The invention relates to a multilayer cooling panel for an industrial furnace such as an electric arc furnace and the furnace itself. Prior art panels and panels according to the invention will be described hereinafter with respect to such an electric arc furnace (EAF) but without limiting the scope of the invention to this furnace type.
The overall design of such an EAF typically comprises:
The upper shell acts as an outer sidewall of the furnace.
Numerous proposals have been made with respect to the construction of this upper furnace shell which on the one hand must protect the furnace surrounding area against metallurgical spill and on the other hand provide best possible insulation properties in view of the total energy consumption of the furnace.
One common design is characterized by a row of lateral panels which are arranged substantially on top of the upper edge of the lower shell (the hearth wall).
According to EP 0790473 B1 these panels provide a cooling device, characterized by an outer layer and at least one inner layer of cooling tubes, wherein said layers are separated by an interspace. This interspace allows slag to enter during the melting process and to be retained within said interspace.
For this reason the outer layer is designed with the cooling tubes adjacent to each other, while the inner layer of the panel includes the cooling tubes separated from each other to allow the slag to enter via spaces between said cooling tubes.
The aim of this design is to use the insulation properties of the solidified slag but said slag only has a low melting temperature and its composition is more or less aggressive vis-a-vis the metallic cooling tubes.
In this respect it is known from practice to fill-up the said interspace with a monolithic refractory material at least partially. The refractory filling avoids a direct contact between the slag and the cooling pipes over a certain period of time until the refractory monolithic material has been worn to such extent that it cannot fulfil this task anymore.
A problem in using a gunned basic refractory material adhering to the cooling tubes is the different thermal expansion coefficient of such MgO-based gunning material and the metallic cooling pipes, which leads to spalling. The replacement of the basic gunning material by a non-basic refractory material such as alumina (Al2O3) is not suitable as it is not stable against basic process slags in the furnace.
Therefore it is an object of the invention to provide a cooling device of improved properties over said prior art designs and in particular to provide a cooling device providing an energy-saving potential for the industrial furnace.
The invention is based on the following findings:
They may be designed as well as larger or relatively small units, thereby reducing the risk of crack formation and can be made of any refractory mix (batch composition), as they are not applied as a lining material onto any other construction element but simply clamped, hanged, cramped or fixed by any other means to corresponding construction parts. A detachable/suspended fixture is preferred.
These refractory plates, as an inner layer of corresponding panel structure, protect the outer panel layer, namely the cooling structure, very efficiently. The plates provide an efficient screening wall against thermal radiation, even high energy radiation deriving from unshielded electric arcs or even arcing. They further allow a space of arbitrary size between refractory plates and cooling tubes, serving as an insulation space.
The refractory plates further fulfil the function to absorb any slag splashing against said plates and insofar again protect the cooling device from any metallurgical attack.
By corresponding fixture means—an example is shown in the attached drawing—even cracks in one or more plates do not disintegrate the construction. In the worst case the plates can easily be replaced.
In its most general embodiment the invention relates to a multilayer cooling panel for an industrial furnace, comprising:
Depending on the shape of the refractory plates and the cooling pipes the outer side of said plates, facing the cooling pipes, may follow the shape of the cooling pipes although it is preferred to either provide a gap between cooling pipes and refractory plates and/or to use refractory plates with a more or less planar outer surface which design immediately leads to a corresponding space between the outer surface of the refractory plates and the corresponding surface sections of the cooling pipes (under the proviso of pipes of circular cross section).
The cooling pipe(s) of the first layer may be arranged in a meandering fashion to provide a substantially continuous cooling layer. In other words: There is no or only little space between adjacent sections of the cooling pipes.
This design will be preferred in case of lack of any further outer wall section as part of the upper furnace shell and its panels respectively.
In another embodiment the upper shell is further characterized by separate outer closed wall to which the cooling panels may be mounted.
In a third embodiment adjacent pipe sections of the panels are bridged by fins to provide a more or less closed layer.
Although it has advantages to use relatively small refractory plates (base area less than 1 m2, <0.5 m2′<0.3 m2 or even <0.1 m2) the invention is applicable as well with larger refractory plates or even with one refractory plate per panel.
Depending on the number and size of the refractory plates it is possible to provide a substantially continuous layer design for said second layer, similar to a tiled wall, wherein joints between adjacent plates may be open.
The space between refractory ceramic plates (inner layer) and cooling pipes (outer layer) may remain empty of may be filled by a suitable material like a high temperature resistant fibre material (ceramic fibres, mineral fibres), wherein high temperature refers to temperatures above 800° C.
