Porous ceramic structure

The invention relates to a porous ceramic member according to Main claim.

Porous ceramic structures, for example, to increase the Heating efficiency of a furnace as a heat insulating element inserted into the exhaust port of the furnace.

For the thermal insulation of the exhaust outlet of a furnace or the like it is known as a gas-permeable heat insulator, a fine ceramic Wa benelement or a porous ceramic body having a three-dimen dimensionally interconnected open cell structure in the exhaust port of the furnace enforce, so that the furnace is shielded from heat radiation and the thermal energy of the exhaust gas through heat exchange with the through the ceramic element flowing exhaust gas is recovered. The to recovered heat energy is in the form of radiant heat directly into the heating of the oven is returned (Japanese Laid-Open Appli tion 57-209892, corresponding to EP-A 068 360).

Conventional gas-permeable heat insulators with a ceramic honeycomb or have a porous ceramic body of the type described above satisfactory on properties, as long as it is under conditions be set, where no significant temperature differentials and no larger amounts occur on dust. If the temperature changes however, occur easily in the conventional ceramic honeycomb elements Cracks or similar damage to the corners or edges. In her conventional porous ceramic bodies, there is the risk that the three-dimensional open-cell structure of the ceramic body with Dust is added when the exhaust gas contains relatively large quantities of dust, as in for example fly ash, which is produced during the combustion process, or how fire crust of the heated material. This results in increased pressure losses in the Ab gas system and thus to difficulties in operation of the furnace.

The invention is therefore based on the object, a ceramic element to create, which can be used as a gas-permeable heat insulator and in which even with a lot of dust and / or strong Temperaturänderun gen neither a blockage of the pores, cracks or similar damage in the ceramic material formed. The ceramic element is, for example, in an exhaust gas cleaner than solid-collector or as a filter for geschmol be ZENES metal used.

The solution of this object, according to the invention from the characterizing nenden part of claim 1.

Advantageous developments of the invention are in the dependent claims to given.

The inventive ceramic element has a honeycomb structure, the aligned through closely spaced, in a series of pairs ge is formed neigter cylindrical cells each in the manner of an angle asked numeral "8" are arranged. The width of the cells is in the range 5-30 mm, the height is 10 to 100 mm. The angle of inclination Cells is 20 to 70 °.

The DE-AS 25 38 613 describes a honeycomb structure in which sämtli che cells exclusively by curved walls between common Seam lines are formed at an improved resistance should have compressive and tensile forces, such as at high unevenly Temperatures. The features of the present invention but not realized in the rest.

The DE-OS 27 08 908 relates to a similar ceramic honeycomb structure with concave and convex curved cell walls. is also in this case, it comes to the mechanical strength due to strong temperature gradients.

The DE-AS 22 10 438 shows and describes a ceramic honeycomb body, which is produced by pressing of pins in a block. The de- AS 22 01 477 and 22 02 152, and DE-OS 23 37 034 show and be Write the formation of honeycomb bodies through alternating arrangement of smooth and corrugated layers. The US-PS 29 77 265 relates to a corresponding ceramic structure with a reinforcing skeleton as carriers and a ceramic material which is deposited as sludge in this. The thus formed honeycomb material is sandwich-like between two Plates are attached.

The honeycomb body according to the invention are preferably as an elongated body formed in arranged in double rows cells. If GE on a given area a heat insulation will wish, so be more such honeycombs with their longitudinal sides against one another with each other together so that together they form an element, filling the surface to be insulated.

When using the inventive ceramic Structure as a thermal insulator in the exhaust gas outlet of a furnace be inclined cylindrical cells Honeycomb core formed the exhaust passages. If the exhaust Outlet completely through the structure of the invention is covered, so is due to the inclination of the cells a straight passage of light or Wärmestrah treatment prevented by the honeycomb body without the Gas flow is significantly impaired. The heat radiation is reflected by the honeycomb element so that radiant heat losses of the furnace can be prevented. In addition, there is a heat exchange between the ceramic honeycomb body and the through-flowing Exhaust, so that the ceramic structure in turn heated and re-radiates heat to the furnace. To this Way is by direct recycling the heat in Form of radiant heat energy a substantial achieved savings. Thermal stresses which in itself give follow strong temperature changes, are the inventive ceramic structure distributed so that the structure has a high resistance to comprises thermal shock. In addition, by the inventive structure of the honeycomb body the risk of blockages of the ceramic element reduced by dust or the like.

