Note: Descriptions are shown in the official language in which they were submitted.
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Title: APPARATUS AND PROCESS SYSTEM FOR PREHEATING OF STEEL
SCRAP FOR MELTING METALLURGICAL FURNACES WITH
CONCURRENT FLOW OF SCRAP AND HEATING GASES
TECHNICAL FIELD
This invention relates to an ecologically friendly and energy highly efficient,
autonomous, gas tight, self-charging apparatus and closed circuit process system for
semi-continuous, self- charging of cold charge ferrous scrap mixture, via integrated
10 inclined scrap bin elevator, its stepped prPIle~ting 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.
15 ~ACKGROUND OF THE ART
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 underst~n-ling of
limitations of non-renewable energy resources and eventually energy cost crisis in
20 1970's have ini~i~te(l intensive activity for lowering of energy consumption also from
the side of energy producers and suppliers. Furthermore, ecological considerations and
the vital necessity of ellvirunlllental 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
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hazardous wastes, it is logical that they are more and more in the spotlight of attention of
public and primarily of government authorities responsible for clean environment.. For
the above reasons there is world wide effort to the improve energy balance of the
metallurgical processes by improving energy efficiency as much as possible. In some
5 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
consideration for ecology, economy and availability. The first priority in reducing
energy consumption in the majority of smelting and melting metallurgical processes is
the highest possible utilisation of the so far unused process system energy losses, such
0 as sensible and chemical heat of waste exhaust gases. By retllrning 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 thought
efforts to utilise waste energy contained in the off-gases, in as possible direct way, lead
15 to designs which incorporate energy recuperating devices for scrap prçhP~ting into a
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 merh~ni.~m~, extensive m:~intenln~e, pollution and safety problems
20 culmin~ting in dangerous explosions are evident reasons for raising questions of their
suitability in general. With current and future environment protection rules, these
question are becoming increasingly pertinent, since toxic emissions from current state of
art scrap preheating devices are not meeting all stipulations and criteria of the valid or
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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
5 scrap, is the high temperature pr~he~ting of a 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 the lack of a fully developed design of this type of scrap
prçhe~tin~ equipment for electric arc furnace steelmaking, it was only sporadically used
in an underdeveloped "scrap in bucket preheating" configuration.
Alongside rising energy and ecological concerns there is ever present endeavour to
intensify any and all phases of the electric arc furnace steelmaking process, above all
increasing productivity and reducing operating costs. For example, further increases of
electric power input via optimally increased secondary voltage complimented with
5 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
20 off-gases plus oxy-fuel burners; and finally, introduction of supersonic gaseous oxygen
lances for in~en.~ification of decarburization and foaming up of slag.
Of the aforementioned process intensification methods, the three methods for increasing
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temperature of scrap by other means then via electric arc, are: in.~t~n~n~ous
recuperation of chemical energy in the vessel via post-combustion; and addition of oxy-
fuel burners to the fumace vessel and preheating of the ferrous scrap charge prior to its
charging into the furnace vessel.
The intent of the first method is inst~nt~neous 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 fllrn~c~c~ basic oxygen
o furnaces and energy optimising furnaces. Preheating of oxygen enriched air by sensible
heat of the exhausted off-gases from the vessel are used instead of gaseous oxygen as a
variant of this 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.
15 Actual energy saving is the result of in-situ scrap preheating. Use of post-combustion in
electric arc furnaces 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 th~ lly insulating and foamy slag. Combustion or so called post-
combustion of combustible components of the off-gases emerging from the foamy slag
20 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
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the same, electric energy requirement for heating of the cold air is elimin~te-l, ultim~tely
resulting in its saving. It should be noted, that in comparison with the post-combustion,
requiring additional oxygen at added cost, an equal or higher energy saving, at no cost,
is achieved by ~dequ~tely sealing of the furnace vessel and on that account preventing
5 intake of the cold air. Moreover, a consequent and exceptional benefit of adequate
sealing the electric arc fumace is in the drastically reduced quantity of hot off-gases to
be exh~u~ted from the furnace. In the case of a 110 tonnes furnace, for example, the
quantity of the gases to be handled was reduced more than 50% (from 90,000 Nm3/h to
40,000 Nm3/h), allowing the stopping of one of the exhaust fans.
The purpose of the second method, for increasing the temperature of the scrap by other
means than via electric arc is, intensification and acceleration of rapid scrap melting by
addition of oxy-fuel burners in the furnace vessel. Although positive results were
obtained from introduction of oxy-fuel burners for faster melting of the scrap in the
5 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 bumers 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 a fashionable
20 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 50% of initial electric energy power input.
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Although this, low cost, addition of overall power input shortens the tap-to-tap times,
with the desired productivity increase and induces some other operating and economic
benefits, many other serious disadvantages are overlooked and suppressed. In general,
some of the major disadvantages are: higher oxidation of the scrap, larger volume of off-
5 gases, substantially lowered heat transfer efficiency if burners are operatedsimultaneously with electric arc power input, especially if the burners are 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~C. This
lo two-stage operating practice resulted in 15-20% electric energy saving and 10-15%
saving of fossil 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 bumers to the existing furnace vessel is relatively low,
yet in almost all cases it resulted in substantial costs for rebuilding and enlarging of the
5 entire exhaust system. From a broad ecological view point, operation of such electric
arc furnaces with excessive use of oxy-fuel burners and lowered energy efficiency,
produce a disproportionately higher volume of hazardous components contained in off-
gases, and such processes are becoming categorically unacceptable.
20 ~he objective of the third method, in 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 use of oxy-fuel burners, if n~cPcs~ry for ecological reasons and concerns.
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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
5 conveyor using a combination of hot waste gases from the furnace and air- and oxy-fuel
burners; continuous vertical pr~he~ting mech~nicm 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 simlllt~n.?ously with electric arc via a variety of
o different designs of air- and oxy-fuel burners. There are several other unique scrap
preheating me~h~ni.cm.c being combinations of the above discussed systems and
operating with more or less success.
