor 433 has a mobile dewatering screw 435 arranged to rotate and thereby take slurry upwards out of the slurry tank 443 and to dewater the slurry during upward motion towards the material outlet 440. As in FIG.6, the first return conduit 474 feeds sludge from the secondary dynamic dewatering unit 460 directly onto the dewatering screw 435, preferably onto a portion immediately above the level of slurry in the slurry tank 443. The slurry overflow 450 has an identical configuration to that of FIG.6. Other components of the installation 400 of FIG.7, are substantially identical in function and/or structure to those of FIGS.1 -5B and thus have reference signs based on FIGS.1 -4 incremented to four hundred. As will be understood, operation of the installations 300, 400 of FIGS.6-7 corresponds to that described in relation to FIGS.1 -5B, and thus also includes the possibility of operating in "continuous overflow" mode, i.e. processing slurry in excess of the dewatering capacity of the main dynamic dewatering units 330, 430.

[0050] As will be noted, by analogy to FIGS.6-7, an installation according to the invention may also comprise other known types of motion-based main dewatering units, such as a horizontal dewatering disc according to US patent no. 3,912,487 or a dewatering bucket elevator according to US patent no. 3,615,329. List of reference signs / Legend: 180 overflow detection device

181 received slurry

FIGS.1-4 182 signal line

installation for processing molten

100 183,

material lower / upper limit

184

1 10

granulation unit 190 upper portion (of 144)

120

192 lower portion (of 144)

1 12

runner tip

122 194 partition

1 14 193,

spray head slurry flow arrows

124 195

1 16 196

granulation basin

126 197,

"clean" water flow arrows

1 18 199

auxiliary spray head

128 FIGS.5A-5B

130 main dynamic dewatering unit installation for processing molten

200

132 dewatering drum material

134 slurry inlet 230 main dynamic dewatering unit

136, 234 slurry inlet

supply conduit

138 236 supply conduit

140 material outlet 244 collecting tank

142 water outlet 245 clean water compartment

144 collecting tank 246 main settling compartment

145 clean water compartment 247 slurry compartment

146 main settling compartment 250 slurry overflow

147 slurry compartment 251 spillway

148 recycling circuit 253 diversion conduit

149 cooling tower 255 slurry overflow arrows

150,

slurry overflow (collecting gutters) 257 slurry inflow arrow

152

260 secondary dynamic dewatering unit

154 drain conduit

262 inlet (of 260)

160 secondary dynamic dewatering unit

264 first outlet (of 260)

162 inlet (of 160)

266 second outlet (of 260)

164 first outlet (of 160)

272 recirculation conduit

166 second outlet (of 160)

274 first return conduit

172 recirculation conduit

275 bypass conduit

173 internal buckets

276 second return conduit

174 first return conduit

277 normal load pump

175 bypass conduit

278 excess load pump

176 second return conduit

177 normal load pump

178 excess load pump FIG.6 FIG.7

installation for processing molten installation for processing molten

300 400

material material

310; 410;

granulation unit granulation unit

320 420

312; 412;

runner tip runner tip

322 422

314; 414;

spray head spray head

324 424

316; 416;

granulation basin granulation basin

326 426

330 main dynamic dewatering unit 430 main dynamic dewatering unit

332 dewatering scoop wheel 433 dewatering screw conveyor

334 slurry inlet 434 slurry inlet

336, 435 dewatering screw

supply conduit

338

436,

supply conduit

340 material outlet 438

342 water outlet 440 material outlet

343 slurry tank 442 water outlet

345 clean water tank 443 slurry tank

348 recycling circuit 445 clean water tank

349 cooling tower 448 recycling circuit

350 slurry overflow 449 cooling tower

353 overflow surge tank 450 slurry overflow

355 overfall 453 overflow surge tank

357 overflow collector 455 overfall

359 outlet opening (of 353) 457 overflow collector

360 secondary dynamic dewatering unit 459 outlet opening (of 353)

362 inlet (of 360) 460 secondary dynamic dewatering unit

364 first outlet (of 360) 462 inlet (of 360)

366 second outlet (of 360) 464 first outlet (of 360)

372 recirculation conduit 466 second outlet (of 360)