The inventive ceramic structure is therefore the use, for example, as a gas-permeable heat isolator under conditions with high levels of dust and severe temperature changes suitable.

According to a preferred embodiment of the inven tion, the walls of the cylindrical cells having provided fractures, by the neighboring cells mitein other are connected. Through these interconnections in the cells of the honeycomb-shaped member is a strong turbulence and mixing of the transmitted reaches the flowing fluid.

The honeycomb body may agree in several layers be located on the other. You can also optionally layers of porous ceramic material on one or both be provided end faces of the honeycomb body. In which porous ceramic material may be, for example, a foam-like ceramic material or a ceramic needle structure or ceramic wool trade.

According to a further embodiment of the invention are in the cell walls of the honeycomb body cavities from formed towards an end side of the honeycomb body are open. Thereby, the durability of the honeycomb body increases with regard to thermal stresses.

In the following, preferred embodiments of the Invention with reference to the drawings in more detail.

<b>Fig.</b> 1 is a partially cutaway perspective view of an Off implementation of the invention;

<b>Fig.</b> 2 is an enlarged plan view to to <b>Fig.</b> 1;

<b>Fig.</b> 3 is a view similar to <b>Fig.</b> 1 and showing another embodiment of the invention;

<b>Fig.</b> 4 is a section through the embodiment for example according <b>Fig.</b> 3;

<b>Fig.</b> 5 is a partially cutaway perspective view of a leaf or ribbon for making a honeycomb core according to <b>Fig.</b> 3 ver used is;

<b>Fig.</b> 6 and 7 are schematic representations wei Exploder embodiments of He invention;

<b>Fig.</b> 8 is a schematic longitudinal section by another Ausführungsbei game of the invention;

<b>Fig.</b> 9 is a section along the line IX-IX in <b>Fig.</b> 8th; and

<b>Fig.</b> 10 is a schematic longitudinal section by another Ausführungsbei game of the invention.

In <b>Fig.</b> 1 is an inventive porous ceramic structure <b>1</b> shown by a honeycomb body <b>3</b> or formed an arrangement of a plurality of such honeycomb bodies becomes. The honeycomb body<b>3</b> consists of a meandering shape or in the form of a slanted letter "8" folded Band of ceramic material whose loops couples aufein cutive tilted cylindrical cells <b>2</b>. <b>2</b>' form with oval cross section. In the specific Ausfüh embodiment according <b>Fig.</b> 1, the ceramic structure <b>1</b> by an arrangement of a plurality of juxtaposed honeycombs <b>3</b> formed facing each other at their folded edges in the in <b>Fig.</b> 1 shown manner with are connected to each other. In<b>Fig.</b> 1, two honeycombs <b>3</b> shown. In this case, the walls of which are cylindrical cells <b>2</b>. <b>2</b>'Form, through another connected, and the cells <b>2</b>. <b>2</b>'Form channels <b>5</b> for a Fluid, such as exhaust gas or the like. The Extent in the longitudinal direction of the honeycomb body <b>3</b>Ie, the length of the inclined cylindrical cells <b>2</b>. <b>2</b>'Formed rows, and the number of the honeycomb body <b>3</b> respectively corresponding to the dimensions of the area set, in which the ceramic structure <b>1</b> arranged shall be. The cross-sectional shape of the cylindrical cells<b>2</b>. <b>2</b>'Is not limited to that shown oval shape. The cells can also have a circular or otherwise have shaped cross section.

According to the invention have the honeycomb-forming cells <b>2</b> and <b>2</b>'Has a width d of 5 to 30 mm (corresponding to the smaller diameter of the cylindrical cell having an oval Cross section according to <b>Fig.</b> 1), a height h of 10 to 100 mm (According to the thickness of the honeycomb body) and a Tilt angle R of 20 to 70 °. By this arrangement, it is achieved that when using the structure <b>1</b> as gas-permeable heat insulator pressure losses avoided and the delay of the combustion process be that otherwise by the clogging of the cells would be caused by accumulation of dust. on the other hand is an effective shield against heat loss Thermal radiation guarantees. The structure comprises also a high mechanical stability and a high resistance skill on to thermal shocks. If the Width d of the cells is less than 5 mm, is contrary risk that the gas channels <b>5</b> by deposition of in Dust contained the exhaust are clogged, and except the taking of pressure loss even at an operating over a relatively short period of time so strongly, that he attained an acceptable level. If on the other hand the width of the cells is greater than 30 mm, the Porosity is too large, and the surface of the walls of the Ceramic material in which the heat exchange with the Exhaust gas takes place, is relatively small, so that the heat transfer from the exhaust gas to the heat insulator is reduced and the cooling down by heat radiation as strong increases that the structure no more than gas permeable heat insulator is suitable.

