Spectrometer for measuring the concentration of components in a fluid stream and method for using same

• US 5,070,246 A
• Filed: 09/22/1989
• Issued: 12/03/1991
• Est. Priority Date: 09/22/1989
• Status: Expired due to Term

• Current Assignee: ADA Technologies, Inc.
• Original Assignee: ADA Technologies, Inc.
• Inventors: Burkhardt, Mark R., Ebner, Timothy G., Durham, Michael D., Stedman, Donald H.
• Primary Examiner(s): Berman, Jack I.
• Assistant Examiner(s): HANIG, RICHARD E
• Application Number:
  US07/410,925
• Time in Patent Office: 802 Days
• Field of Search: 250/373, 250/340, 250/341, 250/343, 356/51, 356/436
• US Class Current: 250/373
• CPC Class Codes: G01J 3/2803 using photoelectric array detector
• CPC Class Codes: G01J 3/42 Absorption spectrometry; Double beam spectrometry; Flicker spectrometry; Reflection spectrometry beam switching arrangements G01J3/08
• CPC Class Codes: G01N 21/31 Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry G01N21/72 takes precedence
• CPC Class Codes: G01N 21/33 using ultraviolet light G01N21/39 takes precedence
• CPC Class Codes: G01N 21/3504 for analysing gases, e.g. multi-gas analysis

Abstract

A device and method for measuring the concentrations of components of a fluid stream. Preferably, the fluid stream is an in situ gas stream, such as a fossil fuel fired flue gas in a smoke stack. The measurements are determined from the intensity of radiation over a selected range of radiation wavelengths using peak-to-trough calculations. The need for a reference intensity is eliminated.

Claims

1. A method for in situ measurement of at least one component in a gas stream comprising:

a) passing radiation through an in situ gas stream,

b) selecting at least one wavelength range in which said component absorbs radiation,

c) measuring the amount of radiation which passes through said gas stream at a plurality of wavelengths within said selected wavelengths range, and

d) calculating the concentration of said component by comparing the difference in the amount of radiation which passes through said gas at two selected points within said selected wavelength range.

2. The method as claimed in claim 1 wherein said gas stream is a flue gas and the in situ environment is a smoke stack.

3. The method as claimed in claim 1 wherein said component is selected from the group consisting of NO, SO₂, NH₃, aromatic hydrocarbons, formaldehyde, ozone, chlorine and bromine.

4. The method as claimed in claim 1 wherein said step of calculating the concentration of the component comprises:

a) determining a first wavelength at which minimum transmitted radiation occurs within said selected range,

b) determining a second wavelength at which maximum transmitted radiation occurs within said selected range,

c) determining the difference between said minimum transmitted radiation and said maximum transmitted radiation, and

d) calculating the concentration of said component using reference data obtained from measurements performed on gases of known concentration.

5. The method as claimed in claim 1 wherein said step of calculating the concentration of a component comprises:

a) determining a first wavelength at which a minimal amount of radiation is transmitted within said selected range,

b) calculating a base line by performing a linear regression calculation on two groups of transmitted radiation values within said selected range, the first group of transmitted radiation values corresponding to wavelengths less than said first wavelength and at which high transmission occurs and the second group of transmitted radiation values corresponding to wavelengths greater than said first wavelength and at which high transmission occurs,

c) determining the difference between said minimal transmitted radiation value and said base line at said first wavelength, and

d) calculating the concentration of said component using reference data obtained from measurements performed on gases of known concentration.

6. The method as claimed in claim 1 wherein at least two wavelengths ranges are selected in order to measure at least two components in said gas stream.

7. The method as claimed in claim 1 wherein the concentration of NH₃ in a gas stream is measured and the selected wavelength range is from about 2040 Angstroms to about 2120 Angstroms.

8. The method as claimed in claim 7 wherein the concentration of NH₃ is calculated by employing both the difference in the amount of radiation which passes through said gas at two selected points within said wavelength range and a calibration curve of the type illustrated in FIGS. 4, 5 and 13.

9. The method as claimed in claim 1 wherein the concentration of NO in a gas stream is measured and the selected wavelength range is from about 2100 Angstroms to about 2200 Angstroms.

