Apparatus, system and method for reducing foam in a foamy metallurgical slag

Abstract

An apparatus (10) for the reduction of foam in a foaming metallurgical slag, comprising at least one electrical signal generator (12), a sound wave emitter unit (11) comprising at least one pair of emitters (13), each of which comprises a transducer (14) connected to the generator (12) and configured to convert the electrical signals generated by the generator (12) into mechanical vibrations along a vibration direction (X) and a mechanical amplifier (15) connected to the transducer (14) and configured to amplify the amplitude of the mechanical vibrations by generating sound waves along a respective preferential propagation direction (Y), and an electronic control unit (16) of the emitter unit (11) and of the generator (12), wherein the emitters (13) are arranged in such a way that the respective preferential propagation directions (Y) converge at a single intersection point (F). Said apparatus (10) is arranged close to a mass of foaming metallurgical slag in such a way that said intersection point (F) is close to the surface of the foaming metallurgical slag and the electronic control unit (16) controls the emitter unit (11) and / or the generator (12) in such a way that the emitters (13) of at least one pair of emitters emit sound waves having frequencies that differ from each other by a maximum of 5%.

Description

[0001] APPARATUS , SYSTEM AND METHOD FOR REDUCING FOAM IN A

[0002] FOAMY METALLURGICAL SLAG

[0003] The present invention relates to an apparatus , a system and a method for the reduction of foam in a foaming metallurgical slag .

[0004] The present invention relates in particular to an apparatus , a system and a method for breaking down foam in a foaming metallurgical slag, in particular steel mill foaming slag at a high temperature ( close to 1600 ° C ) , by means of high frequency ( sound) mechanical waves , preferably higher than 1 kHz , even more preferably at frequency in the field of ultrasound .

[0005] As known, metallurgical slag is a by-product o f steel production . It is produced when the impurities present in the raw materials ( iron ore , coke and fluxing agents included) are separated from the molten steel . The impurities , combined with other materials such as lime and dolomite , form a slag that floats on top of the molten steel and can be removed . During the steel production process , in particular by melting scrap and ferrous materials in an electric arc furnace (EAF) , about 200 kg of slag are produced per each tonne of steel which, immediately at the exit of the furnace , has a temperature close to or above 1600 ° C .

[0006] Slag foaming is an essential phenomenon in the steelmaking process , particularly in the electric arc furnaces (EAFs ) . The formation o f a foaming slag layer covering the molten steel bath has , in fact , numerous operational and economic advantages .

[0007] Equally important is the slagging step, that is , the step of removing the slag from the molten steel and which, generally, takes place by pouring the slag into a slag pot .

[0008] It is not uncommon for an overflow of slag to occur , which happens when the volume of the foaming slag exceeds the containment capacity of the furnace or slag pot or in general of the container in which the slag is poured . Several factors can contribute to this :

[0009] Excessive gas generation : after the slag is poured into the slag pot , some chemical reactions may still occur with gas formation which, in turn, may lead to an uncontrollable increase in slag volume .

[0010] Inadequate foam control : insuf ficient monitoring and control of the slag foaming parameters - such as viscosity, surface tension and temperature - can lead to excessive foaming that remains even during the slagging process .

[0011] Overflow of the slag from the slag pot can cause damage to workers and the surrounding environment ( e . g . fires in the slag handling area ) ; damage which, in turn, can lead to a plant shutdown with consequent nonproduction and economic damage .

[0012] Due to its high temperature and low viscosity, foaming metallurgical slag is a di f ficult material to handle .

[0013] Current anti- foaming methods , i . e . for the reduction or breaking down of the foaming metallurgical slag, are based on the use of sand and water .

[0014] Water in the liquid state is highly dangerous i f used close to an electric arc furnace : when a certain amount of water is accidentally enclosed in a volume of metal or liquid slag at high temperature , it vapori zes very quickly with consequent sudden expansion of volume , which can cause violent explosions . Rapid expansion can ej ect molten metal and other materials at high speed into the surrounding environment , posing serious risks of inj ury to nearby workers and causing extensive damage to surrounding equipment .

[0015] Sand is a valid alternative to water, but , i f used improperly, it can have unwanted side ef fects : the addition of too much sand can alter the overall composition of the slag, potentially af fecting its properties and behaviour . Metallurgical slag, in fact , has become a product subj ect to recycling; therefore , it is important to control its properties . The addition of sand could alter the final properties of the slag making it a waste unsuitable for recycling .

[0016] In order not to use sand or water, some steel mills opt for a partial filling of the slag pots with consequent loss of productivity and higher investment and plant management complexity due to the need to use larger slag pots and / or a greater number of slag pots for slag management .

[0017] Uses of ultrasound to reduce the development of foams in various application areas are known .

[0018] Document CN203846022U describes a system, based on ultrasound, for breaking down foam in a fermentation tank .

[0019] Document CN107058654A describes a system for treating blast furnace slag with rapid cooling in water ; the system comprises ultrasonic emitters immersed in the water bath and cooled slag .

[0020] Some experimental studies on the ef fects of ultrasound applied to test foams to simulate metallurgical slag are also known : "Control of Foam Height by Using Sound Waves" [ISIJ International, Vol. 39 (1999) , No. 12, pp . 1207-1216] , "Suppression of Slag Foaming under Sound Wave Application" [ISIJ International, Vol. 40 (2000) , No. 5, pp . 431-437] , both by Komarov, Kuwabara, Sano.

[0021] The object of the present invention is therefore to provide an apparatus, a system and a method for the reduction of foam in a foaming metallurgical slag which overcome the problems of the prior art.