If the height h of the cylindrical cells <b>2</b>. <b>2</b>' (the fat of the honeycomb body) is smaller than 10 mm, the heat is transition from the exhaust gas to the heat insulator due reducing the surface of the walls of the ceramic material greatly reduced, and the optical thickness of honeycomb <b>3</b> is too small to that of straight Passage of light or heat radiation through the heat isolator still could be prevented, so that a undesirable hypothermia by heat radiation occurs. When the inclination angle of the lines <b>2</b>. <b>2</b>' in relation to the vertical is less than 20 °, it becomes difficult to sufficient suppression of the heat radiation to ensure, and the cylindrical cells would have to this purpose have a large height. Furthermore would a greater risk of losses due to pressure the deposition of dust, so that the objects of the invention are no longer achieved. On the other hand the inclination angle would be greater than 70 °, a strong pressure would result loss, provided that the end faces of the cells to the exhaust gas facing. In the practical application of the structure as a thermal insulator would occur beyond an unacceptable Accumulation of dust on.

The preferred range for the width d be the cell contributes 7-18 mm, the preferred range for the height h of the cells is 15 to 30 mm and the inclination angle is preferably between 30 and 65 °. The invention A honeycomb body is preferably designed such that the Pressure loss of air when passing through a honeycomb body having a thickness of 1 cm at a rate of 1 m / s in the range of 0.05 to 10 mm, preferably 0.1 to 1 mm.

The honeycomb body according to the invention can be prepared by drying and Sintering a ceramic slurry are prepared, the on a carrier honeycomb or an array deposited from a plurality of connected carrier honeycomb bodies is. The carrier honeycomb is itself characterized prepared so that an elongate strip of paper or plastic is folded meandering, so that the loops formed approximately a sequence form tilted eights and by the counter opposite ends of the loops formed by zylin drical cells are cut at an angle. It can any ceramic material can be used. in the With regard to the resistance to thermi rule shocks but materials are preferred as Cordierite, mullite, alumina, silicon carbide or like. The inventive ceramic Structure can ver as gas-permeable heat insulator be used by the structure in a gas outlet or is fitted channel of a furnace, in which a fuel such as gas, oil or the like is burned, for example, the ceramic Structure disposed such that it or the exhaust gas outlet channel or be heated material covers. hereby the material is on the one hand by the heat radiation of the furnace and on the other hand through the gas from the permeable heat insulator reflected heat radiation heated. An additional heating results by itself the radiant heat generated by the heat insulator itself, through the heat exchange between the heat insulator and the flowing hot exhaust gas is caused. In this manner, by utilizing the waste heat of the Exhaust gas, which has not to heat the material could be used in the oven, a very high heat efficiency can be achieved. The inventive geometric shape and dimensions of the honeycomb body is furthermore an effective distribution of the thermal reaches voltages, so that the ceramic body a high having thermal shock resistance. simultaneously is determined by the shape and dimensioning of the ceramic body the risk of deposition of the contained in the exhaust gas avoided dust and clogging of the ceramic body to, be through the combustion process in the furnace would prevent.

In the case described above, the present invention ceramic structure mounted in any position will. To the thermal radiation losses and the addition dust to further decrease, it is advisable, however, to place the ceramic structure such that the End face of the honeycomb body, in which the openings the cells <b>2</b>. <b>2</b>faces' are, the exhaust gas flow is and approximately at right angles to the flow direction proceeds without a rectilinear light passage is made possible by the heat insulator. Exhaust thus strikes the walls of the heat insulator.

If necessary, the honeycomb body or the honeycomb body arrangement have a catalytic effect by for example, nitrogen oxides are eliminated, which in Exhaust gas from a fired with heavy fuel oil furnace are included.

