T. Seeger

Design and characterization of a Raman-scattering-based sensor system for temporally resolved gas analysis and its application in a gas turbine power plant

A sensor system for fast gas composition analysis is presented. Using linear Raman scattering the simultaneous detection of virtually all components of fuel gas mixtures such as natural gas and biogas can be achieved. The system consists of commercially available hardware components, in detail a frequency doubled continuous wave laser at 532 nm and a compact spectrometer with an embedded charge coupled device chip. For the evaluation of the Raman spectra a fast software module based on a contour fit algorithm is developed. Moreover, modules for controlling the hardware components are implemented in the sensor software ensuring simple operability of the entire system. In this paper the sensor is characterized in terms of, e.g., accuracy, reproducibility, detection limits and temporal performance. Finally its application for natural gas analysis in a gas turbine power plant is demonstrated, and the results obtained are compared to gas chromatography results.

Determination of gas composition in a biogas plant using a Raman-based sensor system

We propose a gas sensor, based on spontaneous Raman scattering, for the compositional analysis of typical biogas mixtures and present a description of the sensor, as well as of the calibration procedure, which allows the quantification of condensable gases. Moreover, we carry out a comprehensive characterization of the system, in order to determine the measurement uncertainty, as well as influences of temperature and pressure fluctuation. Finally, the sensor is applied at different locations inside a plant in which biogas is produced from renewable raw materials. The composition is monitored after fermenting, after purification and after the final conditioning, where natural gas is added. The Raman sensor is able to detect all the relevant gas components, i.e. CH4, CO2, N2 and H2O, and report their individual concentrations over time. The results were compared to reference data from a conventional gas analyzer and good agreement was obtained.

Laser-induced breakdown spectroscopy in gases using ungated detection in combination with polarization filtering and online background correction

Quantitative and fast analysis of gas mixtures is an important task in the field of chemical, security and environmental analysis. In this paper we present a diagnostic approach based on laser-induced breakdown spectroscopy (LIBS). A polarization filter in the signal collection system enables sufficient suppression of elastically scattered light which otherwise reduces the dynamic range of the measurement. Running the detector with a doubled repetition rate as compared to the laser online background correction is obtained. Quantitative measurements of molecular air components in synthetic, ambient and expiration air are performed and demonstrate the potential of the method. The detection limits for elemental oxygen and hydrogen are in the order of 15 ppm and 10 ppm, respectively.

A signal enhanced portable Raman probe for anesthetic gas monitoring

A SIGNAL ENHANCED PORTABLE RAMAN PROBE FOR ANESTHETIC GAS MONITORING S. Schlüter, S. Asbach, N. Popovska-Leipertz, Th. Seeger, A. Leipertz a Institute of Engineering Thermodynamics, University of Erlangen-Nuremberg, Erlangen, 91058, Germany b Erlangen Graduate School in Advanced Optical Technologies (SAOT), University of Erlangen-Nuremberg, Erlangen, 91052, Germany с Institute of Engineering Thermodynamics, University of Siegen, Siegen, 57076, Germany d ESYTEC Energieund Systemtechnik GmbH, Erlangen, 91058, Germany Corresponding author: Sebastian.schlueter@uni-siegen.de Article info Received 23.01.15, accepted 25.02. 15 doi: 10.17586/2226-1494-2015-15-2-218-226 Article in English For citation: Schlüter S., Asbach S., Popovska-Leipertz N., Seeger Th., Leipertz A. A signal enhanced portable raman probe for anesthetic gas monitoring. Scientific and Technical Journal of Information Technologies, Mechanics and Optics, 2015, vol.15, no. 2, pp. 218–226. (in English) Abstract. The spontaneous Raman scattering technique is an excellent tool for a quantitative analysis of multi-species gas mixtures. It is a noninvasive optical method for species identification and gas phase concentration measurement of all Raman active molecules, since the intensity of the species specific Raman signal is linearly dependent on the concentration. Applying a continuous wave (CW) laser it typically takes a few seconds to capture a gas phase Raman spectrum at room temperature. Nevertheless in contrast to these advantages the weak Raman signal intensity is a major drawback. Thus, it is still challenging to detect gas phase Raman spectra in alow-pressure regime with a temporal resolution of only a few 100 ms. In this work a fully functional gas phase Raman system for measurements in the low-pressure regime (p ≥ 980 hPa (absolute)) is presented. It overcomes the drawback of a weak Raman signal by using a multipass cavity. A description of the sensor setup and of the multipass arrangement will be presented. Moreover the complete functionality of the sensor system will be demonstrated by measurements at an anesthesia simulator under clinical relevant conditions and in comparison to a conventional gas monitor.

Non-intrusive gas-phase thermometry for industrial oxy-fuel burners

The use of oxy-fuel combustion processes is of large interest for several industrial fields applications since it offers the advantages of low NO x emissions in combination with high combustion temperatures even without additional preheating. For optimization of such processеs a detailed understanding based on precise experimental data is necessary. So far there is still a lack of precise experimental data achieved with high spatial and temporal resolution from industrial relevant turbulent oxy-fuel combustion processes. Beside species concentration information the gas phase temperature is of utmost importance for an improved understanding of the basic chemical reactions and the pollutant formation. The coherent anti-Stokes Raman spectroscopy (CARS) technique is a very well suited laser based tool for a non-intrusive investigation of such turbulent high temperature combustion processes. In this work we analysed an industrial 400 kW oxy-fuel burner with the help of O 2 based vibrational CARS system which is integrated in an industrial relevant test furnace. The burner is fed with pure oxygen and natural gas at an equivalence ratio of f=0.9. At one downstream position temporal and spatial resolved temperatures were measured along a 600 mm line. Additional air sucked in from the environment seems to influence the gas phase temperature significantly.