AU9405698A

AU9405698A - Apparatus and process system for preheating of steel scrap for melting metallurgical furnaces with concurrent flow of scrap and heating gases

Info

Publication number: AU9405698A
Application number: AU94056/98A
Authority: AU
Inventors: Robert Roy Wunsche
Original assignee: SMS Schloemann Siemag AG; Schloemann Siemag AG
Current assignee: SMS Siemag AG
Priority date: 1997-11-27
Filing date: 1998-11-23
Publication date: 1999-06-17
Anticipated expiration: 2018-11-23
Also published as: EP1034313B1; WO1999028513A1; TR199802446A2; ATE224461T1; SK163498A3; AU747445B2; AR014040A1; CA2222401C; CA2222401A1; UA49016C2; CZ388998A3; EP1034313A1; TR199802446A3; CN1224064A; KR19990045642A; AU1875699A; DE59805641D1; ID21733A; JPH11223474A; PL329962A1

Description

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION STANDARD PATENT *r a 4 *r U 0 4. 4 Applicant: SMS SCHLOEMANN-SIEMAG

AKTIENGESELLSCHAFT

Invention Title: APPARATUS AND PROCESS SYSTEM FOR PREHEATING OF STEEL SCRAP FOR MELTING METALLURGICAL FURNACES WITH CONCURRENT FLOW OF SCRAP AND HEATING GASES The following statement is a full description of this invention, including the best method of performing it known to me/us: BACKGROUND OF THE INVENTION I. Field of the Invention This invention relates to an ecologically friendly and energy highly efficient, autonomous, air-tight, self-charging apparatus and closed circuit process system for semi-continuous, self- charging of cold charge ferrous scrap mixture, via integrated inclined scrap bin elevator, its stepped preheating and delivering of preheated charge into adjacent, in tandem operating, metallurgical electric arc furnace, using primarily sensible and chemical heat of the hot waste gases from the metallurgical electric arc furnace, for consequent more energy efficient, rapid melting of the preheated charge. The apparatus mechanism as such is distinctly and clearly specified and set forth in claim 1 hereto and modus operandi of the apparatus and process system as such distinctly and clearly specified and set forth in claim X.

II. Description of the Prior Art SJ.Metallurgical processes of primary iron and steelmaking belong to the most energy intensive of all production processes in the industry as a whole. Therefore, their overall energy balance was always of great interest to metallurgists. Better understanding of limitations of non-renewable energy resources and eventually energy cost crisis in 1970's have initiated intensive activity for lowering of energies consumption also from the side of energy producers and suppliers. Furthermore, ecological considerations and the vital necessity for environmental protection are becoming deciding factors to control all branches of the industry. Since metallurgical processes of iron and steelmaking are leading also in high emissions of air polluting toxic gases, as well of production.of solid hazardous wastes, it is logical that they are more and more in the sp6tlight of attention of public and primarily of government authorities responsible for clean environment. For the above reasons there is worldwide effort to improve energy balance of the metallurgical processes by improving energy efficiency as much as possible. In 2 3 some measure this has been achieved by replacing one type of fuel or energy with another, more suitable for the specific process or its particular stage, with highest respect and considerations for ecology, economy and availability. It is obvious, that first priority to reduce energy consumption of the majority of smelting and melting metallurgical processes is the highest possible utilization of the so far unused process system energy losses, such as sensible and chemical heat of waste exhaust gases. It is obvious that by returning part of this energy, by the most direct route possible, into the metallurgical process which produced the waste exhaust gases, initial energy requirements will be reduced, resulting in overall higher energy efficiency of the process. In compliance, most sincere and well Sdirect way, lead to designs which incorporated energy recuperating devices for scrap preheating into current electric arc furnace structure. So far, in contrast with expectations, these state of the art amalgamated electric arc furnace aggregates, of complicated design, are reaching only some of all anticipated performance results. High initial and installation costs, malfunction of mechanisms, extensive maintenance, pollution and safety problems culminating in dangerous explosions are evident reasons for raising questions of their suitability in general. With S current and future environment protection rules, these question era becoming increasingly pertinent, since toxic emissions from current state of art scrap a preheating devices are not meeiing all stipulations and criteria of the valid or proposed regulations for permissible levels of toxic substances emitted into atmosphere.

On the other hand, it was well known, that the most promising and efficient method for indirect energy saving, especially for electric arc furnace steelmaking from scrap, is the high temperature preheating of metallic charge before charging into the furnace, in a separate heating device, better known as "pre-charge scrap preheating". Be that as it may, because of non-availability of fully developed design of this type of scrap preheating equipment for electric arc furnace steelmaking, it was only sporadically used in underdeveloped "scrap in bucket preheating" configuration.

Alongside arising energy and ecological concerns there is ever present endeavour to intensify any and ali phases of the electric arc furnace steelmaking 3 1 process, above all increase of productivity and operating cost reduction. From variety of means applicable in the framework of process intensification ways and methods, following are leading means used at the present time frequently for process intensifications: Further increase of electric power input via optimally increased secondary voltage complimented with adequate foamy slag practice; Instantaneous recuperation of chemical energy via post-combustion of combustible gases directly in the furnace vessel before they are exhausted; Addition of oxy-fuel burners to the furnace vessel for intensification and acceleration of rapid scrap melting; Preheating of the ferrous scrap charge prior to charging into the furnace by using sensible and chemical heat energy contained in the off-gases plus oxyfuel burners; and finally, Introduction of supersonic gaseous oxygen lances for intensification of decarburization and foaming up of slag.

Of aforementioned process intensification ways and methods, the three methods for increasing temperature of scrap by other means then via electric arc, are: Instantaneous recuperation of chemical energy in the vessel via postcombustion; Addition of oxy-fuel burners to the furnace vessel and preheating of the ferrous scrap charge prior to its charging into the furnace vessel.

SThe intent of the first method is instantaneous recuperation of chemical, energy directly in the furnace vessel, by combusting via gaseous oxygen the combustible components of off-gases developed by the process of scrap melting, before being exhausted. This method is being exploited with variable success in open-hearth furnaces, basic oxygen furnaces and energy optimizing furnaces.

Preheating of oxygen enriched air by sensible heat of already from the vessel exhausted off-gases to be used instead gaseous oxygen is a variant of this S° method. Nevertheless, success of this method, applied to electric arc furnaces is showing'only limited productivity improvement and electric energy saving, primarily when used during the stage of melting scrap simultaneously with electric arc; actual energy saving is result of in-situ scrap preheating. Use of post-combustion in electric arc furnace-with already molten scrap is in reality significantly curbed by unsatisfactory heat transfer efficiency from post-combustion gases into the bath, covered by deep layer of thermally insulating and foamy slag. For that reason, rational explanation to the illusive claims that post-combustion in an electric arc furnace is highly efficient also after the scrap is molten, is forthcoming from the 4 following corroborating facts; Combustion or so called post-combustion of combustible components of the off-gases emerging from the foamy slag increases the temperature and consequently volume of the off-gases in the free space above the slag. Successive, proportionally increased pressure of the off-gases in the furnace vessel is therefore abating aspiration of the cold ambient air into the furnace vessel. Hence, while keeping the necessary internal temperature of the furnace vessel the same, electric energy requirement for heating of the cold air is eliminated, ultimately resulting in its saving. It should be noted, that in comparison with the post-combustion, requiring additional oxygen, which ads costs, equal or higher energy saving, at no cost, is achieved by adequately sealing of the furnace vessel and on that account preventing intake of the cold air. Moreover, consequent and exceptional benefit of adequate sealing of electric arc furnace is drastically I reduced quantity of hot off-gases to be exhausted from the furnace. In the case of a 110 tonnes furnace the quantity of the gases to be handled was reduced more S than 50% (from 90,000 Nm 3 /h to 40,000 Nm 3 allowing sloping of one of the oi: exhaust fans.

