LASER DETECTION SYSTEM AND METHOD

• US 20170299503A1
• Filed: 04/19/2016
• Published: 10/19/2017
• Est. Priority Date: 04/19/2016
• Status: Active Grant

• Current Assignee: Emerson Process Management Limited
• Original Assignee: Cascade Technologies Holdings Limited (Emerson Electric Company)
• Inventors: Black, Paul, Lindley, Ruth
• Granted Patent: US 10,724,945 B2
• Time in Patent Office: Days
• 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 21/3504 for analysing gases, e.g. multi-gas analysis
• CPC Class Codes: G01N 21/39 using tunable lasers
• CPC Class Codes: G01N 2201/06113 Coherent sources; lasers
• CPC Class Codes: G01N 2201/068 Optics, miscellaneous
• CPC Class Codes: G01N 33/0037 for NOx
• CPC Class Codes: Y02A 50/20 Air quality improvement or preservation, e.g. vehicle emission control or emission reduction by using catalytic converters

Abstract

A laser detection system comprises a plurality of lasers wherein each laser is configured to produce a respective laser beam for excitation of one or more different compounds, a sample cell for containing a volume of sample gas, at least one directing device configured to direct the laser beams to the sample cell, wherein the at least one directing device is configured to direct the laser beams along a common optical path to the sample cell, and a detector apparatus for detecting light output from the cell.

Claims

1. A laser detection system comprising:

a plurality of lasers wherein each laser is configured to produce a respective laser beam for excitation of one or more different compounds;

a sample cell for containing a volume of sample gas;

at least one directing device configured to direct the laser beams to the sample cell, wherein the at least one directing device is configured to direct the laser beams along a common optical path to the sample cell, and

a detector apparatus for detecting light output from the cell.

2. A system according to claim 1, wherein the at least one directing device comprises a plurality of optical components arranged such that, for each laser beam a respective at least one of the optical components is arranged to direct said laser beam along the common optical path.

3. A system according to claim 2, wherein the plurality of optical components are arranged substantially in a straight line.

4. A system according to claim 2, wherein each of the lasers is arranged such that in operation each of the lasers transmits its laser beam to its corresponding at least one of the optical components in a direction substantially orthogonal to said straight line.

5. A system according to claim 2, wherein at least one of the optical components comprises a flat or non-wedged optical component

6. A system according to claim 2, where the plurality of optical components comprise at least one partially reflective mirror and/or at least one dichroic mirror.

7. A system according to claim 2, wherein each of the optical components has a thickness in a range 0.1 mm to 1 mm.

8. A system according to claim 2, wherein the optical components are arranged in series and are configured such that in operation each optical component directs a laser beam from its associated laser to join said common optical path, and directs or allows passage of laser beam(s) from preceding optical components in the series along said common optical path.

9. A system according to claim 2, wherein each of the optical components is at least partially reflective and at least partially transmissive.

10. A system according to claim 2, wherein the at least one directing device comprises steering optics between the last of said plurality of optical components and the sample cell and configured to direct the laser beams into the optical cell.

11. A system according to claim 1, wherein the detection apparatus comprises a plurality of detectors, each detector being configured to detect radiation of a respective wavelength or range of wavelengths.

12. A system according to claim 1, further comprising:

a controller configured to control operation of the plurality of lasers such that the laser beams are pulsed laser beams interleaved in time.

13. A system according to claim 12, wherein the controller is configured to synchronise operation of the detection apparatus and the lasers, thereby to obtain a series of detection signals, each detection signal being associated with a respective one of the lasers.

14. A system according to claim 12, wherein the controller is configured to control operation of the lasers such that each laser beams is pulsed at a rate in a range 1 kHz to 200 kHz, optionally in a range 10 kHz to 100 kHz, and/or wherein the controller is configured to control the lasers such that each laser beams is pulsed with pulse lengths in a range 100 ns to 5000 ns.

15. A system according to claim 1, further comprising a processing resource configured to determine an amount of NOx based on the detected light outputs.

16. A system according to claim 1, wherein the plurality of compounds comprise at least one of:

NO, NO₂, H₂O, CO, CO₂, CH₄, SO₂, NH₃, O₂H₂ and O₂.

17. A system according to claim 1, wherein each of the plurality of lasers is configured to produce infrared laser radiation.

18. A system according to claim 1, wherein each of the lasers is configured to produce a laser beam of a respective different wavelength or range of wavelengths.

19. A system according to claim 18, wherein at least one of the ranges of wavelengths is selected from the following ranges:

5.2632 to 5.2356 μ

m;

6.1538 to 6.1162 μ

m;

4.4742 to 4.4743 μ

m;

7.4627 to 7.4349 μ

m;

0.7605 to 0.7599 μ

m; and

10.0 to 10.2 μ

m.

20. A system according to claim 1, wherein the detector apparatus is arranged on the opposite side of the sample cell to the plurality of lasers and the at least one directing device.

21. A system according to claim 1, further comprising a gas supply arrangement configured to supply a remote sample gas to the sample cell.

22. A system according to claim 1, wherein the sample cell comprises a Herriot cell.

23. A system according to claim 1, wherein the system is a continuous emission monitoring system.

24. A method of detecting a plurality of different compounds, comprising producing a plurality of laser beams, each for excitation of one or more different ones of the compounds, directing the laser beams along a common optical path to a sample cell for containing a volume of sample gas, and detecting light output from the cell.