C:urrently scrap pr~he~ting is gaining long time overdue recognition. By recognising its
5 great potential, it is now considered that it will be the next production process milestone
for electric arc fumace 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.
From experience with the process of steelmaking in an electric arc furnace
predominantly from recycled mixture of ferrous charge - cold steel scrap, it could be
conclude-l, that ~lequ~te preheating of the scrap prior to charging into the furnace for
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rapid efficient melting is the most suitable method.
In the recent past, several types of equipment and processes for preheating scrap have
been introduced and made available to the electric arc furnace steelmaking industry,
5 generally in accordance with the following US Patents:
US Pat. No. 4,543,124 (24.09.1985) describes an "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
0 special horizontal preheater tunnel. The scrap is fed into the furnace through the hole in
the shell side wall. The off-gas flows counter-current to the scrap. The EAF m~int~in~
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 requires a large space for conveyors. Scrap
15 preheating on conveyors is not very energy efficient, because scrap is preheated
predominantly from above.
US Pat. No. 4,852,858 (01.08.1989) describes a "Charging Material Preheater for
preheating charging materials for a Metallurgical Smelting Unit". This process known
20 in the industry as "Energy Optimising Furnace" has favourable results and is used in
production. However, this semi-continuous vertical scrap preheating apparatus with
controlled 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
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vessel located under the preheating apparatus. Favourable operating results of this
design eventually inrluc.ed some designers of electro-metallurgical equipment to adapt
this, considerably modified, concept to the electric arc furnace. Overall height and
large, uncontrolled infiltration of the false air into individual chambers are considered as
5 drawbacks.
US Pat. No. 5,153,894 " (06.10.1992) describes a smelting plant with removable shaft-
like charging material preheater", known in the industry as a "Shaft Furnace", is a batch
charged, smelting plant with shaft like material preheater which is an integral part of the
10 furnace and with counter-current hot gas flow. By a horizontal relative movement
b~tween the furnace vessel and the holding structure, together with the vessel cover,
charging material can be charged from a scrap basket directly into the fumace vessel or
through the displaced shaft into different regions of the furnace vessel. Charging
material can be retained in the shaft by means of a blocking member therein, and heated
15 up during the refining phase. One of the alternatives has several design problems such
as a 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
20 heat loses, uncontrolled scrap descent through the shaft causing occasional j~mming 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
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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 elimin~ted and they occur from time to time on
5 each of these kind of furnaces.
US Pat. No. 5,264,020 (23.11.1993) describes a "Smelting plant with two melting
furnaces arranged in juxtaposed relationship", known in the industry as "Double Shaft
Fumace". This is actually an aggregate of two Shaft Furnaces in juxtaposed relationship
0 and which are operated :~ltern~tely, wherein the furnace gases which are produced in the
melting process are respectively introduced into the other melting furnace for the
purposes of preheating the charging material. Associated with each melting furnace is a
shaft which is loaded with charging material. The waste gases from the furnace which is
in the melting mode of operation are introduced from the shaft, after charging of the
15 other furnace, through the cover of the other furnace and are removed from the shaft
thereof. That procedure, throughout the entire smelting 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
20 concerning "Shaft Furnace" are applicable also to this furnace aggregate.
US Pat. No. 5,499,264 (12.03.1996) describes "Process and arrangement 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
fumaces connected via a line, a power supply, a device for charging material, and an
5 arrangement for extraction and purification of gas. The process including the step of
connecting a first one 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
o 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 to the gas purification arrangement
is interrupted while the flue gas is being sucked 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 prlohe~ting 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) describes an "Apparatus for preheating and
charging scrap material". This apparatus for preheating and charging scrap material
encompasses a shaft like pr~he~ting chamber and charging unit. The furnace exhaust
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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 water-cooled wall panels. This furnace is of extremely complex design. Scrap
5 pushing is complicated. The shaft is narrow and therefore is equipped with several anti-
bridging devices. Also the high overall height is a significant drawback.
US Pat. No. 5,555,259 (10.09.1996) describes a "Process and device for melting down
scrap", known in the industry as "Contiarc". The disclosed furnace is a DC arc-heated
lo 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 app~op~iate
system in the upper part of the annular shaft at a rate 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
5 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, ~m~lg~m~ed design.
Scrap charging system is complicated, scrap descent is not controlled, therefore bridging
20 will occur. Furnace has not tilting mech~ni~m and therefore replacement or exchange of
the bottom part will be difficult.
US Pat. No. 5,573,573 (12.11.1996) describes an "Electric arc furnace arrangement for
12
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producing steel", known in the industry as "Comelt". Disclosed is an electric arc
furnace for the production of steel by melting scrap, in particular iron scrap, and/or
sponge iron and/ pig iron as well as fluxes in a furnace vessel, into which at least one
graphite electrode projects, which is displaceable in its longitll-lin~l direction, wherein
5 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 a side and the lower part, in the region of the
graphite electrode, has an enlargement radially protruding outwardly relative to the
upper part. The fumace has an extended vertical shaft and it is continuously charged
10 with cold scrap via a conveyor. It is claimed that off-gases, 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. This is a complex, amalgamated design claiming very low electric
energy consumption.
In addition, all of the above prior art methods have a fundamental, indubitable
disadvantage and drawback: Counter-current flow of hot waste gases to the flow of the
scrap is a flln-l~m~n~l, functionally adverse, feature. In the majority of cases prior art
scrap preheating apparatus, devices and process systems this is the main reason for their
20 unsatisfactory perforn ~nce
In summary, with respect to productivity, energy saving, pollution and safety of
operation, the results from efforts aimed at intensification of electric arc furnace
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steelmaking processing predominantly from scrap, using Prior Art scrap preheating
equipment, clearly indicate that their level of achievement is below achievable
performance levels for a "pre-charge" scrap preheating apparatus properly applying
fundamental laws of physics and correct exploitation of practical experience.
