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Axetris was able to test the functionality of its sensors under real-life conditions thanks to the support of the Linth waste incineration plant. The gas concentration measuring devices called laser gas detectors (LGD sensors) are used for measuring hazardous substances. When a gas is conducted through the sensor, the respective gas molecules weaken the laser beam. Gas concentrations can be determined through this light absorption process.
One of the LGDs deployed at the Linth waste incineration plant measured ammonia data, the other recorded hydrochloric acid data. Axetris was able to collect valuable experience with its sensors integrated into the facility during the field test. Insights for the benefit of sensor research.
Sensor Test under Real-Life Conditions
An Axetris sensor undergoes numerous tests before it reaches the customer. The LGDs are put through their paces in the laboratory. Every sensor undergoes stability tests and is calibrated. Its performance is assessed in regards to accuracy, precision, and short-term stability. Around 20 hours of measurement data are recorded by every sensor under laboratory conditions.
Being able to test sensors under real-life conditions is an important further step in the continuous improvement process. A field test is not only essential because it is a long-term test, but also because environmental influences may occur that were not considered in the laboratory. Could a gas pump in the immediate vicinity produce vibrations that influence the functionality of the measuring device? Is the software consistently stable throughout the measurement period? Do all components withstand the cell temperature of 190°C undamaged? A lot can be learned about the integration process as well because Axetris relies on specialist firms to install the sensor, assuming the role of the customer for itself.
Initially the field test was slated to last a year. Stefan Manzeneder, Project Manager for Product Development, is all the more pleased that this test has been ongoing for two years already and was now extended once again.
He was able to replace the sensors with the current generation in March of 2017 and can continue the test with them.
A Field Test for Sensor Research
The Linth waste incineration plant does not expect any financial consideration for the field test. Neither can it use the values directly. Mr. Ringmann, operator of the Linth waste incineration plant: “We have our own emission measuring equipment, so we do not intend to analyze the emission values that are being recorded here. Nevertheless I am pleased about this data since it benefits important research efforts.”
Manzeneder is very thankful to the Linth waste incineration plant for the opportunity it offers Axetris: “They are supporting our efforts to develop even more reliable sensors. This is by no means a matter of course.”
To develop sensors of high quality, it is essential to know how the offset – the zero value of the sensor – drifts over time. This behavior of the laser over a longer test period is best observed in the field. The sensors are flushed daily with zero gas to compensate for the known zero drift. A higher absolute accuracy can be achieved with the measuring system through regular drift compensation.
Zeroing itself was not included in the measurement data since there were no plans to connect the two LGDs to the control system or the plant’s emissions calculator.
„We have seen how important periodic zeroing of the sensor is, and are now able to support our customers with corresponding empirical values. We have also learned that daily zeroing is sufficient. Such insights are then incorporated directly into research and further development.” Stefan Manzeneder, Project Leader for Product Development
Since the LGDs are currently not certified for the measurement of generating plant emissions, Axetris does not analyze the emission values either. Instead it checks whether the performance of the sensors remains consistent throughout the entire measuring period.
“We know that the Linth waste incineration plant only emits very small amounts of hazardous substances and wanted to test whether our sensors continue to send their signal regularly, even with low gas concentrations over a longer period of time,” Manzeneder continues.
Among other things, it is of great interest to determine how the sensor responds to scenarios that do not occur every day, since the sensor must be able to record values even during maintenance work and system start-up and shutdown – events that occur in a waste incineration plant.
How robust are the LGDs?
Axetris now has more accurate information about this thanks to the field test and is able to assess how robust its sensors really are. “Since the waste incineration plant has a 3-stage spray scrubber with downstream SCR, only very low concentrations were expected. Our sensors consistently captured these in the expected range. The sensors were able to record trace level data even during inspections.”
The software was stable. Thanks to internal sensor technology and continuous status monitoring, the software was also able to adapt to unexpected operating modes.
Even though it may seem positive at first glance that there were no unexpected disruptions, uncovering possible problems with the sensors during the field test is desirable. Only then can defects be extensively analyzed in due time and corrected before the laser gas detectors are delivered to customers.
A problem uncovered in the optical system brought up important questions for Axetris regarding the cause: Did the optics go out of adjustment? Were the electronics faulty? The problem remains to be resolved. Axetris is currently analyzing the cause.
Outlook
Axetris is also striving for QAL1 certification according to EN 15267 for the next generation. In the end, reliable state-of-the-art sensors not only benefit Axetris and its future customers but also the environment.
Keeping the environmental impact low can only be guaranteed when sensors record emission values reliably.
Laser Gas Detection Modules for OEM Integration
Axetris’ Laser Gas Detection (LGD) modules are self-contained, ready-to-use devices for the measurement of gases such as NH3, HCl, CH4, CO2, (H2O). The modules are designed for integration by OEMs, active in the field of gas detection and monitoring in diverse industries. The high sensitivity and the large dynamic range of the TDLS detection technology enables measurement from sub-ppm level to high percentrage concentration without physical adaptation of the device.
The design of the LGD F200 enables a tailor-made application fit for a wide range of gases and applications, including process control, environmental compliance research and medical.
