Patent Publication Number: US-2023151446-A1

Title: Plant for the treatment and recovery of white slag resulting from steelmaking processes

Description:
TECHNICAL FIELD 
     The present invention relates to a plant for the treatment and recovery of white slag (also known as ladle slag) resulting from steelmaking processes, produced in the refining stages of liquid steel. 
     BACKGROUND ART 
     A further application can also be found in the treatment of AOD (Argon Oxygen Decarburation) slag, which is produced in the decarburization process of stainless steels. 
     In addition, the proposed plant can also be conveniently adopted for cooling and sorting in an optimal manner any powder or granular material. 
     The white slag is mainly composed of the lime required for the refining processes, of the reaction products of the de-oxidation and desulphurization stages of the liquid steel bath and of the wear materials of the ladle refractory. 
     The lime still present at the end of the refining process can be enhanced, e.g., by its use in a new steelmaking process, or for other uses. 
     The regulations in force define white slag as special waste that must therefore necessarily be disposed of, with consequent increases in the production costs and considerable consequences on the environment. 
     In order to overcome these drawbacks, over the years there has been a considerable increase in proposals for the recovery of white slag, with the aim of achieving advantages both from a productive point of view, optimizing and economizing the process, and from an environmental point of view thanks to the reduction of disposal in landfills and the exploitation of quarries to obtain limestone for the preparation of lime. And here, without deliberately referring to the great saving obtained in terms of reduction in carbon dioxide emissions produced by limestone firing. The recovery of white slag is generally carried out through a process known as “withering”, wherein, as a result of controlled cooling, di-calcium silicate, one of the main components of white slag, undergoes an increase in volume with consequent fragmentation and pulverization of the entire matrix that makes up the white slag. 
     Several types of plants for the treatment and recovery of the white slag are known, nevertheless they either feature a series of problems or they have not been followed up with a suitable and performing plant application and have been abandoned after their first pilot or industrial test. 
     A first type of plant is the “static” type, i.e. in which the recovery of white slag is carried out by letting it cool down in a chamber of one or more boxes, until it is pulverized. This solution has poor efficiency of thermal exchange, hence the need for very long times to achieve the fragmentation of the material. 
     A plant of the static type is described by U.S. Pat. No. 7 854 785. 
     These “static” type systems, characterized by slow kinetics that require important plant structures, have been surpassed by rotary type reactors, cooled externally with water and/or internally with air and, therefore, in direct contact with the slag. 
     These solutions have the advantage of implementing a continuous mixing of the material inside the drum, thus carrying out the continuous renewal of the slag in contact with the cooling wall. 
     Among these, various types are known that differ from each other, as well as also for the use of air inside the reactor to support the external water, for the different way of carrying out the process (continuous or batch), for the different type of cooling of the water supply (on the external surface, inside liners or free), as well as for the different morphology of the drum construction. 
     Some plants of the rotary type are described by JP S52-13493 and JP S52-17388, EP 2 261 383 A1, EP 3 247 811 A1 and EP 3 323 898 A1. 
     Among these, documents JP S52-13493 and JP S52-17388 describe a method of withering the material, with its indirect cooling through the outer surface of an open tubular reactor in which the white slag is placed. Some water is sprayed on the upper surface of the reactor, which is then collected in a tank located below the reactor itself. The limitations of the proposal are obvious, with only the upper surface to operate the heat exchange, in addition to the considerable dispersion of water and the ease for the liquid, coming into contact with the slag, to degrade it. 
     Document EP 2 261 383 A1 describes a method for the recovery of white slag in an open tubular reactor, wherein cooling is mainly carried out by a stream of air affecting the inner region of the drum, as well as by a series of nozzles positioned under the rotating drum and capable of spraying water against the outer surface. The method, with batch operation, also has the limitation of a reduced exchange surface and the use of air in direct contact with the slag, with the obvious negative consequences it entails. Documents EP 3 247 811 A1 and EP 3 323 898 A1 relate to plants for the treatment and recovery of white slag, through the system of indirect heat exchange with a “closed circuit” coolant. 
