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The present invention relates to a process and a plant for the treatment and recovery of metallurgical or steel slag, for example to obtain ladle white slag or ladle furnace (LF) slag as secondary raw material.
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More in particular, the invention applies to the steel-industry field and relates to a process for the treatment and recovery of metallurgical or steel slag, in particular to obtain ladle white slag, wherein a first slag treatment is made in a first portion of a plant comprising at least one rotating tubular reactor fed with input slag material to be treated downstream of a ladle and subjected to a forced and controlled cooling of an outer jacket thereof.
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The invention also relates to a plant for the treatment and recovery of metallurgical or steel slag, in particular to obtain ladle white slag, of the type comprising:
- a first plant portion provided with a rotating tubular reactor for a first treatment of said metallurgical slag;
- a feeding inlet to the rotating tubular reactor downstream of a ladle;
- a cooling system for an indirect and forced cooling of an outer jacket of said rotating tubular reactor.
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The invention also relates to a method for the modernization of an existing steel plant.
Field of application
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As is well known in this technical field, in almost all the steel plants the need to be able to dispose of or possibly to recover processing slag is particularly felt.
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This need arises mainly from an awareness of environmental themes but also from economical observations and from observations about productivity yield, because the possible recovery of slag would reduce consumption and production costs, thereby increasing the profitability of the industrial process in steel industry.
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Black slag is substantially inert in air or water and can be used for the production of conglomerates for asphalts or for cement foundations of various type. Thus, it can be treated more easily.
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Instead, white slag is instable and expansible and has features that make difficult its direct use; moreover, within few years, its confinement in landfill will become impossible due to specific legislative prohibitions arisen in the meantime.
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It is possible to reuse white slag in steelworks by re-introducing it into the cast as a replacement for other raw material, or it can constitute a source of: CaO, FeO3, SiO2 and MgO in cement production. However, the quality and the performance of white slag depend to a wide extent on the quality and amount of the steel produced, and, therefore, they vary from steelworks to steelworks.
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More in particular, the process leading to the aggregation of white slag comprises a so-called slagging phase, which is carried out in the ladle, during which lime or other additives are added to the liquid steel so as to allow the non-metallic parts contained in the ore to aggregate, due to the heat, into a homogeneous foamy form on top of the molten metal, thereby separating the slag which can be discharged from the ladle.
Prior art
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Static methods for the recovery of white slag through a so-called atomization process, namely a phase transition that pulverizes it, are known from time immemorial. For example, the white slag discharged from the ladle can be let cool on grids or in ventilated environments.
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These methods are not very efficient and involve long times for material pulverization; moreover, said material is subjected to powder dispersion, thereby entailing serious environmental problems and problems for the operators' safety.
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A more effective solution consists in treating the white slag in a rotating reactor, for example structured with a large metallic cylinder operated in rotation and having cooled outer walls.
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A solution of this type is described, for example, in the European patent no.
EP 3 323 898 B1 in the name of STEB. In this patent, the rotating reactor is structured with modular panels enclosing cooling coils, so that cooling of the slag moved forward by the rotation of the reactor occurs in an indirect manner.
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A second technical solution is described, instead, in the Italian patent no.
IT 102010901883093 in the name of SV Impianti. Also in this case, there is an initial phase of white-slag atomization through a forced and controlled cooling of the material by means of a process of indirect heat exchange.
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In this case, the rotating tubular reactor, in which the atomization phase occurs, is drip-cooled by means of a plurality of spray nozzles placed in alignment over said reactor.
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Even if these known solutions are advantageous in various aspects and partially in line with the object, they do not consider the preexisting steel industry situations for which it is not so simple to provide a slag treatment as described in the above-mentioned patent applications.
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Basically, in these preexisting plants there are devices and plant portions with own size and overall dimensions which are not suitable to be associated to separate slag treatment plants.
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In these cases, it would be necessary to make tailored slag treatment plants that consider the preexisting situations, from the point of view of both safety requirements in overall-dimensions distribution and in the management the whole plant.
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The technical problem underlying the present invention is to provide a process and a plant for the treatment and recovery of metallurgical or steel slag, in particular white slag, having structural and functional features that allow to carry out a continuous treatment of white slag while adapting the treatment and the recovery to the configuration of the existing steel plants, thereby overcoming limitations and drawbacks of the prior art solutions.