In <b>Fig.</b> 3 is another embodiment of the inven tion shown in which, similarly to the embodiment for example according <b>Fig.</b> 1, a ceramic honeycomb body <b>3</b> with a series of paired cylindrical cell <b>2</b>. <b>2</b>'Is provided, which has a circular or having oval cross section and together form the form tilted eights. <b>Fig.</b> 3 shows a honeycomb- shaped arrangement <b>4</b>Wherein the plurality of adjacent honeycombs <b>3</b> at the mutually facing folded Edges are interconnected. The cell walls of cell <b>2</b>. <b>2</b>'Are provided with square openings <b>6</b> provided, by the channels <b>5</b> adjacent cells <b>2</b>. <b>2</b>' with a other are connected. In the embodiment according to<b>Fig.</b> 3 are through openings <b>6</b> the cavities or channels <b>5</b> the cells <b>2</b> and <b>2</b>'Of the same honeycomb body <b>3</b> but not with each other with the channels of zylin drical cells of other honeycomb body connected. It however, may also be provided openings which the Cavities of the cells of various honeycomb body together connect.

The size of the openings <b>6</b> should be 20 to 95%, preferably 20 to 50%, the surface of the cylindrical cell walls be. In the longitudinal direction of the respective cell wall one or more of such connecting holes provided be seen. The shape of the openings<b>6</b> is not limited to the square shape shown. The openings may have any other shape.

Although the production of the honeycomb body <b>3</b> or the honeycomb body assembly <b>4</b> not to any particular method is limited, it is advisable, the honeycomb body or the Honeycomb arrangement by drying and sintering a prepare ceramic slurry, which on a honeycomb body or an arrangement of several affiliated honeycomb body is deposited, each honeycomb body by an elongate strip of paper or plastic is formed of at predetermined length intervals with square openings <b>7</b> is provided and meander is folded shape or 8-shaped.

In this embodiment, the cells are the honeycomb body or the honeycomb arrangement straight lignes flow channels formed. However, openings are formed in the cell walls, a part of the by the cylindrical cells flowing fluid right angularly distributed to the flow channels, so that, due to excellent swirling effect caused by the Openings in the cell walls caused a interpenetration and intermixing of Fluid flows is achieved. When the ceramic Structure as a filter for molten metal, or as a Particulate matter collector is employed, therefore in the melt contained impurities be removed reliably, since the invention Structure in addition to the surface-filter effect having an internal filter effect. While using as gas-permeable heat insulator, the fluid effective with the cylindrical cell walls in contact placed, so that a more intense heat exchange sure is provided.

The honeycomb core according to the invention or the honeycomb arrangement can be used in batch form, by way of example according to the embodiment <b>Fig.</b> 6 illustrates becomes. In this case, a plurality of (for example two) the honeycomb core assemblies according to <b>Fig.</b> 4 preferably in staggered arrangement stacked so that the lower openings of the cells <b>2</b>. <b>2</b>'Of the upper honeycomb body <b>3</b> over the open upper ends of the cells <b>2</b>. <b>2</b>'Of the lower honeycomb body <b>3</b> are offset. In this Case, the upper honeycomb body <b>3</b>Which in <b>Fig.</b> 6 by solid lines is shown, compared with the by chain lines indicated lower honeycombs <b>3</b> optional only in the longitudinal direction, only in Transverse direction or both in the longitudinal direction as well as in be offset transversely. The staggered arrangement according to both the longitudinal direction and in the transverse direction <b>Fig.</b> 6 is particularly advantageous. The degree of offset the honeycomb body in the longitudinal direction and in transverse direction preferably is 1/3 to 2/3 of the width of the cells <b>2</b>. <b>2</b>'In the respective direction. The number of overlap the honeycomb body <b>3</b> is depending on the dimensions of the room, in which the ceramic structure to be mounted or determined with respect to other conditions.

The preparation of the overlapping honeycomb body arrangement is preferably carried out by drying and sintering a ceramic slurry, the honeycomb body arrangement on a is deposited, the previously described from several of Paper honeycomb body is connected at their longitudinal sides interconnected and with similarly ver affiliated honeycombs in a staggered arrangement agreement are other layered. If necessary, these staggered superposed honeycomb arrangements be integrally connected to each other. When the structure is mounted on a tundish, then a suitable Number of honeycomb arrangements <b>4</b> in staggered positions be attached. However, when an integrally connected Arrangement used as a filter for molten metal is the overall height of the assembly should not exceed amount to 100 mm, since otherwise the thermal stresses due to the temperature gradient between the upper and lower end portions (inlet and outlet) of the cylindricity rule or cells of the honeycomb body may increase, so that the honeycomb body cracked.

