METHOD FOR PRODUCING A POROUS SINTERED MAGNESIA, BACKFILL FOR PRODUCING A HEAVY-CLAY REFRACTORY PRODUCT WITH A GRANULATION FROM THE SINTERED MAGNESIA, PRODUCT OF THIS TYPE, AND METHOD FOR THE PRODUCTION THEREOF, LINING OF AN INDUSTRIAL FURNACE AND INDUSTRIAL FURNACE

Abstract

A method for producing a granular material from sintered magnesia by sintering of pressed articles, in particular pellets, from MgO powder, preferably from caustic MgO powder, and subsequent mechanical comminution of the pressed articles, the sintering being carried out in such a way that the granular material has a grain porosity (total porosity), according to DIN EN 993-1:1195-04 and DIN EN 993-18:1999-01, of from 15 to 38 vol %, preferably 20 to 38 vol %. Also, a batch for producing a coarse ceramic, refractory, shaped or unshaped product containing the porous sintered magnesia, to such a product produced from the batch and to a method for its production, to a lining, in particular a working casing and/or a backing, of a large-volume industrial furnace, the lining, in particular the working casing and/or the backing, having at least one such product, as well as to such an industrial furnace.

Claims

1. A method for producing a granular material of sintered magnesia, comprising: sintering of pressed articles, in particular pellets, of MgO meal, preferably caustic MgO meal, and subsequently mechanically comminuting the pressed articles to provide a granular material, wherein the sintering takes place in such a way that the granular material has a grain porosity (total porosity) according to DIN EN 993-1:1195-04 and DIN EN 993-18:1999-01 of 15 to 38 vol %, preferably 20 to 38 vol %.

2. The method according to claim 1, wherein the sintering takes place at a maximum temperature between 1100-1600 C., preferably between 1200-1600 C., more preferably between 1200-1550 C., particularly preferably between 1200-1500 C.

3. The method according to claim 1, wherein sintering takes place at a maximum temperature 1600 C., preferably 1550 C., more preferably 1500 C., particularly preferably 1400 C.

4. The method according to claim 1, wherein sintering takes place in such a way that the granular material has a grain bulk density, according to DIN EN 993-1:1195-04 and DIN EN 993-18:1999-01, of 2.20 to 2.85 g/cm.sup.3, preferably 2.20 to 2.75 g/cm.sup.3.

5. The method according to claim 1, wherein the pressed articles, in particular pellets, have a bulk density according to DIN 66133:1993-06 of 1.8 to 2.3 g/cm.sup.3, preferably 1.9 to 2.2 g/cm.sup.3.

6. The method according to claim 1, wherein the pressed articles have a porosity, according to DIN 66133:1993-06, of 32 to 52 vol %, preferably 35 to 45 vol %.

7. The method according to claim 1, wherein the MgO meal, preferably the caustic MgO meal, comprises at least 88 wt %, preferably at least 95 wt %, particularly preferably at least 97 wt % MgO, determined by x-ray fluorescence analysis according to DIN 12677:2013-02.

8. The method according to claim 1, wherein the MgO meal, preferably the caustic MgO meal, has a particle size distribution having at least one of following values, determined using laser granulometry according to DIN ISO 13320:2009: d.sub.90 between 80 and 100 m; d.sub.50 between 5 and 15 m; or d.sub.10 between 1 and 3 m.

9. The method according to claim 1, wherein the pressed articles consist, relative to their dry mass, of at least 96 wt %, preferably of 100 wt %, of MgO meal, preferably of caustic MgO meal, and/or wherein the pressed articles contain no magnesite meal.

10. The method according to claim 1, wherein the granular material made of sintered magnesia is produced without the use of burnout materials.

11. The method according to claim 1, wherein the sintering takes place in such a way that the granular material made of sintered magnesia has an average pore diameter d.sub.50 of 0.1 to 10 m, preferably 2 to 8 m, determined according to DIN 66133:1993-06.

12. The method according to claim 1, wherein the granular material made of sintered magnesia has a grain compression strength, based on DIN 13055-2016-11 (10 mm instead of 20 mm), of 10 to 30 MPa, preferably 11 to 25 MPa.

13. (canceled)

14. The method according to claim 1, wherein a temperature regime of the sintering is set in such a way that the granular material has at least one desired property.

15. A batch for producing a coarse ceramic, refractory, shaped or unshaped product, in particular a product for a working casing or a backing of an industrial furnace, preferably of a cement kiln installation, a lime brick shaft or lime rotary kiln, a magnesite kiln or dolomite kiln, or of a heating kiln or of a kiln for energy production or of a kiln for steel production or of a kiln of the nonferrous metal industry, the batch comprising: at least one granular material made of sintered magnesia, produced according to the method according to claim 1.

