SK163498A3 - Preheating apparatus and method for preheating a ferrous scrap mixture with concurrent downward flow of hot waste gases and downwardly descending scrap, designed for metallurgical melting furnaces - Google Patents

Abstract

The invention relates to a novel preheating device and a method for preheating an iron scrap mixture before delivering the scrap iron into a metallurgical furnace. The invention primarily makes use of heat which is recovered from hot waste gasses that have been emitted from the furnace outlet. The invention is also provided for simultaneously reducing contaminated substances from the scrap iron and from the waste gasses with a downward stream comprised of the hot waste gas and of the downward falling scrap iron which flow in the same direction. The invention has a chamber comprising an upper compartment having a cold scrap iron feed provided for dumping cold scrap iron into the upper compartment and a hot gas inlet which is flow-connected to the furnace outlet. The chamber also has a lower compartment with an unloading mechanism for the heated scrap iron in order to forcibly deliver the heated scrap iron into the furnace and has a waste gas outlet which is flow-connected to a vacuum outlet and provided for evacuating the used waste gas. Gates which allow gas to pass through are arranged between each chamber compartment and sequentially operate between a closed gate position and an open gate position for receiving a scrap iron charge which is delivered in a closed gate position from the cold scrap iron feed in the same direction by means of gravity. During a predetermined hold period, the scrap iron charge is stored while hot waste gas flows downward out of the hot gas inlet in the upper compartment, penetrates through the scrap iron charge and through the closed gate, and flows out of the waste gas outlet in the lower compartment. The gates mix the scrap iron when it falls and serve to control the gravitational downward movement of the scrap iron charge from the upper compartment to the lower compartment after the hold period has elapsed.

Description

PREHEATING EQUIPMENT AND METHOD OF PREHEATING IRON

SCRAP WITH THE CURRENT TRANSITION OF IRON SCRAP AND HEATING GAS, INTENDED FOR METALURGIC melting furnaces

Technical field

The present invention relates to an environmentally-friendly and energy-efficient, autonomous, airtight, self-weighing preheating device and a method for treating a scrap iron charge in a closed circuit, comprising semi-continuous, automatic charging of a cold scrap iron charge to the preheater by tilting pre-heating. charging the preheated charge to an adjacent, in tandem cooperating metallurgical-electric arc furnace through the substantial and efficient thermal energy of the chemical reaction of the hot waste gases exhausted from the metallurgical-electric arc furnace to achieve a more energy efficient, faster melting of the preheated charge. The design of the proposed preheating device is clearly and unambiguously specified in the appended claim 1, while the processing procedure using the proposed preheating device and method is clearly defined by claim 19.

BACKGROUND OF THE INVENTION

I

The metallurgical technologies used to produce pig iron and steel are among the most energy-intensive industrial processing technologies ever. For this reason, the overall energy balance of these technologies has always belonged to the highest interest of the metallurgical industry. Deepening awareness of the constraints and scope of non - renewable energy resources and, ultimately, the energy crisis in the 1970s.

31114 T years of the 20th century marked the beginning of intensive activity, calling for the reduction of energy consumption as well as by energy producers and suppliers. In addition, environmental considerations and the existence of the need to protect the environment are other decisive factors for the necessary control of energy consumption in all industries. Since metallurgical technologies used in the production of pig iron and steel are also leading in the production of high emissions of air polluting toxic gases as well as hazardous solid waste, it is quite logical that such metallurgical technologies are increasingly in focus the interest and attention of the general public, especially government and leaders responsible for environmental cleanliness. As a consequence of the above, there is a global effort to improve the energy balance of metallurgical technologies by increasing energy efficiency as much as possible. Such an increase in energy efficiency has been achieved, to some extent and with maximum consideration and attention, both on environmental issues and on economic costs and affordability, by replacing one type of fuel or energy consumed with another for that specific technology or its individual steps, a more appropriate and usable energy source. Obviously, the first preferred step in reducing the energy consumption of most metallurgical processing plants by melting and remelting is the highest possible utilization of hitherto unused energy losses of the processing plant, for example the substantial and efficient thermal energy of the chemical reaction of the hot waste gases. Obviously, by returning, as short as possible, a direct portion of the energy of the hot waste gases to the metallurgical process that produces them, the desired initial input energy is reduced, which in turn will result in an overall higher energy efficiency of the metallurgical process itself. . Accordingly, most of the truly sincere and well-intentioned efforts to use the unused thermal energy contained in the hot waste gases, given by the shortest direct route possible, suggest

31114T of such constructions in which the energy recovery devices for preheating the iron scrap charge are incorporated directly into the current structure of the electric arc furnace. Meanwhile, contrary to expectations, only some of all the expected and desired results are achieved by these electric arc furnace composite aggregates having a complicated design used in the prior art. The high set-up and assembly costs, the malfunctioning of the individual mechanisms, considerably more extensive maintenance, environmental pollution and operational safety problems, culminating in the possibility of dangerous explosions, are quite obvious the reasons, questions, their suitability and applicability in general. With increasingly harsh environmental laws now and foreseen in the future, such issues are becoming increasingly relevant, mainly because the level of toxic emissions in the state of the art of the scrap iron preheating equipment used does not meet all the conditions and criteria of the applicable or proposed regulations, determining permissible levels of toxic substances that can be released into the atmosphere.

On the other hand, a very promising, favorable and efficient method of indirect energy saving is well known in the art, particularly in the production of steel scrap iron in an electric arc furnace, consisting in preheating a metal batch to a high temperature before charging it into the melting furnace in a separate, a separate heating device, known as pre-heating of scrap before charging. Since correspondingly developed scrap preheating devices based on the use of the described method and satisfactory combination with an electric arc furnace for steel production are unattainable in the prior art, there are only sporadic uses of this principle, in low-tech constructions for called. pre-heating the scrap in the charging bucket.

In addition to increasing energy and environmental problems, there are sometimes efforts to intensify some or all of the phases

31114 T steel production technology in an electric arc furnace, primarily to increase production productivity and reduce operating costs. Of the large number of means used in the described intensification of metallurgical process technology, the following are currently very often used in particular: supporting the increase in electrical power through an optimally increased secondary voltage adapted to the actual behavior of the foamed slag; immediate recovery of the chemical reaction energy obtained by post-combustion of the combustible gases directly in the furnace vessel space prior to their withdrawal; arrangement of supplemental oxy-fuel burners to intensify and increase the rate of rapid melting of the scrap iron charge in the furnace vessel; preheating the scrap iron charge prior to charging the charge to the furnace by utilizing substantial and efficient thermal energy as a result of the chemical reaction contained in the hot waste gases in combination with the oxy-fuel burners; and finally the arrangement of ultrasonic oxygen blasting sets to intensify decarburization and slag foaming.

Of the aforementioned methods of intensifying metallurgical process technology, three methods utilize means other than electric arc energy to increase the temperature of the scrap iron charge, the methods being: immediate recovery of the chemical reaction energy contained in the furnace vessel obtained by post-combustion of combustible gases; arranging additional oxygen-fuel burners in the furnace vessel; and preheating the scrap iron charge before charging it to the interior of the furnace vessel.

The essence of the first method is the immediate recovery of the energy of the chemical reaction generated in the interior of the furnace vessel by burning the combustible components of the waste gases generated during the actual processing of the scrap iron by melting, before being withdrawn out of the process, by oxygen gas. This method has been used with varying success in Martin

31114T furnaces (SM furnaces), alkaline oxygen furnaces and energy optimized furnaces. In an alternative embodiment of this method, the use of oxygen gas is replaced by preheating the oxygen-enriched air by substantial thermal energy from the exhaust gas exhausted furnace vessel. Nevertheless, the results obtained when used in combination with electric arc furnaces show only a limited increase in production productivity and reduced energy savings, especially when the method is used during the melting of a ferrous scrap batch running simultaneously with the electric arc. , with real savings resulting from in-situ pre-heating of scrap. Indeed, the effect of post-combustion in the interior of the electric arc furnace at the stage of already molten iron scrap is substantially suppressed by the lack of heat transfer efficiency between the combusted gases and the molten metal bath, since the metal bath is covered with a deep layer of thermally insulating foamed slag. In the light of the above, a logical explanation of the seemingly confusing assertion that post-combustion of waste gases in the electric arc furnace space is also highly effective after the scrap charge has been melted, based on the following, is supported by the following: by post-combustion of the combustible components of the waste gases exiting the foamed slag, the temperature rises and, consequently, the volume of the waste gases in the free space above the slag increases. The resulting gradual, proportional increase in the pressure of the waste gases in the furnace vessel space then reduces the suction of cold ambient air into the furnace space. On this basis, and as long as the interior temperature is unconditionally maintained in the furnace vessel space, the requirement to consume electricity for the heating of the cold air is eliminated, which in turn results in its savings. It must also be clear from the above that, in comparison with the afterburner, which requires the introduction of additional oxygen,

31114 T, the above-described method exhibits the same or even higher energy savings, moreover, without additional operating costs, which is achieved both by a sufficiently satisfactory sealing of the furnace vessel and, on the other hand, to adequately prevent the suction of cold air. Moreover, the consequence, and in particular the extraordinary benefit resulting from sufficient sealing of the electric arc furnace, is a significant reduction in the amount of hot off-gas withdrawn from the furnace. In the case of an 110-ton electric arc furnace, the exhaust gas off-take is reduced by more than 50% (from the original 90 000 Nm ³ / h to a reduced 40 000 Nm ³ / h), allowing one exhaust fan to be removed from operation.

