Process for the removal of carbon, silicon, manganese and sulphur from molten high carbon ferrous metal

Abstract: An improved process for the removal of silicon, carbon, manganese and sulphur together in a single reaction vessel (ladle) comprises the steps of: a) adding a mixture of iron oxide containing material and a flux into a ladle; b) adding high carbon molten ferrous metal (hot metal) into the said mixture for the oxidation of silicon, carbon, and manganese present in the hot metal, the reaction resulting in the formation of a slag which floats on the surface of the hot metal; c) introducing magnesium below the surface of the hot metal in a perforated plunger, which is gradually lowered into the molten hot metal till it touches the bottom of the ladle and, immediately after the plunger touches the bottom of the ladle, lifting the plunger to a position such that a gap between the bottom of the ladle and the head of the plunger, ranging between 5 to 50 mm is created; whereby magnesium vapour escapes through the holes of the plunger head into the hot metal resulting in the desulphurisation of the molten hot metal; d ) intimate mixing of the molten hot metal and the unreacted iron oxide present in the slag by the turbulence produced during the release of the magnesium vapour, resulting in further oxidation of silicon and manganese and reduction of iron oxide into iron; and e) removing the slag at the completion of the reaction. A corresponding apparatus is also provided.

Description: The present invention relates to an improved process for the removal of silicon, carbon, manganese and sulphur from molten high carbon ferrous metal and an apparatus for carrying out the process. The invention particularly relates to an improved process for the pre-treatment of the molten hot metal, customarily produced in a Blast Furnace, from which silicon, carbon, manganese and sulphur are removed all together in a reaction vessel such as: a customary Blast Furnace or a Transfer ladle used in a steel plant. In the process of the present invention, no re-ladling or removal of the slag is involved till the desired removal of silicon, carbon, manganese and sulphur-all together from the hot molten high carbon ferrous metal - is accomplished. Thus, the process of the present invention is operationally very simple and saves a significant amount of energy. Iron oxides such as iron ore, mill scale, sinter returns etc. can be used. Fluxes such as lime, flurospar, and rice husk and the metallic magnesium either with or without aluminium may be used. The present invention also provides an improved apparatus for carrying out the process envisaged above. In order to convert hot metal from a Blast Furnace or molten cast iron metal from a Cupola (both these two metals are hereinafter referred to as hot metal) into steel, carbon, silicon and manganese present in the hot metal have to be removed. Similarly, the sulphur content of the hot metal has to be decreased so that steels of a better quality or with a higher value, can be produced. The removal of carbon, silicon and manganese from hot metal in a steel plant is usually accomplished in a steel making unit, such as Basic Oxygen Furnace, Open Hearth Furnace, etc. If the process of pre-treatment of hot metal is adapted, the metallurgical work to be done to remove carbon, silicon, and manganese in the steel making units, is partially accomplished during the pretreatment and also the sulphur is removed to an acceptable level before the hot metal is processed in a steel making unit. This accelerates the removal of these elements in the expensive steel making unit which consequently achieves a higher productivity and also enables one to produce steel of better quality and value. In prior art pre-treatment processes, the removal of carbon, silicon and manganese is accomplished through the addition of mill scale optionally followed by oxygen lancing of the hot metal kept in a ladle or a reaction vessel. In such processes, the removal of silicon and of sulphur, is accomplished in separate stages or vessels with successive slag removal each time, producing a stoppage in the movement of the ladle or the hot metal. Also, in such pre-treatment processes, the amount of silicon that can be removed is rather limited (a maximum of about 0.2%). On the other hand, the oxygen lancing which can produce higher desiliconisation or decarbonisation, also results in a loss of iron into the slag phase as iron oxide and also generates significant amount of fumes. At present, the removal of sulphur from the hot metal is accomplished, in most instances, by introducing magnesium in the molten hot metal since magnesium is the most efficient reagent for removing sulphur. The solubility of magnesium in the molten iron is limited. Besides, the recovery of magnesium and efficiency of the treatment when pure or almost pure magnesium is used, is low. Before the magnesium can participate in the desulphurisation reaction, it floats on the surface of the molten metal due to its low density. Also, being combustible, it immediately burns. If the magnesium is plunged into the hot metal, it vapourises as soon as it is brought in contact with the hot metal. The vapourisation leads to a large increase in the volume of magnesium and, as a result, the plunging treatment with magnesium results in an