16. The batch according to claim 15, comprising a dry material mixture having or consisting of: a) at least one coarse granular material made of the sintered magnesia produced according to the method according to claim 1 and having a grain size >200 m, preferably in a total quantity of sintered magnesia produced according to the method according to claim 1 invention of 10 to 90 wt %, preferably 20 to 80 wt %, b) at least one powdered granular material made of magnesia, e.g. the sintered magnesia produced according to the method according to claim 1, having a grain size 200 m, preferably in a quantity of 90 to 10 wt %, preferably 80 to 20 wt %, c) preferably at least one further granular material made of a refractory material, preferably in a total quantity of further granular material of 0.5 to 40 wt %, preferably 3 to 30 wt %, d) if applicable, at least one additive for refractory materials, preferably in a total quantity of additive <5 wt %, e) if applicable, at least one admixture for refractory materials, preferably in a total quantity of <5 wt %, as well as, additive to the dry material mixture, at least one liquid or solid binder for refractory materials, preferably in a total quantity of from 1 to 9 wt %, preferably 2.5 to 6 wt %, relative to the total dry mass of the dry material mixture.

17. The batch according to claim 16, wherein the batch consists of at least 90 wt %, preferably of at least 99 wt %, particularly preferably of 100 wt %, of binder and the dry material mixture, relative to the total mass of the batch.

18. The batch according to claim 16, wherein the dry material mixture comprises 50 wt %, preferably 60 wt %, particularly preferably 70 wt %, of the coarse granular material made of the sintered magnesia.

19. The batch according to claim 16, wherein the coarse granular material made of the sintered magnesia has a maximum grain size 8 mm, preferably 6 mm, particularly preferably 4 mm.

20. (canceled)

21. The batch according to claim 16, wherein the dry material mixture further comprises a further granular material, and wherein the further granulated material is selected from the group consisting of: magnesium aluminate spinel, bauxite, alumina, hercynite, pleonaste, chromium ore, pleonastic spinel, zirconium oxide, olivine, and/or forsterite.

22. The batch according to claim 16, wherein the dry material mixture further comprises a further granular material having a minimum grain size >0 mm, and a maximum grain size 8 mm, preferably 6 mm, particularly preferably 4 mm.

23. The batch according to claim 16, wherein the dry material mixture further comprises a further granular material and wherein a grain distribution of the further granular material is steady.

24. (canceled)

25. A coarse ceramic, refractory, shaped or unshaped product, in particular for a working casing of an industrial furnace, preferably of a cement kiln installation, a lime shaft kiln or a lime rotary kiln, a magnesite or dolomite kiln, or of a heating kiln or of a kiln for energy production or of a kiln for steel production or of a kiln of the nonferrous metal industry, the product comprising: at least one granular material made of sintered magnesia, produced according to the method according to claim 1.

26. A coarse ceramic, refractory, shaped or unshaped product, in particular for a working casing of an industrial furnace, preferably of a cement kiln installation, a lime shaft kiln or lime rotary kiln, a magnesite or dolomite kiln, or of a heating kiln or of a kiln for energy production or of a kiln for steel production or of a kiln of the nonferrous metal industry, wherein the product is produced from a batch according to claim 15.

27. The product according to claim 25, wherein the product comprises a green, shaped, in particular pressed, body, preferably a brick.

28. The product according to claim 25, wherein the product comprises a tempered shaped body, preferably a brick.

29. The product according to claim 25, wherein the product comprises a fired shaped body, preferably a brick.

30. The product according to claim 29, wherein the fired shaped body has a thermal conductivity according to the hot-wire (parallel) method according to DIN 993-15:2005-14 of 4.0 to 6.0 W/mK, preferably 4.5 to 5.8 W/mK, at 300 C., 3.0 to 5.0 W/mK, preferably 3.0 to 4.8 W/mK, at 700 C. and 2.0 to 3.5 W/mK, preferably 2.0 to 3.2 W/mK, at 1000 C.

31. The product according to claim 29, wherein the fired shaped body comprises an open porosity of 22 to 45 vol %, preferably 23 to 35 vol %, determined according to DIN 993-1:1995-4.

32. The product according to claim 29, wherein the fired shaped body has an average value of the pore diameter distribution d.sub.50, determined according to DIN 66133:1993-06, of 0.5 to 10 m, preferably 2 to 10 m.

33. The product according to claim 29, wherein the fired shaped body has a bulk density of 1.9 to 2.9 g/cm.sup.3, in particular 2.0 to 2.8 g/cm.sup.3, determined according to DIN 993-1:1995-04.

34. The product according to claim 29, wherein the fired shaped body has a cold compression strength according to DIN EN 993-5:1998-12 of 30 to 100 MPa, in particular 45 to 90 MPa.

35. The product according to claim 29, wherein the fired shaped body has a cold bending strength according to DIN EN 993-6:1995-04 of from 2 to 18 MPa, in particular 3 to 10 MPa.

36. The product according to claim 29, wherein the fired shaped body has a gas permeability according to DIN EN 993-4:1995-04 of from 0.2 to 8 nPm, in particular 0.5 to 6 nPm.

37. (canceled)

38. A method for producing a coarse ceramic, refractory, shaped product, in particular for a working casing of an industrial furnace, preferably of a cement kiln installation, a lime shaft kiln or lime rotary kiln, a magnesite or dolomite kiln, or of a heating kiln or of a kiln for energy production or of a kiln for steel production or of a kiln of the nonferrous metal industry from a batch according to claim 16, the method comprising the steps of: a) mixing the dry material mixture with the at least one binder, water or both to form a plastic mass, and, b) shaping, preferably pressing, of the plastic mass to form a green shaped body, c) preferably drying of the green shaped body, d) preferably tempering or firing of the green shaped body.

