The present invention relates to sealing devices for an industrial furnace. More precisely, the invention relates to sealing devices for sealingly joining together two furnace spaces, which are rotatable in relation to each other, in an industrial furnace.

Today, industrial furnaces are used for heating various mate- rials, such as different metals. In many cases, rotatable furnace spaces are used, in order to achieve good thermal homogeneity, mixing of the heated load, etc. Such furnaces may be of different types, of which one is a so-called rotary kiln. Examples include cement kilns; lime kilns; rotary kilns for aluminum melting; rotary kilns for pyrolysis of coal, coal residual products, petroleum residues, waste and bio mass; and rotary kilns for drying of bad-smelling material which may require sealing for environmental reasons (sludges from biological purification and the like) . Such furnaces comprise at least one part which defines a rotatable furnace space. Therefore, the problem arises of how such a rotatable part can be sealed to an adjacent part which is not rotatable, or which is freely rotatable in relation to the first rotatable part, and/or how a rotatable door for loading or unloading can be sealed.

It has proven difficult to cost-efficiently achieve a satisfactory seal between two such furnace parts which are rotatable in relation to each other. Good sealing is desirable in order to avoid thermal losses, leakage of air into and flue gases, smell, etc., out from the furnace. Because of the elevated temperatures and of the potentially chemically aggressive gases in the industrial furnace, it is also diffi- cult to find sealing materials with sufficiently long useful lives in the inhospitable environment in and in connection to an industrial furnace. This is so already from as low temperatures as 300°C - 500 °C, but temperatures of up to 1500°C and in certain cases also 2000°C can occur.

Moreover, air leaking in can in certain cases oxidize the treated material, and thereby result in deteriorated quality and efficiency. This is for example the case during aluminum melting, with formation of dross as a consequence.

A known type of rotatable seal is a so-called labyrinth seal. A disadvantage with such a seal is that it is relatively complex and therefore expensive. Moreover, thermal expansion is a problem. As the temperature in a furnace shifts, so does both its length and its width or diameter. The body length of a 50 meter long furnace can, for example, vary with up to 10 cm depending on the temperature. It is difficult to design a seal which is adequate across this whole interval of lengths and diameters of the sealed parts.

For linear geometries, it has in Swedish patent application 0700628-1 been proposed to use water-filled tubes in order to seal a vertically displaceable door, through which tubes an edge of the door runs. Such design solves the problem with reliable and cost-efficient sealing, but not for circular geometries in which one furnace part is rotatable in relation to another. Also, the problem remains of achieving a cost- efficient solution which can function in a satisfactory man- ner also during thermal expansion.

The present invention solves the above problems. Thus, the present invention relates to a sealing device for an industrial furnace comprising a first furnace part, comprising a first circular connection part, and a second furnace part, comprising a second circular connection part, which circular connection parts are arranged to engage with and sealingly connect to each other so that the furnace parts are rotatably and sealingly arranged in relation to each other at the engagement between the connection parts, and is characterised in that the first circular connection part comprises a circular edge which is arranged to run within and along a tube, which tube is provided with an elongated slit, and extends along the second circular connection part and is connected to the second furnace part, so that the circular edge is freely rotatable in the tube, in that the tube is arranged so that it springs back towards a position in which the slit is closed and arranged to surround the circular edge along essentially the whole perimeter length of the edge when the furnace parts are sealingly connected to each other, and in that a liquid coolant is arranged to in this state flow through the tube and essentially fill the whole space which is defined by the combination of the interior surfaces of the tubes and the outer surfaces of the circular edge.

In the following, the invention will be explained in closer detail, partly in connection with embodiments of the invention and with reference to the enclosed drawings, where:

Figure 1 is a simplified perspective view of a rotating furnace with a sealing device according to the present inven- tion;

Figure 2 is a detail of a simplified section view of a preferred sealing device according to the present invention; Figure 3A is a detail of a simplified detail view in perspective of a first preferred supply device; and

Figure 3B is a detail of a simplified detail view in perspective of a second preferred supply device.

All figures share the same reference numbers for corresponding parts. The proportions between various parts are in some cases exaggerated in order to improve clarity.

Figure 1 illustrates on a principal level a rotating furnace 1 comprising a first furnace part 2, a second furnace part 3 as well a third furnace part 4. In the exemplifying furnace 1 as shown in figure 1, either the part 2 or the part 3, or both of these parts, may be rotatable in relation to the third part 4, which is fixedly arranged in relation to the installation location. Thereby, requirements for tight- fitting, rotatable connections between firstly the first 2 and the second 3 part, secondly between the second 3 and the third part 4, and thirdly between the first part 2 and any rotatable loading door (not shown) , arranged at the end 2a of the first part 2 facing away from the second part 3, arise. It is realized that the exemplifying furnace configuration shown in the figures has been selected in order to illustrate various types of rotatable connections where the present invention is applicable, and that also other types of geometric configurations may occur in which a rotatable connection in an industrial furnace needs sealing.

