Storage-Stable Spent Potlining Material, Method for the Production Thereof, and Use of the Same as Fuel

Abstract

Spent potlining material contains spent potliner from aluminium electrolysis cells, and at least one hydrophobic binder. The hydrophobic binder being selected from wax, a waxlike compound or mixtures thereof. A method for producing a spent potlining material includes the steps of (a) providing spent potliner from aluminium electrolysis cells, (b) comminuting the spent potliner in at least one comminuting apparatus, (c) fractionating the spent potliner through a separating apparatus, (d) mixing the spent potliner with at least one hydrophobic binder, selected from wax, a waxlike compound or mixtures thereof, in a mixing apparatus, (e) portioning the mixture obtained in step (d), (f) withdrawing the spent potlining material The steps (b) to (d) are carried out in an inert gas atmosphere. Also, spent potlining material is used as fuel in power stations and also in connection with the production of mineral wool, cement and steel.

Claims

1. Spent potlining material containing spent potliner from aluminum electrolysis cells, and at least one hydrophobic binder, wherein the spent potliner is present in agglomerated form with the hydrophobic binder, wherein the hydrophobic binder is selected from wax, a wax-like compound, or mixtures thereof, wherein the spent potlining material contains 30 to 90 wt. % spent potliner and 10 to 70 wt. % hydrophobic binder, relative to the total weight of the spent potlining material.

2. Spent potlining material according to claim 1, wherein the spent potliner has a grain size of less than 50 mm.

3. Spent potlining material according to claim 1, wherein the spent potliner consists of the first cut or the second cut or a mixture of the first and second cuts, wherein the first cut consists of the graphite of the cathode lining, and the second cut constitutes a mixture of the graphite of the cathode lining and the refractory lining.

4. Spent potlining material according to claim 1, wherein the hydrophobic binder has a dripping point according to DIN ISO 2176 between 35? C. and 75? C.

5. Spent potlining material according to claim 1, wherein the wax is selected from natural wax, semi-synthetic wax or synthetic wax, and mixtures thereof, preferably from polyolefin waxes, in particular polyethylene waxes, or paraffin waxes.

6. Spent potlining material according to claim 1, wherein the wax-like compound is selected from esters of glycerol with fatty acids, preferably from linear carbon chains having 4 to 26, typically 12 to 22, carbon atoms, fatty acids, in particular linear aliphatic monocarboxylic acids having 13 to 21 carbon atoms, and mixtures thereof; preferably the wax-like compound is stearin.

7. Spent potlining material according to claim 1, wherein the spent potlining material is in the form of pellets, cocoons, castings, briquettes, or extrudates.

8. Spent potlining material according to claim 1, wherein the cathode material has a heating value between 10,500 and 31,000 KJ/kg, determined according to the RAL-GZ 724 method of the German Federal Quality Association for Secondary Fuels.

9. Method for producing a spent potlining material, comprising the following steps: (a) providing spent potlining material from aluminum electrolysis cells, (b) comminuting the spent potliner at least in one comminuting apparatus, (c) fractionating the spent potliner through a separating apparatus, (d) mixing the spent potliner with at least one hydrophobic binder, selected from wax, a wax-like compound, or mixtures thereof, in a mixing apparatus, (e) portioning the mixture obtained in step (d), (f) extracting the spent potlining material, wherein steps (b) to (d) are carried out in an inert gas atmosphere.

10. Method for producing a spent potlining material according to claim 9, wherein the at least one comminuting apparatus in step (b) is a mill or a crusher.

11. Method for producing a spent potlining material according to claim 1, wherein the separating apparatus in step (c) is a sieve.

12. Method for producing a spent potlining material according to claim 1, wherein the at least one hydrophobic binder is metered to the mixing apparatus in step (d) in liquid form or is liquefied by heating in the mixing apparatus.

13. Method for producing a spent potlining material according to claim 1, wherein the portioning in step (e) is selected from in-mold casting, briquetting, extruding, or pelletizing.

14. Use of the spent potlining material according to claim 1 as a fuel, preferably in power stations and in the production of mineral wool, cement, and steel.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0086] FIG. 1 is a Schematic representation of an embodiment of the method according to the invention for the production of spent potlining material.

