Continuous Emission Monitoring Systems (CEMS) play a critical role in industrial applications by providing real-time gas detection to ensure compliance with environmental regulations and process optimization. These monitoring systems must operate reliably in harsh industrial environments characterized by high temperatures, humidity, and strong electromagnetic interference. Additionally, some of the monitored gases, such as methane (CH₄) and ammonia (NH₃), are flammable or explosive, making safety a key concern. To mitigate potential hazards, monitoring solutions must be ATEX-compliant, meaning they are designed to operate safely in explosive atmospheres without generating sparks or heat that could ignite volatile gases.
As part of a project funded by Energy Cluster Denmark, a prototype optical absorption spectroscopy-based sensor for in-situ gas monitoring was developed. This sensor employs dedicated lasers that emit specific wavelengths of light, which are selectively absorbed by targeted gases. Optical fibers transmit the laser beams to the location of the gas samples, and the remaining radiation after absorption is collected and analyzed outside the hazardous environment. This approach significantly reduces ATEX-related risks, ensuring safe and reliable operation in explosive atmospheres.
The system was initially designed to detect NH₃, CH₄, and NO, using three lasers carefully selected to match the absorption characteristics of each gas. Wavelength Modulation Spectroscopy (WMS) was employed to enhance sensitivity, allowing for the detection of low gas concentrations with high precision. Advanced mathematical techniques were used to process spectral data and distinguish gas signals, even in complex mixtures. A fiber optical switch combined the laser beams, while a Red Pitaya device controlled the modulation and data acquisition.
To verify the system’s accuracy and reliability, a laboratory experiment was conducted. Calibration at DFM’s laboratory ensured that the measurements were traceable and precise. Test results confirmed the system’s ability to detect NH₃ at low concentrations, with absorption measurements taken at a few millibar partial pressure, demonstrating its effectiveness for real-world applications.
This proof-of-concept paves the way for future developments at the European level. The modularity of the system allows for new lasers to be integrated, enabling the detection of additional gases. Furthermore, multi-point sensing is achievable by incorporating fiber splitters and extra detectors, making the sensor an ideal tool for industrial emission monitoring and environmental surveillance. This innovative technology marks a significant step forward in developing safer, more flexible, and highly accurate gas monitoring solutions for industrial and environmental applications.