Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25C—PROCESSES FOR THE ELECTROLYTIC PRODUCTION, RECOVERY OR REFINING OF METALS; APPARATUS THEREFOR
  • C25C3/00—Electrolytic production, recovery or refining of metals by electrolysis of melts
  • C25C3/06—Electrolytic production, recovery or refining of metals by electrolysis of melts of aluminium
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25C—PROCESSES FOR THE ELECTROLYTIC PRODUCTION, RECOVERY OR REFINING OF METALS; APPARATUS THEREFOR
  • C25C3/00—Electrolytic production, recovery or refining of metals by electrolysis of melts
  • C25C3/06—Electrolytic production, recovery or refining of metals by electrolysis of melts of aluminium
  • C25C3/20—Automatic control or regulation of cells

Definitions

• the invention relates to the production of aluminum by igneous electrolysis according to the Hall-Héroult process and the installations intended for the industrial implementation of this process.
• the invention relates more specifically to the control of the thermal flows of the electrolytic cells and the cooling means which make it possible to obtain this control.
• Aluminum metal is produced industrially by igneous electrolysis, namely by electrolysis of alumina in solution in a bath of molten cryolite, called bath
• the electrolyte bath is contained in a tank comprising a steel box, which is coated internally with refractory and / or insulating materials, and a cathode assembly located at the bottom of the tank.
• the electrolysis current which can reach values of more than 300 IA, operates the alumina reduction reactions and also makes it possible to maintain the electrolyte bath at a temperature of the order of 950 ° C. by the Joule effect. .
• the electrolytic cell is generally controlled in such a way that it is in thermal equilibrium, that is to say that the heat dissipated by the electrolytic cell is generally compensated by the heat produced in the cell, which comes essentially electrolysis current.
• the point of thermal equilibrium is generally chosen so as to achieve the most favorable operating conditions from a point of view not only technical, but also economic.
• the possibility of maintaining an optimal set temperature constitutes a significant saving in the cost of producing aluminum because of the ⁇ I ⁇ M £ PCT / FR99 / 00802 99/54526
• the conditions of thermal equilibrium depend on the physical parameters of the tank, such as the dimensions and the nature of the constituent materials, and on the operating conditions of the tank, such as the electrical resistance of the tank, the temperature of the bath or the intensity of the electrolysis current
• the tank is often formed and conducted so as to cause the formation of a solidifying embankment on the side walls of the tank, which in particular makes it possible to inhibit the attack on the coatings of said walls by the liquid cryolite
• the applicant has sought methods and means for controlling the thermal fluxes and for stabilizing the thermal regime of the electrolytic cells, which, while offering very high efficiency and great adaptability, do not require a high investment and does not entail prohibitive additional operating costs
• the Soviet inventors' certificates SU 605 865 and SU 663 760 propose to provide the tanks with a cooling system, controlled from the outside, which includes airtight cavities on the sides and below the tank, variable thermal screens and pipes fitted with regulating valves. Air is forced into the lines by a fan or compressor. These devices require a large and bulky infrastructure.
• the capture device sucks in the ambient air taken from the sides of the tank through said orifices and causes it to flow in said passages, along the edge slabs, which has the effect of cool them
• the air flow is controlled by means of openings fitted with valves and located on the sides of the capture device, which act as bypass ducts ("bypass" in English)
• This device requires significant modifications of the tank and does not allow independent cooling control, since regular interventions on the tank require the opening of the covers of the collection device which disturb the effect of the valves
• the applicant has set itself the objective of finding means, effective and adaptable, for removing and dissipating the heat produced by the electrolysis tank, which can easily be put in place and which do not require significant modifications to the tank, and in particular the casing, nor any significant infrastructure
• the applicant has sought in particular means which make it possible to modify the power of the tanks, which easily adapt to different types of tank or to different operating modes of the same type of tank, and which are suitable for industrial installations comprising a large number of tanks in se ⁇ e
• the first object of the invention is an electrolysis tank for the production of aluminum by the Hall-Heroult electrolysis process which comprises means of cooling by blowing air with localized and distributed jets
• the second object of the invention is an aluminum production plant using the Hall-Heroult electrolysis process, characterized in that it comprises cells according to the invention
• the electrolysis tank for the production of aluminum by the Hall-Heroult electrolysis process comprises a steel casing, elements for 5 inner lining and a cathode assembly, and is characterized in that it comprises means for cooling by blowing air with localized jets distributed around the box
• the air is blown, that is to say that the circuit is open and has a lost flow.