[0022] Within this general object, a particular object of the present invention is to provide an apparatus, a system and a method for the reduction of foam in a foaming metallurgical slag which are effective in reducing (breaking down) the foaming metallurgical slag, reducing or eliminating the problems related, in particular, to the use of water or sand and which are industrially applicable for the management of foaming metallurgical slag even at high temperature (e.g. close to or above 1600 °C) .

[0023] These objects are achieved with an apparatus, a system and a method for the reduction of foam in a foaming metallurgical slag as set forth in the independent claims.

[0024] Further features are comprised in the dependent claims .

[0025] The features and advantages of an apparatus, a system and a method for the reduction of foam in a foaming metallurgical slag according to the present invention will become more apparent from the following description, by way of non-limiting example, referring to the accompanying schematic drawings in which: figure 1A schematically shows a first possible embodiment of a system according to the present invention; figure IB schematically shows a second possible embodiment of a system according to the present invention; figure 1C schematically shows a third possible embodiment of a system according to the present invention; figure 2 schematically shows a detail of a possible emitter unit and of a generator of the apparatus according to the present invention; figure 3 shows a first possible embodiment of a mechanical ampli fier accompanying an emitter o f the emitter unit of the apparatus according to the present invention; figure 4A schematically shows a possible embodiment of a support structure of an emitter unit of the apparatus according to the present invention; figure 4B schematically shows a possible alternative embodiment of a support structure of an emitter unit of the apparatus according to the present invention; figure 5 schematically shows a possible arrangement of a pair of emitters of an emitter unit of the apparatus according to the present invention; figures 6 and 7 are similar to f igure 2 from which they di f fer in the embodiment of the mechanical ampli fier that accompanies an emitter ; figure 8 shows a further possible arrangement of a plurality of emitters of an emitter unit of the apparatus according to the present invention; figure 9 is a schematic representation of the arrangement of emitters referred to in figure 8 ; figure 10 is a diagram showing the sound pressure field ( dB ) generated by a single emitter of the type depicted in figures 2 and 3 as a function of the distance (m) from the latter ; figure 11 is a diagram showing the sound pressure field ( dB ) generated by a pair of emitters of the type depicted in figures 2 and 3 that cooperate with each other according to the invention as a function of the distance (m) from the latter ; figure 12 is a diagram showing the sound pressure field ( dB ) generated by a plurality of emitters of the type shown in figures 8 and 9 that cooperate with each other according to the invention as a function of the distance (m) from the latter ; figure 13 schematically shows a further possible embodiment of a system according to the present invention; figure 14 shows , in orthogonal and axonometric views , a possible waveguide which can be associated with an ampli fier that accompanies an emitter ; figure 15 shows a longitudinal section according to plane A-A of figure 14 of a waveguide associated with an amp 1 i f i e r .

[0026] The apparatus , the system and the method for the reduction of foam in a foaming metallurgical slag according to the present invention are based on the generation of mechanical ( sound) waves at high frequency, preferably higher than 1 kHz , even more preferably at frequency in the f ield of ultrasound, to break the gas bubbles present in foaming metallurgical slag . Foaming metallurgical slag means any slag produced in metallurgical processes that , in addition to one or more liquid phases , has a signi ficant presence of a gaseous phase inside it in the form of gas bubbles trapped in the liquid phases . Foaming slag is a typical by-product of the steelmaking processes in electric arc furnace (EAF) . The composition of the slag in this case is normally according to the following ranges : Calcium oxide ( CaO) : ~30-50% Iron oxide ( FeO / Fe2O3) : ~ 10-40% Silicon oxide ( SiO2) : ~ 10-20% Magnesium oxide (MgO) : ~5- 15% Manganese oxide (MnO) : ~3- 8% Aluminium oxide (A12O3) : ~2- 8 %

[0027] The viscosity is highly temperature-dependent , in particular decreasing with increasing temperature ; for example , at a temperature of 1600 ° C, the viscos ity is less than 100 cPs [ centi-Poise ] .

[0028] The surface tension is also temperature-dependent and is around 500 - 700 mN / m close to 1500 ° C .

[0029] The apparatus , the system and the method according to the present invention are in any case applicable for reducing (breaking down) foaming slag produced in other metallurgical processes .

[0030] The apparatus according to the present invention comprises a sound wave emitter unit provided with a plurality of sound wave emitters arranged close to the foaming metallurgical slag to be treated, where "close to" means a distance in the order of a few meters , for example less than 5 meters .

[0031] These emitters vibrate with a frequency preferably comprised between 1 kHz and 1 MHz .

[0032] The emitters are arranged so as to increase the magnitude of their ef fect on the gas bubbles present in the slag to be treated .

[0033] As will become clearer hereinafter, the arrangement of the emitter unit and / or of the emitters composing it may be changed during operation of the apparatus according to the present invention . In particular, it is possible to change the spatial orientation of the emitter unit as a whole and / or of one or more emitters that compose it ; it is equally possible to change the distance from the surface of the slag to be treated of the emitter unit as a whole and / or of one or more of the emitters that compose it individually or as a whole .

[0034] The emitter unit as a whole and / or the emitters that compose it can be moved by translation and / or rotation, respectively along at least one direction and around at least one axis or centre of rotation, so that the ef fect of the sound waves on the gas bubbles present in the slag to be treated can be distributed over the entire surface of the slag to be treated, for example according to a speci fic path that accentuates the destruction thereof .

[0035] As will become clearer from the detailed description below, according to the present invention two or more emitters may be arranged to cooperate with each other so as to generate sound wave fields such that there are multiple zones in which the sound waves create constructive interference ( focuses ) .