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An object of the present invention is to separate the phases of treatment and partial atomization of the slag from the phases of transfer and storage of the white slag for a possible reuse of the definitively atomized material in the cast.
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Another object of the invention is to provide a treatment plant having a relatively simple structure and easily manageable so that it needs a relative reduced maintenance.
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A further object of the invention is to allow a process of white-slag atomization that is essentially based on controlled cooling but wherein the thermal gradient is not excessive, so as to prevent formation of excessive iron agglomerates or residues in the slag.
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Another object of the invention is to provide a process and a plant having respective functional and structural features of high efficiency, also from the energetic and environmental point of view, and reduced costs so as to be made in situ at any preexisting steel plant.
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Finally, another object of the invention is to provide an improvement and modernization to a preexisting steel plant.
Summary of the invention
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The solution idea underlying the present invention is to separate into two distinct plant portions the phase of treatment with controlled cooling of the white slag from the phase of recovery and storage, thereby making easier to make and manage the two distinct plant portions that, although coupled and cooperating with each other, can be made in distinct sections of a preexisting steel plant even with independent construction sites.
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Based on said solution idea, the technical problem is solved by a process for the treatment and recovery of metallurgical or steel slag, in particular ladle white slag, wherein a first slag treatment is made in a first portion of a plant comprising at least one rotating tubular reactor fed with input slag material to be treated downstream of a ladle and subjected to a forced and controlled cooling of an outer jacket thereof, characterized in that between the ladle and the feeding inlet of the tubular reactor there is a heatable slag pot and in that at the outlet of the reactor there is a first screen of a granulated product fed into a second portion of the plant through a level-shifting apparatus and towards a second screen; a part of said granulated product being transferred downstream of the second screen into a storage silo and a remaining part of said granulated product being transferred into a crusher with re-introduction and recirculation of the discharge of the crusher into said level-shifting apparatus.
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Advantageously, the slag pot is heated by means of at least one gas torch acting on an outer wall thereof; moreover, said heating extends toward said feeding inlet of the tubular reactor.
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Moreover, the second screen is supported inclined in a hopper that receives the discharge of said level-shifting apparatus and discharges on a conveyor that feeds said silo; a part of the product that is retained by the screen being fed into said crusher.
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It should be noted that the inclination of said screen feeds a second hopper which discharges on a further belt conveyor to feed the crusher.
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The latter belt conveyor is in turn a level-shifting apparatus toward a mouth of said crusher.
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Instead, the first level-shifting apparatus seamlessly comprises a first segment in the form of a conveyor belt and a second segment in the form of a noria for transferring said granulated product to a higher level compared to the outlet of the tubular reactor.
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The invention also relates to a plant for the treatment and recovery of metallurgical or steel slag, in particular to obtain ladle white slag, of the type comprising:
- a first plant portion of a rotating tubular reactor for a first treatment of said metallurgical slag;
- a feeding inlet to the rotating reactor downstream of a ladle;
- a cooling system for an indirect and forced cooling of an outer jacket of said rotating reactor;
wherein said plant for the treatment and recovery of metallurgical or steel slag is characterized in that it also comprises:
- a heatable slag pot for collecting the metallurgical slag, said slag pot being supported between the ladle and said feeding inlet;
- a first screen at the outlet of the rotating reactor for continuously discharging a granulated product;
- a second portion of the plant being fed with said granulated product through a level-shifting apparatus;
- a second screen receiving the discharge of said level-shifting apparatus for transferring a part of said granulated product into a storage silo;
- a crusher receiving a remaining, not screened part of said granulated product;
- means for the re-introduction into circulation of the discharge of the crusher into said level-shifting apparatus.
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More in particular, the above-mentioned means for the re-introduction into circulation of the discharge of the crusher are at least one belt conveyor leading near said level-shifting apparatus.
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Moreover, said belt-conveyor means are configured as a further level-shifting apparatus.
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It should also be noted that a chute or a rotating cylinder made of cast iron is provided between said inlet and said slag pot. Moreover, the heating means of the slag pot also affect the chute and the feeding inlet of the tubular reactor.
