Method and apparatus for recuperative heating of reactants in an reaction matrix

• US 5,320,518 A
• Filed: 09/15/1992
• Issued: 06/14/1994
• Est. Priority Date: 07/05/1991
• Status: Expired due to Term

• Current Assignee: Selas Fluid Processing Corporation
• Original Assignee: Thermatrix, Inc. (Linde Plc)
• Inventors: Martin, Richard J., Holst, Mark R., Stilger, John D.
• Primary Examiner(s): Dority, Carroll B.
• Application Number:
  US07/945,218
• Time in Patent Office: 637 Days
• Field of Search: 431/7, 431/170, 122/4 D
• US Class Current: 431/7
• CPC Class Codes: B01J 12/005 carried out at high temperatures, e.g. by pyrolysis
• CPC Class Codes: B01J 2208/00141 Coils
• CPC Class Codes: B01J 2208/00203 Coils
• CPC Class Codes: B01J 2219/00058 Temperature measurement
• CPC Class Codes: B01J 8/06 in tube reactors; the solid particles being arranged in tubes
• CPC Class Codes: B01J 8/067 Heating or cooling the reactor B01J8/062 takes precedence
• CPC Class Codes: F23C 99/006 Flameless combustion stabilised within a bed of porous heat-resistant material F23C13/00 takes precedence; gas burners with radiant combustion on a porous surface F23D14/16
• CPC Class Codes: F23D 14/66 Preheating the combustion air or gas
• CPC Class Codes: F23G 2202/50 in a matrix bed combustion chamber
• CPC Class Codes: F23G 2209/142 Halogen gases, e.g. silane
• CPC Class Codes: F23G 7/061 with supplementary heating
• CPC Class Codes: F23G 7/066 preheating the waste gas by the heat of the combustion, e.g. recuperation type incinerator
• CPC Class Codes: F23G 7/07 in which combustion takes place in the presence of catalytic material
• CPC Class Codes: F23N 1/022 using electronic means
• CPC Class Codes: F23N 2225/16 burner temperature
• CPC Class Codes: F23N 2237/30 matrix burners
• CPC Class Codes: F23N 5/10 using thermocouples
• CPC Class Codes: F24H 1/00 Water heaters, e.g. boilers, continuous-flow heaters or water-storage heaters steam boilers F22B
• CPC Class Codes: F24H 1/0045 with catalytic combustion
• CPC Class Codes: Y02E 20/34 Indirect CO2mitigation, i.e. by acting on non CO2directly related matters of the process, e.g. pre-heating or heat recovery

Abstract

Methods and apparatus are provided for establishing and controlling the stability and movement of a reaction wave of reacting gases in a matrix of solid heat-resistant matter, wherein such reacting gases may be recuperatively pre-heated. At least a portion of the bed is initially preheated above the autoignition temperature of the mixture whereby the mixture reacts upon being introduced into the matrix thereby initiating a self-sustaining reaction region, after which the pre-heating can be terminated. The stability and movement of the wave within the matrix is maintained by monitoring the temperatures along the flowpath of the gases through the bed and adjusting the flow of the gases and/or vapors or air to maintain and stabilize the wave in the bed. The method and apparatus provide for the reaction or combustion of gases to minimize NO_x and undesired products of incomplete combustion. A recuperative heat exchange system is used to preheat the reactants with heat generated by the reaction by channeling hot exhaust gases through the matrix surrounding reactant inlet tubes.

Claims

1. A method for the exothermic reaction of process gases in a processor comprising the steps of:

(a) heating a portion of a matrix bed of heat resistant material within the processor above the autoignition temperature of the process gases;

(b) feeding the process gases into a plenum within the processor;

(c) directing the process gases from the plenum through one or more feeding tubes, each of the feeding tubes having an inside portion, an entrance end, and an exit end, the one or more feeding tubes extending through a gas impermeable barrier such that the entrance end of the feeding tubes is located within the plenum and the exit end of the feeding tubes is positioned either within the matrix bed or within a void located adjacent to the matrix bed within the processor at a position remote from the gas impermeable barrier;

(d) directing the process gases from the exit end of the one or more feeding tubes through the matrix bed and to a processor outlet, whereby the process gases are combusted in the matrix bed or in the void within a combustion wave, and whereby the process gases are recuperatively pre-heated in the one or more feeding tubes by the thermal energy produced during the combustion process in the matrix bed; and

(e) monitoring or otherwise determining the temperature of the matrix bed along the process gas flowpath and controlling the position of the combustion wave within the matrix bed or the void in response thereto.

