METHOD AND APPARATUS FOR ANALYZING NITROGEN OXIDES IN GAS

• US 3,835,322 A
• Filed: 02/02/1973
• Issued: 09/10/1974
• Est. Priority Date: 02/04/1972
• Status: Expired due to Term

• Current Assignee: Isamu Komatsu
• Original Assignee: Isamu Komatsu
• Inventors: Komatsu, Isamu
• Primary Examiner(s): Lawrence, James W.
• Assistant Examiner(s): Anderson, B. C.
• Application Number:
  US05/329,119
• Time in Patent Office: 585 Days
• Field of Search: 250/343,352,373,340,345
• US Class Current: 436/118
• CPC Class Codes: G01N 31/005 investigating the presence of an element by oxidation G01N31/12 takes precedence
• CPC Class Codes: G01N 33/0013 by a chemical reaction a chemical reaction taking place or a gas being eliminated in one or more analysing channels G01N33/0024
• CPC Class Codes: Y10T 436/179228 Both nitrogen oxide and dioxide

Abstract

Nitrogen oxides in a gas, for example, flue gas from a boiler, are continuously analyzed by (a) adding ozone gas to the gas containing nitrogen oxides thereby converting the nitrogen oxides to dinitrogen pentaoxide, (b) thermally decomposing the dinitrogen pentaoxide in the gas to nitrogen dioxide at a temperature of 300* to 340*C, and (c) continuously measuring nitrogen dioxide content of gas by an optical analyzer, for example, dual wavelength, photoelectric type analyzer of ultraviolet and visible regions.

Claims

2. A method according to claim 1, wherein the amount of ozone gas reacted with said sample gas is at least 1.5 times as much as the amount of NO and NO2 in said sample gas on a molar basis.

3. A method according to claim 1, wherein the temperature to which the gas containing N2O5 is heated is selected to maximize the conversion efficiency of the N2O5 decomposition reaction.

4. A method according to claim 1, wherein the temperature to which the gas containing N2O5 is heated is maintained within a range such that the conversion efficiency of the N2O5 decomposition reaction is kept substantially constant.

5. A method according to claim 4, wherein the temperature range for the decomposition of N2O5 into NO2 and O2 is about 300*C to 340*C.

6. A method according to claim 1, wherein the concentration of NO2 resulting from the decomposition of N2O5 by heating is optically measured by absorbency of light beams having a specific wavelength.

7. A method according to claim 6, wherein at least one of said light beams has a wavelength from about 250 to 600m Mu .

8. A method according to claim 7, wherein at least one of said light beams has a wavelength of about 405m Mu .

9. A method according to claim 8, wherein another of said light beams has a wavelength outside of the absorbence spectrum of NO2.

10. A method according to claim 9, wherein said another of said light beams has a wavelength of about 610m Mu .

11. A method according to claim 6, wherein the concentration of NO2 resulting from the decomposition of N2O5 by heating is measured by a dual wavelength spectrophotometer.

12. A method according to claim 11, wherein said dual wavelength spectrophotometer covers the spectrum range of about 250 to 600m Mu .

13. A method according to claim 6, wherein the concentration of NO2 resulting from the decomposition of N2O5 by heating is measured by a two-light path spectrophotometer.

14. A method according to claim 13, wherein said two-light path spectrophotometer covers the spectrum range of about 250 to 600m Mu .

15. A method according to claim 1, wherein the concentration of NO2 resulting from the decomposition of N2O5 by heating is measured by intermittent colorimetry.

16. A method according to claim 1, wherein the ozone gas reacted with said sample gas is in the form of a mixture of ozone gas and O2 gas.

17. An apparatus for analyzing the total nitrogen oxide concentration of a sample gas containing NO and NO2, said apparatus comprising:

a. sample inlet means for sampling a sample gas containing NO and NO2, b. ozone supply means for supplying O3 gas, c. mixing means for mixing sample gas containing NO and NO2 from said sample inlet means with O3 gas from said ozone supply means, thereby converting NO and NO2 into N2O5, d. heating means connected to said mixing means for decomposing N2O5 in the gas mixture into NO2and O2, and e. measuring means connected to a downstream side of said heating means for measuring the concentration of NO2 generated by the decomposition of N2O5 in said heating means.

18. An apparatus according to claim 17, wherein said measuring means is an optical measuring means capable of measuring the absorbence of light beams having a specific wavelength.

19. The apparatus according to claim 18, wherein said measuring means is a dual wavelength spectrophotometer.

20. The apparatus according to claim 19, wherein said dual wavelength spectrophotometer is capable of covering the spectrum range of about 250 to 600m Mu .

21. The apparatus according to claim 18, wherein said measuring means is a two-light path spectrophotometer.

22. The apparatus according to claim 21, wherein said two-light path spectrophotometer is capable of covering the spectrum range of about 250 to 600m Mu .

23. The apparatus according to claim 18, further including a demoistening means fluidly connected to said sample inlet means upstream of said measuring means for removing moisture from the same gas containing NO and NO2.

24. The apparatus according to claim 18, further including filtering means fluidly connected to said sample inlet means upstream of said measuring means for providing dust from said sample gas.

25. An apparatus according to claim 18, further including fluid controlling means upstream of said mixing means for controlling the mixing ratio of the sample gas and ozone gas mixed in said mixing means.

26. An apparatus according to claim 18, further including temperature control means for controlling the temperature of said heating means.

27. An apparatus according to claim 18, wherein said ozone supply means includes means for generating O3 gas from O2 gas.

28. An apparatus according to claim 27, wherein said ozone supply means further includes an O2 gas supply means.

29. An apparatus for analyzing the total nitrogen oxide concentration of a sample gas containing NO and NO2, said apparatus comprising:

a. sample inlet means for receiving a sample gas, b. means for introducing O3 gas into said sample gas, thereby converting NO and NO2 into N2O5, c. heating means fluidly connected to said inlet means downstream of a point of introduction of the O3 gas for decomposing N2O5 in the resultant gas into N2 and O2, and d. measuring means connected to a downstream side of said heating means for measuring the concentration of NO2 generated by the decomposition of N2O5 in said heating means.