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Moreover, the second screen is inclined and kept in vibration.
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Finally, it should be noted that the invention relates to a method for the modernization of an existing steel or metallurgical plant, wherein an accessory plant is provided to connect an area for movement and discharge from ladle with an area designated for storing steelworks slag. Said accessory plant comprises a first plant portion designated for the treatment and the recovery of metallurgical or steel slag by means of a rotating tubular reactor and a first terminal screen and a second, sequential plant portion designated for the refinement of the granulated product coming out of the first screen of the first plant portion which is subjected to a second screen before being transferred into a storage silo, at least one remaining, still coarse, part of said granulated product being treated in a crusher and re-introduced into a recirculation circuit on which the second screen is inserted.
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The features and advantages of the process and plant according to the invention will become apparent from the following description of an embodiment, given by way of a non-limiting example with reference to the accompanying figures.
Brief description of the drawings
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- Figure 1 shows a schematic view in lateral extension of an industrial plant made according to the present invention for the treatment and recovery of metallurgical or steel slag, in particular ladle white slag;
- Figure 2 shows a perspective and schematic view of the plant of Figure 1;
- Figure 3 shows a perspective and schematic enlarged-scale view of a first portion of the plant of Figure 1;
- Figure 4 shows a perspective and schematic enlarged-scale view of a second portion of the plant of Figure 1;
- Figure 5 shows a perspective and schematic view of a second portion of the plant of Figure 3 observed from a different standpoint;
- Figure 6 shows a perspective and schematic view of a detail of the second plant portion of Figure 4.
Detailed description
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With reference to said figures, and in particular to the example of Figure 1, 1 globally and schematically shows an integrated plant made according to the present invention for the treatment and recovery of metallurgical or steel slag, in particular ladle white slag.
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The plant 1 essentially comprises two portions functionally distinct from each other: a first portion 2, which is intended for a phase of treatment with controlled cooling of a waste material M to be treated to obtain the so-called white slag, and a second portion 3, which is intended for a phase of slag recovery, transfer and storage.
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This second portion may also be defined as for screening and volume reduction of the slag that can not be stored yet.
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The two portions 2 and 3 are substantially cooperating with each other and placed one upstream of the other to substantially form a jointed scaffolding that is mounted between preexisting structures of a large steel plant which is designated, for example, for the production of steel for making billets, for hot-rolling or for making construction section bars or beams.
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Advantageously, the two portions 2, 3 of the plant 1 can also be built separately, so as to reduce the times for making the entire plant 1.
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The plant 1 of the present disclosure is meant as an integration of an existing steel plant, in order to also connect areas that are usually intended for distinct functions with each other, such as for example an area for movement and discharge from ladle by means of a crane or bridge crane and an area for storing material that can be re-introduced into the cast.
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Thanks to the creation and insertion of said plant 1, said distinct areas of the steel plant are coupled and can cooperate with each other, even if they are placed in distinct sections of the preexisting steel plant.
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The first portion 2 of the plant 1 is made in longitudinal extension between the ladle discharge area and an intermediate area for the connection with the area for storing materials.
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This first portion 2 of the plant 1 comprises a large rotating tubular reactor 5, structured with a cooling shell 15 of the type of a horizontally extended rotating cylinder and with a slight and predetermined angular inclination of 2-10°, preferably approximately 5°, with respect to a horizontal plane, so as to facilitate the advancement of the internally treated material M.
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According to the present invention, said horizontal plane is to be understood as being substantially parallel to the walking surface or ground level.
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In particular, the rotating tubular reactor 5 is a single cooling chamber enclosed in said rotating-cylinder cooling shell 15.
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This tubular reactor 5 is supported by revolving rollers 8, or roller bearings, and it may internally comprise some ribs to facilitate the centrifugal entrainment of the material M to be treated.
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The tubular reactor 5 comprises an inlet 12, to receive the material M to be treated for the recovery of the white slag, fed through a chute 13 which is inclined and open at the top and preferably has a semicircular section.
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Said chute 13 can be made of steel with walls coated with refractory material.