2. The method of claim 1 wherein the step of controlling the position of the combustion wave is achieved by adjusting the volume of air or oxygen supplied to the matrix bed.

3. The method of claim 1 wherein the step of controlling the position of the combustion wave is achieved by adjusting the volume of supplemental fuel supplied to the matrix bed.

4. The method of claim 3 wherein the volume of supplemental fuel supplied is controlled in an inverse relationship to the temperature of the matrix bed, thereby stabilizing the temperature and location of the combustion wave.

5. The method of claim 1 wherein the step of controlling the position of the combustion wave is achieved by cooling or heating the matrix bed.

6. The method of claim 1 wherein the step of controlling the position of the combustion wave is achieved by adjusting the flowrate of the process gases.

7. The method of claim 6 wherein the flow velocity of the mixture of gases is controlled in an inverse relationship to the temperature of the matrix bed, thereby stabilizing the temperature and location of the combustion wave.

8. The method of claim 1 wherein the combustion wave is controlled at a process gases feed flowrate such that the calculated velocity of the mixture of gases entering the combustion wave, adjusted to conditions of standard temperature and pressure, is greater than the laminar or turbulent flamespeed of that gaseous mixture at the same conditions in absence of the matrix bed.

9. The method of claim 1 wherein the combustion wave is characterized by a heat release per unit volume that is higher than the heat release per unit volume observed in a laminar or turbulent flame of an identical mixture of gases at identical conditions in the absence of the matrix bed.

10. The method of claim 1 wherein the residence time of the process gases in the matrix bed and void necessary to obtain substantially complete combustion is maintained or decreased upon increase of pressure within said matrix bed.

11. The method of claim 1 wherein the inside portion of the feeding tubes contains heat resistant material.

12. The method of claim 1 wherein the combustion wave is characterized by lack of a flame.

13. The method of claim 1 wherein the recuperative pre-heating further utilizes a radiatively-coupled fin, said radiatively-coupled fin being heated by convection by said combusted gases and transferring heat by radiation to said one or more feeding tubes.

14. The method of claim 1 comprising the further step of admixing air, oxygen, supplemental fuel, or both with the process gases prior to feeding the process gases to the matrix bed.

15. The method of claim 1 wherein the composition of the gases entering the matrix bed is outside the explosion or flammability limits of the gases.

16. The method of claim 15 wherein the composition of the gases entering the matrix bed is between 10% and 75% of the lower flammability limit of the gases.

17. The method of claim 1 wherein the length of the combustion wave is from about 2 to about 16 inches.

18. The method of claim 1 wherein the matrix bed temperature is maintained between about 1400°

F. and about 3500°

F. in the combustion wave.

19. The method of claim 1 wherein the process gases include one or more hydrocarbons selected from the group consisting of simple hydrocarbons, oxygenated hydrocarbons, halogenated compounds, aminated compounds, and sulphur-containing compounds.

20. The method of claim 1 wherein the combusted gases have a NO_x content less than about 40 parts per million by volume and the carbon monoxide content is less than about 50 parts per million by volume, on a dry basis, adjusted to 3% oxygen.

21. The method of claim 1 wherein products of incomplete combustion in the combusted gases comprise less than about 5 ppm of said combusted gases, by volume, dry basis, adjusted to 3% oxygen.

22. The method of claim 1 wherein the gases introduced into the matrix bed have an intermittently varying composition of one or more constituents.

