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
  • C25C3/22—Collecting emitted gases

Definitions

• the invention relates to a device for collecting gases emitted by aluminum electrolysis cells, and an associated aluminum production system.
• the electrolysis reaction generates polluting gases, mainly carbon dioxide, carbon monoxide, sulfur dioxide and gaseous hydrogen fluoride, generally called anodic gas.
• gases mainly carbon dioxide, carbon monoxide, sulfur dioxide and gaseous hydrogen fluoride, generally called anodic gas.
• the electrolysis tanks are covered and the gases generated by them are recovered by a collection device connected to the covers of the electrolysis cells.
• the gases are then guided to gas treatment centers, so-called GTCs, in which the hydrogen fluoride, and possibly the sulfur dioxide, are treated. Suction fans are provided downstream of the GTC centers.
• the covers of an electrolytic cell have interstices so that air penetrates under the covers, warms in contact with the electrolysis bath and anodes which plunge into the electrolysis bath.
• This air is mixed with the anode gas emitted by the electrolytic cell.
• This mixture is hereinafter referred to as gas.
• the gases recovered by the collection device are constituted by the anode gases and by the air heated by the electrolysis cell.
• the mixture of air entering under the hoods and the gases emitted during the electrolysis reaction have a temperature of about 100 ° C to 135 ° C above the ambient air temperature at the location where the aluminum manufacturing plant is located.
• the gases are brought into contact with metallurgical alumina.
• This so-called reactive alumina has an adsorption surface of 50 to 80 m 2 / g, and has the property of adsorbing the acidic components and in particular the gaseous hydrogen fluoride to separate it from the other polluting components of the gases.
• alumina thus fluorinated is separated from the gases in fabric filters that retain the fluorinated alumina particles with an efficiency greater than 99.99%.
• polyester fabric filters do not withstand temperatures above 135-140 ° Celsius.
• the capture efficiency of hydrogen fluoride gas decreases when the temperature exceeds 115 to 120 ° Celsius.
• the invention particularly aims to reduce the temperature of the gas passing through the collection device before their arrival in the gas treatment center.
• Existing collection devices include recovery tubing connected to the electrolysis cells, and a general collector for collecting the gases recovered by the recovery tubing.
• the recovery pipes are generally equipped with a diaphragm or damper type of pressure-reducing device, so as to create a pressure drop and thus obtain the same depression and therefore the same flow rate at the electrolysis tanks over the entire length of the collector. general.
• This deprimogenic member consumes energy.
• Another object of the invention is to remove at least in part these pressure-reducing members.
• the subject of the invention is a collection device capable of collecting the gases emitted by several aluminum electrolysis cells, characterized in that it comprises:
• a collector capable of collecting the gases recovered by the recovery pipes
• the invention also relates to an aluminum production system comprising aluminum electrolysis cells capable of generating gases during an electrolysis reaction, and at least one device for collecting these gases, the collecting device being shaped according to any one of the features mentioned above.
• FIG. 1 is a side view of a portion of a collection device according to the invention.
• FIG. 2 is a view from above of the part of the collection device illustrated in FIG. 1;
• FIG. 3 is a sectional view along the III-III plane of the collection device shown in Figure 1 and a building containing the electrolysis tanks;
• FIG. 4 is a sectional view along the plane IV-IV of the collection device shown in Figure 1;
• FIG. 5 is a sectional view of the collection device according to the plane VV of the collection device illustrated in FIG. 1.
• the aluminum production system 2 according to the invention comprises one or more electrolysis series.
• Each series of electrolysis comprises several electrolysis cells 3, for example 240 to 360 cells, arranged one after the other in a building 4, and electrically connected.
• a series of electrolysis measures from about 700 meters to 1,200 meters.
• the collection device 6 is capable of collecting the gases produced by all the electrolysis cells 3 of a series of electrolyses. It comprises a collector 8 collecting the gases from all the electrolysis tanks 3 and, for each tank of said series, at least one recovery pipe 10 connected at one of its ends to the collector 8 and at the other end to capots12 to recover the gases produced by the corresponding electrolytic cell 3.
• the collector 8 is formed of two sheaths 13 closed at one end 14 and joining at their other end 15. Each sheath 13 extends along a row of electrolysis tanks 3.
• each sheath 13 increases as the number of electrolysis tanks 3 connected to the collector 8 increases to ensure a steady rate of gas transport. For example, the section of the sheath 13 increases from 500/550 millimeters to 4000/5000 millimeters.