explosively violent reaction, wherein almost the entire volume of hot metal may be ejected out of the reaction vessel at high velocity. Such a method of magnesium treatment is unsafe and is highly hazardous. Besides, this treatment is not reliable as the contact time between magnesium and the hot metal is very short. Hence the quantity of sulphur removed is practically negligible. As described above, the plunging of magnesium through a bell shaped crucibles or an open-ended crucible into the hot metal, produces a violent reaction and is, therefore, unsafe. One can, therefore, introduce magnesium as an alloy in the hot metal, either as Mag-Coke; or Ni-Mg Alloy; or as a Fe-Si-Mg alloy the reaction is somewhat controlled thereby and is non-violent. One should note that the use of Ni-Mg or Fe-Si-Mg to remove sulphur is prohibitively expensive and also the plunging of Mg-coke makes the plunging system large and costly. However, sulphur can be removed from the hot metal if steady and continuous source of magnesium vapour is maintained in the hot metal. At present, in one of the widely used techniques of desulphurisation, such a source of magnesium vapour is produced by a technique, wherein granulated magnesium coated with less reactive materials, is suspended in a carrier gas such as nitrogen and is then injected into the hot metal with the help of a specially designed dispenser to deliver the coated granules or powder inside the hot metal. The technique has some inherent problems, such as: availability of the high purity nitrogen; the loss of unreacted magnesium as its vapour would tend to react chemically with nitrogen and is also physically carried up along with the nitrogen as it bubbles up, without fully reacting with the sulphur in the hot metal. This causes lower efficiency of magnesium utilisation for sulphur removal. Such a source of magnesium vapour can also be produced by impregnating magnesium into a pre-heated porous refractory material by dipping and soaking the material in molten magnesium. Subsequently, the refractory material, is plunged into the molten iron to release the magnesium soaked in the refractory material. Alternatively, the magnesium can be contained in a special chamber at the bottom of a special reaction vessel called 'converter'. The magnesium is inserted in the chamber of the converter when the convertor then is empty. The converter is filled with hot metal, the magnesium melts and is released through the hot metal producing desulphurisation. This needs expensive capital equipment. In yet another method, the magnesium can be contained in a plunger head with its open end threaded and finally closed with a threaded plug and with its wall containing perforations, through which the magnesium vapour escapes after the plunger is dipped and held in the hot metal. This needs a new plunger head for every treatment. In yet another method, the open end of the plunger head is closed with a disc shaped piece made using refractory material. The plunger head is lowered independently of the ladle cover and the head is made to touch the bottom of the ladle and kept pressed against the bottom, in physical contact with it. Even though this plunging operation process is simple and attractive, the plunger head used in such a process is expensive, due to the expensive material and fabrication required for its making. Besides, the plunging operation is often unsuccessful since the plunger head may break before the reaction is complete. Also, in such plunging operations, the plunger head may undergo breakage after every treatment for more than one reason. First, the thermal expansion of the plunger rod and head produces mechanical load on the plunger head when kept pressed against the bottom of the ladle, during plunging. Secondly, the breakage also occurs since the turbulence in the molten iron produced by the expanding magnesium vapour, shakes the ladle and transmits the mechanical load to the plunger head, because it is kept pressed in physical contact with the bottom of the ladle. Since the plunger can not be reused, and is itself rather expensive, the use of a fresh plunger for every plunge, can add to the cost of desulphurisation by magnesium treatment. Even though the above invention involves magnesium plunging, it differs very significantly from the present invention described herein subsequently, in four respects. First, the purpose of the above invention is to produce Spheroidal Graphite (Ductile) or Compacted Graphite Iron, whereas the purpose of the present invention is to remove silicon, manganese, carbon together with sulphur from the hot metal. Second, the purpose of magnesium plunging in the above invention is to render the graphite in the solidified cast iron, into a Spheroidal or a Compacted form, whereas the purpose of magnesium plunging in the present invention is to remove sulphur from the hot metal and to produce turbulence inside hot metal which promotes intimate mixing between slag and metal which, in tum, accomplishes the final part, of the desired removal of silicon, manganese and carbon which is otherwise rather difficult to remove. Third, in the above invention neither iron oxide containing material nor flux are added, whereas these are added in the present invention together with magnesium plunging, to accomplish the removal of silicon, carbon and