Furthermore, figure 1 shows a rotatable sealing device 100 according to the present invention, arranged to sealingly connect the first furnace part 2 to the second furnace part 3. The first part is arranged to be telescopically inserted into the second part 3, so that heated material can travel downwards in the direction of gravity from the loading opening of the first part 2 at its end 2a, via the first part 2 and on into the second part 3, while rotating. Figure 2 shows the sealing device 100 in cross-section, together with respective end parts of the first 2 and second 3 furnace parts.

The first part 2 comprises a circular connection part 110, suitably in the form of a flange which in cross-section is L- shaped and which extends outwards from the outer surface of the first part 2. The connection part 110 comprises, according to the preferred embodiment shown in figure 2, a sheet 111a extending outwards perpendicularly from the outer surface of the first part 2 and running peripherically around this surface, as well as a circular edge 111b, extending outwards from the sheet 111a at an angle in relation to the sheet 111a and therefore constituting the foot of the L-shape of the flange, and which also in a rest position advanta- geously is essentially parallel to the outer surface of the first part 2. The second part 3 also comprises a circular connection part 120, in the form of a tube 121, extending around the outer surface of the second part 3 and comprising a longitudinal opening or slit 126 arranged to receive and accommodate the flange 110. The tube 121 further comprises a tight-fitting connection part 123 to the outer surface of the second part 3. It is preferred that the ring which is formed by the tube 121 around the second furnace part 3 is concentrically arranged in relation to the circular cross-section of the second part 3.

The two respective circular connection parts 110, 120 are arranged to engage with and sealingly connect to each other, so that both furnace parts 2, 3 are rotatable in relation to each other at the engagement between the connection parts 110, 120. This is achieved by an end part 112 of the circular edge 111b being inserted through the slit 126, and being allowed to run within and along the tube 121, in a way so that the end part 112 is freely rotatable in the tube 121 in the angular direction of the furnace parts 2, 3.

According to a preferred embodiment, not shown in figure 2, the tube 121 is so designed so that it springs back towards a position in which the slit 126 is closed, and is also arranged to surround the circular edge 111b along the whole of, or at least essentially the whole of, the perimeter length of the edge 111b when the furnace parts 2, 3 are sealingly con- nected to each other. The spring action of the tube 121 is in this case thus accomplished by the tube 121 itself being designed in a resilient material or comprising spring means leading to that the tube 121 springs back towards a position in which the slit 126 is closed.

According to an alternative preferred embodiment, which is illustrated in figure 2, the tube 121 is however made from a rigid material, preferably metal, and comprises an inner tube 122 made from a flexible material. The inner tube 122 com- prises, in a way corresponding to the tube 121, a longitudinal slit 126a, arranged to receive and accommodate the end part 112 of the circular edge 111b.

Such a construction accomplishes a robust and heat-resistant yet simple and therefore cost-efficient solution. The inner tube 122 may be made from a resilient material, it may for example be designed as a thick rubber tube with the slit 126a as a longitudinal through cut. However, according to a preferred embodiment the outer diameter of the flexible tube 122, when the tube 122 is in a state of rest, is larger than the inner diameter of the outer tube 121, whereby the edges of the flexible tube 122 at the slit 126a are bent or folded in towards the centre of the outer tube 121 when it is mounted in the outer tube 121 and when the end part 112 of the circular edge 111b is inserted through the slits 126, 126a. This will result in a very good seal during operation, as described below. According to an especially simple and therefore preferred embodiment, the flexible tube 122 is designed as a mat or sheet of flexible material, advantageously wider than the inner circumference of the outer tube 122, which mat in a state of rest is essentially plane, but is rolled to a tube shape when mounted into the outer tube 121.

It is also possible to complete an outer tube 121 which is resilient as such with an inner, flexible tube 122 according to the above.

