Patent Application
20140042676
The present invention concerns a device, and the corresponding method, to inject solid material under the bath, mostly in granular form, powder and/or particles, in order to minimize the time taken for the material to pass from the device to the bath, thus increasing the volume (weight) of the material introduced, so as to increase efficiency and generate appropriate and desired chemical reactions in a bath of liquid metal, or to add additives to the liquid metal to improve its quality, or for other reasons.
The present invention is mainly although not exclusively applied in processes for melting metals in electric arc furnaces (EAF) in order to improve the efficiency of such processes, to improve the quality of the product obtained, to reduce melting times, to increase the working life of the components that are subject to wear, to increase the energy efficiency of the solids introduced, given the same volume and/or efficiency, to reduce the volumes introduced and hence the consumption thereof, with a reduction in the purchasing costs, to reduce energy consumption, and to obtain other advantages as described hereafter.
Melting processes are known, which use electric arc furnaces to melt metal materials of various types and origin, and to obtain liquid metal to be sent to working processes downstream, such as for example casting, rolling or other.
It is known that, during the melting process, as well as providing electric energy to feed the electrodes, auxiliary devices are normally used which perform various functions which are complementary but extremely important to optimize the process and to obtain a good quality final product.
For example it is known to use burners, oxygen lances and solid material injectors, of varying types and function, to improve the process conditions, reduce energy consumption, and limit wear on the parts, in particular the ends of the electrodes, forming foamy slag, and the refractory material that constitutes the hearth and parts of the lateral walls.
For example it is known to inject or introduce carbonaceous material into the bath of liquid metal, in powder or particles, in order to promote the formation of foamy slag on the surface of the bath, so as to increase the cover factor of the electric arc and thus to reduce both wear on the electrodes and also energy consumption.
In order to perform this function, the carbonaceous material can be introduced into the bath together with the metal material to be melted, for example mixed with it both in the case of a continuous charge with a transporter, and also in the case of an intermittent charge with baskets.
Alternatively, or in combination, the carbonaceous material can be injected into the bath by means of suitable lances disposed above, or even below, the upper level of the bath of liquid metal (meniscus), so as to mix with the bath and allow to achieve chemical reactions that promote the rapid development of the foamy slag.
Examples of such solutions can be found in U.S. Pat. No. 6,614,831 and U.S. Pat. No. 4,110,107.
Other examples of injectors known in the state of the art are shown in DE-C-927.113, U.S. Pat. No. 3,199,924, U.S. Pat. No. 3,239,278 and GB-A-792.192.
DE'113 describes an injector to inject solid material into a furnace, which is mounted horizontally on the wall and, substantially near its terminal end and outside the furnace, has a magnet that regulates the quantity of material to be injected. This solution in no way allows to obtain an injection deep into the bath, keeping the injector outside and above the bath. Moreover, with the regulation methods using the magnet, it is not possible to obtain the emission speeds and energies required to obtain an injection of the carbonaceous material deep into the bath of liquid metal.
US'924 describes an injector to inject solid material through a thin channel made on the wall of the furnace, which leads into the bath of metal. The injection of the solid material directly inside the bath does not allow to obtain an in-depth distribution and determines a loss of efficiency and a delay in the effect of the solid particles in the bath. Furthermore, to prevent the material of the bath from rising inside the channel in the wall of the furnace and into the injector, the pressure in the chamber used for loading the carbonaceous material must be higher than the pressure in the furnace, and this causes operational and management complications.
US'278 also has a solution similar to US'924, with an injector inserted into the furnace wall that leads out directly inside the bath of liquid metal, with the same disadvantages as described above.
GB'192 does not show an injector suitable to be applied to the wall of an electric furnace for melting metal, but shows a tank of solid material from which an adjustable quantity of material is extracted.
It must also be considered that none of the documents described above teaches to use a flow of air or other gas under pressure, delivered in an impulsive manner (that is, with extremely limited emission times, high speed and high energy) to inject sold material from above the meniscus into deep into the bath.
It has been seen that the known methods described above for the introduction of carbonaceous material, and in general other solid materials inside the bath of liquid metal, are not satisfactory from the perspective of increasing the energy efficiency of the solids introduced and optimization of the results sought.