I I II The purpose of the second method, of the process intensification ways and methods, for increasing temperature of the scrap by other means then via electric arc is, intensification and acceleration of rapid scrap melting by addition of oxy-fuel S, burners to ithe furnace vessel. Although positive results were obtained from I, introduction of oxy-fuel burners for faster melting of the scrap in the region of the slag door tunnel of the electric arc furnace vessel over 30 years ago, they have not been used to a great extent until Ultra High Power furnaces with watercooled panels have been built. Beneficial performance of short flame oxy-fuel burners located in the vessel walls in the "cold" zones between electrodes have caused shortening of the time for melting of all scrap in the furnace. These positive results started an fashionable avalanche of burner additions to the vessels of electric arc furnaces. In last few years numerous types of oxy-fuel burner designs with ever increasing capacities have been made available for electric arc furnaces. Currently, the thermal power input of these burners represents in some cases more than of initial electric energy power input. Although this, low cost, addition of overall power input shortens the tap-to-tap times, ergo desired productivity Increase and induces some other operating and economicbenefits, many other serious disadvantages are overlooked and suppressed. In general, some of the major !b disadvantages are: higher oxidation of the scrap, larger volume of off-gases, substantially lowered heat transfer efficiency if burners are operated simultaneously with electric arc power input, especially if the burners re operating all the time during the heat. Practical operating results have proved that highest energy efficiency is achieved when the heat is started with burners only, which are substituted with electric arcs only after the charge has reached temperature of about 800 0 C. This two-stage operating practice resulted in 15-20% electric energy saving and 10-15% saving of fossile fuel and oxygen. However, because of sequential application of both types of thermal energy the tap-to-tap time has increased by 10-12%. Economically, the cost of installation of oxy-fuel burners to the existing furnace vessel is relatively low, yet in almost all cases it resulted in substantial costs for rebuilding-enlarging of the entire exhaust system. From broad ecological view point, operation of electric arc furnace with excessive capacity of S: oxy-fuel burners and lowered energy efficiency, producing disproportionately higher volume of hazardous component containing off-gases, is becoming categorically nonacceptable.

The objective of the third method, of the process intensification ways and 4* methods, increasing the temperature of the scrap by other means then via electric arc is, preheating of the ferrous scrap charge prior to charging into the furnace by efficiently using sensible and chemical heat energy contained in the off-gases plus I use of oxy-fuel burners, if necessary for ecological reasons and concerns.

From its introduction, scrap preheating went through several development stages: batch preheating in the charging bucket with hot waste gases from the furnace or with air- and oxy-fuel burners; continuous preheating via inclined rotating kiln or horizontal vibrating conveyor using a combination of hot waste gases from the furnace and air- and oxy-fuel burners; continuous vertical preheating mechanism with controlled scrap descent, being an integral part of the furnace and using hot waste gases from the furnace in counter current flow; and as well "in situ" preheating of the scrap already charged into the furnace at the beginning of the. heat simultaneously with electric arc via a variety of different designs of air- and oxy-fuel burners. There are several other unique scrap preheating mechanisms being combinations of the above discussed systems and operating with more or less success.

Currently scrap preheating is gaining long time overdue recognition. By recognizing its great potentials, it is now considered that it will be the next production process milestone for electric arc furnace steelmaking mainly from scrap, with respect to electric energy saving, reduction of electrode consumption, productivity increase by shortening the tap-to-tap time and the very important benefit of reduction of environment pollution in general.

Summarized and based on experience, practical operating results of variety of known methods and ways arising from efforts to achieve ultimate improvement of energy efficiency of the process of steelmaking in an electric arc furnace predominantly from recycled mixture of ferrous charge cold steel scrap, it could be concluded, that adequate preheating of the scrap prior to charging into the furnace for rapid efficient melting is the most suitable way. The following outline of an apparatus and process system attempts to specify an autonomous, simple, rugged and reliable apparatus and process system having desirable and practically accomplishable characteristics and parameters for maximal energy efficiency and 41 1 at the same time lucrative steelmaking from cold scrap using an electric arc furnace operating in tandem process system with the scrap preheating apparatus.

Such apparatus and process system, which is also object of present invention, must be mandatory ecologically more advanced, with improved safety and working conditions: For feeding charging of the autonomous preheating apparatus, reasonably sized prepared cold steel scrap must be delivered continuously or semicontinuously from the scrap supply-storage area located in acceptable distance and level into the mechanism for charging of the scrap into preheating apparatus.

S Mechanism for charging-feeding scrap into the scrap preheating apparatus is to be part of the scrap preheating apparatus. Batch charging of the scrap into the scrap preheating apparatus with use of charging bucket and overhead crane is not acceptable. Design and location of the autonomous scrap preheater must not interfere with the adjacent electric arc furnace operation in traditional way, allowing bypassing of the scrap preheating apparatus and top charging of the furnace with swing-removed roof and with use of standard charging bucket transported with overhead crane. When bypassed, the scrap preheating apparatus must be equipped also with a bypass ducting and closures for hot waste gases exiting from 7 I the furnace to be re-directed into final combusting chamber and ducting exiting from the final stage of the scrap preheating apparatus.

In anticipation of production cost reduction it is expected that the scrap preheating apparatus will utilize primarily and to the practical maximum sensible and chemical energy of the waste hot gases exiting from the furnace. At the present time fossile fuel energy, usually in the form of natural gas is used for augmenting of the melting process in the furnace via air- or oxy-fuel burners in different locations of the furnace shell walls and/or roof. For improved energy efficiency it is mandatory to transfer these oxy-fuel burners into appropriate positions and as a part of the scrap preheating apparatus. Expected benefits and improvements resulting from this transfer will be better energy efficiency, reduction of the influence of cyclical character of the temperature of hot gases exiting from the furnace on the operation of the scrap preheating apparatus; significant improvement of the safety, because burners applied to the scrap preheating apparatus are stationary with predominantly solid piping; simplification of the top section of the furnace shell and water cooled wall panels due to absence of the burners and thus beneficially affecting maintenance requirements, reducing overall number of burners and simplifying exchange of the top section assemblies. For further energy cost reduction it is desirable that appropriate quantities of high carbon content waste materials be introduced in the cold scrap mixture charged S* into the scrap preheating apparatus.

It is expected, that resultirig from the process of scrap pre-charge preheating in the autonomous scrap preheating apparatus discharged hot scrap will be preheated to the calculated temperature in the range of 6500C 8000C 1,200F 1,47 0 °F depending on the size of the scrap pieces, with average temperature of 700'C 1,290F with average temperature of the heating gases, having generally reducing character, being held in the range of 1,0500C (1,920 0

F);

So furthermore, it is expected that the temperature of the gases exiting the scrap preheating apparatus and combustion chamber with still reducing character will have temperature in the range of 9500C 1,0000c 1,740OF 1,830OF this temperature range being above the critical value required for burning-cracking of undesirable volatile hydrocarbons, including dioxins and furans.

8 In the recent past, further discussed several types of equipment and processes with the purpose of preheating scrap have been introduced and made available to the electric arc furnace steelmaking industry, generally in accordance with the following US Patents: US Pat.No. 4,543,124 (24.09.1985) "Apparatus for continuous steelmaking", known in the industry as "Consteel Process".The process uses the furnace off-gas and fuel to "pre-charge preheat the scrap moving on a conveyor in a special horizontal preheater tunnel. The scrap is fed into the furnace through the hole in the shell sidewall. The off-gas flows counter-current to the scrap. The EAF maintains a liquid heel following tapping. Electric energy consumption in the range 350-400 kWh/ton is too high, when compared to current electric arc furnace consumption standards. The apparatus by itself is requiring large space for conveyors; scrap preheating on conveyors is not very energy efficient, because scrap is preheated predominantly from above.

US Pat.No. 4,852,858 (01.08.1989)"Charging Material Preheater for preheating charging materials for a Metallurgical Smelting Unit" Known in thelindustry as "Energy optimizing furnace" has favourable results and is used in production.

However, this semi-continuous vertical scrap preheating apparatus with controlled S: scrap descent, is an integral part of a non-electric metallurgical furnace using counter-flow hot waste gases from almost complete post combustion in the furnace vessel located under the preheating apparatus. Favourable operating S results of this design eventually induced some designers of electro-metallurgical equipment to adapt this, considerably modified, concept to the electric arc furnace.

Overall hight and large, uncontrolled infiltration of the false air into individual chambers are considered as drawbacks.

US Pat.No. 5,153,894 (06.10.1992) Smelting plant with removable shaft-like charging material preheater", known in the industry as "Shaft Furnace", is a batch charged, smelting plant with shaft like material preheater which is an integral part of the furnace and with counter-current hot gases flow. By a horizontal relative movement between the furnace vessel and the holding structure, together with the vessel cover, charging material can be charged from a scrap basket directly into the furnace vessel or through the displaced shaft into different regions of the

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furnace vessel. Charging material can be retained in the shaft by means of a blocking member therein, and heated up during the refining phase. One of the alternatives has several inherited design problems such as complicated design manifested by batch charging into furnace from the shaft, two pivoting assemblies in order to allow direct top charging or to exchange shell, disfigured shape of the shell due to side mounted shaft structure for scrap preheating, tilting arrangement of the shell only, creates a large gap between shell and roof resulting in heat loses, uncontrolled scrap descent through the shaft causing occasional Jamming and sliding of large portion of scrap, improper counter-current flow of gases through the shaft resulting in uneven preheating of the scrap in the shaft and two serious processing system problems: temporary, uncontrollable creation of explosive mixture and emission of toxic substances due to low waste gases temperature at the exit from the shaft. In addition to the fact that reheating of this gases via burners is in principle and de facto defeating the purpose of this type of preheating system, the possibility of emission of toxic substances and explosions are not eliminated and they occur from time to time on each of these kind of furnaces.

