Claims
- 1. In the method of removing nitrogen oxides from combustion gas streams by SNCR (Selective Non-Catalytic Reduction) and SCR (Selective Catalytic Reduction) processes, the improvement which comprises heating an aqueous solution of urea, or mixtures of urea containing biuret, or ammonium carbamate on site, to produce a gaseous ammonia-containing product under controlled pressure and rate of flow, said gaseous ammonia-containing product being essentially free of urea, biuret, or ammonium carbamate, and contacting said gaseous ammonia-containing product with the nitrogen oxides in said combustion gas streams.
- 2. The method of claim 1 wherein the ammonia-containing product is produced and contacted with the combustion gas stream at a rate which essentially matches the needs of nitrogen oxides removal in said combustion gas streams.
- 3. The method of claim 1 wherein said improvement further comprises:
a ) Feeding an aqueous solution of urea, and/or mixtures containing biuret, in a concentration range of about 1% to about 76% solids, to a reactor in which it is heated to a temperature of at least about 110° C. but less than about 260° C. and operated at a pressure of at least about 20 PSIG but less than about 500 PSIG, and therein hydrolyzing the urea and biuret to produce a gaseous product stream of ammonia, carbon dioxide and water: b) Separating the gaseous ammonia and carbon dioxide formed from the liquid aqueous reaction media at the operating pressure; c) Retaining the liquid phase reaction media in the reactor for further conversion of unreacted urea, biuret and intermediate ammonium carbamate to gaseous ammonia and carbon dioxide, and/or recycling a portion of the reaction media back into the reactor or feed solution to the reactor for further conversion; d) Withdrawing the gaseous ammonia and carbon dioxide-containing product stream separated, in Step b) at a controlled rate; and e) contacting said product stream with the nitrogen oxides in said combustion gas stream.
- 4. The method of claim 1 in which the reaction rate to form the gaseous ammonia-containing product is enhanced by inclusion in the reaction media of a composition which increases the rate of the hydrolysis urea and biuret and is selected from the following:
a) Oxides and ammonium and alkali metal salts and hydroxides of elements in Groups III-B, IV, V and VI-A of the Periodic Chart Of The Elements, and the hydroxides, carbonates and bicarbonates of Group I. b) Ion-exchange resins of the acidic or basic types, and c) Activated carbon, silica and alumina.
- 5. The method of claim 1 wherein said concentration range of the aqueous solution is from about 10% to 76% solids.
- 6. The method of claim 1 in which the preferred conditions of operation are carried out within the temperature range of about 130° C. to about 170° C. and pressure range of about 20 PSIG to about 120 PSIG.
- 7. The method of claim 1 in which the gaseous ammonia and carbon dioxide product being discharged are maintained at a temperature above 60° C.
- 8. The method of claim 1 in which the aqueous feed solution delivered to the reactor is prepared by dissolving solid urea, and/or urea containing biuret, in purified water in a dissolver vessel.
- 9. The method of claim 8 in which a portion of the liquid reaction media in the hydrolysis reactor is withdrawn and recycled back to the dissolver for resaturation and reuse.
- 10. The method of claim 3 in which a portion of the water vapor in the ammonia and carbon dioxide product stream leaving the reactor is removed by cooling the product gas stream while under pressure, but not to a temperature below 60° C.
- 11. The method of claim 10 in which the water removed from the gaseous ammonia and carbon dioxide product stream is recovered and recycled back to the hydrolysis reactor or used to replace water used int he preparation of the urea feed solution.
- 12. The method of claim 10 in which the urea feed solution is used as the coolant to the condenser, following which the heated solution is delivered to the hydrolysis reactor.
- 13. The method of claim 3 in which the pressure within the reactor is controlled and maintained by regulation of the heat input to the reactor.
- 14. The method of claim 3 in which the liquid media content within the reactor is used to control the feed rate to the reactor.
- 15. The method of claim 3 in which the pressure within the reactor is monitored and controlled by the gas phase pressure, said gas phases pressure gauge, control valve and connection lines being heated to above 60° C.
- 16. The method of claim 3 in which the pressure within the reactor is monitored and controlled by the liquid phase pressure, the pressure gauge and connection line being at temperature from ambient to the temperature of the reactor solution.
- 17. The method of claim 3 in which an emergency pressure relief valve is connected to a dump tank containing water, said tank containing sufficient cold water to cool the reactor solution to stop the hydrolysis process.
- 18. The method of claim 1 in which the reactor discharge control valve is regulated to provide a controlled flow rate of the gaseous ammonia and carbon dioxide product stream which matches the amount of nitrogen oxides in the combustion gas stream, or other process employing ammonia.