manganese along with that of sulphur in the same reaction vessel. Fourthly, the apparatus used in the above invention, keeps the plunger head in physical contact and pressed against the bottom of the ladle, during the reaction, whereas the apparatus used in the present invention, lifts and then locks the plunger to ensure that there is no physical contact between the plunger head and the bottom of the ladle, during the reaction. One should also note that the introduction of magnesium by the present invention as against by all the methods described earlier, requires expensive equipment and consumables. Similarly, the removal of silicon, manganese and carbon using the methods mentioned earlier, involves several separate steps. These methods also involve reladling and deslagging, thereby making the process for the removal of silicon, manganese and carbon rather complicated and expensive. The reason for the use of several steps and deslagging as mentioned above, is explained below: The removal of silicon (as also manganese and carbon) from molten metal for the manufacture of steel requires that the oxygen potential in the hot metal be very high (about 10 -4 ). On the other hand, removal of sulphur requires that the oxygen potential be very low (about 10 -13 ). In other words, removal of silicon from hot metal requires an oxidizing atmosphere, whereas the removal of sulphur requires a highly reducing atmosphere. As a result, it is commonly believed that the silicon and sulphur present in the hot metal cannot be removed all together in the same reaction vessel. Currently, there is no process known to remove silicon, manganese and carbon together with sulphur, from the hot metal in a single reaction vessel without deslagging and or reladling. If silicon, carbon, manganese and sulphur are removed together in a single reaction vessel without reladling and deslagging, the cost decreases, the ladle moves smoothly with fewer stoppages inside the plant, the temperature drop is minimised and the number of operations is decreased. The present invention is based on an altogether new approach wherein the highly reducing and the highly oxidising reactions are conducted at two different sites within the same reaction vessel. Thus, the removal of sulphur is accomplished at the bottom of the reaction vessel whereas, the removal of silicon, manganese and carbon are achieved at the top layer of the molten metal where slag is present. Accordingly, in this invention, highly differing conditions of the reactions are accomplislled together, in the same reaction vessel. The process of the present invention is defined in claim 1. According to the process of the invention silicon, carbon and manganese are removed from the hot metal by adding iron oxide containing material to it. The iron oxide present in the material partly reacts with the silicon, manganese and carbon present in the hot metal and is itself reduced to produce iron which combines with the molten hot metal. The unreacted iron-oxide thereafter goes to the slag phase, floating on the surface of the hot metal. The iron oxide present in the slag phase is further reduced to iron due to the intimate mixing produced by the turbulence created during the plunging of magnesium to accomplish the desulphurisation reaction. As a result, some more iron oxide is again reduced to iron, which mixes with the molten hot metal. This increases the quantity of iron present in the reaction vessel, while simultaneously accomplishing the decarburisation, desiliconisation, demanganisation and desulphurisation from the hot metal in the same ladle. The apparatus of the present invention has been developed based on the principle that when the plunger, consisting of the plunger rod and the plunger head, which is movably fixed to the cover of the reaction vessel (hereinafter referred to as ladle), is pressed down to touch the bottom of the ladle, a lock and lift system lifts the plunger such that a gap is created between the bottom of the ladle and the plunger head and locks the plunger to the cover which is secured to the ladle. The lock and lift phenomenon can be accomplished by a variety of methods. In the preferred embodiment, it can be accomplished by two jaws which are movable towards each other in a plane inclined at 45°, on the top of the cover of the ladle. As the jaws move towards each other to grip the plunger rod, they lift it up and then lock the rod to the cover of the ladle. When the jaws fixed on the cover are joined to the rod, they make it an integral part of the cover of the ladle. The movement of the jaws can be effected electromechanically, pneumatically or hydraulically, as per convenience. The plunger may be kept pressed against the bottom of the ladle by adapting the upper end of the plunger to move freely in the annular hole provided in the cover of the ladle, the plunger supported by molten metal when present and a groove in the cover of the ladle. When the plunger head touches the ladle bottom, the lock and lift system is actuated, by a suitable mechanism and a drive and as a result, the plunger is lifted and then locked to the steel shell of the cover of the ladle. Since the lock and lift assesmly is rigidly connected to the cover of the ladle, the plunger becomes an integral part of the apparatus. Any suitable and convenient assembly can be