WO2017199263A1 - Ensemble anode à bout étagé en forme de tige pour une cellule électrolytique d'aluminium - Google Patents

Ensemble anode à bout étagé en forme de tige pour une cellule électrolytique d'aluminium Download PDF

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Publication number
WO2017199263A1
WO2017199263A1 PCT/IN2017/050076 IN2017050076W WO2017199263A1 WO 2017199263 A1 WO2017199263 A1 WO 2017199263A1 IN 2017050076 W IN2017050076 W IN 2017050076W WO 2017199263 A1 WO2017199263 A1 WO 2017199263A1
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WO
WIPO (PCT)
Prior art keywords
stub
anode
end portion
anode assembly
carbon
Prior art date
Application number
PCT/IN2017/050076
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English (en)
Inventor
Amit Kumar Mishra
Original Assignee
Hindalco Industries Limited
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Hindalco Industries Limited filed Critical Hindalco Industries Limited
Publication of WO2017199263A1 publication Critical patent/WO2017199263A1/fr

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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
    • C25C3/08—Cell construction, e.g. bottoms, walls, cathodes
    • C25C3/12—Anodes

Definitions

  • the present disclosure relates to an anode assembly for aluminium electrolysis cells used for aluminium production. More particularly, the present disclosure relates to a reduced voltage drop rodded stepped stub anode assembly for an aluminium electrolytic cell.
  • Aluminium has turned out to be the wonder metal of the industrialized world. No other single metal is so versatile in use and economics. Aluminium's growth rate is the highest amongst the major basic metals today. However, the aluminium production is highly energy consuming. The major cost components of aluminium production are DC Power, Alumina and Carbon anode. Aluminium is conventionally produced by the Hall-Heroult process in which alumina is dissolved in molten cryolite and electrolyzed with an intense direct current (DC). The cryolite bath is contained in electrolytic cells lined with carbon cathodes while carbon anodes hang from rods connected to an electrical bus bar.
  • DC direct current
  • the alumina is reduced with oxygen being deposited on the anodes and forming mostly carbon dioxide while the molten aluminium is deposited on the cell bottom and periodically tapped.
  • the reduction process is performed in a large aluminium reduction cell which includes a container or "pot” lined with refractory and carbon. Within the pot is a molten mixture of alumina dissolved in cryolite and other materials, such as various fluorides, which are generally referred to as "bath".
  • a voltage potential is applied between the carbon anodes and the pot, resulting in a large current flow from the anodes, through the molten bath mixture, to the pot.
  • the electrical current passing through the bath mixture reduces the alumina into its aluminium and oxygen components.
  • the aluminium drops to the bottom of the pot, forming the metal pad.
  • the oxygen combines with the carbon from the anodes and escapes as carbon dioxide gas, which is vented from the pot.
  • As the alumina is consumed more alumina is added to the bath in the cell.
  • the carbon anodes are consumed, therefore, the spent anodes are routinely replaced by fresh anodes so that the aluminium production can continue in an efficient manner.
  • the decomposition voltage of alumina to aluminium is 1.60 V but the normal voltage required for smooth pot operation is 4.40 V. This excess power consumption during smelting is due to various drops :-
  • the anode connection has to be replaceable, tight and resistance to deterioration.
  • a loose connection causes high voltage drops, while a cramped connection causes crack in the anode block.
  • the aggressive environment of the aluminium production cell causes continuous stub deterioration and stub bending.
  • the known prior arts of anode assembly have the drawbacks of high voltage drop at stub-anode connection and have high power consumption and involve high cost.
  • the non-patent disclosure titled as "Low resistance anode assembly using steel stubhole conductors across the cast iron to carbon interface (Edward Williams, W. Berends, S. Haley and M. Gagnon) relates to anode assemblies which suffer a significant electrical contact resistance across the cast iron to carbon interface that is inversely dependent on contact pressure and area. Industry efforts have incrementally reduced this electrical resistance by increasing stub diameter, changing iron chemistry and by improving the stubhole shape. The additional use of multiple steel conductors to bridge across the cast iron to carbon interface provides a means to further reduce the electrical resistance. The function of the conductors is independent of the iron to carbon contact pressure, the stub temperature, iron chemistry, and the stubhole shape.
  • the anode assembly includes a baked anode block, a plurality of elongated connection elements each having an anode block contact surface and an electrical connection surface, at least one electromechanical crossbar connector covering the electrical connection surfaces of the elongated connection elements, and a crossbar electrically connected to the elongated connection elements.
  • the method of manufacturing an anode assembly includes the steps of forming a block of green anode paste, inserting a plurality of elongated connection elements in the green anode paste, baking the green anode, positioning a crossbar above the electrical connection surfaces of the plurality of elongated connection elements, and covering the electrical connection surfaces and at least partially the crossbar with a surface-conforming electrically-conductive material.
  • the conductor have been forged with plurality of elongated connection elements and stub has not been used.
  • the elongated structure has to be baked along with in baking furnace for strengthening.
  • EP2006419 titled "reduced voltage drop anode assembly for aluminium electrolysis cell” discloses an anode assembly for aluminium electrolysis cells comprising carbon anodes with stubholes and an anode hanger having stubs, whereas the anodes are fixed to the anode hanger by cast iron, characterized in that the stubholes are fully or partially lined with an expanded graphite lining. Further, mechanical stresses in the stubhole area are reduced. By further forming a collar from the lining, the spilling of cast iron over the anode surface is prevented and optionally a protective shot plug or a protective collar prevent direct contact of the hot electrolyte bath with the stub and the cast iron.
