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Measurement concept of GasLab Q2
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G a s Q u a l i t y A n a l y z e r
GasLab Q2
Figure 3.2: Infrared measurement principle
All significant hydrocarbon components in typical natural gas can be detected by IR absorption.
The contribution of the hydrocarbon content can be determined for gas specifications such as gas
heating value, density or heat conductivity, by using the IR absorption.
The method additionally uses a thermal conductivity detector (TCD) in parallel. This is a
microsystem-technical device and sensitive to all gas components. It also captures
the
nitrogen
contribution. The
figure below outlines
the principle.
Figure 3.3: TCD measuring method
The
thermal
conductivity
detector includes a heated
element (membrane) that heats
a second element (base) by
using the heat conduction of the
gas mixture. The gas mixture to
be tested has a lower or higher
thermal conductivity, depending
on the composition of the gas
mixture, so that the sensing
element (base) is more or less
altered in its temperature. The
temperature
change
also
therefore results in a change in
the electrical circuit (current
voltage
resistance).
These
changes will be evaluated and
analysed.
A system of equations can be set up together with the IR measurements, which provide the
contribution of the components CO2 and CH to heat conductivity and the normalization condition
for three-component gas. The searched hydrocarbon fraction xCH is found through the solution.
This means that all relevant gas components are described directly or indirectly through measured
variables.