provided to have the lock and lift effects. The dead weight provided on the plunger head is so adjusted that the plunger head moves down into the ladle containing the hot metal in a controlled manner smoothly and does not suffer any breakage when it makes contact with the bottom of the ladle. As soon as the plunger head rests over the bottom of the ladle, electrical drive on the cover is switched on which moves the jaws towards the plunger rod. As a result, the plunger rod together with the head gets lifted and then locked to the cover of the ladle. Due to the lock and lift system provided in the apparatus of the present invention, as explained above, a gap is created between the plunger head and bottom of the ladle which minimises any transmittance of force to the plunger head, either produced by the vibration of the ladle during plunging, or due to the thermal expansion of the heated plunger rod locked into the bottom of the ladle. Figure 1 of the drawings accompanying this specification represents a cross section of one embodiment of the assembly of: the cover of the ladle; the plunger; and the ladle; as provided in the present invention. The figure also shows the location of the lock and lift assembly. Figures 2 and 3 accompanying this specification illustrate the front and plan view respectively of the lock and lift system incorporated in the apparatus of the present invention. Figures 4 and 5 show the lock and lift mechanism of figures 2 and 5 with jaws open! Referring to figure 1 a plunger head 1 can be kept at a distance ranging from 5 to 50 mm from the bottom of the ladle in a number of ways, while the plunger 1 is firmly secured to the ladle cover 2. The ladle cover 2, has to be seated securedly on the ladle 3. For this, the cover is usually attached with a dead weight to make the cover sufficiently heavy, so that magnesium vapour is not able to lift the plunger with crucible. Alternatively, the ladle cover is made light (only sufficient for structural rigidity) and it is locked with the foundation or the structures or pressed over the ladle with pneumatic/hydraulic cylinders. Positive mechanical locking of the ladle cover with other rigid structures, properly founded on the ground, also serves the purpose. It would be observed that the plunger head 1 is kept at a distance from the bottom of the ladle 3 with the open end of the plunger head 1 at its bottom, closed by a detachable lid (or plug) which has a step. The step has a diameter slightly smaller than the diameter of a recess of the plunger head 1. The step, therefore, enters into the recess of the plunger head. The lid continues to stay in position at the ladle bottom and keeps the open end of plunger closed during the process, even after the plunger is lifted by 5 to 50 mm. The lid stays in position since the step provided in the lid has a height of 25 to 50 mm. The diameter of the lid (or plug) is equal to or larger than the external diameter of the cylindrical plunger head. According to another feature of the present invention there is also provided an apparatus for carrying out the process of the invention which is defined in the independent apparatus claim herein. Preferably the apparatus which comprises a plunger having three parts (see Figures 1, 2 and 3), an upper plunger rod 5, a lower plunger rod 6 and a plunger head 1, the upper plunger rod 5 being made of steel and its upper end being provided with a counterweight 4 and a hook 7 for lifting the cover, the upper plunger rod 5 provided with a plurality of horizontal circular grooves 12, the inner core of the lower plunger rod 6 being made of steel and with a refractory material coated at its outside, the plunger head 1 being provided with plurality of holes on its sides with its bottom closed by a stepped lid with the step which fits into the recess of the plunger head, all the above three parts being joined with suitable means to form a single integrated structure, a steel cover 2 being securedly seated on the ladle 3 by suitable means and fastened at its four corners by ropes to the hook 7, the inside surface of the steel cover 2 being coated with a refractory material, the cover 2 also being provided with vent pipes 8 for the release of excess gases and fumes, a lock and lift assembly 11 consisting of a base plate 13 having an opening through which the plunger 5 is movably fixed to the cover 2 of the ladle, a pair of jaws 14 provided with horizontal semi-circular grooves in its inner cylindrical surface which matches with the grooves 12 provided at the upper end of the upper plunger rod 5 movably fixed to the base plate 13, means being provided on each side of the base plate for moving the jaws against each other in a plane at 45° so as to grip the plunger at the end of its travel and lock the same to the cover. The apparatus of the invention is described with reference to the Figures 1, 2 and 3 which is one embodiment of the invention. As explained earlier, many other mechanisms can be employed and is within the perview of this invention, for effecting the lock and lift effect to the apparatus. Figure 1 shows that the cover 2 of the ladle rests on the ladle 3. The plunger consists of an assembly of three parts: the upper plunger rod 5; the lower plunger rod 6; and the plunger head (1). The counterweight 4 on the top of the plunger is so adjusted that