Indeed it has been found that, where the injector is above or inside the bath, the efficiency of the process is limited because the carbonaceous powders or particles affect only the upper layer, or in any case a limited layer, of the bath of liquid metal, and only later do they affect the remaining part.
In these cases, the delayed and limited start of the chemical reactions between the carbonaceous material and the bath of liquid metal causes the foamy slag to form late, and therefore the effect of covering the arc is contained, and hence the function of preserving the electrodes from wear is not performed efficiently, nor are energy savings achieved.
Another disadvantage is that this type of introduction promotes a loss of the product, which burns and goes into the fumes, without any advantage whatsoever for the process.
One purpose of the present invention is therefore to increase the efficiency of introducing the solid material, mostly in granular, powder and/or particle form, inside a bath of liquid metal in a melting process, in order to maximize the volume or weight of material introduced into the bath and the depth into the same, with the advantage that when it is under the bath it reacts with maximum yield.
Another purpose is to accelerate the start of the chemical reactions, involving all the liquid metal of the bath so as to maximize the final result of said reactions.
The Applicant has devised, tested and embodied the present invention to overcome the shortcomings of the state of the art and to obtain these and other purposes and advantages.
The present invention is set forth and characterized in the independent claims, while the dependent claims describe other characteristics of the invention or variants to the main inventive idea.
According to the present invention, an injection device is provided with high kinetic energy and high quantity of motion, to inject a discrete amount of solid material in particles, powder or granulated form, of varying grain size, for example comprised between 0.15 and 15-20 mm, preferably between 5 and 8 mm. The injection device comprises a tubular pipe which can be applied on a lateral wall of a melting furnace so as to dispose its exit end inside the volume of the melting furnace, with a desired orientation with respect to the vertical, for example comprised between 15 and 70 degrees, above the meniscus of the liquid metal contained in the melting furnace.
The injection device is suitable to inject a predetermined amount of solid material inside the bath of liquid metal, substantially of any type in relation to the result to be obtained, for example carbonaceous material, slag formers such as for example lime, inert materials, slag, materials from demolitions, for example fluff from shredders, powders from fume sleeve filters, minerals of different types, etc.
According to the present invention, upstream of the tubular pipe and associated with it, the injection device comprises a chamber or tank to contain the solid material, and emitter means able to be selectively connected to the chamber or tank, and configured and suitable to produce an impulsive jet of pre-compressed gaseous fluid which, in combination with an exit valve that can be selectively opened, disposed at one end of the pipe, determines the emission of an impulsive flow of the material contained in the chamber or tank, with high kinetic energy and high quantity of motion, such as to substantially reach the bottom of the hearth, passing through the whole layer of slag and the bath of liquid metal.
In a preferred solution, the impulsive jet of fluid consists of a high pressure gas that is introduced, making it expand, inside the chamber or tank containing the solid material, in a position upstream of the exit valve, in temporal coordination with the opening of the valve.
By doing this, that is, by substantially synchronizing the introduction of the pressurized fluid, for example gas or air, inside the device and the opening of the exit valve, and using extremely limited opening times both of the valve that introduces the pressurized gas inside the device where it expands, and also the exit valve of the material from the device, a flow of material is obtained with high kinetic energy and high quantity of motion, which penetrates and passes through the layer of slag and liquid metal and substantially reaches the bottom of the hearth.
In a preferential form of embodiment of the invention, a speed to introduce the material is used which is more than 4 m/s, advantageously more than 8 m/s, even more preferably more than 9-10 m/s.
In another preferential form of embodiment of the invention, the opening time of the valve which introduces the pressurized gas or air inside the tubular pipe of the device is less than 0.4 seconds, advantageously less than 0.3 seconds and even more advantageously less than 0.2 seconds.
In a preferential form of embodiment, the pressure of the gas introduced into the tubular pipe of the device to achieve the emission of the impulsive flow of material is higher than 5 bar, advantageously higher than 7 bar, even more advantageously higher than 8-10 bar.
The flow rate of material emitted with every impulsive emission cycle, in a preferential solution of the invention, is advantageously higher than 2 kg/s, more advantageously higher than 3 kg/s, even more advantageously higher than 4-5 kg/s.