39. The method according to claim 38, wherein the shaped body is fired at a temperature of 1200 to 1800 C., preferably 1400 to 1700 C.

40. (canceled)

41. A lining of a large-volume industrial furnace, preferably of a burning kiln of the non-metallic industry, preferably of a cement kiln installation, a lime shaft kiln or lime rotary kiln, a magnesite kiln or dolomite kiln, or of a heating kiln or of a kiln for energy production or of a kiln for steel production or of a kiln of the nonferrous metal industry, wherein the lining comprises at least one product according to claim 25.

42. The lining according to claim 41, wherein the lining has a working casing that comprises the at least one product.

43. The lining according to claim 42, wherein the working casing is installed in a one-layer or a multilayer masonry structure.

44. The lining according to claim 41, wherein the lining has an insulating backing that comprises the at least one product.

45. A large-volume industrial furnace, preferably a burning kiln of the non-metallic industry, preferably a cement kiln installation, a lime shaft kiln or lime rotary kiln, a magnesite or dolomite kiln, or a heating kiln or a kiln for energy production or a kiln for steel production or a kiln of the nonferrous metal industry, wherein the industrial furnace has a lining according to claim 41.

Description

DESCRIPTION OF THE DRAWINGS

[0020] In the following, the present invention is explained in exemplary fashion on the basis of a drawing.

[0021] FIG. 1 shows, as an example, a pore diameter distribution of a granular material according to the present invention made of porous sintered magnesia;

[0022] FIG. 2 shows, as an example, a pore diameter distribution of a shaped brick according to the present invention;

[0023] FIG. 3 shows a light microscopic image (reflected light) of a sintered magnesia according to the present invention, sintered in an HT kiln at 1530 C., firing duration 6 h.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

[0024] In the context of the present invention, it has been surprisingly discovered that by sintering of pressed articles, in particular pellets, from MgO meal, preferably caustic MgO meal, at a reduced maximum temperature (instead of the standard temperatures of >1700 C.), and subsequent mechanical comminution of the pressed articles, a sintered magnesia can be produced that has a grain porosity (total porosity) according to DIN EN 993-1:1195-04 and DIN EN 993-18:1999-01 of 15 to 38 vol %, preferably 20 to 38 vol %.

[0025] The MgO meal can also be made up for example of dead-burned magnesia (DBM) or fused magnesia. However, it is preferably caustic MgO meal.

[0026] And, using this granular, porous sintered magnesia, refractory products can be produced having typical mechanical and chemical properties, having higher porosity and therefore lower thermal conductivity compared to the products previously used, but nonetheless having low tendency to infiltration.

[0027] In particular, in the context of the present invention it has been discovered that, it is possible, without the addition of burnout materials, solely through a reduced maximum firing temperature instead of the standard temperatures >1700 C., to produce a granular material made of sintered magnesia from the pressed articles made of MgO meal grains, preferably caustic MgO particles, having, compared to known sintered magnesia and fused magnesia, a significantly lower grain bulk density and significantly higher porosity, in turn resulting in the improved properties of the products produced therefrom.

[0028] The firing duration and the sintering temperatures, i.e. the temperature curve or temperature regime or temperature profile, of the sintering, or of the sintering process, are also set according to the present invention in such a way that the granular material according to the present invention made of porous sintered magnesia has a grain porosity (total porosity) according to DIN 993-18:2002-11 and DIN 993-1:1995-4 of 15 to 38 vol %, preferably 20 to 38 vol %, and preferably has a grain bulk density according to DIN 993-18:2002-11 of 2.20 to 2.85 g/cm.sup.3, preferably 2.20 to 2.75 g/cm.sup.3. Thereby, for example, the temperature regime depends on the type of magnesia (its reactivity) and the particle size of the MgO meal.

[0029] Preferably, the sintering takes place at a maximum temperature 1600 C., preferably 1550 C., more preferably 1500 C., particularly preferably 1400 C.

[0030] That is, the sintering preferably takes place at a maximum temperature of between 1100-1600 C., preferably between 1200-1600 C., more preferably between 1200-1550 C., particularly preferably between 1200-1500 C.

[0031] The firing duration at the maximum temperature for the production of the sintered magnesia according to the present invention is preferably from 0.5 h to 7 h, preferably 2 h to 6 h. The total firing duration preferably corresponds to that of the standard production of sintered magnesia.

[0032] The firing preferably takes place in an oxidizing atmosphere, but can also take place in a reducing atmosphere. After the firing, the sintered magnesia is mechanically comminuted, in particular broken, and is classified by sieving.

[0033] The used mealy MgO causter or caustic MgO meal is preferably produced in the standard manner from magnesium hydroxide or from magnesium carbonate.

[0034] In addition, the MgO meal, preferably the caustic MgO meal, that is used preferably has a particle size distribution having the following values:

[0035] d.sub.90 between 80 and 100 m and/or d.sub.50 between 5 and 15 m and/or d.sub.10 between 1 and 3 m. As is known, the d.sub.x value means that x wt % of the particles are smaller than the indicated value. It is determined by laser granulometry according to DIN ISO 13320:2009. For this purpose, the MgO meal is dispersed in ethanol using ultrasound.

