A process can be used for the treatment of an offgas stream, which is formed in a plant for the production of aluminum by electrolytic reduction of aluminum oxide in a melt, using at least one anode composed of a carbon-containing material. The offgas stream contains carbon oxides due to the reduction of the aluminum oxide by the carbon. At least a substream of the carbon oxides contained in the offgas stream is reacted with hydrogen or mixed with a hydrogen stream and is subsequently passed to a use. After purification and conditioning of the offgas stream in a device, an enrichment, for example with carbon monoxide, can subsequently be carried out in a reactor and the synthesis gas obtained in this way can be fed to a chemical or biotechnological plant for the synthesis of chemicals of value.

A process can be used for the treatment of an offgas stream, which is formed in a plant for the production of aluminum by electrolytic reduction of aluminum oxide in a melt, using at least one anode composed of a carbon-containing material. The offgas stream contains carbon oxides due to the reduction of the aluminum oxide by the carbon. At least a substream of the carbon oxides contained in the offgas stream is reacted with hydrogen or mixed with a hydrogen stream and is subsequently passed to a use. After purification and conditioning of the offgas stream in a device, an enrichment, for example with carbon monoxide, can subsequently be carried out in a reactor and the synthesis gas obtained in this way can be fed to a chemical or biotechnological plant for the synthesis of chemicals of value.

The invention relates to non-ferrous metallurgy, more particularly to producing aluminium by electrolysis, and even more particularly to a structural element for covering the space above a melt in an electrolysis cell for producing aluminium by the electrolysis of cryolite-alumina melts. In a cover for an electrolysis cell for producing aluminium, which is in contact with a vapour-gas phase when the electrolysis cell is in operation and which is in the form of central and peripheral sections which are movably arranged relative to each other, the central and peripheral sections are made from a corrosion-resistant and erosion-resistant material which comprises 80.0-99.0 wt % of fluorophlogopite and 20.0-1.0 wt % of a refractory filler. The central sections of the cover may be permanently fixed on each anode rod, and the peripheral sections may be configured as convex panels rigidly and removably fixed on the top surface of a cathode and supported by the central section of the cover. Moreover, the refractory filler may be chosen from the following chemical substances: clay, calcium fluoride, rutile, sodium aluminosilicate, fluorapophyllite, nepheline, olivine, magnesium fluoride, and spinel. The end and side joints of the central and peripheral covers may be coated with a sealant layer in the form of a layer of alumina, and the central section of the cover may be provided with apertures. The use of this invention provides for the hermetic sealing of the cover, the reliability and safety of the structure, and a reduction in energy consumption.

The invention relates to non-ferrous metallurgy, more particularly to producing aluminium by electrolysis, and even more particularly to a structural element for covering the space above a melt in an electrolysis cell for producing aluminium by the electrolysis of cryolite-alumina melts. In a cover for an electrolysis cell for producing aluminium, which is in contact with a vapour-gas phase when the electrolysis cell is in operation and which is in the form of central and peripheral sections which are movably arranged relative to each other, the central and peripheral sections are made from a corrosion-resistant and erosion-resistant material which comprises 80.0-99.0 wt % of fluorophlogopite and 20.0-1.0 wt % of a refractory filler. The central sections of the cover may be permanently fixed on each anode rod, and the peripheral sections may be configured as convex panels rigidly and removably fixed on the top surface of a cathode and supported by the central section of the cover. Moreover, the refractory filler may be chosen from the following chemical substances: clay, calcium fluoride, rutile, sodium aluminosilicate, fluorapophyllite, nepheline, olivine, magnesium fluoride, and spinel. The end and side joints of the central and peripheral covers may be coated with a sealant layer in the form of a layer of alumina, and the central section of the cover may be provided with apertures. The use of this invention provides for the hermetic sealing of the cover, the reliability and safety of the structure, and a reduction in energy consumption.

The present invention relates to a method and equipment for recovering heat from exhaust gas removed from an industrial process, such as an electrolysis process for the production of aluminum. Heat is recovered by means of an extraction/suction system, where the exhaust gas contains dust and/or particles. The heat is recovered as the exhaust gas being brought into contact with heat-recovery elements. Flow conditions and the design of the heat recovery elements are such that the deposits of the dust and/or particles on the surfaces stated are kept at a stable, limited level. In preferred embodiments, the heat-recovery elements have a circular or an extended, elliptical cross-section and may be equipped with fins or ribs.

The present invention relates to a method and equipment for recovering heat from exhaust gas removed from an industrial process, such as an electrolysis process for the production of aluminum. Heat is recovered by means of an extraction/suction system, where the exhaust gas contains dust and/or particles. The heat is recovered as the exhaust gas being brought into contact with heat-recovery elements. Flow conditions and the design of the heat recovery elements are such that the deposits of the dust and/or particles on the surfaces stated are kept at a stable, limited level. In preferred embodiments, the heat-recovery elements have a circular or an extended, elliptical cross-section and may be equipped with fins or ribs.

An aluminum production electrolytic cell comprises a bath with bath contents, at least one cathode electrode in contact with said contents, at least one anode electrode in contact with said contents, and a hood, defining interior area, covering at least a portion of said bath. The electrolytic cell is equipped for vent gases to be drawn from said interior area. The electrolytic cell also comprises at least one heat exchanger for cooling at least a portion of the vent gases drawn from interior area, prior to circulation thereof to interior area.

An aluminum production electrolytic cell comprises a bath with bath contents, at least one cathode electrode in contact with said contents, at least one anode electrode in contact with said contents, and a hood, defining interior area, covering at least a portion of said bath. The electrolytic cell is equipped for vent gases to be drawn from said interior area. The electrolytic cell also comprises at least one heat exchanger for cooling at least a portion of the vent gases drawn from interior area, prior to circulation thereof to interior area.

There is provided a process for purifying aluminum ions comprising: reacting an aluminum-containing material with an acid so as to obtain a composition comprising aluminum ions; precipitating said aluminum ions in the form of AlCl.sub.3; optionally converting AlCl.sub.3 into Al(OH).sub.3; and heating said AlCl.sub.3 or said Al(OH).sub.3 under conditions effective for converting AlCl.sub.3 or Al(OH).sub.3 into Al.sub.2O.sub.3 and optionally recovering gaseous HCl so-produced. Aluminum ions so purified are thus useful for preparing various types of alumina.

There is provided a process for purifying aluminum ions comprising: reacting an aluminum-containing material with an acid so as to obtain a composition comprising aluminum ions; precipitating said aluminum ions in the form of AlCl.sub.3; optionally converting AlCl.sub.3 into Al(OH).sub.3; and heating said AlCl.sub.3 or said Al(OH).sub.3 under conditions effective for converting AlCl.sub.3 or Al(OH).sub.3 into Al.sub.2O.sub.3 and optionally recovering gaseous HCl so-produced. Aluminum ions so purified are thus useful for preparing various types of alumina.