0.025 0.020
1.8
10 psia 13 psia 15 pisa 25 pisa 19 pisa
1.6
0.015
1.4
0.010
1.2
0.005
1.0
0.000
0.8
-0.005
0.6
-0.010
C /C=-1.75(P/P ) +7.51(P/P ) -11.86(P/P )+6.35
-0.015
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
Wavelength, nm
P/P
Figure 7 Pressure compensation curve for the hydrogen analyser replicate a conventional wavelength modulation spectroscopy experiment. Further, the digital signal processing methods employed in this system successfully removed minor background interferences caused by other absorbing species in the sample matrices. Specifically, the digital signal-processing methods employed in this system were used to successfully implement a multivariate calibration, enabling the instrument to accurately measure hydrogen in the presence of the overlapped spectral responses. The hydrogen measurements yielded an accuracy of better than 2% over a concentration range of 0-100%. With TDLAS-based analysers being widely accepted as process and emissions measuring devices, integration in hydrogen production and transmission applications is a logical alternative to other measurement devices that directly expose sensors to the gas stream, have a high cost of operation, or are complicated to operate and maintain. Acknowledgements The authors wish to thank AMETEK Process Instruments for their continuous support, during development of this project.
Figure 6 Hydrogen spectra under different pressure
After the calibration was carried out under normal atmospheric pressure (P 0 ), the analyser response (C) for a fixed hydrogen concentration (C 0 ) was recorded under several selected values of pressure (P) in the sample cell. To correct for pressure dependence, a pressure compensation routine was implemented. The pressure- compensation factor was calculated from a third-order polynomial, which used the ratio of the absolute pressure under the measurement conditions to that of the standard value (i.e., 1.0 atmosphere). For the curve shown in Figure 7 , polynomial regression was
( ) ( ) C 0 C P P 0 ∑ = 3 a j =0 j
Where: C 0 = fixed hydrogen concentration C = analyser readings P = pressure in the sample cell P 0 = normal atmospheric pressure (a j ) = the coefficients estimated for this instrument. Conclusions The test gas analyser was built for the
VIEW REFERENCES
measurements of hydrogen content in a couple of anticipated petrochemical and hydrocarbon applications but could also be designed for other production units. The analyser employed an all-digital measurement protocol configured to
Airat Amerov airat.amerov@ametek.com
Michael Gaura michael.gaura@ametek.com
www.decarbonisationtechnology.com
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