23. The method of claim 1 wherein the gases introduced into the matrix bed have an intermittently varying temperature.

24. The method of claim 1 wherein the gases introduced into the matrix bed have an intermittently varying flowrate.

25. The method of claim 1 comprising the further steps of:

(i) providing a heat exchange tube that passes through the processor and through a portion of the matrix bed; and

(ii) circulating a fluid through the tube, whereby the fluid gains thermal energy upon passing through the tube by heat transfer from the matrix bed.

26. The method of claim 1 wherein the processor outlet is positioned as an outlet from the matrix bed such that the combustion products flow in a countercurrent fashion along an outer portion of the one or more feeding tubes prior to exiting the processor through the processor outlet.

27. The method of claim 1 comprising the further step of mixing the gases prior to introducing the gases into the matrix bed.

28. The method of claim 1 wherein the heat resistant material is chosen from the group consisting of ceramic balls, ceramic saddles, ceramic pall rings, or ceramic rasching rings.

29. The method of claim 1 wherein the heat resistant material is chosen from the group consisting of ceramic foam, ceramic wool, metal foam, or metal wool.

30. The method of claim 28 wherein the matrix bed comprises variously sized heat resistant material.

31. The method of claim 28 Wherein the matrix bed comprises at least two layers of heat resistant material wherein the layers are comprised of differently sized heat resistant material.

32. The method of claim 1 wherein the matrix bed is comprised of a material with a characteristic interstitial length of 1/30 inch to 6 inches.

33. The method of claim 1 wherein the matrix bed has a void fraction from 0.3 to 0.9.

34. The method of claim 1 wherein the material in the matrix bed has a specific surface area from 40 m² /m³ to 1040 m² /m³.

35. The method of claim 1 wherein the material in the matrix bed comprises a catalyst.

36. A method for the exothermic combustion of process gases including one or more hydrocarbons in a processor comprising the steps of:

(a) heating a portion of a matrix bed of heat resistant material having a void fraction from 0.3 to 0.9 and a specific surface area from 40 m² /m³ to 1040 m² /m³ within the processor above the autoignition temperature of the process gases;

(b) feeding the process gases into a plenum within the processor

(c) directing the process gases from the plenum through one or more feeding tubes containing heat resistant material, each of the feeding tubes having an inside portion, an entrance end, and an exit end, the one or more feeding tubes extending through a gas impermeable barrier such that the entrance end of the feeding tubes is located within the plenum and the exit end of the feeding tubes is positioned within the matrix bed or within a void located adjacent to the matrix bed within the processor at a position remote from the gas impermeable barrier;

(d) directing the process gases from the exit end of the one or more feeding tubes through the matrix bed and to a processor outlet, whereby the process gases are combusted within the matrix bed or the void within a flameless combustion wave, the processor outlet being positioned as an outlet from the matrix bed such that the combustion products flow in a countercurrent fashion along an outer portion of the one or more feeding tubes prior to exiting the processor through the processor outlet thereby recuperatively pre-heating the process gases in the one or more feeding tubes by the thermal energy produced during the combustion process in the matrix bed; and

(e) monitoring the temperature of the matrix bed along the process gas flowpath and controlling the position of the combustion wave in response thereto by adjusting the volume of air, oxygen, or supplemental fuel supplied to the matrix bed, or by adjusting the flowrate of the process gases.

37. An apparatus comprising:

(a) a processor having an inlet for process gases and an outlet for reaction gaseous products;

(b) a portion of the processor including a matrix bed comprising packed heat resistant material connected to the outlet and a void space adjacent to the matrix bed;

(c) a plenum located between the processor inlet and the matrix bed within the processor;

(d) a gas impermeable barrier separating the matrix bed from the plenum;

(e) one or more feeding tubes having an inside portion, an entrance end, and an exit end, the on or more feeding tubes extending through the barrier such that the entrance end of the one or more feeding tubes is located in the plenum and the exit end of the one or more feeding tubes is positioned either within the matrix bed or within the void space;

(f) thermocouples for sensing the temperature of the matrix bed; and

(g) means for adjusting the flow rate of the process gases.

