HEAT-PERMEABLE TUBE CONTAINING COMPOSITE FIBER CERAMIC

Abstract

The present invention relates to a heat-permeable tube which has a double-walled construction. The material of the interior wall contains fiber composite ceramic. The material of the exterior wall contains metal. The present invention further relates to the use of this tube in a rotary tube furnace and the use of the rotary tube furnace for thermal treatment of materials. Furthermore, the invention relates to the use of a single-walled tube containing fiber composite ceramic as rotary tube.

Claims

1. A tube, comprising: an interior wall and an exterior wall, wherein an interior wall material comprises fiber composite ceramic, an exterior wall material comprises metal, and the tube wall has a heat transfer coefficient at 800 C. of >50 W/(m.sup.2.Math.K).

2. The tube according to claim 1, wherein fibers and/or matrix of the fiber composite ceramic comprise at least one oxide of an element selected from the group consisting of: Be, Mg, Ca, Sr, Ba, a rare earth element, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Fe, Co, Ni, Zn, B, Al, Ga, Si, Ge, Sn, Re, Ru, Os, Ir, and In.

3. The tube according to claim 1, wherein SiC/SiC, C/SiC, ZrO.sub.2/ZrO.sub.2, ZrO.sub.2/AI.sub.2O.sub.3, AI.sub.2O.sub.3/ZrO.sub.2, AI.sub.2O.sub.3/AI.sub.2O.sub.3 and/or mullite/mullite is used as the fiber composite ceramic.

4. The tube according to claim 1, wherein, at an internal tube diameter of from 100 to 500 mm, a wall thickness of the fiber composite ceramic ranges from 1 mm to 10 mm and a wall thickness of the metal ranges from 2 nm to 30 mm.

5. The tube according to claim 1, wherein, at an internal diameter of from 200 mm to 500 mm, a total wall thickness is from 2 mm to 100 mm, with a thickness of the interior wall being less than 90% of the total wall thickness.

6. The tube according to claim 1, further comprising: at least one other wall selected from the group consisting of a protective layer against abrasion, a damping layer, an electrical insulation layer, a sealing layer, a heating layer, and a hollow layer on the outside.

7-8. (canceled)

9. A rotary tube furnace, comprising the tube according to claim 1.

10. (canceled)

11. A method for calcinating an alkaline material, the method comprising: calcinating the alkaline material in the rotary tube furnace according to claim 9.

Description

DESCRIPTION OF THE FIGURES

[0097] FIG. 1 is a schematic depiction of an indirectly heated rotary tube furnace having three heating zones [3] in cross section viewed from the side. The axis of rotation is shown as a dash-dot line. The tube circumferences [1] to be sealed at the end face of the inner tube [2], which in this depiction is somewhat shorter than the outer tube [4], are indicated. The outer tube [4] has overflow weirs at the inlet and outlet in this illustrative figure; these are optional.

[0098] FIG. 2 shows the double-walled tube viewed from the end face. In this illustrative, schematic depiction which is not true to scale, the inner tube [5] is held in position in the outer tube [7] by four springs [6] located at an angle of 90 relative to one another. The springs serve to compensate for different thermal expansions of inner and outer tube.

EXAMPLES

[0099] Gas volumes are reported in standard cubic meters, i.e. at 1 bar and 20 C. in accordance with ISO 6358/ISO 8778.

I. Production of a Mixture

[0100] A dry mixture of Li.sub.2CO.sub.3 with MO(OH) precursor particles, M=Ni, Co and Mn in a molar ratio of 1:1:1, average particle diameter 10 m, was produced. The mass ratio of Li.sub.2CO.sub.3 to MO(OH) was 1:2. A mixture was obtained.

II. Calcination Experiments

[0101] Comparative experiments: Calcination of NCM cathode materials in a metal tube. NCM cathode materials are corrosive and during the thermal treatment in a rotary tube at high temperatures above about 700 C. tend to adhere strongly to the tube wall. This makes the use of auxiliaries such as knockers or scrapers necessary. Without use of such auxiliaries, the interior wall of the tube becomes completely covered with caked-on material.