SUS Pat.No. 5,264,020 (23.11.1993) "Smelting plant with two melting furnaces iarranged in juxtaposed relationship"known in the industry as "Double Shaft Furnace",is actually an aggregate of two Shaft Furnaces in juxtaposed relationship and which are operated alternately, wherein the furnace gases which are produced in the melting process are respectively introduced into the other melting furnace S for the purposes of preheating the charging material; associated with each melting furnace is a shaft which is loaded with charging material, and the waste gases from the furnace which is in the melting mode of operation are introduced from the shaft, after charging of the other furnace, through the cover of the other furnace and are removed from the shaft thereof. That procedure, throughout the entire Ssmelting operation, permits preheating of the charging material and filtration of the furnace gases when they are passed through the charging material. Since "Double Shaft Furnace "is de facto very similar to the "Shaft Furnace" with slightly different charging arrangement, all of the comments concerning "Shaft Furnace" are applicable also to this furnace aggregate.

US Pat.No. 5,499,264 (12.03.1996) "Process and arrarfgement for operating a double furnace installation", known in the industry as "Twin-shell furnace". This

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arrangement is also de facto an aggregate of two practically complete mechanical assemblies of single electric arc furnaces, eventually in juxtaposed relation. It is disclosed as: A process for operating a double furnace installation having two arc furnaces connected via a line, a power supply, a device for charging material, and an arrangement for extraction and purification of gas. The process including the step of connecting a firstone of the two furnaces with the power supply for melting a charge located therein, completely cutting off a second one of the furnaces from the power supply. The second furnace is the charged with charging material and is closed with a cover. Flue gas located in the closed second furnace is sucked out above the burden column and flue gas is sucked out of the first furnace above the surface of the melted charge through the second furnace via the connection line provided between the two furnaces. A flue gas connection of the first furnace 4 to the gas purification arrangement isinterrupted while the flue gas is being sucked S out of the second furnace while feed air is simultaneously taken on in the region of a cover of the first furnace. In principle, the flow of preheating gases is counter current with respect to the scrap. Higher productivity is achieved with complex design of exhaust system. Scrap preheating is non-uniform, resulting in higher oxidation losses. Top charging of the two vessels still requires removing of the furnace roof, resulting in additional heat losses.

US Pat.No. 5,513,206 (30.04.1996) "Apparatus for preheatinb and charging scrap material". Apparatus for preheating and charging'scrap material encompasses a shaft like preheating chamber and charging unit. The furnace exhaust gas flows counter current to the falling scrap. A two stage scrap pusher delivers the charge through the opening in the roof into a space between the two DC electrodes. The two electrode DC furnace receiving preheated scrap is completely sealed and does not use watercooled wall panels. This furnace is of extremely complex design.

Scrap pushing is complicated. Shaft is narrow and therefore is equipped with several anti-bridging devices. Also overall hight is a significant drawback.

US Pat.No. 5,555,259 (10.09.1996)"Process and device for melting down scrap", known in the industry as "Contiarc". The disclosed furnace is a DC arc-heated shaft furnace with an annular shaft formed by outer and inner vessels that surround and protect a central graphite electrode. Scrap is fed continuously with an appropriate system in the upper part of the annular shaft at a rate 11 corresponding to the melt-down rate in the lower section of the furnace. During its descent, scrap is preheated by the ascending gases. When these gases leave at low temperature from the top of the scrap column, they are captured in a ring duct and conveyed away for waste gas treatment. It is claimed that this furnace will have low volume of dust emission through off-gases owing to the filtering effect of the scrap column. This design is in accordance with efforts to combine an electric furnace and scrap preheating in one, amalgamated design. Scrap charging system is complicated, scrap descent is not controlled, therefore bridging will occur.

Furnace has not tilting mechanism and therefore replacement or exchange of the bottom part will be difficult.

US Pat.No. 5,573,573 (12.11.1996) "Electric arc furnace arrangement for producing steel", known in the industry as "Comelt". Disclosed is an electric arc S furnace for the production of steel by melting scrap, in particular iron scrap, and/or S sponge iron and/ pig iron as well as fluxes in a furnace vessel, into which at least S one graphite electrode projects, which is displaceable in its longitudinal direction, wherein an electric arc is ignited between the graphite electrode and the charging stock. To achieve particularly high energy input, the sloping graphite electrode projects into a lower part of the furnace vessel from aside and the lower part, in the region of the graphite electrode, has an enlargement radially protruding outwardly relative to the upper part. The furnace has an extended vertical shaft and it is continuously charged with cold scrap via a conveyor. It is claimed that offgases, in counter flow to descending scrap are at the top of the shaft, after preheating the scrap, still sufficiently hot and rapidly cooled by dilution, so that no toxic gases are evolved. In another version, gases are collected. Complex, amalgamated design claiming very low electric energy consumption.

I In addition to pertinent and specific comments concerning disadvantages and drawbacks, to each of previously listed and discussed apparatus, devices and process systems of Prior Art and related to Process Intensification Ways and Methods, all of them have a fundamental, indubitable disadvantage and drawback: Counter-current flow of hot waste gases to the flow of the scrap. This fundamental, functionally adverse, feature is in majority cases of Prior Art scrap preheating apparatus, devices and process systems the main reason for their not fully satisfactory performance.

In summary, with respect to productivity, energy saving, pollution and last but not least, safety of operation, results from efforts for intensification of the process of electric arc furnace steelmaking predominantly from scrap, using Prior Art scrap preheating equipment, are clearly indicating that their level of achievement is bellow achievable performance levels of a "pre-charge" scrap preheating apparatus properly applying fundamental laws of physics and correct exploitation of practical experience.

t I OBJECT OF THE INVENTION An object of the present invention is to provide an autonomous, independently operating, supplementary, energy efficient, pollution reducing and safe to operate apparatus and process system with concurrent flow of scrap and hot waste gases, for semi-continuous self-charging, controlled, stepped and gradual preheating of cold ferrous scrap mixture steel scrap and dischargingforce delivering of preheated scrap into adjacent, in tandem operating, sealed S, metallurgical-electric arc furnace, all of which makes it possible to overcome all aforementioned drawbacks and disadvantages.

Another object of the invention is to provide main vertical chamber of inherent prismatic form having pyramidic converging portion at its bottom and removable sealing cover at the chambers top for semi continuous feeding charging of the cold charge of ferrous scrap mixture into the chamber.

Another object of the invention is to provide main vertical chamber with walls consisting of refractory or water cooled segments attached to appropriate selfstanding supporting structure.

Another object of the invention is to provide independently operating, simple and sturdy charging-supplying mechanism for semi-continuous feeding of cold ferrous scrap mixture from the adjacent scrap storage, preferably located on the lower floor level and without use of charging bucket or overhead crane, into the uppermost compartment of the main vertical chamber, equipped with charging opening sealing closure, the charging mechanism consisting in principle of at least one inclined high velocity elevator outfitted with an permanent charging bin.

3 Another object of the invention is to provide oie or more robust and adequately cooled scrap gravitational descent controlling mechanisms, each consisting of frames with semi-gridirons performing controlled sequential rotating and retracting-extending motions, dividing the volume of the main vertical chamber S, in at least two compartments, being capable of holding at any time no less than one and a half of the nominal charge required for one heat of the adjacent, in tandem operating, metallurgical-electric arc furnace.

Another object of the invention is to provide one or more oxy-fuel burners, with swift control of variable oxygen/fuel ratio, into each compartment of the main vertical chamber for continuously controlled combustion of eventually developing Scombustible gases through the entire height of the main vertical chamber, resulting in controlled gradual preheating of the charged ferrous scrap mixture to the required temperature before discharging.

ie,,i Another object of the invention is to provide sensors in each compartment of the main vertical chamber and other locations of the gas flow ducting for real S time instant analysis of gases and temperature measurement, used for prompt correction and control of proper evacuating pressure and gradual combustion of the combustible gases developed during preheating process.

Another object of the invention is to provide simple, sturdy heat resisting discharge mechanism for controlled discharging of high temperature preheated scrap from the opening in the converging lower part of the main vertical chamber and forced delivering of preheated scrap into adjacent metallurgical-electric arc furnace through the opening in the shell side wall or roof, the discharging mechanism consisting in principle of a sliding closure of the opening in converging part of main vertical chamber, scrap levelling roll and inclined, reciprocating elevating device having a trolley-trough outfitted with an internal ram with reciprocating motion.

