EXTRACTION DES GAZ IMPURS ENGENDRES PAR LA PRECHAUFFE DES FERRAILLES, ET INSTALLATION CONCUE A CETTE FIN

METHOD OF REMOVAL OF IMPURE GASES AT THE TIME OF SCRAP PREHEATING, AND EQUIPMENT FOR USE OF SAME

Abrégé anglais

ABSTRACT OF THE DISCLOSURE
A method of preheating scrap metal with impure gases
discharging from a metallurgical vessel includes the steps of
conducting a first portion of the gases to a container of scrap
metal, contacting the scrap metal with the gases for preheating
the same whereby additional impurities are generated, withdrawing
the impure gases after contact with the scrap metal and mixing
the same with a second portion of impure gases from the
metallurgical vessel, thermally cracking the mixture in a
combustion chamber to remove impurities and thereafter removing
particular matter from the gases prior to the discharge to the
atmosphere.

Revendications

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A method of preheating scrap with impure gases
containing particulates and discharging from a metallurgical
furnace, the method comprising the steps of:
conducting at least a portion of said furnace gases
directly from said furnace to a container of scrap metal for
preheating the same wherein additional impurities are
generated for entrainment by said gases as a result of the
contact between said furnace gases and said scrap metal,
withdrawing said gases from said container after
contact with said scrap metal and conducting the same to a
first treatment vessel for reducing the level of said
impurities therein,
withdrawing gases from said first treatment vessel
after the reduction of said impurities and conducting the
same to a second treatment vessel for removing particulates
therefrom,
said furnace gases being conducted from said
furnace to said container without mixing the same with gases
withdrawn from said container.
2. The method set forth in claim 1 wherein said first
treatment vessel is a combustion chamber and thermally
cracking said impurities in said first treatment vessel
whereby the level thereof is reduced.
3. The method set forth in claim 2 and including the
steps of conducting a first portion of the impure gases
directly from said metallurgical furnace to said container of

scrap metal, conducting a second portion of said impure gases
directly to said combustion chamber, and mixing the impure
gases conducted from said container of said scrap metal with
the second portion of said impure gases removed from said
metallurgical furnace, and conducting said mixture to said
combustion chamber.
4. The method set forth in claim 3 wherein said second
portion of the impure gases from said metallurgical furnace
and the impure gases from said container of scrap are allowed
to mix for about .5 seconds prior to the delivery thereof to
said combustion chamber.
5. The method set forth in claim 4 wherein there are
two containers of scrap metal, the additional steps of
conducting the first portion of the impure gases to the first
scrap metal container and charging scrap into the second
container, terminating the delivery of said impure gases to
said first container after the scrap therein has been
preheated and commencing the delivery of said combustion
products to said second container for preheating the scrap
therein and discharging the heated scrap from the first
container.
6. Apparatus for preheating scrap metal with impure
gases containing particulates and discharging from a
metallurgical furnace,
a container for scrap metal having an inlet and an
outlet,
first means for dividing the gases discharging from
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said furnace into first and second portions,
means for conducting said first portion of the
gases discharging from said metallurgical furnace to the
inlet of said container,
a combustion chamber for burning waste gases and
having an inlet and an outlet,
second means for conducting said second portion of
said gases to the inlet of said combustion chamber,
means for conducting waste gases from the outlet of
said container to the inlet of a combustion chamber,
particulate removing means for removing
particulates from waste gases, and
means for conducting combustion products from the
outlet of the combustion chamber to the particulate removal
means.
7. The apparatus set forth in claim 6 and including
mixing means and third means for conducting the impure gases
from the scrap metal container to said mixing means and
additional means for conducting the gas mixture from said
mixing means to said combustion chamber.
8. The method set forth in claim 1 and including the
steps of conducting a first portion of the impure gases
directly from said metallurgical furnace to said container of
scrap metal, conducting a second portion of said impure
furnace gases directly to said treatment vessel, and mixing
the impure gases withdrawn from said container of scrap metal
with the second portion of said impure gases removed from
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said metallurgical furnace, and conducting said mixture to
said treatment vessel.
9. The method set forth in claim 1 and including the
steps of conducting a first portion of the impure gases
directly from said metallurgical. furnace to said container of
scrap metal, conducting a second portion of said impure
furnace gases directly to said treatment vessel, and mixing
in a combustion chamber the impure gases conducted from said
container of scrap metal with the second portion of said
impure gases removed from said metallurgical furnace.
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Description

27~5i
BACKGROUND OF THE INVENTION
This invention relates to a method and apparatus for
preheating scrap metal with metallurgical furnace waste gases and
more particularly to the purification and removal of such gases.
Electric arc furnaces employed for steel production are
relatively large in size and produce large quantities of pouting
gases. In order to prevent the direct discharge of such gases
into the atmosphere, dust collecting equipment are normally
installed in connection with electric arc furnaces. With the
recent sharp rise in power costs, these electric arc furnace
discharge gases have been employed for preheating scrap as an
energy saving measure. This is accomplished by directly
contacting scrap to be preheated with the high temperature waste
gases evacuated from the furnace.
When electric arc furnace waste gases have been employed for
scrap preheating, secondary pollution has occurred as a result of
the incomplete combustion of the impurities and oily substances
adhering to the surface of the scrap and which are released
during preheating.