The essence of the second method of intensifying the operation of the metallurgical process technology, using means other than electric arc energy, to increase the temperature of the iron scrap charge, is to amplify the action and increase the rate of rapid melting of the charge. scrap by arranging supplementary oxy-fuel burners in the furnace vessel. Although the results of the oxy-fuel burners have been positive for a faster melting of scrap in the slag tap area of an electric arc furnace 30 years ago, this process has not been used extensively until high-performance designs have been constructed. melting furnaces with water-cooled wall parts. The useful capacity of short-flame oxy-fuel burners arranged in the walls of the furnace vessel and conveniently located in the so-called " Cold zones located between the electrodes cause a shortening of the melting time of the total charge in the furnace. These positive results triggered the inclusion of additional burners in the design of electric arc furnaces, and this has become an almost fashionable matter. In the last few years, a number of different design types of oxy-fuel burners have been developed, which can be used in electric arc furnaces, with increasing and higher performance. The thermal power input of the currently used oxygen 31114 T fuel burners represents in some cases more than 50% of the initial power input. Although this implies low operating costs and an increase in the overall power consumption of shortening the time between taps, resulting in an increase in the required production productivity and resulting in further operational and economic improvements, a number of other significant disadvantages are overlooked. Generally speaking, some of the main and major drawbacks are: higher oxidation of scrap batch, greater volume of generated waste gases, substantially reduced heat transfer efficiency when the burners are operating concurrently with the arc, especially when the burners are operating all the time during heating. Practical operating results have shown that the highest energy efficiency is achieved when the actual melting or heating is started only by using burners, which are then replaced after the batch has reached a temperature of about 800 ° C by the action of electric arc. The result of this two-stage technological process is the saving of electrical t

energy in the range of 15 to 20% and savings in fossil fuel and oxygen in the range of 10 to 15%. Unfortunately, the gradual application of both types of thermal energy results in an increase in the time between individual taps by 10 to 12%. Although the cost of installing oxy - fuel burners in already operating melting furnaces is relatively low from an economic point of view, in almost all cases this leads to a substantial increase in costs due to the necessity of rebuilding and expanding the entire exhaust system. From an ecological point of view, only in a rough manner, the operation of an electric arc furnace with an excessively high performance of oxy-fuel burners and reduced energy efficiency, producing a disproportionately large amount of hazardous component containing waste gases, becomes unconditionally unacceptable.

The essence of the third method of intensifying the efficiency of metallurgical process technology, using means other than electric arc energy to raise the temperature of the iron scrap charge, is to preheat

31114T scrap iron batches before they are introduced into the interior of the furnace vessel using substantial and efficient thermal energy obtained by the chemical reaction and contained in the hot waste gases combined, if necessary for environmental reasons or on demand, using oxygen - fuel burners.

Since the introduction of the method of preheating the scrap iron batch, the method has undergone several developmental stages: preheating the scrap batch in the charging bucket using hot waste gases or by means of air-fuel and oxy-fuel burners; continuous preheating in an inclined rotary kiln or on a horizontal vibrating conveyor using a combination of hot waste gases withdrawn from the metallurgical kiln and air-fuel and oxy-fuel burners; continuous preheating in a vertical preheater of a controlled controlled downcomer device which forms an integral part of the furnace and which utilizes hot waste gases from the furnace passing in countercurrent to preheat; and preheating the in situ batch of scrap introduced into the furnace at the beginning of the melting by simultaneously heating under the action of an electric arc and by means of a plurality of air-fuel and oxy-fuel burners of different designs. In addition, there are several other specific designs of preheating mechanisms formed by combinations of the above systems and operating with more or less significant results.

The currently used scrap preheating technology is the result of knowledge that has been preceded by long-term surveys. Based on the finding of its great potential and theoretical possibilities, it is expected to represent another cornerstone in the development of steelmaking technology in electric arc furnaces, consisting in the production of steel predominantly from scrap iron and taking into account electricity savings, reducing electrode consumption, increasing production productivity by shortening time between each

31114 T taps and a particularly significant and useful advantage in reducing the amount of environmentally polluting emissions.

Based on the overall summary and practical experience of the actual operating conditions of a number of known technological processes and methods associated with the attempt to achieve a substantially significant increase in the energy efficiency of the technological process of steel arc electric furnaces, largely made from a mixture of scrap and steel scrap , it has been decided that in terms of rapid and efficient melting, the most suitable technology is adequate pre-heating of scrap before it is fed into the melting furnace. The aim of the following outline of the device and method of technological processing is to endeavor to specify in its basic features an autonomous, simple, robust and reliable device and method showing the required and practically achievable characteristics and parameters concerning maximum energy efficiency and economically advantageous production of cold scrap steel. using an electric arc furnace cooperating in tandem with a preheater for scrap preheating. At the same time, such preheating devices and the method of preheating, which are at the same time an object of the present invention, must be obligatory modernized and progressively ecologically advanced and must show increased safety in combination with improved working conditions.

For charging the autonomous preheating device, a modified, appropriately sized, sized scrap iron is used, which must be supplied to the device continuously or semi-continuously from an area of the scrap landfill located at an acceptable distance and at an acceptable level relative to the mechanism for conveying and charging scrap to the preheater. In this case, the mechanism for transporting and charging the scrap to the preheater must be an integral part of the preheater. Accordingly, the charging of scrap into the preheater is not batch-wise using

31114 T loading bucket and overhead crane acceptable. The design and positioning of the autonomous preheating device shall not be impeded in the adjacent location of an arranged electric arc furnace operated in the normal way, nor shall it permit the decommissioning of the preheating device and the charging of the melting furnace through the swiveling lid and the loading bucket. In the event of the pre-heating plant being decommissioned, it shall be fitted with a bypass line and gaskets to extract the hot waste gases exiting the melting furnace for transfer to the afterburner chamber for final afterburning and the final stage of the pre-heating plant.

In accordance with the requirement to reduce production costs, it is expected that the proposed preheater will utilize primarily and to the maximum extent possible the substantial and efficient thermal energy of the chemical reaction of the hot waste gases exiting the melting furnace. Currently, fossil fuel, usually natural gas, is used as an energy source to support and increase the melting process in the furnace by means of air-fuel or oxy-fuel burners arranged at different locations in the side walls of the shell and / or at the furnace age. In order to increase energy efficiency, it is necessary to ensure that these air-fuel or oxy-fuel burners are installed in the appropriate locations and as part of the preheating device. The expected benefits, improvements and benefits of this embodiment will be improved energy efficiency; reducing the effect of the cyclically fluctuating nature of the temperature of the hot waste gases exiting the melting furnace on the operation of the preheater; a significant increase in the safety of operation, given that the combustion burners arranged in the preheater are fixed and equipped with a predominantly non-divided supply line; simplification of the design of the upper section and the water-cooled wall sections of the furnace shell due to the absence of and from the burner arrangement

31114 T resulting in a beneficial effect on maintenance requirements, a reduction in the total number of combustion burners and a simplified replacement of the upper furnace section assembly. In order to further reduce energy costs, it is desirable to introduce an appropriate amount of high carbon waste materials into the cold batch of scrap to be charged to the preheater.

It is expected that the technological treatment of the scrap batch by preheating it prior to charging into the melting furnace in an autonomous preheater of the apparatus will result in the scrap batch leaving the apparatus preheated to a predicted temperature ranging from 650 to 800 ° C (1,200 to 1,470 ° C). F) depending on the lump size of the scrap, at an average temperature of 700 ° C (1290 ° F) and an average heating gas temperature of a generally reducing nature maintained in the range of about 1 050 ° C (1 920 ° F); whereas, in addition, it is expected that the temperature of the hot exhaust gases exiting the preheater and into the combustion chamber - still of a reducing nature - will be in the range of 950 to 1000 ° C (1740 to 1830 ° F), which represents temperatures above the critical value necessary for the cleavage of undesirable volatile hydrocarbons, including dioxins and furans, by combustion.

In accordance with the above new apparatus and method, several types of apparatus and methods having the purpose of incorporating scrap preheating and designed for use in the manufacture of steel in an electric arc furnace will generally be described based on the facts set forth in the following US patents.

U.S. Pat. No. 4,543,124 (Sep. 24, 1985) Apparatus for continuous steelmaking, known in the art as Steel Contouring. In this technology, furnace waste gases and fuel are used to preheat scrap moving on a conveyor in a special horizontally arranged preheater tunnel, before it is charged to the furnace. Then the scrap is fed into the furnace through the charging

31114 T hole in the side wall of the tire. Waste gases pass through scrap in countercurrent. The electric arc furnace keeps the bath melted even when the furnace is tilted after tapping. Electricity consumption ranging from 350 to 400 kWh / tonne is too high compared to the standard power consumption of a conventional electric arc furnace. The device itself requires a large space for the conveyor arrangement; and the actual pre-heating of the scrap on the conveyor is not very energy efficient because the scrap is preheated predominantly from above.

U.S. Pat. No. 4,852,858 (August 1, 1989) Preheater for Charging Material Preheater for Preheater Charging Materials for a Metallurgical Smelting Unit, known in the art as an Energy Optimized Oven, shows favorable results and is often used in iron production . However, the semi-continuous vertical preheater device with a controlled controlled downward passage of scrap is an integral part of the non-electric metallurgical melting furnace and utilizes a countercurrent flow of hot exhaust gases withdrawn from the furnace arranged below the preheater after almost complete post-combustion. Finally, the satisfactory operating results of this design have led some developers in the field of electrical metallurgical plants to adapt some of its features, modified accordingly, to the understanding of the electric arc furnace. The overall height, overall spatial range and uncontrollable suction of false air into the individual chambers are considered to be significant shortcomings.

