EP0134188A1 - Firing kiln car - Google Patents

Abstract

Furnace vehicule for baking furnaces, comprising a moving steel frame (1) on which there is arranged a vehicule platform (11) having two layers. The upper layer (13) of the vehicule platform is used as a covering layer and is comprised of an ever lasting material resisting to temperature effects, for example chamotte or steel. The lower layer (12) of the vehicule platform (11) is a heat-insulating layer which is comprised of a highly insulating material resisting to temperature effects and having a low thermal conductivity, for example a cellular material based on aluminium and calcium hydrate. The homogeneous and uniform construction according to the present invention of the heat-insulating layer (12) enables to evenly distribute the mechanical and thermal stress throughout the surface of the vehicule platform (11). The low thermal conductivity of the material provided in the heat-insulated layer (12) further enables to provide for the necessary temperature decrease on a short stroke, so that the heat-insulating layer (12) of the vehicle platform (11) may have a considerably reduced height with respect to known vehicule platforms. Thereby, a substantial weight reduction for the vehicle platform, a considerable decrease of stored heat in the vehicule platform and a reduction of heat losses are obtained.

Description

In the ceramic industry, in addition to chamber and bogie hearth furnaces, especially tunnel furnaces are used as firing furnaces for the firing of ceramic products, the fired goods generally being introduced into the furnaces on kiln cars.

Such kiln cars consist essentially of a mobile steel frame and a two-layer car plateau arranged thereon, the upper layer being formed from a wear-resistant and temperature-resistant material and the lower layer lying on the steel frame containing a heat insulation core which is surrounded by an edge made of refractory material . When operating such a kiln car, the kiln is on the plateau of the kiln car. At the same time, the car plateau protects the steel frame from the high temperatures that act on the plateau in the firing zone of the kiln.

In known embodiments, the heat insulation core is formed from layers of insulating bricks and layers of light bricks. The insulating stones on the steel frame, e.g. diatomite stones, have a very low density and the associated high porosity. This high porosity achieves a low thermal conductivity required for good insulation purposes, but at the same time a low Fe stability of the insulating stone. Since the insulating bricks also only have a low application temperature, i.e. a low upper limit temperature for the use of these bricks in the thermal insulation core, the layer of fire bricks arranged above the insulating bricks is of sufficient light strength and application temperature for sufficient mechanical strength and application temperature of the entire thermal insulation core and have a slightly higher density, indispensable.

The layer of light-weight bricks usually requires additional heat protection, since in practice the temperatures prevailing in the furnace room are usually higher than the application temperature of the light-weight bricks. In addition, the entire thermal insulation core must be protected against external mechanical stresses, e.g. Abrasion or impact loads, and in view of the decreasing strength of the insulating and fire bricks as temperature rises, because the entire insulation core has a relatively low strength and surface hardness due to its porous structure.

This double protective function is achieved in known kiln cars by the edge in the lower layer and by the upper layer of the car plateau. The edge and the top layer are usually made of a wear-resistant, temperature-resistant material. This material has to be resistant to changing temperature loads, since constant heating and cooling of the wagon plateau cannot be avoided while moving in and out of the kiln. 'At the same time, the material must also be characterized by good resistance to pressure fire, ie good softening behavior with constant load and increasing temperature, in order to adequately protect the thermal insulation core from external mechanical stresses. These two requirements are usually best met by firebrick or fireclay refractory concrete qualities, the quality of which is usually in addition to the maximum temperature load in the Firing zone of the kiln are adapted. In order for the upper layer to have a sufficient load-bearing capacity, the thickness of the upper layer is normally 100-150 mm. The thermal insulation core is mostly 200 - 250 mm thick due to the mechanically necessary subdivision into the insulating stone and fire light stone layer, so that there is a total height of the carriage plateau of at least 300 - 400 mm.

In terms of its function, the kiln car can be seen as a thermally-periodically working element. When considering the firing process in terms of energy, the high wagon plateau of known kiln wagon constructions proves to be disadvantageous. The large volume of solids in the high wagon plateau cannot be heated quickly, so that a long heating phase in the kiln is required in order to adjust the wagon plateau to the firing temperature required for the material to be fired. In practice, however, only the upper layer of the wagon plateau is adjusted to the firing temperature, since the best possible protection of the steel frame against the firing temperature is only achieved if there is a temperature gradient between the upper and lower layers of the wagon plateau. In addition, this temperature adjustment of the upper layer is also absolutely necessary for a problem-free fire of the firing material lying directly on the wagon plateau.