• Each sheath 13 is closed at its end 14 of small section, its end 15 of large section being connected to the other sheath 13.
• the collector 8 is intended to be connected to a gas treatment center, said GTC, not shown.
• a gas suction device for example a fan, is disposed downstream of the gas treatment center to capture all the gases. This device is not represented.
• the collector 8 is, for example, mounted on stilts 16 regularly spaced.
• the collection device 6 further comprises bypass loops 20 also called bypass lines, the flow of gases able to pass through a medium whose temperature is below the temperature of the gas.
• Each bypass line 20 is adapted to increase the heat exchange surface between the gases and said medium to cool the gases.
• This medium comprises the external environment, that is to say the ambient air.
• a water supply can be made in the form of watering, for example.
• the collection device 6 comprises branch lines 20 connected only to a section 26 of each sheath 13 having a section greater than the section of another section 28.
• the collection device 6 comprises bypass lines 20 regularly spaced along each sheath 13.
• each sheath 13 comprises a single bypass line 20.
• Each branch line 20 has an end 22 connected to it. a respective collection pipe 10 and another end 24 connected to the collector 8.
• Each bypass line 20 has a generally inverted "U" shape, the two branches of which extend substantially vertically.
• the branch line 20 has a circular shape or any other shape having at least one upward portion.
• bypass line 20 is provided with cooling fins, preferably projecting outwardly.
• bypass lines 20 are covered with a special coating to improve the heat exchange between them and the ambient air.
• the branch lines 20 all have the same length.
• the bypass lines 20 have a different length making it possible to modulate the rate of cooling of the gases coming from each electrolytic cell 3. This modulation of the temperature of the gases coming from each electrolysis cell makes it possible to modulate the temperature of the gases. leaving the collection device 6.
• the branch lines 20 are formed by pipes having a constant section.
• the various branch lines 20 have pipes with different sections.
• the gases entering the manifold 8 and from a branch branch branch 20 will have a different temperature to the gases entering the manifold 8 and from another branch branch branch.
• a deflector 30 is mounted in the collection device 6 at the connection between the recovery pipe 10 and the branch pipe 20. This deflector 30 is movable between a closed position of the recovery pipe 10 and the opening of the bypass line 20, and an opening position of the recovery pipe 10 and closure of the branch pipe 20.
• the deflector 30 is replaced by a shutter adapted to close or open the bypass line 20, the recovery tubing 10 remaining open.
• the deflector 30 allows in particular to bypass the branch lines 20 when it is not necessary to use them or during maintenance periods.
• the collection device 6 advantageously comprises a support 32 capable of carrying each bypass line 20.
• This support 32 comprises, for example, a horizontal crosspiece carried by two feet joined at one end to form a
• V reversed The crosspiece supports each branch of the branch pipe 20.
• the feet are fixed to the sheath 13.
• the collection device further comprises a holding member of at least one bypass line, said holding member being fixed to the building structure.
• the recovery tubings 10 are devoid of pressure-reducing members.
• the bypass lines 20 have a pressure drop which at least partly replaces the pressure drop created by the pressure-reducing members which are, in the collection devices of the state of the art, installed in the recovery pipes.
• the bypass lines 20 do not increase the total pressure drop of the collector 8 upstream of the gas treatment center because only the section 26 of the collecting device 6 is equipped with them, the length of the section 26 being fixed by the overall temperature drop sought at the inlet of the gas treatment center and the permissible pressure drop value without modification of the network.
• the presence of bypass lines 20 is an efficient and inexpensive system, not consuming additional pressure drop when a limited temperature drop is sought.
• bypass lines makes it possible to cool the gases passing through the collection device before their arrival in the gas treatment center.
• Each bypass line has a greater length than each recovery line. Longer pipe allows for better gas cooling by providing more surface exchange with outside air.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Electrolytic Production Of Metals (AREA)

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Citations (2)

• 2009
  • 2009-07-20 FR FR0955044A patent/FR2948128B1/fr active Active
• 2010
  • 2010-07-16 CA CA2768648A patent/CA2768648C/fr not_active Expired - Fee Related
  • 2010-07-16 WO PCT/FR2010/051493 patent/WO2011010050A1/fr not_active Ceased
  • 2010-07-16 IN IN413DEN2012 patent/IN2012DN00413A/en unknown
  • 2010-07-16 CN CN201090001017.4U patent/CN202717856U/zh not_active Expired - Lifetime

Patent Citations (2)

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