[0036] In addition, the used MgO meal, preferably the used caustic MgO meal preferably contains at least 88 wt %, preferably at least 95 wt %, MgO, particularly preferably at least 97 wt % MgO, determined using X-ray fluorescence analysis (XRF) according to DIN 12677:2013-02. In addition, the used MgO meal, preferably the used caustic MgO meal, preferably contains a maximum of 4 wt %, preferably a maximum of 2 wt %, CaO, determined using X-ray fluorescence analysis (XRF) according to DIN 12677:2013-02.

[0037] The MgO meal, preferably the caustic MgO meal, is in addition pressed in a standard press, preferably a pelleting press or briquetting press or hydraulic press, in such a way that the pressed articles have a bulk density, according to DIN 66133:1993-06, of 1.8 to 2.3 g/cm.sup.3, preferably 1.9 to 2.2 g/cm.sup.3, and/or a porosity, according to DIN 66133:1993-06, of 32 to 52 vol %, preferably 35 to 45 vol %. The pressed articles are preferably pellets. However, they can also advantageously be briquettes or bricks.

[0038] Thereby preferably, exclusively the MgO meal, preferably the caustic MgO meal, is pressed, if applicable with the addition of some water, i.e. without a binder and thus without any burnout materials.

[0039] The pressed articles thus consist, with regard to their dry mass, preferably of at least 96 wt %, more preferably of at least 98 wt %, particularly preferably of 100 wt %, of MgO meal, preferably of caustic MgO meal.

[0040] In particular, the pressed articles do not contain any magnesite meal.

[0041] As explained above, the firing duration and the sintering temperatures are set such that the granular material according to the present invention made of porous sintered magnesia has a grain porosity (total porosity) according to DIN 993-18:2002-11 and DIN 993-1:1995-4 of 15 to 38 vol %, preferably 20 to 38 vol %, and preferably has a grain bulk density according to DIN 993-18:2002-11 of 2.20 to 2.85 g/cm.sup.3, preferably 2.20 to 2.75 g/cm.sup.3. This also holds for the other properties of the granular material.

[0042] In particular, the granular material according to the present invention made of porous sintered magnesia preferably has a small average pore diameter d.sub.50 of 0.1 to 10 m, preferably of 2 to 8 m, determined in accordance with DIN 66133:1993-06. Thereby the pore diameter distribution can be monomodal (see FIG. 1).

[0043] FIG. 3 shows the microstructure of the sintered magnesia according to the present invention. It has a homogenous distribution of magnesia particles 1 and small pores 2. No larger pores are visible. The brighter pores 2 are pores filled with epoxy resin, the somewhat darker pores 2 are unfilled.

[0044] The granular material according to the present invention made of porous sintered magnesia additionally has a grain compression strength, based on DIN 13055:2016-11 (10 mm instead of 20 mm) of 10 to 30 MPa, preferably 11 to 25 MPa.

[0045] The granular material made of porous sintered magnesia according to the present invention in addition preferably has the following thermal conductivity values (TC), in accordance with DIN EN 821-2:1997-08:

TABLE-US-00001 TABLE 1 Preferred thermal conductivity values of the sintered magnesia according to the present invention TC preferably 400 C. [W/mK] 3 to 9 4 to 8 800 C. [W/mK] 2 to 7 3 to 6 1200 C. [W/mK] 2 to 7 3 to 6

[0046] The granular material according to the present invention is distinguished in particular by the following properties:

TABLE-US-00002 TABLE 2 Properties of porous sintered magnesia according to the present invention and of dense sintered magnesia Sintered magnesia according to the Conventional dense present invention sintered magnesia Grain bulk density [g/cm.sup.3] .sup.2.20-2.85 .sup.3.15-3.46 Grain porosity [vol %] .sup.11-40 4-10 MgO [wt %] .sup.88->99 .sup.88->99 Al.sub.2O.sub.3 [wt %] <1 <1 Fe.sub.2O.sub.3 [wt %] 0.1-8 0.1-8 CaO [wt %] 0.3-8 0.3-8 SiO.sub.2 [wt %] 0.2-5 0.2-5 TC 400 C. [W/mK] 5.84 (9) 13.29 (>9) 800 C. [W/mK] 3.71 (7) 8.33 (>7) 1200 C. [W/mK] 3.41 (7) 7.22 (>7)

[0047] As explained above, the sintered magnesia according to the present invention is used in batches according to the present invention for the production of shaped or unshaped refractory products according to the present invention.

[0048] A batch according to the present invention comprises a dry material mixture containing the sintered magnesia, and binder. That is, the quantity of binder (dry or liquid) is additively added, and relates to the total dry mass of the dry material mixture. If applicable, another liquid additive, also added additively, and also relating to the total dry mass of the dry material mixture, can be contained. Preferably, the batch consists of at least 90 wt %, more preferably of at least 99 wt %, particularly preferably of 100 wt %, of binder and the dry material mixture, relative to the total mass of the batch.