     Both of these plants have a rotating chamber in which controlled cooling of the white slag takes place, so as to allow the so-called withering to occur, followed by subsequent screening of the powder obtained through this process. 
     Other plants for the cooling of white slag are known from U.S. Pat. No. 1,769,412 A, CN 1 944 685 A, and IT VE 20 100 055 A1. 
     Document U.S. Pat. No. 1,769,412 A describes a cooling device, in particular for calcined ores, having a work chamber movable around a relevant axis and inside which are housed a plurality of treatment channels intended to receive the material to be treated. During the rotation of the work chamber, each treatment channel is subjected to cooling through two separate modes. In fact, in the lower part, the treatment channels pass through a tank filled with water under static conditions, while subsequently, when they rise upwards and reach the top in their circular movement, they are subjected to further cooling by means of water spray. The cooling water therefore only skims the work chamber from the outside. As a result, the heat exchange processes are characterized by low efficiency. 
     Moreover, there are considerable losses of water due to evaporation processes, with the system requiring significant availability of “disposable” water, in addition to making the work environment decidedly impractical, for the vapors and mists occurring. 
     Another device to cool the slag down is known from CN 1 944 685 A, which discloses a rotary reactor characterized by an outer annular section in which water flows so as to keep the outer surface “cold”, and by an inner coaxial cylinder. The latter in turn contains a certain number of drums, submerged in water. The material to be cooled down is inserted both in each of the drums and inside an interspace defined between the outer circular crown and the inner cylinder. The cooling water is sent countercurrent to the direction of forward movement of the material to be cooled and, in particular, it is introduced at the point where the outlet area of the cooled material is located and it exits at the point where the loading area of the material to be cooled is located. Before the main pipe of the cooling water inlet enters the reactor, a branch of the pipe is separated to feed the outer circular crown. At the inlet of the slag, an air insufflation system is also installed which is adapted to promote the material to cool down. 
     The document IT VE 20 100 055 A1 discloses, on the other hand, the withering process in an open tubular reactor, with free water that is dosed through the aid of sprays on the upper external surface of the reactor shell, and then collected in a tank located below the same machine. Also this solution has some drawbacks, such as the deterioration of the slag, the reduced heat exchange surface, the loss of cooling liquid, the lack of cooling of the hot slag loading area, the difficulty in managing the process parameters. 
     The heat exchange between the slag layer and the reactor wall, being managed by basically conductive type processes, is characterized by low values of the exchange coefficient. This implies the need to have large surfaces and, therefore, reactors characterized by important dimensions to be able to ensure the appropriate capacity. A relevant aspect concerns the plant dimensions, which are often a big issue due to the limited space available in the factories. 
     Again, the standardization of the machines is complex, with consequent increase in both engineering and construction costs. 
     DESCRIPTION OF THE INVENTION 
     The main aim of the present invention is to devise a plant for the treatment and recovery of white slag resulting from steelmaking processes which allows optimizing the cooling process of the white slag in a confined environment. 
     Another object of the present invention is to devise a plant for the treatment and recovery of white slag resulting from steelmaking processes which allows the efficient and easy treatment of even large quantities of white slag, in small reactors. 
     A further object of the present invention is to obtain large exchange surfaces, without limiting the possibility of feeding pasty material and/or with the presence of coarse sized solid blocks. 
     Another object of the present invention is to devise a plant for the treatment and recovery of white slag resulting from steelmaking processes which is small in size and which allows adapting to the factory in which it is installed and to the production requirements of the same by making, in the same reactor and continuously, the phases of cooling and recovery through the selection of the withered material. 
     A further object of the present invention is to devise a plant for the treatment and recovery of white slag resulting from steelmaking processes which allows facing different plant capacity, thus reducing engineering, construction and maintenance costs. 
     Another object of the present invention is to devise a plant for the treatment and recovery of white slag resulting from steelmaking processes which allows overcoming the aforementioned drawbacks of the prior art within a simple, rational, easy, effective to use and low cost solution. 