Another object of the invention is to provide two inlet openings at the highest point of the top compartment, one of them for entrance of hot waste gases from the metallurgical-electric arc furnace and containing sensible and chemical thermal energy and the second opening for entrance of partially recirculated recuperative hot gases from the final post-combustion chamber.

Another object of the invention is to provide commensurate negative pressure and which creates appropriate suction effects at different points of the apparatus and most importantly forcing combination of any and all gases entering the main vertical chamber, to flow from the highest point of the top compartment downwards through the layers of scrap in direction of flow concurrent with the flow S' of gravitationally descending scrap, combined hot gases encompassing the initial hct waste gases from the in tandem operating, metallurgical-electric arc furnace, recuperative hot gases from terminal post combustion chamber, hot gases generated by oxy-fuel burners located in the walls of the compartments and as well hot gases resulting from oxidation of combustible substances contained in the charge via administered oxygen, oxygen enriched air or air.

I' Another object of the invention is to provide a set of two parallel and analogical, combined final combustion chamber/diverging dust catchers and a drop out box directly and vertically in-line under the discharging converging bottom compartment of the main vertical chamber, with hot waste gases from the two slit openings in the main vertical chamber converging bottom are directed into the top part of each of final combustion chamber/dust catchers equipped with variable ratio oxy-fuel burners for final total combustion of combustible substances and temperature conditioning, preventing dioxin and furan development.

Another object of the invention is to provide more than one, preferably two hot waste gases by-pass ducts, equipped with appropriate closing/opening ducts valving for connecting the main exhaust duct from the, in tandem operating, electric arc furnace into preheating apparatus with the upper spaces of the two combined final combustion chamber/diverging dust catcher enabling hot waste gases to be exhausted directly from furnace into final combustion chambers, hence facilitating total by-passing of the preheating apparatus and allowing the electric arc furnace to operate independently, without scrap preheating apparatus; Another object of the invention is to provide a slit type Venturi scrubber with priority function to provide instantaneous shock cooling of the hot waste gases, bellow lower critical temperature of de novo synthesis of dioxins, and with an additional function to clean the gases.

Other objects and features of the present invention will become apparent from the following summary of the preferred embodiments of the invention and detailed description considered in conjunction with the accompanying drawings.

It is to be understood, however, that the drawings are introduced solely for the i purposes of illustration and not as definition of the limits of the invention, for which reference should be made to thq appended claims.

i SUMMARY OF THE INVENTION Accordingly, to overcome disadvantages drawbacks of scrap preheating devices and methods of known and prior art, scrap preheating per object of invention is to be performed in an independent and autonomous, separate, selfstanding, self-charging and discharging, of a simple and robust design, almost maintenance free scrap preheating apparatus and process system, adjacent to the sealed metallurgical-electric arc furnace, said preheating apparatus structure could be added, economically and without large modifications to the existing and/or new 16 17 electric arc furnace melting facility. By working in tandem with sealed metallurgicalelectric arc furnace, the high energy efficiency and operating performance of the scrap preheating apparatus and closed-circuit process system in accordance with the object of invention will substantially influence the steelmaking process as such.

In addition to particularly important benefit of significant lowering of volume of polluting toxic gases and substances, the scrap preheating apparatus and closedcircuit process system in accordance with the object of invention will, inter alia, contribute to reduction of consumption of electric and other energies, reduction of electrode consumption and shortening of the tap-to-tap time, associated with improved safety and working environment, on the whole culminating in overall improved performance and profitability.

Pursuant to the invention, the object is achieved in that novel and unique exploitation is applied of physical and chemical process phenomena specific to heat generation and heat transfer by different thermal energy sources related directly or indirectly to the process of steelmaking from cold ferrous scrap mixture in electric arc furnace and in that novel, more advanced and suitable and as well highly functional structural design and components are introduced for the same purpose.

'When considering operation of a conventional contemporary steelmaking electric arc furnace with top charged cold ferrous scrap mixture via one or more charging bucket loads, the amount of process gases exhausted or escaped from the furnace depends on several factors. These factors are: composition of the charge, quantity and quality of used lime and other additives, amount of gases generated by the oxy-fuel burners, quantity of carbon and oxygen introduced for foaming up of slag et and what is of foremost importance, on the quantity of ambient cold air inspired into the furnace. Without sealing, air-tightening of the furnace vessel as practically possible, even in the case of so called direct evacuation via fourth hole in the roof, the amount of exhausted gases could reach 350-450 m 3 /tonne of produced steel. In absence of cold air inspiration, what is achieved with air-tight sealing of the furnace and without use of gaseous oxygen decarburizing lance, the amount of hot waste gases exhausted via fourth hole drops to a range of 90-120 m 3 /tonne of produced steel. With use of decarburizing oxygen lance the amount of gases exhausted increases proportionally to the 17 amount of injected decarburizing oxygen to a range of 200-220 m 3 /ton of produced steel.

Furthermore exhausted hot waste gases contain significant amount of hazardous byproducts. One example of some impurities in the hot waste gases exhausted via fourth hole, when air is inspired into furnace vessel, is shown in the table I. The very high temperature surrounding the electric arc and high temperatures in the furnace vessel in general brings about formation of large amounts of carbon oxides, and as well the following micro byproducts: Nitrogenand sulphur oxides, cyanides, fluorides, dioxins and furans. With regards to concentration of nitrogen oxides and cyanides they depend primarily on the quantity of nitrogen inspired into the furnace with the cold air, the power of the electric arcs and the degree of dissociation of molecular nitrogen inside the furnace. The amount of the sulphur oxides in the gases is usually not very large.

The concentration of fluorides in the gases is also low and it is directly related to the content of fluorspar in the slag. Content of dioxins and furans is governed by the quantity of combustible contaminants included in charged scrap, their generation and destruction being controlled by the temperature of the off-gases.

4 Content of harmful gaseous products in hot waste gases exhausted from electric arc furnace ©j Table 1.

Harmful Average Amount of by-products substances concentration exhausted g/tonne mg/m3 of produced steel S" Carbon oxides 13,500.o 1,350.o Nitrogen oxides 550.o 270.o Sulphur oxides 5.0 1.6 Cyanides 60.o 28.4 Fluorides 1.2 0.56 18 19 Concerning the dust exhausted from the furnace with gases, the bulk of it, up to 60-70%, consists of particles less than 3 micrometers across. The dust generated during a heat, with inspiration of air into the furnace, contains large amount of ferroxide Fe20 3 When considering present state of pollution of the environment in general it is vitally important to reduce to the achievable minimum generation of harmful products primarily by industrial processes as a whole. However, this task must be achieved by the means acceptable to the industry. Reduction of pollutant generation by industrial manufacturing processes must be done by their reengineering with strict economical orientation, so that its implementation will compulsory result also in economical benefits, supplemented with,. safer and S- improved working conditions.

i t I a I a In summary, the Apparatus and Process System With Concurrent Flow of Scrap and Hot Gases for Stepped Preheating of Steel Scrap for Melting S Metallurgical Furnace in accordance with the object of invention encompasses a a. multitude of major and minor functional and process system operating S characteristics and parameters harmoniously aggregated into an embodiment, giving it: Ability of the entire scrap preheating apparatus and process system to be added to majority electric arc furnaces in existing Melt Shops, with short return of investment time; a Ability to work in synchronized tandem with most of metallurgical melting furnaces, preferably with air-tight sealed electric arc furnace for steelmaking a from cold ferrous scrap mixture; Ability to significantly reduce the amount of hot gases exhausted from the electric arc furnace by completely eliminating oxy-fuel burners and so called process of "pdst combustion" from the furnace vessel; Ability to improve energy efficiency by operating scrap preheating

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apparatus in tandem with electric arc furnace and by eliminating the energy inefficient oxy-fuel burners from the furnace shell vessel and relocating them to the scrap preheating apparatus; Ability to improve energy efficiency by eliminating the so called "post combusioV In the electric arc furnace vessel and by exploiting the sensible and chemical thermal energy contained in the hot off-gases exhausted from the electric arc furnace in the compartments of the preheating apparatus with almost double efficiency of heat transfer from the gases to the scrap; Ability to improve energy efficiency by eliminating need to remove roof of *1 electric arc furnace every time when a charge of scrap is to be delivered 4 into the furnace via overhead crane and charging bucket.