J of this device ·

U.S. Pat. 5 153 894 (6.10.1992) A remelting aggregate with a removable shaft preheater of a shaft type material, known in the art as a shaft furnace, is a batch remelting device provided with a shaft type material preheater, which is an integral part of the melting furnace and which uses a countercurrent flow

31114 T of hot waste gases. By relative movement in the horizontal direction between the furnace vessel and the furnace lid by means of a support structure arranged on the lid, the furnace is opened and can be loaded from the hopper either directly into the furnace vessel space or into the shaft displaced relative to each other. The feed material can be maintained in these shafts by means of the construction means arranged therein and at the same time heated during the refining phase. One alternative embodiment of this arrangement exhibits several, due to its complex and complicated construction, the resulting problems, which are the complex transfer of the charge from the shafts to the furnace space; two swivel mounting assemblies to allow loading from above or for handling the furnace vessel; a clumsy shape configuration of the sheath caused by the arrangement of the shaft structure for preheating scrap; a separate tilting structure for handling the casing and the associated formation of a large gap between the casing and the furnace lid causing heat loss; the uncontrollable descending passage of scrap through the shaft, which causes occasional clogging, pushing and slipping of large batches of scrap; Inadequate flow of gases through the shaft in countercurrent, which causes uneven preheating of the scrap in the shaft and the existence of two serious problems of the technological process: transient, uncontrolled formation of explosive mixture and emission of toxic substances caused by low temperature of waste gases at the outlet. In addition to the fact that reheating cooler gases by combustion burners is in principle and de facto contrary to the purpose of this type of preheating system, there is virtually no possibility of eliminating emissions of toxic substances and the occurrence of explosions, as a result of which occur.

U.S. Pat. No. 5,264,020 (Nov. 23, 1993) A remelting aggregate with two melting furnaces arranged side by side (known as a two-chamber shaft furnace) is actually an aggregation of two shaft furnaces.

31114 T furnaces arranged side-by-side with an alternating process in which the furnace gases generated during the melting process in one melting furnace are introduced into the other melting furnace in order to preheat the feed material; each melting furnace is coupled to a shaft that is charged with feed material, and the waste gases from the furnace in which the melting process is carried out are introduced through the furnace-coupled shaft through the lid into the second furnace and from there after passing through a manhole that is coupled to it, pulling away from the device. This technological process, which runs through the entire process, allows preheating of the feed material and filtering of the furnace gases as they pass through the feed material. Since the two-chamber shaft furnace is in fact very similar to the shaft furnace, with the exception of insignificant differences in the charging arrangement of the charge material, all notes and comments in relation to the shaft furnace are applicable to this remelting unit.

U.S. Pat. No. 5,499,264 (March 13, 1996) A method and arrangement for controlling the operation of a dual metallurgical plant known from the prior art as a double jacket furnace. In fact, this arrangement is also an aggregation of two almost complete self-operating groups in a single electric arc furnace arranged side by side. The description of said aggregation is as follows: a metallurgical doubled apparatus includes two electric arc furnaces interconnected by means of a duct, an energy source, a feed material charging mechanism and a waste gas removal and purification system. The method includes the step of connecting the first of the two furnaces to the power source for the purpose of melting the charge therein while simultaneously disconnecting the second of the two furnaces from the power source. The second furnace is charged with the charge material and then closed with a lid. The waste gases present in the first furnace above the molten charge are withdrawn from the furnace and are sucked into and pass through the second furnace by means of a pipeline arranged between the two furnaces, while the waste gases,

31114 T, located in the second closed furnace, pass through and are sucked above the charging column and outside the furnace. When exhausting the off-gases outside the second furnace and simultaneously supplying air to the lid area of the first furnace, the off-gas connection of the off-gases between the first furnace and the gas scrubbing system is interrupted. The flow of preheating gases with respect to the arrangement of the scrap charge is essentially countercurrent. Higher productivity in this system is achieved through the complex design of the suction system. The preheating of scrap batch is uneven, resulting in higher oxidation losses. In addition, the top loading of two containers requires the oven lid to be pulled, resulting in additional heat loss.

U.S. Pat. 5 513 206 (30.4.1996) Apparatus for preheating and charging scrap material. The device for preheating and charging the waste material comprises preheating chambers of the shaft configuration and a charging unit. The exhaust gases extracted from the furnace pass through ¹ downwardly passing scrap in countercurrent. The scrap feed is conveyed by means of a two-stage syringe through a charging opening in the furnace lid to the space between two DC electrodes. The charging of the preheated scrap into the furnace takes place with complete sealing and without the use of water-cooled wall parts. In addition, this furnace has an extremely complex construction. The furnace shaft is narrow and is therefore equipped with anti-clogging means. Likewise, its overall height constitutes a significant disadvantage.

U.S. Pat. Process and device for melting down scrap, known in the art as a remelting In the furnace used in the furnace, the DC electric arc is a heated shaft furnace with an annular configuration shaft formed by means of an external and inner vessels that surround and protect the centrally arranged graphite electrode. The scrap feed is fed to a container using a suitable conveying mechanism

31114T of the upper section of the annular shaft at a rate corresponding to the speed of the melting process in the lower section of the furnace. During the downward passage, the scrap is preheated by the upwardly passing gases. At the outlet, above the scrap column, low temperature gases are introduced into the annular piping and conveyed to the system for processing: The patent claims that the operation of this furnace, due to the filter effect of the scrap column, has low dust emissions in the waste gases. In accordance with the desire to unify the electric arc furnace and the preheating of the scrap into one unit, this arrangement constitutes a combined construction. The scrap charging system of this arrangement is structurally complex, does not guarantee controlled control of the downward scrap passage, and consequently undesirable clogging. In addition, the furnace is not equipped with a tilting mechanism, which makes moving or replacing the lower part very difficult.

U.S. Pat. No. 5,573,573 (Nov. 12, 1996) An electric furnace arrangement for producing steel, known in the art as simultaneous remelting. The document discloses an electric arc furnace for the production of steel by remelting scrap, in particular broken iron and / or iron sponge and / or pig iron, together with slag additives in the furnace vessel, into which at least one graphite electrode extends in the direction of its longitudinal axis. wherein an electric arc is ignited between the graphite electrode and the charge material. To achieve a particularly high power input, the lower portion of the vessel in the region of the graphite electrode exhibits a radial extension extending outwardly relative to the upper portion, and an inclined graphite electrode extends laterally into this lower portion of the furnace vessel. The furnace has an elongated vertical shaft and is continuously charged with a cold batch of scrap through a conveyor. The patent claims that the waste gases flowing through the downwardly passing scrap in countercurrent, which are still sufficiently warm in the upper part of the shaft even after the scrap preheating, are rapidly cooled by dilution so that no toxic gases are produced.

31114 T

According to another embodiment, the waste gases are transferred to a collection system. The complex combined design is characterized by very low power consumption.

In addition to these contiguous and specifically accurate notes and comments relating to the disadvantages and drawbacks of each of the prior art calculations of the above-described system and processing equipment and method of processing, intensifying the metallurgical process technology, all of these arrangements exhibit a fundamental disadvantage and drawback. : the passage of hot waste gases through the scrap feed in countercurrent. This essential, essential and operationally unfavorable feature is in most cases known in the prior art preheating devices, systems and methods a major reason for their poor performance.

In summary, the results achieved in terms of production productivity, energy savings, polluting emissions and, last but not least, operational safety, intensification of the metallurgical process technology of steel in an electric arc furnace predominantly from scrap, using prior art preheating equipment, systems and methods they quite clearly indicate that their level is below the pre-charge pre-heating performance level of the pre-charge pre-heating device with appropriately applied basic physical laws and appropriately utilized practical experience.

SUMMARY OF THE INVENTION

Accordingly, it is an essential object of the present invention to provide an autonomous, additional, independently operating, energy efficient, operationally safe and emission polluting exhalation-reducing preheater and a method for treating a ferrous scrap feedstock with co-current passage of iron scrap and heating gases in a closed circle. automatic,

31114T controlled, gradual and gradual pre-heating of cold scrap iron / steel waste mixture, and operation - charging the preheated charge to an adjacent, tandem cooperating sealed metallurgical-electric arc furnace, which allows to overcome and overcome all the disadvantages mentioned above.

Another object of the present invention is to provide a main vertically arranged preheating chamber of generally prismatic configuration with a converging section in the shape of an inverted pyramid arranged at its bottom and a removable seal closure at its top to feed-charge the cold charge of the iron chamber into the scrap chamber.

Another object of the present invention is to provide a main vertically arranged preheating chamber, the walls of which consist of refractory or water-cooled parts attached to a respective independent self-supporting structural structure.

It is a further object of the present invention to provide an independently operating, simple and robust transport-charging mechanism for semi-continuous supply of cold scrap iron from an adjacent scrap scrap dump, preferably located at a lower level without the need for a bucket loader or overhead crane into the uppermost compartment. a main vertically arranged preheating chamber, provided with a charging opening with a sealing closure, said transporting-loading mechanism consisting essentially of at least one inclined high-speed lifting mechanism provided with a fixed hopper.

Another object of the present invention is to provide one or more robust and sufficiently cooled control systems for the controlled gravity control of the downward passage of the iron scrap batch, each consisting of frames with grate assemblies, controlled by successive pivoting and reciprocating movements between retracted and retracted movements.