In <b>Fig.</b> 7 is still another embodiment a porous ceramic structure of the invention illustrated in which the honeycomb body described above <b>3</b> or a honeycomb arrangement <b>4</b> sandwiched between between two rectangular plate-shaped porous ceramic bodies <b>9</b> and <b>10</b> is inserted, a three-dimensional have lattice structure, so that the flowing Repeated fluid impinges on the grating. At this ceramic structure, the fluid flows in the direction of arrow in <b>Fig.</b> 7 by an exposed surface <b>11</b> on the upstream side of a first porous ceramic j rule body <b>9</b>, Through the interior of the first ceramic body <b>9</b>, By a second or middle layer by the honeycomb body <b>3</b> is formed, and by a third porous ceramic body <b>10</b>From which it dates to a lying surface <b>12</b> exits.

For the first and third ceramic body may be a foam-like ceramic material may be used, the a three-dimensionally connected in its interior open having cellular structure. In this case, the foam has shaped ceramic material preferably has a specific Space density of 0.25 to 0.7 associated with cavities an average diameter of 0.2 to 10 mm, a Porosity of 75 to 95% and an air pressure drop of 0.1 to 40 mm water column during the passage of air by a layer thickness of 1 cm with a VELOCITY speed of 1 m / s. Preferably this should foamy Ceramic material connected cavities with an average have diameters of from 1 to 10 mm, so that the pressure losses are reduced.

To produce such a foam-type ceramic material, it is expedient, a ceramic slurry a reticulated, flexible polyurethane foam without applying cell membranes, then to sinter and the polyurethane foam by carbonizing to ent distant. The foam-type produced in this manner Ceramic material has due to the structure of the cell membrane loose, reticulate Polyurathenschaums a cage-like Structure that regular only the edge areas Dodecahedron is. The material has a view on reducing pressure losses sufficient poro sity and interconnected in a complicated way inner cavities of via intensive contact ensure the flowing fluid with the lattice, so that the above-mentioned effects are obtained.

Alternatively, a porous ceramic material for the first and third layers <b>9</b>. <b>10</b> in <b>Fig.</b> 7 also uses a so-called ceramic needle structure are formed by extruding a ceramic slurry in needle form, cross-linking or superimposition of the needles a porous structure, the rectilinear light occurs prevented, and then sintering this Structure is produced. By using the foam-like or needle-shaped ceramic material, which prevents the straight passage of light, for the first and third layers <b>9</b>. <b>10</b> results overall a porous ceramic structure, the effective one provides protection against cooling by radiation losses. The needle-shaped ceramic material has with regard to the specific bulk density, the average diameter of the Voids, porosity and the air pressure loss before preferably similar properties to the aforementioned foamy material.

Alternatively, it is also possible for the first layer a foam-like ceramic material and the third layer a needle-shaped ceramic material to be used, or swept.

The first layer <b>9</b> on the str omaufwärtigen side of honeycomb <b>3</b> should have a thickness of less than 30 mm, preferably less than 10 mm, since otherwise occur cracks or fractures due to thermal stresses could. In such cases where because of a strong Temperature gradient over the first ceramic body on the upstream side or between the first ceramic body and the honeycomb body with strong ther mix voltages must be expected, can in the first ceramic body slots to reduce be formed of thermal stresses.

The third ceramic body on the downstream side has due to the foreclosure of the radiant heat and because of the heat exchange between the fluid and the first ceramic body significantly lower Temperature than the first layer on the upstream Page on. Thus, since also the temperature difference between the front and back of this third body is less, there is little risk of damage to the third ceramic body by thermal tensions gen. The third layer has therefore preferably a thickness of more than 10 mm, so that the insulating effect of is improved over creeping heat losses.

