Process for vitrifying asbestos containing waste, infectious waste, toxic materials and radioactive waste

• US 5,188,649 A
• Filed: 08/07/1991
• Issued: 02/23/1993
• Est. Priority Date: 08/07/1991
• Status: Expired due to Term

• Current Assignee: Pedro Buarque De Maceado, Theodore Aaron Litovitz
• Original Assignee: Pedro Buarque De Macedo, Theodore Aaron Litovitz
• Inventors: Mohr, Robert K., Macedo, Pedro B.
• Primary Examiner(s): LINDSAY JR, ROBERT
• Application Number:
  US07/741,301
• Time in Patent Office: 566 Days
• Field of Search: 65/21.2, 65/21.3, 65/27, 65/134, 65/136, 65/178, 501/155
• US Class Current: 65/21.3
• CPC Class Codes: B09B 3/0066 Disposal of asbestos
• CPC Class Codes: B09B 3/0075 Disposal of medical waste casings for used articles, e.g. sharps A61B50/362; sterilisation of refuse A61L11/00; disposal of used needles or syringes A61M5/3205; disintegrating medical waste B02C19/0075
• CPC Class Codes: B09B 3/29 involving a melting or softening step
• CPC Class Codes: C03B 19/1005 Forming solid beads chemical aspects C03C12/00
• CPC Class Codes: C03B 19/109 Glass-melting furnaces specially adapted for making beads
• CPC Class Codes: C03B 5/005 of glass-forming waste materials disposal or transformation of solid waste in general B09B; treatment of radioactive waste G21F9/00
• CPC Class Codes: C03B 5/0275 Shaft furnaces C03B5/0277 takes precedence
• CPC Class Codes: C03B 5/193 using gas, e.g. bubblers
• CPC Class Codes: C04B 18/026 Melted materials C04B14/22 takes precedence
• CPC Class Codes: G21F 9/305 Glass or glass like matrix C03B5/005 takes precedence; compositional aspects C03C
• CPC Class Codes: Y02P 40/50 Glass production, e.g. reusing waste heat during processing or shaping

Abstract

Material, such as, for example, sealed double bags of asbestos containing waste or ash from infectious waste or toxic material or radioactive waste, is transferred into a glass melt of a furnace. Gas bubbles released into the melt form a gas curtain which causes enhanced mixing of the material to accelerate the dissolution of the components of the added material. The presence of the gas bubbles reduces the cross-section of the molten glass through which current passes, which in turn increases the electrical resistance of the glass melt and therefore increases power generation of the melt or power density at constant current. A highly oxidizing hot region is produced under the location where the material is introduced into the furnace. Drawn off glass is shaped and quenched into at least two sizes of approximate spheres. The spheres are cooled sufficiently fast to be thermally tempered and have a surface compressive strength level above 5000 psi.

Claims

1. A process for vitrifying materials into a silicate, comprising:

heating a silicate melt within an electrical glass melting furnace by passing an electric current through the melt between at least two electrodes so as to maintain the melt at a temperature above the decomposition temperature of the materials;

generating a curtain of gas bubbles in the melt across a substantial portion of the current path between the at least two electrodes to increase the power density of the melt in the region of the curtain of gas bubbles;

supplying materials to the furnace above the melt so that the materials fall onto the melt and the materials are melted to silicate; and

withdrawing molten silicate from the furnace at a temperature of at least 900°

C.

2. The process of claim 1, and further comprising shaping the withdrawn molten silicate into spherical shape having at least two sizes in which the diameter of the smaller spheres is less than half the diameter of the larger spheres.

3. The process of claim 1, in which the furnace includes a drain outlet to periodically remove melted debris which accumulates on the bottom of the furnace.

4. The process of claim 1, in which the molten silicate is withdrawn from the furnace through a melt outlet adjacent the bottom of the furnace, the melt outlet being connected to an airlift conduit in which gas bubbles are introduced to create an effective head pressure to force the melt up the airlift and out of the furnace.

5. The process of claim 1, in which the region defined by the curtain of gas bubbles has a volume fraction of gas ranging from 10-60%.

6. The process of claim 5, in which the region defined by the curtain of gas bubbles has a volume fraction of gas ranging from 15-40%.

7. The process of claim 6, in which the region defined by the curtain of gas bubbles has a volume fraction of gas ranging from 20-30%.