[0036] The emitters can be switched on with an alternating pattern .

[0037] As detailed further below, moreover, the emitter unit is configured in such a way that the components thereof - and, in particular, each emitter - are protected from the risks of overheating and from the irradiation produced by the slag . In particular, there is provided a protective casing for the emitters , individually or as a whole , which is structured to allow the free emission and transmission of the sound waves . The protective casing, in particular, is structured to house or otherwise shield the emitters , individually or as a whole , except for the ampli fier that accompanies each of them .

[0038] Advantageously, a cooling circuit for the emitter unit and / or the emitters that compose it is provided .

[0039] The apparatus according to the present invention is then preferably provided with a unit for detecting and / or measuring at least one parameter of the foaming metallurgical slag which is in signal communication with a control unit configured to control the emitter unit as a function of the detected or measured parameters .

[0040] Advantageously, such a detection and / or measurement unit can be installed in the aforementioned protective casing or can be installed externally thereto and, in this case , preferably provided with its own overheating and irradiation protection housing .

[0041] Such a detection and / or measurement unit may comprise one or more detection and / or measurement devices including, for example , an optical camera, an optical pyrometer or a laser . The data collected by such a detection and / or measurement unit may include , for example , images , both in the visible and in the infrared or ultraviolet field, which, when analysed, make it possible to obtain estimates of slag temperature , irradiation intensity, distance between it and the surface of the slag .

[0042] The electronic control unit with which the apparatus according to the present invention is provided receives the signals from the detection and / or measurement unit and, through processing and control algorithms , controls the emitter unit and / or other components of the apparatus by setting, for example , the switching on of one or more emitters only after the distance meter reading is falling below a certain threshold ( for example because a phenomenon of swelling of the slag is occurring, thus leading to an increase in the level of the slag and therefore to a decrease in the distance between the surface of the slag and the emitter unit ) , or by sending an alert signal suggesting to move the apparatus away from the slag i f a too high emissivity has been measured .

[0043] With reference to the attached figures , an apparatus for the reduction of foam in a foaming metallurgical slag, in particular a high temperature foaming metallurgical slag and even more in particular a foaming metallurgical slag at a temperature close to 1600 ° C resulting from a steel production process conducted in an electric arc furnace (EAF) has been indicated with the reference number 10 .

[0044] The apparatus 10 comprises :

[0045] - at least one generator 12 of electrical signals ;

[0046] - a sound wave emitter unit 11 which, in turn, comprises :

[0047] - at least one pair of emitters 13 , each of which is configured to generate sound waves and comprises a transducer 14 or converter connected to the generator 12 and configured to convert the electrical signals generated by the generator 12 into mechanical vibrations along a vibration direction X and a mechanical ampl i fier 15 connected to the transducer 14 and configured to ampli fy the amplitude of said mechanical vibrations by generating sound waves along a respective preferential propagation direction Y; and

[0048] - an electronic control unit 16 for controlling the emitter unit 11 and the generator 12 .

[0049] The emitters 13 are arranged in such a way that the respective preferential propagation directions Y converge at a single intersection point F close to the surface of the foaming metallurgical slag to be treated (hereinafter referred to as " slag S" ) . As will be illustrated below, a high sound pressure zone Z is created around the intersection point F and with dimensions in the order of those of the ampli fiers 15 used : this zone Z is arranged at the foaming metallurgical slag to be broken down .

[0050] Preferably, the emitters 13 are all the same between them .

[0051] The transducer ( converter ) 14 of each emitter 13 is connected to the generator 12 by means of a cable 18 .

[0052] The generator 12 may be a generator that is common to two or more emitters 13 or one or more emitters 13 , advantageously each of them, may comprise its respective own generator 12 .

[0053] In other words , the emitters 13 can each be connected to a generator 12 dedicated to the single emitter 13 , where each generator 12 is controlled by the electronic control unit 16 . Alternatively, two or more , advantageously, all emitters 13 can be connected to a single common generator 12 , so that the same law of motion is applied to each of them simultaneously, thus creating constructive ( or destructive , depending on the point in space ) interference phenomena .

[0054] The generator 12 is connected to the electronic control unit 16 and supplies electrical energy to the transducer 14 of each emitter 13 by means of an electrical cable 18 . The electric cable 18 can have a length also in the order of 5 m a 10 m, so as to be able to arrange the generator or generators 12 even at a considerable distance from the emitters 13 . The total power supplied to each transducer 14 may range from 1 kW to tens of kW, for example up to 20 kW .

[0055] Optionally, the generator ( s ) 12 are integrated into the electronic control unit 16 , or within the emitter unit 11 .

[0056] The transducer 14 is configured to convert the electrical signals generated by the generator 12 into mechanical vibrations along a vibration direction X . The transducer 14 may for example be of the piezoelectric type .

[0057] The mechanical vibration generated by the transducer 14 is transmitted to the ampli fier 15 which vibrates following a speci fic way of vibrating, linked both to the law of motion ( i . e . the displacement as a function of time ) imposed by the transducer 14 , and to the intrinsic characteristics of the ampli fier itsel f ( in particular shape and material , which determine the frequency response of the amplifier itsel f ) . In this way, the ampli fier 15 is able to improve the transmission of the sound waves towards the surrounding ( fluid) medium and greatly increase the sound pressure level .

[0058] Preferably, at least one and, advantageously, each emitter 13 is orientable with respect to a respective axis or centre of rotation schematized by the pin or joint 17 to vary the distance or in general the position in space of the intersection point F from the emitters themselves .