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Alternatively, said chute 13 can be replaced with a rotating cylinder made of cast iron, so as to allow less retaining of the material on the lateral walls and a more homogeneous feeding on the inner cooling shell of the tubular reactor 5. Obviously, in this case a specific rotation support system should be provided.
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The mouth of the chute might receive the material directly from a spillage of a ladle S of the preexisting steel plant.
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The ladle S of the steel plant is operated by means of a crane or a bridge crane and allows to spill the material M to be treated into the slag pot 10, making sure to avoid trickling the solid part on the bottom too, which is periodically cleaned elsewhere.
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However, according to an aspect of the present invention, it is preferred that the spillage from the ladle S occurs inside a slag pot 10, or inside an intermediate bucket, supported at an intermediate height between the ladle S and the mouth of the chute 13.
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Advantageously, said slag pot 10 has an inner seat having a substantially hemispherical shape, to facilitate emptying the same.
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The slag pot 10 is preferably made of steel with an inner coating of refractory material and is installed on at least two opposite hinge recesses 14, 16 intended to receive respective rotation pins, not shown since conventional, operated to mutually move toward or away from each other by motorized means when an inclination of the slag pot 10 toward the mouth of the chute 13 or of the equivalent rotating cylinder made of cast iron is needed.
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Advantageously, according to the invention, the slag pot 10 may be heated or in any case kept at a predetermined temperature, for example by means of at least one or more gas torches 48 acting on its outer walls.
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Moreover, the heating may also affect the chute 13, the inlet 12 and the first part of the reactor 5.
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Said heating allows to improve a more regular decline of the thermal gradient during the treatment of white-slag recovery.
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Unlike some solutions proposed in the prior art, which even provide an initial cooling of the material M before its introduction into the tubular reactor, the solution proposed by the present invention makes the decline of the thermal gradient in the phase of slag treatment more gradual. This also reduces the initial formation of metallic aggregates that should then pass through the rotating tubular reactor reducing the yield in the slag recovery.
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Moreover, heating the slag pot 10 prevents the formation of internal condensate that would be very detrimental in the phase of first spillage of the material to be treated because moisture and cold are detrimental to white slag and promote its immediate oxidation.
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Returning now to the structure of the rotating tubular reactor 5, it should be noted that the reactor 5 is supported by a plurality of spacers 7, regularly arranged in a prefixed spaced apart position, that establish the height from the ground and the slight inclination on horizontal plane with predetermined angulation.
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Said spacers 7 extend vertically from a base 4 which also comprises containment side walls 18. The base 4 and the side walls 18 form a tank for the collection of cooling water for the rotating reactor 5.
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To minimize the vertical overall dimensions of the tank, said tank is made with a cement manufacture produced on site, i.e. in situ.
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The roller bearings 8 are supported on top of the spacers 7, said roller bearings allowing the reactor to rotate upon operation of electrically motorized means, which are not shown since they are conventional.
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An irrigation system 6 is provided to cool the outer surface of the cooling shell 15 of the rotating tubular reactor 5.
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This irrigation system 6 provides a plurality of longitudinal main pipes 22 which are connected with each other by means of a plurality of secondary pipes 23.
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The main pipes 22 are intended to deliver by sprinkling or by dripping a cooling fluid, for example water, toward the outer wall of the cooling shell 15 by means of multiple nozzles provided in a prefixed spaced apart relationship along the entire extension of the reactor 5.
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At least three main pipes 22 are provided, wherein one is placed at the top and two are placed laterally near the top of the reactor 5.
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The water sprinkled or dripped by the nozzles of the irrigation system 6 is collected in the base 4 acting as a collection tank from which it is recollected by recirculation pumps to be re-introduced into the irrigation system 6.
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During each cooling cycle, the cooling fluid or the water is delivered toward the outer part of the cooling shell 15 and, without any direct heat exchange with the material contained inside the reactor 5, a heated heat-exchange fluid, preferably heated water, is obtained.
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Advantageously, at the end of each cooling cycle, the heated heat-exchange fluid, preferably heated water, is collected in the collection tank and, before the next cooling cycle, it is cooled, in particular by simple mixing by convection with the residual mass of cooling fluid contained in the tank.