• the air flow projected on the surface is then diluted in the ambient air so that it is not essential to add special means to cool the projected air, which heats up in contact with the walls
• the blowing of air in the form of localized jets i.e. the projection of air in the form of substantially directional and confined flows, thus striking the box on a relatively small surface, makes it possible to effectively cool the wall of the tank at specific locations
• the jets are distributed around the box so as to fix the preferred cooling zones on the surface of the box, these areas being advantageously determined as a function of the thermal profile of the tank, with the aim in particular of increasing the overall cooling efficiency
• Said cooling means are more precisely characterized in that they comprise air blowing means for cooling the box, that is to say to evacuate and dissipate the heat produced by the tank at the level of the box, said means for blowing forming localized jets, and in that they comprise means for distributing the jets around the box according to a determined distribution
• the invention thus makes it possible to control or modulate the power of the electrolytic cells by adding or adding efficient and adaptable cooling means, which may possibly take the form of an additional cooling power, fixed or variable, by compared to the nominal power
• efficient and adaptable cooling means which may possibly take the form of an additional cooling power, fixed or variable, by compared to the nominal power
• the invention thus offers the possibility of modifying the power of each tank individually
• the air flow rate of the blowing means according to the invention can be variable, so as to allow finer control of the cooling, or even possibly a 6 cooling regulation It is also advantageous to be able to integrate the movens according to the invention to the regulation systems which are fitted to the most modern electrolysis cells
• the cooling means can then be controlled, or even piloted, by the regulation system of the tank, so that the heat flow can be regulated more efficiently and possibly automatically
• the tank may include additional cooling means such as static cooling means
• the cooling means are optionally removable, in the sense that they can be easily put in place or removed from the tank, in certain cases even when the latter is in operation. Thus, for example, during reconditioning. a tank, the cooling means can be wholly or partly removed, which facilitates access to the box and maintenance work
• the cooling means according to the invention in the form of a completely or partially autonomous cooling device. Such an assembly can then lead to a globalized design and to greater ease of operation The air flow will interfere with said device may be variable
• the cooling means comprise air distribution means, for distributing the air flow around the box, an air delivery means, which makes it possible to discharge the air in the air distribution means, and local blowing means, which make it possible to project the air locally in the form of jets, said local blowing means being arranged at determined locations in the box.
• the distribution means preferably comprise channeling means, such as pipes
• the local blowing means can be nozzles, ejectors, tubes, nozzles or pipes
• the local blowing means are advantageously distributed along ducting means
• the air flow rate of the delivery means can be variable
• the air flow rate of one or more of the localized blowing means can also be variable
• the tanks can be individually equipped with the cooling device according to the invention, which can optionally be controlled centrally
• the electrolysis cells are grouped or arranged in series.
• the cells can advantageously be equipped with cooling means according to the invention, which are, in whole or in part, common to two or more tanks, that is to say that two or more tanks have one of said cooling means in common
• FIG. 1 illustrates, schematically and in cross section, an electrolytic cell comprising cooling means, assembled in the form of a cooling device, according to a preferred embodiment of the invention
• FIG. 1 illustrates, schematically, in side view, an electrolysis cell according to the embodiment of the invention of Figure 1
• FIG. 3 illustrates, diagrammatically, seen from below, an electrolysis cell according to the embodiment of the invention of FIG. 1
• Figure 4 illustrates, without limitation, variants of the invention according to which the channeling means surround the electrolytic cell in all (b) or part (a)
• FIGS 5 and 6 illustrate, without limitation, variants of the invention according to which the same delivery means is common to more than one tank
• the electrolysis tank (1) for the production of aluminum by the Hall-Heroult electrolysis process comprises a box (2) made of steel, internal coating elements (3) and a cathode assembly (4 ), and means for cooling by blowing air with localized jets distributed around the box (2)
• the interior cladding elements (3) are generally blocks of refractory materials, which can be thermal insulators.
• the cathode assembly (4) comprises connection bars (9) to which the electrical conductors serving for the current flow are fixed. electrolysis
• the coating elements and the cathode assembly form a crucible inside the tank, which crucible makes it possible to contain the electrolyte bam (7) and the sheet of liquid metal (6) when the tank is in charge
• the anodes (11) are partially immersed in the electrolyte bam (7)
• the electrolyte bath contains dissolved alumina and, as a general rule, an alumina cover (8) covers the electrolyte bath
• the aluminum metal (6) which is produced during the electrolysis accumulates at the bottom of the tank, so that it establishes a fairly clear interface between the liquid metal (6) and the bam of molten cryohthe (7)
• the position of this bath-metal interface changes over time, it rises as the liquid metal accumulates at the bottom of the tank and it drops when liquid metal is extracted from the tank
• the conduct of the electrolytic cells is generally carried out by controlling several parameters, such as the alumina concentration of the electrolyte, the temperature of the electrolyte bam, the total height of the bam or the position of the anodes.