II.1: Continuous Calcination at 675 C.

II.1.1: Use of a Tube Composed of a Nickel-Based Alloy

[0102] The mixture from I. was fed via a feed screw into a rotary tube furnace from Linn High Therm (tube length 2 m, of which 1 m was heated in three zones, internal tube diameter 100 mm, no internals) having a tube composed of the nickel-based alloy of the grade 2.4851. The feed rate of mixture was set to 1.3 kg/h. The furnace had three heating zones each having a length of 330 mm; in the illustrative case of the thermal treatment in the rotary tube furnace, these were set to 550 C., 675 C. and 675 C. The inclination of the tube was 1, and the speed of rotation was two revolutions per minute. No knockers were used.

[0103] In the thermal treatment, the mixture traveled through an unheated part of the tube having a length of about 400 mm (the end of the feed screw projected about 100 mm into the tube) and was preheated there by convection (gas in countercurrent, coming from the heated region), conduction (thermal conduction in bulk material and metal tube) and radiation. The heating zones were followed by a further unheated section having a length of 500 mm before the material was discharged. The rotary tube furnace was operated in countercurrent; two standard m.sup.3/h of air were fed to the solids discharge end.

[0104] The chemical reactions which led to product formation proceeded in all zones, including the unheated intake zone and even in the metering/feed screw. This could be confirmed by the partial decomposition of the lithium carbonate into lithium oxide (and CO.sub.2) by taking a sample from the feed screw.

II.1.2: Use of a Tube Composed of Steel SS 330

[0105] The mixture from I. was thermally treated in a rotary tube furnace from the manufacturer Harper International. A tube which was free of internals and composed of the steel alloy SS 330 and had a total length of 10 feet (US, corresponding to 3.05 m) and an internal diameter of 10 inches (25.4 cm) was used here. Of the total length, 8 feet are heated in four heating zones each having a length of 2 feet. The temperatures of the heating zones were set to 550 C. (first zone) and 675 C. (zones 2-4).

[0106] 8.4 kg/h of the mixture from I. were fed to the furnace. The inclination of the tube was set to 1.5, and the speed of rotation was set to 1.5 revolutions per minute. Ten standard m.sup.3/h of air were introduced in countercurrent. Knockers were used.

[0107] During the thermal treatment process, chromium from the tube alloy accumulated in the product in both experiments. No contamination of the product by chromium was found in the feed mixture and in the feed screw. The experiments were repeated three times and the averaged analytical values for the chromium concentration are shown in table 1.

TABLE-US-00001 TABLE 1 Chromium contamination after calcination at 675 C. Position of sampling Comparative example 1.1 Comparative example 1.2 Feed mixture <10 ppm <10 ppm Feed screw <10 ppm <10 ppm Furnace outlet 20 ppm 30 ppm

[0108] The measurement accuracy for Cr is 2 ppm.

II.2: Continuous Calcination at 900 C.Comparative Example

[0109] In a manner analogous to experiment II.1.1, a calcination was carried out at 900 C. in the same rotary tube furnace having a tube composed of 2.4851 (nickel-based alloy).

[0110] 1.2 kg/h of material produced by the process described in example 11.1.1 was fed in. The heating zones were each set to 925 C. The inclination of the tube was 2, and the speed of rotation was two revolutions per minute.

[0111] The experiment had to be stopped because of severe caking. The material caked on the tube wall because of its properties: sticky at high temperatures. The product taken out manually displayed contamination as per table 2.

TABLE-US-00002 TABLE 2 Chromium and iron contamination (by mass) after calcination at 925 C. Chromium from nickel- Iron from nickel- based alloy of based alloy of Position of sampling the grade 2.4851 the grade 2.4851 Manual sampling after 0.15%/1500 ppm 0.009%/90 ppm experiment had been stopped

[0112] The measurement accuracy for Cr and Fe is 2 ppm.

