S03.18 Tunable Diode Laser Absorption Spectroscopy TDLAS Based Trace Moisture and Hydrogen Sulfide D

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S-03.18 Tunable Diode Laser Absorption
Spectroscopy (TDLAS) Based Trace Moisture and
Hydrogen Sulfide Detection in Hydrocarbon Gases

• Dr. Xin Zhou, Dr. Xiang (Sherry) Liu
• Dr. Alfred Feitisch, Dr. Greg Sanger
• SpectraSensors Inc.
• 11027 Arrow Route, Rancho Cucamonga, CA 91730

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Outline

• Motivation
• Moisture in hydrocarbon mix (NG)
• Hydrogen Sulfide in refinery gas
• Hydrogen Sulfide in natural gas
• Diode laser absorption spectroscopy
• Sensor design
• Line selection
• Measurement scheme
• System layout
• Sensor calibration and validation
• Conclusions

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Motivation

• Moisture in hydrocarbon gases needs to be
  minimized to prevent feedstock contamination,
  equipment damage, BTU reduction and pipeline
  corrosion hazards
• LNG processing
• Ice formation ? Equipment damage
• NG purification and distribution
• Pipeline corrosion, due to H2SO4 and H2CO3 ?
  Safety repair costs
• NG dilution ? BTU reduction
• Hydrogen Sulfide in refinery gas and natural gas
  needs to be minimized to prevent toxicity
  hazards, harmful environmental emission and
  pipeline corrosion
• Emission of SO2, upon incineration the leading
  cause of acid rain
• Corrosion of delivery pipelines due to formation
  of H2SO4
• ? Serious explosion and leakage hazards
• Diode laser absorption spectroscopy provides an
  excellent tool for sensitive real time
  measurement of H2O and H2S in hydrocarbon gases

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Selection of Optimum Transitions

• Simulation based on
• HITRAN2004
• T 296 K
• P 1 atm
• L 1 m
• Criteria
• Line strength
• Interference
• Laser availability
• Best H2O line below 2.0 mm
• Strong
• Min. CH4 interference
• DFB-TDL
• Commercially available
• Robust
• Not cost prohibitive

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Raw Data and Data Reduction
CH4
H2OCH4

• 2f peak-to-valley height increases appreciably
  with moisture concentration XH2O
• DC change imperceptible ? WMS-2f improves
  sensitivity over DAS

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Moisture in Natural Gas

• Natural gas background CH4 81.7, C2H6 9.7,
  C3H8 3.9, C4H10 1.3, CO2 3.4
• Repeatability of 25 ppb demonstrated for
  moisture measurements in natural gas

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Varying Background Composition

• Composition change every 5 minutes
• 10 random (3s, norm distribution) changes in
  non-Methane background gases

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Repeatability with Varying Background

• Impact of 10 random composition changes on
  repeatability
• Good repeatability ( 52 ppb) with proprietary
  compensation (Patent Pending)

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Modular H2S Analyzer
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Differential TDL SchemeH2S in Refinery Gas

• Gas composition
• Methane 55
• Ethylene 10
• Propane 9
• CO2 1
• Hydrogen 25

• Measurements in typical refinery background gas
  composition
• Differential scheme used to eliminate
  interference from background gases
• H2S concentration inferred from the differential
  spectra

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Differential 2f-TDL SpectraH2S in Refinery Gas

• Gas composition
• Methane 55
• Ethylene 10
• Propane 9
• CO2 1
• Hydrogen 25

• H2S clearly shown in differential spectra from 50
  ppm to 3 ppm concentration

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H2S in Refinery Gas Background

• Gas composition
• Methane 55
• Ethylene 10
• Propane 9
• CO2 1
• Hydrogen 25

• Repeatability of 0.89 ppm to 1.62 ppm
  demonstrated for H2S measurements in refinery gas

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Differential 2f-TDL Scheme H2S in Natural Gas

• Differential scheme used to eliminate
  interference from background gases
• H2S concentration inferred from the differential
  spectra

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Differential 2f-TDL SpectraH2S in Natural Gas

• H2S clearly shown in differential spectra from 10
  ppm to 1 ppm concentration

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H2S in Natural Gas Background

• Repeatability of 300 ppb to 450 ppb
  demonstrated for H2S measurements in natural gas

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Conclusions

• SpectraSensors TDLAS-based analyzers have
  demonstrated excellent sensitivity and
  repeatability for trace moisture in natural gas
• 25 ppb for moisture in natural gas
• 52 ppb for moisture in natural gas, with
  varying background
• Excellent sensitivity and repeatability have been
  demonstrated for trace hydrogen sulfide detection
  in natural gas and refinery gas
• Successful design of sample handling system and
  incorporation of differential 2f-TDL scheme
• 0.89 ppm to 1.62 ppm repeatability for H2S in
  refinery gas
• 300 ppb to 450 ppb repeatability for H2S in
  natural gas
• Sensitivity and repeatability can be further
  improved going forward