5 OBJECTS OF THE INVENTION
An object of the present invention is to provide an autonomous, independently
operating, supplementary, energy efficient, pollution reducing and safely operable
apparatus and process system with concurrent dowllward flow of scrap and downward
flow of hot waste gases. The invention provides a semi-continuous self-charging,
10 controlled, stepped and gradual preheating of cold ferrous scrap mixture - steel scrap and
discharging of preheated scrap into an adjacent, in tandem operating, sealed
metallurgical-electric arc furnace, to overcome all aforementioned drawbacks and
disadvantages.
15 Another object of the invention is to provide a main vertical chamber of inherent
prismatic form having pyramidal converging portion at its bottom and removable
sealing cover at the chamber top for semi-continuous feeding and charging of the cold
charge of ferrous scrap mixture into the chamber.
20 Another object of the invention is to provide a main vertical chamber with walls
con~ ting of refractory or water cooled segments attached to ap,orollliate self-s~:~n-ling
supporting structure.
14
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Another object of the invention is to provide an independently operating, simple and
sturdy charging-supplying merh~ni~m for semi-continuous feeding of cold ferrous scrap
mixture from the adjacent scrap storage. The charging mechanism is preferably located
on a lower floor level and operates independently without requiring use of separate
5 charging bucket or overhead crane. Also preferably the scrap is dumped into the
uppermost colllp~lll-ent of the main vertical chamber, equipped with charging opening
sealing closure, the charging merh~ni~m consisting in principle of at least one inclined
high velocity elevator outfitted with an permanent charging bin.
0 Another object of the invention is to provide one or more robust and adequately cooled
scrap gravitational descent controlling mech~ni.~m~, each consisting of frames with
semi-gridirons performing controlled ~equenti~l rotating and retracting-extçn~ling
motions, dividing the volume of the main vertical chamber in at least two
compartments, being capable of holding at any time no less than the nominal charge
5 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 co-.-pa.llllent of the main vertical
20 chamber for continuously controlled combustion of combustible gases developed
through the entire height of the main vertical chamber, resulting in controlled gradual
prçhç~ting of the charged ferrous scrap mixture to the required temperature before
discharging into the furnace.
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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 time instant
analysis of gases and temperature measurement, used for prompt correction and control
5 of proper evacuating pressure and gradual combustion of the combustible gases
developed during preheating process.
Another object of the invention is to provide a simple, sturdy heat resisting discharge
mech~ni.~m for controlled discharging of high temperature preheated scrap from the
o opening in the converging lower part of the main vertical chamber and forced delivering
of preheated scrap into ~dj~cf~nt metallurgical-electric arc fumace through the opening in
the shell side wall or roof. The discharging mechanism consisting in principle of a
sliding closure of the opening in a converging part of main vertical chamber, scrap
levelling roll and inclined, reciprocating elevating device having a trolley-trough
15 outfitted with an intemal 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 fumace and cont~ining sensible and chemical themmal energy
20 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 a commensurate negative pressure and
16
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which creates apl)lup~iate suction effects at different points of the apparatus and most
importantly forces combination of any and all gases entering the main vertical chamber,
to flow from the highest point of the top conlpalllllent downwards through the layers of
scrap in the direction of flow concurrent with the flow of gravitationally descending
5 scrap, combined hot gases encompassing the initial hot 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
compa~ ents and as well hot gases resulting from oxidation of combustible substances
contained in the charge via ~lmini.~tered oxygen, oxygen enriched air or air.
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 comp~ lnlent of the main
vertical rh~mher, with hot waste gases from the two slit openings in the main vertical
5 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.
20 Another object of the invention is to provide more than one, preferably two hot waste
gases by-pass ducts, equipped with applopliate closing/opening ducts valving for
conn~cting the main exhaust duct from the, in tandem operating, electric arc furnace into
pr~he~ting apparatus with the upper spaces of the two combined final combustion
17
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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 flowing through the scrap preheating apparatus;
Another object of the invention is to provide a slit type Venturi scrubber with priority
function to provide in.~t~nt~n~ous shock cooling of the hot waste gases, below the lower
critical temperature of de novo synthesis of dioxins, and with the additional function of
further cleaning 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 purposes of5 illustration and not as definition of the limits of the invention, for which reference
should be made to the appended claims.
DISCLOSURE OF THE INVENTION
The invention provides a novel preheating apparatus and method for preheating a
20 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
simultaneously reducing cont~min~nt.~ from the scrap and from the waste gases, with
concurrent downward flow of hot waste gases and downwardly descending scrap.
18
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The appala~lls has a chamber, including a top compartment with a cold scrap input for
depositing cold scrap into the top compartment and a hot waste gas inlet in flow
communication with the furnace exhaust port. The chamber also has a bottom
compartment with a heated scrap discharging mech~nicm for feeding the heated scrap
5 into the furnace and a waste gas outlet in flow communication with a vacuum exhaust
for evacuating spent waste gas. Gas permeable gates are disposed between each
chamber compartment and sequentially operate between a closed gate position and an
open gate position, for concurrently receiving a gravity fed charge of scrap from the
cold scrap input in a closed gate position, and during a predetermined dwell period
o supporting the scrap charge while hot waste gas flows downwardly from the hot gas
inlet in the top compartment, permeates downwardly through the scrap charge and
through the closed gates, and flows out the waste gas outlet in the bottom
compartment. The gates mix the scrap as it falls and serve to control the gravitational
descent of the scrap charge from the top compartment to the bottom compartment on
15 expiry of the dwell period.