III.: Batchwise Calcination

III.1: Materials Test/Contamination Test for Aluminum Oxide:

[0113] In materials tests, it was shown that aluminum oxide, both in the form of densely sintered or porous ceramic and as fiber composite ceramic (Al.sub.2O.sub.3/Al.sub.2O.sub.3) is resistant to the material to be treated.

[0114] Fiber composite ceramics based on continuous fibers 3M Nextel Ceramic Fiber 610 were used. The fibers have a proportion of Al.sub.2O.sub.3 of >99%. In addition, the fiber composite ceramics used were based on a ceramic slip having a proportion of >99% of Al.sub.2O.sub.3 in the solid. The fiber composite ceramics differed in terms of further properties such as density, porosity, nature of the surface.

[0115] The experiments were carried out in a chamber furnace operated batchwise. A sample of the material was brought into contact with mixture from I., heated to 900 C. (at 3 K/min) and, after a hold time of 6 hours, cooled. A temperature change stress is in this way applied in addition to the chemical stress. After cooling, product obtained was replaced by fresh mixture as per I. and the cycle was repeated. The samples withstood more than 30 cycles or 90/100 cycles. 30 cycles are a typical number according to which the suitability of a material can be determined.

[0116] In these materials tests, no contamination of the product was detected.

TABLE-US-00003 TABLE 3 Chemical resistance of ceramic and fiber composite ceramic Aluminum Aluminum Fiber composite oxide, oxide, ceramic densely sintered porous ceramic (Al.sub.2O.sub.3/Al.sub.2O.sub.3) Cycle >100 >30 >90 Contamination by Cr, Fe and Cu

III.2: Materials Test/Contamination Test for High-Temperature-Resistant Steels and Nickel-Based Alloys:

[0117] In a manner analogous to the materials test for aluminum, fresh mixture as per I. was placed on test plates before each cycle. The test plates were plates having dimensions of 100100 mm with thicknesses of from 2 to 3 mm.

[0118] In the comparative tests using high-temperature-resistant steels of the grade 1.4845 and nickel-based alloys of the grade 2.4856, contamination by Cr and Fe as per table 4 was detected in the tests carried out in the same way with maximum temperatures of 900 C. or 700 C. Even after the 5th cycle, renewed contamination occurred; stabilization could not be detected. The test series at 900 C. was stopped after the 5th cycle because of the tremendously high contamination of the product.

TABLE-US-00004 TABLE 4 Contamination by metallic materials Contamination after one cycle 900 C. 700 C. Material 2.4856 1.4845 2.4856 1.4845 NiCr22Mo9Nb X8CrNi25-21 NiCr22Mo9Nb X8CrNi25-21 Cr 2100 14400 5 583 Fe 320 300 3 5 Contamination after five cycles 900 C. 700 C. Material 2.4856 1.4845 2.4856 1.4845 NiCr22Mo9Nb X8CrNi25-21 NiCr22Mo9Nb X8CrNi25-21 Cr 2400 2500 <1 229 Fe 300 1500 3 37 Contamination after ten cycles 700 C. Material 2.4856 1.4845 NiCr22Mo9Nb X8CrNi25-21 Cr 31 251 Fe 10 7

Experiment III.3 Calcination in a Tube Reactor According to the Invention

[0119] Putting together a rotary tube reactor having an inner wall composed of fiber composite ceramic, Al.sub.2O.sub.3/Al.sub.2O.sub.3, outer wall composed of steel SS 330 results in a rotary tube furnace according to the invention with ratio of thermal conductivity and wall thickness (heat transfer coefficient) at 800 C. of >50 W/(m.sup.2.Math.K) but less than 5000 W/(m.sup.2.Math.K). The inclination of the tube can be set to 1.5. When 8.4 kg/h of the mixture from I. is introduced into the rotary tube furnace according to the invention and is calcined at 675 C. and a speed of rotation of 1.5 revolutions per minute and an air input of 10 standard m.sup.3/h of air in countercurrent, it is found that the resulting cathode material has lower contamination with Fe and Cr than a cathode material produced as per 11.1.2. The joined tube allows the use of knockers to prevent caking on the tube wall.