     The objects set out above are achieved by the present plant for the treatment and recovery of white slag resulting from steelmaking processes having the characteristics of claim  1 . 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other characteristics and advantages of the present invention will become more evident from the description of a preferred, but not exclusive, embodiment of a plant for the treatment and recovery of white slag resulting from steelmaking processes, illustrated by way of an indicative, yet non-limiting example, in the accompanying tables of drawings wherein: 
         FIG.  1    is a side, partly broken view, of a plant for the treatment and recovery of white slag according to the invention, in a first embodiment; 
         FIG.  2    is a first plan view from above of a plant according to the invention, in a second embodiment; 
         FIG.  3    is a cross-sectional view along the III-III track plane of  FIG.  2   ; 
         FIG.  4    is a cross-sectional view along the IV-IV track plane of  FIG.  2   , in which the path of the coolant is shown; 
         FIG.  5    is an axonometric view of the section in  FIG.  4   , in which the involved streams are identified; 
         FIG.  6    is a second plan view from above of the plant in  FIG.  2   , rotated by 45° with respect to the view in  FIG.  2   ; 
         FIG.  7    is a cross-sectional view along the VII-VII track plane of  FIG.  6   ; 
         FIG.  8    is a cross-sectional view along the VIII-VIII track plane of  FIG.  6   ; 
         FIG.  9    is an axonometric view of the section in  FIG.  8   , in which the path of the coolant is identified; 
         FIG.  10    is an exploded view of a component of the plant in  FIG.  1   ; 
         FIGS.  11  and  12    are cross-sectional views along the XI-XI and XII-XII track planes of  FIG.  1   , respectively. 
     
    
    
     EMBODIMENTS OF THE INVENTION 
     With particular reference to these figures, reference numeral  1  globally indicates a plant for the treatment and recovery of white slag resulting from steelmaking processes. 
     In the context of the present disclosure, the term “white slag” relates to a by-product of the steelmaking processes for the production of liquid steel. 
     The plant  1  comprises at least one basic frame  2  positionable resting on a supporting surface P. 
     In particular, the supporting surface P is substantially horizontal and, preferably, coincides with the ground. 
     The plant  1  comprises at least one work chamber  3  associated with the basic frame  2 , movable in rotation around a relevant axis A and configured to receive and treat the white slag S resulting from steelmaking processes by means of a withering process. 
     In the context of the present disclosure, by the term “withering process” is meant the controlled cooling of the white slag, preferably in a confined atmosphere to avoid the chemical degradation thereof, which leads to a change in the volume of the crystal lattice of one of its main components, di-calcium silicate, with consequent fragmentation and pulverization of the material. The resulting lime-rich powder is enhanced by its use in a new steelmaking process (recycling of the material inside the same production cycle) or for other applications. 
     The work chamber  3  has an elongated conformation and the axis A substantially coincides with the longitudinal axis of the work chamber itself. 
     The plant  1  further comprises movement means  4  of the work chamber  3  adapted to set the work chamber itself in rotation. 
     In the embodiment shown in the figures, the movement means  4  comprise:
         at least one crown gear  5  associated externally with the work chamber  3  and arranged to surround the latter;   at least one pinion  6  that meshes with the crown gear  5 ;   at least one motor  7 , variable speed, associated with the basic frame  2  and adapted to operate the pinion  6 .       

     It cannot, however, be ruled out that the movement means  4  are of a different type and that the rotation of the work chamber  3  is carried out in another way. 
     During the withering process, the white slag S is moved forward along at least one direction of treatment D. 
     In particular, the rotation of the work chamber  3  determines the forward movement of the white slag S. 
     The direction of treatment D is substantially parallel to the axis A. 