I
SUMMARY Of THE INVENTION
The invention comprises the method of preheating scrap with
electric arc furnace waste gases and including the steps of
conducting a first portion of the arc furnace waste gas through a
preheating inlet duct to the scrap preheating equipment. After
the scrap has been preheated, the gases are conducted to a
combustion chamber where the impure gases containing the
partially combusted substances released at the time of scrap
preheat are treated by thermal cracking.
The scrap preheating equipment is connected by a preheating
inlet duct to the electric arc furnace fume collector and by an
outlet duct and a gas volume control damper to a combustion
chamber. As an alternate embodiment of the invention, the outlet
duct may be connected to the inlet duct between the combustion
chamber and a gas volume control damper connected to the electric
arc furnace gas collector.
BRIEF DESCRIPTION OF THE DRAWINGS
_
FIGURE 1 schematically illustrates one prior art scrap
preheating system;
FIGURE 2 schematically illustrates the preferred embodiment
of the scrap preheating system in accordance with the invention;
and
IGU~E 3 schematically illustrates an arc furnace fume
collector.

OX
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The prior art scrap preheating system shown in FIGURE 1
includes the combination of scrap preheating equipment,
identified in the drawing as Line B, connected in a bypass
relation to an electric arc furnace dust collecting system,
identified in the drawing as Line A. In particular, an electric
arc furnace 1 has a cover 2 and a waste gas suction opening which
may be formed in the cover 2 by drilling. A water cooled elbow 4
is connected by a water cooled sleeve 5 to a water cooled inlet
duct 6 of a combustion chamber 7. A water cooled outlet duct 8
from chamber 7 includes a gas volume control damper 17 and is
connected to a dust collector 20. Also connected in duct 8 are a
booster fan 18 which is required for intensifying pressure
following the installation of the scrap preheating equipment. In
addition, a dust collecting fan 19 is provided for drawing the
waste gases into a dust collector 20. A bypass line or
preheating inlet duct 9 is connected to a pair of switching
on/off dampers 10 which are in turn connectable to an inlet
sleeve 11 of the cover 12 of a scrap bucket 13 which may be
disposed in one of the pair of preheating pits 140 Volume
control dampers 15 convect each of the preheating pits 14 to an
outlet duct 16 which is connected to the combustion chamber
outlet duct 8.
In operation of the prior art system shown in FIGURE 1, the
high temperature waste gases from the electric arc furnace 1 will
preheat scrap disposed within the scrap bucket 13. Thereafter,
the waste gas will pass through the bypass line 16 to its

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junction with duct 8. my adjusting Lowe opening of the preheating
outlet damper 15 and the direct suction gas volume control damper
17r the volume of gas flowing in the preheating conduit 9 and the
unction line 3 can be controlled.
In the prior art system just discussed the impurities and
oily substances adhering to the surface of the scrap will only be
partially combusted by the waste gas during the scrap preheating
step. A foul smelling white smoke containing unburned substances
is thus produced and is delivered to the water cooled duct 3
through the preheating outlet duct 16. This results in a
undesirable foul smelling white gas discharging from the dust
collector 20 into the atmosphere.
The system in accordance with the preferred embodiment of the
invention resolves the problem of incomplete combustion of the
impurities and oily substances included with the scrap by
conducting a portion of the arc furnace waste gas directly to the
scrap preheating equipment by a preheating inlet duct which
branches off the water cooled duct coupled to the furnace suction
opening. After the waste gas has heated the scrap, it is
conducted to a combustion chamber where thermal cracking of the
impure gasses containing unburned substances will occur. This
alleviates the problem of the foul odor associated with prior art
systems.
The preferred embodiment of the invention will now be
discussed in relation to FIGURE 2. Here an electric arc furnace
l includes a furnace cover 2 which may freely be moved between
open and closed positions. A suction hole 3 is drilled into the
furnace cover 2 and is connected to one end of a water cooled
I