CS,. Ability to eliminate need of overhead charging cranes and classic charging I 82''buckets because of self- charging capability via integrated, semi-continuous self-charging, scrap bin elevating mechanism -Ability to simply and problem free charge refill scrap bin of the integrated, semi-continuous scrap bin elevating mechanism via conventional, low level, scrap moving horizontal conveyors or road transport scrap handling equipment; -Ability to efficiently preheat cold ferrous scrap mixture semi-continuously charged into the top compartment of the apparatus to the predetermined temperature at its discharge from the bottom compartment, including highest possible combustion of all combustible substances being introduced into the apparatus and which provides appropriate suction effects at different points of the apparatus and most importantly forcing combination of any and all gases entering the main vertical chamber to flow from the highest point of the top compartment downwards through the scrap in direction of flow concurrent with the flow of gravitationally descending scrap, combined hot gases encompassing the in~itial hot waste gases from the metallurgical-electric arc furnace, recuperative hot gases from terminal post combustion chamber, hot gases generated by oxy-fuel burners located in 2-1 the walls of the compartments and as well hot gases resulting from oxidation of combustible substances contained in the charge via administered oxygen, oxygen enriched air or air.

Ability to preheat ferrous scrap mixture to the required nominal preheating temperature, without hot waste gases from the adjacent, operating in tandem electric arc furnace, by using only oxy-fuel burners of the preheating apparatus, and force delivering of the preheated scrap into the furnace vessel at initial increased rate, prior to "cold start-up" of the furnace, and by doing so, rapidly achieve normal, "flat bath" operating conditions due to prompt creation of the pool of molten metal under electrode(s), especially when augmented with oxy-fuel/oxygen lance and early formation of foamy slag; Ability to reduce oxidation loss of scrap by controlled gradual, stepped S' preheating of ferrous scrap mixture with intermediate temperature and gas composition conditioning via real time controlled oxy-fuel burners power input and introduction of oxidants; Ability to control semi-continuous gravitational descent of the ferrous scrap mixture via simple and robust adequately cooled, scrap descent controlling mechanism; Ability to reliably and problem free discharge preheated ferrous scrap mixture from the converging bottom into the heat resisting trolley-trough for forced delivery into the furnace, including weighing with required accuracy of each force delivered quantity of scrap; Ability to, semi-continuously force deliver preheated ferrous scrap mixture from the preheating apparatus into the adjacent, operating in tandem, electric arc furnace, at the rate of melting capability of the furnace, enabling furnace operation with unceasing hot metal bath, with electric arcs permanently submerged in foamy slag of suitable depth, consistency and chemistry and as a consequence high thermal efficiency rapid melting dissolving of scrap immersed into hot metal bath; Ability to enable adjacent, operating in tandem, sealed metallurgical electric arc furnace to continuously operate with hot metal bath due to semicontinuous forced delivering of preheated, prepared reasonably sized ferrous scrap mixture into the furnace vessel at a rate of melting capability of the furnace; When compared with traditional furnace operation, using cold scrap, the above listed abilities in accordance with the object of invention result in substantial improvements of the following technical parameters -and economic factors: Reduction of electric power input and furnace transformer capacity in the range of 30-35%; Reduction of electric energy consumption in the range of 25-35%; Reduction of electrode consumption in the range of 15-20%; Reduction of amount of exhausted waste gases in the range of 40-45%; Reduction of dust and hazardous substances generation in the range of 20-25%; Reduction of dioxins and furans bellow currently permitted limits; Reduction of voltage flicker bellow permitted noticeable limits; Possible elimination of electric HV compensating apparatus with optimized impedance of the furnace; Shortening of tap-to-tap time in the range of 15-20%; Possible down-sizing of the baghouse capacity in the range of 25-30%; Reduced maintenance requirements due to drastic reduction of short circuit and fluctuating power input character of operation.

Improved safety and working environment conditions primarily due to semi-continuous and semi-automatic charging of the furnace with preheated scrap thus eliminating explosion predisposed hazardous open furnace, wet scrap charging via charging bucket and as well effective lowering of the noise pollution level.

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23 BRIEF DESCRIPTION OF THE DRAWINGS For better understanding of the invention and process system, it will now be explained and illustrated in more detail with reference to drawings and non-limiting general examples. In the attached drawings, wherein like reference characters denote similar elements throughout the several views: FIG. 1 shows vertical longitudinal left hand section taken along line IV IV in FIG 2, of the scrap preheating apparatus, and in tandem operating adjacent electric arc furnace, according to the invention.

S.

FIG. 2 shows vertical lateral right hand section and view taken along line S- e of the FIG. 1, of the scrap preheating apparatus according to the invention.

FIG. 3 shows vertical lateral section of an alternative of the embodiment taken along line III III in FIG. 1.

FIG. 4 shows diagrammatic horizontal view of the two gridiron halfs of the scrap gravitational descending controlling mechanism of the object of 2 invention at level taken along line I I of FIG. 2.

FIG. 5a, 5b, 5c, 5d, 5e and 5f show enlarged diagrammatic vertical sections taken along line V V in FIG. 4, through the scrap descent controlling mechanism with its rotating and retracting and extending functional "t movements.

I Ii FIG. 6 shows enlarged detail of the scrap bin as shown in FIG. 1, in its top discharging position, with main preheating chamber top compartment sealing closure open.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION The scrap preheating apparatus and process system of the preferred embodiment shown in FIG. 1 and the other drawings includes the two, functionally interconnected, fundamental constituents of the object of invention: the scrap preheating apparatus 1, and the process system with the adjacent, in tandem operating electric arc furnace 2. Furthermore, the autonomous scrap preheating apparatus 1, shown in FIG. 1 of the preferred embodiment consists of the three major structural and functional assemblies: the main vertical preheating chamber 3, the inclined scrap bin 37 elevating self-charging equipment assembly 72 and inclined ferrous scrap mixture 8/3 transferring charging mechanism 57, for transferring preheated ferrous scrap mixture 8/3 from the converging bottom of the main vertical preheating chamber 3 and force delivering ferrous scrap mixture 8/3 into adjacent electric arc furnace 2.

The major component of the scrap preheating apparatus 1, is the main 4: vertical preheating chamber 3, divided by the two sets of scrap descent controlling gridirons 4/1 plus 4/2 and as well 5/1 plus 5/2 into three compartments, top compartment 5, middle compartment 6 and Iottom compartment 7. Each of these fthree compartments has a specific task andipurpose for most efficient controlled gradual temperature increase of the cold ferrous scrap mixture 8/1, introduced into the scrap preheating apparatus 1 and descbending semi-continuously by gravity, when allowed to do so in sequence by the controlled movement of the gridirons S 4/1 and 4/2 and as well 5/1 and 5/2.

The entire main vertical chamber 3 of the preheating apparatus 1, as well as the inner space 38 of the top compartment 5 FIG. 1, is intended to be sealed from the surrounding atmosphere and for that purpose its enclosing structure consists of airtight, watercooled walls. The shorter lower wall portion 10 of this compartment of rectangular shape has its bottom ends bent inwards, where they come together with gridirons 4/1 and 4/2 to create cradle like guides for better descent control of scrap 8/1 when the gridirons 4/1 and 4/2 are lowered. At the same time the cavities 11 behind inwards bent bottom ends of the shorter wall portion 10, together with free space 12 between scrap 8/2 in the middle compartment 6 and bottoms of gridirons 4/1 and 4/2 are forming sufficient space for mixing and if necessary combusting the gases permeating through the gridirons 4/1 and 4/2 from the top compartment 5 and gases from oxy-fuel burners 13 installed in the refractory lined walls 14 enclosing air tight the space of the middle compartment 6. The bottom ends of the longer lower walls portion 15 shown in FIG. 3 of the top compartment 5 are also bent inwards for better scrap 8/1 guidance and for accommodation of the hydraulic cylinders actuated lever mechanisms 16, shown in FIG. 3, for controlling the movements of the comb like gridirons 4/1 and 4/2.

To the furnace closer, shorter upper wall 17, FIG. 1, of the top compartment 1 5 extends vertically until it meets the generally horizontal closing panel 18. For entrance of the hot waste gases from the electric arc furnace 2, via square water 1 cooled duct 20, into the top compartment 5, the shorter upper wall is equipped t, with square opening 19. In the case of requirement to prevent hot waste gases from the electric arc furnace to enter the top compartment 5 via square opening 19, the water cooled duct 20 is outfitted with water cooled square door 32, capable of rotating around water cooled shaft 33, controlled via lever mechanisms 34 and hydraulic cylinder 35. From the furnace farther shorter upper wall 21 of the compartment 5 is converging upward toward the centre and it ends at the bottom S of the square opening 22 for erntrance of the scrap bin 37 during semi-continuous S. charging of the scrap into the space of the top compartment 5. The upper end of the square charging opening 22 is defined by the water cooled shaft 23 to which is connected curved and square in projection water cooled sealing enclosure 24.