[0049] The dry material mixture preferably comprises the following components, related in each case to the total dry mass of the dry material mixture (the quantity indications indicate in each case the total sum of the respective components, i.e. for example the total amount of coarse granular material of sintered magnesia according to the present invention, the total amount of powdered granular material, or of further granular material): [0050] a) at least one coarse granular material made of the sintered magnesia according to the present invention having a grain size >200 m, preferably in a quantity of 10 to 90 wt %, more preferably of 20 to 80 wt % [0051] b) at least one powdered granular material made of magnesia, e.g. of the sintered magnesia according to the present invention, having a grain size <200 m, preferably in a quantity of 90 to 10 wt %, more preferably of 80 to 20 wt % [0052] c) if applicable, at least one further granular material made of a refractory material, preferably in a total quantity of additional granular material of 0.5 to 40 wt %, preferably of 3 to 30 wt % [0053] d) if applicable, at least one additive for refractory materials, preferably in a total quantity <5 wt % [0054] e) if applicable, at least one admixture for refractory materials, preferably in a total quantity of 5 wt %.

[0055] The components can be contained in any combination in the dry material mixture.

[0056] In addition, as already explained, the batch according to the present invention contains, additively to the dry material mixture, at least one liquid or solid binder for refractory materials, preferably in a total quantity of 1 to 9 wt %, preferably 2.5 to 6 wt %, relative to the dry total mass of the dry material mixture.

[0057] In the case of unshaped products, the liquid binder is preferably packed in a container separate from the dry components of the batch.

[0058] In addition, the coarse granular material made of the sintered magnesia according to the present invention preferably has a grain size of up to a maximum of 8 mm, more preferably up to a maximum of 6 mm, particularly preferably up to a maximum of 4 mm.

[0059] The grain distribution of the coarse granular material made of the sintered magnesia according to the present invention and/or of the dry material mixture according to the present invention, is preferably steady, preferably in accordance with a Litzow, Furnas, or Fuller curve, or has a Gaussian distribution.

[0060] The further granular material is preferably made up of an elastifying raw material, i.e. a raw material that is typically used to lower the modulus of elasticity.

[0061] Preferably, the further granular material consists of a raw material from the following group: Magnesium aluminate spinel, bauxite, alumina, hercynite, pleonaste, chromium ore, pleonastic spinel, zirconium oxide, olivine, and/or forsterite.

[0062] The present invention succeeds quite particularly effectively with a dry material mixture of the following materials: [0063] magnesia [0064] magnesia with magnesium aluminate spinel [0065] magnesia with hercynite [0066] magnesia with forsterite [0067] magnesia with pleonaste or pleonastic spinel [0068] magnesia with chromium ore [0069] magnesia with zirconium oxide.

[0070] As explained, combinations of various further granular materials are also possible, preferably a combination of a further granular material of hercynite with a further granular material of magnesium aluminate spinel.

[0071] In addition, the further granular material preferably has a maximum grain size of 8 mm, more preferably 6 mm, particularly preferably 4 mm.

[0072] The dry binder is a binder suitable for refractory products. These binders are indicated for example in the Practical Handbook, page 28/point 3.2.

[0073] Preferably, the liquid binder is a binder from the following group: thermally curing synthetic resin binder, in particular phenol formaldehyde resin, or molasses or lignin sulfonate or a sulfur-free binder, in particular a binder based on dextrose, an organic acid, saccharose, an Al.sub.2O.sub.3 binder, phosphoric acid, a phosphate binder, water glass, ethyl silicate, or a sulfate, e.g. magnesium sulfate or aluminum sulfate, or a sol-gel system.

[0074] The dry additive is an additive suitable for refractory products. These additives are indicated for example in the Practical Handbook, page 28/point 3.3. They are used to improve processability or deformability, or to modify the microstructure of the products and in this way to achieve particular properties.

[0075] As already explained, the batch according to the present invention is used to produce refractory shaped or unshaped products according to the present invention.

[0076] For the production of shaped products, in particular bricks, a mixture or plastic mass is produced from the dry material mixture of the batch according to the present invention, with at least one liquid and/or solid binder and/or water. If the batch contains a liquid binder, the addition of water is not necessary, but is possible.

[0077] For the optimal distribution of the binder or binders, and/or of the water, mixing takes place for e.g. 3 to 10 minutes.

[0078] The mixture is poured into molds and is pressed so that shaped bodies are formed. The molding pressures are within standard ranges, e.g. 60-180 MPa, preferably 100-150 MPa.

[0079] Preferably, after pressing a drying is carried out, e.g. at between 60 and 200 C., in particular between 90 and 140 C. The drying preferably takes place until there is a residual moisture between 0.1 and 0.6 wt %, in particular between 0.2 and 0.5 wt %, determined according to DIN 51078:2002-12.

[0080] Thus, in context of the present invention it has turned out that the production of shaped bodies is possible using standard molding pressures in order to achieve the named porosities with the corresponding mechanical and thermal properties. Apparently, the porosity of the sintered magnesia according to the present invention, used in particular in standard granulations in accordance with the Fuller or Litzow grain distribution of the material mixtures, in the overall granular material mixture ensures that, in particular during pressing, the pore volume according to the present invention can form without the grains having to form a support framework in the microstructure as described in DE 10 2013 020 732 A1.

[0081] The shaped bodies according to the present invention, in particular the bricks, can be used in unfired form or in tempered form or in fired form. Preferably, however, they are used in fired form.

[0082] The green pressed bricks are tempered in a ceramic burning kiln, e.g. a tunnel kiln, at between 400 and 100 C., in particular between 500 and 800 C.