As a result of the large volume of solids, the wagon plateau also has a high storage heat, which is released into the atmosphere as heat loss when the kiln wagon cools down after the combustion process has been completed.

For an energetically favorable mode of operation of the kiln car, however, the heating-up phase must be short and the heat loss when cooling the kiln car must be low.

In known newer designs of kiln cars, the upper layer of the car plateau is partially filled with a mineral fiber material and additionally with plat arranged above it made of a wear-resistant, dense refractory material, e.g. chamotte. In another embodiment, the upper layer of the carriage plateau is covered with mineral fiber material. In both trolley plateaus, the arrangement of the material lowers the temperature in one or both layers of the trolley plateau, thus reducing the storage heat, which at the same time reduces the heat losses from the furnace trolley. However, the values achieved are not sufficiently lowered compared to the well-known values and are therefore not yet satisfactory in practice. In addition, this newer construction does not avoid significant disadvantages of known kiln cars.

As a result of the delivery of the wagon plateau made of different refractory stone qualities (insulating stone, lightweight fire stone, wear-resistant, dense refractory stone), which is provided in the well-known as well as in the newer constructions, there are different thermal expansions of the heat insulation core and edge in the lower layer of the wagon plateau. In addition, the case may arise that the thermal insulation core shrinks more than the edge of the carriage plateau due to its porous structure under thermal load. During the shrinkage or expansion process of the thermal insulation core, forces develop in the lower layer, which must be compensated for by the edge of the carriage plateau. For a sufficient mechanical strength, the edge must therefore be made in a corresponding width, which increases the weight and storage heat of the carriage plateau. In addition, the shrinkage and expansion processes in the wagon plateau create thermal stresses, which are reduced in the case of ceramic materials by crack formation and thus lead to premature wear of the wagon plateau.

Finally, a ceramic material is not able to deform elastically, so that the edge of the carriage plateau, for example due to the impact stresses that occur during the shunting operation of the kiln cars, is highly susceptible to breakage and requires a relatively high repair effort.

With the invention, a kiln car is now to be created, the car plateau of which ensures an energetically favorable mode of operation, withstands high mechanical loads and can be exchanged quickly and cost-effectively for existing car plateaus.

The invention achieves this aim in that the thermal insulation core, including the edge of the lower layer of the carriage plateau, is made of the same highly insulating, temperature-resistant material.

Due to the uniform, homogeneous structure of the lower layer of the carriage plateau, which is referred to hereinafter only as an insulation layer, in the heat insulation core and in the edge made of a highly insulating material, the invention completely eliminates all the disadvantages that arise when the insulation layer is constructed from different materials. The mechanical and thermal stress as well as the heat transfer are evenly distributed over the entire surface of the carriage plateau. The low thermal conductivity of the highly insulating material provided according to the invention also makes it possible to reduce the height of the insulating layer of the carriage plateau to up to about 30% of a known thermal insulation core height. This results in a weight saving of up to about 50% for the wagon plateau, the storage heat of the wagon plateau is significantly reduced, the heat loss is reduced and the possibility for shorter heating and cooling phases is given, so that the kiln can be operated more economically. In addition, the material savings when repairing the wagon plateau will reduce costs.

In addition, the stock of the kiln car is increased by the volume saved on the car plateau, so that a higher productivity of the kiln is achieved with the same number of kiln cars. The kiln's fuel requirements change usually not, because the total volume of fuel and wagon plateau to be heated is almost constant.

A cellular material based on calcium aluminate hydrate is preferably provided as the material.

A thin protective sheath provided in a further embodiment of the invention, which at least laterally encloses the insulating layer vertically, offers the highly insulating material protection from external mechanical stresses and, in its embodiment, which preferably encompasses both layers of the carriage plateau, prevents these layers from slipping horizontally on the steel frame. Finally, in the construction of the kiln car according to the invention, it is often possible to reuse the mobile steel frame of older kiln cars and only a replacement of the old car plateau is necessary, so that a quick and inexpensive replacement of older kiln cars is possible.