8. The process of claim 1, in which the gas is air.

9. The process of claim 8, in which the gas is preheated air.

10. The process of claim 1, in which the gas is oxygen.

11. The process of claim 1, in which the curtain of gas bubbles is approximately equidistant from the at least two electrodes.

12. The process of claim 1, in which the curtain of gas bubbles is generated in the melt below the at least two electrodes.

13. The process of claim 1, in which a plurality of curtains of gas bubbles are generated in the melt.

14. The process of claim 1, in which the molten silicate is withdrawn from the furnace at a temperature above 1000°

C.

15. The process of claim 1, wherein the materials include asbestos containing material.

16. The process of claim 1, wherein the materials include infectious waste.

17. The process of claim 1, wherein the materials include toxic materials.

18. The process of claim 1, wherein the materials include low level radioactive waste.

19. The process of claim 15, in which the asbestos containing materials are supplied to the furnace in closed plastic bags.

20. The process of claim 15, in which the asbestos containing materials include gypsum and further comprising periodically discontinuing the supply of materials to the furnace once the gypsum is dehydrated to calcium sulfate and the calcium sulfate has accumulated on the surface of the melt so that the area above the melt is heated to above about 900°

C. and still further comprising removing the accumulated calcium sulfate from the surface of the melt.

21. The process of claim 15, in which the asbestos containing materials include ferrous metals and further comprising heating the glass melt under oxidizing conditions so that the ferrous metals are substantially oxidized and the ratio of Fe⁺⁺ to total oxidized iron is less than 0.1.

22. The process of claim 1, wherein the materials are waste materials.

23. The process of claim 1, wherein a gall layer accumulates on the surface of the melt, and the generated curtain of gas bubbles disrupts conductivity of the gall layer.

24. A process for converting waste materials into a silicate, comprising:

heating a silicate melt within an electrical glass melting furnace by passing an electric current through the melt between at least two electrodes so as to maintain the melt at a temperature above the decomposition temperature of the waste materials;

supplying waste materials to the furnace above the melt so that the waste materials fall onto the melt and the waste materials are melted to silicate;

withdrawing molten silicate from the furnace at a temperature of at least 900°

C.; and

shaping the withdrawn molten silicate into spherical shape having at least two sizes in which the diameter of the smaller spheres is less than half the diameter of the larger spheres.

25. The process of claim 24, further comprising generating a curtain of gas bubbles across a substantial portion of the current path between the at least two electrodes to increase the power density of the melt in the region of the curtain of gas bubbles.

26. The process of claim 24, in which the molten silicate is withdrawn from the furnace through a melt outlet adjacent the bottom of the furnace, the melt outlet being connected to an airlift conduit in which gas bubbles are introduced to create an effective head pressure to force the melt up the airlift and out of the furnace.

27. The process of claim 24, in which the spherically shaped silicate is thermally tempered by cooling.

28. The process of claim 24, in which the spherically shaped silicate has a surface compressive thermal stress higher than about 5000 psi.

29. The process of claim 24, wherein the waste materials include asbestos containing material.

30. The process of claim 24, wherein the waste materials include infectious waste.

31. The process of claim 24, wherein the waste materials include toxic materials.

32. The process of claim 24, wherein the waste materials include low level radioactive waste.

33. A process for vitrifying asbestos containing waste materials comprising:

heating a silicate melt within an electrical glass melting furnace by passing an electric current through the melt between at least two electrodes so as to maintain the melt at a temperature above the decomposition temperature of asbestos, the furnace having a melt outlet and a skimmer outlet adjacent the top of the melt;

supplying asbestos containing waste materials to the furnace above the melt so that the asbestos-containing materials fall onto the melt, the asbestos is melted to a molten silicate and dehydrated calcium sulfate which accumulates on the surface of the melt;

periodically discontinuing the supply of asbestos containing waste materials to the furnace so that the area above the melt is heated to above about 900°

C.;

removing the accumulated calcium sulfate from the surface of the melt through the skimmer outlet;

withdrawing molten silicate from the furnace at a temperature of at least 900°

C.; and

generating a curtain of gas bubbles across a substantial portion of the current path between the at least two electrodes to increase the power density of the melt in the region of the curtain of gas bubbles.

34. The process of claim 33, in which the asbestos containing waste materials are supplied to the furnace in closed plastic bags.