Position of the sealing enclosure 24 is controlled by the lever mechanisms 25 and S hydraulic cylinders 26.

S.l 44 The longer upper walls 27, FIG. 2, of the top compartment 5 are from the connecting line with the longer lower walls 15 first converging inward, toward the centre and then they are extending vertically, defining the vertical sides of the square charging opening 22. The shape of the longer upper walls 27 in their upper portion has an arcuate, fan blade form. The arcuate shape of the of the vertical longer upper walls 27 is partially connected with the permanent and curved, generally horizontal panel 28. The remaining portion of the arcuate shape between vertical longer upper walls 27 is covered by a curved, generally horizontal panel 29, capable of rotating around horizontally oriented water cooled shaft 30, FIG. 1.

The length of the curved panel 29 is governed by the position of the partially rotated scrap bin 37, meaning that the top square profile- ledge of the partially rotated scrap bin 37 must be already under the end of the curved panel 29 before the start of discharging of the ferrous scrap mixture 8 from the partially rotated scrap bin 37. In this way determined length of the curved panel 29 is also dictating the position of the, farther from the centre, inclined ending ledge of the longer upper walls 27.

Generally vertical wall panel 31, FIG. 1; FIG 3 and FIG.6, is closing the void between the vertical longer upper walls 27, closer to the centre end of the J permanent and curved panel 29 and horizontally oriented water cooled shaft 23.

The above described arrangement of the sealed, airtight structural enclosure of the top compartment 5 is at the same time creating a cavity for achieving of temporary sealing between sides of the charging scrap bin 37 and vertical longer upper walls 27 and as well between rotating scrap bin 37 and curved panel 29 during charging of the cold ferrous scrap mixture 8/1 into the preheating apparatus 1 via charging Sbin 37.

One of the specific purposes and tasks of the top compartment 5 FIG 1. of the main vertical preheating chamber 3 is to initially receive and compile on the S comb like gridirons 4/1 and 4/2 appropriate quantity of ferrous scrap mixture 8/1 required for achieving of its initial desired temperature during allotted resident time, S the cold ferrous scrap mixture 8/1 being delivered semi-continuously, in one or S more rapid repetitive travels of the charging scrap bin 37 into the top compartment via opening 22, normally closed by the sealing enclosure 24. Intake of large quantity of undesirable false air during charging of the cold ferrous scrap mixture 8/1 from charging scrap bin 37 into top compartment 5 via opening 22 is prevented because opening and closing of the sealing closure 24 is synchronized with the sealed position of the charging scrap bin 37 during its emptying. Another specific task and purpose of the top compartment 5 is to enable and assure proper and safe mixing of hot waste gases from electric arc furnace 2, delivered via opening 19 into the free space 38 above compiled appropriate quantity of ferrous scrap 8/1, with recuperative hot gases from final post combustion chamber 79 also delivered via duct 54 and 55 into the free space 38 of the top compartment 5 via opening 39 for suitable combustion of the created mixture of 27 t 1 all gases involved. This is achieved via standardized variable fuel oxygen ratio oxyfuel burners 13 controlled by real time electronic regulating system based on information from gases analysis, pressure and temperature sensors 40. After achieving the required temperature of the resulting final gas mixture through their adequate ratio preset partial combustion, the temperature conditioned gases are forced to a con-current downward flow through the compiled quantity of ferrous scrap mixture 8/1 residing on permeable gridirons 4/1 and 4/2. Due to optimal ratio of the area and depth of the quantity of the ferrous scrap mixture 8/1 the hot gases are permeating through the ferrous scrap mixture 8/1 with most favourable velocity and with prominent heat transfer efficiency.

Finally it is another specific purpose and task of the top compartment 5 to deliver by gravity, and in one simple operation, with certain degree of mixing but without impact the entire compiled quantity of ferrous scrap mixture 8/1, partially preheated during allotted resident time, into previously emptied middle S compartment 6, by the release operation of the gridirons 4/1 and 4/2.

Specific purposes and tasks of the middle compartment 6 of the main vertical preheating chamber 3 are similar to the purposes and tasks of the top compartmet 5. The prime task and purpose of the middle compartment 6 is to accept and safely hold on its gridirons 5/1 and 5/2 the entire quantity of already partially heated ferrous scrap mixture 8/2 transferred by gravity from top S compartment 5, when gridirons 4/1 and 4/2 are removed from their position under S the ferrous scrap mixture 8/1. The next purpose and task of the middle compartment 6 is to enable and assure additional adequate partial combustion of gas mixture emerging through the gridirons 4/1 and 4/2 into the free spaces 11 S' and 12 above ferrous scrap mixture 8/3 with its temperature previously increased.

As a rule, the gas mixture permeating through the gridirons 4/1 and 4/2 contain significant quantity of gaseous combustible components originating mainly from combustible contaminating impurities included in ferrous scrap mixture 8/2 and which were exposed to high temperatures without presence of oxidant during the previous heating stage in top compartment 5. Also during the previous heating stage in the top comprrtment 5, the initially higher temperature gases when flowing downwards through the ferrous scrap mixture 8/1, Have transferred certain amount of their thermal energy to the ferrous scrap mixture 8/1 and therefore they must 28 I I be also temperature conditioned. To achieve required additional and adequate partial combustion of gas mixture emerging through the gridirons 4/1 and 4/2 in the free spaces 11 and 12 above ferrous scrap mixture 8/2 in middle compartment 6 with simultaneous increase of the temperature of the gases standardized variable fuel oxygen ratio, oxy-fuel burners are used in the- same way as in top compartment 5. The standardized burners 13 are controlled in the same way as in the top compartment 5. The downward concurrent flow of re-heated gases through the ferrous scrap mixture 8/2 in the middle compartment 6 as well as heat transfer efficiency is the same as in top compartment 5. Ferrous scrap mixture 8/2 preheated in the middle compartment 6 to further increased temperature during allotted resident time is delivered by gravity into previously emptied bottom compartment 7 by the release operation of the gridirons 5/1 and 5/2.

,,,,,Specific purposes and tasks of the bottom compartment 7 of the main SI, vertical preheating chamber 3 are also similar to the purposes and tasks of the top compartment 5 and middle compartment 6. The main task of the bottom compartment 7 is to accept and safely hold in its inverted pyramidic cavity the entire quantity of the highly preheated ferrous scrap mixture 8/3 transferred by gravity from the middle compartment 6. The converging, pyramidic form of the S bottom compartment 7 is made up from refractory lined walls 14 and water cooled shaped segments 41; 42; 44/1 and 44/2, all of which are at their bottom establishing rectangular opening 47. Opening 47 serves for discharging of the ferrous scrap mixture 8/3 preheated to an average temperature of 700"C into S inclined, transferring charging mechanism 57. Transferring charging mechanism 57 serves for transferring and forced charging of the ferrous scrap mixture 8/3, preheated to the required high temperature, from the preheating apparatus 1 into adjacent electric arc furnace 2 through an opening 76 in the shell side wall 78, closed during furnace tilting operation with the water cooled door 77. The transferring-charging mechanism 57 consists of partially water cooled, conduit of rectangular cross-section 58, having a width matching the width of the discharge opening 47. Rectangular conduit 58 is equipped with an internal, also of matching rectangular cross-section, reciprocating plunger-ram 61. Reciprocating movements of the plunger-ram 61 inside of the rectangular conduit 58 are controlled by a watercooled double acting hydraulic cylinder 62. The rectangular conduit 58 is located on rollers 60 enabling it to be mobile along its longitudinal axis. Relocating 29 moves of the rectangular conduit 58 along its longitudinal axis are controlled by the double acting hydraulic cylinder 59. For receiving preheated ferrous scrap mixture from the discharge opening 47 the top wall of the rectangular conduit 58 has an opening 63, its dimensions and location corresponding to the dimensions of the discharge opening 47. In the stand-by, not charging mode the double acting cylinder 59 is retracted, the rectangular conduit 58 is withdrawn from the electric arc furnace 2, however, the plunger 61 remains in extended mode inside of the conduit 58 and therefore covers and seals the entire discharge opening 47 preventing preheated ferrous scrap mixture to fall into the charging mechanism 57.

