Chemistry: electrical and wave energy – Apparatus – Electrolytic
Reexamination Certificate
2000-04-25
2002-06-25
Valentine, Donald R. (Department: 1741)
Chemistry: electrical and wave energy
Apparatus
Electrolytic
C204S245000
Reexamination Certificate
active
06409894
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to aluminum production plants using the Hall-Héroult electrolysis smelting process. It particularly relates to the lay-out of installations for such plants.
2. Prior art
Metal aluminum is produced at the industrial level by igneous electrolysis, that is to say by the electrolysis of alumina in solution in a bath of smelted cryolite, called an electrolytic bath, using the well-known Hall-Héroult process. The electrolytic bath is contained in pots comprising a steel shell lined on the inside with refractory and/or insulating material, and a cathode assembly positioned at the bottom of the pot. Anodes in carbon material are partly immersed in the electrolytic bath. Each pot and its anodes form what is often called an electrolytic cell. The electrolysis current, which circulates in the electrolytic bath and the liquid aluminum layer via the anodes and cathode parts, conducts alumina reduction reactions and also enables the electrolytic bath to be maintained at a temperature in the region of 950° C. through the Joule effect.
Most modern plants have a large number of electrolytic cells arranged in lines, in buildings called electrolysis halls, which are electrically connected in series by means of link conductors so as to optimize the use of floor space in plants. The pots are generally arranged so as to form two or more parallel lines which are electrically connected to each other by end conductors. The electrolysis current therefore passes cascade fashion from one cell to the next. The length and mass of the conductors are as small as possible in order to limit investment and operating costs, in particular by reduction of losses through the Joule effect in the conductors. The conductors are also configured such as to reduce or offset, in whole or in part, the effects of magnetic fields produced by the electrolysis current.
When in operation, an electrolysis plant comprises a series of flows, in particular flows of raw materials (alumina, carbon powder, pitch), flows of intermediate products (solidified bath crusts, anode assemblies . . . ), flows of end products (liquid and/or solid aluminum), flows of personnel (persons on foot or drivers of automotive equipment), flows of energy (in particular flows of electric energy), flows of demolition products (in particular from anode baking furnaces), flows of tooling, flows of pot components (such as cathodes or pot shells) and flows of maintenance equipment. Some flows are essentially continuous (such as flows of raw materials), others are semi-continuous (such as flows of liquid aluminum, anode assemblies and solidified bath) and others are essentially discontinuous (such as flows of cathodes or pot shells).
These different flows are generated by the electrolysis process. For example, the Hall-Héroult process causes consumption of carbon anodes during electrochemical reactions of alumina reduction; this consumption requires the regular supply of new anodes and the replacement of spent anodes from the electrolysis cells, which generate flows of new anode assemblies from the anode production sites towards the electrolysis pots, and flows of spent anode assemblies from the pots towards the reprocessing and recycling sites.
For reasons relating to plant productivity, it is sought firstly to reduce investment and operating costs, and secondly simultaneously to obtain Faraday intensities and yields that are as high as possible while maintaining, even improving, the operating conditions of the electrolytic cells and giving consideration to a series of restrictions of a technical nature.
In particular, some flows generated by the operation of electrolysis plants may be conveyed by specific conveyance means, which is often the case for alumina flows and flows of emitted gases which are conveyed by specific channels which generally form fixed networks. However, several flows of materials follow pathways in common with other flows and/or with personnel access routes which is the case for so-called “heavy” flows of liquid metal, carbon products (such as anode assemblies) and solid bath (crusts, removed excess bath and recycled bath). Typically, these heavy flows which are in general essentially discontinuous, are conveyed by means of motorized equipment using transport routes (outside or inside the buildings) which run alongside the electrolysis pots, which routes are also used by personnel. The cohabitation of considerable movements of materials, equipment and personnel in the same working space also imposes a limit on the search for improving working and safety conditions. These problems are heightened by the fact that several flows require handling precautions and/or special environmental precautions.
In addition, the impact of problems related to flow density within a given plant and to physical interactions between flows and installations becomes rapidly greater if it is sought to increase the productivity of a plant. For example, the increase in electrolytic cell production, through an increase in current intensity, leads to a swift increase in the density of flows, in the intensity of magnetic interactions and in the unit loads to be transported.
The applicant therefore set out to find plant arrangements which take into account these different constraints, which lead to a reduction in investment and maintenance costs, and with which it is possible to increase plant production capacity.
BRIEF SUMMARY OF THE INVENTION
The subject of the invention is a layout for an electrolysis plant for the production of aluminum using the Hall-Héroult process, said plant comprising at least one liquid aluminum production zone H, characterized in that it comprises:
specific operational support zones such as a zone C which groups together the supply and recycling installations for the anode assemblies, a zone B which groups together the supply and recycling installations for the electrolytic baths and a zone A grouping together the liquid aluminum processing installations,
transport means for the conveyance, between said operational zones and according to determined intermediate flows, of said heavy products such as liquid aluminum, anode assemblies and solid electrolytic bath,
at least one transit zone reserved for all or part of said transport means for heavy intermediate products.
In the search for a solution to the problems raised by known electrolysis plants, the applicant had the idea, firstly of grouping together certain installations of some heavy flows and, secondly, of using a reserved transit zone which would reduce distances travelled while avoiding the cohabitation of flows having low compatibility such as heavy flows, and flows of personnel. With the arrangement of the invention it is therefore possible both to optimise the distances travelled by the main heavy flows of an electrolysis plant, which carry a potential risk, and to take into account the effects of physical interactions between flows and installations.
The presence of a reserved transit zone also allows for greater control over operator working conditions and safety, in particular by restricting movements of personnel in this zone. It also provides for greater control over co-ordination of the process, over operational management and over environmental conditions required for certain heavy flows, such as the flow of spent anode assemblies removed from the electrolysis pots, which may require aspiration and effluent treatment means.
REFERENCES:
patent: 4474611 (1984-10-01), Blanc et al.
patent: 4592821 (1986-06-01), Keinborg et al.
patent: 4683047 (1987-07-01), Bolvin et al.
patent: 5882499 (1999-03-01), Bonnardel et al.
Plant Design and Economics for Chemical Engineers, McGraw-Hill, 3rded., 1980, Chapter 1, pp. 1-11.*
La Technique Moderne, vol. 64, No. 12, 1972, pp. 65-67, XP002155185 (with English Abstract).
Aluminium Pechiney
Heller Ehrman White and McAuliffe LLP
Parsons Thomas H.
Valentine Donald R.
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