Note: Descriptions are shown in the official language in which they were submitted.
'~Q2~22
This invention relates to improvements ln electrlc
arc furnaces. ln partlcular, it relates to improved apparatus
whereby graphite electrodes of an electric arc furnace may
be protected against costly loss and wasteful consumption
due to oxidation corrosion.
Typical electric arc furnaces use one or more
graphite electrodes which are suspended, by means of an electrode
holder, above a batch of ore or metal to be melted or smelted.
Heat is generated by energizing the electrodes so that an
arc is created between the electrodes and the ore or metal
in the batch contained in the furnace.
Of course, the constant electric discharge, the
heat of the furnace and the atmosphere of the hot gases above
the bath contribute to gradual erosion and consumption of
the electrodes and constitute a substantial cost in the process
of operating an electric arc furnace.
Although some of this consumption is necessary
and inevitable, a large portion is due to oxidation of the
sides of the electrode above the bath which is unrelated
and unnecessary to the creation of the arc or the generation
of heat. In fact, the erosion and severe pencilling of the
lower portion often consumes in excess of 50% of the electrode
material, especially in regions where the temperatures are
above 400 Fahrenheit.
It has long been recognized that the heat of the
atmosphere and the availability of oxygen or other corrosive
gases will cause the sides of the electrode well above the
point to become eaten away and consumed wastefully, thus
contributing to costs.
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20'~2622
Various attempts to overcome this problem have
been tried with some success. One such technique involves
the positioning of a jacket around the upper parts of the
electrode extending down from the electrode holder. Another
involves the use of inert gases to protect the electrode
from corrosion.
A third involves the use of coated electrodes
which shield the graphite from corrosion.
One of the most successful techniques has been
to direct a stream of water on the upper reaches of the electrode
stalk just below the electrode holder and allow it to run
down to nearly the bottom of the electrode where it vaporizes.
This stream of water cools and shields the upper reaches
of the electrode against contact with hot gases and the consequent
corrosion.
One of the problems associated with the use of
a cooling water to protect electrodes is the fact that water
is considered difficult to manage and dangerous in some operations.
In particular, the melting of aluminum oxides are a problem
because of the extremely high heats generated which accelerate
the rate of oxidation corrosion. In addition, water has
always been considered hazardous because any excessive amount
of water which runs down the electrode into the bath is likely
to create dangerous explosions in the crust at the top of
the bath. Therefore, it has been found that although water
is effective to prevent wasteful loss of graphite electrodes
in the high temperature and corrosive atmosphere of an electric
arc furnace used to smelt aluminum oxides, it is very important
to control the flow of water so that it does not reach the
bath and create hazardous conditions.
2~22~2~
It is therefore the object of this invention to
provide means for directing a stream of water on an electrode
in such a way that the flow of water is well regulated and
controllable.
This objective is achieved by means of the present
invention which provides a water ring surrounding the electrode
in the region immediately beneath the electrode holder having
nozzles at spaced intervals around the ring directed onto
the adjacent surface of the electrode and having an inlet
whereby water may be conducted to the water ring and an outlet
whereby water flowing through the ring may be drawn off.
Ideally, the nozzles of the water ring proviae
a shaped spray designed to cover a wide sector of the periphery
of the electrode.
Preferably the source of water to the inlet may
be controlled by pressure or adjustable valves to effect
the flow in the water ring and the amount of water emitted
by the nozzles.
The invention may be best understood by a description
of one embodiment thereof with reference to the drawings
in which:
Figure 1 is a perspective view of an electric arc furnace
incorporating the present invention;
Figure 2 is a cross sectional view of an electric arc
electrode having a water ring of the present
invention;
Figure 3 is a detailed elevation view of the water ring
in Figure 2;
Figure 4 is a plan view of the water ring shown in Figures
1, 2 and 3;
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Figure 5 is an elevation view of the nozzle in Figure
3;
Figure 6 ls a plan view of the nozzle in Figure 3;
Figure 7 is a schematic view of the water supply system
associated with the water ring shown in Figure
1.
Figure 1 illustrates simplistically the typical
arrangement of an electric arc furnace in which a shell 2
contains a bath of molten material 4 which is being heated
by electrical energy arced to the bath from the electrode
6 which is held above the bath by the electrode holder 8
having a central aperture 10 through which the electrode
6 is placed and clamped. As the electrode becomes consumed
at the lower end adjacent to the bath, the electrode holder
is lowered to maintain the desired proximity to the bath.