when the hook is lowered the plunger descends gradually into the hot metal. The cover of the ladle is provided with vent pipes 8 for the release of exhaust gases/fumes formed during the reactions. Plunger guide system 9 is welded/fixed detachably over the top of the cover 2. The two guide plates 10 slide along the guide posts 9. The movement of guide plates within the guide posts, permit only a vertical movement of the plunger. The lock and lift assembly 11 is used for the locking and lifting of the plunger after it has been lowered and after it touches the bottom of the ladle. One embodiment of the 'Lock and Lift Assembly' is illustrated in Figure 2 and 3 which mainly consists of: Grooved Upper Plunger Rod 5; Fixed Inclined Blocks 15; Base Plate 13; Geared Motor 16; Grooved Sliding Jaws 14; Counter Weight 4; Refractory coated lower plunger rod 6 is fixed to the plunger head 1 and this is then assembled to the upper plunger rod 5. A base plate 13 is mounted over a suitable frame on the top of the ladle cover. According to a feature of the invention, the plunger head is firmly fixed to the plunger rod either through threaded joints or through cotter or fixing bolts. The disc shaped lid (or the plug) made by using refractory material and/or steel, is used to close the opening at the bottom of the plunger head. The lid must be fastened at the open end at the bottom of the plunger head after the magnesium is placed inside the plunger head. The lid holds the magnesium inside and prevents direct contact between the molten metal and magnesium, while the plunger is lowered and also while it is held at a distance of 5 to 50 mm above the bottom of the ladle. To positively secure the lid into the plunger head, a step of 25 to 50 mm height is provided on one surface of the disc-shaped lid. The step enters into the recess and matches with the inner diameter of the plunger head. The step prevents the lid from sliding out, while the plunger is lowered and also after the lock and lift assembly lifts the plunger during the reaction. According to another feature of the invention, the refractory coated lower plunger rod is assembled and fastened to an upper plunger rod 5 which is a grooved cylindrical steel piece. The grooved part of the upper plunger rod is held firmly by the grooved sliding jaws 14, with the grooves in their inner surfaces matching with those in the upper plunger rod. The jaws move back and forth actuated electro-mechanically or pneumatically or hydraulically in a plane inclined at 45°, above the ladle cover (see figures 4 and 5). The motion of the actuators and consequent engagement with the grooved cylindrical part of the upper plunger, ensures the operation of lock and lift system. According to yet another feature of the invention, the plunger is guided to move vertically through the ladle cover by installing two pairs of rollers suitably spaced and fixed to the top of the cover of the ladle. The guides may be appropriately designed and fabricated and joined to the cover of the ladle which together with the guides, ensure upright vertical movement of the plunger. When the lock and lift system is idle, there is sufficient clearance between the grooved jaws and the upper plunger rod for a free vertical movement of the upper plunger rod without interference. After the cover is placed on the top of the ladle and the plunger head is lowered gradually to seat over the bottom of the ladle, the electrical drive is switched on (in the case of electro-mechanical actuation of the system, as illustrated in Figures 2 and 3). This gives an inclined movement to the grooved jaws through appropriate mechanism and linkages (figures 4 and 5). The grooved jaws and the grooved upper plunger rod are so designed that after locking, the shaft is lifted up through a height which depends on the depth of the grooves by the cam action of the grooves engaging. Various limit switches are provided to safeguard the overload and safety aspect of the system. As a result, the treatment of the molten iron in the ladle occurs by a steady flow of the magnesium vapour which escapes from the perforations in the plunger head. The magnesium vapour also escapes through the gap, between the plunger head and the ladle bottom, whenever there is an accidental build up of the pressure of magnesium vapour within the plunger head. This gives rise to a controlled and highly reliable magnesium treatment of hot metal. It is to be observed that the details given above regarding the construction of the apparatus should not be construed to limit the scope of the invention as any modification within the ambit of the invention is also contemplated by the present invention. In other words, the mechanism shown for effecting the lock and lift principles is only illustrative and not limited to the system explained. The details of carrying out the invention utilising the apparatus proposed is explained below: A mixture consisting of iron oxide bearing material is heated to a temperature of 200 to 400°C. The mixture is placed in the ladle and the hot metal at a temperature of about 1350 to 1500°C, is added to the above said mixture in the ladle. The reaction between the hot metal and the mixtures takes place. Magnesium metal is put inside a can. The can is then inserted into the plunger. Afterwards, the plunger head is closed by the disc