Method and system for detecting moisture in natural gas

1. A system, comprising:

a moisture analyzer configured to detect moisture comprising water present in natural gas, comprising:

an absorption cell enclosing and conducting the natural gas;

a pressure control device configured to reduce a pressure of the natural gas inside the absorption cell to generate de-pressurized natural gas at a pressure lower than an ambient pressure of the natural gas;

a light emitting device configured to transmit light through the de-pressurized natural gas inside the absorption cell; and

a photodetector configured to detect an intensity of the light transmitted through the de-pressurized natural gas and exiting the absorption cell.

2. The system of claim 1 , comprising electronic circuitry configured to acquire and process a spectrum of the natural gas.

3. The system of claim 2 , wherein the electronic circuitry is configured to determine a concentration of moisture in the natural gas based on the spectrum.

4. The system of claim 2 , wherein the electronic circuitry is configured to subtract a background value from a spectral feature within the spectrum of the natural gas based on a predetermined ratio to determine a concentration of moisture in the natural gas.

5. The system of claim 2 , wherein the spectrum comprises an absorption-based spectrum.

6. The system of claim 2 , wherein the spectrum comprises a direct absorption spectrum.

7. The system of claim 2 , wherein the spectrum comprises a derivative spectrum.

8. The system of claim 2 , wherein the spectrum is based on photoacoustic spectroscopy.

9. The system of claim 2 , wherein the spectrum is based on cavity ring down spectroscopy.

10. The system of claim 2 , wherein the spectrum is based on fluorescence spectroscopy.

11. The system of claim 1 , wherein the light emitting device comprises a laser, a diode laser, or a quantum cascade laser.

12. The system of claim 11 , wherein the diode laser comprises:

a thermoelectric cooler;

a temperature sensor; and

a built-in photodetector configured to detect an intensity of backward emission from the diode laser.

13. The system of claim 1 , wherein the pressure control device comprises a vacuum pump or an aspirator.

14. The system of claim 1 , wherein the pressure control device is configured to reduce the pressure of the natural gas to between approximately 1 psia and 5 psia.

15. The system of claim 1 , wherein the natural gas comprises pipeline natural gas, liquified natural gas feed gas, or regasified liquefied natural gas.

16. The system of claim 1 , wherein the absorption cell comprises a multipass absorption cell.

17. A method, comprising:

reducing a pressure of natural gas by a pressure control device to generate de-pressurized natural gas at a pressure lower than an ambient pressure of the natural gas;

transmitting a light through the de-pressurized natural gas at a pre-selected wavelength or across a wavelength range;

recording a spectrum of the de-pressurized natural gas; and

determining via electronic circuitry a concentration of moisture comprising water present in the natural gas based on the spectrum of the natural gas.

18. The method of claim 17 , comprising reducing the pressure of the natural gas to generate de-pressurized natural gas at a pressure of no more than approximately 5 psi.

19. The method of claim 17 , comprising reducing the pressure of the natural gas to generate de-pressurized natural gas at a pressure of no more than approximately 2.5 psi.

20. The method of claim 17 , wherein the concentration of moisture is determined by subtracting a background value from a spectral feature within the spectrum of the de-pressurized natural gas based on a predetermined ratio.