     The work chamber  3  comprises:
         at least one loading portion  8  provided with at least one inlet port  9  through which the white slag S is loaded;   at least one cooling portion  10  arranged downstream of the loading portion  8  with respect to the direction of treatment D and comprising:   at least one treatment channel  11  of the white slag S; and   cooling means  12  comprising at least one coolant F adapted to operate in conjunction with the treatment channel  11  to cool the white slag S contained therein so as to obtain at least one recovery powder R;   at least one sorting and separation portion  13  of the recovery powder R arranged downstream of the cooling portion  10  with respect to the direction of treatment D.       

     In detail, as a result of its loading inside the work chamber  3 , the white slag S is moved along the direction of treatment D in succession through the aforementioned portions  8 , 10 , 13 . 
     Advantageously, the work chamber  3  is inclined with respect to the horizon, with the loading portion  8  positioned at a higher level than the sorting and separation portion  13 . 
     In other words, the sorting and separation portion  13  is closer to the supporting surface P with respect to the loading portion  8 . 
     Thus, as a result of the loading of the white slag S inside the loading portion  8 , a stream of white slag S is generated by gravity and directed towards the sorting and separation portion  13 , i.e. downwards. 
     The plant  1  is also provided with inclination adjustment means  14 , 15  for adjusting the inclination which are associated with the basic frame  2 . 
     The adjustment means  14 , 15  are adapted to allow simple and easy variation of the inclination of the work chamber  3 . 
     It is easy to understand that greater inclination of the work chamber  3 , with the rotational speed being equal, leads to an increase in the transit speed of the white slag S inside the work chamber itself. 
     The adjustment means  14 , 15  thus allow adjusting the residence time of the white slag S to be treated in the plant to the final temperature of the white slag S at the outlet. 
     The adjustment means  14 , 15  comprise a hinging member  14  arranged in the proximity of one of either the loading portion  8  or the sorting and separation portion  13  and a movement device  15 , of the type of, e.g., a jack arranged in the proximity of the other of either the loading portion  8  or the sorting and separation portion  13 . 
     Advantageously, the plant  1  comprises at least one control and command unit  52  operatively connected to at least one of either the movement means  4  or the adjustment means  14 , 15  and configured to control the operation thereof. 
     Conveniently, the control and command unit  52  is operatively connected also to the slag feeding system, so as to reduce or increase the flow rate of the slag introduced into the plant  1  according to the loading or unloading temperatures to be managed. 
     Appropriately, sensor means, not visible in detail in the figures, are provided, adapted to detect the temperature of the recovery powder R and operatively connected to the control and command unit  52 , which is configured to adjust at least one of either the movement means  4  or the adjustment means  14 , 15  according to the temperature detected by the sensor means. The sensor means are positioned, e.g., at the point where the sorting and separation portion  13  is located. 
     More particularly, the control and command unit  52  is configured to increase the rotational speed of the work chamber  3  by operating on the movement means  4  and/or to vary the inclination of the work chamber itself by operating on the adjustment means  14 , 15  when the temperature detected by the sensor means exceeds a preset reference value. 
     The loading portion  8  has a substantially truncated-cone shape, diverging away from the inlet port  9 . 
     Such a shape facilitates the outflow of the white slag S towards next cooling portion  10 . According to the invention, the cooling portion  10  comprises a plurality of treatment channels  11  which are separate from each other and communicating with the loading portion  8 , each of which is adapted to receive a part of the white slag S as a result of the rotation of the work chamber  3 , to cool and convey it towards the sorting and separation portion  13 . 
     As can be seen from the figures, such an embodiment allows splitting the white slag S to be treated into a plurality of streams, separate from each other, thus increasing the exchange surface between the white slag S and the cooling means  12 , thus optimizing the withering process and reducing the size of the plant  1 . Still according to the invention, the cooling means  12  are arranged to at least partly enfold the treatment channels  11  and comprise at least one delivery channel  21 , which extends at least through the cooling portion  10  to send the coolant F towards the loading portion  8  counter-currently with respect to the direction of treatment D, and at least one return channel  22 , which extends at least through the cooling portion  10  and is arranged to surround the delivery channel  21  to send the coolant F towards the sorting and separation portion  13  in a parallel manner, i.e., equi-currently, to the direction of treatment D. 