[0059] In this case, one or more actuators (not depicted) configured to move the emitters 13 with respect to the respective axis or centre of rotation 17 are provided.

[0060] The possibility of rotating the emitters 13 allows to change the mutual orientation of the same in order to meet different process needs, as better specified below.

[0061] It is noted for example that, depending on the type of mechanical amplifier 15 adopted, the propagation of the sound waves is different.

[0062] Figures 1 to 5 show a first possible embodiment of the mechanical amplifier 15 of the plate or rather disc type and detailed further below.

[0063] In this case, as shown in figure 3, the preferential propagation direction Y of the waves coincides with the central axis of the plate.

[0064] Figure 10 shows a diagram showing the trend of the sound pressure field generated by an emitter 13 with a discoidal plate amplifier 15 of the type as the one depicted in figure 3 (the amplifier is located on the lower edge of the diagram of figure 10) . As visible, the sound pressure decreases significantly moving away from the axis Y; moreover, the pressure decreases moving away from the amplifier 15 itself, so that at a distance from the amplifier 15 equal to about twice its diameter the sound pressure decreases by about 20dB with respect to the maximum value.

[0065] By arranging two emitters 13 as schematized in figure 5 , i . e . in such a way that the respective preferential propagation directions Y of the waves intersect at a point F, it is possible to generate a particularly ef fective interference between the two wave fields generated by the two emitters 13 themselves . Furthermore , by appropriately controlling the generator ( s ) 12 , it is possible to ensure that the two fields generate constructive interference , obtainable when the waves generated at point F by the two emitters 13 are in phase with each other . As clearly intuitive from figure 5 , depending on the angle delimited by the two preferential propagation directions Y, the intersection point F can be moved closer to or away from the emitters 13 and, therefore , from the emitter unit 11 . In particular, the width of this angle can be chosen so that the intersection point F is close to the slag surface S , as better detailed below .

[0066] The synergistic ef fect between a plurality of emitters 13 is clearly visible in figure 11 , which represents the trend of the sound pressure field generated by two emitters 13 with discoidal plate ampli fiers 15 equal to those referred to in figure 3 and oriented so as to converge the respective preferential propagation directions Y at a single intersection point F ( it should be noted that figures 10 and 11 have di f ferent representation scales ) . As can be seen, a zone Z of maximum sound pressure is created which is signi ficantly further away from the ampli fiers 15 , as well as being wider in terms of volume , than that of figure 10 for the case with only one emitter 13 .

[0067] Such a synergistic ef fect is also depicted in figure 12 which represents the trend of the sound pressure field generated by a plurality ( five ) emitters 13 with discoidal plate ampli fiers 15 identical to those in figure 3 and oriented so as to converge the respective preferential propagation directions Y at a single intersection point F as shown in figures 8 and 9 . Also in this case , as can be seen, a zone Z of maximum sound pressure is created which is signi ficantly further away from the ampli fiers 15 , as well as being wider in terms of volume , than that of figure 10 for the case with only one emitter 13 .

[0068] With reference to figures 8 and 9 , it can be noted that the emitters 13 are arranged symmetrically with respect to one or more planes of symmetry, the traces of which are shown in Figure 9 .

[0069] The proximity of the intersection point F to the slag mentioned above consists in the fact that the high- pressure zone Z is located at or immediately below the surface of the foaming slag to be treated .

[0070] Therefore , according to the invention, the emitters 13 are at least two and are arranged in such a way that the respective preferential propagation directions Y mutually intersect at a single intersection point F .

[0071] Preferably, moreover, the distance between each ampli fier 15 and the intersection point F is substantially the same for all emitters 13 . The ampli fiers 15 of each emitter 13 are equidistant from the intersection point F .

[0072] Preferably, the intersection point F is arranged close to the surface of the foaming slag to be treated, in the sense described above .

[0073] Preferably, the emitters 13 are arranged symmetrically with respect to an axis or a plane of symmetry passing through the intersection point F, and, in the case of emitters 13 whose propagation directions Y all reside in a single plane , they are symmetrically arranged with respect to a plane of symmetry perpendicular to the plane in which the propagation directions Y lie .

[0074] Preferably, at least one plane of symmetry is vertical , i . e . perpendicular to the surface of the slag S .

[0075] Preferably, the apparatus 10 comprises a unit for detecting and / or measuring 19 of at least one parameter of the slag S that is in signal communication with the control unit 16 , wherein the control unit 16 is configured to control the emitter unit 11 and the generator ( s ) 12 as a function of said at least one parameter .

[0076] The detection and / or measurement unit 19 may comprise one or more detection devices or sensors , including, for example : an optical camera, an optical pyrometer, a laser . The information that the detection and / or measurement unit 19 is able to detect , or that can be obtained by analysis of the detected or measured data, may comprise : slag temperature , irradiation intensity, distance from the unit for detecting and / or measuring it , level of the slag S within the cauldron or slagging channel , and any further information about the slag S that can be detected by image acquisition and processing, even outside the visible spectrum . This allows , among other things , to avoid exposure of human operators to the environment near the slag S .

[0077] The detection and / or measurement unit 19 may emit and / or receive signals 19 ' ( e . g . images in and / or out of the visible spectrum) .