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Therefore, according to the present invention, the collection tank has such a capacity to ensure the storage of a mass of cooling fluid sufficient to provide a suitable amount of cooling fluid, which is adapted to carry out a cooling cycle, and a residual mass of cooling fluid, the latter being sufficient to determine the cooling of the cooling fluid heated during the cooling cycle and subsequently collected in the tank.
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The process of the invention is preferably carried out in continuous. Actually, the total duration of the treatment of the material M until the storage into silos of a part of the white slag is of about 45 minutes, as will be better understood in the following in the description.
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A protection housing or coating 9 protecting the entire plant portion 2 intended for a phase of treatment with controlled cooling of the waste material M is provided.
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The housing 9 is substantially a polygonal five-side coating covering the rotating reactor 5 as a tunnel for both safety reasons and for containing the overall dimensions, and for protecting the environment from the spurts of the cooling nozzles.
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The housing 9 is at the top of the side walls 18 of the base 4 substantially as a vertical extension of said side walls.
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However, the reactor 5 and the housing 9 are open on a side of outlet or discharge of the treated material M.
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More in particular, the reactor 5 has an accessible outlet 20 which discharges on a bucket 25 that collects metallic agglomerates.
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These agglomerates are the metallic component having a large particle size that falls due to gravity into the bucket 25 placed at a lower level than the level of the reactor 5.
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More precisely, the discharging part, i.e the final part of the reactor 20, is protected by the protection housing 9. Only the last portion of said housing, near the discharge caisson 25, is hinged to facilitate movement maneuvers and for visual inspections.
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However, the terminal portion of the rotating tubular reactor 5 is structured as a cylindrical grid 26 or in the form of a rotating perforated drum, seamlessly with respect to the rotating walls of the cooling shell 15 of the reactor 5.
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Said tubular grid 26 prevents the metallic agglomerates from laterally going out, which fall indeed into the bucket 25, whereas the slag recovered by means of the treatment and the forced cooling through the reactor 5 is screened through the grid 26 and, by falling, is collected by means of a horizontal first conveyor belt 21 extended under the grid 26.
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Said belt 21 is oriented transversely with respect to the longitudinal axis of the reactor 5 to laterally discharge the slag thereby screened by the grid 26 and, at the end of this phase, in the form of a granulated product having particle size varying between about 0 and 80 mm, preferably between 1 and 70 mm.
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Another transverse emergency belt 28 is also provided, which is operated in the opposite direction with respect to the above-mentioned belt 21 and is operated only in the case the plant portion 3 for screening and volume reduction underwent a failure. That is to say, it is possible that, in case of a stop of the plant portion 3, the grid screen 26 may let fall the material onto the ground or into a designated container.
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Once the downstream plant portion 3 is reactivated, it will be possible to take the material discharged on the ground, for example by means of a loader, so that it can be put again into an accessory service hopper 41 in order to complete the production cycle that did not occurred previously due to the failure.
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Then, the hopper 41 discharges on an inclined conveyor 46 which is in turn capable of feeding the plant portion 3 as will be shown below.
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At this point, the first portion 2 of the plant 1 and the first phase of the process according to the invention can be considered completed, wherein said first phase allows to obtain an initial treatment with indirect cooling of the material M to be transformed into white slag at the end of the entire process.
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The below-described structural components downstream of the outlet 20 of the rotating tubular reactor 5 can be considered as being part of the second portion 3 of the plant 1.
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Said second portion 3 is designated for a further screening and volume reduction of the slag and for the actual recovery of the white slag which may be stored and reused inside the steel plant.
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The slag coming out of the tubular reactor 5 is in fact a granular product with different particle sizes, for example less than 20 mm, but is not yet completely 100% usable in the steel plant and must be subjected to other processing phases that, according to the invention, are carried out in a totally automatic and continuous way.
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The conveyor belt 21 for collecting the slag screened by the tubular grid 26 carries and discharges the granular product on a second conveyor belt 27 which is extended perpendicularly to the above-mentioned belt 21.
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Said second conveyor belt 27 is a first flat part of a level-shifting apparatus 30 configured, for example, as a scoop noria to transfer the granulated product coming out of the tubular reactor 5 to a breaker or crusher 35.