31114 T extended position dividing the interior space of the main vertically arranged preheating chamber into at least two chamber sections capable and adapted to maintain at least half the amount of scrap of its nominal charge required for one melting performed in an adjacent, tandem cooperating metallurgical-electric arc furnace.

Another object of the present invention is to provide one or more oxy-fuel burners with instantaneous regulation of the oxygen / fuel ratio change in each chamber section of the main vertically arranged preheating chamber for the purpose of continuously controlling the combustion of continuously evolved gases as they pass through the entire preheater space. as a result of which the gradual pre-heating of the scrap iron batch is controlled to a desired, predetermined temperature before being fed into the metallurgical melting furnace.

Another object of the present invention is to provide sensing means in each chamber section of the main vertical preheater.

The chambers and other positions present in the gas flow for measuring actual instantaneous quantities of temperature, pressure and chemical analysis of the gases used to instantly correct and control the characteristic exhaust pressure and the progressive combustion of the combustible gases generated during the actual preheating process.

Another object of the present invention is to provide a simple and robust refractory transport and charging mechanism for controlled unloading to a high temperature preheated charge of scrap metal from the exit opening of the converging section located at the bottom of the main vertically arranged preheating chamber and to carry out this pre-heated charge. a cooperating metallurgical-electric arc furnace through an opening arranged in the side wall of the jacket in the furnace lid, the conveying and charging mechanism consisting essentially of a sliding gate valve of the exit opening of the converging section of the preheating chamber, of alignment and rolling rollers and inclined,

31114T reversible sliding lifting mechanism, equipped with a roller trough with rollers with an internally arranged reversible sliding plunger ram.

It is a further object of the present invention to provide two inlet openings at the highest point of the upper chamber section, one opening for supplying hot waste gases from a metallurgical-electric arc furnace containing substantial and efficient thermal energy resulting from the chemical reaction of these gases. the orifice is intended to receive partially recirculated recuperated hot gases from the afterburner chamber for final afterburning.

It is a further object of the present invention to provide a correspondingly adequate vacuum, which generates appropriate suction effects at various points in the preheater and in particular to significantly combine and equalize the individual pressures of any and all gases entering the main vertically arranged preheating chamber for flow from the highest. a point of the upper chamber section downward through the charge in the direction of the downstream descending passage of the scrap iron charge by gravity and causing the hot gases to be mixed, including the initial hot waste gases withdrawn from the adjacent tandem cooperating metallurgical electric arc furnace to the recuperated chamber after combustion, hot gases generated by the action of oxygen-fuel burners arranged in the walls of the individual chamber sections as well as the hot gases that evolve during the oxidation of the combustible substances contained in the batch, assisted by oxygen, oxygen-enriched air or air.

It is a further object of the present invention to provide a set of two parallel and analogous stacking chamber / diverging dust collector and collection boxes, arranged directly and vertically arranged below the bottom emptying converging bottom.

31114 T chamber section of the main vertically arranged preheating chamber, wherein the hot combustion gases pass through two slotted openings in the converging bottom and are directed to the top of each combination chamber / divergent dust collector equipped with oxygen / fuel burners / oxygen ratio control due to the final post-combustion of combustible substances and gas temperature adjustment, eliminating the formation of undesirable dioxins and furans.

It is a further object of the present invention to provide more than one and preferably two hot waste gas by-pass lines equipped with suitable shut-off throttle means for interconnecting the main exhaust duct leading from an adjacent tandem cooperating metallurgical-electric furnace to the upper preheater. through the interior of the combination chamber / diverging dust collector allowing hot exhaust gases to be drawn from the furnace directly to the combustion chambers for final post-combustion, thereby facilitating complete by-pass of the preheater and allowing the electric arc furnace to operate independently of the preheater.

Another object of the present invention is to provide a venturi scrubber slot with priority function, consisting in the instantaneous rapid cooling of hot waste gases to a temperature below the lower critical temperature of dioxin re-synthesis and a secondary gas purification function.

t ’

Other objects and features of the present invention will be apparent from the following summary of preferred embodiments thereof and the detailed description of these embodiments in combination with the accompanying drawings. It should be understood, however, that the purpose of the appended drawings is to be given by way of illustration only, not to be construed as limiting the scope of the present invention in any way solely on the basis of the appended claims.

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In view of the foregoing, and in order to overcome the disadvantages and disadvantages of prior art iron scrap preheating devices and methods, iron scrap preheating in accordance with the present invention is accomplished by independent and autonomous, self-weighting, minimal operational maintenance requiring, a preheating device and a method for preheating scrap, of simple and robust construction adjacent to a sealed and tandem cooperating metallurgical-electric arc furnace, the design of such a preheating device allowing it to be connected economically and without the need for a larger scale to existing and operating accessories and / or a new melting electric arc furnace. Operating in tandem with a sealed metallurgical-electric arc furnace will achieve high energy efficiency and high operating performance of the preheater, and the closed-circuit scrap processing method in accordance with the present invention will substantially affect the technological process of steel production as such. In addition to the particularly significant benefit of substantially reducing the volume of air polluting toxic gases and solids during operation of the preheater and closed loop process in accordance with the present invention, the proposed solution will, inter alia, contribute to reducing electricity and other energy consumption; electrode consumption and shortening of time between taps in conjunction with increased safety; and. improved working environment and how. the whole culminate in overall increased operating performance and economic profitability.

According to the present invention, its objective is achieved by applying a new and specific exploitation of the characteristic physical and chemical phenomena during processing related to heat generation and heat transfer through various thermal energy sources related directly or indirectly to the technological process of steel production during the journey from cold

31114 T, \ = ä (Í 3 i * *) - scrap iron feeds into an electric arc furnace, while applying new, more advanced and convenient, as well as a highly functional design and individual components.

Taking into account the operation of a conventional steel arc electric furnace, charged from above by a cold charge of scrap iron through one or more charging bucket loaders, the amount of waste gases withdrawn or escaping from the steel furnace is dependent on several basic factors. These factors are: the composition, quantity and quality of the lime and other additives used, the amount of gases generated by the oxy-fuel burners, the amount of carbon and oxygen introduced to froth the slag and the like, and most importantly the amount of ambient cold air drawn into the circulation steel furnace. Without airtight sealing of the furnace vessel, which is practically impossible even in the case of so-called. For example, by direct withdrawal through the four openings arranged in the furnace lid, the volume of the off-gases to be withdrawn can be in the range of 350 to 450 m ³ / tonne of steel produced. By eliminating the intake of cold air, which can be achieved by means of an airtight seal of the furnace, and without the use of a decarburising oxygen blasting kit, the amount of hot exhaust gases drawn through the four holes in the furnace lid can be substantially reduced to 90-120 m ³ / tonne steel. By using a decarburizing oxygen blasting kit, the volume of the off-gas withdrawn proportionally, relative to the amount of decarburising oxygen injected, is increased to an amount ranging from 200 to 220 m ³ / tonne of steel produced.

In addition, the exhausted hot waste gases contain a significant amount of hazardous by-products. One example of some of the impurities contained in the hot exhaust gases drawn through the openings in the furnace lid at which air is drawn into the furnace vessel is shown in Table I. Very high temperature surrounding the surroundings

The 31114T electric arc and the high temperatures found in the interior of the furnace vessel generally produce large amounts of carbon oxides as well as the following by-products: nitrogen and sulfur oxides, cyanides, fluorides, dioxins and furans. As regards the concentration of nitrogen oxides and cyanides, which is mainly dependent on the amount of nitrogen sucked into the cold air furnace space, this depends on the power of the electric arc furnaces and the degree of molecular nitrogen dissociation in the interior of the furnace. The amount of sulfur oxides in the waste gases is not usually too high. The fluoride concentration in the waste gases is equally low and is directly related to the fluorspar content of the slag. The content of dioxins and furans is controlled by the amount of flammable contaminants contained in the charged iron scrap, and their evolution and decomposition is controlled by the temperature of the off-gases exhausted.

Table I

Content of harmful contaminating gaseous substances in hot waste gases withdrawn from electric arc furnace Harmful contaminants Average concentration (mg / m ³ ) Amount of withdrawn next. products (g / tonne, steel) Carbon oxides 13 000.0 1 350.0 Nitrogen oxides 550.0 270.0 Sulfur oxides 5.0 1.6 cyanides 60.0 28.4 Fluoride 1.2, 0.56

31114 T

The dust concentration of the exhaust gas furnace, whose volume is up to 60 - 70%, consists of particles smaller than 3 microns in diameter. This dust generated during heating, assisted by the suction of cold air into the furnace, contains a large amount of Fe ₂ O ₃ . ¹

Taking into account the general state of environmental pollution, it is vital to reduce to a minimum the generation of any harmful products, mainly through industrial processing as a whole. However, this task must be carried out by means which are equally acceptable in terms of their own industrial processing. Reducing the amount of contaminating products generated during industrial production processes must be done by changing their technological process, taking into account overall economy and cost, so that its implementation will not only protect the environment but also economic benefits combined with greater safety at work and improved operating conditions.

In summary, the pre-heating device and the method of pre-heating steel scrap by stepwise preheating with the co-current passage of steel scrap and hot waste gases intended for metallurgical melting furnaces according to the present invention as a whole, due to their design include a number of complementary and interacting more or less significant functional, constructional and operational characteristics and parameters that make the proposed arrangement exhibit the following capabilities:

The ability to couple the preheater and the method of preheating the steel scrap as a whole in combination with most of the prior art electric arc furnaces known and used in smelting plants with a short return on investment.

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The ability of synchronized operation in tandem with most of the known metallurgical melting furnaces, preferably with an airtight sealed electric arc furnace for the production of steel from a cold batch of ferrous waste.