[0083] For the firing, the preferably dried pressed bricks are ceramically fired in a ceramic burning kiln, e.g. a tunnel kiln, preferably at between 1200 and 1800 C., in particular between 1400 and 1700 C. Preferably, firing is done in oxidizing fashion, but, depending on the material composition, a reducing firing may also be advantageous.

[0084] The thermal conductivity, according to the hot-wire (parallel) method according to DIN 993-15:2005-14, of the fired shaped products according to the present invention, in particular the bricks, is preferably 4.0 to 6.0 W/mK, more preferably 4.5 to 5.8 W/mK, at 300 C., 3.0 to 5.0 W/mK, more preferably 3.0 to 4.8 W/mK, at 700 C. and 2.0 to 3.5 W/mK, more preferably 2.0 to 3.2 W/mK, at 1000 C.

[0085] The fired, shaped products, in particular the bricks, preferably have a high open porosity of 22 to 45 vol %, more preferably 23 to 35 vol %, determined according to DIN EN 993-1:1995-04.

[0086] In addition, they preferably have a mean value d.sub.50 of the pore size distribution (diameter), determined according to DIN 66133:1993-06, of 0.5 to 10 m, preferably 2 to 8 m.

[0087] In addition, the fired, shaped products, in particular the bricks, preferably have a low bulk density of 1.9 to 2.9 g/cm.sup.3, in particular 2.0 to 2.8 g/cm.sup.3, determined according to DIN 993-1:1995-04.

[0088] The cold compression strength according to DIN EN 993-5:1998-12 of the fired shaped products according to the present invention, in particular the bricks, is preferably 30 and 100 MPa, in particular 45 and 90 MPa. The cold bending strength according to DIN EN 993-6:1995-04 of the fired shaped products according to the present invention, in particular the bricks, is preferably 2 to 18 MPa, in particular 3 to 10 MPa.

[0089] The gas permeability according to DIN EN 993-4:1995-04 of the fired shaped products according to the present invention, in particular the bricks, is preferably 0.2 to 8 nPm, in particular 0.5 to 6 nPm.

[0090] The resistance to thermal shock, determined according to DIN EN 993-11:2008-03, in air at an elevated testing temperature of 1100 C. of the fired shaped products according to the present invention, in particular the bricks, is preferably >20 quenching cycles, in particular >30 quenching cycles.

[0091] For the production of unshaped products, in particular masses, preferably injection masses or vibration masses or casting masses or stoker masses, a mixture is likewise produced from the dry material mixture according to the present invention, with at least one dry and/or liquid binder and/or water. If the batch contains a liquid binder, the addition of water is not necessary, but is possible.

[0092] In sum, the present invention provides refractory products that are highly porous but are outstandingly suitable for use as working casings and also as backings, with regard to thermal conductivity and pore size, and thus gas permeability. Particularly advantageous is the low average pore diameter d.sub.50 of the sintered magnesia according to the present invention, which is preferably 2-8 m and which is also present in the produced product alongside the average pore diameter d.sub.50 of the matrix of approximately 4 m (see FIG. 2).

[0093] The shaped, in particular pressed, or unshaped coarse ceramic refractory products according to the present invention can be used as working casings in a fired industrial furnace aggregate despite their high porosity, because they have the required mechanical, thermomechanical, and thermochemical working casing properties.

[0094] The use of fine particulate material, approximately 50-90 wt % with d.sub.90<100 m, is not necessary, rather, granulations of up to 8 mm, which are standard in refractory technology, may be used. In this way, the production effort for providing the granular material is reduced, in particular the grinding comminution energy.

[0095] In addition, CO.sub.2 emissions are reduced due to the lower firing temperature of the sintered magnesia according to the present invention. According to the present invention, the addition of burnout materials, which is very complex, to integrate the burnout materials into the batch in homogenous fashion, and which also increases environmental impact due to CO.sub.2 emissions, can be omitted.

[0096] In addition, the savings of material and weight for a volume to be lined is to be considered a positive factor.

[0097] Up to now, the reduction of the thermal conductivity of refractory linings was usually brought about through multilayer casing configurations made of working layers and insulating layers. Particularly in moving aggregates, such as cement rotary kilns, multilayer linings are mechanically very sensitive, or susceptible to breakage. Moreover, their installation is complicated. In order to avoid uncertainty during operation resulting from so-called intermediate layer casings, the installation of working casings not having an insulating layer is therefore not unusual. However, this is associated with higher temperatures, which stress the material of an aggregate cladding, and higher heat losses. A working casing according to the present invention can be used with outstanding results even without an intermediate layer, in particular due to its low thermal conductivity.

[0098] On the basis of the following examples, the superiority of coarse ceramic products according to the present invention, compared to products according to the closest existing prior art according to DE 10 2013 020732 A1 and compared to known dense products, is illustrated.

Production of the Sintered Magnesia According to the Present Invention for Examples 1 to 3:

[0099] The production of the granular material made of the porous sintered magnesia was done as follows:

[0100] A filter cake obtained from a Mg(OH).sub.2 suspension using a vacuum press, having a solids amount >50%, was dried in a kiln and subsequently calcinated at 1100 C. and comminuted, so that a caustic magnesia was obtained from the Mg(OH).sub.2, whose typical particle size distribution d.sub.50 was =10 m.