- 19. The method of claim 1 wherein the ammonia product is produced and contacted at a location of use otherwise remote from a source of ammonia and in which the urea is transported in dry bulk form to the location.
- 20. The method of claim 1 wherein the ammonia product is produced and contacted at a location of use otherwise remote from a source of ammonia and in which the urea is transported as a concentrated solution of urea in water.
- 21. The method of claim 1 wherein the ammonia product is held at an elevated temperature of at least about 60° C. and is maintained at an elevated temperature to the point of contact with said nitrogen oxides in the combustion gas streams.
- 22. A method for producing a gaseous ammonia-containing product from urea, or mixtures of urea containing biuret, or ammonium carbamate, said ammonia-containing product being essentially free of urea, biuret, or ammonium carbamate, the process comprising;
a) Feeding an aqueous solution of urea, and/or mixtures containing biuret, in a concentration range of about 1% to about 76% solids, to a reactor in which it is heated to a temperature of at least about 110° C. but less than about 200° C. and operated at a pressure of at least about 20 PSIG but less than about 500 PSIG, and therein hydrolyzing the urea and biuret to produce a gaseous product stream of ammonia, carbon dioxide and water: b) Separating the gaseous ammonia and carbon dioxide formed from the liquid aqueous reaction media at the operating pressure; c) Retaining the liquid phase reaction media in the reactor for further conversion of unreacted urea, biuret and intermediate ammonium carbamate to gaseous ammonia and carbon dioxide, and/or recycling a portion of the reaction media back into the reactor or feed solution to the reactor for further conversion; and d) Withdrawing the gaseous ammonia and carbon dioxide-containing product stream separated in Step b) at a controlled pressure and controlled rate of flow, and for external use.
- 23. The method of claim 22-Step a) in which the gaseous products of the hydrolysis reaction and the liquid reaction media are withdrawn from the reactor as a mixed gas and liquid stream; following which
a) The gaseous ammonia and carbon dioxide products formed are separated from the liquid reaction media while under the operating pressure in a separation device; b) Recycling the liquid phase reaction media from the separator back into the reaction media or urea feed solution for further conversion of unreacted urea, biuret and intermediate ammonium carbamate therein; and c) Withdrawing the gaseous ammonia and carbon dioxide product formed in Step a) at a controlled pressure and controlled rate of flow for an external use.
- 24. The method of claim 22 in which the reaction rate to form the gaseous ammonia-containing product is enhanced by inclusion in the reaction media of a composition which increases the rate of the hydrolysis urea and biuret and is selected from the following:
a) Oxides and ammonium and alkali metal salts and hydroxides of elements in Groups III-B, IV, V and VI-A of the Periodic Chart Of The Elements, and the hydroxides, carbonates and bicarbonates of Group I. b) Ion-exchange resins of the acidic or basic types, and c) Activated carbon, silica and alumina.
- 25. The method of claim 22 wherein said concentration range is from about 10% to 76% solids.
- 26. The method of claim 22 in which the preferred conditions of operation are carried out within the temperature range of 130° C. to 160° C. and pressure range of about 20 PSIG to about 120 PSIG.
- 27. The method of claim 22 in which the gaseous ammonia and carbon dioxide product being discharged are maintained at a temperature above 60° C.
- 28. The method of claim 22 in which said external use of the ammonia in the product ammonia and carbon dioxide produced includes being used for removing nitrogen oxides from combustion gas streams by SNCR (Selective Non-Catalytic Reduction and SCR (Selective Catalytic Reduction) processes.
- 29. The method of claim 22 in which said external use of ammonia in the product ammonia and carbon dioxide produced includes being used for the removing particulate matter from combustion gas streams by conditioning the particulate matter for improved removal by electrostatic precipitators and fabric filters.
- 30. The method of claim 22 in which the aqueous feed solution delivered to the reactor is prepared by dissolving solid urea, and/or urea containing biuret, in purified water in a dissolver vessel.
- 31. The method of claim 30 in which a portion of the liquid reaction media in the hydrolysis reactor is withdrawn and recycled back to the dissolver for resaturation and reuse.
- 32. The method of claim 22 in which a portion of the water vapor in the ammonia and carbon dioxide product stream leaving the reactor is removed by cooling the product gas stream while under pressure, but not to a temperature below 60° C.
- 33. The method of claim 32 in which the water removed form the gaseous ammonia and carbon dioxide gaseous product stream is recovered and recycled back to the hydrolysis reactor or used to replace water used in the preparation of the urea feed solution.