According to the invention, a liquid coolant is arranged to continuously flow through the tube 121, and to essentially fill out the whole space defined by the combination of the inner surfaces of the tube 121 and the outer surfaces of the circular edge 111b. In case several concentric tubes are used, for example an inner flexible tube 122 together with an outer, rigid tube 121 as described above, the coolant is arranged to flow through the inner tube 122 and essentially fill the space defined by the combination of the inner surfaces of the inner tube 122 and the outer surfaces of the circular edge 11. Preferably, the coolant is water, but it may be any suitable, liquid coolant, such as water with a suitable, conventional, friction-decreasing and/or abrasion-decreasing additive, or a suitable, conventional, liquid low friction coolant. As is illustrated in figures 1, 3A and 3B, a supply device 200, 300 is arranged to continuously supply the coolant to the tube

121, 122 at a respective point 201, 301 which is located on the tube 121, 122 furthest up in the direction of gravity. The sealing device 100 is arranged to continuously drain the coolant away from the tube 121, 122 by the use of gravity, for example via leakage from the tube 121, 122 through the slit 126, 126a or through leakinesses or other openings in the tube 121, 122. Alternatively, the coolant may be diverted at the bottom of the tube 121, 122 using a device similar either to the one shown in figure 3A or to the one shown in figure 3B. According to a preferred embodiment, the coolant is recirculated by a circulation device (not shown) , by collecting the coolant below the sealing device 100 and thereafter again pumping it up back to the supply device 200, 300. Since the coolant continuously flows through the tube 121,

122, the tube 121, 122 is efficiently cooled during operation, and it is therefore possible to achieve a satisfactory useful life for the tube 121, 122. Furthermore, the spring action of the tube 121, 122 back towards the position in which the slit 126, 126a is closed, ensures that the slit 126, 126a seals tight-fittingly around the outer surfaces of the circular edge 111b. That the slit 126, 126a "seals tight- fittingly" shall herein be construed to mean that no gas can pass through the slit 126, 126a when the tube 121, 122 is filled with coolant. The coolant, on the other hand, can leak out through the slit 126, 126a to a certain extent, even if it is preferred that the slit 126, 126a is so closed around the edge 111b that the leakage per time unit of coolant through the slit 126 _s 126a is so large in comparison to the total amount of coolant that a suitable circulation of coolant is achieved in the tube 121, 122. As described above, the tube 121, 122 is sealingly fastened to the outer wall of the second furnace part 3 via the connection part 123. Moreover, the connection part 110 is in itself sealingly fastened to the outer wall of the first furnace part 2. Moreover, an overpressure arises inside the tube 121, 122, because of the liquid column of coolant inside the tube 121, 122, resulting in that the volume which is defined by the inner surface of the tube 121, 122 in combination with the outer surface of the circular edge 111b is always completely or essentially completely filled with coo- lant during operation. Thereby, an efficient sealing is achieved between the two furnace parts 2, 3, so that atmospheric gases cannot leak into the industrial furnace 1, and so that furnace atmosphere gases cannot leak out of the industrial furnace 1 via the rotatable sealing device 100.

According to a preferred embodiment, illustrated in figure 3A, the furnace part 3 on which the tube 121, 122 is arranged is fixed. In other words, the furnace part 2 on which the circular edge 111b is arranged is rotatably connected to the furnace part 3, while the furnace part 3 is fixed in relation to the installation location of the furnace 1. In this case, the tube 121, 122 comprises a fixedly arranged supply conduit 200 for coolant at the top of the tube 121, 122 in the direc- tion of gravity. Such an arrangement is uncomplicated and therefore reliable.

In case the furnace part 3 on which the tube 121, 122 is arranged is rotatable in relation to the installation location, it is, however, preferred to design a supply device 300 for coolant as illustrated in figure 3B. The supply device 300 is slidably arranged in relation to the tube 121, 122, and arranged to supply coolant through the slit 126, 126a using a supply means 302. Since the supply device 300 is slidably arranged in relation to the tube 121, 122, supply of coolant can always take place at the point 301 which at each instant during operation is furthest up in the direction of gravity, which achieves good through-flow of coolant through- out the whole tube 121, 122.

It is preferred that the underside of the supply means 302 is designed with a domed form, so that it may slide along the outer surface of the circular edge 111b with minimal friction and with a minimum of leakage of coolant. In case a flexible, inner tube 122 is used, it is preferred that the supply means 302 is so flat so that it may be inserted in through the slit 126a and on into the interior of the tube 122 in order to therein supply coolant without affecting the form of the slit 126a more than to an extent where the leakage of coolant out through the slit 126a is minimized at the location for supply of coolant.

According to an especially preferred embodiment, illustrated in figure 3B, the supply means 302 displays, in a cross- section which is perpendicular to the main direction of elongation of the tube 121, 122 when the supply means 302 is mounted and which cross-section coincides with the cross- sections of furnace parts 2, 3, a soft bell shape, which bell shape allows for a tight-fitting connection between the supply means 302 and the slit 126a when the supply means 302 is inserted into the tube 122 and thereby presses the tube parts apart in the slit 126a.