• the walls side may include preformed blocks or ribs, preferably homogeneous, made of a mate ⁇ au of high thermal conductivity, at least higher than that of pot lining, and more preferably at least equal to that of da the normally used borders, such as for example a SiC-based material
• the tank is also provided with a capture device making it possible to capture and recover the gaseous effluents emitted by the electrolyte bam during electrolysis.
• the capture device comprises a cover over the whole of the tank. (10) generally provided with opening covers and access
• the cooling means comprise channeling means (28), such as pipes (21-24), a discharge means (25) for discharging air into said means ducting, and local blowing means (27) making it possible to project the air in the form of localized jets
• channeling means such as pipes (21-24)
• discharge means for discharging air into said means ducting
• local blowing means making it possible to project the air in the form of localized jets
• the channeling means (28) can be held in position by different movens In particular, they can be fixed to the structural or reinforcing elements of the tank, such as stiffeners, which can be modified or adapted for this purpose.
• pipe (28) can also be leaned against the box or placed against it or fixed to the gunwale of the box 10
• the general air flow of the device (20) can advantageously be variable, for example by means of valves or by a variation of the flow of the delivery means (25)
• the air flow of one or more of the localized blowing can also be variable, possibly individually, with possibly also the possibility of reducing to zero the flow of certain blowing means Air can in certain cases be drawn
• the cooling means, or the cooling device, according to the invention are optionally wholly or partly removable.
• the pipes can be easily dismantled and transportable, thanks in particular to a design by sections and to suitable assembly means.
• the air discharged into the ducting means is blown onto the walls of the box, at determined locations, using localized blowing means (27), which are advantageously distributed along the ducting means
• the localized blowing means are not necessarily evenly distributed over the surface of the box, it may sometimes be preferable to concentrate them in certain specific areas
• the local blowing means (27) make it possible to direct the air flow at specific locations in the box, for example at the height of the electrolyte bath (7). It is advantageous for one or more of the localized blowing means (27) to be orientable.
• the local blowing means project the blown air at a speed, called the ejection speed, which is preferably between 10 and 100 m / s, and more preferably between 20 and 70 m / s
• the number, the position and the dimensions of the localized blowing means (27), the power of the delivery means (25), as well as the configuration and the dimensions of the ducting means (21 to 24), are chosen so that that the air flow is sufficient to allow efficient cooling and so as to ensure 11 cooling power determined at the selected blowing points, taking into account in particular the air flow of the network
• the air delivery means (25) can be a ventilator, which discharges ambient air, or a blower with compressed air, such as a ventilo-tube, or a compressed air system or a network of surpresse air
• an electrical isolation means such as a pipe section in electrical insulating material
• the pipes (21-24) can be made of metallic materials, preferably non-magnetic (such as non-magnetic stainless steel or aluminum), or of insulating materials (such as glass fibers), or a combination of these (such as a metal conduit provided with an insulating sheath)
• metallic materials preferably non-magnetic (such as non-magnetic stainless steel or aluminum), or of insulating materials (such as glass fibers), or a combination of these (such as a metal conduit provided with an insulating sheath)
• the cooling device (20) can possibly be controlled by the regulating system which will interfere with the tank, so as to ensure more efficient centralized global regulation.
• the tank can also be provided with additional cooling means, in particular static cooling means, such as fins or equivalent means.
• additional cooling means in particular static cooling means, such as fins or equivalent means.
• the channeling means form twigs, that is to say that they are constituted in such a way that a main channeling means (21) branches into ho ⁇ zontal branches 12 under the tank (22), vertical on the sides and tank heads (23) and horizontal on the sides and tank heads (24)
• a main channeling means (21) branches into ho ⁇ zontal branches 12 under the tank (22), vertical on the sides and tank heads (23) and horizontal on the sides and tank heads (24)
• the vertical branches can be placed between the cathode bars (9)
• the channeling means (28) surround or surround all or part of the box (2) of the electrolysis tank
• a single delivery means (25) is common to more than one tank, and more precisely to two or more tanks from a factory
• the delivery means (25) distributes the air flow via a network (29) comprising a common main conduit (30) and a connection point (31) for each tank
• the connection points are optionally provided with valves to isolate each tank individually and air vents to rebalance the distribution of air flows Valves and air vents are particularly useful during interventions on a particular tank or on some of them since they allow to isolate the tank (s) concerned while preserving satisfactory air flow rates for the other tanks connected to the network
• the cooling means are advantageously controlled or piloted using a regulation system common to more than one tank
• each tank provided with its own cooling means or each group of tanks provided with cooling means having elements in common can be piloted by a so-called first level regulation system, and all the cells or groups of cells of a particular plant electrolysis hall can, in addition, to be piloted in a global manner by a so-called second level regulation system 13
• first level regulation system the so-called first level regulation system
• second level regulation system 13 Example
• a main pipe (21) passes longitudinally under the box (2) to near the center of the tank, then divides into three branches (22a 22b, 22c) perpendicular to each other and of smaller section than the main pipe, a longitudinal branch (22a) extends under the box to the other end of it, then forms a vertical branch (23a), which goes up along the head from the tank to the height of the border slab, approximately, then branches off into two vertical branches (24a, 24a ') which extend to the side edges of the tank, the other two branches (22b, 22c), transverse, extend as far as the side ribs of the box, then form vertical branches (23b, 23c) which go up along it up to the height of the edge slab, approximately then branch off into two ho ⁇ zontal branches (24b, 24b ', 24c, 24c'), on each side of the tank, which extend up to the heads of the tank
• a vertical branch (23 c) equivalent to the branch (23 a) is connected directly to the main pipe,
• Nozzles (27) were arranged uniformly along the branches According to the tests, the number of nozzles was 5 to 8 nozzles along each tank head and 15 to 20 nozzles on each side of the tank The nozzles were directed approximately towards the theoretical bam-metal level in most of the tests In some tests, some nozzles were directed towards structural reinforcement elements of the box, which thus served as cooling fins
• the pipes and nozzles were made of steel, and partly stainless steel
• the air delivery means (25) was, in some tests, a mechanical ventilator and, in other tests, a ventilo-tube
• the cooling devices were provided with means making it possible to vary the air flow 14
• thermocouples and pyrometers showed that the device made it possible to obtain average temperature reductions from 50 to 100 ° C at the height of the side walls.
