Method of and apparatus for heating a reaction vessel with microwave energy

• US 5,532,462 A
• Filed: 04/29/1994
• Issued: 07/02/1996
• Est. Priority Date: 04/29/1994
• Status: Expired due to Term

• Current Assignee: Communications & Power Industries Incorporated
• Original Assignee: Communications & Power Industries Incorporated
• Inventors: Green, Michael, McCune, Earl, Legarra, James R., Butwell, Robert J., Huey, Hugo, Wilcox, Ross
• Primary Examiner(s): Leung, Philip H.
• Application Number:
  US08/236,759
• Time in Patent Office: 795 Days
• Field of Search: 219/695, 219/696, 219/746, 219/747, 219/748, 219/750, 219/759, 219/756
• US Class Current: 219/695
• CPC Class Codes: B01J 19/126 Microwaves
• CPC Class Codes: H05B 6/6402 Aspects relating to the microwave cavity
• CPC Class Codes: H05B 6/705 using microwave tuning
• CPC Class Codes: H05B 6/707 using waveguides

Abstract

A reaction vessel used in industrial applications is heated by a multiple mode microwave beam that is directed to an interior wall of the reaction vessel. The beam is in an inclined-angular fashion and the wall is arranged so the beam is absorbed and reflected from it many times to provide a helical-like reflection and absorption pattern within the vessel interior to uniformly heat the vessel wall and the material. A microwave isolator connected between a source of the microwave energy and the reaction vessel includes a quartz plate and a seal for compensating disparities in thermal expansion coefficients between the plate and a housing for the plate.

Claims

1. An apparatus for heating material comprising a closed vessel for receiving the material and

means for generating microwave energy,

a waveguide operably coupled to said microwave generating means at a first end and having a means for exciting multiple microwave propagation modes in a second end, said second end integrally coupled to the closed vessel in an angled configuration with respect to the lateral axis of said vessel to induce a helical-type reflection of microwave energy which propagates throughout the closed vessel in a whispering gallery-type mode;

and

a microwave transparent isolation means operably interposed between said microwave generating means and said closed vessel, said isolation means comprising a housing and a microwave transparent barrier fixedly attached to said housing by a thermal expansion compensating seal.

2. The combination as provided in claim 1 wherein the means for exciting the multiple microwave propagation modes is an increase in diameter of the waveguide at said second end.

3. The apparatus of claim 2 wherein the cross-sectional waveguide at the first end is rectangular and at the second end is circular.

4. The apparatus of claim 2 or 3 wherein the increase in waveguide diameter is a function of cutoff frequency.

5. The apparatus of claim 2 wherein the second end is coupled to the closed vessel at a tangential incline angled configuration.

6. The apparatus of claim 5 wherein the second end of said waveguide is positioned within the interior of said closed vessel such that a launched microwave avoids initially impinging a sidewall of said vessel adjacent said second end.

7. The apparatus of claim 1 wherein the microwave transparent barrier is a quartz disc.

8. The apparatus of claim 7 wherein the quartz is fused quartz.

9. The apparatus of claim 7 wherein the quartz is crystal quartz.

10. The apparatus of claim 1 wherein the closed vessel is a reaction vessel including an inner electrically conductive refractory lining and an insulation lining subjacent said inner lining.

11. The apparatus of claim 10 wherein the inner lining is a carbon based material.

12. The combination of claim 1 wherein the vessel includes wall material for partially absorbing and partially reflecting the microwave energy which propagates through the vessel in the whispering gallery-type mode, the absorption of the microwave energy causing the vessel walls to be heated to a temperature to cause material in the vessel to be heated to a desired temperature.

13. The combination of claim 12 wherein the housing is metal and the barrier includes a dielectric plate that (a) is transparent to the microwave energy, (b) is exposed to high temperature resulting from heating of the vessel and the material therein, (c) exposed to corrosive gases in the vessel, (d) has a relatively low coefficient of thermal expansion and (e) is able to withstand the corrosive gases without substantial chemical and mechanical change, the plate being surrounded by the metal housing, the metal housing having a coefficient of thermal expansion substantially different from the dielectric plate, and the seal is between the dielectric plate and the metal housing for maintaining a seal between opposite sides of the plate and the housing throughout the temperature range experienced by the plate and the housing.

14. The combination of claim 1 wherein the vessel undergoes substantial temperature change and corrosive gases are therein, the housing is metal and the barrier includes a dielectric plate that (a) is transparent to the microwave energy, (b) is exposed to high temperature resulting from heating of the vessel and the material therein, (c) exposed to corrosive gases in the vessel, (d) has a relatively low coefficient of thermal expansion and (e) is able to withstand the corrosive gases without substantial chemical and mechanical change, the plate being surrounded by the metal housing, the metal housing having a coefficient of thermal expansion substantially different from the dielectric plate, and the seal is between the dielectric plate and the metal housing for maintaining a seal between opposite sides of the plate and the housing throughout the temperature range experienced by the plate and the housing.