     One stretch of the return channel  22  is therefore positioned between the delivery channel  21  and the treatment channels  11 . The return channel  22  therefore surrounds the treatment channels  11 . 
     The cooling means  12  comprise, then, at least one inlet manifold  42  arranged at the point where the loading portion  8  is located and adapted to transfer the coolant F from the delivery channel  21  to the return channel  22 . 
     More particularly, the inlet manifold  42  is positioned between the loading portion  8  and the cooling portion  10 . 
     The delivery channel  21  and the return channel  22  are contained inside the work chamber  3 . 
     The cooling means  12  and the treatment channels  11  rotate integrally with each other around the axis A. 
     More particularly, the inlet manifold  42  defines at least one transfer chamber  50  of the coolant F communicating with the delivery channel  21  and with the return channel  22  and through which the treatment channels  11  pass. 
     Advantageously, the loading portion  8  is arranged opposite the cooling portion  10  with respect to the inlet manifold  42  and defines at least one interspace  51  communicating with the transfer chamber  50 . 
     More in detail, the interspace  51  comprises at least one inlet gap  51   a  of the coolant F communicating with the transfer chamber  50  and at least one outlet gap  51   b  of the coolant F communicating with the return channel  22 . The interspace  51  is therefore adapted to receive the coolant F coming from the delivery channel  21 , so as to cool the slag S that is introduced therein, and then conveys the coolant itself inside the return channel  22 . 
     Preferably, the cooling means  12  comprise at least one internally hollow cooling liner  18 ; the delivery channel  21  and the return channel  22  are arranged inside the cooling liner  18 . 
     In particular, the return channel  22  is positioned between the cooling liner  18  and the delivery channel  21  and the treatment channels  11  are inserted inside the return channel  22 . 
     Conveniently, the cooling means  12  also comprise an outlet manifold  47 , communicating with the return channel  22 , which is adapted to collect the coolant F passing through the return channel itself and to convey it outwards. 
     The delivery channel  21  passes through the outlet manifold  47 , exiting outside the work chamber  3 . 
     The outlet manifold  47  is positioned between the cooling portion  10  and the sorting and separation portion  13 . 
     In the embodiment shown in  FIGS.  2  to  9   , both the delivery channel  21  and the return channel  22  exit outside the work chamber  3  by means of the relevant piping at the point where the outlet manifold  47  is located. 
     Advantageously, the plant  1  comprises supply means  44  of the coolant F communicating with the delivery channel  21  and discharge means  45  of the coolant F communicating with the return channel  22 , where the supply means  44  and the discharge means  45  are arranged outside the work chamber  3 . 
     More particularly, the supply means  44  comprise at least one fixed supply duct and the discharge means  45  comprise at least one fixed discharge duct, which are arranged downstream of the sorting and separation portion  13  and are connected, respectively, to the delivery channel  21  and to the return channel  22  by means of a rotary joint  46 . Preferably, the control and command unit  52  is operatively connected also to the supply means  44  and is configured to operate thereon, so as to vary the flow rate of the coolant F, depending on the temperature detected by the sensor means. 
     In particular, the control and command unit  52  is configured to increase the flow rate of the coolant F when the temperature of the recovery powder R detected by the sensor means exceeds a preset reference value. 
     Conveniently, the treatment channels  11  are substantially parallel to each other. 
     The dimensions of the treatment channels  11  are such that even coarse pieces can pass through. 
     Furthermore, the treatment channels  11  are arranged in a radial pattern with respect to the axis A and each of them comprises a supply port  16  communicating with the loading portion  8 . 
     In the embodiment shown in the figures, the treatment channels  11  have a substantially cylindrical shape. 
     It cannot however be ruled out that the treatment channels  11  may have a shape of different geometry. 
     The white slag S is distributed into the treatment channels  11  by gravity, as a result of the rotation of the work chamber  3 . 
