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
  • C25C3/125—Anodes based on carbon
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
  • C25B11/04—Electrodes; Manufacture thereof not otherwise provided for characterised by the material
  • C25B11/042—Electrodes formed of a single material
  • C25B11/043—Carbon, e.g. diamond or graphene
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
  • C25B11/04—Electrodes; Manufacture thereof not otherwise provided for characterised by the material
  • C25B11/042—Electrodes formed of a single material
  • C25B11/043—Carbon, e.g. diamond or graphene
  • C25B11/044—Impregnation of carbon
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25C—PROCESSES FOR THE ELECTROLYTIC PRODUCTION, RECOVERY OR REFINING OF METALS; APPARATUS THEREFOR
  • C25C7/00—Constructional parts, or assemblies thereof, of cells; Servicing or operating of cells
  • C25C7/02—Electrodes; Connections thereof
  • C25C7/025—Electrodes; Connections thereof used in cells for the electrolysis of melts

Definitions

• This invention relates to carbon electrodes and the manner of their preparation from mixtures of delayed and fluid coke. More particularly it relates to the preparation of electrodes of this nature which can be utilized for the obtaining of aluminum from its ores.
• Delayed coking is the well known cracking method for the thermal conversion of heavy hydrocarbon oils to lighter fractions and coke.
• the process employs a reaction or coking chamber designed to accumulate. substantial quantities of coke between cleanings.
• Two vertical coke drums are generally employed, one of which is decoked while the other is onstream. Temperatures of about 750 to 900 F. are employed.
• the calcined, delayed coke product has a high real or particle density, i. e., 2 or higher.
• the size distribution of the delayed coke particles utilized in electrode manufacture is such that a predominant portion, i. e., about 80 wt. percent, has a diameter in the range of about /2" to 200 mesh with the balance finer than 200 mesh. It has thus been thought that comparatively large particles and high real densities wererequired for satisfactory elec trodes.
• the principal criteria of these finished electrodes are a minimum compression strength of 4400 pounds per square inch, a minimum real density of about 1.45 and a maximum resistivity of 3 l0 ohm-inch.
• the fluid coke is utilized in an amount of from 1 to 50 wt. percent, preferably 20 to 40 wt. percent, based on the total coke charge.
• electrodes made from the blends are the equals of those made from delayed coke alone in all other requirements and in addition are essentially free of the dusting problem.
• the calcined delayed coke employed has the characteristics enumerated above, i. e., real density and particle size distribution.
• the calcined fluid coke utilized is prepared by the recently developed fluid coking process, e. g., see Serial No. 375,088, filed August 10, 1953. For completeness the process is supplied in further detail although it should be understood the fluid coking process is no part of this invention.
• the fluid coking unit consists basically of a reaction vessel or coker and a heater or burner vessel.
• the heavy oil to be processed is injected into the reaction vessel containing a dense turbulent fluidized bed of hot inert solid particles, preferably coke particles.
• a transfer line reactor or staged reactors can be employed. Uniform temperature exists in the coking bed. Uniform mixing in the bed results in virtually isothermal conditions and efiects instantaneous distribution of the feed stock.
• the feed stock is partially vaporized and partially cracked.
• Product vapors are removed from the coking vessel and sent to a fractionator for the recovery of gas and light distillates therefrom. Any heavy bottoms is usually returned to the coking vessel.
• the coke produced in the process remains in the bed coated on the solid particles. Stripping steam is injected into the stripper to remove oil from the coke particles prior to the passage of the coke to the burner.
• the heat for carrying out the endothermic coking reaction is generated in the burner vessel, usually but not necessarily separate.
• a stream of coke is thus transferred from the reactor to the burner vessel, such as a transfer line or fluid bed burner, employing a standpipe and riser system; air being supplied to the riser for conveying the solids to the burner.
• Sufiicient coke or added carbonaceous matter is burned in the burning vessel to bring the solids therein up to a temperature suflicient to maintain the system in heat balance.
• the burner solids are maintained at a higher temperature than the solids in the reactor.