In operation the apparatus carries out a method of preheating a ferrous scrap mixture
prior to feeding the scrap into a metallurgical fumace, primarily using heat recovered
from hot waste gases emitted from the furnace exhaust port, and simultaneously
20 reducing cont~min~nt.~ from the scrap and from the waste gases, with concurrent
downward flow of hot waste gases and downwardly descending scrap, as follows. A
charge of cold scrap is deposited on a gas permeable closed gate within a top
compartment of a chamber, the top compartment including a hot waste gas inlet in
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flow communication with the furnace exhaust port. The scrap is supported on the
closed gate for a predetermined dwell period while hot waste gas flows downward
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
5 the chamber. By opening the gates the gravitational descent of the scrap is controlled
permitting scrap flow from the top compartment to the bottom colllpa~ ~ment on expiry
of the dwell period. Thereafter, the heated scrap is force delivered from the bottom
compartment into the furnace. Successive discreet charges of scrap are preheated by
repeating the above steps in a sequentially stepped manner.
Accordingly, to overcome the disadvantages and drawbacks of scrap preheating devices
and methods of known in the prior art, scrap preheating according to the invention is to
be performed in an independent and autonomous, separate, self-st~ntling, self-charging
and discharging, simple, robust, almost m~intf~n~n(~e free scrap preheating apparatus and
15 process system, adjacent to the sealed metallurgical-electric arc furnace. The preheating
apparatus structure could be added, economically and without large modifications to an
existing or new electric arc furnace melting facility. By working in tandem with sealed
metallurgical-electric arc furnace, the high energy efficiency and operating performance
of the scrap preheating apparatus and closed-circuit process system in accordance with
20 the object of invention will substantially influence the efficiency of the steelmaking
process.
In addition a particularly important benefit is the significant lowering of the volume of
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polluting toxic gases and substances. The scrap preheating apparatus and closed-circuit
process system in accordance with the object of invention will, contribute to reduction in
the consumption of electric and other energies, reduction of electrode consumption and
shortening of the tap-to-tap time, with improved safety and working environment, and
5 on the whole clllmin~ting in overall improved performance and profitability.
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 escaping from the furnace depends on
o 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 etc., and what is of
foremost importance, on the quantity of ambient cold air inspired into the furnace.
Without sealing, gas tight~ning of the furnace vessel as much as practically possible,
5 even in the case of so called direct evacuation via fourth hole in the roof, the amount of
exhausted gases could reach 350-450 m3/tonne of produced steel. In absence of cold air
inspi.~lion, what is achieved with gas tight sealing of the furnace and without use of
gaseous oxygen decarburizing lance, the amount of hot waste gases exh~u~te-l via the
fourth hole drops to a range of 90-120 m3/tonne of produced steel. With use of
20 decarburizing oxygen lance the amount of gases exh~llste-1 increases proportionally to
the amount of injected decarburizing oxygen to a range of 200-220 m3/ton of produced
steel.
CA 02222401 1998-11-17
Furthermore e?~h~ ted hot waste gases contain significant amounts of hazardous by-
products. 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
5 general brings about formation of large amounts of carbon oxides, and as well the
following micro by-products: nitrogen- and sulphur oxides, cyanides, fluorides, dioxins
and furans. The concentration of nitrogen oxides and cyanides depends 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 fumace. The
10 amount of 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
cont~min~nt~ included in charged scrap, their generation and destruction being
controlled by the temperature of the off-gases.
CA 02222401 1998-11-17
Table I.
Content of harmful gaseous products in hot waste gases exhausted from electric arc
furnace
Harmful Average Amount of by-products
substances concentration exhausted g/tonne
mg/m3 of produced steel
Carbon oxides 13,500.0 1,350.0
Nitrogen oxides 550.0 270.0
Sulphur oxides 5.0 1.6
Cyanides 60.0 28.4
Fluorides 1.2 0.56
Conc~rning the dust exhausted from the fumace 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 inspi aLion of air into the furnace, contains large amount of ferroxide Fe203.
20 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 re-engineering with an economical
25 orientation, so that its implementation will necessarily result also in economical
benefits, supplemented with safer and improved working conditions.
In summary, the Apparatus and Process System With Dowllw~d Concurrent Flow of
Scrap and Hot Gases for Stepped Preheating of Steel Scrap for Melting Metallurgical
CA 02222401 1998-11-17
Fumace in accordance with the object of invention encompasses a multitude of major
and minor functional and process system operating characteristics and parametershammoniously aggregated into an embodiment, giving it:
- Ability of the entire scrap preheating apparatus and process system to be added
to majority electric arc fumaces in existing melt shops, with short retum of
investment time;
- Ability to work in a synchronised tandem manner with most of the existing
o metallurgical melting filrn~ces, preferably with gas tight sealed electric arc
fumace for steelmaking from cold ferrous scrap mixture;
- Ability to significantly reduce the amount of hot gases exhausted from the
electric arc fumace by completely elimin~ting oxy-fuel bumers and so called
process of "post combustion" from the fumace vessel;
- Ability to improve energy efficiency by operating a scrap preheating apparatusin tandem with an electric arc fumace and by elimin~ting the energy inefficient
oxy-fuel bumers from the fumace shell vessel and relocating them to the scrap
preheating apparatus;
- Ability to improve energy efficiency by elimin~ting the so called "post
combustion" in the electric arc fumace vessel and by exploiting the sensible and 24
CA 02222401 1998-11-17
chemical thermal energy contained in the hot off-gases exhausted from the
electric arc furnace in the compartments of the preheating apparatus with almostdouble efficiency of heat transfer from the gases to the scrap;
- Ability to improve energy efficiency by elimin~ting the need to remove the
roof of electric arc furnace when a charge of scrap is to be delivered into the
furnace via an overhead crane with a conventional charging bucket.
- Ability to elimin~te need of overhead charging cranes and classic charging
o buckets by including a self- charging capability via integrated, semi-continuous
self-charging, scrap bin elevating mechanism.