Ability to substantially reduce the amount of hot waste gases withdrawn from the electric arc furnace by totally removing oxygen - fuel burners and so - called. post-combustion from the furnace vessel.

- The ability to increase energy efficiency by operating the preheating device in tandem with an electric arc furnace and removing energy-inefficient oxy-fuel burners from the furnace vessel and transferring them efficiently to the preheating device.

- The ability to increase energy efficiency by removing post-combustion in the interior of the electric arc furnace vessel and utilizing the substantial and effective thermal energy of the chemical reaction contained in the hot waste gases withdrawn from the electric arc furnace in the chamber sections of the preheater with nearly twice the heat transfer efficiency from the waste gases to the scrap.

- The ability to increase energy efficiency by eliminating the need to retract the furnace lid each time the scrap is loaded and fed into the furnace using a bridge overhead crane and a bucket loader.

- Ability to eliminate the need for the arrangement of overhead loading cranes and conventional loading bucket loaders due to the self-weighing capability, provided by an integrated, semi-continuous self-loading loading mechanism equipped with a hopper.

31114 T

- The capability of simple and trouble-free loading and reloading of the integrated, semi-continuous, self-loading loading hopper via conventional, low-level horizontal conveyors or the handling equipment of road transport equipment.

The ability to effectively preheat a cold batch of scrap iron semi-continuously charged into the upper chamber section of the preheater to a predetermined temperature at the outlet of the lower chamber section, comprising burning all combustible substances introduced into the preheating device to the greatest possible extent and positioning equipment and, in particular, a significant forced combination of any and all gases entering the main vertical preheating chamber for the purpose of flowing downwardly from the upper chamber section through the scrap batch in coincidence with the downward scrap passage by gravity, the mixture of combined hot gases comprising initial hot waste gases; withdrawn from the metallurgical-electric arc furnace, recovered hot gases from the afterburner chamber for final afterburner, hot gases, generated by means of oxy-fuel burners arranged in the walls of the individual chamber sections, as well as hot gases which are produced by the oxidation of flammable substances contained in the oxygen assisted charge, oxygen-enriched air or air.

- The ability to efficiently preheat the scrap batch to the desired nominal preheat temperature, without the use of hot waste gases drawn from an adjacent, tandem cooperating electric arc furnace and only using oxy-fuel burners arranged in the preheater of the preheater and forced charging of the preheater vessel. furnaces, which takes place at the beginning of the operation before the so-called. cold start of the furnace with increased intensity and which, after starting it, quickly reach normal operating conditions with a flat bath

31114T as a result of the immediate formation of a bath of molten metal under the electrode (s), especially when the system is expanded to include an oxygen fuel / oxygen breathing kit and the early formation of foamed slag.

Ability to reduce scrap oxidation losses by controlled gradual, stepwise preheating of scrap iron batches by adjusting intermediate temperatures and gas composition through controlled control of the actual power consumption of oxy - fuel burners and the introduction of oxidizing agents.

The ability to control the semi-continuous downward passage of the scrap iron by gravity by means of a simple and robust, appropriately cooled, control mechanism for the controlled control of the downward passage of the scrap iron batch.

- The ability to ensure reliable and trouble-free emptying of the preheated iron scrap batch from the converging bottom to the refractory transporting mechanism for forcing the preheated batch into the furnace, including weighing with the required accuracy of each scrap scrap being carried.

The ability to provide a semi-continuous forced transfer of a preheated charge of scrap iron from a preheater to an adjacent, in tandem cooperating electric arc furnace, with an intensity corresponding to the melting performance of the furnace allowing the operation of the furnace with a continuously existing the corresponding depth, density, chemical composition and characteristics, and in connection therewith ensuring the high thermal efficiency of the melting and remelting of scrap introduced into the molten metal bath.

- Ability to allow continuous operation of an adjacent, tandem cooperating airtight sealed metallurgical-electric arc furnace with a bath of molten metal as a result of semi-continuous forced feed preheated, sized in size

31114 T scrap iron charge into the furnace vessel, with an intensity corresponding to the melting performance of the furnace.

When compared to conventional steel production and standard metallurgical equipment using cold scrap scrap, the above calculation of performance achieved in accordance with the present invention results in a substantial improvement in the following technical parameters and economic factors:

- Reduction of electric power and power of furnace transformer in the range of 25 to 35%.

- Reduction in electricity consumption between 25 and 35%.

- Electrode consumption reduction between 15 and 20%.

- Reducing the amount of waste gases withdrawn from 40 to 45%.

- Reducing the amount of dust and hazardous by-products generated between 20 and 25%.

- Reducing the levels of dioxins and furans below the limits currently in force.

- Reduce voltage fluctuations below specified limits.

- Possible elimination of electrical high-voltage equalizer to optimize furnace impedance.

- Shortening the time between taps between 15 and 20%.

- A typical reduction in the capacity of a gas cleaning station between 25 and 30%.

- Reduced maintenance requirements due to drastic short-circuit reduction and characteristic power fluctuations during operation.

- Increased safety and improved working environment conditions, in particular as a result of semi-continuous and semi-automatic charging of the furnace with pre-heated scrap charge, which both eliminates possible explosions due to dangerous opening of the furnace,

31114 T by charging wet scrap with a loading bucket loader as well as reducing unwanted noise levels.

BRIEF DESCRIPTION OF THE DRAWINGS

For the sake of easier understanding of the proposed apparatus and method for preheating scrap in accordance with the present invention, these will be described and illustrated in detail with reference to the non-limiting general examples in combination with the accompanying drawings. In the accompanying drawings, the same or similar components are designated with the same reference numerals.

Fig. 1 shows a preheating device for preheating and an adjacent, tandem cooperating electric arc furnace in accordance with the present invention, shown in a left vertical longitudinal section along the lines IV-IV of FIG.

Second

Fig. 2 is a pre-heating device according to the present invention, shown in a right-side vertical side view and a partial section along line II-II in FIG. First

Fig. 3 shows an alternative embodiment of the device according to the present invention, shown in a vertical side section along the line III - III in FIG. First

Fig. 4 illustrates two opposing grate assemblies of an actuating mechanism for controlling gravity of a downward passage of an iron scrap batch in accordance with the present invention, shown in a schematic horizontal view in plane I-I of FIG. Second

Fig. 5a, 5b, 5c, 5d, 5e and 5f show a control mechanism for the controlled control of the downward passage of a scrap iron batch by gravity in various operational operating positions;

31114T shown in enlarged schematic vertical sections along the V-V plane of FIG. 4th

Fig. 6 shows the scrap hopper in the upper unloading position with the upper chamber section of the main preheating chamber of the device of FIG. 1, shown in an enlarged detail view.

DETAILED DESCRIPTION OF THE INVENTION

A preferred embodiment of the preheater and its operation for the preheating of scrap in accordance with the present invention shown in FIG. 1 and other drawings of the accompanying drawings, comprising two functionally interconnected bases: a preheating device 7 and an operating system for preheating scrap and an adjacent tandem cooperating electric arc furnace 2. In addition, the autonomous preheating device 1i consists of three basic design and functional elements. the main vertical preheating chamber 3, the inclined self-weighing lifting mechanism 72 for conveying the hoppers 37, and the inclined conveying charging mechanism 57 for conveying the iron scrap batch 8/3 emerging from the converging bottom of the main vertical preheating chamber 3 and forcing the feed iron scrap 8/3 into an adjacent, tandem cooperating electric arc furnace 2.

The basic part of the preheating device T is the main vertical preheating chamber 3, which is by means of two sets of grate assemblies, namely a pair of grate assemblies 4/1 and 4/2 and a pair of grate assemblies 5/1 and 5/2 for controlled control of the downward passage of scrap divided into three chamber sections, an upper chamber section 5, a middle chamber section 6 and a lower chamber section 7. The arrangement of each of these three chamber sections has a specific objective and purpose of controlling the gradual increase in the cold temperature as efficiently as possible.

31114 T of scrap iron 8/1 introduced into the preheating device 7 and its semi-continuous downward passage by gravity, which in succession is enabled to control operation of both the grate assemblies 4/1 and 4/2 and the grate assemblies 5/1 and 5 / second

Since it is envisaged to seal the entire main vertical preheating chamber 3 of the scrap preheating device 1 as well as the interior space 38 of the upper chamber section (see FIG. 1) from the ambient atmosphere, a closure structure consisting of airtight, water-cooled walls. The shorter wall portions 10 of the upper chamber section 5, having a rectangular configuration, have the lower ends bent inwardly, by means of which they are in contact with the grate assemblies 4/1 and 4/2 and thus form a receiving trough serving as guide surfaces for the to improve the controlled control of the downward passage of the scrap batch 8/1 when the grate assemblies 4/1 and 4/2 are lowered to the downwardly inclined open position. At the same time, the cavities 11 thus formed behind the inwardly curved lower ends of the shorter wall panels 10, together with the free interior 12, located between the scrap charge 8/2 in the middle chamber section 6 and the lower surfaces of the grate assemblies 4/1 and 4/2 provide sufficient space for mixing and, if necessary, combustion of gases passing through the grate assemblies 4/1 and 4/2 from the upper chamber section 5 and the gases from the oxy-fuel burners 13 arranged in the refractory wall liner 14, which closes airtightly the interior of the middle chamber section 6. The lower ends of the other bottom wall sections 15 of the upper chamber section 5 of the alternative embodiment shown in FIG. 3, moreover, in order to better guide the batch of scrap 8/1 and to accommodate the arrangement of the hydraulic cylinder-driven control mechanism 16 (see FIG. 3), to control the operation of the grate assemblies 4/1 and 4/2 formed in the rack configuration , curved inwards.