     In detail, the rotation of the work chamber  3  causes each supply port  16 , in turn, to be at the point where an accumulation is located of the white slag S being loaded into the loading portion  8 , allowing it to be automatically split. 
     In this regard, the loading portion  8  is conveniently provided with a plurality of conveying elements  17  adapted to direct the white slag S towards the treatment channels  11 . 
     The conveying elements  17 , of the type of, e.g., helical fins, are internally associated with the loading portion  8  and extend between the inlet port  9  and the supply ports  16 . 
     Inside each of the treatment channels  11 , the white slag S is subjected to a continuous and controlled cooling process that causes the fragmentation thereof so as to obtain the recovery powder R. 
     Cooling is carried out indirectly through the walls of the treatment channels  11 , by means of the coolant F flowing inside the return channel  22  located around the treatment channels  11 . 
     In this regard, the plant  1  allows dividing the white slag S into several separate streams and cooling them down, by means of a considerably increased exchange surface, with the external dimensions being equal, so that even large quantities of white slag S can be treated, thus ensuring at the same time effective cooling, while keeping the dimensions of the plant  1  considerably reduced. 
     As a result of the rotation of the work chamber  3 , the white slag S continuously contacts, by moving forward and mixing, the areas of the treatment channel  11  which are cooled by the coolant F. 
     The rotation of the work chamber  3 , in fact, causes the white slag S to rotate in turn and always be in contact with a continuously cooled area of the treatment channel  11 . 
     In addition, the rotational speed of the work chamber  3  defines the transit speed of the white slag S inside both the cooling portion  10  and the sorting portion  13 , thereby establishing the plant flow rate. 
     Conveniently, each of the treatment channels  11  comprises a plurality of mixing elements  23  which extend along the direction of treatment D, and which are adapted to mix the white slag S and to convey it towards the sorting and separation portion  13 . 
     The mixing elements  23 , configured e.g. as fin segments, are preferably arranged axially on the inner wall of each treatment channel  11 . 
     Alternatively or in combination thereof, the mixing elements  23  may extend in a continuous or semi-continuous spiral pattern on the inner wall of each treatment channel  11  along the respective direction of treatment D. 
     The mixing elements  23 , as a result of the rotation of the work chamber  3  around the axis A, cause the white slag S to be lifted and mixed, thereby promoting the cooling thereof. 
     In addition, the mixing elements  23  contribute to the forward movement of the stream of white slag S along the direction of treatment D. 
     Even if the environment is always confined, in an embodiment of the present invention, the plant  1  may also comprise inertization means, not shown in detail in the figures, associated with the work chamber  3  and adapted to generate a controlled atmosphere inside at least the cooling portion  10 . 
     In this way, the withering process takes place in an atmosphere with a reduced content of humidity and carbon dioxide, in order to avoid possible processes of hydration, carbonation and, therefore, the degradation of the withered white slag S. 
     Each of the treatment channels  11  comprises an outlet port  24 , opposite the inlet port  9  and communicating with the sorting and separation portion  13 . 
     In particular, the sorting and separation portion  13  is adjacent and integral with the cooling portion  10 . 
     The recovery powder R that is generated by the withering process of the white slag S exits the treatment channels  11  through the respective outlet ports  24  and flows out, by discharging it into the sorting and separation portion  13 . 
     Conveniently, the sorting and separation portion  13  comprises a plurality of holes  25 , each provided with at least a predefined size, adapted to allow the outflow of the recovery powder R. 
     Conveniently, it could be provided inside with a series of longitudinal fins, not shown here, which are adapted to lift the powder to avoid any packing and facilitate the sorting thereof. 
     The holes  25 , adequately calibrated, allow screening the recovery powder R enabling only the recovery powder R to flow out which has undergone a correct withering process. 
     The plant  1  also comprises collection means  26  of the recovery powder R arranged below the sorting and separation portion  13 . The recovery powder R falls by gravity from the sorting and separation portion  13  to the collection means  26 . 
