EP0085461A1 - Liquid-cooled side walls for electric-arc furnaces - Google Patents

Abstract

To increase the service life of the thermally stressed wall parts (27) of arc furnaces, cooling pipes (30, 31) are arranged in two layers in a refractory building material (35), which form the reinforcement for the refractory building material (35). The position of the cooling tubes (30) facing the interior of the vessel is made in one piece and is bent in a U-shape at the upper and lower ends and leads into the outer position of the cooling tubes (31). The ends of the outer layer of the cooling pipes (31) open into a liquid distribution channel (32) which is provided with an integrated bypass opening (s) (34). Due to the one-piece design of the cooling tubes (30) facing the interior of the vessel, through arcuate transitions to the outer cooling tube (31) and by avoiding weld seams and other material connections in the cooling tube (30), the cooling tube (30) is thermally homogeneously loaded or relieved, so that thermal stresses in the cooling system 30, 31, 32 are almost impossible and that the cooling system is largely decoupled from the effects of temperature changes

Description

The invention relates to an electric furnace, in particular an arc furnace, with a liquid cooling device for thermally highly stressed wall parts of the furnace vessel, with essentially vertically arranged liquid flow-through series-connected cooling tubes, a bypass opening being provided in the upper part of the vessel between adjacent cooling channels, which provides the cooling channels at least partially short-circuits.

Such an oven is the subject of CH patent application 3280 / 81-4 dated May 20, 1981. In particular, solutions are shown how the gas bubbles resulting from local overheating, which can lead to impairment of the cooling effect or even destruction of the cooling device, are removed from the cooling system in a simple manner by the vertically arranged cooling pipes connected in series in the upper part Bypass openings are arranged.

From the publication "Korf-Fuchs-Systemtechnik; steel production, water cooling systems for electric arc furnaces", undated, cooling boxes are known which can be installed individually or as complete cooling systems for forming vessel walls in the electric arc furnace. Constructional measures are intended to prevent cooling water from entering the furnace chamber in the event of breakthroughs in the cooling boxes. In relation to the thickness of a conventional uncooled vessel wall made of refractory material from an electric arc furnace, a relatively thin protective layer made of refractory material is applied to the walls of the cooling boxes facing the inside of the furnace, which protects the cooling boxes against heat radiation and prevents excessive heat extraction from the melting chamber. During the melting process, this protective layer is additionally reinforced by slag splashes which are thrown against the walls by the influence of the electric arc and stick there. The adhesion of the refractory material and the slag splashes is increased by cam-like projections which are attached to the walls of the cooling boxes.

A similar water cooling of the vessel walls of arc furnaces is known from the publication "Lectromelt Corporation; water cooled panels" from April 1980.

When using cooling boxes to cool the vessel walls of electric arc furnaces, fireproof material can be saved on the one hand, but on the other hand there is a risk with the relatively thin protective layers on the walls of the cooling boxes that they will come loose in certain places, for example due to mechanical effects during the charging process Iron or slag splashing during the melting process or due to thermal stresses within the layers due to inhomogeneous heat radiation, uneven cooling or when the vessel walls cool down. The heat transfer and thus the heat loss is particularly high at the exposed locations where the metal surface of the cooling box is directly illuminated by the arcs.

In addition, the non-protected areas become thermal more heavily loaded than the rest of the protected cooler wall, and during, in steel mills and foundries, continuous melting in two or three shifts, hot spots can form without being noticed by the furnace operator. In the worst cases, if they remain uncovered and the cooling conditions are inadequate, these spots can overheat in such a way that they can lead to breakthroughs and the associated serious sequelae. Detection systems for cooling system monitoring are complex and expensive. In the event of an error message, the furnace would then have to be taken out of operation in order to repair the damaged areas.

In addition, the cooling walls of the cooling boxes facing the inside of the oven, even though they are covered with a protective layer and were stress-relieved before assembly, are constantly exposed to expansion and contraction forces due to the strong temperature fluctuations. These forces have a particular effect on the corners and edges of the cooling surfaces and thermal stresses arise in the weld seams connecting the cooling surfaces, in which cracks can form under certain circumstances, which then lead to water breakthrough.

Starting from the prior art described above, the invention has for its object to provide a cooling system, in particular for arc furnaces, which is simple in construction and economical to manufacture, with which a long service life of the vessel walls can be achieved and the construction of which offers security for this, that damage can almost be excluded.

To solve this issue, it is provided according to the invention that the cooling tubes are designed in two layers, the cooling tubes of the layer facing the interior of the furnace in one piece and on the lower and upper ends are bent in a U-shape, at which ends the cooling tubes of the outer layer connect and open into a liquid distribution chamber with integrated bypass openings, at least the cooling tubes, the layer facing the interior of the furnace, being embedded in a refractory building material and its reinforcement form.

