Gas measurement system

Patent metadata

Field	Value
Publication number	US-10228324-B2
Application number	US-201715658470-A
Country	US
Kind code	B2
Filing date	Jul 25, 2017
Priority date	Jul 25, 2016
Publication date	Mar 12, 2019
Grant date	Mar 12, 2019

Abstract

Presented herein are systems and methods for quantifying trace and/or ultra-trace levels of a species—for example, H 2 S or H 2 O—in a natural gas line. The systems and methods employ a tunable laser, such as a tunable diode laser, vertical-cavity surface-emitting laser (VCSEL), external cavity diode laser or a vertical external-cavity surface-emitting laser (VECSEL) or a tunable quantum cascade laser (QCL). The laser produces an output beam over a set of one or more relatively narrow, high resolution wavelength bands at a scan rate from about 0.1 Hz to about 1000 Hz. A natural gas sample comprising a trace level of a species of interest passes through a flow cell into which the output beam from the laser is guided. An optical detector receives light from the flow cell, producing a signal indicative of the absorption attenuation from which the concentration of the trace species is determined.

First claim

What is claimed is:

1. A spectroscopy system for measuring a trace level and/or an ultra-trace level of a gas in a natural gas sample, the system comprising:
a laser for producing an output beam over a set of one or more discrete or continuous wavelength bands at a scan rate from about 0.1 Hz to about 1000 Hz over the set of one or more discrete or continuous wavelength bands;
transmitting optics for guiding and/or shaping the output beam from the laser to the natural gas sample;
an optical detector for receiving light from the natural gas sample and producing a detector signal corresponding to the received light; and
a processor of a computing device and a memory having instructions stored thereon, wherein the instructions, when executed by the processor, cause the processor to compute the trace level and/or ultra-trace level of the gas in the natural gas sample from the signal corresponding to the received light,
wherein the gas is hydrogen sulfide and wherein the set of one or more discrete or continuous wavelength bands comprises one or both of bands (i) and (ii) as follows:
(i) a first band at least 0.05 cm −1 in width, said first band containing at least one value between 5066 cm −1 and 5076 cm −1 ; and
(ii) a second band at least 0.05 cm −1 in width, said second band containing at least one value between 5086 cm −1 and 5097 cm −1 .

2. The system of claim 1 , wherein the instructions, when executed by the processor, cause the processor to synchronize wavelength scanning of the laser with the detector signal to align, in a time domain, measurement of the detector signal with the wavelength scanning to generate an absorption spectrum.

3. The system of claim 2 , wherein the instructions, when executed by the processor, cause the processor to analyze the generated absorption to determine the trace level and/or ultra-trace level of the gas in the natural gas sample.

4. The system of claim 1 , wherein the natural gas sample is at least 20% methane and/or an ultra-trace amount.

5. The system of claim 1 , wherein the instructions, when executed by the processor, identify an absorption peak corresponding to methane in the natural gas sample and use the absorption peak corresponding to methane to line-lock output wavelength of the laser and stabilize one or more output wavelength bands of the laser, thereby reducing error caused by laser drift without use of a separate reference gas cell.

6. The system of claim 1 , further comprising a supplemental optical detector for receiving light from the output beam of the laser that does not pass through the natural gas sample, and for producing a resulting supplemental signal, wherein the instructions, when executed by the processor, analyze the supplemental signal to determine a reference channel baseline signature and subtract the reference channel baseline signature from a sample gas baseline signal, thereby reducing noise.

7. The system of claim 1 , further comprising a sample gas conditioning system.

8. The system of claim 1 , further comprising a flow control device for controlling a flow rate of the natural gas sample into/through the flow cell.

9. The system of claim 1 , further comprising a pump for controlling and/or reducing pressure of the natural gas sample prior to flow of the sample into/through the flow cell.

10. The system of claim 1 , further comprising a vacuum pump for producing a vacuum of the natural gas sample in the flow cell.