[0078] Advantageously, the detection and / or measurement unit 19 is arranged in a protective housing uniquely intended for it or which can be obtained in a protective casing of the emitters 13 as described further below . Such a protective housing can advantageously be provided with an opening that can possibly be closed of f by a wall capable of letting through the signals 19 ' made , for example , of glass . The detection and / or measurement unit 19 is then preferably associated with a cooling circuit , which may be dedicated to it or which may be derived or part of the cooling circuit 112 of the emitters 13 as described below, so as to prevent the electrical / electronic circuits from being damaged due to the high temperatures to which the apparatus 10 may be exposed .

[0079] The detection and / or measurement unit 19 can be arranged on the plane of symmetry according to which the emitters 13 can be arranged, or on a plane of nonsymmetry .

[0080] The detection and / or measurement unit 19 receives the signals 19 ' and, by means of internal logics , i . e . processing and / or control algorithms , can cooperate with the electronic control unit 16 so that the apparatus 10 operates autonomously and smartly, for example , by activating the switching on of the emitter unit 11 only after the distance meter reading is falling below a certain threshold ( indicative of the fact that the level of the foaming slag has exceeded a predetermined threshold) , or by sending a danger signal warning to move the apparatus 10 away from the slag S after measuring a too high emissivity . In a preferred embodiment ( figures 2 and 3 ) , the mechanical ampli fier 15 consists of a plate 150 , preferably a disc of circular shape , provided with a central axis substantially orthogonal thereto and arranged substantially coaxial to the vibration direction X of the respective transducer 14 . In such a case , the preferential propagation direction Y is defined by the central axis of the plate 150 .

[0081] The plate 150 is rigidly connected, in its central part , to the movable part of the transducer 14 , so that the central axis of the plate 150 coincides with the vibration direction X of the transducer 14 .

[0082] Preferably, the plate 150 is made of titanium or its alloys .

[0083] Preferably, the plate 150 has , on at least one of the flat faces , a series of circumferential protuberances 1500 concentric to the central axis o f the plate 150 itsel f , so as to create a pattern of valleys and peaks . The protuberances 1500 may have a crosssection such as triangular, rectangular, with any chamfers or fillets . For greater ef ficiency, the protuberances 1500 are made on the face of the plate 150 facing the slag S .

[0084] This first embodiment of the mechanical ampli fier 15 is preferred because , compared to the embodiments described below, it is characteri zed by particular constructional simplicity, compactness , adaptability to the cooling system, as well as generating a more ef fective pressure field for the intended purpose .

[0085] In a possible alternative embodiment ( figure 6 ) the ampli fier 15 of the mechanical type consists of a hornshaped element 151 with a longitudinal central axis coaxial to the vibration direction X of the respective transducer 14 . In this case , therefore , the preferential propagation direction Y is defined by the longitudinal central axis of the horn-shaped element 151 . The hornshaped element 151 consists of a metal sheet and has , for example , an exponential course ( i . e . in which the horn section has an area proportional to the exponential of the distance from the bottom section) , with a cylindrical or square section, developing along an axis with a shorter base and a greater base , wherein at its shorter base it is constrained to the movable part of the transducer 14 in such a way that the longitudinal central axis of the horn coincides with the vibration direction X in turn defining the preferential propagation direction Y . The considerations and configurations described above in relation to the shape of the plate ampli fier 15 also apply in relation to an ampli fier 15 consisting of a horn-shaped element 151 .

[0086] In a further possible alternative embodiment ( figure 7 ) the ampli fier 15 of the mechanical type consists of a plate 152 having a central axis orthogonal thereto and coaxial to the vibration direction X of the respective transducer 14 , wherein said plate 152 is arranged in the centre of a reflector 153 provided with two reflecting surfaces 153a, 153b each forming an angle of 45 ° with the plane defined by the plate 152 , wherein the preferential propagation direction Y is defined by an axis of symmetry of the reflector 153 or rather by an axis belonging to the plane of symmetry of the reflector 153 (plane along which the plate 152 lies ) and which is orthogonal to the vibration direction X .

[0087] Preferably, the plate 152 is rectangular . The sound waves generated by the vibration of the plate 153 , oscillating along the vibration direction X of the transducer 14 , are deflected by 90 ° from the inner surfaces of the walls 153a, 153b of the reflector 153 and exit therefrom along the preferential propagation direction Y defined by an axis of symmetry of the reflector 153 . The considerations and configurations described above in relation to the shape of the plate ampli fier 15 also apply in relation to an ampli f ier 15 consisting of a plate 152 arranged along a plane of symmetry of a reflector 153 as described above .

[0088] Preferably, the emitter unit 11 comprises a support structure 110 of the emitters 13 and at least one protective casing 111 , 111 ' at least of the transducers 14 of the emitters 13 , individually or as a whole , which is obtained in the support structure 110 or associated with the support structure 110 .

[0089] The generator ( s ) 12 may be supported by the same support structure 110 and, advantageously, housed in the protective casing 111 , 111 ' or may be mounted on a separate support and / or containment and protective structure .

[0090] Preferably, there is provided at least one cooling circuit 112 for cooling the emitters 13 , wherein the cooling circuit 112 is obtained in the protective casing 111 , 111 ' or associated with the protective casing 111 , 111 ' .

[0091] Figure 4A shows a first embodiment in which the support structure 110 is shaped to constitute itsel f a single protective casing 111 defining a housing inside which the transducers 14 of all emitters 13 are housed, each of which proj ects outside the protective casing 111 through a respective through opening 1111 so that the respective ampli fier 15 is arranged outside the protective casing 111 . In a possible alternative embodiment , a single through opening 1111 common to two or more , advantageously all , emitters 13 may be provided .