• - Durch die einstückige Ausbildungsform und die abgerundeten Enden der Kühlrohre wird die Wärme gleichmässig von den Kühlrohren aufgenommen bzw. abgegeben. Da Kanten und Ecken sowie Materialverbindungen in dem dem Ofeninneren zugewandten Teil der Kühlrohre vermieden werden, können sich keine thermischen Spannungen in diesem Teil ausbilden und das Kühlsystem ist weitgehend von den Wirkungen einer Temperaturwechselbeanspruchung entkoppelt.
• - Durch die Kühlung eines qualitativ hochwertigen feuerfesten Baustoffes wird dessen Verschleiss reduziert, woraus sich hohe Standzeiten der Gefässwände ergeben.
• - Die in der Flüssigkeitsverteilkammer integrierten Bypassöffnungen ermöglichen, dass sich die in den gruppenweise in Serie geschalteten Kühlrohren erhitzte Kühlflüssigkeit mit kalter Kühlflüssigkeit mischt, und dadurch Ueberhitzungen vermieden werden.

This embodiment has the following advantages:

• - Due to the one-piece design and the rounded ends of the cooling tubes, the heat is evenly absorbed or released by the cooling tubes. Since edges and corners as well as material connections in the part of the cooling pipes facing the furnace interior are avoided, no thermal stresses can form in this part and the cooling system is largely decoupled from the effects of temperature changes.
• - By cooling a high-quality, refractory building material, its wear is reduced, resulting in a long service life for the vessel walls.
• - The bypass openings integrated in the liquid distribution chamber enable the cooling liquid heated in the cooling pipes connected in series in groups to mix with cold cooling liquid, thereby avoiding overheating.

According to claim 2, the distance between the mutually adjacent cooling tubes of the inner layer is approximately twice as large as their outer diameter. In this way, while ensuring optimal cooling of the refractory building material and with sufficient strength of the supporting structure for the refractory building material, the weight of the composite of cooling pipes and refractory building material can be kept low.

According to claim 3, the cooling pipes together with the refractory building material can be used as a prefabricated segment-like wall element in the furnace vessel. This results in a rational installation and removal of the segment-like wall elements, and the decommissioning of the ovens can be limited to a minimum in time.

According to claim 4, each wall element has its own cooling circuit. The advantage according to claim 4 can be seen in the fact that the cooling can be designed clearly and intensively for each wall element.

According to claim 5, the bypass opening (s) in the distribution channel are dimensioned such that, taking into account the hydraulic resistance of the assigned cooling channels, a predeterminable amount of cooling liquid flows through the bypass opening (s) that is smaller than that which flows through the assigned cooling channels.

According to claim 6, the bypass opening (s) in the distribution channel are dimensioned such that, taking into account the hydraulic resistance of the assigned cooling channels, a predeterminable amount of cooling liquid flows through the bypass opening (s) which is the same size or larger than that which flows through the assigned cooling channels.

The advantage according to claims 5 and 6 is that the flow rate, flow rate etc. of the cooling liquid which is introduced into the cooling channels and the cooling channels themselves can be dimensioned such that when part of the cooling liquid evaporates in the cooling channels, the steam immediately is removed from the cooling system through the assigned bypass opening (s) of each assigned cooling channel pair in the coolant distribution chamber without causing a mutual, for the cooling effect comes from adverse influence between coolant and steam. In this way, in contrast to classic liquid cooling, a combined liquid-steam cooling is obtained, the heat required for evaporation being extracted from the components to be cooled and thus being used for cooling. The flow rate of the cooling liquid in the cooling pipes is dimensioned in such a way that no vapor bubbles can become lodged in the upper pipe bends of the cooling pipes, but rather that they are carried away with the cooling liquid and transported into the distribution channel.

The invention is explained in more detail below with reference to exemplary embodiments shown in the drawing:

• Fig. 1 eine schematische Darstellung der Vorderansicht einer beispielsweisen Ausführungsform eines Lichtbogenofens ;
• Fig. 2 eine schematische Draufsicht auf den Ofen gemäss Fig. 1, jedoch mit entferntem Ofendeckel;
• Fig. 3 einen Schnitt durch die Seitenansicht des Ofens gemäss Fig. 2;
• Fig. 4 einen vergrösserten teilweisen vertikalen Schnitt durch eine Kühlrohranordnung samt feuerfestem Baustoff gemäss Fig. 3;
• Fig. 5 einen vertikalen Schnitt durch eine Kühlanordnung samt feuerfestem Baustoff gemäss Fig. 4;
• Fig. 6 einen horizontalen Schnitt durch eine Kühlanordnung mit feuerfestem Baustoff gemäss Fig. 5.

