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How do you solve a problem like sampling?

1. Having the wetted surfaces of the FIGURE 5 VE TECHNOLOGY CONDITIONED SYSTEM (BLUE) FOLLOWING SIMULATOR RESPONSE TO GAS CHANGES (RED)
simulator machined to a fine surface
finish, followed by electropolishing
and finally coating with SilcoNert
surface treatment.
2. Minimising any entrapment areas.
3. Using specially FEP coated seals.
4. Being dynamically designed to
enable flow through purging.
5. Sighting the probe tip away from
surfaces in an area where flow
through purging is almost ideal.
It was found that the response from
a conditioned standard VE Technology
system, in comparison to the ‘step’
change response, closely follows the
pipeline simulator response with
minimal delay.
Meanwhile, the response from a FIGURE 6 CONVENTIONAL CONDITIONED SAMPLE SYSTEM SHOWING SIGNIFICANT DELAY
conditioned conventional system had AND INACCURACY IN REPORTING CHANGES TO GAS QUALITY
a significant amount of lag and became
out of sync with what was happening in
the pipeline. This demonstrates just how
far a conventional sampling system can
cause errors in the analytical results.
Although Figure 7 does not show real
data from the experiments, the real data
sets were extrapolated so as to represent
a span gas in excess of the network entry
limits defined by the HSE. It highlights
that a measurement system using
the conventional probe and sample
system is unable to measure and report
when network entry limits for H₂S
are reached; therefore, permitting for
the entry of dangerous gas into the
network, undetected.

What’s next? FIGURE 7 EXTRAPOLATION OF EXPERIMENTAL DATA TO ILLUSTRATE HOW OUT-OF-SPECIFICATION GAS COULD ENTER THE NETWORK IF A
It is imperative when taking POORLY DESIGNED SAMPLE SYSTEM DELIVERED AN UNREPRESENTATIVE SAMPLE
measurements of a component as
safety- and operations-critical as H₂S to
thoroughly consider the consequences 5.0mg/m3
of not implementing an effective (3.3ppm)
sampling system. Particularly in
biomethane, where H₂S is continuously
and consistently produced.
Each component in the system is
as important as the next in achieving
a meaningful and representative
sample, both intact and in time. Any
one feature of the system can break the
synchronicity of the system and distort
readings/results if not appropriately
designed. From this example, the use
of an inappropriate probe could have
profound ramifications on uncertainty
of measurement, such as:
Not meeting key specifications flow into the gas network. the consequences of not achieving a
and legislation that rely on the Corrosion to downstream pipework due representative sample for measuring
measurements of, for example, H₂S to higher levels of H₂S being present. and controlling them?
and total sulphur content. Further to the analysis of H₂S to
Potential financial and safety meet the GS(M)R, a wider discussion Orbital is a global leader in gas
implications for companies of what other harmful contaminants solutions to the energy, power and
depending on these measurements by are being introduced to the network processing sectors. For more information,
unknowingly allowing ‘unsafe’ gas to via biomethane is necessary. What are visit www.orbitalgas.com

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