  • this prior art discloses the graphite lining in which baked anode block is coated with graphite to reduce the voltage drop.
  • WO 2015089654 titled “Low resistance electrode assemblies for production of metals” discloses an electrode assembly for use in a reduction cell for the production of metal such as aluminium.
  • the electrode comprises an electrically conductive carbon electrode block with an electrically conductive metal member connected thereto.
  • the connection provides an improved electrically conductive connection between the carbon electrode block and the conductive metal member, with reduced resistance.
  • the insert may provide a direct connection between the electrode block and the metal member, or the connection may be provided through a layer of cast iron or other metal element provided between the electrode block and the metal member.
  • electrical connection is done by copper / aluminium rod with stub and in Rodding Shop molten cast iron is poured in the hole / carbon block through which current passed to the Pot. Therefore, in smelter, high Stub to Carbon drop has an impact on specific power consumption, cost of aluminium production and life of Anode rod assembly.
  • An objective of the present disclosure is to reduce the voltage drop at the anode connection by increasing contact surface area between anode block and stub.
  • Another objective of the present disclosure is to reduce stub to carbon drop in a smelter.
  • Still another objective of the present disclosure is to reduce heat dissipation through the stub. Still another objective of the present disclosure is to reduce the cost of aluminium production.
  • An aspect of the present disclosure is to provide a rodded anode assembly for an aluminium electrolytic cell, the anode assembly comprising: - an anode block, the anode block having a stubhole;
  • a stub having a first end portion and a second end portion, the first end portion of the stub accommodated in the stubhole in the anode block;
  • the first end portion of the stub has an enlarged diameter and the second end portion of the stub has a reduced diameter, the first end portion abutting the second end portion;
  • the dimensions of the first end portion and second end portion being configured such that the first end portion accommodated in the stub hole has maximized surface area thereby reducing the voltage drop between the anode and the first end portion of the stub.
  • the stub is made of mild steel.
  • Still another embodiment of the present disclosure provides that the anode block is made of carbon. Still another embodiment of the present disclosure provides that clearance between the stubhole and the first end portion of the stub has cast iron filling forming a thimble around the first end portion of the stub.
  • Still another embodiment of the present disclosure provides that dimensions of the stubhole are configured in proportion to dimensions of the first end portion of the stub.
  • the stub is mechanically, thermally and electrically connected to the anode block by casting molten iron.
  • Another embodiment of the present disclosure provides that an elongated copper bar is connected to the stub through stiffener made of mild steel and it helps in penetrating copper bar in mild steel stub to strengthen the weld joint.
  • Figure 1 shows rodded anode assembly with stepped stub for an aluminium electrolytic cell (pot cell);
  • Figure 2 shows stepped Stub anode assembly in the electrolytic cells (pot cells) of a smelter;
  • Figure 3 shows the stepped stub accommodated in stubhole;
  • Figure 4 (a) shows the stepped stub according to the present disclosure
  • Figure 4 (b) shows normal stub as per the prior arts
  • Figure 5 shows graph for voltage of an electrolytic cell (pot cell) with stepped stub
  • Figure 5(b) shows graph for voltage of an electrolytic cell (pot cell) with normal stub.
  • alumina Primary aluminium is produced by electrolytic reduction of alumina, the process is commonly known as Hall-Heroult Process, alumina is dissolved in molten cryolite bath and electrolysis is carried out in specially designed aluminium electrolysis cells commonly known as 'pots'.
  • An electrolytic cell consists of the following components :- Anode (the +ve terminal) - Prebaked, made of CP coke and coal tar pitch;
  • Cathode (the -ve terminal) - made of cathode carbon blocks in which steel collector bars are embedded to make electrical connection;
  • Electrolyte - Medium for carrying out electrolysis consisting of mainly, cryolyte, aluminium fluoride and calcium fluoride in which alumina is dissolved for electrolysis;
  • Electrolytic cells are connected in series along with certain bus bar configuration for passage of current constitutes a potline, spread over in two rooms.
  • an electrolytic cell In an electrolytic cell, when DC current is passed from anode to cathode through molten electrolyte, alumina dissolved in electrolyte is dissociated into aluminium & oxygen. Aluminium being positively charged goes to the cathode while oxygen being negatively charged goes to anode, aluminium continues to deposit at cathode, which is tapped out periodically. Oxygen reacts with anode carbon forming C02 & CO, which ultimately goes out of cell as pot gases. The consumed anodes are replaced in certain sequence periodically with new anode to continue the process.
  • Reduction Plant in particular comprises of Carbon Plant, and Pot rooms.
  • Carbon Plant carbon electrodes (anodes and cathode Paste) are produced which are utilized during electrolytic process of reducing alumina powder to molten aluminium metal.
  • the metal produced in pot rooms is finally converted into value added products viz. Properzi wire rods, Slabs, Billets, ingots. Further value on these products is added in Fabrication Plant.
  • Carbon anode is one of the major raw material in aluminium smelter operation. It takes active part in electrolysis and gets consumed in the process. On completion of its scheduled stay in pots, the anode is replaced by a new one and the remaining portion known as butt is processed together with calcined coke and Binder Pitch for fresh anode production.