shaped plunger lid with the step of the lid inside the plunger head. The plunger lid is fastened to the plunger head. After this, the cover of the ladle is made to sit secured onto the ladle. The plunger is then lowered into hot metal inside the ladle, till it touches the bottom of the ladle. A turbulence is created in the hot metal inside the ladle due to the upward movement of the expanding magnesium vapour. Immediately on touching the bottom, the plunger is lifted so as to create a gap between the bottom of the ladle and the plunger head in the range of 5 to 50 mm. This is achieved by moving the grooved jaws by switching the drive. This turbulence inside the metal produces intimate mixing of the silicon, manganese and carbon of the hot metal with the unreacted iron oxide contained in the slag at the top of the metal. The removal of silicon, manganese and carbon and the recovery of iron, are achieved by the reduction of the iron oxide in the slag phase, which takes place all along. The reaction of the magnesium vapour with the hot metal produces excellent desulphurisation, as the magnesium vapour intimately interacts as it moves up in a controlled manner through the hot metal. After the magnesium plunging is over, the plunger is withdrawn and the cover is removed from the ladle. The temperature drop due to magnesium plunging is negligible. The removal of silicon, manganese, carbon and sulphur is evident from the analysis of the hot metal after the reaction is complete. Afterwards, the slag is removed by conventional method with the help of a Deslagging Unit and the hot metal can be charged into the Basic Oxygen Furnace to convert it into low sulphur, high quality steel. The point that reversion of sulphur from slag to metal in this invention is negligible, is evident from the following: a ladle was made to wait for two hours after magnesium plunging. Thereafter the entire slag and the hot metal was charged into another ladle which caused an intimate mixing between the sulphuric slag and the hot metal. Even after such waiting and mix-up, the sulphur in the hot metal did not increase. This result demonstrates that unlike in all other desulphurisation processes, no sulphur reversion occurred during such prolonged holding and mixing, in the present invention. The invention has the following advantages: 1. Simultaneous desiliconisation, demanganisation, decarbonisation and desulphurisation of the hot metal, for instance of high carbon metal, in a single vessel with only one deslagging at the end. This makes the process simple, economical, easy to implement and enables its convenient integration in any system of the transfer of hot metal from the iron making to the steel making unit, that may exist in a steel plant. As a result, the transfer can be accomplished faster and without the use of the Mixer unit which is used to store hot metal enroute to the steel making unit in a steel plant. 2. The reactions in the process are controlled and are free from the usual hazards of magnesium plunging processes. 3. The slag produced due to the desiliconisation and demanganisation need not be removed prior to the desulphurisation, which is done in other pretreatment process. 4. The introduction of magnesium into the molten metal is smooth and controlled. 5. A very high degree of desulphurisation can be achieved. 6. The reversion of sulphur which occurs in all the other processes after the hot metal is desulphurised, is almost absent in the present invention. Also the temperature drop during the treatment even after prolonged holding in contact with slag was negligible. Both these features impart a great deal of flexibility in transporting the pre-treated hot metal, by-passing the mixer inside a steel plant. 7. Since the temperature drop in the process of the invention is low, the desulphurisation can be carried out even when the hot metal temperature is low. 8. The quantity of magnesium used to accomplish a given amount of desulphurisation is very low. 9. A very high degree of desiliconisation can be achieved without the generation of fumes. 10. Due to less temperature drop of hot metal, the hot metal after the pretreatment can be charged at a higher temperature into the steel making unit, resulting in higher productivity of steel from the unit. 11. The process uses very inexpensive oxidizing agent such as iron ore/sinter fines/mill scale. 12. The process recovers a substantial part of the iron from the iron oxide bearing material and then transfers it into the hot metal, the value of the iron recovered can effectively defray the cost of desulphurisation, making the process still more inexpensive. 13. Locking and lifting of the plunger used for pre-treatment of hot metal prevents breakage of the plunger and its head due to mechanical damage and enables their repeated use mitigating the cost, maintenance and operational problems. 14. Violent reaction between hot metal and magnesium is avoided since the plunger head is closed with a lid throughout the magnesium plunging reaction. 15. The apparatus of the invention used, enables repeated use of the same plunger head without breakage and a very controlled release of magnesium vapour through the hot metal. 16. The apparatus allows a higher quantity of hot metal to be used in the reaction vessel, thereby increasing the amount of hot metal treated.