     The collection means  26  comprise at least one collection member  27 , of the type, e.g., of a hopper, adapted to convey the recovery powder towards other recovery stations. 
     Advantageously, below this collection hopper for the recovery powder there is a damper, not visible in detail in the figures, which can be operated manually to allow the powder to be discharged. 
     The plant  1  is further provided with a powder containment system  28  associated with the work chamber  3  and arranged to surround at least the sorting and separation portion  13 . 
     In particular, the containment system  28  comprises a powder containment chamber  29  adapted to house the sorting and separation portion  13  and part of the collection member  27 . 
     The function of the powder containment chamber  29  is to prevent the recovery powder R from being dispersed into the external environment, and it is provided with rotary seals on the outside. 
     For this purpose, the containment system  28  also comprises a suction device  30  associated with the powder containment chamber  29 . 
     The products that maintain a greater size than the predefined size at the end of the withering process form a waste product of the treatment process, basically consisting of a metal-slag mixture. 
     Conveniently, the work chamber  3  comprises at least one unloading portion  31  arranged downstream of the sorting and separation portion  13  with respect to the direction of treatment D and adapted to allow the unloading of the waste product resulting from the withering process. 
     Preferably, below this unloading portion  31  there is a damper, not shown in detail in the figures, which is manually operable to allow unloading the waste product. 
     Through the unloading portion  31 , the waste product exits the work chamber  3  and is conveyed to further disposal or recovery stations. 
     Advantageously, the plant  1  comprises a plurality of modular elements  32  that can be assembled together to define at least said cooling portion  10 . 
     This embodiment makes it possible to modify and adapt the plant  1  on the basis of the amount of white slag S to be treated in a simple and easy manner, simply by implementing or reducing the number of modular elements. 
     As shown in  FIG.  10   , each modular element  32  comprises at least one central member  33  that partly defines the work chamber  3  and a pair of lateral faces  34  opposite each other, each adapted to contact a lateral face  34  of an adjacent modular element  32 . 
     In more detail, the central member  33  has a substantially cylindrical shape and extends along the axis A, while the lateral faces  34  have a substantially circular shape and are substantially perpendicular to the axis A. 
     Conveniently, the plant  1  comprises connecting means  35  of the modular elements  32  adapted to connect and keep the modular elements themselves joined together. 
     The connecting means  35  are, e.g., perforated flanges associated with the outer wall of each modular element  32 . 
     In more detail, the connecting means  35  are associated with the lateral faces  34  of the modular element  32 . 
     The plant  1  also comprises sealing means  36 , of the type e.g. of circular gaskets, positioned between the modular elements  32  and adapted to operate in conjunction with the connecting means  35  to hermetically connect the modular elements  32 . 
     The modular elements  32  comprise at least cooling modules  37  that can be assembled together to define the cooling portion  10 . 
     The cooling modules  37  are, therefore, adapted to define the treatment channels  11  and the cooling liner  18 . 
     Each cooling module  37  also defines a relevant portion of the delivery channel  21  and of the return channel  22  adapted to contain the coolant F. 
     As shown in  FIG.  11   , each of the lateral faces  34  of the cooling modules  37  comprises a closing plate  38  provided with:
         a plurality of first openings  39  for the passage of the white slag S, corresponding to the number of the treatment channels  11 ;   at least a second opening  40  communicating with the delivery channel  21  for the passage of the coolant F; and   a plurality of third openings  43  communicating with the return channel  22  for the passage of the coolant F.       

     The cooling modules  37  are, therefore, assembled in succession with each other to form the cooling portion  10  based on the required plant capacity. 
     It is easy to appreciate that as the size of the cooling portion  10  increases, the sorting and separating portion  13  must also be suitably sized in order to allow for an effective screening of the recovery powder R. 
     To this end, the modular elements  32  also comprise sorting modules  41  that can be assembled together to define the sorting and separation portion  13 . 
     The central member  33  of the sorting modules  41  is provided with the holes  25  and the lateral faces  34  are open to allow the passage of the recovery powder R and of the waste product. 