Typically, the first and second layer are arranged at a distance to each other, as mentioned above but the invention includes an embodiment wherein the first and the second layer contact each other at least partially.
This includes an embodiment wherein the at least one refractory plate is fixed at the first layer, preferably in a detachable manner. This can be achieved by hooks, anchors or the like, protruding towards the refractory plates from the inner surface of the cooling tubes onto which the refractory plates are hung, onto which the refractory plates are placed or between which the refractory plates arranged, for example by clamping.
The arrangement and fixation of the refractory plates may also be achieved in an embodiment comprising a third layer, arranged at a distance to the first layer and housing the second layer between said first and third layer.
The third layer may cover only part of the second layer, for example <10%, <20% or <30% of the surface area of the second layer.
This can be achieved by further cooling pipes (tubes) or corresponding rails which are fixedly secured or functionally attached to the first layer. At least one possible embodiment is shown in the drawing hereinafter.
This design allows to clamp the refractory plates of the second layer between said first and third layer with further advantages in mounting and replacing said plates in case of need.
In order to avoid any stresses between adjacent refractory plates the invention includes an arrangement with a little gap between adjacent refractory plates.
In view of their high melting temperature and resistance against basic process slags basic refractory materials have advantages over non-basic compositions.
A refractory material based on magnesia (MgO) or doloma (MgO CaO) is recommended.
In case of low or no carbon content within these refractory batches low thermal conductivities may be achieved as well as a good stability against oxidation, with the advantage of high energy efficiency and high metallurgical stability.
The refractory plates may have a flat or profiled surface structure. A profile structure on its surface opposite to the first layer (meaning: towards the furnace chamber) allows the slag to better adhere onto the refractory plates, thus providing a further insulation layer.
The profiled surface structure may be achieved by at least one of the following features: protrusion, depression, tongue, groove, grate structure, bolt, anchor.
The overall operation mode of the furnace, especially the electric arc furnace, is by no means influenced by the lifetime of the new multilayer cooling panels as these plates may be replaced at any time without demounting the entire upper shell, partially (only one or more plates) or completely. Larger repair actions as in prior art constructions may be avoided. The first layer (water cooled tubes) remain intact/functional when the second layer (refractory plates) is damaged and must be replaced.
The refractory plates, typically of rectangular or hexagonal/polygonal shape, are easy and cheap to produce.
It is even possible to provide the refractory plates with an inherent carbon gradient, namely a carbon free side (the cold side with a low thermal conductivity) and a carbon containing side (the hot side) of increased slag resistance.
Typically dimensions of the refractory plates may be (L=length, W=width, T=thickness)
L: 200-1.000 mm, in particular 250-600 mm.
W: 200-1.000 mm, in particular 250-600 mm.
T: 5-100 mm, in particular 20-70 mm.
The invention further comprises an EAF including at least one of said cooling panels along its upper shell. In this respect it is to be understood that only part of the upper shell may be constructed with the panels described.
Further features of the invention may be derived from the sub-claims and the other application documents, including the following schematic drawing and its description.
In the drawing the following is shown:
The cooling pipe 12 is designed in a meandering fashion as shown in the left part of
As best seen from
In order to arrange said plates 16 in the desired orientation the free leg of lower rail 18.2 is shorter than that of the upper rail 18.1.
The refractory plates 16 provide a second, inner layer 14 of the panel in its mounted state, which is shown in connection with a different embodiment in
The embodiment according to
The second layer 14 is made of smaller refractory plates 16.
The panel of
The said cooling pipe sections 26.1, 26.2 are arranged at a distance to said first layer 10, thereby allowing the refractory plates 16 to be arranged within a space 22 between first layer 10 and second layer 24.
The embodiment of
The embodiment of
H represents the upper end of the furnace hearth, made of refractory bricks, followed upwardly by the so-called upper shell of the furnace, comprising panels 10 according to the invention.
For a better understanding only one of these panels (in the middle of
Connections to the cooling medium, especially water, are not shown.
On the very left of
According to
Pipe sections 26.1, 26.2 may be seen, acting as clamping means for the refractory plates 16.
Any slag will either hit the refractory plates 16 or the cooling pipe sections 26.1, 26.2 instead of the cooling pipe 12 of the first layer 10 and thus increase the overall lifetime of said panel.
The refractory plates 16 are made of an MgO-based ceramic material in accordance with the general description above. This is true as well with respect to its profiled surface.
Number | Date | Country | Kind |
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13174259.5 | Jun 2013 | EP | regional |
Filing Document | Filing Date | Country | Kind |
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PCT/EP2014/057906 | 4/17/2014 | WO | 00 |