Claims
- 1. A process for the reduction of the concentration of nitrogen oxides in the effluent from the combustion of a carbonaceous fuel, the process comprising injecting a treatment agent which comprises furfural into the effluent under conditions effective to reduce the concentration of nitrogen oxides in the effluent.
- 2. The process of claim 1 wherein said treatment agent further comprises urea.
- 3. The process of claim 1 wherein the temperature of the effluent is greater than about 1300.degree. F.
- 4. The process of claim 3 wherein the temperature of the effluent is greater than about 1450.degree. F.
- 5. The process of claim 1 wherein the temperature of the effluent is below about 2000.degree. F.
- 6. The process of claim 3 wherein said treatment agent is injected into the effluent at a molar ratio of the nitrogen contained in said treatment agent to the baseline nitrogen oxides level of 1:5 to about 10:1.
- 7. The process of claim 6 wherein the molar ratio of treatment agent nitrogen to the baseline nitrogen oxides level is about 1:3 to about 5:1.
- 8. The process of claim 1 wherein said treatment agent is in solution, in a mixture or in a dispersion.
- 9. The process of claim 8 wherein the solvent used in said solution, mixture or dispersion comprises water.
- 10. The process of claim 9 wherein urea is present in said solution, mixture or dispersion in an amount of about 2% to about 60% by weight.
- 11. The process of claim 10 wherein furfural is present in said solution, mixture or dispersion in an amount of about 0.5% to about 25% by weight.
- 12. The process of claim 1 wherein the effluent is comprises an excess of oxygen.
- 13. The process of claim 12 wherein said effluent has an excess of oxygen of no greater than about 12% by volume.
- 14. The process of claim 13 wherein said excess of oxygen in the effluent is about 1% to about 6% by volume.
- 15. A process for the reduction of the concentration of nitrogen oxides in the oxygen rich effluent from the combustion of a carbonaceous fuel, the process comprising injecting a treatment agent which comprises urea and furfural into an effluent having a temperature of greater than about 1300.degree. F. under conditions effective to reduce the concentration of nitrogen oxides in the effluent.
- 16. The process of claim 15 wherein the effluent is at a temperature of greater than about 1450.degree. F.
- 17. The process of claim 15 wherein the temperature of the effluent is below about 2000.degree. F.
- 18. The process of claim 15 wherein said treatment agent is in solution, in a mixture or in a dispersion.
- 19. The process of claim 18 wherein the solvent used in said solution, mixture or dispersion comprises water.
- 20. The process of claim 19 wherein urea is present in said solution, mixture or dispersion in an amount of about 2% to about 60% by weight.
- 21. The process of claim 20 wherein furfural is present in said solution, mixture or dispersion in an amount of about 0.5% to about 25% by weight.
- 22. The process of claim 15 wherein said treatment agent is injected into the effluent at a molar ratio of the nitrogen contained in said treatment agent to the baseline nitrogen oxides level of about 1:5 to about 10:1.
- 23. The process of claim 22 wherein the molar ratio of treatment agent nitrogen to baseline nitrogen oxides level is about 1:3 to about 5:1.
- 24. The process of claim 15 wherein said effluent has an excess of oxygen of no greater than about 12% by volume.
- 25. A process for the reduction of the concentration of nitrogen oxides in the oxygen-rich effluent from the combustion of a carbonaceous fuel, the process comprising injecting a treatment agent which comprises an aqueous solution, mixture or dispersion of about 2% to about 60% urea by weight and about 0.5% to about 25% furfural by weight into an effluent having an excess of oxygen of about 1% to about 6% by volume and a temperature of about 1450.degree. F. to about 1900.degree. F. in an amount sufficient to provide a molar ratio of the nitrogen contained in said treatment agent to the baseline nitrogen oxides level of about 1:3 to about 5:1, under conditions effective to reduce the nitrogen oxides level in the effluent.
DISCLOSURE OF INVENTION
This is a continuation of co-pending application Ser. No. 025,493 filed on Mar. 13, 1987 now abandoned.
1. Technical Field The present invention relates to a process for the reduction of nitrogen oxides (NO.sub.x) in the effluent, especially the oxygen-rich effluent, from the combustion of a carbonaceous fuel by injection of a treatment agent comprising a heterocyclic hydrocarbon having at least one cyclic oxygen into the effluent.
