Chemistry: electrical and wave energy – Processes and products
Patent
1994-04-22
1995-10-10
Gorgos, Kathryn
Chemistry: electrical and wave energy
Processes and products
204222, 204223, 204243R, 204245, 204286, 204297R, C25C 308
Patent
active
054568080
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to aluminium smelting cell improvements aimed at facilitating the use of continuous prebaked anodes, and more particularly relates to improved anode support structures as well as preferred support structure arrangements which enable associated improvements in cell efficiency. The present invention also relates to a method of operating an aluminium electrolysis cell.
BACKGROUND OF THE INVENTION
The conventional aluminium smelting technology which uses discontinuous prebaked anodes has major limitations in the areas of electrical energy efficiency, environmental pollution and worker health. Replacement of anodes contributes to low power efficiency and high fluoride emissions from pots, potrooms, butts processing areas and baking furnaces. Anode replacement involves a number of activities which are necessitated by the need to access the pots, remove spent anodes, add new anodes, cover these up, recover anode rods, cast iron and carbon from spent anodes, clean, crush and reprocess butts, return butt bath to the pots, etc. All this adds to the cost of production and to environmental and health problems.
The conventional strategy used to deal with problems emanating from anode replacement has been to learn to live with them by alleviating their impact on worker health and safety and to reduce their cost through better economies of scale and increased mechanisation. The aluminium industry has in the past developed butts cleaning technology and currently is looking for better ways of handling anodes, butts and bath and reducing pot emissions in potrooms. The underlying problem with this strategy is that no matter what is done with anode replacement and how this is done, no value is being added to the metal produced, or to any of the by-products of the process.
The discontinuous anode technology has impacted on the smelting technology in a number of ways. Cell design and construction, plant design, layout and capital infrastructure have all been affected. Apart from these, there are a number of jobs and operations which stem from anode replacement, all of which add to the cost, but not to the value of metal produced. These are: anode setting, butts handling, cleaning, crushing and grinding, bath crushing and handling, oreing-up of pots, anode rodding, fume treatment and others. Each of these steps and processes require significant capital investment and incur substantial operating costs.
The need to access the pots to replace anodes has meant that pots could not be adequately sealed. Excessive air flow rates are used to effectively purge the pots to keep the pot emissions in potlines down. During anode setting, the pots have to be opened and large volumes of fumes are released into the potroom atmosphere from open anode hole. Spent hot butts are often left in the potrooms to cool off before moving. Gaseous fluorides are produced by a reaction between the hot butts and moisture in the air which is drawn in from outside by the potroom and pot ventilation systems. This strategy of using large volumes of air to effectively purge the potlines and pots in order to keep the concentration of hazardous HF gas down, is doubly self-defeating. On the one hand, purging gas (atmospheric air) is the principal source of the hazard (HF production is directly proportional to the amount of moisture in the air), and on the other, the hazardous gas becomes so diluted that a very large and very efficient scrubbing system is required to achieve environmentally safe fluoride discharge levels.
Recycling of butts leads to introduction of fluoride salts into green anodes. These can react with hydrogen in the pitch binder during baking to give off HF. At higher temperatures, fluoride salts can also be vaporized. Fluorides contaminate the flue gas, react with refractories and accelerate the flue walls failures. Baking furnace flue gas is a major source of fluoride emissions which in the future may require scrubbing.
Anode replacement has negative influence on the pot operations and its efficien
REFERENCES:
patent: 2958641 (1960-11-01), Reynolds
patent: 4608134 (1986-08-01), Brown
patent: 4608135 (1986-08-01), Brown
patent: 4749463 (1988-06-01), Holmen
patent: 5071534 (1991-12-01), Holmen et al.
patent: 5364513 (1994-11-01), Sekhar et al.
F. H. Dethloff, "Heat Recovery From Pot Gas From Electrolytic Reduction Cells for Producing Aluminium", (1983).
Comalco Aluminium Limited
Gorgos Kathryn
LandOfFree
Method for operating a continuous prebaked anode cell by locatin does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for operating a continuous prebaked anode cell by locatin, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for operating a continuous prebaked anode cell by locatin will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2308447