• About 5% of coke, based on the feed, is burned for this purpose. This may amount to approximately 15% to 30% of the coke made in the process.
• the net coke production which represents the coke made less the coke burned, is withdrawn.
• Heavy hydrocarbon oil feeds suitable for the coking process include heavy crudes, atmospheric and crude vacuum bottoms, pitch, asphalt, or heavy hydrocarbon petroleum residua or mixtures thereof.
• feeds can have an initial boiling point of about 700 F. or higher, an A. P. I. gravity of about 0 to 20, and a Conradson carbon residue content of about 5 to 40 wt. percent. (As to Conradson carbon residue see A. S. T. M. Test D-18052.)
• the fluid coke product is laminar in structure and may comprise some 30 to 100 superposed layers of coke.
• the size distribution is normally such that a predominant portion, i. e., about 90 weight percent has adiameter in the range of about 20 to mesh.
• the real density of these coke particles after the required calcining is in the range of 1.83 to 1.93, preferably 1.87 to 1.92.
• the calcining of the delayed and fluid coke is performed in the conventional manner, i. e., a calcination at a temperature in the range of about 2000 to 2800 F. or higher. This can be done in a fluid, moving or fixed bed in the presence of an atmosphere such as air, nitrogen, carbon dioxide, hydrogen, or by the use of shot. The calcination is conducted until real densities in the specified range are obtained. The time necessary is thus in the range of about 0.5 to hours. Longer calcining times may be used, especially in the lower temperature range, without deleterious effects.
• the coke blend is admixed with and charged together with a carbonaceous binder to the fabrication system.
• the binders utilized are conventional and include materials such as the aromatic coal tar pitch binders e. g. see U. S. Patent No. 2,683,107. Such binders generally have melting points lying within the range of 70120 C. They contain small amounts of hydrogen (about 5% or less). The concentration of benzene and nitrobenzene insoluble portions represent preferably about to and 5% to 15%, respectively, of the binder.
• the binder is utilized in an amount of about 18 to parts by weight per 100 parts of coke blend.
• two types of electrodes are employed by the industry (a) prebaked and (b) Soderberg self-baking electrodes.
• a mixture comprising about 78-82% of calcined coke blend and about 18-22% of coal tar pitch is molded at pressures of about 3000-6500 p. s. i. or extruded, and then baked for periods up to 30 days at l800 to 2400 F.
• These preformed electrodes are then used in electrolytic cells, being slowly lowered into the molten alumina as they are consumed. Butts of the unconsumed electrodes are reground and used in subsequent electrode preparations. Some green coke can be calcined during the baking operation.
• the Soderberg process involves the continuous or intermittent addition of a coke-coal tar pitch paste to the top of the cell as the electrode components in the lower part of the cell are consumed.
• the paste represents a blend of about 70% to 72% coke charge and 28% to 30% of pitch.
• the cells operate usually at temperatures of 1700 to 1900 F. and electrodes are consumed at the rate of about 0.5 to 1.0 inch per day.
• the paste is baked into an electrode by the hot cell gases in the period between the time it is added at the top and time it is used.
• the net consumption of coke represents 0.4 to 0.7 lb. per pound of aluminum metal produced. Both methods have in common the baking of the mixed coke charge and binder at a temperature in the range of 1700 to 2400 F.
• EXAMPLE 1 Prebaked electrodes were prepared from diiferent calcined coke charging stocks using about 30 parts by weight of coal tar pitch as binder and temperatures of about 1820 F. Further conditions of preparation and test results are given in Table I.
• the advantages of this invention are the elimination of dusting and reduction of heat loss from the cells with the lower density electrodes.
• the fact that the fluid coke can be used without grinding is an asset. Grinding the fluid coke permits the use of larger quantities in the blend.

Landscapes

• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Coke Industry (AREA)
• Carbon And Carbon Compounds (AREA)

Priority Applications (2)

Applications Claiming Priority (2)

Publications (1)

Family

ID=26759702

Family Applications (1)

Country Status (2)

Cited By (6)

Citations (3)

• 1954
  • 1954-11-29 US US471881A patent/US2835605A/en not_active Expired - Lifetime
• 1955
  • 1955-10-20 SE SE943055A patent/SE192759C1/sv unknown

Patent Citations (3)

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