[0092] The protective casing 111 is structured and / or made so as to thermally insulate the components of the emitter unit 11 housed therein . The apparatus 10 , in fact , is intended to be positioned close to foaming metallurgical slag S which, generally, is at high temperatures close to or even higher than 1600 ° C, in particular when j ust tapped from a furnace , thus constituting a relevant source of irradiation towards the emitter unit 11 .

[0093] In this embodiment , therefore , the support structure 110 has both structural functions , in fact the emitters 13 are coupled to it , and protective functions , in fact it is itsel f structured and shaped so as to create a protective casing 111 having, in particular, thermal insulation properties .

[0094] Preferably, the cooling circuit 112 comprises an inlet 1120 through which a cooling fluid CF ( e . g . air ) is introduced into the protective casing 111 . The cooling fluid introduced into the protective casing 111 leaks towards the external environment through the through opening ( s ) 1111 so as to perform a cooling action by forced convection of the ampli fiers 15 .

[0095] Preferably, the detection and / or measurement unit 19 is housed inside the same protective casing 111 which, in correspondence thereof , can be provided with a window 1112 made of material transparent to the exchanged signals . The detection and / or measurement unit 19 can alternatively be arranged externally to the protective casing 111 and, advantageously, housed in its own protective housing .

[0096] Figure 4B shows a possible alternative embodiment in which the support structure 110 has a structural function, on which, in fact , the emitters 13 and the components of the cooling circuit 112 are mounted . In this case , each emitter 13 is provided with its own protective casing 111 ' formed for example by a tubular j acket that houses the respective transducer 14 ( as well as the cables that connect it to the generator ) and externally to which the corresponding ampli fier 15 is arranged .

[0097] In this case , the cooling circuit 112 provides a cooling fluid supply duct 1121 from which a plurality of branch ducts 1122 branch of f and open into a plurality of distributors 1123 , each of which is coupled to a respective protective casing 111 ' and is provided with one or more ori fices for the exit of the cooling fluid through them towards the ampli fier 15 of the corresponding emitter 13 .

[0098] As mentioned above , the apparatus 10 is configured to generate sound waves USW and direct them, for example , towards the slag S whose volume is to be reduced by reducing (breaking down) the foam present therein . The slag S can be contained in a slag pot 20 or flow along the channel 21 for example a slagging channel of a furnace .

[0099] To this end, the apparatus 10 is configured to be fixedly or movably arranged close to a slag pot 20 or an outflow channel 21 .

[0100] Advantageously, therefore , the apparatus 10 comprises an assembly of support and movement 22 of the emitter unit 11 in translation and / or rotation along at least one translation direction and around at least one axis or centre of rotation, respectively .

[0101] Preferably, the support and movement assembly 22 comprises a trolley 221 or in any case a vehicle or a translation system along one or more directions on which the emitter unit 11 is mounted . The trolley 221 may be configured to approach the out flow channel 21 , as schematically depicted in Figure IB, or to approach the flow of slag that descends downward by gravity in the air after leaving the outf low channel 21 , as schematically depicted in figure 1C .

[0102] Preferably, the support and movement assembly 22 comprises a kinematic mechanism 222 configured to rotate the emitter unit 11 around at least one rotation axis . In the exempli fied embodiment , this kinematic mechanism 222 comprises an upright 223 integral with the trolley 221 and at the top of which the emitter unit 11 is rotatably articulated around a hori zontal hinge axis and at least one linear actuator 224 that acts between the trolley 221 and the emitter unit 11 to move the latter around said hinge axis .

[0103] However, the possibility that the emitter unit 11 , i . e . the support structure 110 is fixed and rigidly constrained to the ground or to another available fixed structure is not excluded .

[0104] Preferably, the apparatus 10 comprises a suction unit configured to suck the gases released by the treated slag, including, in particular CO, so as to limit their release into the environment .

[0105] In a further embodiment , shown schematically in Figure 13 , a waveguide 1140 is associated with each ampli fier 15 . The waveguide 1140 is preferably detached from the respective ampli fier 15 , therefore from its vibrations , and is supported by special structures (not shown in Figure 13 ) in turn constrained to the support structure 110 and / or to the protective casing 111 . Alternatively, the waveguide 1140 can be an integral part of each ampli fier 15 . The waveguide 1140 generally consists of an internally hollow cylindrical body of preferably circular section, made so as to withstand the thermal load due to irradiation from the liquid slag S , for example by air cooling, or by making the structure of refractory material . The waveguide 1140 develops along a longitudinal axis A advantageously straight and substantially coincident with the preferential propagation direction Y of the respective ampli fier 15 . The waveguide 1140 is positioned close to the ampli fier 15 downstream thereof towards the intersection point F, i . e . on the side of the ampli fier 15 facing the slag S to be treated . As depicted in Figure 14 , the waveguide 1140 generally has at least one cylindrical section with a constant cross-section 1140a ; preferably, two respective converging / diverging sections 1140b, 1140c are also present at its ends . As schematically shown in Figure 15 , the waveguide 1140 allows the sound waves emitted by the ampli fier 15 to be conveyed along its own axis : the conveyed sound waves re-emerge at the end of the waveguide 1140 opposite to the one close to which the respective ampli fier 15 is positioned . The use of waveguides 1140 allows to further increase the sound pressure at the intersection point F, to move the emitter unit 11 away thus decreasing the irradiation suf fered by it , and to limit the di f fusion of the sound waves to the surrounding environment . The same waveguides 1140 may be applied in a manner analogous to the embodiments depicted in figures IB and 1C .

[0106] The present invention also relates to a system comprising an apparatus 10 as described above associated with a containment vessel or a channel of outflow of a mass of slag to be treated .

