Background & Challenge
A customer in New Zealand wanted to use a TDLAS200A pumped methane sensor as a flow-through online monitor for the off-gas of a bioreactor. The reactor works at ambient temperature and pressure, the off-gas flow is about 1 L/min, and the gas composition changes over a run — it starts as methane and shifts toward CO₂. The customer therefore wanted to know the sensor’s CO₂ range and its tolerance to humidity, and planned to buy one sample unit for laboratory testing before committing further.
Why the TDLAS200A
The TDLAS200A is a pumped laser methane sensor: an internal pump draws the sample gas through the measuring cell, which makes it straightforward to arrange a flow-through connection to a bioreactor off-gas line rather than relying on diffusion. The sensor is specified for a 0–5000 ppm methane range, which matches the low methane concentrations of a bioreactor off-gas measurement.
Solution & Installation
For a flow-through arrangement the off-gas is routed from the reactor headspace to the sensor inlet at the reactor’s own flow rate, so the pump provides the sampling rather than the process. Two practical points were raised and confirmed with the customer:
- Because the gas changes from methane to CO₂ over the run, the sensor is used for its methane measurement while the CO₂ range of the application is confirmed separately.
- Humidity in the off-gas has to be managed at the sample inlet, as with any pumped gas measurement, so that condensation does not reach the measuring cell.
Results
The customer took a single sample unit for laboratory testing of the flow-through arrangement and the measurement range before integrating it into their system — a repeat order followed, which confirms that the applied configuration suited the bioreactor off-gas duty.
Related Products
- TDLAS200A pumped laser methane sensor
- TDLAS200B laser methane sensor
- TDLAS103 laser methane sensor
- TD-LAS gas sensors (category)
Frequently Asked Questions
Q: Can a pumped methane sensor be used for flow-through monitoring?
A: Yes. A pumped instrument draws the sample through its own measuring cell, so connecting a sample line from the process makes it a flow-through analyser. The sample flow, pressure and moisture have to be matched to the instrument specification.
Q: What has to be checked if the measured gas changes from methane to carbon dioxide?
A: The instrument’s measurement range and optical configuration have to cover the new gas and the concentrations involved. This must be confirmed against the specification before ordering, since the detection is tuned to a specific absorption line.
Q: Does humidity affect the measurement?
A: Water vapour absorbs infrared light, so a saturated sample can influence an optical gas measurement. The usual approach is to condition the sample, keep the line above the dew point, and confirm the instrument’s stated humidity limits for the application.
Q: Is a single sample unit enough for a laboratory test?
A: For a bench evaluation of a flow-through arrangement, yes. A single pumped unit connected to the off-gas line can demonstrate whether the measurement is stable before a permanent installation is specified.
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