Carbonaceous fuels can be made to burn more completely, and with reduced emissions of carbon monoxide and unburned hydrocarbons, when the oxygen concentrations and air/fuel ratios employed are those which permit high flame temperatures. When fossil fuels are used to fire large utility boilers, temperatures above about 2000.degree. F. and typically about 2200.degree. F. to about 3000.degree. F. are generated. Unfortunately, such high temperatures, as well as hot spots of higher temperatures, tend to cause the production of thermal NO.sub.x, the temperatures being so high that free radicals of oxygen and nitrogen are formed and chemically combine as nitrogen oxides. Nitrogen oxides can form even in circulating fluidized bed boilers which operate at temperatures which typically range from 1300.degree. F. to 1700.degree. F.
Nitrogen oxides, especially NO.sub.2, are troublesome pollutants which are found in the combustion effluent streams of boilers when fired as described above, and comprise a major irritant in smog. It is further believed that nitrogen oxides can undergo a process known as photo-chemical smog formation, through a series of reactions in the presence of sunlight and hydrocarbons. Moreover, nitrogen oxides comprise a major portion of acid rain.
Unfortunately, the temperatures within a utility or circulating fluidized bed boiler render most common methods of reducing NO.sub.x concentrations, such as effluent scrubbing or catalyst grids, either uneconomical, infeasible, or both.
2. Background Art
Various methods and compositions for reducing the NO.sub.x concentration in the effluent from the combustion of a carbonaceous fuel have been proposed. For instance, Arand et al, in U.S. Pat. No. 4,208,386, disclose a method for reducing NO.sub.x in combustion effluents by injecting urea, either as a solid powder or in solution, at effluent temperatures in excess of 1300.degree. F. The preferred urea solutions are those having at least 10 weight percent urea. For operation at temperatures below 1600.degree. F., the use of reducing materials such as paraffinic, olefinic, aromatic and oxygenated hydrocarbons, as well as hydrogen, are required.
Bowers, in copending and commonly assigned U.S. patent application Ser. No. 906,671, filed Sept. 10, 1986 now U.S. Pat. No. 4,737,065, discloses the use of a solution which comprises urea and hexamethylenetetramine (HMTA) to reduce the NO.sub.x concentration in oxygen-rich effluents having temperatures above 1300.degree. F. Similarly, Bowers, in copending and commonly assigned U.S. patent application Ser. No. 784,828, filed Oct. 4, 1985 now U.S. Pat. No. 4,719,092, discloses a solution comprising urea and an oxygenated hydrocarbon solvent which is disclosed as being effective at reducing NO.sub.x concentrations with reduced ammonia slippage in effluents at temperatures above 1600.degree. F.
In copending and commonly assigned U.S. patent application entitled "Process for Reducing Nitrogen Oxides in an Effluent Using a Hydrocarbon or Hydrogen Peroxide" having Ser. No. 022,776 filed Mar. 6, 1987, Sullivan discloses the use of hydrocarbons to reduce NO.sub.x levels in effluents at low temperatures (i.e., below 1450.degree. F., especially below 1300.degree. F.).
Although the prior art processes for reducing nitrogen oxides concentrations are generally effective, there exists a present need for a process which elicits still further NO.sub.x reductions in an economical and convenient manner.
The present invention relates to a process for reducing nitrogen oxides in the effluent from the combustion of a carbonaceous fuel. More particularly, the present invention relates to a process which comprises injecting into the effluent from the combustion of a carbonaceous fuel a treatment agent comprising a heterocyclic hydrocarbon having at least one cyclic oxygen under conditions effective to reduce the nitrogen oxides concentration in the effluent. Most preferably, the heterocyclic hydrocarbon comprises furfural.
US Referenced Citations (3)
| Number |
Name |
Date |
Kind |
| 4208376 |
Arand et al. |
Jun 1980 |
|
| 4325924 |
Arand et al. |
Apr 1982 |
|
| 4350669 |
Izumi et al. |
Sep 1982 |
|
Foreign Referenced Citations (5)
| Number |
Date |
Country |
| 2703882 |
Apr 1977 |
DEX |
| 53-30975 |
Mar 1978 |
JPX |
| 53-79762 |
Jul 1978 |
JPX |
| 52-42643 |
Nov 1978 |
JPX |
| 53-130274 |
Nov 1978 |
JPX |
Continuations (1)
|
Number |
Date |
Country |
| Parent |
25493 |
Mar 1987 |
|
Patent Grant
4888165