In another preferential solution, the opening time of the exit valve of the material, associated with the end of the tubular pipe of the device, is comprised between 0.2 and 0.8 seconds, advantageously between 0.3 and 0.7 seconds, and even more advantageously between 0.4 and 0.6 seconds.
According to the invention, the values indicated above can be modified according to the operating conditions and the result to be obtained.
For example, the values can be modified according to the height of the liquid bath into which the material is injected, which can vary according to the melting cycle under way. During and at the end of the tapping step, for example, the level of the liquid bath inside the furnace is very low, in the range of 200-400 mm, corresponding to the height of the “hot heel” that is always maintained inside the furnace.
This situation, that is, the introduction of carbonaceous material at the end of tapping, is very important for the optimization of the process in that it is necessary that, when the new melting cycle starts, a foamy slag is obtained with a height and volume such as to guarantee the adequate cover of the electric arc and the material of the furnace that is subject to wear.
In this situation, the introduction parameters, mainly speed of flow, delivery rate and opening times of the valves, will be suitably calibrated in order to ensure that the bottom of the hearth is reached without ruining it by part of the jet of materials, and that the latter are distributed to affect the whole liquid bath.
If solid material is introduced during the melting process and/or during refining, when the level of the bath can reach 800-1000 mm or more, the introduction parameters will be increased compared to the previous case concerning the post-tapping step, achieving the same advantages that the present invention allows to obtain.
The geometric parameters of the device, for example length and diameter of the tubular pipe, distance of the exit end from the upper level of the bath, angle with respect to the vertical, etc., can also be modified both during the initial assembly step and also during the introduction of the material into the bath.
These and other characteristics of the present invention will become apparent from the following description of a preferential form of embodiment, given as a non-restrictive example with reference to the attached drawings wherein:
With reference to the attached
The electric furnace 11, during use, contains a bath of liquid metal 12 with an upper surface 12a that can have a variable height, normally from a minimum of about 200-400 mm, usually corresponding to the “hot heel” that always remains inside the furnace, even after tapping, to a maximum of about 800-1000 mm, during the completion of the melting step and refining.
The liquid metal 12 can be covered by a layer of slag 13 normally having a height of about 200-500 mm when inactive.
The furnace 11 comprises a hearth 14 made of refractory material, which defines the bottom of the hearth 14 and lower part of the lateral walls, above which cooling panels 15 are disposed. The whole thing is closed by a roof (not shown) through which the electrodes (also not shown) are inserted: all this is substantially known in the state of the art.
The device 10 is applied in cooperation with the cooling panels 15 and substantially comprises a tubular pipe 16, having a diameter that can vary between 60 and 150-200 mm, advantageously between 80 and 120 mm, and a length that can vary between 800 and 1500 mm.
In the case shown as an example in
A lower end 16a of the tubular pipe 16 is inside the electric furnace 11, facing toward the liquid metal 12 for the injection of the solid material, and disposed during use above the level of the upper layer of slag 13, and an upper end 16b of the tubular pipe 16 is associated, that is, rigidly fixed, to a first exit valve 17, and in axis with the latter.
The first exit valve 17 selectively connects the tubular pipe 16 with the lower end of a chamber or tank 18, able to contain a predetermined and discrete quantity of material.
The tank 18 is elongated in shape and substantially aligned axially with the tubular pipe 16.
In the form of embodiment shown in
The pipe 20 can be any type, and is connected to an accumulation tank, an automatic feed line or other apparatus to store and feed the solid material in powder or granular form of the type in question.
The pipe 20 can also be associated to deflector mechanisms and/or multi-way valves for connection to a plurality of tanks, each containing a material of a different type and grain size according to the type of processing and/or the processing step in progress.
A pipe 21 to introduce a pre-compressed fluid, in this case pressurized gas, for example air or preferably another, substantially inert gas, is provided in association with the device 10: the connection or coupling position of the introduction pipe 21 is provided advantageously in correspondence with the upper part of the tank 18.