373 dewatering scoops 472 recirculation conduit

374 first return conduit 474 first return conduit

375 bypass conduit 475 bypass conduit

376 second return conduit 476 second return conduit

377 pump 477 pump

Claims

1 . An installation (100) for processing molten material produced by a metallurgical plant, in particular for processing blast furnace slag, said installation comprising:

at least one granulation unit (1 10; 120) for granulating a stream of molten material by quenching said stream with water to produce a slurry of granulated material and water;

a main dynamic dewatering unit (130) having a slurry inlet (134) connected to said granulation unit via a supply conduit (136; 138), in particular via a runner or pipeline, for receiving slurry produced by said granulation unit, a material outlet (140) for recovering granulated material and a water outlet (142) for recovering process water, said main dynamic dewatering unit comprising a mobile component, in particular a rotary dewatering drum (132), for separating slurry received via said slurry inlet into a granulated material fraction to be fed to said slurry outlet (140) and into a water fraction to be fed to said water outlet (142); characterized by

a slurry overflow (150, 152, 154) that is arranged upstream of or at said slurry inlet (134) and upstream of said water outlet (142), said slurry overflow being configured for draining excess slurry in excess of the dewatering capacity of said main dynamic dewatering unit (130);

a secondary dewatering unit (160) for separating slurry into a secondary dewatered fraction and a secondary water fraction, said secondary dewatering unit having an inlet (162) connected for receiving excess slurry drained via said slurry overflow, a first outlet (164) connected for returning said secondary dewatered fraction to said main dynamic dewatering unit (130) and a second outlet (166) connected for recovering said secondary water fraction;

so that said installation (100) is configured for draining excess slurry so as to preclude excess slurry from reaching said water outlet (142) and for separating drained excess slurry into a secondary dewatered fraction that returns to said main dynamic dewatering unit (130) and into a secondary water fraction that is recovered without passing through said main dynamic dewatering unit (130).

2. The installation according to claim 1 , characterized in that said main dynamic dewatering unit (130) comprises

a rotary dewatering drum (132) as a mobile component for dewatering slurry produced by said granulation unit;

a collecting tank (144) that is arranged underneath said rotary dewatering drum (132) for collecting said water fraction separated by said rotary dewatering drum, said collecting tank having an upper portion (190) and a lower portion (192) in which material can settle, said slurry overflow (150, 152) being connected (154) to feed drained excess slurry into said collecting tank (144);

and in that said installation (100) comprises a recirculation conduit (172) comprising at least one recirculation pump (178) and connecting said lower portion (192) of said collecting tank (144) to said inlet (162) of said secondary dewatering unit (160) so that drained excess slurry can be pumped from said lower portion (192) of said collecting tank to said secondary dewatering unit (160).

3. The installation according to claim 2, characterized in that said upper portion of said collecting tank comprises:

a main settling compartment (146), arranged to receive said water fraction separated by said rotary dewatering drum and to communicate (197, 199) with said water outlet (142); and

a slurry compartment (147) separated from said main settling compartment (146) by means of a partition (194) so as to preclude excess slurry from reaching said water outlet (142), said slurry overflow (150, 152) being connected (154) to feed drained excess slurry into said slurry compartment;

wherein said separated slurry compartment (147) communicates with said lower portion (192) of said collecting tank (144) so that drained excess slurry can be pumped from said separated slurry compartment (147) via said lower portion (192) to said secondary dewatering unit (160).

4. The installation according to claim 2 or 3, characterized in that said first outlet (164) of said secondary dewatering unit is connected to a return conduit (174) arranged for feeding said secondary dewatered fraction onto an inside surface of said dewatering drum (132), preferably onto a layer of granulated material on an inside surface of said dewatering drum.

5. The installation according to claim 2, 3 or 4, characterized in that said recirculation conduit (172) comprises a normal load pump (178) having an intake connected to said lower portion (192) of said collecting tank and an excess load pump (177) connected in parallel to said primary load pump and having an intake connected to said lower portion (192) of said collecting tank, said installation preferably further comprising an overflow detection device (180) for detecting whether excess slurry in excess of the dewatering capacity of said main dynamic dewatering unit is fed to said main dynamic dewatering unit and for controlling operation of said excess load pump accordingly.

6. The installation according to to any one of claims 2 to 5, characterized in that said recirculation conduit (172) comprises a bypass conduit (175) configured to feed slurry pumped from said lower portion of said collecting tank to said main dynamic dewatering unit, preferably onto an inside surface of said dewatering drum, more preferably onto a layer of granulated material on an inside surface of said dewatering drum.

