Non-dispersive IR-absorption for emission testing
In 2016, there were approximately 13 million gas boilers, 5.6 million oil heating boilers, and 0.7 million boilers for burning solid materials in Germany. Furthermore, there were approximately 11.7 million fireplaces or tile ovens which operated with either wood or coal. The resulting exhaust gases from these combustion processes affect the environment, climate, and health, and therefore are governed by federal regulations, as stated in the Federal Emissions Protection Regulation for small- and medium-sized firing systems.
To control these regulations, a chimney sweep measures the relevant parameters such as carbon monoxide (CO) and oxygen (O2) every two years. For these monitoring measurements, electrochemical sensors are used, which are liable to frequent inspections as well as heavy wear due to their construction. Furthermore, the greenhouse gas and main combustion product carbon dioxide (CO2) is not detected with electrochemical sensors. Its concentration is determined through CO and O2 measurement, resulting in an error for the calculation of the emission.
The goal of our work in collaboration with Vereta GmbH is the development of an optical sensor that can simultaneously measure the concentration of CO and CO2 in the exhaust gas of a firing system.
Non-dispersive infrared spectroscopy (NDIR) is used as the measurement technique. With the help of the Beer-Lambert law, the concentration of the gases in the exhaust gas flow can be determined. Working at the mid-infrared regime has the advantage of large absorption cross sections and small overlap of the absorption bands of CO2 and CO.
The construction of the optical set-up of the sensor is subject to the constraints of compactness, robustness, as well as low cost. Simultaneously, the system has to match requirements of high measurement accuracy, which requires a high signal-to-noise ratio and, in the case of CO, requires a long absorption distance. This conflict of the demands is a challenge for the development of such sensors.
C. Niklas, Quantification of CO2 and CO concentrations via non-dispersive infrared spectroscopy, Master thesis, University of Göttingen and LLG, 18. July 2018.
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Laser-Laboratorium Göttingen e.V. (LLG)
Head of Department
Dr. Hainer Wackerbarth
"Photonic Sensor Technologies"