[0107] The present invention also relates to a method for the reduction of foam in a foaming metallurgical slag comprising at least the steps of : a ) providing an apparatus 10 for the reduction o f foam in a foaming metallurgical slag as described above ; b ) arranging said apparatus 10 close to a mass of foaming metallurgical slag S , whether contained in a slag pot 20 or flowing along an outflow channel 21 , for example a slagging channel , or flowing by gravity in the air after leaving said outflow channel 21 , in such a way that the intersection point F between the preferential propagation directions Y of the sound waves generated by two or more emitters 13 is close to the surface of the slag S ; c ) controlling by means of the control unit 16 the emitter unit 11 and / or the generator or the generators 12 in such a way that the emitters 13 of at least one pair of emitters emit sound waves having frequencies that di f fer from each other by a maximum of 5% , preferably by 1 % , even more preferably by 0 . 1 % .

[0108] Preferably, the control unit 16 controls the emitter unit 11 and / or the generator ( s ) 12 in such a way that the emitters 13 of at least one pair of emitters emit sound waves in phase between them at the intersection point F of the respective preferential propagation directions Y so that the sound waves generated by them are constructively interfering with each other at the intersection point F .

[0109] It is noted that the distance between the emitters 13 and the intersection point F plays an important role because , as illustrated above , the sound waves create a constructive interference at a particular point ( focus ) placed at a certain distance from the ampli fier . It is possible to change the angle o f inclination o f the emitters 13 so as to vary the position in space of the intersection point F .

[0110] The control unit 16 controls the emitter unit 11 and / or the generators 12 to generate sound waves . The waves generated will have a certain frequency and a certain level of sound pressure , correlated to the electrical power supplied to the generator 12 and the geometry of the ampli fiers 15 .

[0111] The frequency of the waves generated by each emitter 13 must di f fer from the frequency of the waves generated by the other emitters by less than 5% / 1 % / 0 . 1 % .

[0112] The sound pressure generated around the intersection point F may be greater than 140 dB, preferably greater than 160 dB .

[0113] The power of the electrical signal generator 12 is preferably at least 1 kW .

[0114] The emitter unit 11 must be oriented in such a way that the sound waves are directed towards the slag S .

[0115] The emitter unit 11 is positioned in such a way that the intersection point F is located close to the surface of the slag to be treated, i . e . in such a way that the respective high-pressure zone Z generated by it is located at or immediately below the surface of the foaming slag to be treated .

[0116] The time in which the emitter unit 11 is active and stationary depends on the extent of the collapsing ef fect that the sound waves have on the gas bubbles present in the slag S .

[0117] The sound waves exert a force on the slag S correlated to the oscillation of the fluid ( air ) in which they propagate . I f an assembly o f support and movement of the emitter unit 11 is provided, it is possible to orient and / or move the emitter unit 11 in such a way that the ef fects of the force described above are applied along a path having a desired course ( for example l inear, circular, spiral ) , so as to optimi ze the break-down ef fect .

[0118] The sound waves reach the surface of the layer of slag S and induce sudden pressure changes on the gas bubbles present in it that alternate cycles of high pressure ( compression) and low pressure ( rarefaction) in the liquid .

[0119] Microscopic bubbles or cavities form during low pressure cycles . These bubbles grow in successive cycles due to the continuous inflow of gas or steam . When the bubbles reach a critical si ze , the high-pressure cycles cause them to implode violently . This collapse generates intense local pressure and temperature spikes , as well as strong shock waves . The rapid bubble collapse can create locali zed hot spots with very high temperatures , which can drastically decrease the viscosity and thus can help break down and disperse gas or steam in the bubbles . I f the breakage of the bubbles generates a suf ficiently strong shock wave , the balance between liquid and bubbles can collapse and this ef fect can propagate throughout the fluid, contributing to the collapse of the entire foam structure .

[0120] The present invention has the following advantages :

[0121] - It allows to obtain a rapid and ef fective decomposition of the gas bubbles present in foaming metallurgical slag with a consequent faster and more ef ficient de- foaming ef fect .

[0122] - It allows to minimi ze or eliminate the need for the use of chemical anti- foaming agents , reducing the costs associated with their use and the risks of potential contamination .

[0123] - It allows to reduce the risk of explosions and other hazards associated with the manipulation of foaming metallurgical slag by quickly collapsing the gas bubbles in them and releasing the gases trapped in them (mainly CO2 , with traces of CO) .

[0124] - It allows to reduce the operating costs and energy consumption by reducing the frequency with which the slag pots have to be moved or to proceed with slagging or with which manual interventions are necessary for slag management . This ensures smooth operation of the metallurgical furnaces .

[0125] - It allows to reduce the total amount of slag produced, decreasing the amount of material added ( e . g . sand) to the slag itsel f for its control , contributing to better safeguarding the environment .

[0126] It allows to reduce the variance of metallurgical processes by eliminating the use of material added to slag .

[0127] Finally, it is clear that the apparatus and the method thus conceived is susceptible of numerous modi fications and variations , all of which are within the scope of the invention; moreover, all the details can be replaced by technically equivalent elements . In practice , the materials used, as well as their dimensions , can be of any type according to the technical requirements .

