Claims
- 1. A method of at least lessening the tendency for carbon to deposit on a metal surface when that surface is exposed, while heated, to a gaseous stream containing hydrocarbons during a thermal cracking process, the method comprising forming a thin, adherent coating of a glass-ceramic material on the metal surface prior to heating that surface and contacting it with the hot gaseous stream, thereby isolating the metal surface from the hot gaseous stream.
- 2. A method in accordance with claim 1 which comprises forming a glass-ceramic coating in a thickness of 0.0375-0.250 mm (1.5-10 mils) on the exposed metal surface.
- 3. A method in accordance with claim 1 which comprises forming on the metal surface a glass-ceramic coating that contains a crystal phase selected from the group consisting of alkaline earth metal silicate, alkaline earth metal aluminoborosilicate and alkaline earth metal aluminoborate crystal phases.
- 4. A method in accordance with claim 3 which comprises forming a glass-ceramic coating containing at least one silicate crystal phase.
- 5. A method in accordance with claim 4 which comprises forming a glass-ceramic coating that contains a cristobalite crystal phase.
- 6. A method in accordance with claim 3 which comprises forming a barium aluminosilicate or a strontium-nickel aluminosilicate glass-ceramic coating on the metal surface.
- 7. A method in accordance with claim 6 which comprises forming a barium aluminosilicate glass-ceramic coating that contains primary crystal phases of sanbornite and cristobalite and that consists essentially of, in percent by weight on an oxide basis, 20-65% BaO, 25-65% SiO2 and up to 15% Al2O3.
- 8. A method in accordance with claim 6 which comprises forming a strontium-nickel aluminosilicate glass-ceramic coating that contains primary crystal phases of SrSiO3 and Ni2SiO4 and that consists essentially of, in weight percent on an oxide basis, 20-60% SrO, 30-70% SiO2, up to 15% Al2O3 and up to 25% NiO.
- 9. A method in accordance with claim 1 which comprises forming the glass-ceramic coating on the inside wall of an entire pyrolysis furnace system including tube lengths and fittings.
- 10. A method in accordance with claim 9 which comprises forming the glass-ceramic coating by preparing a slurry of a finely divided frit of the precursor glass for the glass-ceramic, coating the inside wall of the tube with a thin layer of the slurry, drying the coating and heating it to adhere the coating to the tube wall and to convert the glass to a glass-ceramic.
- 11. A method in accordance with claim 10 which comprises heating the dried coating to a first temperature at which the glass flows to form a continuous, essentially non-porous coating on the metal, cooling to a lower, second temperature and holding at that temperature to convert the glass to a glass-ceramic.
- 12. A method in accordance with claim 1 which comprises exposing the coated metal surface to a gaseous stream containing ethane.
- 13. In a process for thermal cracking a gaseous stream containing hydrocarbons which comprises passing the gaseous stream over a heated metal surface, the method of lessening the tendency of carbon to deposit on the metal surface which comprises forming a slurry containing the finely divided frit of a precursor glass for a glass-ceramic, coating the metal surface with a thin layer of the slurry, drying the coating and heating it to cause the glass to soften and flow sufficiently to adhere to the metal surface and convert the glass to a glass-ceramic.
- 14. A method in accordance with claim 13 which comprises heating the dried coating to a first temperature at which the glass flows to form a continuous, essentially non-porous coating on the metal, cooling to a lower, second temperature, and holding at that temperature to convert the glass to a glass-ceramic.
- 15. A method in accordance with claim 13 which comprises coating the inside wall of a metal tube and heating the coating through the metal.
- 16. A method in accordance with claim 13 which comprises forming the slurry with a glass frit having an average particle size not over about 20 microns.
- 17. A method in accordance with claim 13 which comprises coating the tube wall with a sufficient slurry to form a glass-ceramic coating having a thickness of 0.0375-0.250 mm (1.5-10 mils).
Parent Case Info
This is a division of application Ser. No. 08/427,338, filed Apr. 24, 1995, now U.S. Pat. No. 5,807,616.
US Referenced Citations (1)
Number |
Name |
Date |
Kind |
5250360 |
Andrus |
Oct 1993 |
|