     The collection means  26  and the containment system  28  are conveniently made to match the size of the sorting and separation portion  13 . 
     Conveniently, the modular elements  32  also comprise the inlet manifold  42 , which connects the loading portion  8  to a subsequent cooling module  37 , and the outlet manifold  47 , which connects the last of the cooling modules  37  to the first sorting module  41 . 
     Substantially, the inlet manifold  42  and the outlet manifold  47  define the cooling portion  10 , by limiting it, with the cooling modules  37 . 
     As shown in  FIG.  12   , the lateral face  34  of the inlet manifold  42  communicating with the loading portion  8  comprises a closing plate  38  provided only with the plurality of first openings  39  for the passage of the white slag S, corresponding to the number of treatment channels  11  and defining the supply ports  16 . 
     The opposite lateral face  34 , on the other hand, is similar to the cooling module  37 . 
     In the outlet manifold  47 , on the other hand, both lateral faces  34  are similar to those of the cooling module  37 , shown in  FIG.  10   . 
     In more detail, in the lateral face  34  communicating with the sorting module  41 , the first openings  39  allow the transfer of the recovery powder R and of the waste product inside the sorting modules  41 , while the third openings  43  are connectable to respective rotating discharge ducts to allow the discharge of the coolant F. 
     The operation of the plant  1  is as follows. 
     First, the supply is provided of the white slag S resulting from the steelmaking processes as well as the loading of the white slag S inside at least one treatment and recovery plant  1 . 
     Specifically, loading occurs inside the loading portion  8 . 
     Loading can be done by means known to the technician skilled in the art such as, e.g., an auger, a conveyor belt, an extractor, or other similar systems, which take the material, e.g., from a collection hopper, where the slag S still hot is initially stored. 
     The white slag S is then made to move forward along at least one direction of treatment D so as to generate at least one stream of white slag S and controlled cooling of the stream of white slag S so as to obtain a recovery powder R. 
     According to the invention, the loading comprises a stage of splitting the white slag S along a plurality of mutually separate streams of white slag S. 
     Cooling is carried out on each of the streams of white slag S using a heat exchange system of the indirect type. 
     The movement and cooling stages are carried out inside the cooling portion  10  thanks to the presence of the plurality of treatment channels  11 . 
     In particular, as described above, the splitting into multiple streams of white slag S occurs due to the rotation of the work chamber  3  during which the white slag S cyclically flows into one of the treatment channels  11 . 
     During the transit of the white slag S inside the treatment channels  11 , the coolant F transiting inside the return channel  22  arranged externally to the treatment channels themselves allows for a controlled cooling of the slag leading to the formation of the recovery powder R. 
     More particularly, as anticipated above, the coolant F is conveyed to the inlet manifold  42  by means of the delivery channel  21 , which is centrally arranged inside the work chamber  3 , and through the manifold itself it is conveyed along the return channel  22 . 
     Subsequently, and continuously, sorting and picking of the recovery powder R from the plant  1  are carried out. 
     This stage takes place inside the sorting and separation portion  13  and by means of the collection means  26 , the recovery powder R is collected and conveyed to any and further treatment and recovery stations. 
     It has in practice been ascertained that the described invention achieves the intended objects, and in particular the fact is emphasized that the plant for the treatment and recovery of white slag resulting from steelmaking processes according to the present invention allows optimizing the cooling process of the white slag, thus minimizing the plant dimensions. 
     In fact, the presence of a plurality of treatment channels allows splitting the white slag into several separate streams leading to an increase in the exchange surface between the white slag and the coolant. 
     The coolant supply system allows optimizing the compromise between energy efficiency and constructive simplicity. 
     In addition, the presence of a plurality of treatment channels allows the efficient and easy treatment of even large quantities of white slag. 
     Finally, the particular solution of having modular elements that can be assembled together allows the plant according to the invention to adapt easily to the production needs of the plant in which it is installed, while keeping its dimensions small.