The drawing shows:

• Figure 1 is a schematic representation of the front view of an exemplary embodiment of an arc furnace.
• FIG. 2 shows a schematic plan view of the furnace according to FIG. 1, but with the furnace cover removed;
• 3 shows a section through the side view of the furnace according to FIG. 2;
• FIG. 4 shows an enlarged partial vertical section through a cooling tube arrangement including the refractory building material according to FIG. 3;
• 5 shows a vertical section through a cooling arrangement including the refractory building material according to FIG. 4;
• 6 shows a horizontal section through a cooling arrangement with refractory building material according to FIG. 5.

Fig. 1 shows a schematic representation of the front view of an exemplary embodiment of an arc furnace.

The arc furnace 1 with furnace cover 5 is mounted in an opening on the platform 6, which is supported on two roller cradles 7, which in turn are supported on the weighing beams 8, which are firmly anchored to the foundation 9. The pouring spout 2 can also be seen in FIG. 1. A movable rotary console 10 is arranged on the platform 6, to which the cover lifting and swiveling device 11 is fastened. The cover lifting and swiveling device 11 consists of a support arm 13 and a support arm column 12.

The platform 6 also carries three electrode positioning columns 13, of which only one is visible in FIG. 1. The electrode adjusting columns 14 are hydraulically connected to be movable individually in the vertical direction with electrode adjusting cylinders 15. The electrode support arms 16 are fastened to the electrode adjusting columns 14 and the electrodes 18 are held in electrode holders 17 at their outer ends.

Of the total of three electrode support arms 16, only one is again completely visible, and only two of the electrodes 18 can be seen, the third being covered. On the furnace cover 5, the cover ring 4 of which rests on the cover support ring 3 of the furnace 1, the flue gas outlet 19 with flange 20 is arranged. The attachment of the socket 19 is not shown in FIG. 1 and its guide arrangement within the support arm 13 of the cover lifting and pivoting device 11 is only indicated by the guide rail 21. On the cover ring 4 of the furnace cover 5, support eyes 22 are attached, in which in the exemplary embodiment from FIG. 1 Support ropes 23 are attached, of which only two are visible from a total of four. The support cables 23 are guided over rollers 24 which are mounted in roller carriers 25 on the support arm 13. The support cables 23 are connected to the hydraulic cylinder 26, which can lift or lower the furnace cover 5 from the furnace boiler 1.

The reference numbers in the following drawings refer to the same parts as in FIG. 1.

FIG. 2 shows a top view of the furnace according to FIG. 1, but with the furnace cover 5 removed. The prefabricated wall elements 27 can be seen, which are arranged inside the furnace vessel casing 1. In the exemplary embodiment according to FIG. 2, six wall elements 27 are attached. However, their number is different and depends on the size of the furnace. It has proven to be advantageous if the number of wall elements 27 increases with increasing furnace size. The inside of the furnace vessel 28 shows the bottom 28 of the furnace and the slag door 29 opposite the cast spout 2.

FIG. 3 shows a section through the side view of the furnace according to FIG. 2. In the cut wall elements 27, the cooling system 30, 31, 32 can be seen, which consists of the cooling tube layer 30 facing the interior of the vessel, the outer cooling tube layer 31 and the coolant distribution channel 32. The connection lines required for the cooling system 30, 31, 32 outside the furnace vessel jacket 1 are not shown in Figure 3 for reasons of a better overview.

FIG. 1 shows an enlarged partial vertical section through a cooling tube arrangement 30, 31, 32 together with a refractory building material 35 according to FIG. 3.

4 again shows the cooling tube layer 30 facing the interior of the vessel with the upper and lower U-shaped arches, at the ends of which the outer cooling tube layer 31 is integrally connected. The ends of the cooling ducts 31 'of the outer cooling tube layer 31 open, on the one hand, with the cooling duct inlet opening 37 and, on the other hand, with the cooling duct outlet opening 38 into the coolant distribution duct 32. The reference number 36 denotes a fastening lug with which the wall element is fastened in the furnace vessel jacket 1, which is made from the Cooling system 30, 31, 32 and the refractory building material 35 there.

4 and likewise in FIG. 5, the partition walls 33 are shown, between which and the bypass opening (s) 34 are located and the upper end plate 32 'of the liquid distribution channel 32.