• Fig. 1 eine Draufsicht einer bevorzugten Ausführungsform der Erfindung,
• Fig. 2 eine Schnittansicht der Ausführungsform gemäß Figur 1 in der Ebene II - II,
• Fig. 3 eine Draufsicht einer alternativen Ausführungsform der Erfindung, und
• Fig. 4 eine Schnittansi.cht der Ausführungsform gemäß Figur 3 in der Ebene IV - IV.

Refinements and developments of the kiln car according to the invention are defined in the subclaims and are explained in more detail in the following description of individual embodiments with reference to the drawings. Show here:

• 1 is a plan view of a preferred embodiment of the invention,
• 2 shows a sectional view of the embodiment according to FIG. 1 in the plane II-II,
• 3 is a top view of an alternative embodiment of the invention, and
• Fig. 4 is a sectional view of the embodiment of Figure 3 in the plane IV - IV.

In the embodiment according to FIGS. 1 and 2, the mobile steel frame 1 is composed of two steel carrier layers 2 and 3 arranged one above the other and two wheel sets 4 and 5 fastened to the lower steel carrier layer 2. Each of the two steel girder layers 2 and 3 is formed from several steel girders running parallel to one another at a distance, the steel girder of the lower steel girder layer 2 in the direction of travel of the kiln car and the steel girder of the upper steel girder layer 3 at right angles to the direction of travel parallel to the two wheel sets 4 and 5 run. The two outer steel girders 6 and 7 of each steel girder layer are U-shaped and arranged such that a bottom of a U-shaped steel girder 6 or 7 forms an outer edge of a steel girder layer 2 or 3, respectively. The other steel girders of each steel girder layer are double-T girders 8 and 9. In the two steel girder layers 2, 3, the number and spacing of the double-T girders 8, 9 from one another are not fixed, but result from the respective one static load acting on the mobile steel frame 1 from above.

On the upper steel support layer 3 there is an insulation layer 12 which, according to the invention, consists of a highly insulating, temperature-resistant material and protects the mobile steel frame 1 from the high temperatures which act on the carriage plateau 11 in the furnace's firing zone during operation of a kiln car. A cellular material based on caleium aluminate hydrate is preferably used as the material. In the manufacture of this material, the starting materials are slurried in an aqueous solution. The sludge is then foamed and poured into appropriate molds. After setting, the material is removed from the mold and is available as a finished cellular product (e.g. stone or plate) for further use.

In the simplest embodiment, the insulation layer 12 can be made of individual stones or plates lying next to one another Material be formed, the dimensions of the individual stones or plates must be chosen such that the distances between the individual steel beams 7 and 9 serving as supports of the steel beam layer 3 are bridged.

The insulation layer 12 is covered with an upper layer 13 arranged above it, which is referred to below as the cover layer. This cover layer 13 is preferably made of a wear-resistant and temperature-resistant material, e.g. a chamotte. Both layers 12 and 13 form the carriage plateau 11, at least the insulation layer 12, but preferably both layers 12 and 13, being enclosed by a thin protective jacket 10. The protective jacket 10 expediently consists of a wear-resistant, temperature-resistant steel with a wall thickness of 8-10 mm, but it is also possible for the protective jacket to be made of a dense, temperature-resistant ceramic material, e.g. a zirconium oxide material. The protective jacket 10 is connected in a suitable manner to the two U-shaped steel beams 7 of the steel beam layer 3. In the case of a steel protective sheath 10, this connection is preferably designed as a weld seam, but it can also be provided as a screw or rivet connection.

In practice, it is expedient, as shown in FIG. 2, to additionally arrange a steel floor 20 between the carriage plateau 11 and the mobile steel frame 1, which is connected to the protective jacket 10 to form a trough 21, which at least accommodates the insulating layer of the carriage plateau 11 . This trough 21 has the advantage that the dimensions of the plates or stones in the insulation layer 12 are no longer dependent on the spacing of the steel beams in the steel beam layer 3, since these distances are bridged by the floor 20. This makes it possible to arrange slabs and stones of any dimension in the insulation layer 12 of the carriage plateau 11.