15. The combination of claim 14 wherein the dielectric plate is made of quartz.

17. The apparatus of claim 12 wherein the first end of the waveguide is rectangular in cross section and the second end of the waveguide is circular in cross section.

16. An apparatus for heating material comprising

a reaction vessel for receiving the material,

means for generating microwave energy having a frequency between about 850 MHz and about 30 GHz;

a waveguide having a first end of a first diameter, and a second end of a second diameter larger than said first diameter, said first end operably coupled to said microwave generating means and said second end integrally coupled to the reaction vessel in a tangentially angled configuration with respect to the lateral axis of said reaction vessel to induce a helical-type reflection pattern of microwave energy which propagates throughout the reaction vessel in a whispering gallery-type mode; and

a microwave transparent isolation means operably coupled between the waveguide and the reaction vessel, said isolation means comprising a housing and a dielectric material fixedly mounted in said housing, perpendicular to the longitudinal axis of the waveguide, by a thermal expansion compensating seal.

18. The apparatus of claim 16 wherein the tangentially angled configuration is at an offset inclined angle with respect to the lateral axis of said vessel.

19. The apparatus of claim 16 wherein the reaction vessel further comprises an inner electrically conductive refractory lining and an insulation lining subjacent to said inner lining.

20. The apparatus of claim 16 wherein the first diameter and the second diameter of the waveguide are approximately equal.

21. The apparatus of claim 16 wherein the dielectric material is quartz.

22. The method of heating a reactor vessel using microwave energy, comprising the steps of

generating microwave energy;

exciting multiple propagation modes of said microwave energy;

directing said excited microwave energy into the reactor vessel at an offset, angled position relative to the lateral axis of said vessel to induce a helical-type reflection pattern propagating throughout the vessel in a whispering gallery-type mode.

23. The method of claim 22 wherein the excited microwave energy is directed at an offset, inclined, launch angle with respect to the vessel lateral axis.

24. The method of claim 23 wherein the offset angle avoids initially impinging a launched microwave on a sidewall of the vessel adjacent the location in the vessel where the energy is initially directed at the offset angled position.

25. A method of heating material in a reaction vessel having a wall with facing interior portions, the wall including microwave absorbing and reflecting material, comprising the steps of supplying a microwave energy beam to a first of said interior portions, the energy being supplied to the first portion at an angle so energy in the energy beam is partially absorbed by the wall at the first portion and is partially reflected from the wall at the first portion, the energy reflected from the first portion propagating to a second of said portions that faces the first portion, the energy propagating from the first portion to the second portion being partially absorbed and partially reflected at the second portion, the energy reflected from the second portion propagating to a third of said portions that faces the second portion, the energy propagating from the second portion to the third portion being partially absorbed and partially reflected at the third portion, all of said first, second and third portions being spaced from each other and being heated by the microwave energy absorbed thereby, the reflection and absorption of the energy being repeated for many additional different ones of said facing portions so the many additional different portions are heated by the microwave energy absorbed thereby, the energy being supplied to the first, second, third and many different portions for a sufficiently long period to heat the wall to a temperature to cause the material to be heated to a desired temperature.

26. The method of claim 25 wherein the vessel has a longitudinal axis, the microwave energy beam being directed at the first, second, third and many different portions so that the different portions are differentially spaced relative to each other along the longitudinal axis.

27. The method of claim 26 wherein the energy is scattered from the portions.

28. The method of claim 26 wherein the energy has a helical like path between the portions within the vessel.

29. The method of claim 25 wherein the microwave energy beam has multiple modes.

30. Apparatus for heating material comprising

a reaction vessel for receiving the material, the reaction vessel having a wall with facing interior portions, the wall including microwave absorbing and reflecting material,

a microwave feed for supplying a microwave energy beam to a first of said interior wall portions, the energy being supplied to the first portion on the interior wall at an angle so energy in the energy beam is partially absorbed by the wall at the first portion and is partially reflected from the wall at the first portion, the first wall portion and the angle of the energy beam being such that the energy reflected from the first portion propagates to a second of said portions that faces the first portion, the energy propagating from the first portion to the second portion being partially absorbed and partially reflected at the second portion, the energy reflected from the second portion propagating to a third of said portions on the interior wall that faces the second portion, the energy propagating from the second portion to the third portion being partially absorbed and partially reflected at the third portion, all of said first, second and third portions being spaced from each other and being heated by the microwave energy absorbed thereby, the reflection and absorption of the energy being repeated for many additional different facing portions on the interior wall so the many additional different portions are heated by the microwave energy absorbed thereby, whereby in response to the energy being supplied to the first, second, third and many different portions for a sufficiently long period the wall is heated to a temperature to cause the material to be heated to a desired temperature.

31. The apparatus of claim 30 wherein the wall portions are constructed and the microwave energy is such that the microwave energy incident on the wall portions is scattered from them.