However, periodically it is necessary to loosen the grip
on the electrode and slip the electrode downward or advance
it within the holder.
Also shown in Figure 1 is a water ring 12 which
is suspended beneath the electrode holder 8 and substantially
surrounds the circumference of the electrode 6.
Figure 2 is an enlarged cross sectional view of
the electrode 6 and the electrode holder 8 showing in greater
detail the water ring 12 which is supported by brackets 14
fastened to the underside of the holder at spaced intervals
around the electrode. Also shown in Figure 2 are nozzles
16 which extend downward and inward at about 45 degrees from
the horizontal and adapted to direct a spray 18 onto the
wall of the electrode 6.
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2~22~22
Figure 3 illustrates a sectional view of the water
ring 12 and the nozzle 16 supported by the bracket 14 fastened
to the underside of the electrode holder 8.
Figure 4 illustrates the water ring alone with
the brackets 14 attached at four intervals around the periphery.
Note that the water ring 12 has an inlet line 20 and an outlet
line 22 so that water may flow into the ring around the circular
course of the ring and out the outlet 22.
Figure 5 is one cross sectional view of a typical
nozzle 16 having a threaded male end 24 and an outlet 26,
a V notch 28 designed to create a spray 18 which is narrow
in the dimension parallel to the axis of the electrode.
Figure 6 is a cross sectional view at right angles
to that in Figure 5 and illustrates the same nozzle showing
the spray 18 with a wider angle in a direction perpendicular
to the axis of the electrode 6 so that the water spray from
a number of spaced nozzles will cover the entire circumference
of the electrode.
Figure 7 illustrates schematically the electrode
holder 8 having brackets 14 depending therefrom to support
the ring 12 with four nozzles 16 directed toward the electrode~
In Figure 7 the water supply to the water ring 12 is shown
schematically and comprises a reservoir tank 30 containing
a supply of relatively cool makeup water to the inlet line
32 which is fed by a pump 34 monitored by pressure valve
36 and adjusted by a valve 38. The water supplied under
pressure to the water ring 12 is then returned by the line
40 to the reservoir 30. The return line 40 may also be monitored
by a gauge 37 and a control valve 39 which may be either
manual or automatic depending on the degree of automation
for which it is designed.
2022~2~ 1
By means of the illustrated apparatus, the electrode
of an electric arc furnace may be protected from corrosion
by a spray of water which is directed onto the electrode
from the nozzles 16. Although four are shown, any number
may be selected but preferably should be numerous enough
to cover the entire circumference of the electrode with water.
As previously mentioned, it is important, especially
in some processes, to adequately control the amount of water
that is delivered to the electrode by spray so that adequate
protection is provided without delivering excess water which
may reach the bath and create hazardous conditions.
To this end, the pump 34 may deliver the water
to the water ring at whatever pressure is desired (which
can be monitored by the gauge 36 and controlled by the valve
38. The amount of pressure in the water ring 12 can then
be controlled by the back pressure and restriction adjusted
at the valve 39 so that the pressure in the ring 12 provides
a spray which is adequate but not excessive.
Although the water ring could be supplied with
an inlet line only and the spray regulated by means of the
pressure of the supply line, this configuration creates difficulty,
especially in high temperature operations because the excessive
temperature causes vaporization of the water in the water
line before it reaches the spray nozzles or the electrode.
This can result in a deficient water spray or even worse,
may result in an attempt to supply an adequate water spray
by increasing the pressure and the flow which may then result
in excessive water resulting in the hazardous conditions
mentioned above.
20'~2622
By means of the present inventlon and the arrangement
illustrated in Figures 4 and 7, the flow of water through
the water ring may be maintained which may be well in excess
of the amount of water required or dispensed through the
nozzles 16 and the surplus is taken out through the return
line 40 and returned to the make up reservoir 30. In this
way sufficient volume of cool water is maintained so that
vaporization does not take place in the water ring, even
under high temperature conditions. Thus premature vaporization
of the water is eliminated and a measured and controllable
flow of water from the nozzles can be maintained to ensure
coverage of the electrode without excessive water reaching
the molten bath.
Because of the large volume of flow through the
ring, the water supplied to the nozzles and therefor to the
electrodes, will be cooler than would otherwise be the case.
Although the foregoing description contains numerous
details of the apparatus thought to be preferred in the embodiment
illustrated, it will be realized that numerous modifications
and variations might be employed without departing from the
inventive concept herein.