31114 T

A shorter upper wall portion 17 of the upper chamber section 5 (see FIG. 1) extending in the vertical direction is arranged closer to the electric arc furnace and is in contact with a generally horizontal shut-off plate W. For the purpose of supplying hot waste gases from the electric arc furnace 2 In the upper chamber section 5, a shorter upper wall section 17 is provided with a square opening 19, provided by means of a water-cooled conduit 20. In the case of the requirement of eliminating the entry of hot waste gases from the electric arc furnace into the upper chamber section 5, a conduit 20 equipped with a water-cooled square door 32 which is capable and adapted to rotate about a water-cooled shaft 33, operated by means of a lever mechanism 34 and a hydraulic cylinder 35. Further away from the electric arc furnace The upper wall portion 21 of the upper chamber section 5 is oriented upward, angled inwardly and terminated at the lower edge of the square charging opening 22, intended to enter the hopper 37 during the semi-continuous feeding of scrap into the interior of the upper chamber section 5. Upper edge of the square charging section The opening 22 is delimited by a water-cooled shaft 23, which is coupled to an arc-shaped, square-shaped, water-cooled sealing closure 24. The position of this sealing closure 24 is controlled by a lever mechanism 25 and a hydraulic cylinder 26.

The other vertically arranged upper wall portions 27 of the upper compartment 5 (see FIG. 2) converge from the connection line with the longer lower wall portions 15 initially inwardly to the center of the compartment and then extend vertically upward to define the side edges of the square The longer upper wall portions 27 have in their upper portions an arcuate fan-shaped configuration. The arcuate configuration of the longer upper wall panels 27 is partially coupled to a rigid and arcuate, generally horizontal panel 28. The remainder of the arcuate curve

The 31114 T configuration is covered by an arched, generally horizontal panel 29, capable and adapted to rotate about a horizontally oriented, water-cooled shaft 30 (see FIG. 1). The length of the curved panel 29 is governed by the position of the partially rotated hopper 37, the meaning and meaning of which is that the upper rear portion of the square profile of the partly rotated scrap container 37 is dispensed from the hopper 37 in each hopper 37. In this way, the length of the curved panel 29 determined in this way also defines a position further away from the centrally arranged, curved end projections of the longer upper wall panels 27.

The unfilled space between the vertically disposed longer upper wall panels 27, located closer to the central end of the fixed and curved panel 29, and horizontally oriented. The water-cooled shaft 23 closes the generally vertical wall panel 31 (see FIGS. 1, 3 and 6 of the accompanying drawing). The above-mentioned arrangement of the airtightly sealed closure structure of the upper chamber section 5 at the same time provides for the formation of a cavity in order to achieve the desired intermediate seal between the lateral sides of the hopper 37 when emptying and the vertically arranged longer upper wall panels 27 and curvature 37 a panel 29 during the operation of charging the cold charge of the jelly scrap 8/1 to the preheating device 1 via the hopper 37.

One of the basic and specific tasks and purposes of the upper chamber section 5 of the main vertical preheating chamber 3 (see Fig. 1) is, at the start of operation, receiving and collecting on the 4/1 and 4/2 rack rack configurations of the respective amount of scrap iron charge. 8/1, necessary and intended for preheating to

31114 T the desired initial temperature during a predetermined residence time, fed by a semi-continuous charging in one or more rapidly repeating strokes of the hopper 37 to the upper chamber section 5 via a square charging opening 22 which is normally closed by a sealing closure 24. Suction of large quantities of undesirable of air during charging of the cold scrap iron charge from the hopper 37 to the upper chamber section 5 through the square charging opening 22 is eliminated due to the synchronization of the opening and closing of the sealing closure 4 with the sealed position of the hopper during its emptying. Another specific purpose and purpose of the upper chamber section 5 is to enable and ensure adequate and safe mixing of the hot waste gases exhausted from the electric arc furnace 2 and introduced through the square opening 19 into the free space above the collected quantity of iron scrap 8/1. hot gases from the afterburner chamber 79 for final post-combustion also fed via ducts 54 and 55 also to the free interior 38 of the upper chamber section 5 through the aperture 39 for proper and adequate combustion of all of the mixed gases formed. Said requirement is achieved by equalizing by changing the oxygen / fuel ratio of the oxy-fuel burners 13, controlled by an instantaneous electronic control system, based on the evaluation of the information received from the gas chemical composition, pressure and temperature sensors 40. Upon reaching the desired temperature of the resulting gas mixture by adjusting their adequate ratio by partial combustion, the heated gas mixture thus forced is forced into the downstream flow through the accumulated amount of scrap iron charge 8/1, resting on the gas-permeable grate assemblies. 4/1. and 4/2. Due to the optimum ratio of the surface area and the depth of the collected amount of iron scrap 8/1, hot

31114 T gases through this charge at maximum favorable speed and with excellent heat transfer efficiency.

Finally, the last specific task and purpose of the arrangement of the upper chamber section 5 is to operate by gravity and in a single simple operation with a certain degree of mixing but without pushing, the total accumulated amount of scrap iron 8/1. partially pre-heated during a predetermined residence time to the previously emptied middle chamber section 6, by means of the release operation of the grate assemblies 4/1. and 4/2.

The specific objectives and purposes of arranging the intermediate chamber section 6 of the main vertical preheating chamber 3 are similar to those of the upper chamber section 5. The main purpose and purpose of the intermediate chamber section 6 is to receive and reliably maintain the total amount of partially preheated batch of 8/2 iron scrap. grate assemblies arranged therein 5/1. and 5/2, transported by the action

Also gravity from the upper chamber section 5 after the grate assemblies 4/1 have been withdrawn. A further object and purpose of the intermediate chamber section 6 is to enable and ensure further adequate partial combustion of the gas mixture passing through the grate assemblies 4/1. and 4/2 into the cavities 11 and the free interior 12 above the scrap iron batch 8/2, with the temperature increased in the preceding stage. Obviously a gas mixture permeating through grate assemblies 4/1. and 4/2, contains a substantial amount of gaseous combustible constituents evolved predominantly from the combustible contaminating impurities contained in the iron scrap 8/2 batch and exposed to high temperatures in the absence of an oxidizing agent during the previous degree of preheating in the upper compartment 5. during the preceding pre-heating stage in the upper chamber section 5, a gas mixture with an initial higher temperature as it flows downwards and passes through the scrap iron batch 8/1. it transfers a certain amount of its thermal energy to this charge, and therefore the temperature must be

31114 T of this gas mixture to the necessary value. This is achieved by further and adequately partial combustion of the gas mixture passing through the grate assemblies 4/1 and 4/2 into the cavities 11 and the free interior 12 above the iron charge, the scrap 8/2 in the middle chamber section 6 while the temperature increases the use of oxy-fuel burners 13 by equalizing by changing the oxygen / fuel ratio in the same manner as in the upper chamber 5. The equalizing operation of the burners 13 is controlled in the same way as in the case of partial combustion in the upper chamber 5. Downstream flow of reheated gas mixture. through the scrap iron charge 8/2 in the middle chamber section 6 as well as the heat transfer efficiency are substantially the same as in the upper chamber section 5. The scrap iron charge 8/2 preheated in the middle chamber section 6 to a further elevated temperature for a specified period residence time, with pr by gravity into the previously depleted lower chamber section 7 by means of the release operation of the grate assemblies 5/1. and 5/2. '

The specific objectives and purposes of the lower chamber section 7 of the main vertical preheating chamber 3 are substantially the same as those of the upper chamber section 5 and the intermediate chamber section 6. The basic purpose of the lower chamber section 7 is to receive and reliably maintain the total amount of highly preheated charge. 8/3 in its inverted pyramid-shaped cavity, conveyed by gravity from the middle chamber section 6. The lower chamber section 7 of the converging pyramid-shaped inverted configuration is formed of a refractory wall lining 14 and water-cooled shaped segments 41, 42, 44 /. first and 44/2, the lower ends of which form a rectangular discharge opening 47. This opening 47 serves for emptying a batch of iron scrap 8/3 preheated to an average temperature of 700 ° C into an inclined transporting-loading mechanism 57. The transporting-loading mechanism 57 serves for transfer and forced charging of the iron scrap 8/3 preheated to the desired temperature from the preheating device 1 to the adjacent, in tandem cooperating

31114T of an electric arc furnace 2 through an aperture 76 disposed in a sidewall 78 of the housing that is sealed by a water-cooled door 77 supported on the sidewall 78 of the housing during tilting of the furnace. The feed-loading mechanism 57 consists of a partially water-cooled rectangular cross-sectional pipe 58 whose width corresponds to the width of the discharge opening 47. The rectangular cross-sectional pipe 58 is provided in its interior with a reciprocating slide plunger ram 61 of rectangular cross section. The rectangular reciprocating movement of the sliding plunger pile 61 in the interior of the rectangular cross-sectional pipeline 58 is controlled by a water-cooled double-acting hydraulic cylinder 62. The rectangular cross-sectional piping 58 is disposed on the rollers 60 to allow pipeline mobility along its longitudinal axis. The displacement of the rectangular cross-sectional pipe 58 in the direction of its longitudinal axis is controlled by a double-acting hydraulic cylinder 59. To receive the preheated iron scrap charge exiting the discharge opening 47, the upper wall of the rectangular cross-sectional pipe 58 is provided with an aperture 63 whose dimensions and location correspond In the stand-by mode, in which the scrap is not being charged, the double-acting hydraulic cylinder 59 is retracted to retract, thereby withdrawing the pipe 58 from the electric arc furnace 2, but with the plunger pile 61 remaining in its interior space. in this way, it closes and seals the entire discharge opening 47, while preventing the pre-heated charge of scrap iron from falling into the transport charging mechanism 57.