38. The apparatus of claim 37 further comprising:

(i) one or more inlets for control air, oxygen, or supplemental fuel; and

(ii) means for adjusting the flow rate of the control air, oxygen, or supplemental fuel.

39. The apparatus of claim 37 comprising further a control system for accepting input from the thermocouples and, in response thereto, controlling the means for adjusting the flow rate of the process gases.

40. The apparatus of claim 38 comprising further a control system for accepting input from the thermocouples and, in response thereto, controlling the means for adjusting the flow rate of the control air, oxygen, or supplemental fuel.

41. The apparatus of claim 37 wherein the inside portion of the one or more feeding tubes contains heat resistant material.

42. The apparatus of claim 37 wherein the spacing-to-diameter ratio of the feeding tubes is from 1.5 to 5.

43. The apparatus of claim 37 further comprising a preheating means for heating the matrix bed to a temperature above the autoignition temperature of the process gases.

44. The apparatus of claim 37 wherein the outlet is positioned as an outlet from the matrix bed such that the process gases flow in a countercurrent fashion along an outer portion of the one or more feeding tubes prior to exiting the processor through the processor outlet.

45. The apparatus of claim 37 wherein the heat resistant material is chosen from the group consisting of ceramic balls, ceramic saddles, ceramic pall rings, or ceramic raschig rings.

46. The apparatus of claim 37 wherein the heat resistant material is chosen from the group consisting of ceramic foam, ceramic wool, metal foam, or metal wool.

47. The apparatus of claim 45 wherein the matrix bed comprises variously sized heat resistant material.

48. The apparatus of claim 45 wherein the matrix bed comprises at least two layers of heat resistant material wherein the layers are comprised of differently sized heat resistant material.

49. The apparatus of claim 37 further comprising one or more heat exchange tubes extending through the processor and through a portion of the matrix bed.

50. The apparatus of claim 37 wherein the matrix bed is comprised of a material with a characteristic interstitial length of 1/30 inch to 6 inches.

51. The apparatus of claim 37 wherein the matrix bed has a void fraction from 0.3 to 0.9.

52. The apparatus of claim 37 wherein the material in the matrix bed have a specific surface area from 40 m² /m³ to 1040 m² /m³.

53. The apparatus of claim 37 wherein the material in the matrix bed comprises a catalyst.

54. The apparatus of claim 37 further comprising an outlet plenum located between the matrix bed and the outlet.

55. The apparatus of claim 37 wherein the matrix bed includes staggered layers of differently sized ceramic balls near the outlet.

56. An apparatus comprising:

(a) a processor having an inlet for process gases and an outlet for reaction gaseous products;

(b) a portion of the processor including a matrix bed comprising packed heat resistant material having a void fraction from 0.3 to 0.9 and a specific surface area from 40 m² /m³ to 1040 m² /m³ connected to the outlet and a void space adjacent to the matrix bed;

(c) a plenum located between the processor inlet and thematrix bed within the processor;

(d) a gaseous impermeable barrier separating the matrix bed from the plenum;

(e) one or more feeding tubes having an inside portion, an entrance end, and an exit end, the one or more feeding tubes containing heat resistant material extending through the barrier such that the entrance end of the one or more feeding tubes is located in the plenum and the exit end of the one or more feeding tubes is positioned within the matrix bed or within the void space, wherein the outlet is positioned as an outlet from the matrix bed such that the process gases flow in a countercurrent fashion along an outer portion of the one or more feeding tubes prior to exiting the processor through the outlet;

(f) a preheating means for heating the matrix bed to a temperature above the autoignition temperature of the process gases;

(g) thermocouples for sensing the temperature of the matrix bed;

(h) one or more inlets for control air, oxygen, or supplemental fuel;

(i) means for adjusting the flow rate of the control air, oxygen, or supplemental fuel;

(j) means for adjusting the flow rate of the process gases;

(k) a control system for accepting input from the thermocouples and, in response thereto, controlling the means for adjusting the flow rate of the process gases and the means for adjusting the flow rate of the control air, oxygen, or supplemental fuel.