- Ability to refill the scrap bin of the integrated, semi-continuous scrap bin
elevating mech~nicm via conventional, low level, scrap moving horizontal
conveyors or road transport scrap h~n-lling equipment preferably at a low groundlevel.
- Ability to efficiently preheat cold ferrous scrap mixture semi-continuously
charged into the top COIllpal llllent of the apparatus to the predetermined
temperature at its discharge from the bottom compartment, including the highest
possible level of combustion of all combustible cont~min~nt substances being
introduced into the apparatus and which provides appropriate suction effects at
different points of the apparatus and most importantly forcing combination of
CA 02222401 1998-11-17
any and all gases entering the main vertical chamber to flow from the highest
point of the top compartment downw~ds through the scrap in direction of flow
concurrent with the flow of gl~vil~ionally descending scrap, combined hot
gases encomp~s.cing the initial 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 the walls of the compartments
and as well hot gases resulting from oxidation of combustible substances
contained in the charge via ~(lmini~t~red oxygen, oxygen enriched air or air.
o - Ability to preheat ferrous scrap mixture to the required nominal preheating
temperature, without hot waste gases from the adjacent, ~~pel~ling 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 the oxidation loss of scrap by controlled gradual, stepped
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;
26
CA 02222401 1998-11-17
- Ability to control the semi-continuous gravitational descent of the ferrous scrap
mixture via simple and robust adequately cooled, scrap descent controlling
mech~ni~m;
- Ability to reliably discharge preheated ferrous scrap mixture from the
converging bottom of the chamber into the heat resisting trolley-trough for
forced delivery into the furnace, including weighing with required accuracy of
each force delivered quantity of scrap;
0 - Ability to, semi-continuously force deliver preheated ferrous scrap mixture
from the preheating apparatus into the adjacent, tandem operating electric arc
furnace, at the rate of the melting capability of the furnace, enabling furnace
operation with an uninterrupted hot metal bath, with electric arcs perm~nently
submerged in foamy slag of suitable depth, consistency and chemistry and as a
con.cequence high thermal efficiency rapid melting - dissolving of scrap
immersed into hot metal bath.
- Ability to enable adjacent, tandem operation of a sealed metallurgical - electric
arc furnace to continuously operate with hot metal bath due to semi-continuous
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
27
CA 02222401 1998-11-17
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 exhausted waste gases in the range of 40-45%;
lo -- Reduction of dust and hazardous substances generation in the range of 20-
25%;
-- Reduction of dioxins and furans below currently permitted limits;
-- Reduction of voltage flicker bellow permitted noticeable limits;
-- Possible elimin~tion of electric HV compen.~ting apparatus with optimised
impedance of the furnace;
-- Shortening of tap-to-tap time in the range of 15-20%;
-- Possible down-sizing of the air filtering baghouse capacity in the range of 25-
30%;
-- Reduced m~inten~n~e requirements due to drastic reduction in short circuit
and fluctll~ting 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 çlimin~ting the explosion risk of hazardous open furnace dumping of wet
28
CA 02222401 1998-11-17
scrap via a conventional charging bucket and as well effective lowering of the
noise pollution level.
Further details of the invention and its advantages will be apparent from the detailed
5 description and drawings included below.
BRIEF DESCRIPTION OF THE DRAWINGS
In order that the invention may be readily understood, one preferred embodiment of
the invention will be described by way of example, with reference to the
0 accompanying drawings wherein:
FIG. 1 shows a vertical lon~itllflin~l left hand section taken along line IV - IV in
FIG 2, of the scrap preheating apparatus, and the tandem operating adjacent
electric arc furnace.
FIG. 2 shows a vertical lateral right hand elevation view taken along line II - II
of the FIG. 1, of the scrap preheating apparatus.
FIG. 3 shows vertical lateral section taken along line III - III in FIG. 1.
FIG. 4 shows a horizontal section view of the two gridiron halves of the scrap
gravitational descending controlling merh~ni~m at the level taken along line IV -
IV of FIG. 2.
29
CA 02222401 1998-11-17
FIG. 5a, 5b, 5c, 5d, 5e and 5f show progressive vertical sections taken along line
V - V in FIG. 4, showing the progress of scrap descent and the descent
controlling mechanism with its rotating and retracting and ex~en~ling functional
movements.
FIG. 6 shows enlarged vertical sectional detail of the scrap bin as shown in FIG.
1, in its top discharging position, with main prehe~ing chamber top
co np~l~l~ent sealing closure open.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
The scrap preheating apparatus and process system of the preferred embodiment
shown in FIG. 1 and the other drawings includes the two, functionally interconnected,
components: the scrap preheating apparatus 1, and an adjacent tandem operating electric
15 arc furnace 2. The autonomous scrap preheating apparatus 1, shown in FIG. 1 consists
of 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 charging mechanism 57, for transferring preheated
ferrous scrap mixture 8 from the converging bottom compartment 7 of the main vertical
20 preheating chamber 3 and force delivering ferrous scrap mixture 8 into the adjacent
electric arc furnace 2.
The major component of the scrap preheating apparatus 1, is the main vertical
CA 02222401 1998-11-17
preheating chamber 3, divided by the two sets of scrap descent controlling gridirons 4
into three colllpalllllents~ namely the top compartment 5, middle compartment 6 and
bottom colllpa~ ent 7. Each of these three compartments 5, 6, and 7, has a specific
task and purpose for ensuring the most efficient controlled gradual temperature increase
5 of the cold ferrous scrap mixture 8. The mixture 8 is introduced into the scrap
preheating apparatus 1 and descends semi-continuously by gravity, in sequence by the
controlled swing and retract movement of the gridirons 4 as indicated in Figs. 5a-5f.