When using the kiln car in kilns with a Solid fuel, (e.g. coal dust or wood flour), it is unavoidable that ashes or incompletely burned fuel residues fall onto the plateau of the kiln car. These material residues, referred to below as foreign substances, can additionally be increased in quantity by chipping on the top layer 13 of the carriage plateau or on the firing material and on the lining material of the furnace chamber. Because the penetration of these foreign substances into the joints between the plates or stones of the insulation layer 12 prevents an unimpeded expansion of the plates or stones into the joint spaces when this layer is heated, and as a result, thermal stresses form in the insulation layer 12 which lead to premature wear of the Lead slabs or stones, in these cases, the best possible joint-free insulation layer 12 must be sought. In this respect too, the tub 21 proves to be very advantageous in connection with the cellular material based on calcium aluminate hydrate. The starting materials of this material can now be poured directly into the tub 21 after slurrying and foaming instead of in a mold. After setting, a joint-free monolithic insulation layer 12 is then formed from the cellular material in situ. Such a homogeneous and self-contained layer is characterized by a uniform heat and thermal stress distribution and a uniform heat transfer across the entire carriage platform surface. At the same time, the joint-free formation of the layer prevents the penetration of foreign substances.

Finally, a tub has the advantage that a worn old wagon plateau of an existing older kiln car can in many cases be replaced with the wagon plateau according to the invention with a short assembly time, since the wagon plateau 11 is completely prefabricated in the tub 21 and quickly on the existing mobile steel frame few welds or screw or rivet connections can be attached. The possibility of reusing the existing mobile steel frame makes it possible to replace an old wagon plateau with the Trough 21 with the carriage plateau 11 according to the invention is also very inexpensive.

All materials which meet the requirements for low thermal conductivity and which are also temperature-resistant are suitable as highly insulating, temperature-resistant material for the insulation layer 12, i.e. have a high application temperature limit. The preferably used material based on cellular calcium aluminate hydrate has an application limit temperature of about 1200 ° C. Compared to known materials with approximately the same application temperature, the thermal conductivity of this material is unusually low and, at the same time, the compressive strength is relatively high compared to known materials with low thermal conductivities. These values are compared in Table 1 for some insulating refractory materials with an application temperature above 1000 ° C. Due to the low thermal conductivity, a high temperature reduction can be carried out over a short distance, so that the layer thickness of the insulation layer 12 required for adequate temperature protection of the steel frame 1 can be selected to be very small.

The very low thermal conductivity of the proposed material results from a highly porous structure, while the surface hardness of this material is low, so that the surface of the material is protected against external mechanical loads (e.g. abrasion, stress due to impact as well as scraping or scratching) a tool) is indispensable. This protective function is achieved on the surface of the insulation layer 12 by the cover layer 13 and in the edge region of the insulation layer 12 by the protective jacket 10 which at least surrounds this layer. If this protective jacket 10 in the preferred embodiment consists of a wear-resistant temperature-resistant steel, there is a risk of breakage of the curbs at least in the insulation layer 12 of the conventional furnace car plateaus Avoided wagon plateaus and at the same time achieved the best possible protection against external mechanical loads with a few millimeters of steel material while saving weight. Because steel has the ability to withstand tension caused by elastic or plastic. Deformation without cracking, premature wear of the edges of the plateau is excluded.

In addition, the relatively high application temperature of the material provided in the insulation layer 12 of approximately 1200 ° C. in most cases, i. H. at temperatures in the furnace room up to 1200 ° C, this temperature can be applied directly to the insulation layer. In many cases, additional thermal insulation between the insulation layer 12 and the furnace space is therefore not necessary, and the cover layer 13 therefore mostly only has a purely mechanical protective function, in contrast to known carriage plateaus. Therefore, this cover layer 13 can then also be made substantially thinner, so that the total height of the two-layer car plateau 11 can be reduced in such cases by up to about 70% compared to known kiln car plateaus.

In a modification of this embodiment of the carriage plateau 11, which is not shown in any more detail, the insulation layer 12 can also be protected from external mechanical stresses by a cover which is made of wear-resistant, temperature-resistant steel and is connected to the protective jacket 10 in a suitable manner. It is expedient to provide screws, rivets or the like as a connection in order to enable a convenient and quick exchange of the heat insulation core.

The vertical height of the protective jacket 10 is selected in the embodiment shown in FIG. 2 such that the carriage plateau 11 is enclosed in its full height by the protective jacket 10. This also prevents the cover layer 13 of the wagon plateau 11 from slipping horizontally, as can occur, for example, in shunting operation when two kiln cars collide.