[0101] Using a pelleting press, the caustic magnesia was pressed to form almond-shaped pellets having dimensions of 132030 mm.sup.3. These green pellets had a grain bulk density of 2.0 g/cm.sup.3.

[0102] These pellets were sintered in a high-temperature laboratory kiln with a temperature profile in which the temperature was increased by 2 K/min until 800 C. was reached. After a holding time of 6 h, the temperature was further increased by 2 K/min to 1450 C. The holding time at this temperature was 5 h. Cooling took place continuously through heat dissipation from the high-temperature laboratory kiln to the surrounding environment.

[0103] Subsequently, the porous sintered magnesia was broken up and classified by sieving. The granular material according to the present invention made of the porous sintered magnesia had a grain bulk density of 2.59 g/cm.sup.3. The corresponding open porosity was 25.8 vol % (DIN EN 993-18:2002-11; DIN EN 993-1:1195-04).

Example 1

[0104] In Example 1, bricks were produced based on the same materials and the same mineralogical composition (84 wt % magnesia, 16 wt % sintered spinel, magnesia meal made of dense sintered magnesia):

TABLE-US-00003 TABLE 3 Composition of the batches for Example 1 Bricks Bricks Bricks a) b) c) Sintered magnesia according to the present 54 invention [wt %], 0-4 mm Dense sintered magnesia [wt %], 0-4 mm 54 10 Dense sintered magnesia [wt %], 0.1-0.5 mm 32 Sintered spinel [wt %], 0-4 mm 16 16 16 Magnesia meal, 200 m 30 30 42 Binder lignin sulfonate [wt %, relative to 3.7 3.7 6 dry mass] Compression [MPa] 130 130 40 Firing temperature [ C.] 1600 1600 1600

[0105] The used raw materials had the following properties:

TABLE-US-00004 TABLE 4 Properties of the sintered magnesia according to the present invention Sintered magnesia according to the present invention Grain bulk density according to 2.59 g/cm.sup.3 DIN 993-1: 1995-04, 993-18: 2002-11 Grain porosity according to 25.8 vol % DIN 993-1: 1995-04, 993-18: 2002-11

TABLE-US-00005 TABLE 5 Properties of the dense sintered magnesia for bricks b) and c) Dense sintered magnesia Grain bulk density according to 3.41 g/cm.sup.3 DIN 993-1: 1995-04, 993-18: 2002-11 Grain porosity according to 1 Vol.-% DIN 993-1: 1995-04, 993-18: 2002-11

TABLE-US-00006 TABLE 6 Properties of the sintered spinel for bricks a), b) and c) Sintered spinel Grain bulk density according to 3.37 g/cm.sup.3 DIN 993-1: 1995-04, 993-18: 2002-11 Grain porosity according to 2 vol %.sup.5 DIN 993-1: 1995-04, 993-18: 2002-11

[0106] The production of the bricks a)-c) took place in each case as follows:

[0107] The corresponding raw materials according to Table 3, having a grain size distribution according to Fuller, were mixed dry in a mixer for 3 minutes, provided with the liquid binder, and further mixed for 5 minutes. The mixture was brought to a hydraulic press and was pressed in a B format for rotary kiln bricks, with a molding pressure as shown in Table 3. The bricks were dried in a dryer at approximately 130 C. and were subsequently fired in oxidizing fashion at 1600 C. in a tunnel kiln for 50 hours. The holding time at the maximum temperature was 5 h. The firing shrinkage was determined by measuring, the final bulk density was determined by measuring and weighing, the porosity was determined according to DIN EN 993-1:1995-04, the cold compression strength was determined according to DIN EN 993-5:1998-12, the cold bending strength was determined according to DIN EN 993-6:1995-04, the gas permeability was determined according to DIN EN 993-4:1995-04, and the thermal conductivity was determined according to the hot-wire (parallel) method DIN 993-15:2005-14. The resistance to thermal shock was determined according to DIN EN 993-11:2008-03 in air at an elevated test temperature of 1100 C.:

TABLE-US-00007 TABLE 7 Properties of the fired bricks of Example 1 Bricks Bricks Bricks a) b) c) Bulk density [g/cm.sup.3] 2.68 2.95 2.63 Porosity [vol %] 24.1 16.0 25.2 Cold compression strength [MPa] 88 70 80 Cold bending strength [MPa] 5.98 5.6 6.0 Gas permeability [nPm] 0.85 1.6 1.2 Firing shrinkage [%] 1.18 0.30 0.60 Pore diameter d.sub.50 [m] 3.8 14.2 10.4 TSR [cycles] >30 >30 >30 TC 300 C. [W/mK] 5.4 6.7 5.5 700 C. [W/mK] 3.5 5.1 3.6 1000 C. [W/mK] 2.6 4.0 2.8

[0108] Compared to the conventional dense bricks according to b), the brick properties change in the case of a) and also of c), where the bricks have a significantly higher porosity and a significantly reduced bulk density, without having a negative influence on the other brick properties. In particular, the gas permeability and the pore diameter are reduced in the bricks according to the present invention.

[0109] In the case of a) according to the present invention, in which the granular material is made up of porous magnesia according to the present invention, the reduction of the bulk density and the increase in the open porosity are considerable compared to b).