A valve 22, or third valve, is provided along the pipe 21 in order to activate/de-activate the introduction of the pre-compressed gas upstream of the tank 18, thus generating, in coordination with the opening of the first valve or exit valve 17, the emission of an impulsive flow of material, indicated in
In a coordinated manner, the tank has a zone 18a of selective communication, thanks to the third valve 22, with the pipe 21, that is, a zone 18a of the tank 18, in correspondence with the coupling of the pipe 21, where the pre-compressed gas enters, expanding, into the tank 18: for the functioning of the device 10 the zone 18a must preferably remain free of material.
The procedure for filling the tank 18 provides to close the first exit valve 17, or exit valve, to open the second valve 19, or entrance valve, and to activate a mechanism to feed the material (not shown, and generally known) through the pipe 20. Once the tank 18 has been filled with the desired quantity of material, the second valve 19 is closed and the device 10 is ready for the introduction of the material inside the liquid bath when the valves 17 and 22 are subsequently opened. In particular, the material is introduced toward the liquid metal 12 by opening the first exit valve 17 and then, in rapid sequence, the third valve 22, to allow the impulsive jet of pre-compressed gas to expand inside the tank 18. The impulsive jet of pre-compressed gas is mixed substantially instantaneously with the solid material in the tank 18 and draws it through the tubular pipe 16, obtaining the emission of the impulsive flow F of material contained in the tank 18 with high kinetic energy and high quantity of motion through the tubular pipe 16 toward the liquid metal 12.
Depending on the type of material, the processing conditions, the result to be obtained, the quantity of liquid metal 12 inside the furnace 11, the position and structure of the device 10, the operating parameters of the device 10 can be regulated and varied to obtain the best functionality, even during the course of the introduction step itself.
The present parameters, preferential but not binding or restrictive, were tested by Applicant for a procedure to introduce carbonaceous material used to activate the formation of foamy slag in a step after tapping a quantity of liquid metal from the furnace 10.
To obtain an introduction speed of the material higher than 9-10 m/s, which has proved itself to be advantageous to allow the material to reach the bottom of the hearth 14 and allow an effective propagation of the material to a great quantity of metal, the third valve 22 was opened for a time of less than 0.2 seconds.
The pressure of the pre-compressed gas introduced from the pipe 21 inside the tubular pipe 16 of the device 10 to achieve the emission of the impulsive flow F of material was higher than 8 bar.
The flow rate of material emitted with every impulsive cycle was higher than 4.5 kg/s, while the first exit valve 17 for the material was opened for between 0.4 and 0.6 seconds. The overall cycle for the impulsive flow F of material was less than 1 second.
The flow rate of material injected into the liquid bath was about 5-6 kg/s, while the flow rate of the pressurized gas was about 40-70 l/s.
Using these values, with an average grain size of the carbonaceous material about 2-4 mm, the time taken to pass through the whole height of the liquid bath was about 0.1 sec, thus obtaining the result that all the carbonaceous material passed through the layer of slag 13 above and the whole thickness of liquid metal 12 without dispersing or creating flashes or other losses during the passage.
In this way, an extremely high percentage of the carbonaceous material injected was able to react substantially immediately with the liquid metal 12, quickly creating the conditions for the formation of a large volume of foamy slag, giving advantages to the processing conditions for re-starting a new casting cycle.
The above parameters can be modified in the case of different materials, and/or different processing conditions, but shall in any case come within the ranges indicated in the present description.
The device 110 shown in
When the valve 22 for the air or other gas is opened and the introduction of the pressurized gas is activated and, in coordination, the exit valve 17 is opened, in the way and with the times as described above, the material in the tank 18 is shot through the pipe 16 into the liquid metal 12 at extremely high speed to obtain a high penetrating energy. As already described, the pressure used for the expulsion is more than 5 bar, advantageously more than 7 bar, even more advantageously more than 8-10 bar, and is therefore much higher than the pressure at which the material is introduced inside the tank 18; thanks to the difference between these two pressures, during the expulsion, the introduction of material into the tank 18 is blocked. When the introduction of the gas is finished, the tank 18 is automatically refilled and is ready for a new cycle to introduce material into the bath.
This variant allows to obtain a smaller device than the device in
It is clear that modifications and/or additions of parts may be made to the device as described heretofore, without departing from the field and scope of the present invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| UD2011A00060 | Apr 2011 | IT | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/IB2012/000753 | 4/17/2012 | WO | 00 | 10/18/2013 |