The entire main vertical chamber 3 of the preheating apparatus 1, as well as the inner
10 space 38 of the top compartment 5 FIG. 1, is intçn(lçd to be sealed from the surrounding
atmosphere and for that purpose its enclosing structure consists of gas tight, watercooled
walls. The shorter lower wall portion 10 of the rectangular compartments have its
bottom ends bent inwards, where they come together with gridirons 4 to create cradle
like guides for better descent control of scrap 8 when the gridirons 4 are swung and
15 lowered. At the same time the cavities 11 behind the inward bent bottom ends of the
shorter wall portion 10, together with free space 12 between the scrap 8 in the middle
colllpal~nlent 6 and bottoms of gridirons 4 form sufficient space for mixing and
combusting the gases permç~ting through the gridirons 4 from the top compartment 5
and gases from the oxy-fuel burners 13 installed in the refractory lined walls 14
20 enclosing in an gas tight manner, the space of the middle c~lllpallll-ent 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 guidance and for accommodation of the hydraulic
cylinder actuated lever mech~nicms 16, shown in FIG. 3, for controlling the movements
31
CA 02222401 1998-11-17
of the comb like gridirons 4.
Adjacent to the furnace, shorter upper wall 17, FIG. 1, of the top compartment 5 extends
vertically until it meets the generally horizontal closing panel 18. For entry of the hot
waste gases from the electric arc furnace 2, via square water cooled duct 20, into the top
compartment 5, the shorter upper wall 17 is equipped with square opening 19. To
p~event hot waste gases from the electric arc furnace entering 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 mech~niem.e
0 34 and hydraulic cylinder 35. The shorter upper wall 21 of the top compartment 5
converges upward toward the centre and ends at the bottom of the square opening 22
that provides an entrance for the scrap bin 37 during semi-continuous charging of the
scrap into the space of the top co~ lllent 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. The operation of the sealing
enclosure 24 is controlled by the lever me~h~ni.ems 25 and hydraulic cylinders 26.
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
20 extend 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 vertical longer upper walls 27 is partially connecte~ with the
curved, generally horizontal panel 28. The rem~ining portion of the arcuate shape
CA 02222401 1998-11-17
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, such that the top square profile ledge of the partially rotated scrap bin 37
5 must be under the end of the curved panel 29 before the ferrous scrap mixture 8 begins
discharging from the partially rotated scrap bin 37. In this way the length of the curved
panel 29 also dictates the position of the inclined ending ledge of the longer upper walls
27.
0 Generally vertical wall panel 31, FIG.1; FIG 3 and FIG.6, closes the void between the
vertical longer upper walls 27, closer to the centre end of the pPrm~n~nt and curved
panel 29 and horizontally oriented water cooled shaft 23. The above described
arrangement of the sealed, gas tight structural enclosure of the top compartment 5 at the
same time creates a cavity for 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 into the preheating
apparatus 1 via charging bin 37.
One of the specific purposes of the top co",pall",ent 5 of the main vertical preheating
chamber 3 is to initially receive and compile on the comb like gridirons 4 an appropriate
quantity of ferrous scrap mixture 8 required for achieving of its initial desired
temperature during allotted resident time. The cold ferrous scrap mixture 8 is delivered
semi-continuously, in one or more rapid repetitive travels of the charging scrap bin 37
33
CA 02222401 1998-11-17
into the top compartment 5 via opening 22, normally closed by the sealing enclosure 24.
Intake of a large quantity of undesirable false air during charging of the cold ferrous
scrap mixture 8/1 from the charging scrap bin 37 into top compartment 5 via opening 22
is prevented because opening and closing of the sealing closure 24 is synchronised with
5 the sealed position of the charging scrap bin 37 during its emptying. Another specific
task and purpose of the top conlp~,llent 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 ferrous scrap 8. Recuperative hot gases from final post combustion
chamber 79, are also delivered via duct 54 and 55 into the free space 38 of the top
lo comp~ .~ent 5 via opening 39 for suitable combustion of the created mixture of all
gases involved. This is achieved via standardised variable fuel oxygen ratio oxy-fuel
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 pre-set partial
15 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. Due to the optimal ratio of the area and depth of the quantity of the ferrous
scrap mixture 8, the hot gases are perrne~ting through the ferrous scrap mixture 8 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 a certain degree of mixing but without impact
the entire compiled quantity of ferrous scrap mixture 8, partially preheated during
34
CA 02222401 1998-11-17
allotted resident time, into the previously emptied middle compartment 6, by the release
operation of the gridirons 4.
Specific purposes and tasks of the middle compartment 6 of the main vertical preheating
5 chamber 3 are similar to the purposes and tasks of the top co-l-pall --ent 5. The prime
task and purpose of the middle compartment 6 is to accept and safely hold on its
gridirons 4 the entire quantity of already partially heated ferrous scrap mixture 8
transferred by gravity from top conlpa-l --ent 5, when gridirons 4/are moved from their
horizontal position under the ferrous scrap mixture 8. The next purpose of the middle
10 co-llp~l---ent 6 is to enable and assure additional ~dequ~te partial combustion of gas
mixture emerging through the gridirons 4into the free spaces 11 and 12 above ferrous
scrap mixture 8 with its temperature previously increased by operation of the burners 13
and waste furnace gases. As a rule, the gas mixture permeating through the gridirons 4
contains significant quantities of gaseous combustible components origin~tin~ mainly
15 from combustible cont~min~ting impurities included in ferrous scrap mixture 8 and
which were exposed to high temperatures without presence of sufficient oxidant during
the previous heating stage in top compartment 5. Also during the previous heating stage
in the top compartment 5, the initially higher temperature gases when flowing
downwards through the ferrous scrap mixture 8, have transferred a certain amount of
20 their thermal energy to the ferrous scrap mixture 8 and therefore they must be also
te~peldlllre conditioned. To achieve the required additional and adequate partial
combustion of gas mixture emerging through the gridirons 4 into the free spaces 11 and
12 above ferrous scrap mixture 8 in middle compartment 6 with simultaneous increase
CA 02222401 1998-11-17
of the temperature of the gases with standardised variable fuel oxygen ratio, oxy-fuel
burners 13 are used in the same way as in top compartment 5. The standardised burners
13 are controlled in the same way as in the top compartment 5. The dowllw~ld
concurrent flow of re-heated gases through the ferrous scrap mixture 8 in the middle
5 co.np~.lent 6 as well as heat transfer efficiency is the same as in top compartment 5.