According to a preferred embodiment, as illustrated in figure 2, the connection part 123 is designed as a piece of sheet metal which is pleated in its radial direction. Such a con- nection part 123 can absorb temperature induced radial material movements of the second furnace part 3. Since the tube 121, 122 is cooled by aid of the coolant, the temperature induced material expansion of the tube 121, 122 will be small in comparison to that of the second furnace part, even in case a rigid outer metal tube 121 is used. In other words, the tube 121, 122 will essentially not expand with increasing furnace temperature. Therefore, the distance between the outer wall of the second part 3 and the tube 121, 122 will vary with varying furnace temperature, which distance varia- tions can be absorbed by the pleated connection part 123 without the sealing connection between the second part 3 and the tube 121, 122 being negatively affected.

The preferred embodiment of the connection part 110 which is illustrated in figure 2, with a flange comprising the circular edge 111b which is connected to the first furnace part 2 by use of a peripheral, perpendicular sheet 111a, also admits, since it has an uncomplicated structure, that temperature induced changes of the outer diameter of the first fur- nace part 2 are absorbed without deteriorating the properties of the sealing device 100. Since the circular edge 111b is cooled by the coolant in the tube 121, 122, the temperature of the end part 112 of the circular edge will not vary mate- rially as compared to the surface temperature of the first part 2. Thus, during operation a relatively large temperature gradient will arise in the connection part 110. This temperature gradient will lead to the connection part 110 twisting, so that the respective angles between on the one hand the sheet 111a and the first part 2, and on the other hand the sheet 111a and the circular edge 111b, will decrease. As the outer surface of the first part 2 expands, as a consequence of raised temperature, the end part 112 will bend down to- wards the said outer surface. Since the temperature at the edge 111b close to the end part 112 will change only little, its position in the tube 121, 122 will not be affected materially, possibly except for the angle for the circular edge 111b. In other words, the sealing effect of the sealing de- vice 100 will not be affected negatively during thermal expansion of the first furnace part 2. The fact that the circular edge twists, so that the angle at which the end part 112 intrudes into the tube 121, 122 is changed, does not lead to deteriorated sealing, since the interior of the tube 121, 122 is circular and completely filled with coolant. By suitable choices of dimensions for the sheet 111a and the circular edge 111b, as well as the mutual angles at temperature homogeneity, a connection device 110 may be designed which functions in a satisfying way across a broad spectrum of tempera- tures for the outer wall of the first part 2.

The sealing device 100 can also absorb temperature induced changes of the lengths of both furnace parts 2, 3, which may lead to displacements in the longitudinal direction between the parts 2, 3. Since the end part 112 is inserted a certain distance into the tube 121, 122, it may be brought back out some ways without being completely pulled out of the slit 126, 126a and thereby losing its sealing connection to the tube 121, 122. Furthermore, the end part 112 may be arranged in a position not completely inserted into the tube 121, 122, so that the end part 112 can be pushed in through the slit 126, 126a an additional distance before it abuts at the inner wall of the tube 121, 122 at the opposite side. Thus, the connection part 110 can be arranged with a certain play between the circular edge 111b and the tube 121, 122 in the direction of elongation of furnace parts 2, 3. This play may hence absorb longitudinal displacements between the parts 2, 3 without deteriorated sealing properties of the sealing device 100.

According to a preferred embodiment, most clearly illustrated in figure 2, the outer tube 121 further comprises an elon- gated, first tube part 121a, which is fixedly connected to the connection part 123, as well as a second tube part 121b, which runs longitudinally and is adapted to the first tube part, which tube parts 121a, 121b together form the rigid tube 121. The tube parts 121a, 121b are joined together by the use of an elongated fastening device 124. The fastening device 124 may be conventional as such, for example in the form of a screwed joint reinforcement, and is arranged to allow loosening of the second tube part 121b from the first tube part 121a for maintenance of the sealing device 100. Such an arrangement permits quick and direct access to the interior, flexible tube 122 and to other components in the sealing device 100.

Above, the present invention has been explained with refer- ence to exemplifying embodiments. However, the invention is not limited to these embodiments. It is, for example, realized that similar sealing devices 100 as the one described between the first 2 and the second 3 furnace may also be arranged between any rotatable furnace door (not shown) for charging of material into the first furnace part 2 and/or between the second furnace part 3, which in this case is rotatably arranged, and the third furnace part 4.

Thus, the invention may be varied within the scope of the enclosed claims.