11. The system of claim 1 , wherein the laser comprises a member selected from the group consisting of:
a tunable diode laser,
an external cavity diode laser or a vertical external-cavity surface-emitting laser (VECSEL), and
a tunable quantum cascade laser (QCL).

12. A spectroscopy method for measuring a trace level and/or an ultra-trace level of a gas in a natural gas sample, the method comprising:
producing an output beam from a laser over a set of one or more discrete or continuous wavelength bands at a scan rate from about 0.1 Hz to about 1000 Hz over the set of one or more discrete or continuous wavelength bands;
introducing a natural gas sample into a flow cell, wherein the natural gas sample comprises a trace level and/or an ultra-trace level;
guiding and/or shaping the output beam from the laser to the natural gas sample;
receiving light, by an optical detector, from the natural gas sample and producing a detector signal corresponding to the received light; and
determining, by a processor of a computing device and a memory having instructions stored thereon, the trace level and/or ultra-trace level of the gas in the natural gas sample from the signal corresponding to the received light,
wherein the gas is hydrogen sulfide and wherein the set of one or more discrete or continuous wavelength bands comprises one or both of bands (i) and (ii) as follows:
(i) a first band at least 0.05 cm −1 in width, said first band containing at least one value between 5066 cm −1 and 5076 cm −1 ; and
(ii) a second band at least 0.05 cm −1 in, said second band containing at least one value between 5086 cm −1 and 5097 cm −1 .

13. The method of claim 12 , further comprising:
synchronizing, by the processor, wavelength scanning of the laser with the detector signal to align, in a time domain, measurement of the detector signal with the wavelength scanning to generate an absorption spectrum.

14. The method of claim 13 , further comprising:
analyzing, by the processor, the generated absorption spectrum to determine the trace level and/or ultra-trace level of the gas in the natural gas sample.

15. The method of claim 14 , further comprising:
performing a chemometric analysis of the generated absorption spectrum either in the time domain or frequency domain.

16. The method of claim 12 , wherein the natural gas sample is at least 20% methane.

17. The method of claim 12 , further comprising:
identifying, by the processor, an absorption peak corresponding to methane in the natural gas sample; and
using the absorption peak corresponding to methane to line-lock, by the processor, output wavelength of the laser and stabilize one or more output wavelength bands of the laser, thereby reducing error caused by laser drift without use of a separate reference gas cell.

18. The method of claim 12 , further comprising:
receiving light from the output beam of the laser that does not pass through the natural gas sample;
producing a resulting supplemental signal; and
analyzing, by the processor, the supplemental signal to determine a reference channel baseline signature and subtracting the reference channel baseline signature from a sample gas baseline signal, thereby reducing noise.

19. The method of claim 12 , further comprising:
conditioning the natural gas sample.

20. The method of claim 12 , further comprising
controlling a flow rate of the natural gas sample into/through the flow cell.

21. The method of claim 12 , further comprising
controlling and/or reducing pressure of the natural gas sample prior to flow of the sample into/through the flow cell.

22. The method of claim 12 , further comprising
producing a vacuum of the natural gas sample in the flow cell.

23. The method of claim 12 , wherein the laser comprises a member selected from the group consisting of:
a tunable diode laser,
an external cavity diode laser or a vertical external-cavity surface-emitting laser (VECSEL), and
a tunable quantum cascade laser (QCL).

24. A

Assignees

• Mks Instr Inc

Inventors

• Zemek Peter
• Carangelo Robert M
• Ye Hongke
• Wright Andrew

Classifications

• G01J2003/423

  Spectral arrangements using lasers, e.g. tunable · CPC title

• G01J3/4338

  Frequency modulated spectrometry · CPC title

• G01J3/0264

  Electrical interface; User interface · CPC title

• G01J1/4257

  applied to monitoring the characteristics of a beam, e.g. laser beam, headlamp beam (monitoring arrangements for lasers in general H01S3/0014) · CPC title

• G01N2021/399

  Diode laser · CPC title