32. The apparatus of claim 31 wherein the vessel has a longitudinal axis, the microwave feed being arranged so the angle of the energy beam is such that the first, second, third and many different portions are differentially spaced relative to each other along the longitudinal axis.

33. The apparatus of claim 30 wherein the vessel has a longitudinal axis, the microwave feed being arranged so the angle of the energy beam is such that the first, second, third and many different portions are differentially spaced relative to each other along the longitudinal axis.

34. The apparatus of claim 30 wherein the wall includes a ceramic cylindrical liner overlying a metal cylinder.

35. The apparatus of claim 30 wherein the wall includes an electrically conductive refractory cylindrical lining.

36. The apparatus of claim 30 wherein the wall includes an electrically conductive refractory cylindrical lining overlying a cylindrical ceramic liner, the ceramic liner overlying a metal cylinder.

37. The apparatus of claim 30 wherein the wall includes a metal cylinder.

38. The apparatus of claim 30 wherein the feed is arranged for supplying multiple modes to the interior of the vessel.

39. In combination

a chemical reaction vessel,

a microwave coupling circuit connected to the interior of the reaction vessel for supplying energy from a source of microwave energy to the interior of the vessel, the vessel being adapted to include materials that are heated to relatively high temperatures and produce corrosive gases and cause the vessel to have a wide range of temperatures from ambient to about the high temperature,

the coupling circuit including a microwave window with a dielectric plate that (a) is transparent to the microwave energy, (b) is exposed to the high temperature, (c) is exposed to the corrosive gases, (d) has a relatively low coefficient of thermal expansion and (e) is able to withstand the corrosive gases without substantial chemical and mechanical change,

the plate being surrounded by a metal housing having a coefficient of thermal expansion substantially different from that of the dielectric plate, and

a thermal expansion matching seal between the dielectric plate and the metal housing for maintaining a seal between opposite sides of the plate and the housing throughout the temperature range experienced by the plate and the housing.

40. The combination of claim 39 wherein the dielectric plate is made of quartz.

41. The combination of claim 39 further including another microwave window in the coupling circuit between an end of the circuit adapted to be connected to the source and the window including the plate exposed to the corrosive gases.

42. The combination of claim 41 wherein the windows are spaced from each other by (2n+1) spaced from each other by (2n+1) ##EQU1## where n is zero or a positive integer and λ

is the wavelength of microwave energy supplied to the circuit by the source.

43. The combination of claim 41 wherein the windows have substantially the same construction.

44. The combination of claim 41 wherein the microwave circuit includes a pressurized waveguide between the windows.

45. The combination of claim 41 wherein the waveguide between the windows is filled with a non-reactive gas.

46. The combination of claim 39 wherein the vessel has a wall with facing interior portions, the wall including microwave absorbing and reflecting material, the vessel and an end of the microwave coupling circuit in the vessel being arranged so a beam of the microwave energy coupled to the vessel interior is supplied to a first of said interior wall portions at an angle to the first portion so energy in the energy beam is partially absorbed by the wall at the first portion and is partially reflected from the wall at the first portion, the first wall portion and the angle of the energy beam being such that the energy reflected from the first portion propagates to a second of said portions that faces the first portion, the energy propagating from the first portion to the second portion being partially absorbed and partially reflected at the second portion, the energy reflected from the second portion propagating to a third of said portions on the interior wall that faces the second portion, the energy propagating from the second portion to the third portion being partially absorbed and partially reflected at the third portion, all of said first, second and third portions being spaced from each other and being heated by the microwave energy absorbed thereby, the reflection and absorption of the energy being repeated for many additional different facing portions on the interior wall so the many additional different portions are heated by the microwave energy absorbed thereby, whereby in response to the energy being supplied to the first, second, third and many different portions for a sufficiently long period the wall is heated to a temperature to cause the material to be heated to a desired temperature.

47. The combination of claim 46 wherein the vessel has a longitudinal axis, the microwave feed being arranged so the angle of the energy beam is such that the first, second, third and many different portions are differentially spaced relative to each other along the longitudinal axis.

48. The combination of claim 39 wherein the housing includes a slit receiving the peripheral portion of the plate, the seal being a compression seal between opposite faces of the peripheral portion of the plate and opposing adjacent faces of the slit.

49. The combination of claim 39 wherein the housing includes a flat surface substantially at right angles to and spaced from the plane of the plate and the seal includes a member extending between a peripheral portion of the plate and the flat surface at right angles to the plane of the plate to provide a region of thermal expansion coefficient transition between the housing and plate.

50. The combination of claim 49 wherein the plate has a substantially greater coefficient of thermal expansion in the plane of the plate than the planes at right angles to the plane of the plate.

51. The combination of claim 39 wherein the seal is arranged to provide a region of thermal expansion coefficient transition between the housing and plate.

52. The combination of claim 51 wherein the plate has a substantially greater coefficient of thermal expansion in the plane of the plate than the planes at right angles to the plane of the plate.