Abstract
Abstract. This paper presents an explosion-proof two-channel Raman photometer designed for chemical process monitoring in hazardous explosive atmospheres. Due to its design, alignment of components is simplified and economic in comparison to spectrometer systems. Raman spectrometers have the potential of becoming an increasingly important tool in process analysis technologies as part of molecular-specific concentration monitoring. However, in addition to the required laser power, which restricts use in potentially explosive atmospheres, the financial hurdle is also high. Within the scope of a proof of concept, it is shown that photometric measurements of Raman scattering are possible. The use of highly sensitive detectors allows the required excitation power to be reduced to levels compliant for operation in potentially explosive atmospheres. The addition of an embedded platform enables stable use as a self-sufficient sensor, since it carries out all calculations internally. Multi-pixel photon counters (MPPCs) with large detection areas of 1350 µm2 are implemented as detectors. As a result, the sensitivity of the sensor is strongly increased. This gain in sensitivity is primarily achieved through two characteristics: first, the operating principle “avalanche breakdown” to detect single photons is used; second, the size of the image projected onto the MPPC is much bigger than the pixel area in competing Raman-Spectrometers resulting in higher photon flux. This combination enables reduction of the required excitation power to levels compliant for operation in potentially explosive atmospheres. All presented experiments are performed with strongly attenuated laser power of 35 mW. These include the monitoring of the analytes ethanol and hydrogen peroxide as well as the reversible binding of CO2 to amine. Accordingly, the described embedded sensor is ideally suited as a process analytical technology (PAT) tool for applications in environments with limitations on power input.
Highlights
Molecular-specific concentration monitoring based on the Raman effect is becoming an inline tool for process analysis technology (PAT) in an increasing number of areas of the chemical industry
Reversible binding of CO2 to amine can be monitored by Raman spectroscopy (Vogt et al, 2011)
Design and construction of a Raman photometer conforming to Ex-d standards has been successfully implemented
Summary
Molecular-specific concentration monitoring based on the Raman effect is becoming an inline tool for process analysis technology (PAT) in an increasing number of areas of the chemical industry. Up to now, this function has mainly been operated by spectrometer systems and spectra are recorded over the complete measuring range. In the field of UV–VIS–NIR and fluorescence spectroscopy, photometric concepts have become established in addition to spectrometer systems. These reduce the data throughput considerably, since only bands specific to the process are detected and, for example, forwarded to a process control system (PCS). A particular focus is on the selection and integration of the sensors used as well as the overall sensor concept (VDI/VDE, 2015; Schwolow et al, 2015; IEC60079-28:2015, 2015; IEC60079-0:2017, 2017)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