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It should be noted that the flat portion of the conveyor belt 27 and the noria of the level-shifting apparatus 30 are seamless with respect to each other.
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Containment side walls 38 for containing the material that has been shifted in level are provided. It is not strictly necessary to cover the level-shifting apparatus 30 at the top, because the plant 1 is all contained within the accommodating steel plant and is thus, in fact, covered.
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In fact, the plant 1 is conceived to be all comprised inside a large shed or inside the span of the steelworks. If this were not the case, an upper protection of the level-shifting apparatus 30 or even an extension thereof in tunnel could also be provided.
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Advantageously, the level-shifting apparatus 30 has a discharge outlet 32 leading to a hopper 31 internally provided with a further screen 33 which has inclined surface and can possibly be kept in vibration through motorized means not shown in the drawings.
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The outlet 32 of the shifting apparatus 30 is protected through a housing 19 which is open at the bottom toward the hopper 31.
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More in particular, the second portion 3 of the plant 1 comprises a play of the hoppers 31, 34 and 37 that are needed, on the one hand, to select the white slag which is now storable and ready to be used in the steel plant and, on the other hand, to recycle the portion of white slag that still does not have the suitable particle size to be reused in the steel plant.
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As is well shown in Figures 5 and 6, under the screen 33 of the hopper 31, the slag having the finest particle size, namely the one that passed through the sieve consisting in the screen 33, is ready to be transferred toward a silo S1.
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This occurs by means of a second level-shifting apparatus 40 on which the funnel portion of the hopper 31 discharges.
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Also in this case, a level-shifting apparatus 40 is used, which may be also structured as a scoop noria or an analogous elevator, for feeding a silo S1, or for the storage in big bags.
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The figures also show a second silo S2, which may be needed if the production of white slag is even higher than the amount that can be reused in said steel plant.
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In this case, once the silo S1 is full, the feeding of the level-shifting apparatus 40 to the second silo S2 may be adjusted, wherein the second silo can be a storage place for a subsequent transfer of the excess white slag towards other steel plants, for example by means of a road transport C which is schematically shown in Figure 1.
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Instead, the granular product having a still coarse particle size, which has not been screened through the inclined sieve 33, is collected in the hopper 34 that communicates on top and laterally with the hopper 31 at the end of the descent of the sieve 33.
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In substance, the slag having the largest particle size, namely the one collected in the screen 33, is discharged by gravity into the portion of lateral hopper 34 that allows to feed with a constant flow an underlying mill crusher 35.
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The hopper 34 discharges on an underlying hopper 37 which feeds an elevator 39 of the conveyor belt type. This elevator 39 may in turn be configured as a scoop noria, similarly to the level-shifting apparatus 30 or 40.
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The elevator 39 leads to and discharges on the mouth of a breaker or crusher 35, for example a rotating-hammer mills, or a drum mill, to reduce to the desired size the material that reached the same.
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The play of the hoppers 31, 34 and 37 and of the elevators 30, 39 and 40 serves the purpose of saving space in height so as to optimally manage the overall dimensions of all said components without occupying excessive spaces in the existing steel plant.
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For example, the crusher 35 is supported in an elevated position on a flat platform 45 supported by a tubular scaffolding 11 which, on an upper part thereof, also supports the hoppers 31, 34 and 37 and against which the level-shifting apparatuses 30, 39 and 40 also lean.
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In this way, the discharge outlet of the crusher 35 is at a higher level than the outlet 20 of the tubular reactor 5, namely the outlet discharging on the first transverse belt 21.
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Therefore, the discharge outlet 42 of the crusher 35 can feed a further belt conveyor 43 that discharges the crushed material above the flat segment 27 of the first level-shifting apparatus 30 through a small hopper 44 to bring back into circulation at least one portion of slag, possibly still mixed with granular product, wherein said portion can be brought back to the play of the hoppers 31, 34 and 37 for a further refinement and selection.
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Obviously, the crusher outlet 42 could also be fed directly on the level-shifting apparatus 30, for example by means of a horizontally extended belt conveyor.
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Basically, the second portion 3 of the plant 1 has an important function of effective, continuous recovery of the white slag having a particle size suitable for its reuse in the steel plant from which it was recovered.
