Heating – Processes of heating or heater operation – Including apparatus heat-up – cool-down or protection
Patent
1988-01-15
1989-08-22
Yuen, Henry C.
Heating
Processes of heating or heater operation
Including apparatus heat-up, cool-down or protection
432 5, 432 76, 432192, 432193, F27D 700
Patent
active
048591750
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention concerns an apparatus and a process for optimising combustion in furnaces having open chambers of baking carbonaceous blocks which are intended particularly but not exclusively for tanks for the production of aluminum using the Hall-Heroult process, but also generally for electrometallurgy.
STATE OF THE ART
The expression `carbonaceous block` will be used hereinafter to denote any product obtained by shaping a carbonaceous paste and intended after baking to be used in electrometallurgical furnaces.
For example, carbonaceous anodes which are intended for the tanks for the production of aluminum by the electrolysis of alumina dissolved in molten cryolite are produced by shaping a carbonaceous paste resulting from working a mixture of pitch and crushed coke at around 120.degree. to 200.degree. C. After the shaping operation, the anodes are fired or baked for around a hundred hours at a temperature of the order of 1100.degree. to 1200.degree. C. Other types of carbonaceous blocks are produced by the same process.
Although there are some processes for continuous baking in a tunnel furnace, a large proportion of the baking installations which are in operation throughout the world at this date are of the `chamber furnace` type, referred to as having `rotary firing` (ring furnace) or having `advancing firing`. Those furnaces are themselves divided into two categories, closed furnaces and furnaces referred to as having `open chambers`, which are the most widely used, as described in particualr in U.S. Pat. No. 2 699 931. The present invention is applied more particularly to open chamber furnaces. That type of furnace comprises two parallel arrays, the total length of which may attain more than around a hundred meters.
Each array comprises a succession of chambers which are separated by transverse walls and which are open in their upper part to permit charging with the raw blocks and unloading of the cooled baked blocks. Each chamber comprises, disposed in parallel to the major axis of the furnace, an assmebly of hollow partitions having thin walls in which the hot gases which produce the baking effect will circulate, the partitions alternating with compartments in which the blocks to be baked are stacked, being immersed in a carbonaceous dust (coke, anthracite or carbonaceous residues in crushed form or any other powder filling material). There are for example six compartments and seven partitions in alternate arrangement per chamber.
In their upper part the hollow partitions are provided with closable openings referred to as `ports `; they aslo comprise baffle arrangements for increasing the length of and more uniformly distributing the flow of the combustion gases.
The furnace is heated by arrays of burners of a length equal to the width of the chambers and whose injectors are positioned on the port openings of the chambers in question. Upstream of the burners (in relation to the direction of advance of the firing effect), there is a combustion air blowing pipe while downstream there is a pipe for sucking away the burnt gases. Heating is effected both by combustion of the injected fuel (gas or fuel oil) and by combustion of the pitch vapours emitted by the carbonaceous blocks as they undergo baking.
As the baking process takes place, the assembly consisting of the combustion air blowing pipe, the burners and the burnt gas suction pipe is advanced every 24 hours for example, each chamber thus successively performing the functions of charging with raw carbonaceous blocks, natural preheating (by means of the combustion gases), forced preheating and baking at 1100.degree. to 1200.degree. C. (in the zone referred to as full firing), cooling of the carbonaceous blocks (and preheating of the combustion gases), unloading of the baked carbonaceous blocks, repair operations if required, and the resumption of a fresh cycle.
TECHNICAL PROBLEM TO BE SOLVED
The quality of the carbonaceous blocks (anodes, cathodes or lateral linings) being one of the essential elements involved in the
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Dreyer Christian
Thomas Jean-Claude
VanVoren Claude
Aluminium Pechiney
Yuen Henry C.
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