Ferrous scrap mixture 8 preheated in the middle co-llpal~ --ent 6 to a further increased
temperature during the allotted resident time is delivered by gravity into previously
emptied bottom compartment 7 by the release operation of the gridirons 4.
10 The bottom compartment 7 of the main vertical preheating chamber 3 has a similar
function to that 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 pyramidal cavity or
converging bottom the entire quantity of the highly preheated ferrous scrap mixture 8
transferred by gravity from the middle compartment 6. The converging, pyramidal form
15 of the bottom compartment 7 is made up from refractory lined walls 14 and water
cooled shaped segments 41; 42; 43 and 44, all of which are at their bottom establishing
rectangular opening 47. Opening 47 serves for discharging of the ferrous scrap mixture
8 preheated to an average temperature of 700~C into inclined, transferring charging
mech~ni~m 57. Transferring charging mech~ni.~m 57 serves for transferring and forced
20 charging of the ferrous scrap mixture 8, 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, which is closed the during furnace tilting operation with the water
cooled door 77. The transferring-charging mechanism 57 consists of a partially water
36
CA 02222401 1998-11-17
cooled trough or conduit of rectangular cross-section 58, having a width m~trhing the
width of the discharge opening 47. Rectangular conduit 58 is equipped with an internal,
m~tçhing rectangular 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 longitll-lin~l axis. Extçn-ling and retracting movement
of the rectangular conduit 58 along its longitu-lin~l axis is 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
0 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 me~h~ni.~m 57.
To commçnre forced transfer and charging of the high temperature ferrous scrap
mixture 8 into the electric arc fumace 2, the plunger 61 inside of the rectangular conduit
58 is retracted allowing ferrous scrap mixture 8 to fall into the cavity of the rectangular
20 conduit 58, which is then moved forward on rollers 60 and inserted into the electric arc
furnace 2 by ~ctu~ting ext~n~ing double acting hydraulic cylinder 59. The fonvard
move of the rectangular conduit 58 closes with its top wall the discharge opening 47.
Since double acting hydraulic cylinder 62 and reciprocating plunger-ram 61 are in a
37
CA 02222401 1998-11-17
retracted position, high temperature preheated ferrous scrap mixture 8/3 travels inside of
the conduit 58. Forward movement of the reciprocating plunger-ràm 61 caused by
actll~ting e~ten~ling of the double acting hydraulic cylinder 62, results in forward
pushing of the high temperature preheated ferrous scrap mixture 8 through the interior of
the rectangular conduit 58. After forward movement of the plunger-ram 61, the high
temperature preheated ferrous scrap mixture 8 starts falling into the electric arc furnace 2
molten bath, in the vicinity of electric arc, where it rapidly melts by direct convection.
Although the high temperature preheated ferrous scrap mixture 8 is pushed gradually
through the interior of the inclined rectangular conduit 58, due to relatively low friction
lo 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 dow~lwards through the
gridirons 4 into the free spaces 11 and 12 above ferrous scrap mixture 8. Again, as in
the previous stage, the initially higher temperature gases when flowing downwards
through the ferrous scrap mixture 8, have transferred a certain amount of their thermal
energy to the ferrous scrap mixture 8 and must again temperature conditioned to the
optimum required temperature. To achieve final required additional and adequate
maximum combustion of gas mixture flowing downwards through the gridirons 4 in the
20 free spaces 11 and 12 above ferrous scrap mixture 8 in the bottom compartment 7, with
simultaneous final increase of the temperature of the gases standardised, variable fuel
oxygen ratio, oxy-fuel bumers 13, are employed in the same way as in top compartment
5 and middle coll,pa,l-l-ent 6. The standardised bumers 13 are controlled in the same
38
CA 02222401 1998-11-17
way as in the previous top compartment 5 and middle co~,-pallnlent 6. The dow"wa~d
concurrent flow of again re-heated gases, after permeating through the ferrous scrap
mixture 8, is exhausted from the bottom compartment 7 through the two rectangular
openings 45, FIG. 3, into diverging, refractory lined rectangular ducts 48, outfitted with
5 butterfly closing valves 46 for preventing flow of the gases from the preheating
apparatus 1, when required during operation without the preheating apparatus 1, and
allowing a bypass flow of gases from electric arc furnace 2, directly into dust c~tçhing,
diverging, rectangular, refractory lined ducts 48. Interior spaces 49 of ducts 48 serve
also as final post-combustion chambers 79. For that reason they are equipped with
0 standardised oxy-fuel burners 13, controlled in the same way as in the compartments 5,
6 and 7. Duct interiors 49 are joined at the top of the drop-out box 50, where the
exhausted gases after loosing their velocity, allow sedimentation of heavier dust
particles 51 at the bottom of the drop-out box 50. Totally combusted gases having
temperature higher than the critical value required for burning - cracking of undesirable
5 volatile hydrocarbons including dioxins and 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 by merh~ni~m
assemblies 16, (abbreviated "descent controlling mech~ni~m 16") shown in different
39
CA 02222401 1998-11-17
views and cross-sections, whole or in part in FIG. 1, FIG. 2, FIG. 3, FIG. 4. For better
underst~nl1ing 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. 5a; FIG. 5b; FIG. 5c, FIG. 5d; FIG. 5e
5 and FIG. 5f. Basic functional components of the descent controlling mech~ni~m~ 16 are
: Stationary, water cooled, multipoint frame supports 68, Main rotating frame 66,
rotation controlling, double acting hydraulic cylinders 64, extension and retraction of
gridirons 4 controlling, double acting hydraulic cylinders 67, and connecting beam 81.