• the regulation of the cooling was easily obtained by a change in the discharge air flow
• the sound level of the device was particularly low 15
• the cooling means make it possible to evacuate and dissipate the thermal energy produced in the electrolytic cell, by optimal control of certain thermal flows, which can be adapted to different climatic and / or operating conditions. of the tank, which can deviate significantly from the nominal or standard conditions
• the cooling means also make it possible to precisely control the formation of the solidified cryohthe bath slope
• the cooling means, or the cooling device, according to the invention easily adapt to any type of tank and to different environments. They can easily be installed on existing tanks, in particular within the framework of their refurbishment, of the integration of a thermal regulation and / or of a modification of the nominal intensity More specifically, the invention facilitates the modulations of the power of the tanks which make it possible to take into account, for example, technical, economic and / or contractual In particular, the invention allows an increase in the nominal intensity of existing tanks, without causing premature deterioration of the tanks
• the possibility of adapting cell to cell the means, or the device, of cooling, as well as its operating conditions makes it possible to optimize the operation of several cells at the same time, or even a complete series of tanks, so as in particular to standardize the operating point of the tanks.
• the invention allows individualized thermal control of the tanks of a factory, which is often necessary in large factories. productivity This is the case, for example, during the transient phases which occur when certain tanks of the same series have new or different solderings from those of the rest of the series 16
• the invention also allows the modernization of existing factories without requiring infrastructure works which would make such operations prohibitive.
• the invention also makes it possible to extend the life of a tank at the end of its life. whose box has abnormal hot spots

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• 1998
  • 1998-04-16 FR FR9805040A patent/FR2777574B1/fr not_active Expired - Fee Related
• 1999
  • 1999-04-03 EG EG34499A patent/EG21924A/xx active
  • 1999-04-04 GC GCP1999116 patent/GC0000048A/xx active
  • 1999-04-07 SI SI9930491T patent/SI1070158T2/sl unknown
  • 1999-04-07 WO PCT/FR1999/000802 patent/WO1999054526A1/fr active IP Right Grant
  • 1999-04-07 ES ES99911893T patent/ES2209412T5/es not_active Expired - Lifetime
  • 1999-04-07 RU RU2000128725/02A patent/RU2201476C2/ru active
  • 1999-04-07 SK SK1533-2000A patent/SK285426B6/sk not_active IP Right Cessation
  • 1999-04-07 EP EP99911893A patent/EP1070158B2/de not_active Expired - Lifetime
  • 1999-04-07 DE DE69911758T patent/DE69911758T2/de not_active Expired - Lifetime
  • 1999-04-07 CA CA002328768A patent/CA2328768C/fr not_active Expired - Lifetime
  • 1999-04-07 AU AU30419/99A patent/AU746349B2/en not_active Expired
  • 1999-04-07 BR BRPI9909613-7A patent/BR9909613B1/pt not_active IP Right Cessation
  • 1999-04-16 AR ARP990101787A patent/AR026090A1/es active IP Right Grant
  • 1999-11-18 US US09/442,758 patent/US6251237B1/en not_active Expired - Lifetime
• 2000
  • 2000-10-04 ZA ZA200005405A patent/ZA200005405B/xx unknown
  • 2000-10-11 IS IS5655A patent/IS2692B/is unknown
  • 2000-10-13 NO NO20005174A patent/NO328847B1/no not_active IP Right Cessation

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