To commence forced transfer and charging of the high temperature ferrous scrap So o mixture 8/3 into the electric arc furnace 2, the plunger 61 inside of the rectangular conduit 58 is retracted allowing ferrous scrap mixture 8/3 to fall into the cavity of the rectangular conduit 58 which is then moved forward on rollers 60 and inserted into the electric arc furnace 2 by actuating extending double acting S hydraulic cylinder 59. The forward move of the rectangular conduit 58 closes with 4 its top wall the discharge opening 47. Since double acting hydraulic cylinder 62 and reciprocating plunger-ram 61 are in retracted position, high temperature preheated ferrous scrap mixture 8/3 travels inside of the conduit 58. Forward S" move of the reciprocating plunger-ram 61 caused by actuating extending of the double acting hydraulic cylinder 62, results in forward pushing of the high S* temperature preheated ferrous scrap mixture 8/3 through the interior of the rectangular conduit 58. After forward move of the plunger-ram 61, the high q 25 temperature preheated ferrous scrap mixture 8/3 starts falling into the electric arc furnace 2 molten bath, in the vicinity of electric arc, where it rapidly melts by direct convection. Although high temperature preheated ferrous scrap mixture 8/3 is pushed gradually through the interior of the inclined rectangular conduit 58, due to relatively low friction factor, only moderate force is required for the pushing operation.

The next purpose and task of the bottom compartment 7 is to enable and assure additional highest possible combustion of gas mixture flowing downwards through the gridirons-5/1 and 5/2 into the free spaces 11 and 12 above ferrous scrap mixture 8/3. Again, as in the previous stage,'the initially hiigher temperature gases when flowing downwards through the ferrous scrap mixture 8/2, have f transferred certain amount of their thermal energy to the ferrous scrap mixture 8/2 and must again temperature conditioned. To achieve final required additional and adequate maximum combustion. of gas mixture flowing downwards through the gridirons 5/1 ansd 5/2 in the free spaces 11 and 12 above ferrous scrap mixture 8/3 in the bottom compartment 7, with simultaneous final increase of the temperature of the gases standardized, variable fuel oxygen ratio, oxy-fuel burners, are employed in the same way as in top compartment 5 and middle compartment 6. The standardized burners 13 are controlled in the same way as in the previous top compartment 5 and middle compartment 6. The downward concurrent flow of again re-heated gases, after permeating through the ferrous scrap mixture 8/3, is exhausted from the bottom compartment 7 through the two rectangular openings 45/1 and 45/2, FIG. 3, into diverging, refractory lined rectangular ducts 48/1 and S48/2, outfitted with butterfly closing valves 46/1 and 46/2 for preventing flow of the gases from the preheating apparatus 1, when required during operation without preheating apparatus i, and allowing bypass flow of gases from electric arc furnace 2, directly into dust catching, diverging, rectangular, refractory lined ducts 1 a 49/1 and 49/2. Interior spaces 49/1 and 49/2 of ducts 48/1 and 48/2 serve also as final post-combustion chambers 79. For that reason they are equipped with standardized oxy-fuel burners 13, controlled in the same way as in the compartments 5, 6 and 7. Ducts interiors 49/1 and 49/2 are joined at the top of S the drop-out box 50, where the exhausted gases after loosing their velocity, allow S. sedimenting of heavier dust particles 51 at the bottom of the drop-out box 4 Totally combusted gases having temperature higher than the critical value required S for burning cracking of undesirable Volatile hydrocarbons including dioxins and S furans are exhausted via inverted gas channel 53 at the centre top of the drop-out box 50 through the opening 52 and duct 54 for further use and treatment. For additional improvement of energy recuperation a portion of the hot waste gases is returned from the duct 54 via duct 55, equipped with butterfly closing valve 56, into top compartment 5 through the opening 39.

One of the. important features of the presented embodiment is the control of semi-continuous gravitational descent of the ferrous scrap mixture 8/1 and 8/2, controlled by the gravitational descent of the ferrous scrap mixture controlling mechanism assemblies 16, (abbreviated "descent controlling mechanism") shown in different views and cross-sections, whole or in part in FIG. 1, FIG. 2, FIG. 3, FIG.

31 0 32 4. For better understanding of characteristic and advantageous functional movements of the parts and components of the descent controlling mechanism 16, detail vertical cross-sections along line V-V of the FIG. 4, are shown in FIG. FIG. 5b; FIG. 5c, FIG. 5d; FIG. 5e and FIG. 5f. Basic functional components of the descent controlling mechanisms 16 are: Stationary, water cooled, multipoint frame supports 68, Main rotating frame 66, rotation controlling, single acting hydraulic cylinders 64, gridirons 5/1 and 5/2 (4/1 and extension and retraction of gridirons 5/1 and 5/2 controlling, double acting hydraulic cylinders 67, and gridirons 5/1 and 5/2 connecting beam 81. Main rotating frame 66 is an one piece mechanical structure featuring spaced rectangular guiding openings for each of grid irons 5/1 and 5/2 and allowing their movement along their longitudinal axis.

Rotation of the main rotating frame 66 is made possible by hockey puck shaped extensions 65, attached to the frame 66 and located in the spaces between rectangular guiding openings of the frame 66. To the other, outside end of the rotating frame are on its top attached rollers 80 for reduction of friction between rotating frame structure 66 and individual gridirons 5/1 and 5/2 during their S movement along their longitudinal axis. Each of the gridirons 5/1 and 5/2 is on its outside end connected via rod eye clevis type connection 82 to the horizontally oriented, beam 81. Beam 81 is connected via double acting hydraulic cylinder 67 S to the main rotating frame 66. Rotation of the main rotating frame 66 around centre line of its hockey puck shaped extensions 65 inserted freely into matching semicircular openings of the stationary multipoint supports 68 is controlled by retracting or extending of single acting telescopic hydraulic cylinders 64.

As shown in FIG. 5a, in its basic operating position, the comb like formation of gridirons assemblies 5/1 and 5/2 are extended horizontally, inwards into the main vertical preheating chamber 3 for holding and preventing gravitational descent of the ferrous scrap mixture 8/2. This is achieved by pressurizing of extended telescopic hydraulic cylinders 64. When controlled gravitational descent of the ferrous scrap mixture 8/2 is desired, retraction of the normally extended single acting, telescopic hydraulic cylinders 64 is initiated by controlled releasing of the hydraulic fluid from the cylinder 64. Shown in FIG. 5b, due to the mass of the ferrous scrap mixture 8/2, the main rotating frame 66 including extended gridirons 5/1 and 5/2 rotate around centre line of the hockey puck shaped frame extensions 65 causing inside ends of the extended comb like gridirons 5/1 and 32 t 33 5/2 formation to rotate downwards. By this controlled initial operation a portion of the ferrous scrap mixture 8/2 is allowed to descent by gravity into the bottom compartment 7. To complete gravitational descent of the entire load of the ferrous scrap mixture 8/2 into the bottom compartment 7, double acting hydraulic cylinders 67 are actuated. Since cylinders 67 are installed between the structure of the main rotating frame 66 and horizontally oriented beam 81, both gridirons assemblies 5/1 and 5/2 are withdrawn in generally vertical direction from the compartment 7 allowing the rest of the ferrous scrap mixture to descent by gravity into the bottom compartment as shown in FIG. 5c. In order to return the comb like gridiron formation 5/1 and 5/2 into its initial inwards inserted position, the hydraulic cylinder 64 are extended forcing the main rotating frame 66 including S, retracted gridirons 5/1 and 5/2 to return mainly by gravity into their. horizontal position, as shown in FIG. 5d and FIG. 5e. After this first step is completed, the double acting hydraulic cylinders 67 are actuated to retract. Retraction of the hydraulic cylinders 67 results in no-load insertion of the comb like gridiron A, t" formation 5/1 and 5/2 to resume their initial horizontal position, above ferrous scrap mixture 8/3 in the bottom compartment shown in FIG. 5f. By resuming their initial inserted horizontal position, the gridirons assemblies 5/1 and 5/2 are immediately ready to accept transfer of an other partially preheated load of ferrous scrap mixture 8/,t from the top compartment 5. The described unique sequential rotating and retracting extending movements of the main rotating frame 66 and S comb like gridiron formation 5/1 and 5/2 are extremely important feature of the S embodiment. The described:arrangement eliminates delays and waiting times and 3 reduces the overall structural hight of the preheating apparatus 1. This in turn Sallows installation of the ferrous scrap mixture preheating apparatus 1 in existing meltshops, which is utmost important for reducing significantly the cost of l installation.

In accordance with the invention, one alternative of the embodiment of the integral, inclined elevator mechanism 72, serving for elevating of cold ferrous scrap mixture 8/1 via cold scrap bin 37, for semi-continuous self-charging of the preheating apparatus and process system 1, is shown in FIG. 1 and in more detail in FIG. 6. The main component of the scrap elevator mechanism 72 is the cold scrap bin 37, of simple heavy duty design, having specific shape and adequate volume, and equipped with wheels 71. Wheels 71 are engaged with and guided by the robust and properly configurated U-profiled guides 70, forcing cold scrap bin 37 to travel from its bottom loading position 84 into the top unloading position as per exactly predetermined path, dictated by the configuration of the guides Lifting and lowering travel of the cold scrap bin 37 is controlled by the hoisting device 75, cables 73, cables redirecting pulleys 82 and cables direction reversing pulleys 74. Cables 73 are connected to sides of the cold scrap bin 37 via swivelling connections 83.