The reference number 40 in FIG. 5 denotes the cooling liquid inlet opening and the arrows according to reference number 39 indicate the direction of flow of the cooling liquid. In the exemplary embodiment according to FIG. 5, the cooling liquid first flows downward through the outer right cooling tube 30, which is assigned to the interior of the vessel, is deflected by the lower bend and finally flows upward through the cooling channel 31 ′ of the outer cooling tube 31 and enters through the coolant inlet opening 37 into the coolant distribution channel 32. In the distribution channel 32, the coolant flow is divided into two partial flows according to the arrows with the reference number 39. A first partial flow leaves the distribution channel 32 again through the cooling liquid outlet opening 38, first flows upward in the direction of the arrow, is deflected by the upper bend, flows downward through the cooling tube 30, is deflected by the lower bend and flows through the cooling channel 31 ′ of the cooling tube 31 again upwards and passes through the coolant inlet opening 37 into the distribution channel 32. Since the cooling tube 30 is assigned to the interior of the vessel, the cooling liquid of the first cooling stream has heated up and strikes in the distribution channel 32 with the second part of the cooling stream, which was deflected horizontally and has flowed through the bypass opening 34 in the area between the two shown in FIG. 5 Partitions 33 together. Since the second part of the coolant flow has a comparatively higher temperature level than the first part which has flowed through the cooling pipe 30, the first part of the coolant flow is cooled by the second part. This process of cooling the part of the cooling liquid which has passed through the cooling pipes 30 which face the interior of the vessel and which has been warmed up by the part of the cooling liquid which has remained in the distribution channel 32 and has passed through the bypass opening (s) 34 is continuously repeated in FIG the cooling pipes 30, 31 of each wall element 27 of the furnace vessel connected in groups in series.

If steam bubbles should possibly form in the cooling pipe 30, they would accumulate in the upper pipe bend and impair or interrupt the cooling circuit. In order to prevent this, however, the flow rate of the cooling liquid is selected such that any vapor bubbles that form in the upper pipe bend are conveyed through the cooling liquid into the distribution chamber.

5 shows only one exemplary embodiment of the inventive idea. A further development of the inventive idea would be to arrange the distribution channel obliquely with respect to the horizontal, specifically in the direction of flow of the cooling liquid with an opening angle. In this way, vapor bubbles could be removed from the distribution channel 32 more quickly. The upper and lower pipe bends of the cooling pipes 30, 31 are necessary for the sake of a homogeneous heat load and cannot be dispensed with.

FIG. 6 shows a horizontal section through a cooling arrangement 30, 31, 32 together with the refractory building material 35 according to FIG. 5.

6 shows the helical design or the horizontal lateral displacement of the cooling pipes 30, 31 with the cooling channels 30 ', 31.

6, only the lower lateral offset, indicated by the lower rotor arch, can be seen. The upper lateral offset is not shown in FIG. 6, but in FIG. 5.

4 and 6, the double layers of the cooling tubes 30, 31 can be seen clearly and also the decoupling of the cooling tubes 30, which are subject to high levels of heat, from, for example, welded connections. In addition, any edges and corners in the cooling tubes 30 and at the transitions to the cooling tubes 31 have been omitted in order to thermally relieve the cooling system 30, 31, 32.

Claims (6)

1. Electric furnace, in particular an arc furnace, with a liquid cooling device for thermally highly stressed wall parts (27) of the furnace vessel, with essentially vertically arranged cooling tubes (30, 31) connected in series with liquid flowing through them in groups, the upper part of the vessel between adjacent cooling channels (30 , 31) bypass opening (s) (34) is provided, which at least partially short-circuits the cooling channels (30, 31), characterized in that the cooling tubes (30, 31) are designed in two layers, the cooling tubes (30), which the interior of the vessel facing position in one piece and bent in a U-shape at the lower and upper ends, to which ends the cooling pipes (31) of the outer layer connect and open into a liquid distribution chamber (32) with an integrated bypass opening (s) (34), at least the cooling pipes (30), the layer facing the inside of the furnace, are embedded in a refractory building material (35) and form its reinforcement. 2. Electric furnace according to claim 1, characterized in that the distance between the mutually adjacent cooling tubes (30) of the inner layer is approximately twice as large as their outer diameter. 3. Electric furnace according to claim 1 and 2, characterized in that the cooling pipes (30, 31) together with the refractory building material (35) can be used as a prefabricated segment-like wall element (22) in the furnace vessel. 4. Electric furnace according to claim 3, characterized in that each wall element (27) has its own cooling circuit. 5. Electric furnace according to one of claims 1 to 4, characterized in that the bypass opening (s) (34) in the distribution channel (32) are dimensioned such that, taking into account the hydraulic resistance of the assigned cooling channels (30, 31), a predetermined amount of cooling liquid flows through the bypass opening (s) (34), which is smaller than that which flows through the associated cooling pipes (30, 31). 6. Electric furnace according to one of claims 1 to 4, characterized in that the bypass opening (s) (34) in the distribution channel (32) are dimensioned such that, taking into account the hydraulic resistance of the assigned cooling channels (30, 31), a predetermined amount of cooling liquid flows through the bypass opening (s) (34), which is the same size or larger than that which flows through the associated cooling pipes (30, 31).

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