- 34. The method of claim 32 in which the urea feed solution is used as the coolant to the condenser, following which the heated solution is delivered to the hydrolysis reactor.
- 35. The method of claim 22 in which the pressure within the reactor is controlled and maintained by regulation of the heat input to the reactor.
- 36. The method of claim 22 in which the liquid media content within the reactor is used to control the feed rate to the reactor.
- 37. The method of claim 36 in which the pressure within the reactor is monitored and controlled by the gas phase pressure, said gas phase pressure gauge, control valve and connection lines being heated to above 60° C.
- 38. The method of claim 35 in which the pressure within the reactor is monitored and controlled by the liquid phase pressure, the pressure gauge and connection line being at temperature from ambient to the temperature of the reactor solution.
- 39. The method of claim 22 in which an emergency pressure relief valve is connected to a dump tank containing water, said tank containing sufficient cold water to cool the reactor solution to stop the hydrolysis process.
- 40. The method of claim 27 in which the reactor discharge control valve is regulated to provide a controlled flow rate of the gaseous ammonia and carbon dioxide product stream which matches the amount of nitrogen oxides in the combustion gas stream, or other process employing ammonia.
- 41. The method of claim 29 in which the reactor discharge control valve is regulated to provide a controlled flow rate of the gaseous ammonia and carbon dioxide product stream for conditioning the flue gas to provide improved collection of particulate matter in the combustion gas stream, or other process.
- 42. The method of claim 38 in which the product ammonia and carbon dioxide gas stream is mixed with a dilution gas, said dilution gas being comprised of air, steam or flue gas, or mixtures thereof, prior to feeding to the flue gas stream.
- 43. The method of claim 22 in which the heat required for the hydrolysis reaction is derived from the hot combustion gas stream.
- 44. The method of claim 40 in which the heat required for the dilution gas is derived from the hot combustion gas stream.
- 45. The method in which sulfur oxides and ammonia are added to combustion gas streams to obtain better removals of fine particulate matter by baghouses or electrostatic precipitators, the improvement comprising producing the ammonia under controlled pressure and rate of flow from urea, biuret, or ammonium carbamate, and mixtures thereof, as a gaseous mixture of ammonia and carbon dioxide, and contacting said ammonia with sulfur oxides and particulate matter in said combustion gas stream.
- 46. The method of claim 45 wherein the ammonia is produced and contacted with the combustion gas streams at a rate which essentially matches the needs of sulfur oxides and particulate matter removal in said combustion gas stream.
- 47. The method of claim 45 wherein the ammonia is produced from an aqueous solution of urea, biuret or ammonium carbamate.
- 48. The method of claim 47 wherein said concentration range of the aqueous solution is from about 10% to 76% solids.
- 49. The method of claim 46 in which the preferred conditions of operation are carried out within the temperature range of about 130° C. to about 170° C. and pressure range of about 20 PSIG to about 120 PSIG.
- 50. The method of claim 47 in which the gaseous ammonia and carbon dioxide product being discharged are maintained at a temperature above 60° C.
- 51. The method of claim 47 in which a portion of the water vapor in the ammonia and carbon dioxide product stream leaving the reactor is removed by cooling the product gas stream while under pressure, but not to a temperature below 60° C.
- 52. The method of claim 51 in which the water removed from the gaseous ammonia and carbon dioxide gaseous product stream is recovered and recycled back to the hydrolysis reactor or used to replace water used in the preparation of the urea feed solution.
- 53. The method of claim 51 in which the urea food solution is used as the coolant to the condenser, following which the heated solution is delivered to the hydrolysis reactor.
- 54. The method of claim 47 in which the pressure within the reactor is controlled and maintained by regulation of the heat input to the reactor.
- 55. The method of claim 47 in which the liquid media content within the reactor is used to control the feed rate to the reactor.
- 56. The method of claim 47 in which the pressure within the reactor is monitored and controlled by the gas phase pressure, said gas phases pressure gauge, control valve and connection lines being heated to above 60° C.
Government Interests
[0001] This invention was made with government support under Contract No. 68D50144 awarded by the Environmental Protection Agency. The government has certain rights in the invention.
Divisions (1)
|
Number |
Date |
Country |
Parent |
08822932 |
Mar 1997 |
US |
Child |
09507623 |
Feb 2000 |
US |
Continuations (1)
|
Number |
Date |
Country |
Parent |
09507623 |
Feb 2000 |
US |
Child |
10023040 |
Oct 2001 |
US |