Further description of the operating procedure of the presented alternative )of the embodiment of the inclined elevator mechanism 72, is demonstrating its S•advantageous, reliable and practically maintenance free simplicity of functioning, perfectly suitable for the meltshop operating conditions. When actuated in lifting mode, the hoisting device 75 is pulling-lifting cold scrap bin 37, previously loaded with adequate quantity of cold ferrous scrap mixture 8/1, via cables 73 and pulleys S 82 and 74, from its bottom cold scrap loading position 84 into the top cold scrap unloading position 85. For sealed charging of the preheating apparatus 1, as soon Sas the square top profile-ledge of the cold scrap bin 37 reaches the ledge 27 and enters the square cavity at the top of the preheating apparatus 1, double acting hydraulic cylinder 26 rotates the sealing enclosure 24, freeing completely operping 22. In that manner, square profile of the cavity in the top of the preheating apparatus 1 and the square profile of the top profile of the scrap bin 37.are creating adequate dynamic seal preventing communication of the space 38 of the top compartment 5 with the surrounding atmosphere. Rotational removal of'the sealing enclosure 24 allows free and unrestricted unloading of the cold ferrous scrap mixture 8/1 into the top compartment 5. After emptying of the cold ferrous scrap mixture 8/1 from the cold scrap bin 37, the hoisting device 75 is reversed into lowering mode and the cold scrap bin 37 starts, by its mass, gravitational return travel until it reaches its bottom loading position 84. The sealing enclosure 24 is closed by the cylinder 26 before the dynamic sealing between cold scrap bin 37 and the top square cavity of the preheating apparatus 1 is interrupted by return travel movement of the cold scrap bin 37.

In the case of necessity, the hot gases from the electric arc furnace 2, could 34 be rerouted bypassed from the main duct 20, and two bypass ducts 86/1 and 86/2 directly into final combustion chambers 79, by closing square water cooled door 32 when actuated by the hydraulic cylinder 26, and by opening normally closed butterfly valves 46/1 and 46/2.

The invention is not limited by the embodiments described above which are presented as example only but can be modified in various ways within the scope of protection defined by the appended patent claims.

In the claims which follow and in the preceding description of the invention, except where the context requires otherwise due to express language or necessary implication, the word "comprising" is used in the sense of "including", i.e. the features specified may be associated with further features in various embodiments of the invention.

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Claims

1. A preheating apparatus, for preheating a ferrous scrap mixture prior to feeding the scrap into a metallurgical furnace, primarily using heat recovered from hot waste gases emitted from the furnace exhaust port, and for simultaneously reducing contaminants from the scrap and from the waste gases, with concurrent downward flow of hot waste gases and downwardly descending scrap, the apparatus comprising.- a chamber, including- ;Loa top compartment with cold scrap input means for depositing cold scrap into the top compartment and a hot waste gas inlet in Dlow

5. communication with the furnace exhaust port; and a bottom compartment with heated scrap discharging means for 4 1 1 4feeding the heated scrap into the furnace and a waste gas outlet in flow communication with vacuum means for evacuating spent waste gas; gas permeable gate means disposed between each said chamber compartment and sequentially operable between a closed gate position and an open gate position, for concurrently receiving a gravity fed charge of scrap ftrm the cold scrap input means in a closed gate position, and during a predetermined dwell period supporting said charge while hot waste gas flows from the hot gas inlet in the top compartment, permeates downwardly through the scrap charge arnd through the closed gate means, 3-7 and flows out the waste gas outlet in the bottom compartment; anid for controlling the gravitational descent of said charge when in the open position from the top compartment to the bottom compartment on expiry of the dwell period. 2. A preheating apparatus according to claim I wherein the gas permeable gate *means comprise: two oppos ig mirror image gridiron assemblies extending into the chamber; tilting meanis for rotating the gridiron assemblies from a horizontal scrap supporting dlosed position to a downwardly sloping open position; and gridiron axial extension and retraction means for retracting the gridion assemblies within the chamber in a withdrawn position and for extending the gridiron assemblies horizontally to an extended position. iS1 3. A preheating apparatus according to claim 2 wherein the gridiron assemblies I comprise a plurality of spaced apart gridirons extending within. the chamber. 4. A preheating apparatus according to claim I wherein the heated scrap discharging means~ comprise; a converging bottom comprising inclined botto m walls of the bottom compartment with a bottom opening; a charging conduit extending between the bottom opening and the furnace, with a heated scrap accumulating space within the charging conduit for rcceiving scrap descending through the opening; and heated scrap force delivering means for forcing scrap into the furnace through the charging conduit. A preheating apparatus according to claim 4 wherein the heated scrap force delivering means comprise a reciprocating ram with a scrap pushing bulkhead, the ram operable between a standby position wherein a charge of heated scrap falls through the bottom opening to accumulate in advance of the bulkhead, and a charging mode wherein A..t the ramn pushes the heated scrap into the furnace.

6. A preheating apparatus according to claimn I wherein the chamber includes at least one intermediate compartment disposed between the top and bottom compartments with said gas permeable gate means disposed betwcen each said compartment. I 7. A preheating apparatus according to claim I wherein each compartment includes sensor means for monitoring the characteristics of the wagte gas and scrap resident therein selected ffomn the group consisting of gas chemical composition; gas temperature; gas pressure; arnd scrap temperature, for controlling the burners.

8. A preheating apparatus according to claim I wherein each compartmenit includes compartment burner means for controlling the combustion rate and temperature of the waste gas and scrap resident therein.

9. A Preheating apparatus according to claim I wherein the hot waste gas inlet includes a bypass duct in flow communication with the waste gas outlet and bypass valve means for diverting hot waste gas directly to the waste gas outlet.

10. A preheating apparatus according to claim I wherein the cold scrap input means comprise a charging bin shutthig bctween a loading position a distance from the chamber and an unloading position extending within a scalable opening in the top compartment. a

11. A preheating apparatus according to claimn 10 wherein the sealed opening comprises at least one sealed door and wherein internal edges of the sealed opening mate 4* 3 with adjacent outer walls of the charging bin in the unloading position. Is1 12. A preheating apparatus according to claim 10 wherein the charging bin rolls on an inclined elevating ramp propelled by a hoisting device.

13. A preheating apparatus according to claim 1 wherein the waste gas outlet includes a post combustion compartment with precipitaton means for reducing solid particulate contaminates from the waste gas.

14. A preheating apparutus according to claim 13 wherein the post combustion 0 chamber includes post burner means for burning combustible contamninants in the wa-ste gas resident therein- A preheating apparatus according to claim 13 including a gas recycling conlduit oommunicating between the post combustion compartment and the top compartment.

16. A preheating apparatus according to claim 13 wherein the precipitation mearts comprise a vertically beat duct.

17. A preheating apparatus according to claim 13 wherein the precipitation means comprise a flared diffliser duct.

18. Apreheating apparatus according to claim 13 wherein the precipitation means include a solid particulate drop out box.

19. A method of preheating a ferrous scrap mixture prior to feeding the scrap into a metallurgical furnace, using heat recovered from hot waste gases emnitted from the furnace exhaust port, and simultaneously reducing contaminants from the scrap and ffrm the waste gases, with concurrent downward flow of hot waste gases and downwardly ZD descendinig scrap, the method comprising: depositing a charge of cold wcrap on a gas permeable closed gate within a top compaitment of a chamber, the top compartment including a hot waste gas inlet in flow L communication with the flwnace exhaust port- supporting the scrap on the closed gate for a predetermined dwell period while hot waste gas flows from the hot gas inlet in the top compartment, permeates through the scrap charge and through the closed gate, and flows out a waste gas outlet in a bottom compartment of the chamber; controlling the gravitational descent of by opening the gate and permitting scrap flow from the top compartment to the bottom compartment on expiry of the dwell period, force delivering the heated scrap from the bottom compartment into the flurnce; and TO11 repeating the above steps int a sequentially stepped mnanner for successive discreet charges of scrap. A method according to claim 19 wherein the step of supporting the scrap for said dwell period includes further heating the waste gas and scrap with compartment burners 115 within each compartment. DATED THIS 23RD DAY OF NOVEMBER 1998 SMS SCHLOEMANN-SIEMAG AKTIENGESELLSCHAFT By its Patent Attorneys: GRIFFITH HACK Fellows Institute of Patent Attorneys of Australia