10. The method as claimed in claim 9 wherein the concentration of NO is calculated by employing both the difference in the amount of radiation which passes through said gas at two selected points within said wavelength range and a calibration curve of the type illustrated in FIG. 8.

11. The method as claimed in claim 1 wherein the concentration of SO₂ in a gas stream is measured and the selected wavelength range is from about 2270 Angstroms to about 2300 Angstroms.

12. The method as claimed in claim 11 wherein the concentration of SO₂ is calculated by employing both the difference in the amount of radiation which passes through said gas at two selected points within said wavelength range and a calibration curve of the type illustrated in FIG. 10.

13. A device for in situ measurement of components in a gas stream comprising:

a) a radiation source;

b) a radiation detection means for measuring radiation transmitted through said gas stream at a plurality of wavelengths within at least one selected wavelength range,

c) means for passing radiation from said radiation source through said in situ gas stream before impinging on said radiation detection means, wherein said means comprises components which are positionally fixed during the measuring of said radiation,

d) calculation means for determining the concentration of a component in said gas stream by employing the transmitted radiation values obtained for said selected wavelength range to obtain a deference between a maximum transmitted radiation value and a minimum transmitted radiation value within said selected wavelength range and comparing said difference to calibration values obtained by measuring relative transmitted radiation values for gases of known concentration within said selected wavelength range.

14. The device as claimed in claim 13 wherein said components include NH₃, NO and SO₂ which are individually or simultaneously present in said gas stream.

15. The device as claimed in claim 13 wherein said radiation detection means comprises a linear photodiode array having a resolution from about 1 to about 4 Angstroms per diode.

16. The device as claimed in claim 13 wherein said radiation detection means comprises a linear photodiode array having a resolution of about one Angstrom per diode.

17. A method for calculating the concentration of a component in a fluid comprising:

a) selecting a wavelength range, wherein said component absorbs radiation at some wavelengths within said wavelength range,

b) passing radiation through said fluid,

c) measuring the amount of radiation transmitted at wavelengths within said wavelength range,

d) determining a first wavelength at which the minimum amount of radiation is transmitted within said wavelength range,

e) calculating a base line for said wavelength range, said base line passing through points of relatively high transmitted of radiation values,

f) calculating the difference between said base line and said minimum transmitted radiation point at said first wavelength, and

g) calculating the concentration of the component based on said difference.

18. The method as claimed in claim 17 wherein the concentration of NH₃ is a gas stream is calculated and the selected wavelength range is from about 2040 Angstroms to about 2120 Angstroms.

19. The method as claimed in claim 18 wherein the concentration of NH₃ is calculated by employing both the log values of said difference and a calibration curve of the type illustrated in FIGS. 4, 5 and 13.

20. The method as claimed in claim 17 wherein said component is NH₃ and said base line is calculated by performing a linear regression operation on a first group of selected points corresponding to transmitted radiation values for wavelengths in the range of from about 20 to about 50 Angstroms less than said first wavelength and a second group of selected points corresponding to transmitted radiation values for wavelengths in the range of from about 20 to about 50 Angstroms more than said first wavelength.

21. The method as claimed in claim 17 wherein the concentration of NO in a gas stream is calculated and the selected wavelength range is from about 2200 Angstroms to about 2300 Angstroms.

22. The method as claimed in claim 21 wherein the concentration of NO is calculated by employing both the log values of said difference and a calibration curve of the type illustrated in FIG. 8.

23. The method as claimed in claim 17 wherein said component is NO and said base line is calculated by performing a linear regression operation on a first group of selected points corresponding to transmitted radiation values for wavelengths in the range of from about 20 to about 50 Angstroms less than said wavelength and a second group of selected points corresponding to transmitted radiation values for wavelengths in the range of from about 20 to about 50 Angstroms more than said first wavelength.

24. The method as claimed in claim 17 wherein the concentration of SO₂ gas in a gas stream is calculated and the selected wavelength range is from about 2170 Angstroms to about 2200 Angstroms.