In the porous ceramic structure with the above-described surrounded triple layer structure, the various thermal effects of the respective layers used, in order to reduce thermal stresses and a higher resistance of the structure against over ther to ensure mix voltages. In the first layer occurring on the upstream side thermal stresses are second through the (average) softened layer having a low air-flow resistance and high heat-resistance to creep on has, so that an immediate transfer of thermal Voltages from the first layer to the third layer is prevented.

<b>Fig.</b> 8 shows a further embodiment of the invention, wherein in the walls <b>2</b>a of the inclined cylindrical cells <b>2</b> cavities <b>13</b> are formed, the axial to a End of the cells are open towards.

In this case, the cavities <b>13</b> in the longitudinal direction in the peripheral walls <b>2</b>a of the respective cylindrical cells <b>2</b> in connection with the cavities of the adjacent cells <b>2</b> educated. As further shown in<b>Fig.</b> 8 can be seen, the cavities <b>13</b> continuously from an axial End of the cell wall <b>2</b>a to a point in the vicinity of the other end face of the honeycomb body is formed. The cell walls <b>2</b>A are thus formed as hollow walls, and two parallel wall sections of the cavity wall are at one end connected to each other and at the other end detached separately. Hereby is achieved that the cell walls of the separated free ends a exhibit greater mobility in the transverse direction of the cells, so that thermal deformation to a greater extent from can be compensated.

Since the honeycomb body described above <b>3</b> with cavities <b>13</b> in the cell walls <b>2</b>is a provided that a full cause division of the cell walls and at an axial End of the cells are open to the outside, are the free ends of the two-part cell walls easily in Transversely movable so that thermal deformation can be recorded. This will be thermal distributed stresses in a particularly effective manner so that damage to the honeycomb core <b>3</b> even at a considerable thermal shock is avoided, the with a strong temperature difference due to Tempe raturanstiegs or a drop in temperature occurs.

The hollow cell walls in the porous ceramic structure according to <b>Fig.</b> 8 and 9 are not limited to a particular Shape limited. However, it is advantageous to provide the hollow space continuously from one end of the cell walls to a position in the vicinity of the other end of the cell wall form, as in <b>Fig.</b> 9 is shown. In this case have the cavities preferably have a width in the range of 10/01 to 02/01 of the thickness of the cell wall and a depth in Range 10/09 to 10/03 of the height of the cell wall.

The ceramic honeycomb body having such voids in the cell walls can be produced for example, up by ceramic slurry to a core material will carry that a shape similar to the in <b>Fig.</b> 1 having honeycomb body shown. After drying the applied ceramic slurry the sludge Located at one axial end, to the core material is exposed, and formed in this way, unfired Structure is sintered. The core material is in the Sintering by Ausschwelen or carbonizing removed so that the voids in the sintered Kera mix structure remain. It is also possible, the ceramic material at one end of the honeycomb body to Remove and the cavities after sintering and carbo remove nize the core material. In this Method, however, under certain circumstances the disadvantage that the ceramic honeycomb body is damaged.

When used as gas-permeable thermal insulator , the above-described porous ceramic structure be arranged in any manner. However, it is advantageously, the open ends of the cavities for electroless upstream side of the fluid flow, ie for high temperature align turseite out. If the open end of the hollow spaces which are easily thermoformable, the Hochtem temperature side facing, so may as a result of Temperature difference between the upstream and the downstream side occurring thermal Stresses are distributed in a favorable manner so that a rupture or tear of the honeycomb body is prevented.

<b>Fig.</b> 10 shows a further embodiment of the inven dung, in which a ver with cavities in the cell walls overlooked ceramic honeycomb according to the Off leadership example in accordance <b>Fig.</b> 8 and 9 on the side in which the cavities are closed with a porous ceramic body <b>14</b> is provided. While using This porous ceramic structure as a gas-permeable Heat insulator is, the honeycomb body or the Wabenkörper- Assembly on the upstream side or high tempera arranged turseite, and the porous ceramic body <b>14</b> is located on the downstream side, the a has lower temperature. In this case, too be the caused by temperature differences thermal stresses due to the voids in the Cell walls of the honeycomb body is reduced. Through the above described two-layer structure is furthermore the direct transfer of thermal stresses of the honeycomb body to the downstream ceramic avoided body so that the thermal stresses ver be reduced, to a fraction of the porous ceramic could lead body.

For the porous ceramic body <b>14</b> can continue above foam-like or needle-like ceramic material used.