  • the carbon anode is manufactured in three stages: GREEN ANODE
  • the ingredients in anode manufacturing are Calcined Petroleum Coke (C.P.coke), High softening point Coal Tar Pitch and Pot room returned butts.
  • Coke consignment received from various sources is stored in coke silos.
  • coke is passed through primary and secondary crushers and screened. Potroom return butts are fed to jaw crushers and crushed in 4"-6" sizes. The same is passed through hammer mill and crushed into -3/4" particle size.
  • This material is stored in butt silo and transferred to bins as butt fraction. Pitch is stored holding tanks from where it is transferred to buffer tank then weighing scale for consumption.
  • Dry aggregate constituting 5 fractions coarse, medium, fine, BMP and filter dust fractions are separately weighed, as per the standards specified, and charged into preheater.
  • the dry aggregate is mixed and heated up in preheater and then transferred to buss mixer where measured quantity of molten pitch is added to the mixer and prepared paste. Hot paste is then transferred to surge hopper. From surge hopper, the weighed quantity of paste is feed to transfer trolley which finally feeds to vibroforming mould and form anode subsequently into green anodes.
  • Formed anodes are water cooled and unloaded on skips (carrier for carrying green anodes). These anodes are checked for their physical appearance, height, weight & density and only good anodes are transferred for baking.
  • the good green anodes from paste plant are packed in empty pits of Baking Furnace. All the anodes are covered by CP. coke all around. The top of the last layer anode is covered with CP. Coke as blanket material. These anodes are baked at a temperature around ⁇ 1100 deg. C (min) in the pits and the total baking cycle takes about 15-20 days. During the baking process the binder pitch gets converted into pitch coke. The released volatile matter contributes in baking of anodes.
  • the firing system in baking furnace consists of computerized oil (F/Oil) fired burners regulated by temperature feedback of flue thermocouples. The baking process improves anode quality interns of strength, reactivity, thermal and electrical conductivity etc.
  • Baked anodes are fixed with Cu-steel stub assembly by pouring molten cast iron around the steel stub, in the anode hole. On solidification the Cu - stub assembly gets fixed with the carbon anode. A reference mark is marked at about 2.2 meters from the bottom of the anode, on copper bar. The ready anode is then sent to Potroom for replacing the old consumed anodes in pots.
  • the rodding shop has the induction furnaces where the cast iron charge is prepared.
  • a rodded assembly with anode block comprises of copper bar and stub welded in house the length of the individual material i.e. Cu bar stub and an anode block may varies from one assembly to another therefore the marka (painted line) is marked from bottom reference these marka line helps for purposed of anode setting.
  • the present disclosure provides a rodded anode assembly with stepped stub for an aluminium electrolytic cell wherein stub is designed in such a fashion that the contact surface area inside the hole is kept maximum to reduce the stub to carbon drop for anode thereby minimizing the cost involved.
  • FIG 1 which shows rodded anode assembly with stepped stub.
  • the rodded anode assembly ( 1) comprising a carbon anode block (2), an electrically conductive stub (4) having a first end portion (Al) and second end portion (A2), the first end portion (Al) of the stub (4) is accommodated in the stubhole (3) of the anode block (2), a copper bar (5) electrically and mechanically connected through stiffener by welded joint to the second end portion (A2) of the stub.
  • the clearance between the stubhole (3) and the first end portion (Al) of the stub has cast iron filling (6) forming a thimble around the first end portion (Al) of the stub.
  • figure 2 which shows the stepped Stub anode assembly in pot cells of the smelter. Various components of the assembly are described as below: -
  • Anode block (2) It is a consumable material comprising of calcined petroleum coke and hard pitch. When current passes through it to perform electrolysis reaction it gets consumed.
  • Stepped Stub (4) it is made of mild steel and conduct electric current from copper bar to Anode Block through cast iron.
  • Copper bar (5) It is a rectangular section of copper for conducting electric current anode ring bus to carbon block.
  • Figure 3 shows the stepped stub accommodated in a stubhole and it is a cross sectional view of anode hole with stepped stub.
  • Cast iron thickness was increased in steps and then optimized to keep a balance between the rate of butt cracking & molten cast iron required for Pouring in Rodding Shop without affecting normal supply of anodes (Nos.) to potrooms.
  • D- 19 is experimental Pot which have 200 mm stub diameter.
  • D-21 is Reference Pot which have 160 mm stub diameter.
  • the stepped step anode assembly has been implemented in 44 pots and if replicated in all 2138 pots of a smelter unit, it provides voltage drop of 40-50 mV/ pot, which results in cost saving of approximately 140 million INR based on the production 405000 ton/annum and power saving of 126 units/ton, wherein energy unit charges have been taken as INR 2.8 /unit.
  • Stall no are the position of individual anode mounted on pots. If there are 24 anodes then 24 stall are there in a particular pot and if there are 20 anodes then 20 stall in a particular pot.
  • Cast Iron Filling material for fixing of stub with carbon block. Also it carries current from stub to carbon block.
  • Pot Cover These are made of aluminium to cover the pots there by reducing the dusting and also arresting toxic gasses such as HF and C02.
  • Stiffener To strengthen the welding joint between copper bar and steel stub and made of Mild Steel.
  • Copper bar It is a rectangular section of copper for conducting electric current anode ring bus to carbon block.
  • Carbon Block It is a consumable material comprising of calcined petroleum coke and hard pitch. When current passes through it to perform electrolysis reaction it gets consumed.
  • Bath It is an electrolyte solution, work as a catalyst for electrolysis.
  • Cathode Block It is made of carbon and used for electrolysis reaction as a -ve potential.