Since the wear-resistant, temperature-resistant material of the cover layer 13 does not require protection against external mechanical stresses, the vertical height of the protective jacket 10 can be selected in a further modification, also not shown, in such a way that only the insulation layer 12 is surrounded vertically laterally by the protective jacket 10.

Figures 3 and 4 illustrate an alternative embodiment of the carriage plateau, in which the protective jacket 10 consists of individual ceramic plates 14 of a wear-resistant refractory material. Dense ceramic materials such as. B. provided on the basis of zirconium oxide. The individual ceramic plates 14 can be inserted into a U-shaped profile, not shown, made of a temperature-resistant steel, which is welded or screwed to the steel girders of the upper steel girder layer 3.

However, all ceramic plates 14 must have the same dimensions in their thickness in order to ensure a snug fit between the two legs of the U-shaped profile. In practice, it is therefore more convenient to arrange the plates 14 between two steel plates 15 and 18 according to FIG. 4. The inner steel plate 18 is welded or screwed to the steel beams of the upper steel beam layer 3. Here are with a screw z. B. tapped holes in the steel beams or threaded sleeves welded to the steel beams. In this embodiment, too, the height of the plates 14 forming the protective jacket 10 is preferably selected such that the carriage plateau 11 is enclosed in its full height by the protective jacket 10. Since the inner steel plate 18 is not exposed to such high temperatures, it consists of a simple steel, while the outer steel plate 15 is made of a wear-resistant and temperature-resistant steel. The outer steel plate 15 is fastened to the steel plate 18 with screws 16, and the plates 14 are provided with holes in the area of the steel plates surrounding them, the screws 16 from the outer to the inner steel plate are inserted through this hole.

The screwing of the steel plates on the steel frame has the advantage over the welding that a quick disassembly is possible if an exchange z. B. is required after damage. By means of the tightened screws 16, the outer steel plate 15 is connected to the inner steel plate 18 regardless of the different thicknesses of the plates 14, and a positive fit of the plates between the two steel plates is achieved. At the same time, a precise fit of the plates 14 is ensured even after prolonged use, since the distance between the two steel plates can be adapted to the wear-reduced plate thickness by tightening the screws 16 again.

The insulating layer 17, which can also be introduced into the carriage plateau of FIGS. 1 and 2, largely prevents an increase in temperature in the insulation layer 12, as a result of which the storage heat in the carriage plateau 11 is additionally reduced, so that, as an advantage, the furnace is operated more economically and more favorably . In addition, the insulating layer prevents the penetration of foreign matter into the insulation layer of the carriage plateau, so that a seamless, monolithic formation of the insulation layer is not absolutely necessary.

Claims (8)

1. Kiln car for kilns, with a mobile steel frame on which a two-layer car plateau is arranged, the upper layer consisting of a wear-resistant and temperature-resistant material, and the lower layer lying on the steel frame contains a heat insulation core, which is made of an edge made of refractory material is surrounded, characterized in that the heat insulation core including the edge of the lower layer (12) of the carriage plateau (11). consists of the same highly insulating temperature-resistant material. 2. Kiln car according to claim 1, characterized in that the highly insulating temperature-resistant material is a cellular material based on calcium aluminate hydrate. 3. Kiln car according to claim 1 or 2, characterized in that an at least the lower layer of the car plateau (11) laterally vertically enclosing thin protective jacket (10) is arranged from a wear-resistant material. 4. Kiln car according to claim 3, characterized in that the protective jacket (10) consists of a temperature-resistant steel. 5. Kiln car according to claim 3, characterized in that the protective jacket (10) consists of a dense refractory ceramic. 6. Kiln car according to claim 3 and 4, characterized in that between the steel frame (1) and the carriage plateau (11) a bottom (20) made of steel and with the protective jacket (10) is connected to a trough (21) which receives at least the lower layer of the carriage plateau (11). 7. Kiln car according to one of the preceding claims, characterized in that an insulating layer (17) is arranged between the lower layer (12) and the upper layer (13) of the carriage plateau (11). 8. Kiln car according to claim 6, characterized in that on the lower layer (12) a cover made of a wear-resistant temperature-resistant steel is arranged and connected to the trough (21) such that the lower layer (12) is completely enclosed.

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