Claims

CLAIMS1) Apparatus (10) for the reduction of foam in a foaming metallurgical slag, comprising:- at least one generator (12) of electrical signals;- a sound wave emitter unit (11) comprising:- at least one pair of emitters (13) , each of which comprises a transducer (14) connected to said generator (12) and configured to convert the electrical signals generated by said generator (12) into mechanical vibrations along a vibration direction (X) and a mechanical amplifier (15) connected to said transducer (14) and configured to amplify the amplitude of said mechanical vibrations by generating sound waves along a respective preferential propagation direction (Y) ; and- an electronic control unit (16) of said emitter unit (11) and of said generator (12) ;- wherein said emitters (13) are arranged in such a way that said respective preferential propagation directions (Y) converge at a single intersection point (F) .2) Apparatus (10) for the reduction of foam in a foaming metallurgical slag according to claim 1, wherein the mechanical amplifiers (15) of each of said emitters (13) are equidistant from said intersection point (F) .3) Apparatus (10) for the reduction of foam in a foaming metallurgical slag according to claim 1 or 2, wherein said emitters (13) are arranged symmetrically with respect to an axis or a plane of symmetry passing through said intersection point (F) .4) Apparatus (10) for the reduction of foam in a foaming metallurgical slag according to claim 3, wherein the respective preferential propagation directions (Y) of said emitters (13) reside in a single plane and whereinsaid emitters (13) are arranged symmetrically with respect to a plane of symmetry perpendicular to the plane in which the respective preferential propagation directions (Y) lie.5) Apparatus (10) for the reduction of foam in a foaming metallurgical slag according to any one of the preceding claims, wherein at least one of said emitters (13) is orientable with respect to a respective axis or centre of rotation (17) to vary the distance of said intersection point (F) from said emitters (13) .6) Apparatus (10) for the reduction of foam in a foaming metallurgical slag according to one or more of the preceding claims, comprising a unit for detecting and / or measuring (19) at least one parameter of said metallurgical foaming slag which is in signal communication with said electronic control unit (16) , wherein said electronic control unit (16) is configured to control said emitter unit (11) and / or said generator(12) as a function of said at least one parameter.7) Apparatus (10) for the reduction of foam in a foaming metallurgical slag according to one or more of the preceding claims, comprising for each of said emitters(13) a respective own generator (12) .8) Apparatus (10) for the reduction of foam in a foaming metallurgical slag according to any one of the preceding claims, wherein said mechanical amplifier (15) consists of a plate (150) provided with a central axis substantially orthogonal thereto and substantially coaxial to the vibration direction (X) of the respective transducer (14) , said preferential propagation direction (Y) being defined by said central axis of said plate (150) .9) Apparatus (10) for the reduction of foam in a foaming metallurgical slag according to claim 8, wherein said plate (150) has one or more annular protuberances (1500) concentric to said central axis.10) Apparatus (10) for the reduction of foam in a foaming metallurgical slag according to any one of the preceding claims, wherein said mechanical amplifier (15) consists of a horn-shaped element (151) with a longitudinal central axis coaxial to the vibration direction (X) of the respective transducer (14) , said preferential propagation direction (Y) being defined by said longitudinal central axis of said horn-shaped element (151) .11) Apparatus (10) for the reduction of foam in a foaming metallurgical slag according to any one of the preceding claims, wherein said mechanical amplifier (15) consists of a plate (152) having a central axis orthogonal thereto and coaxial to the vibration direction (X) of the respective transducer (14) , wherein said plate (152) is arranged in the centre of a reflector (153) provided with two reflecting surfaces (153a, 153b) each forming an angle of 45° with the plane defined by said plate (152) , wherein said preferential propagation direction (Y) is defined by an axis of symmetry of said reflector (153) .12) Apparatus (10) for the reduction of foam in a foaming metallurgical slag according to any one of the preceding claims, wherein said emitter unit (11) comprises a support structure (110) of said emitters and at least one protective casing (111, 111' ) at least of the transducers (14) of said emitters, individually or as a whole, obtained in said support structure (110) or associated with said support structure.13) Apparatus (10) for the reduction of foam in a foaming metallurgical slag according to claim 12, comprising a cooling circuit (112) for said emitters (13) obtained in said protective casing (111, 111' ) or associated with said protective casing (111,111' ) .14) Apparatus (10) for the reduction of foam in a foaming metallurgical slag according to claim 12 or 13, comprising an assembly of support and movement (22) of said emitter unit (11) in translation and / or rotation along at least one translation direction and around at least one axis or centre of rotation, respectively.15) Apparatus (10) for the reduction of foam in a foaming metallurgical slag according to one or more of the preceding claims, wherein each amplifier (15) is associated with a respective waveguide (1140) comprising an internally hollow cylindrical body having a longitudinal axis (A) and having at least one longitudinal section of constant cross-section (1140a) , wherein said waveguide (1140) is arranged downstream of, optionally in contact with, the respective amplifier (15) with its longitudinal axis (A) coaxial with the preferential propagation direction (Y) of said respective amplifier (15) .16) System for the reduction of foam in a foaming metallurgical slag comprising an apparatus (10) for the reduction of foam in a foaming metallurgical slag according to one or more of the preceding claims and a containment vessel or a channel of outflow of a slag mass to be treated, wherein said apparatus (10) is arranged in such a way that said intersection point (F) is close to the surface of said slag mass to be treated.17) Method for the reduction of foam in a foamingmetallurgical slag comprising at least the steps of:- providing an apparatus (10) for the reduction of foam in a foaming metallurgical slag according to one or more of claims 1 to 15; arranging said apparatus (10) close to a mass of foaming metallurgical slag in such a way that said intersection point (F) is close to the surface of the metallurgical foaming slag;- controlling by means of said electronic control unit (16) said emitter unit (11) and / or said generator (12) in such a way that the emitters (13) of at least one pair of emitters emit sound waves having frequencies that differ from each other by a maximum of 5%.

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