Claims: A process for the removal of silicon, carbon, manganese and sulphur together in a ladle which comprises: a) adding a mixture of iron oxide containing material and a flux into a ladle; b) adding not metal into the said mixture for the oxidation of silicon, carbon, and manganese present in the hot metal, the reaction resulting in the formation of a slag which floats on the surface of the hot metal; c) introducing magnesium below the surface of the hot metal in a perforated plunger, which is gradually lowered into the molten hot metal till it touches the bottom of the ladle and, immediately after the plunger touches the bottom of the ladle, lifting the plunger to a position such that a gap between the bottom of the ladle and the head of the plunger, ranging between 5 to 50 mm is created; whereby magnesium vapour escapes through the holes of the plunger head into the hot metal resulting in the desulphurisation of the molten hot metal; d) intimate mixing of the molten hot metal and the unreacted iron oxide present in the slag by the turbulence produced during the release of the magnesium vapour, resulting in further oxidation of silicon and manganese and reduction of iron oxide into iron; and e) removing the slag at the completion of the reaction. A process as claimed in claim 1 wherein the material containing iron oxide is iron ore, blue dust mill scale, or sinter returns. A process as claimed in claim 1 or claim 2 wherein the flux is lime, flurospar or rice husk. A process as claimed in any preceding claim, wherein the magnesium metal also comprises with aluminium. A process as claimed in any preceding claim, wherein the reaction mixture of step a) is preheated to a temperature in the range of 200 to 400°C before being added to the ladle. Apparatus comprising a ladle(3) for hot metal, a ladle cover(2) and, cooperatively fixed to the cover, a plunger, the plunger comprising a rod(5,6) and, fixed to the lower end of the rod, a head into which magnesium metal can be placed, the head having at least one hole in its side through which molten magnesium may pass, in which the plunger provided with lowering means(4,7) for lowering the plunger from a raised position in which the head is above the surface of hot metal in the ladle, to a lowered position, in which the head contacts the bottom of the ladle, and in which the apparatus comprises also lift and lock means (11) operatively joined to the plunger rod capable of raising the plunger head to an operational position in which it is fixed relative to the ladle cover suspended in the hot metal out of contact with the bottom of the ladle. Apparatus according to claim 6, in which the lift and lock means are carried on the ladle cover. Apparatus according to claim 6 or claim 7, in which the plunger head comprises a hollow vessel with a downwardly facing mouth and a lid received in the mouth for closing the vessel. Apparatus according to any of claims 6 to 8, in which the lift and lock means lifts the plunger head a distance of 5-50 mm from the bottom of the ladle. Apparatus according to any of claims 6 to 9, in which the lift and lock means comprise a pair of jaws(14) between which the plunger rod(5) passes and whereby the jaws may be opened to allow vertical movement of the rod and may be closed around the plunger rod, the jaws preferably being provided with engagement means on their inner faces which cooperate with mutual engagement means on the outer surface of the rod, the engagement means being adapted to prevent mutual vertical movement between the jaws and the rod, with the jaws closed around the rod. Apparatus according to any of claims 6 to 10, in which the plunger rod comprises a lower part(6) adapted for being submerged in hot metal preferably by being coated with refractory material, and an upper part(5) adapted for engagement with lowering and lift and lock means, preferably by being provided with circumferential grooves.

Inventors: BANERJEE SHILOWBHADRA, PANDEY KEDAR NATH, ROY BHARAT CHANDRA, SAHU ASIM KUMAR, SHARMA OM PRAKASH, BANERJEE, SHILOWBHADRA, PANDEY, KEDAR NATH, ROY, BHARAT CHANDRA, SAHU, ASIM KUMAR, SHARMA, OM PRAKASH
Applicants: INDIA STEEL AUTHORITY, STEEL AUTHORITY OF INDIA LIMITED
Application year: 1998
Main classification: C21C1
IPC codes: C22C33, C21C1, F27D3, F27D23