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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)

Abstract

La présente invention concerne un ensemble anode (1) pour des cellules d'électrolyse d'aluminium utilisées pour la production d'aluminium. Plus particulièrement, l'invention concerne un ensemble anode en forme de tige à chute de tension réduite pour une cellule électrolytique d'aluminium, dans lequel le bout (4) est conçu de telle manière que la superficie de la surface de contact à l'intérieur du trou est maintenue au maximum afin de réduire la réduction du carbone pour l'anode.
PCT/IN2017/050076 2016-05-17 2017-02-27 Ensemble anode à bout étagé en forme de tige pour une cellule électrolytique d'aluminium WO2017199263A1 (fr)

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IN201611017078 2016-05-17
IN201611017078 2016-05-17

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
RU2682507C1 (ru) * 2018-01-10 2019-03-19 Федеральное государственное автономное образовательное учреждение высшего образования "Сибирский федеральный университет" Способ снижения контактного напряжения в алюминиевом электролизере

Citations (1)

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Publication number Priority date Publication date Assignee Title
CN101743344A (zh) * 2007-06-22 2010-06-16 Sgl碳股份公司 用于铝电解槽的减小电压降的阳极组件

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN101743344A (zh) * 2007-06-22 2010-06-16 Sgl碳股份公司 用于铝电解槽的减小电压降的阳极组件

Non-Patent Citations (2)

* Cited by examiner, † Cited by third party
Title
EBRAHIM JEDDI: "NUMERICAL STUDY OF ANODIC VOLTAGE DROP IN THE HALL-HEROULT CELLS BY FINITE ELEMENT METHOD", THESIS, 2012, XP055440206, Retrieved from the Internet <URL:http://constellation.uqac.ca/2663/1/030430500.pdf> *
MAHMOUD A.ALY ET AL.: "A STUDY OF ANODIC VOLTAGE DROP IN ALUMINUM REDUCTION CELL BY FINITE ELEMENT ANALYSIS", INT. JOURNAL OF ENGINEERING RESEARCH AND APPLICATIONS, vol. 6, no. 1, January 2016 (2016-01-01), pages 01 - 11, XP055440205, ISSN: 2248-9622 *

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
RU2682507C1 (ru) * 2018-01-10 2019-03-19 Федеральное государственное автономное образовательное учреждение высшего образования "Сибирский федеральный университет" Способ снижения контактного напряжения в алюминиевом электролизере

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