For the purpose of initiating the forced transfer and charging to the high temperature of the preheated iron scrap batch 8/3 into the electric arc furnace 2, the plunger pile 61 located in the interior of the rectangular cross-section pipe 58 is brought into a retracted position allowing the iron scrap batch to fall. into the interior of the pipe

31114 T

58, which, after being filled, by rolling rollers 60 and bringing the double-acting hydraulic cylinder 59 to the extended position, moves forward and introduces into the electric arc furnace space 2. The forward movement of the rectangular cross-sectional piping 58 proceeds with closed rectangular discharge aperture 47 arranged. its upper wall. Since the double-acting hydraulic cylinder 62 and the reciprocating plunger pile 61 are in the retracted position, the preheated batch of iron scrap 8/3, located in the interior of the pipe 58, is transported to the high temperature only by moving it towards the charging opening. The self-conveying to the high temperature of the preheated charge 8/3 in the inner space of the rectangular cross-sectional pipe 58 by pressure spraying then occurs as a result of the advancing movement of the reciprocating plunger ram 61 caused by moving the double-acting hydraulic cylinder 62 to the extended position. Upon moving the plunger pile 61 to the extended position, the preheated batch of iron scrap 8/3 begins to fall into the interior and into the bath of molten metal, in close proximity to the electric arc passage, where it is rapidly melted by direct convection. Although the high-temperature preheated batch 8/3 is forced out by the internal space of the obliquely arranged rectangular cross-section pipe 58, only a relatively small, not too high force is required for the extrusion operation due to the relatively low friction coefficient.

Another specific object and purpose of the lower chamber section 7 is to allow and ensure further maximum possible combustion of the gas mixture passing down through the grate assemblies 5/1 and 5/2 into the cavities 16 and the free interior V2 above the iron scrap charge 8/3. Again, as in the previous step, the gas mixture at the initial elevated temperature transfers some of its thermal energy to the batch as it passes through the iron scrap 8/2 batch, and accordingly its temperature must be adjusted to the desired size. This adjustment is achieved

31114 T by means of a further and preferably maximum final post-combustion of the gas mixture, permeating in the direction of operation, through the grate assemblies 5/1. and 5/2 into the cavities 11 and the free interior 12 above the scrap iron charge 8/3 in the lower chamber section 7 while the final temperature increase of the gas combustion using the oxy-fuel burners 13 is controlled, by equalizing immediately changing the oxygen / fuel ratio by the same as in the upper chamber section 5 and the intermediate chamber section 6. The equalizing operation of the burners 13 is controlled in the same manner as in the case of the previous partial combustion in the upper chamber section 5 and the intermediate chamber section 6. The downstream flow of reheated gases is passed. withdraws from the lower chamber section 7 through two rectangular openings 45/1 via a scrap iron charge 8/3. and 45/2 (see FIG. 3) into diverging, refractory linings provided with rectangular cross-sectional channels 48/1 and 48/2 provided with shut-off throttle valves 46/1. and 46/2 in order to prevent the flow of gases from the preheating device 1. in the case of a requirement to operate without preheating device 1. for the purpose of allowing bypass passage of the waste gases from the electric arc furnace 2 directly into the interior 49/1 and 49/2 dust collecting , with a refractory lining provided with diverging channels 48/1 and 48/2 of a rectangular cross-section. Interior 49/1. and 49/2 diverging channels 48/1. and 48/2 of the rectangular cross section also serves as a post-combustion chamber 79 for final post-combustion. For this purpose, the growth chamber 79 is equipped with equalizing oxy-fuel burners 13 operated in the same way as the oxy-fuel burners 13 arranged in the individual chamber sections 5, 6 and 7. Interior spaces 49/1 and 49/2 of diverging channels 48/1 . and 48/2 are connected to the collection box 50 at the outlet. Fully combusted gases at a temperature higher than the critical value necessary for the cleavage of undesirable volatile hydrocarbons, including dioxins and furans, by combustion, are withdrawn through the inverted gas duct 53 centrally arranged at the collection outlet. the housing 50, through the aperture 52 and through the duct 54 due to

31114 T for further use and processing. For the purpose of additionally recovering the recovery energy, a portion of the hot waste gases is returned from line 54 through line 55, equipped with a shut-off throttle valve 56, through the opening 39 to the upper chamber section 5.

One of the substantially significant features of the described embodiment, formed in accordance with the present invention, is the controlled control of the semi-continuous downward passage of the scrap iron batch 8/1 and 8/2 by gravity, performed by the control system 16 for controlling the downstream passage of the scrap iron batch. the feed passage mechanism), shown in cross section and in various views, either in whole or in part, in FIG. 1, FIG. 2, FIG. 3 and FIG. 4 of the accompanying drawings. For a better understanding of the characteristic and advantageous functional operations of the individual construction nodes and components of the feed passage control mechanism 16, the drawings are supplemented with detailed views of the control mechanism 16 at various functional operating positions, shown in schematic vertical sections along the V-V plane of FIG. 4 (see Fig. 5a, Fig. 5b, Fig. 5c, Fig. 5d, Fig. 5e and Fig. 5f). The basic functional components of the feed passage control mechanism 16 are: fixed, water-cooled, multiple frame supports 68; a main swing frame 66, a single acting telescopic hydraulic cylinder 64 for controlling the rotation of the main swing frame 66; grate assemblies 5/1 and 5/2 (respectively grate assemblies 4/1 and 4/2); double-acting hydraulic cylinders 67 for controlled control of the grate assemblies 5/1 and 5/2 and the beams 81 for attaching the grate assemblies 5/1 and 5/2. The main pivoting frame 66 is a one-piece structure characterized by spaced rectangular guide holes for receiving each of the grate assemblies 5/1 and 5/2 and allowing them to move in the direction of the longitudinal axis. The actual pivoting of the main swivel frame 66 is made possible by the hockey puck-shaped shaped attachments 65 formed thereon attached to the frame 66 and positioned in the gaps formed therein.

31114 T rectangular guide holes. At the other, outer end of the main pivoting frame 66, on its top side, rollers 80 are attached to reduce friction between the pivoting frame 66 and the individual grates of the grate assemblies 5/1. and 5/2 during their relative movement in the direction of the longitudinal axis. Each grate assembly grate 5/1. and 5/2 is coupled at its outer lateral ends via a yoke connection 82 to a horizontally oriented beam 81. The beam 81, in turn, is coupled to a main swivel frame 66 by means of a double-acting hydraulic cylinder 67. mounted freely in the correspondingly matched apertures of the semicircular configuration formed in the fixed multiple frame supports 68, is actuated by extending or retracting the single acting telescopic hydraulic cylinder 64.

In the basic operational operating position of the grate assemblies 5/1. and 5/2 of the ridge configuration seen in FIG. 5 and the accompanying drawing j

In order to maintain and prevent the downward passage of the scrap iron 8/2 batch by gravity in the horizontal direction, the individual grates are extended into the interior of the main vertical preheating chamber 3. This ejection is achieved by the hydraulic fluid pressure of the extended single acting telescopic hydraulic cylinders 64. The controlled downward passage of the scrap iron batch 8/2 by gravity is accomplished by retraction in the normal state of extended single-acting telescopic hydraulic cylinders 64, which is accomplished by controlled discharge of hydraulic fluid from the working space of hydraulic cylinder 64. As can be seen from FIG. 5b of the accompanying drawings, due to the weight of the iron scrap batch 8/2, the main swivel frame 66 is rotated including the extended grate assemblies 5/1. and 5/2, about the central axis of the frame form extensions 65, which causes the ends of the racks forming the grate assemblies 5/1 to pivot in the interior space. and 5/2, downward. Thanks to this controlled start-up operation, part of the scrap scrap can be 8/2

31114 T descending by gravity to the lower chamber 7. To complete the downward passage of the entire scrap iron batch 8/2 into the lower chamber 7, double-acting hydraulic cylinders 67 are actuated. Since the hydraulic cylinders 67 are arranged between By designing the main pivoting frame 66 and the horizontally oriented beam 81, both grate assemblies 5/1 and 5/2 are pulled from the lower chamber section 7 in a generally vertical direction, allowing downward passage of the rest of the batch by gravity into the lower chamber section 7 as illustrated shown in FIG. 5c. In order to return the racks forming the grate assemblies 5/1 and 5/2 to their initial, interior space of the preheating chamber 3 in the extended position, a single-acting telescopic hydraulic cylinder 64 extends on the main pivoting frame 66, including the grate assemblies 5 / 1 and 5/2 in the retracted position and causes it to return, mainly by gravity, to the previous horizontal position, as shown in FIG. 5d and FIG. 5e. Upon completion of this step, the double-acting hydraulic cylinders 67 are actuated, during which they move to the retracted position. The pulling of the hydraulic cylinders 67 causes the grating assemblies 5/1 and 5/2 of the rack configuration to be introduced into the interior space of the preheating chamber 3, which results in their restoring and reaching their initial initial horizontal position in the unloaded condition located above the iron scrap batch 8/3 in the lower. chamber section 7 (see Fig. 5f). By returning to their original, initial horizontal position, the grate assemblies 5/1 ^and 5/2 are immediately ready to receive and control the downward passage of another partially preheated batch of iron scrap 8/1 from the upper chamber section 5 to another chamber section below it. The specific operation described above, consisting in the gradual rotation of the main pivoting frame 66 and the withdrawal of the individual ridges constituting the grate assemblies 5/1 and 5/2, is an extremely important feature of the proposed embodiment. The above-described arrangement eliminates both time delays and waiting times and at the same time reduces the overall height of the pre-heating device 1.