35. The process of claim 33, in which the asbestos containing waste materials include ferrous metals and further comprising heating the silicate melt under oxidizing conditions so that the ferrous metals are substantially oxidized and the ratio of Fe⁺⁺ to total oxidized iron is less than 0.1.

36. The process of claim 33, and further comprising shaping the withdrawn molten silicate into spherical shape having at least two sizes in which the diameter of the smaller spheres is less than half the diameter of the larger spheres.

37. The process of claim 33, in which the furnace includes a drain outlet to periodically remove melted debris which accumulates on the bottom of the furnace.

38. The process of claim 33, in which the molten glass is withdrawn from the furnace through a melt outlet adjacent the bottom of the furnace, the melt outlet being connected to a airlift conduit in which gas bubbles are introduced to create an effective head pressure to force the melt up the airlift and out of the furnace.

39. The process of claim 33, in which the melt is maintained at a temperature of about 1100°

-1200°

C.

56. The process of claim 33, in which the area above the melt is heated to above about 1000°

C. while periodically discontinuing the supply of asbestos-containing materials.

40. A process for converting waste materials onto a silicate, comprising:

heating a silicate melt with a glass melting furnace so as to maintain the melt at a temperature above the decomposition temperature of the waste materials;

supplying waste materials to the furnace above the melt so that the waste materials fall onto the melt and the waste materials are melted to silicate;

withdrawing molten silicate from the furnace at a temperature of at least 900°

C.; and

shaping the withdrawn molten silicate into spherical shape having at least two sizes in which the diameter of the smaller spheres is less than half the diameter of the larger spheres.

41. The process of claim 40, in which the molten silicate is withdrawn from the furnace through a melt outlet adjacent the bottom of the furnace, the melt outlet being connected to an airlift conduit in which gas bubbles are introduced to create an effective head pressure to force the melt up the airlift and out of the furnace.

42. The process of claim 40, in which the spherically shaped silicate is thermally temperature by cooling.

43. The process of claim 40, in which the spherically shaped silicate has a surface compressive thermal stress higher than about 5000 psi.

44. The process of claim 40, wherein the waste materials include asbestos containing material.

45. The process of claim 40, wherein the waste materials include infectious waste.

46. The process of claim 40, wherein the waste materials include toxic materials.

47. The process of claim 40, wherein the waste materials include low level radioactive waste.

48. A process for vitrifying asbestos containing waste materials comprising:

heating a silicate melt within an electrical glass melting furnace by passing an electric current through the melt between at least two electrodes so as to maintain the melt at a temperature above the decomposition temperature of asbestos, the furnace having a melt outlet and a skimmer outlet adjacent the top of the melt;

supplying asbestos containing waste materials to the furnace above the melt so that the asbestos-containing materials fall onto the melt, the asbestos is melted to a molten silicate and dehydrated calcium sulfate which accumulates on the surface of the melt;

periodically discontinuing the supply of asbestos containing waste materials to the furnace so that the area above the melt is heated to above about 900°

C.;

removing the accumulated calcium sulfate from the surface of the melt through the skimmer outlet;

withdrawing molten silicate from the furnace at a temperature of at least 900°

C.; and

withdrawing the molten glass from the furnace through a melt outlet adjacent the bottom of the furnace, the melt outlet being connected to an airlift conduit in which gas bubbles are introduced to create an effective head pressure to force the melt up the airlift and out of the furnace.

49. The process of claim 48, in which the asbestos containing waste materials are supplied to the furnace in closed plastic bags.

50. The process of claim 48, further comprising generating a curtain of gas bubbles across a substantial portion of the current path between the at least two electrodes to increase the power density of the melt in the region of the curtain of gas bubbles.

51. The process of claim 48, in which the asbestos containing waste materials include ferrous metals and further comprising heating the silicate melt under oxidizing conditions so that the ferrous metals are substantially oxidized and the ratio of Fe⁺⁺ to total oxidized iron is less than 0.1.

52. The process of claim 48, and further comprising shaping the withdrawn molten silicate into spherical shape having at least two sizes in which the diameter of the smaller spheres is less than half the diameter of the larger spheres.

53. The process of claim 48, in which the furnace includes a drain outlet to periodically remove melted debris which accumulates on the bottom of the furnace.

54. The process of claim 48, in which the area above the melt is heated to above about 1000°

C. while periodically discontinuing the supply of asbestos-containing materials.

55. The process of claim 48, in which the melt is maintained at a temperature of about 1100°

-1200°

C.