Industrial electric heating furnaces – Arc furnace device – Furnace body detail
Reexamination Certificate
1997-12-10
2001-06-12
Walberg, Teresa (Department: 3742)
Industrial electric heating furnaces
Arc furnace device
Furnace body detail
C373S074000, C164S459000
Reexamination Certificate
active
06246712
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to an arc furnace and more particularly to electrical instabilities which arise in an arc furnace during its operation.
The torn “stray arcing” has been used to describe this type of instability for some evidence seems to indicate that stray arcing may take place inside the furnace e.g. between the electrode and the furnace roof, or between other surfaces inside the furnace.
The present invention has application to DC and AC electric arc furnaces.
During the operation of a DC-arc furnace slag is displaced by the action of the arc from the molten slag layer onto the side walls and roof of the furnace. Hot dust particles and condensing vapours also adhere to the side walls and the roof. The slags are generally non-conductive, or poor conductors, in a cold state.
At elevated temperatures the insulating properties of slag, and in particular of slags which contain high percentages of certain oxides such as titanium dioxide, deteriorate. The resistivity of these slags can drop to such an extent that the material becomes electrically conductive. Consequently, inside the furnace, a conducting layer exists on the roof and side walls thereby imparting to the roof and side walls the same electrical potential as the top of the molten bath inside the furnace. The conducting layer thus promotes arcing for it provides a current path between cathode and anode.
The conditions inside the furnace, which give rise to stray arcing, are variable. For example the main arc is not perfectly stable, frothing and sparking take place, the slag is produced over a period of time, the level of the molten bath changes, and fluctuations exist in the rate, and the composition, of material feed to the furnace. Consequently measures which are taken to control stray arcing should, preferably, be adaptable in response to changes inside the furnace whether of the aforementioned kind or due to other factors such as temperature and pressure fluctuations, and in response to variations in the power supply to the furnace i.e. in the voltage applied to, and the current drawn by, the furnace.
The arcing can damage components of the roof, shell and hearth of the furnace and can lead to substantial reductions in furnace productivity. In water cooled furnaces the rupturing of water conduits by arcing can lead to water entering the furnace which can result in a powerful and damaging explosion.
The invention is concerned with improving the economic performance of an electric arc furnace by reducing the likelihood of arc damage to the furnace.
SUMMARY OF THE INVENTION
The present invention provides an arc furnace which includes a shell with a hearth, a roof for the shell, the roof including a plurality of segments which are substantially electrically isolated from each other and from the shell, an electrode, and a refractory section on the roof, wherein the refractory section is at least partly electrically conductive.
The refractory section may be made from or include refractory material which, itself, may be electrically conductive. Alternatively or additionally at least one electrically conductive member, which may be of any suitable shape and size, is located at least partly in the refractory section.
In one form of the present invention the electrically conductive member is exposed to the interior of the furnace.
In a different form of the present invention the electrically conductive member is not exposed to the interior of the furnace i.e. it is shielded by the refractory section.
In the last-mentioned embodiment a direct conductive connection between the furnace interior and the electrically conductive member can thus take place only when the refractory section has been eroded to expose, at least partly, the electrically conductive member.
A plurality of the electrically conductive members may be used, located to different extents, according to requirement, in zones of the refractory section. The exposure of an electrically conductive member, due to erosion of the refractory section material, may therefore provide a means of assessing the deterioration or wear of the refractory section and consequently of indicating when damage to sensitive components, such as water cooling circuits in the refractory section, is likely to occur. This approach may make it possible to develop a diagnostic system which gives an early warning of the degradation of the mechanical deterioration of the system.
The electrically conductive member may be of any suitable electrically conductive material and preferably is copper.
The electrically conductive member may be made in any suitable shape or size and may be pin-shaped, in the nature of a circular cylinder. A suitable length is of the order of 550 mm with a diameter of approximately 120 mm. Those dimensions are given only by way of example, and are non-limiting, for other dimensions which take electrical and thermal conductivity into account will also function satisfactorily.
A plurality of electrically conductive members may be used. Those members may be arranged around the electrode in any suitable pattern, for example at spaced intervals on the circumference of one or more circles which are centered on the electrode.
The electrically conductive members are positioned so that they do not contact the electrode nor the roof and are electrically isolated from the electrode and roof.
At least some of the members may be wholly embedded in at least some of the roof segments.
Alternatively or additionally at least some of the members may be positioned so that they are partly embedded in at least some of the roof segments and are partly exposed to the slag which is formed during the operation of the furnace and which adheres to the roof segments.
The electrically conductive members may be electrically connected to each other, or to one or more controlled electrical potentials, in any appropriate and desired way or configuration.
The roof may be water cooled and may be formed from a number of water cooled roof segments or panels, although the present invention affords protection to other roof types e.g. of the type which includes spray cooled roof segments or panels.
The electrically conductive members may be cooled using any suitable fluid e.g. water or an air/water mixture and a fluid cooling circuit to the electrically conductive members may be positioned away from the refractory section so that, if the refractory section is damaged by arcing, the likelihood of damage to the cooling circuit of the electrically conductive members is reduced. The cooling fluid or technique should be such that the amount of water which enters the furnace, when the cooling circuit is damaged, is minimized.
Depending on the furnace type the voltage gradient may be established using a fixed AC or DC voltage, and hence may be a static or steady state gradient generated, for example, by means of a resistive network.
The gradient may alternatively be variable or dynamic and may be established by switching devices which are responsive to operating conditions in the furnace. Again, depending on the furnace type, the switching devices operate on AC or DC voltages.
The voltage difference, e.g. between the refractory section and an adjacent component of the furnace, established by the voltage gradient may be between 5% and 50% of a supply voltage which is applied to the furnace. In one example the voltage difference is of the order from 50 volts to 80 volts.
The connection of the electrically conductive members to earth or any other controlled electrical potential enables any current attracted to the electrically conductive members during arcing to be directed to earth or any other controlled electrical potential. By varying the controlled electrical potential, on the other hand, conditions which give rise to arcing may be controlled and the incidence of arcing may be limited.
The electrically conductive members may be connected to earth or any other controlled electrical potential using any appropriate device or devices. It is also possible to connect diff
Faveere Dirk Renaat Gabriel
Ferreira Jan Abraham
Johnston Andrew Bryan
Roos Edwin Harm
Wewege Anthony Wayne
Jones Tullar & Cooper P.C.
Van Quang
Walberg Teresa
LandOfFree
Arc furnace protection does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Arc furnace protection, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Arc furnace protection will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2491856