DETAILED DESCRIPTION OF THE INVENTION

[0087] FIG. 1 schematically shows an embodiment of the method according to the invention for the production of spent potlining material. First, a nitrogen-inert mill is fed with the spent potliner 2 having a particle size of less than 50 mm via a vibrating hopper 3. If fragments are too coarse or the range in the size distribution is too large to be fed to a mill, a nitrogen-inert crusher can also be installed upstream. The served spent potliner 2 also acts as a dust separator. The final particle size with which the fine fraction of the spent potliner is released from the mill into the heated mixer 5 is determined using a sieve 4 close to the bottom. In the mixer 5, liquefied wax is added via a dosing unit 6 up to a concentration of 20 to 40 wt. % wax, relative to the total weight of the spent potlining material. The wax has been previously liquefied in a heated wax storage container 7. When the correct mixing ratio of wax and spent potliner is reached in mixer 5, the mill 1, the crusher (if connected upstream), and the addition of wax are stopped via dosing unit 6. The mixing direction in mixer 5 is changed, and the spent potlining material/wax mixture is poured into slightly conical molds 8. After cooling to room temperature, the finished spent potlining material can be removed from the casting molds 8 and is thus present as a casting.

Examples

[0088] 1,300 kg of spent potliner were delivered to a vertical mill. The spent potliner was pre-sorted, free of impurities such as corundum or aluminum, and contained no pieces larger than 5 cm.

[0089] The grinding process took place in a nitrogen atmosphere and was carried out with a target fineness of 10%>90 ?m. This means that 90% of the spent potliner was smaller than 90 ?m at the end of grinding, with the remaining 10% between 150 and 200 ?m.

Pellet ProductionVariant APartial Pelletizing

[0090] 1,800 g of the ground spent potliner were placed on a pelletizing plate, which was preheated to 70? C. By adding 10 to 15 wt. % wax, pellets were obtained which had formed a firm, round shell on the outside, but contained almost dry ground material on the inside.

Pellet ProductionVariant BFull Pelletizing

[0091] In another example, 1,800 g of the ground spent potliner were placed on a pelletizing plate preheated to 80? C., and 17 to 21 wt. % wax was added. Pellets were obtained that contained a mixture of wax and ground material over the entire diameter. The angle of incidence of the pelletizing plate during the production of the pellets was 30? relative to plumb, and the rotational speed was 30 rpm.

[0092] Pelletizing was carried out in a semi-continuous method in which the ground spent potliner was fed in such a way that the pellet extraction (falling over the edge) was proportional to the mass. The preheated, liquid wax was also dosed (or sprayed on) in the appropriate ratio. The angle of incidence of the pelletizing plate during the production of the pellets was 30? relative to plumb, and the rotational speed was 30 rpm.

[0093] Heating value and calorific value analyses according to RAL-GZ 724 were subsequently carried out for both partial pelletizing and full pelletizing. The results are summarized in Table 1.

TABLE-US-00001 TABLE 1 Calorific Calorific Heating value Heating value original value dry original value dry substance substance substance substance partially 22,982 23,121 21,359 21,502 pelletized [kJ/kg] [kJ/kg] [kJ/kg] [kJ/kg] pelletized 28,606 28,692 26,596 26,684 [kJ/kg] [kJ/kg] [kJ/kg] [kJ/kg]

[0094] The original substance specified in Table 1 refers to the pellets as they were extracted from the pelletizing machine. The term dry substance refers to pellets that have undergone drying according to DIN EN 14346 after extraction from the pelletizing machine.

[0095] By varying the rotational speed from 20 to 40 rpm and the angle of incidence from 15? to 30? relative to plumb, pellets having different average diameters d=8 to 17 mm can in principle be obtained.

Production of Castings

[0096] In another example, castings were produced. For this purpose, a screen fraction <3 mm was separated from the fine fraction of the spent potliner and used.

[0097] In a batch process, approx. 3 kg of paraffin with a melting point between 70 and 80? C. were liquefied and heated to approx. 100? C. The kinematic viscosity at 100? C. is between 3 and 10 mm.sup.2/sec.

[0098] With constant stirring, 10 kg of the screen fraction <3 mm separated from the fine fraction of the spent potliner were slowly added in small portions. After everything was stirred into a homogeneous mass, an 8 kg casting was first poured. Another 3 kg of paraffin were added to the mass remaining in the mixer and, after melting, another 10 kg of the screen fraction <3 mm separated from the fine fraction of the spent potliner were added while stirring. The second casting was created from this. Further castings were created accordingly by repeating the respective steps.

[0099] The castings of the screen fraction <3 mm separated from the fine fraction of the spent potliner dehomogenize somewhat during the solidification process. This leads to a higher concentration of wax near the surface of the casting.

[0100] It can be assumed that, with increasing fineness of the spent potlining material, less wax is required for stable shaping, regardless of the chosen form of administration. Adding more wax than is necessary for physical stability is a good way of increasing the heating value as desired and adapting it to the requirements of subsequent use.

[0101] All references, including publications, patent applications, and patents cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein.

[0102] The use of the terms a and an and the and similar referents in the context of describing the invention (especially in the context of the following claims) is to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms comprising, having, including, and containing are to be construed as open-ended terms (i.e., meaning including, but not limited to,) unless otherwise noted. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., such as) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.

[0103] Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those preferred embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.