31114 T, in fact, allows the installation of a device 7 for preheating the scrap iron charge into already existing metallurgical melts, which is very important mainly because of the substantial reduction of installation and assembly costs.

In accordance with the present invention and with reference to FIG. 1 and in more detail in FIG. 6, an alternative design of an integral, obliquely arranged lifting mechanism 72 is provided for conveying a scrap iron batch 8/7 via a hopper 37 and a semi-continuous automatic charging of the preheating device 7. The main structural component of the lifting mechanism 72 is a cold scrap hopper 37 of simple, robust construction, having a specific shape configuration and adequate volume and equipped with pulleys 71. The pulleys 71 are aligned with each other and guided in a correspondingly configured guide. 70 in the form of a robust structure that is forcibly relocating the scrap container 37 from its lower loading position 84 to an upper unloading position 85 along a predetermined path determined by the configuration of the guide 70. The lifting and lowering of the hopper 37 is controlled by the lifting mechanism 57 73, guide rollers 82 and reversing rollers 74 to change the direction of travel of the ropes 73. The ropes 73 are anchored to the sides of the hopper 37 via a pivotable swivel joint 83.

The further description of the operation of the described alternative construction design of the inclined lifting mechanism 72 clearly demonstrates its convenient, reliable and trouble-free, virtually maintenance-free, simple functional operation that perfectly meets the operating conditions of metallurgical melts. Upon commissioning in the hoist mode, the hoisting mechanism 75 by dragging through the ropes 73 of the pulleys 82 and 74 lifts the hopper 37, which was previously loaded with a corresponding amount of cold iron charge.

31114T of scrap 8/1., From its lower loading position 84 to the upper unloading position 85. Due to the sealed charging of the preheater 1, once the upper square profile of the hopper 37 reaches the level of the end projections of the longer upper wall panels 27 and enters the square cavity. arranged in the upper part of the preheating device 1, the double-acting hydraulic cylinder 26 begins to rotate the sealing closure 24 and thus gradually release the square charging opening 22. Accordingly, the square profile of the cavity at the top of the preheater 1 and the upper square profile of the hopper 37 adequately satisfies a dynamic seal which effectively eliminates the possibility of the interior space 38 of the upper chamber section 5 being connected to the surrounding atmosphere. In addition, opening or retracting the seal closure 24 by swiveling allows free and unrestricted unloading of the cold scrap 8/1 charge into the interior of the upper chamber section 5. After unloading the cold scrap 8/1 charge from the hopper 37, the lift mechanism 57 reverses the return operation in the lowering mode and the hopper 37 begins to return to its previous, lower loading position 84 by gravity and by gravity 84. The sealing closure 24 is disposed before the dynamic seal between the hopper 37 and the square cavity at the top of the preheater is interrupted. 1, caused by the return movement of the unloaded container 37, closes by operation of the hydraulic cylinder 26.

If desired, the hot waste gases exhausted from the electric arc furnace 2 can be redirected through the bypass lines 86/1 and 86/2 from the main line 20 and diverted directly to the combustion chamber 79 for final post-combustion, by closing the water-cooled square the door 32 by operating the hydraulic cylinder 26 and opening the shut-off throttle valves 46/1 and 46/2 in the normal state.

31114

The scope of the present invention, elucidated on the basis of the exemplary embodiments described above, given by way of illustration only, is not limited in any way; on the contrary, various modifications and modifications may be made thereto within the claimed scope of protection.

Claims (20)

1. Pre-heating device for preheating an iron scrap charge prior to charging it to a metallurgical melting furnace, in particular by utilizing the heat obtained by recovering the hot waste gases drawn from the furnace exhaust outlet and simultaneously reducing contaminants from the scrap iron charge and waste gases by co-flow a vertically directed flow of hot waste gases and a downward passage of the scrap iron charge by gravity, characterized in that it comprises a vertical preheating chamber, comprising: an upper chamber section provided with feed means for conveying and charging the cold scrap into said chamber section and an inlet for hot waste gas arranged in fluid communication with the outlet of the exhaust gas furnace, a lower chamber section provided with unloading means for conveying the preheated furnace and an exhaust gas outlet arranged in fluid communication with the exhaust means for exhausting the exhausted gases, gas permeable shut-off means located between each! two sequentially arranged chamber sections and operable in succession between the closed position and the open position, for receiving the gravitationally introduced scrap feed from the feed means and maintaining the batch in the closed position for a predetermined holding time, during which concurrently, the effluent flows of gases sucked in from the inlet for the introduction of gases into the interior space of the upper chamber section, passing them in the vertical direction through the charge and through the closing means located 31114T in the closed position and flows to the exhaust gas exhaust outlet in the lower chamber section; and for controlling the downward passage of the batch by gravity at the open position of the closure means from the upper chamber section to the lower chamber section after the corresponding residence time has elapsed. Preheating device according to claim 1, characterized in that the gas permeable closing means comprise: a pair of mirror-arrayed, mutually opposed grate assemblies extending into the chamber, tilting means for pivoting the grate assemblies from the horizontal closed position to maintain the scrap charge in a downwardly inclined open position, and in the axial direction reciprocating sliding means for pulling the grate assemblies into the space , the retracted position, and to extend them horizontally to the extended position. Preheating device according to claim 2, characterized in that each grate assembly comprises a plurality of separate grates extending into the interior of the chamber. Preheating device according to claim 1, characterized in that the unloading means for carrying the preheated scrap batch comprise: a convergent bottom, comprising inclined wall portions of the lower chamber section and provided with an outlet opening, a transfer line extending between the bottom discharge opening and the furnace in which a preheated scrap batch collects descending through the opening and collecting means therein; transferring the preheated scrap batch to the furnace through a transfer line. 31,14 T Preheating device according to claim 4, characterized in that the means for forcing the pre-heated scrap batch comprises a reversible sliding plunger pusher with a pusher which operates between a standby mode in which the pre-heated scrap batch falls through the lower opening and collects before a pusher and a charging mode in which the plunger pile forces the preheated scrap batch into the furnace space. Preheating device according to claim 1, characterized in that the chamber comprises at least one intermediate chamber section, located between the upper chamber section and the lower chamber section and correspondingly between each two sequentially arranged chamber sections provided with gas-permeable closing means. The preheating device of claim 1, wherein each chamber section comprises sensing means for monitoring characteristic waste gas quantities and scrap loads therein selected from the group consisting of: chemical composition of gases, gas temperature, gas pressure, and batch temperature. scrap, for the regulation of burners. The preheating device of claim 1, wherein each chamber section comprises chamber burner means for controlling the combustion intensity and the temperature of the waste gases and the scrap charge present therein. The preheating apparatus of claim 1, wherein the hot waste gas inlet comprises a bypass line arranged in fluid communication with the waste gas outlet and bypass valve means for diverting the hot waste gas stream directly to the waste gas exhaust outlet. The preheating device of claim 1, wherein the feed means for conveying and charging the cold scrap include 31114T hopper, movable pendulum between the loading position located at a distance from the preheating chamber and the unloading position extending in the sealable opening of the upper chamber section. Preheating device according to claim 10, characterized in that the sealed opening comprises at least one sealed door and that its inner peripheral edges are flush with the adjacent outer walls of the hopper located in the unloading position. Pre-heating device according to claim 10, characterized in that the hopper passes on an inclined platform ramp driven by a lifting mechanism. The preheating device of claim 1, wherein the waste gas outlet port includes a deposition chamber with settling means for reducing the proportion of solid contaminant particles from the waste gas. The preheating device of claim 13, wherein the afterburning chamber comprises burner means for combusting combustible contaminants contained in the waste gases. 15. The preheating device of claim 13, further comprising a gas recirculation line arranged in fluid communication between the annealing chamber and the upper chamber section. Preheating device according to claim 13, characterized in that the settling means comprise a vertically bent channel. Preheating device according to claim 13, characterized in that the settling means comprise a funnel-shaped diffusion channel. Preheating device according to claim 13, characterized in that the settling means comprise a collection box for separated solid particles. 19. A method for preheating a scrap iron charge prior to charging it to a metallurgical melting furnace, utilizing the heat recovered 31114T of hot waste gases withdrawn from the furnace exhaust port and at the same time reducing contaminants from the scrap iron batch and from the waste gases with a parallel vertical flow of hot waste gases and a downward passage of the scrap iron batch, comprising: depositing a cold iron scrap batch for gas permeable sealing means in a closed position in the upper chamber section of the chamber, provided with an inlet for supplying hot waste gases arranged in fluid communication with the outlet of the exhaust gas withdrawal furnace, keeping said batch in the sealing enclosures position for a predetermined residence time while hot waste gases flow from the gas inlet to the upper chamber section, passing through the scrap charge and closure means and flowing to the waste gas outlet outlet arranged in the lower chamber section, controlling the downcomer passage scrap by gravity by opening the closing means and passing the charge from the upper chamber section to the lower chamber section after the residence time has elapsed, forced to preheat and repeating the above steps in a sequential stepwise sequence for successive discrete batches of ferrous scrap. 20. The method of claim 19, wherein the step of maintaining the scrap charge during a predetermined residence time comprises further heating the waste gases and the scrap charge by means of combustion burners arranged in each chamber section.