Main rotating frame 66 is a one piece mechanical structure featuring spaced rectangular
o guiding openings for each of grid irons 4 and allowing their movement along their
longitu-lin~l axis. Rotation of the main rotating frame 66 is made possible by disc
shaped extensions 65, ~tt~ched 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
5 structure 66 and individual gridirons 4 during their movement along their longitudinal
axis. Each of the gridirons 4 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 to the main rotating frame 66. Rotation of the main rotating
frame 66 around centre line of its disc shaped extensions 65 inserted freely into
20 m~tching semi-circular openings of the stationary multipoint supports 68 is controlled
by retracting or ext~n-ling of single acting telescopic hydraulic cylinders 64.
As shown in FIG. 5a, in its basic operating position, the comb like formation of
CA 02222401 1998-11-17
gridirons assemblies 4 are extended horizontally, inwards into the main vertical
preheatin~ chamber 3 for holding and preventing gravitational descent of the ferrous
scrap mixture 8. This is achieved by pressurising of the ~xt~ntled telescopic hydraulic
cylinders 64. When controlled gravitational descent of the ferrous scrap mixture 8 is
5 desired, retraction of the normally extended single acting, telescopic hydraulic cylinders
64 is initi~ted 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, the main rotating frame 66,
including ~~xtenrl~d gridirons 4 rotate around centre line of the disc shaped frame
extensions 65 causing inside ends of the extended comb like gridirons 4 to rotate
o downwards. By this controlled initial operation a portion of the ferrous scrap mixture 8
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 into the bottom
comp~,nent 7, double acting hydraulic cylinders 67 are actuated. Since cylinders 67
are installed between the structure of the main rotating frame 66 and horizontally
5 oriented beam 81, both gridirons assemblies 4 are withdrawn in generally vertical
direction from the compartment 7 allowing the rest of the ferrous scrap mixture 8 to
descent by gravity into the bottom compartment 7., as shown in FIG. 5c. In order to
return the comb like gridiron formation 4 into its initial inwards inserted position, the
hydraulic cylinder 64 are extended forcing the main rotating frame 66 including
20 retracted gridirons 4 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 formation 4 to resume their initial horizontal
41
CA 02222401 1998-11-17
position, above ferrous scrap mixture 8 in the bottom compartment shown in FIG. 5f.
E)y resuming their initial inserted horizontal position, the gridirons assemblies 4 are
immediately ready to accept transfer of another partially preheated load of ferrous scrap
mixture 8 from the top co~ allnlent 5. The described unique sequential rotating and
s retracting - extending movements of the main rotating frame 66 and comb like gridiron
formation 4 are extremely important feature of the embodiment. The described
arrangement eliminAte.~ delays and waiting times and reduces the overall structural
height of the preheating apparatus 1. This in turn allows installation of the ferrous scrap
mixture prPhP~ting apparatus 1 in existing meltshops, which is of utmost importance for
10 reducing significantly the cost of installation.
In accordance with the invention, a preferred embodiment includes an integral, inclined
elevator me~h~ni.cm 72, serving for elevating of cold ferrous scrap mixture 8 via cold
scrap bin 37, for semi-continuous self-charging of the preheating apparatus and process
15 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 ~dequ~te volume, and equipped with wheels 71. Wheels 71
are engaged with and guided by the robust and properly configured U-profiled guides
70, forcing cold scrap bin 37 to travel from its bottom loading position shown in Figure
20 1 into the top unloading position shown in Figure 6 as per an exactly predetermined
path, dictated by the configuration of the guides 70. Lifting and lowering travel of the
cold scrap bin 37 is controlled by the hoisting device 75, cables 73, cables redirecting
pulleys 89 and cables direction reversing pulleys 74. Cables 73 are connected to sides
42
CA 02222401 1998-11-17
of the cold scrap bin 37 via swivelling connections 83.
The inf linP-I elevator mech~nism 72, has advantageous, reliable and practically
m~int~n~nce free simple functioning, perfectly suitable for the extreme meltshop
5 operating conditions. When achl~ted in lifting mode, the hoisting device 75 lifts the
cold scrap bin 37, previously loaded with adequate quantity of cold ferrous scrap
mixture 8, via cables 73 and pulleys 89 and 74, from its bottom cold scrap loading
position (Fig. 1) into the top cold scrap unloading position (Fig. 6). For sealed charging
of the prehPating apparatus 1, as soon as the square top profile-ledge of the cold scrap
10 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,
completely disengaging the opening 22. In this manner, the square profile of the cavity
in the top of the preheating apparatus 1 and the square profile of the top of the scrap bin
37 create an ~deq~te dynamic seal preventing communication between the space 38 of
15 the top compartment 5 and the surrounding atmosphere. Rotational removal of the
sealing enclosure 24 allows free and unrestricted unloading of the cold ferrous scrap
mixture 8 into the top c~ -pa-llllent 5. After elllplyillg of the cold ferrous scrap mixture
8 from the cold scrap bin 37, the hoisting device 75 is reversed into lowering mode and
the cold scrap bin 37 retums to its bottom loading position 84. The sealing enclosure 24
20 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 retum travel
movement of the cold scrap bin 37.
CA 02222401 1998-11-17
If necessary for m~inten~n~,e or operational requirements, the hot gases from the electric
arc furnace 2, could be bypassed from the main duct 20, through the bypass opening 87
and into two bypass ducts 86 by opening bypass butterfly valves 88. The hot gases are
directly into final combustion chambers 79, by also closing square water cooled door 32
5 when ~ctu~ted by the hydraulic cylinder 26, and by closing normally open butterfly
valves 46.
~lthough the above description and accompanying drawings relate to a specific
preferred embodiment as presently contemplated by the inventor, it will be understood
that the invention in its broad aspect includes mechanical and functional equivalents
of the elements described and illustrated.
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