[0110] In addition, the average pore diameter d.sub.50 is dramatically reduced in comparison with b) and c), so that there is a reduced tendency to infiltration by alkalis and clinker melts. In comparison with b), the cold compression strength and cold bending strength continue to be reliably in the range typical for dense bricks. The resistance to thermal shock is, at >30 quench cycles, at the same required high level without breakage for all brick types.

[0111] In addition, for bricks according to the present invention according to a), the results show significantly reduced thermal conductivity values compared to the dense magnesia spinel bricks b).

Example 2

[0112] For Example 2, bricks d), a porous spinel was used instead of the sintered spinel of Example 1:

TABLE-US-00008 TABLE 8 Composition of the batches for Example 2 Bricks Bricks Bricks a) b) d) Magnesia according to the present 54 54 invention [wt %], 0-4 mm Dense sintered magnesia [wt %], 54 0-4 mm Sintered spinel [wt %], 0-4 mm 16 16 Porous sintered spinel, 0-4 mm 16 Magnesia meal 200 m 30 30 30 Binder lignin sulfonate [wt %, 3.7 3.7 3.7 relative to dry mass] Compression [MPa] 130 130 40 Firing temperature [ C.] 1600 1600 1600

[0113] The properties of the magnesia according to the present invention for d) correspond to those of Example 1.

TABLE-US-00009 TABLE 9 Properties of the porous sintered spinel for bricks d) Porous sintered spinel Grain bulk density according to 2.66 g/cm.sup.3 DIN 993-1: 1995-04, 993-18: 2002-11 Grain porosity according to 25 vol % DIN 993-1: 1995-04, 993-18: 2002-11

[0114] The bricks d) were produced and tested analogously to Example 1:

TABLE-US-00010 TABLE 10 Properties of the fired bricks of Example 2 Bricks Bricks Bricks a) b) d) Bulk density [g/cm.sup.3] 2.68 2.95 2.64 Porosity [vol %] 24.1 16.0 25.2 Cold compression strength [MPa] 88 70 85 Cold bending strength [MPa] 5.98 5.6 6.4 Gas permeability [nPm] 0.85 1.6 0.92 Firing shrinkage [%] 1.18 0.30 1.2 Pore diameter d.sub.50 [m] 3.8 14.2 4.2 TSR [cycles] >30 >30 >30 TC 300 C. [W/mK] 5.4 6.7 5.2 700 C. [W/mK] 3.5 5.1 3.3 1000 C. [W/mK] 2.6 4.0 2.4

[0115] Compared to the bricks of Example 1, here the brick properties differ only slightly due to the use of porous magnesia and porous spinel, but a further reduced thermal conductivity can be seen. All other positive mechanical and thermal properties are maintained.

Example 3

[0116] In the first Examples 1 and 2, the advantages of the porous sintered magnesia according to the present invention for magnesia spinel bricks were explained. In order to demonstrate the effectiveness of the present invention in products made of other refractory materials, in Example 3 bricks based on sintered magnesia in combination with fused pleonaste (pleonastic fused spinel) were examined. Bricks e) were based on sintered magnesia according to the present invention, and bricks f), provided for comparison, were based on dense sintered magnesia. The production took place as in Example 1, at a firing temperature of 1450 C.:

TABLE-US-00011 TABLE 11 Composition of the batches for Example 3 Steine e) Steine f) Magnesia according to the present 54 invention [wt %], 0-4 mm Dense sintered magnesia [wt %], 0-4 mm 54 Fused pleonaste [wt %], 0-4 mm 16 16 Magnesia meal 200 m 30 30 Binder lignin sulfonate [wt %, 3.7 3.7 relative to dry mass] Compression [MPa] 130 130 Firing temperature [ C.] 1450 1450

TABLE-US-00012 TABLE 12 Properties of the fused pleonaste for bricks e) and f) Fused pleonaste Grain bulk density according to 3.74 g/cm.sup.3 DIN 993-1: 1995-04, 993-18: 2002-11 Grain porosity according to 2 vol % DIN 993-1: 1995-04, 993-18: 2002-11

[0117] The following table shows the results of Example 3:

TABLE-US-00013 TABLE 13 Properties of the fired bricks of Example 3 Steine e) Steine f) Bulk density [g/cm.sup.3] 2.66 3.00 Porosity [vol %] 24.8 15.7 Cold compression strength [MPa] 98 100 Cold bending strength [MPa] 6.25 6.75 Gas permeability [nPm] 0.98 1.45 Firing shrinkage [%] 1.12 0.20 Pore diameter d.sub.50 [m] 4.8 14.6 TSR [cycles] >30 >30 TC 300 C. [W/mK] 5.3 6.9 700 C. [W/mK] 3.4 5.3 1000 C. [W/mK] 2.5 4.2

[0118] Table 4 shows that the porous sintered magnesia according to the present invention can also be used in magnesia pleonaste bricks, the porosity increases significantly due to the use of the sintered magnesia according to the present invention, and all positive mechanical and thermal properties are maintained.

[0119] While at least one exemplary embodiment has been presented in the foregoing detailed description of the invention, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment of the invention, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope of the invention as set forth in the appended claims and their legal equivalents.