Claims
- 1. A process for heat treating spent pot linings obtained from Hall-Heroult electrolytic cells and comprising carbon and silico-aluminous materials impregnated with fluorides, comprising the steps of:
- grinding said spent pot linings to a particle size less than 5 mm;
- forming an intimate mixture of said ground spent pot linings and a pulverulent mineral additive of particle size less than 1 mm selected from the group consisting of anhydrous CaSO.sub.4, CaSO.sub.4. 2H.sub.2 O and mixtures thereof;
- injecting said intimate mixture into the center of a vortex formed by a flow of circulating hot gas arriving tangentially at the top part of a reactor at a temperature T between 700.degree. and 1100.degree. C. and having a whirling movement;
- contacting said injected intimate mixture with said circulating hot gas to form a suspension of concentration between 0.1 and 3 kg/Nm.sup.3 ;
- extracting said suspension from a bottom part of the reactor at a temperature t between 400.degree. and 750.degree. C. after a contact time between said injected intimate mixture and said circulating hot gas of less than 2 seconds;
- maintaining the gas flow at the bottom of said reactor at a temperature T.sub.o between 450.degree. and 700.degree. C. and such that T>T.sub.o .gtoreq.t;
- cooling said extracted suspension; and
- separating the gas flow of said cooled extracted suspension from solid particles of insoluble residue contained therein.
- 2. Process according to claim 1, wherein said fluorides are selected from the group consisting of NaF, CaF.sub.2, AlF.sub.3 and mixtures thereof.
- 3. Process according to claim 1, wherein in the spent pot linings, the maximum weight contents of fluoride, cyanide, silicon and sodium are respectively 20, 1, 25 and 20%.
- 4. Process according to claim 1, wherein the size of the spent pot linings particles, after grinding, is smaller than 2 mm.
- 5. Process according to claim 1 or 4, wherein the additive weight proportion in the mixture is less than 50%.
- 6. Process according to claim 1, wherein the temperature T of the gas flow formed by the fuel gases circulating in the upper part of the reactor is between 800.degree. and 1000.degree. C.
- 7. Process according to claim 1 or 6, wherein the gas flow at temperature T circulates at a speed of at least 1 m/sec.
- 8. Process according to claim 1, wherein the concentration of said pulverulent suspension is between 0.3 and 2 kg/Nm.sup.3.
- 9. Process according to claim 1, wherein temperature T.sub.o is maintained by adjusting the weight flow rate of the intimate mixture injected into the gas flow at temperature T.
- 10. Process according to claim 9, wherein the intimate mixture weight flow rate is controlled by varying the speed of a feed screw injecting said mixture.
- 11. Process according to claim 1, wherein said hot gas is a product of combustion of a fuel gas.
- 12. Process according to claim 11, wherein temperature T.sub.o is maintained by controlled flow of a fuel gas conditioning the gas flow temperature.
- 13. Process according to claim 1, wherein said separated gas flow is subjected to an additional cooling and additional separation of solid particles therefrom.
Priority Claims (1)
Number |
Date |
Country |
Kind |
90 09174 |
Jul 1990 |
FRX |
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Parent Case Info
This application is a continuation-in-part of U.S. application Ser. No. 07/716,104, filed Jun. 17, 1991, now U.S. Pat. No. 5,245,115.
US Referenced Citations (1)
Number |
Name |
Date |
Kind |
5245115 |
Barrillon et al. |
Sep 1993 |
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Continuation in Parts (1)
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Number |
Date |
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Parent |
716104 |
Jun 1991 |
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