Rapid, sensitive hydrogen detector with active hydrogen-derived water vapor signal modulation
In various embodiments, rapid, sensitive detection of molecular hydrogen is achieved by chemically converting hydrogen to water vapor and then detecting the water vapor as a surrogate for the hydrogen. Detection may be enhanced by dampening variation in ambient water vapor and rapidly actively modulating a hydrogen-derived water vapor component. For example, the detector may receive sample gas that includes ambient water vapor and hydrogen, dry the sample gas to dampen variation in the ambient water vapor, divide the sample gas into a chemical conversion flow and a bypass flow, chemically convert hydrogen in the chemical conversion flow to water vapor, alternate between measuring water vapor in the converted chemical conversion flow or the bypass flow to produce a water vapor signal, separate the water vapor signal in the time domain to extract a hydrogen-derived water vapor signal, and output a hydrogen signal based on the hydrogen-derived water vapor signal.
1. A method for detecting molecular hydrogen, comprising:
receiving sample gas that includes ambient water vapor and hydrogen;
drying the sample gas to dampen variation in the ambient water vapor in the sample gas;
dividing the sample gas into a chemical conversion flow and a bypass flow;
chemically converting hydrogen in the chemical conversion flow to water vapor;
alternating between measuring water vapor in the converted chemical conversion flow or the bypass flow to produce a water vapor signal;
separating the water vapor signal into components based on differing variation over time to extract a hydrogen-derived water vapor signal from the water vapor signal; and
outputting a hydrogen signal that describes molecular hydrogen in the sample gas based on the hydrogen-derived water vapor signal.
2. The method of claim 1 , wherein the measuring water vapor is performed in a water vapor monitoring cell, and the alternating maintains constant flow through the water vapor monitoring cell.
3. The method of claim 2 , wherein the constant flow through the water vapor monitoring cell has a constant pressure.
4. The method of claim 1 , wherein the measuring is performed at a measurement rate and the alternating is performed at a switching rate that is at least 10 times less than the measurement rate.
5. The method of claim 1 , wherein the drying is performed by a sulfonated tetrafluoroethylene based fluoropolymer-copolymer membrane gas dryer and the chemically converting is performed by heating the sample gas in a catalytic oven.
6. The method of claim 1 , wherein the measuring water vapor is performed by optically detecting water vapor using laser spectroscopy or non-dispersive infrared (NDIR) absorption spectroscopy.
7. The method of claim 1 , further comprising:
humidifying the sample gas to a predetermined relative humidity prior to passing the sample gas through the gas dryer.
8. The method of claim 1 , further comprising:
suppressing hydrogen bearing molecules in the sample gas by trapping the hydrogen bearing molecules using at least one of a filter material, membrane, molecular sieve, or cryogenic trap.
9. The method of claim 1 , further comprising:
suppressing hydrogen bearing molecules in the sample gas by tuning the chemical conversion to selectively oxidize hydrogen while avoiding conversion of hydrogen bearing molecules to water vapor.
10. The method of claim 1 , further comprising:
compensating for hydrogen bearing molecules in the sample gas by measuring hydrogen bearing molecule concentrations in the sample gas, calculating an amount of hydrogen bearing molecule-derived water vapor based on the measured hydrogen bearing molecule concentrations, and subtracting out hydrogen bearing molecule-derived water vapor from the water vapor signal.
11. A molecular hydrogen detector, comprising:
an inlet configured to receive sample gas that includes ambient water vapor and hydrogen;
a gas dyer having a segment configured to receive sample gas from the inlet and to dampen variation in the ambient water vapor in the sample gas;
a flow divider configured to divide the sample gas into a chemical conversion flow and a bypass flow;
a catalytic oven configured to chemically convert hydrogen in the chemical conversion flow to water vapor;
one or more valves configured to alternately pass the converted chemical conversion flow or the bypass flow;
a water vapor monitoring cell configured to alternately measure water vapor in the converted chemical conversion flow or the bypass flow to produce a water vapor signal; and
a processor configured to separate the water vapor signal into components based on differing variation over time to produce an ambient water vapor signal and a hydrogen-derived water vapor signal, and to output a hydrogen signal based on the hydrogen-derived water vapor signal to describe molecular hydrogen in the sample gas.
12. The molecular hydrogen detector of claim 11 , wherein the one or more valves comprise:
a first valve configured to selectively direct the chemical conversion flow to either the water vapor monitoring cell or to bypass the water vapor monitoring cell; and
a second flow valve configured to selectively direct the bypass flow to either the water vapor monitoring cell or to bypass the water vapor monitoring cell,
wherein the processor is configured to activate and deactivate the first valve and the second valve to cause the water vapor monitoring cell to alternately measure water vapor in the converted chemical conversion flow or the bypass flow.
13. The molecular hydrogen detector of claim 11 , wherein the one or more valves are configured to maintain constant flow through the water vapor monitoring cell.
14. The molecular hydrogen detector of claim 11 , wherein the water vapor monitoring cell is configured to measure water vapor in the converted chemical conversion flow or the bypass flow at a measurement rate and the one or more valves are configured to alternately pass the converted chemical conversion flow or the bypass flow at a switching rate that is at least 10 times less than the measurement rate.
15. The molecular hydrogen detector of claim 11 , wherein the gas dryer comprises a sulfonated tetrafluoroethylene based fluoropolymer-copolymer membrane gas dryer and the water vapor monitoring cell comprises a laser spectrometer or a non-dispersive infrared (NDIR) absorption spectrometer.
16. The molecular hydrogen detector of claim 11 , further comprising:
a humidifier disposed between the inlet and the gas dryer and configured to bring the sample gas to a predetermined relative humidity.
17. The molecular hydrogen detector of claim 11 , further comprising:
a filter material, membrane, molecular sieve, or cryogenic trap configured to suppress hydrogen bearing molecules in the sample gas.
18. The molecular hydrogen detector of claim 11 , further comprising:
a monitor configured to measure hydrogen bearing molecule concentrations in the sample gas,
wherein the processor is configured to compensate for hydrogen bearing molecules in the sample gas by calculating an amount of hydrogen bearing molecule-derived water vapor based on the measured hydrogen bearing molecule concentrations and subtracting out hydrogen bearing molecule-derived water vapor from the water vapor signal.
19. A molecular hydrogen detector, comprising:
means for receiving sample gas that includes ambient water vapor and hydrogen;
means for drying the sample gas to dampen variation in the ambient water vapor;
means for dividing the sample gas into a chemical conversion flow and a bypass flow;
means for chemically converting hydrogen in the chemical conversion flow to water vapor;
means for alternating between measuring water vapor in the converted chemical conversion flow or the bypass flow to produce a water vapor signal; and
means for separating the water vapor signal into components based on differing variation over time to extract a hydrogen-derived water vapor signal, and for outputting a hydrogen signal based on the hydrogen-derived water vapor signal to describe molecular hydrogen in the sample gas.
20. The molecular hydrogen detector of claim 19 , wherein the means for dividing is configured to maintain constant flow through the water vapor monitoring cell.