7. The installation according to any one of claims 2 to 6, characterized in that said slurry overflow comprises at least one collecting gutter (150, 152) arranged below a front face of said dewatering drum (132) to receive slurry flowing over from said dewatering drum.

8. The installation according to claim 7, characterized in that said slurry overflow comprises a first collecting gutter (150) arranged below the upstream front face of said dewatering drum, a second collecting gutter (152) arranged below the downstream front face of said dewatering drum, and a drain conduit (154) connected to said first and second collecting gutters and leading into said collecting tank (144), in particular into said slurry compartment (147).

9. The installation (200) according to any one of claims 2 to 6, characterized in that said slurry overflow (250) comprises a spillway (251 ) arranged in said supply conduit (236) upstream of said main dewatering unit and a drain conduit (253) connecting said spillway to said secondary dewatering unit (160), in particular via said collecting tank (144).

10. The installation (200; 300; 400) according to claim 1 , characterized in that said slurry overflow comprises: a spillway (251 ) arranged in said supply conduit upstream of said main dewatering unit and with a diversion conduit connecting said spillway to said inlet of said secondary dewatering unit (260); or

an overflow surge tank (353; 453) arranged in between said supply conduit and said main dewatering unit, said surge tank having a drain (355; 455) connected to said inlet of said secondary dewatering unit (360; 460).

1 1 . The installation according to claim 10, characterized in that said overflow surge tank has a drain in the form an overfall (355; 455) that leads excess slurry into an overflow collector (357; 457) connected to said inlet of said secondary dewatering unit (360; 460), and an outlet opening (359; 459) forming said slurry inlet of said main dynamic dewatering unit.

12. The installation (300; 400) according to any one of claims 10 to 1 1 , in particular according to claim 2, wherein said mobile component of said main dynamic dewatering unit is a dewatering screw (430), a dewatering scoop wheel (330) with external dewatering scoops, a horizontal dewatering disc or a dewatering bucket type elevator.

13. The installation according to any one of claims 1 to 12, comprising a first granulation unit (1 10) for granulating a stream of molten and a second granulation unit (120) for granulating a stream of molten, characterized in that said main dynamic dewatering unit has a slurry inlet connected to said first granulation unit and to said second granulation unit.

14. The installation according to any one of claims 1 to 13, wherein said dynamic main dewatering unit comprises a rotary dewatering drum and said secondary dewatering unit is a dynamic secondary dewatering unit that comprises at least one hydrocyclone and that has a dewatering capacity in the range of 20-50% of the dewatering capacity of said main dewatering unit.

15. The installation according to any one of the preceding claims, characterized in that said installation further comprises an overflow detection device for detecting whether excess slurry in excess of the dewatering capacity of said main dynamic dewatering unit is fed to said main dynamic dewatering unit, and a recirculation conduit that is equipped with a pump for feeding excess slurry drained via said slurry overflow to said inlet of said secondary dewatering unit, said overflow detection device being connected to control operation of said pump.

16. Blast furnace plant comprising an installation according to any one of the preceding claims for processing blast furnace slag.

17. A method for processing molten material produced by a metallurgical plant, in particular for processing blast furnace slag, said method comprising:

granulating a stream of molten material by quenching said stream with water to produce a slurry of granulated material and water;

feeding said slurry to a slurry inlet of a main dynamic dewatering unit that comprises a mobile component, in particular a rotary dewatering drum, via a supply conduit, in particular via a runner or pipeline,

separating slurry received via said slurry inlet by said main dynamic dewatering unit into a granulated material fraction to be recovered at a slurry outlet and into a water fraction to be recovered at a water outlet;

characterized by

feeding a flow of slurry that exceeds the dewatering capacity of said main dynamic dewatering unit via said supply conduit to said main dynamic dewatering unit;

draining excess slurry, which is in excess of said dewatering capacity, upstream of said water outlet so as to preclude it from reaching said water outlet and via a slurry overflow arranged upstream of or at said slurry inlet; feeding drained excess slurry from said slurry overflow to a secondary dewatering unit; separating drained excess slurry by said secondary dewatering unit into a secondary dewatered fraction and a secondary water fraction,

returning said secondary dewatered fraction to said main dynamic dewatering unit and recovering said secondary water fraction without passing said secondary water fraction through said main dynamic dewatering unit.