25. The method as claimed in claim 24 wherein the concentration of SO₂ is calculated by employing both the log values of said difference and a calibration curve of the type illustrated in FIG. 10.

26. The method as claimed in claim 17 wherein said component is SO₂ and said base line is calculated by performing a linear regression operation on a first group of selected points corresponding to transmitted radiation values for wavelengths in the range of from about 15 to about 25 Angstroms less than said first wavelength and a second group of selected points corresponding to transmitted radiation values for wavelengths in the range of from about 15 to about 25 Angstroms more than said first wavelength.

27. A device for determining the concentrations of at least one component in a fluid comprising:

a) a positionally fixed radiation source;

b) a positionally fixed chromator,

c) a positionally fixed filter,

d) a positionally fixed radiation detection means capable of sensing the intensity of incident radiation within at least one selected wavelength range, and

e) means to convert the output from the radiation detection means to a concentration for the desired component based upon a single reading of radiation intensities across said selected wavelength range and using a predetermined calibration curve.

28. A device as claimed in claim 27 wherein said fluid is a gas and said component is NH₃.

29. A device as claimed in claim 27 wherein said fluid is a gas and said component is NO.

30. A device as claimed in claim 27 wherein said fluid is a gas and said component is SO₂.

31. A device as claimed in claim 27 wherein said radiation source comprises a deuterium lamp which produces ultraviolet and visible radiation in the wavelength region of from about 1900 to about 6000 Angstroms.

32. A device as claimed in claim 27 wherein said polychromator comprises a prism or an optical grating.

33. A device as claimed in claim 27 wherein said filter comprises a slit.

34. A device as claimed in claim 27 wherein said radiation detection means comprises a linear photodiode array.

35. A device as claimed in claim 27 wherein said radiation detection means comprises a linear photodiode array having a resolution effective for identifying appropriate peaks and preventing the undesirable blending of adjacent peaks.

36. A device as claimed in claim 27 wherein said radiation detection means comprises a linear photodiode array having a resolution from about 1 to about 4 Angstroms per diode.

37. A device as claimed in claim 27 wherein said radiation detection means comprises a linear photodiode array having a resolution of about one Angstrom per diode.

38. A method for measuring the concentration of a component in a sample comprising:

a) passing radiation through said sample,

b) dispersing said radiation in order to generate a spectrum,

c) measuring the intensity of a selected wavelength range within said spectrum after said radiation has passed through said sample,

d) determining the difference between the maximum transmitted radiation and the minimum transmitted radiation within said selected range,

e) calculating the concentration of said component by comparing said difference to previously determined differences for known concentrations.

39. The method as claimed in claim 38 wherein said step of measuring the intensity of a selected wavelength range within said spectrum is accomplished using a radiation detection means comprising a linear photodiode array having a resolution of from 1 to about 4 Angstroms per diode.

40. The method as claimed in claim 38 wherein said step of measuring the intensity of a selected wavelength range within said spectrum is accomplished using a radiation detector comprising a linear photodiode array having a resolution of approximately one Angstrom per diode.

41. A method for determining the concentration of NH₃, NO and SO₂ in a gas stream comprising:

a) measuring the intensity of radiation passing through the gas stream at wavelengths which correspond to absorption by SO₂ between about 2170 Angstroms and about 2200 Angstroms,

b) employing peak-to-trough calculations to determine the concentration of SO₂,

c) determining the spectrum corresponding to the SO₂ alone based upon the peak-to-trough calculations and predetermined calibration curves,

d) mathematically subtracting the spectrum due to SO₂ alone from the overall spectrum,

e) measuring the intensity of radiation passing through the gas stream at wavelengths which correspond to absorption by NH₃ between about 2040 Angstroms and about 2120 Angstroms,

f) employing peak-to-trough calculations to determine the concentration of NH₃,

g) measuring the intensity of radiation passing through the gas stream at wavelength which corresponds to absorption by NO between about 2200 Angstroms and about 2300 Angstroms,

i) employing peak-to-trough calculations to determine the concentration of NO.

42. The method as claimed in claim 41 further comprising the step of chemically removing SO₂ from the gas stream by selective scrubbing prior to the calculation of NH₃ and NO concentration.