by Applied Analytics
Natural gas for direct consumption is odorized for safety reasons. In
the odorizing process, a substance with extremely high odor is added to
natural gas in a controlled method.
Natural gas for direct consumption is odorized for safety
reasons. In the odorizing process, a substance with extremely high odor
is added to natural gas in a controlled method. The odorized natural gas
is then transmitted via pipelines into crowded urban settings and
eventually into homes, schools, and workplaces.
In many cases, the smell of the gas is the only mechanism for
leak detection and prevention of catastrophic explosions. Mercaptans are
often used as odorants due to their low odor threshold. In Europe,
tetrahydrothiophene (THT) is commonly used. Since the pipeline material
absorbs some of the odorant out of the natural gas stream, the THT level
is continuously monitored to ensure the gas is adequately odorized
throughout the pipeline.
Case study:
At one border crossing in Western Europe, where custody of a
natural gas pipeline is transferred, the operators depend on Applied
Analytics technology to continuously validate odorant level at several
points. An
OMA-300 Process Analyzer is installed at each monitoring point with a dedicated sampling system for handling the high pressure natural gas.
| Application: |
THT in Natural gas |
| Location: |
Western Europe |
| Equipment: |
OMA-300 Process Analyzer |
| Span Check: |
5 PPM THT in Methane |
|
|
Figure 1 visualizes how the OMA-300 sees the
absorbance spectra of (a) un-odorized natural gas, (b) natural gas
odorized with THT, and (c) 5 ppm THT in span gas. Sales-quality natural
gas contains mostly methane, which does not absorb in the UV range. The
absorbance curve seen in Figure 1 from 245-285 nm is the fingerprint of
the aromatic compounds often present in low amounts in natural gas. To
isolate THT absorbance, the unit is calibrated to the aromatic
background. This procedure for interference-free, reliable odorant
measurement is only possible with a multi-wavelength instrument that can
properly subtract the aromatic absorbance.
Figure 1: UV absorbance spectra of un-odorized natural gas, odorized natural gas, and THT in span gas.
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 |
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Each of the measurement checkpoints at this site receives
natural gas flowing from a different source, such that each analyzer is
being fed a stream with unique gas background matrix.
Figure 2 shows the absorbance spectra measured by the OMA-300
at various checkpoints. Table 1 shows the actual readings of THT in
these natural gas streams.
Figure 2: UV absorbance spectra of THT in different natural gas sources.
|
| Table 1: THT readings obtained from the lab and the online OMA-300 Process Analyzer. |
| Gas Source |
THT(PPM) |
THT OMA(PPM) |
| Gas 1 |
4.78 |
4.42 |
| Gas 2 |
1.96 |
1.81 |
| Gas 3 |
4.50 |
4.32 |
| Gas 4 |
4.60 |
4.26 |
| Gas 5 |
2.75 |
2.83 |
|
Conclusion
At this site, the OMA-300 has simplified pipeline operation by
providing interference-free, automated odorant monitoring, giving the
operators at-a-glance odorant levels at multiple checkpoints. Applied
Analytics technology is trusted with the critical task of ensuring gas
safety downstream into populated areas.