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In fact, the granular product coming out of the first portion 2 of the plant 1 is partially recirculated in the second plant portion 3 in order to be further refined until the suitable particle size for its storage and reuse in the starting steel plant is reached.
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Indeed, the crushed material at the lower outlet 42 of the mill 35 is brought back into circulation and conveyed by means of the additional conveyor belt 43 toward the small hopper 44 that discharges on the first flat segment 27 of the level-shifting apparatus 30, to be treated again by means of the second portion 3 of the plant 1.
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A slag of intermediate particle size comes out of the outlet of the mill crusher 35. Once said slag comes onto the first flat segment of the conveyor belt 27, it will be raised again by the level-shifting apparatus 30 to come back into the play of the hoppers 31, 34 and 37 and also partially into the crusher 35.
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In fact, in the plant 1 of the present invention, complete atomization of the white slag does not occur without the passage into the mill crusher 35.
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In an alternative embodiment, it is also possible to provide a tunnel shielding of the additional belt conveyor 43 downstream of the crusher 35, because the particle size at the outlet 42 becomes quite small and might form powders.
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Finally, it should be noted that, downstream of the first silo S1, a pneumatic feeder 50 is also provided, wherein said feeder is in communication with a furnace of the steel plant for the re-introduction of a predetermined percentage of recovered white slag. Instead, the slag stored in the second silo can be sent outside the factory, for example for other uses as an additive in the cement industry, or to phases even more upstream of the productive process although in the same factory.
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As will be clear to a person skilled in the art in the light of the above description, the invention also allows to make a preexisting steel plant more modern.
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Therefore, the present disclosure also relates to a method for the modernization of an existing steel or metallurgical plant comprising an area for cast processing, an area for movement and discharge from ladle, said area for movement and discharge from ladle comprising a ladle S, preferably operated by means of a crane or bridge crane, and an area for storing material, preferably designated for storing steelworks slag, wherein said modernization method comprises the following phases:
- a) connecting said area for movement and discharge from ladle with said area designated for storing steelworks slag;
- b) connecting said area designated for storing steelworks slag with said area for cast processing.
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Moreover, more in particular, the above-mentioned phase a) essentially comprises the following steps:
- downstream of the ladle S, providing a first portion 2 of a plant 1 for the treatment and recovery of metallurgical or steel slag by means of a rotating tubular reactor 5, structured with a horizontally extended cooling shell 15 with a predetermined angular inclination, fed with material M to be treated through an inclined chute 13 for an initial recovery of a granulated material from which white slag can be obtained.
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The above-mentioned predetermined angular inclination is preferably between 2 and 10°, more preferably about 5°, with respect to a horizontal plane.
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The chute 13 is open at the top and preferably has a semicircular section. Alternatively, a rotating cylinder made of cast iron could be provided in place of said chute.
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Downstream of the ladle S and upstream of the chute 13 or of the rotating cylinder made of cast iron, the use of a heatable slag pot 10 is preferred, said slag pot being supported at an intermediate height between the ladle S and the mouth of the chute 13 or of the rotating cylinder made of cast iron.
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Preferably, in the modernization method of the invention, phase a) comprises the preliminary step of providing a tank for the collection of cooling water for the rotating reactor 5, wherein said tank is made with a cement manufacture produced in situ and comprises a base 4 comprising containment side walls 18, said base 4 being arranged to support said rotating tubular reactor 5.
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The modernization method according to the present invention also comprises providing a second portion 3 of the plant 1 inserted between a discharge outlet and first screen of the tubular reactor 5 and the area designated for storing steelworks slag.
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This second plant portion 3 comprises a support scaffolding 11 to support at least one hopper 31 provided with an inclined second screen 33 on which the level-shifting apparatus discharges.
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A part of said granulated product being transferred downstream of the second screen into a storage silo and a remaining coarser part of said granulated product being transferred into a crusher with re-introduction and recirculation of the discharge of the crusher into said level-shifting apparatus so as to let the still coarse slag come back into the refining circuit consisting in the second portion 3 of the plant 1.
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Finally, it should be noted that the modernization method of the invention is very suitable for an existing steel or metallurgical plant designated for the production of steel, for example for making billets, for hot-rolling or for making construction section bars or beams.