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elbow 4. A water cooled duct 6 is connected at one end Jo the
elbow 4 through a water cooled sleeve 5 and at its other end to a
combustion chamber 8. A preheating inlet duct 9 branches off
from the duct 6 at a point between a gas volume control damper 7
and the water cooled sleeve 5. DUCT 9 it connected to a pair of
on/off switching dampers 10~ Each damper 10 is adapted to be
coupled to the inlet sleeve 11 of the cover 12 of a scrap
preheating bucket 13 disposed within a preheating pit 14. Mach
of the preheating pits 14 are connected through gas volume
control dampers 15 to a preheating outlet duct 16 which may be
connected to the combustion chamber at a point close to the
inlet water cooled duct 6 or to the duct itself. A water cooled
outlet duct 18 connects the combustion chamber B through a gas
volume control damper 17 to a dust collector 21. As in the prior
art systems, a booster fan 19 and a dust collecting fan 20 are
connected in duct 18.
The preexisting equipment identified as the A line consists
of the furnace 1, the water cowled elbow 4, the combustion
chamber 8, the gas volume control damper 17, the water cooled
duct 13, the dust collecting fan 20 and the dust collector 21.
To this is added the preheating equipment identified as B line.
In addition, a direct suction gas volume control damper 7 is
connected at some point in the water cooled duct 6 between the
bypass line 9 for the scrap preheating equipment and the
combustion chamber 8.
Gas exiting the furnace 1 through elbow 4 passes into the
duct 5 and flows to one of the preheating inlet switching on/off
dampers 10. The spas then flows through inlet sleeve 11 to the
scrap preheating bucket 13. After contact with the scrap, the

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gas flows through the gas volume control damper 15 to the
preheating outlet duct 16. The gas is then returned either to
the water cooled duct 6 between the combustion chamber 8 and the
damper 7 or directly to the chamber 8.
During furnace operation, booster fan 19 and the dust
collector fan 20 are activated causing the high temperature
furnace waste gas to flow into conduit 6 where it splits into a
first portion flowing through the conduit 9 to the scrap
preheater and a second portion flowing to the combustion chamber
8. The proportion of the gases flowing through each path can be
suitably controlled by adjusting the opening of the gas volume
control damper 7. In order to effectively preheat the scrap and
to insure against secondary pollution, it is necessary to adjust
the ratio of the waste gas flowing to the bypass line 9 and to
the combustion chamber 8 by adjusting the volume control damper 7
and taking into consideration the layout of the equipment
installed. In this manner, the waste gas drawn into the bypass
line 9 will be at a fairly high temperature so that as it passes
through the scrap preheating bucket 13, it will raise the
temperature of the scrap to an extent sufficient to provide
substantial energy savings in electric arc furnace operation.
When the waste gas preheats the scrap, impurities and oily
substances which adhere to the surface of the scrap will be
partially combusted 80 that the waste gas and unburned substances
will become a source of foul smelling gases. If these unburned
substances are carried away by the waste gases and then
discharged into the atmosphere, a source of secondary pollution
will be created.

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Only partial combustion of the waste gasses occurs as a
result of the low temperature inside the preheating outlet duct
16. In order to prevent the discharge of these materials into
the atmosphere, thermal cracking is performed by mixing the
partially combusted material with high temperature gases from the
arc furnace 1. This is accomplished by allowing the waste gasses
discharging from the preheating pit 14 and containing unburned
substances to remain in contact for a suitable time with the high
temperature gas. In actual jests performed, the desired effect
was obtained with 0.5 seconds of contact. This mixing and
contact is accomplished by conducting the waste gases containing
unburned substances to that part of the water cooled duct 6
beyond the gas volume control damper 7 or directly to the
combustion chamber 8. In either case, the gas will be allowed to
contact the high temperature waste gas from the arc furnace 1.
As a result of this contact, thermal cracking is achieved.
As in the prior art system, two scrap preheating buckets 13
are arranged in parallel Jo that while scrap preheating occurs in
one bucket, the scrap for the second bucket may be prepared. In
order to prevent the suction of outside air from the standby pit
14 into the preheating outlet duct 16, the gas volume control
damper 15 which it connected to the standby pit 14 will be
closed. In this manner, the gas volume control damper 15 will
also perform the switching off operation for the preheating
outlet circuit.

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FIGURE 3 shows the case of suction of the waste gas on the
furnace side from the gas suction hole 3' drilled into the
furnace wall of the electric arc furnace I While only the
furnace itself is shown in FIGURE 3, the system according to the
invention can be used in this case exactly the same as in the
embodiment of FIGURE 2.
As discussed above, in the system according to the invention,
low temperature waste gas containing unburned sub~tanoes is
withdrawn from the preheating pit 14 and mixed with high
temperature waste gas in the combustion chamber 8. This results
in thermal cracking of the unburned substances which may then be
passed through the dust collector 21 for discharge into the
atmosphere. The prior art problem of secondary pollution and
unpleasant odor is thereby resolved. Moreover, in accordance
with the invention, the waste gas to be conducted to the scrap
preheating equipment is taken from the water cooled duct 6 at a
point. fairly close to the electric arc furnace 1. As a result,
the waste gas passing through the preheating equipment will have
a relatively high temperature so that a high scrap preheating
effect is achieved. In addition, the system according to the
invention will require only minor modification to existing
ductwork. In particular, all that will be required is to branch
the preheating inlet duct 9 from the water cooled duct 6 and
connect the preheating outlet duct 16 to either the water cooled
duct 6 or the combustion chamber 8.--.
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