Sønnik Clausen

FTIR emission spectroscopy methods and procedures for real time quantitative gas analysis in industrial environments

Diagnostic tools for real time and direct gas analysis have been developed. The simultaneous measurements of gas and particle temperatures (280-330 °C) and gas concentrations (CO, CO2, HCl, H2O) are demonstrated in a hot particle-laden flue gas with a fibre-optic probe connected to a Fourier transform infrared spectrometer. The gas temperature is found from the thermal radiation at the 2350 cm-1 CO2 fundamental band, whereas the gas concentrations are determined by comparing the measured transmittance spectra with a spectroscopic database and validation measurements using the Hotgas facility at Riso. Measurement uncertainties are discussed. The measured local gas temperatures and concentrations are in good agreement with measurements made with conventional equipment.

Measurement of surface temperature and emissivity by a multitemperature method for Fourier-transform infrared spectrometers

Surface temperatures are estimated with high precision based on a multitemperature method for Fourier-transform spectrometers. The method is based on Plancks radiation law and a nonlinear least-squares fitting algorithm applied to two or more spectra at different sample temperatures and a single measurement at a known sample temperature, for example, at ambient temperature. The temperature of the sample surface can be measured rather easily at ambient temperature. The spectrum at ambient temperature is used to eliminate background effects from spectra as measured at other surface temperatures. The temperatures of the sample are found in a single calculation from the measured spectra independently of the response function of the instrument and the emissivity of the sample. The spectral emissivity of a sample can be measured if the instrument is calibrated against a blackbody source. Temperatures of blackbody sources are estimated with an uncertainty of 0.2-2 K. The method is demonstrated for measuring the spectral emissivity of a brass specimen and an oxidized nickel specimen.

ExoMol molecular line lists – XIV. The rotation–vibration spectrum of hot SO2

Sulphur trioxide (SO3) is a trace species in the atmospheres of the Earth and Venus, as well as being an industrial product and an environmental pollutant. A variational line list for 32S16O3, named UYT2, is presented containing 21 billion vibration–rotation transitions. UYT2 can be used to model infrared spectra of SO3 at wavelengths longwards of 2 μm (ν < 5000 cm−1) for temperatures up to 800 K. Infrared absorption cross-sections recorded at 300 and 500 C are used to validate the UYT2 line list. The intensities in UYT2 are scaled to match the measured cross-sections. The line list is made available in electronic form as supplementary data to this article and at www.exomol.com.

Physical limits of semiconductor laser operation: A time-resolved analysis of catastrophic optical damage

The early stages of catastrophic optical damage (COD) in 808 nm emitting diode lasers are mapped by simultaneously monitoring the optical emission with a 1 ns time resolution and deriving the device temperature from thermal images. COD occurs in highly localized damage regions on a 30 to 400 ns time scale which is determined by the accumulation of excess energy absorbed from the optical output. We identify regimes in which COD is avoided by the proper choice of operation parameters.

A hot gas facility for high-temperature spectrometry

A hot gas facility is described for determining molecular absorption data and validating spectroscopically based gas analyser systems. The facility comprises a newly developed heated 0.50 m stainless steel gas flow cell mounted with CaF2 windows, which can be operated from ambient to 1100 K. The heated cell is interfaced to a Fourier transform infrared spectrometer and a black body source, and is characterized by a uniform temperature profile over the entire path length. This profile is demonstrated by measuring the gas temperature of carbon dioxide using spectroscopic methods based on transmission-emission spectra measured simultaneously and comparing the results of these measurements with those using thermocouples. It is found that the temperatures determined by spectroscopic methods are within the uncertainty of those measured by thermocouples (±2.9 K at 1072.0 K and ±0.7 K at 462.9 K). The gas enclosed in the cell is therefore to be considered as a uniform slab of gas. In addition, the shape of the measured emission spectra, which are very sensitive to self-absorption effects caused by small amounts of cold gas molecules present in the light path, are shown to be equal to those of the transmittance spectra to within 1% (~1-2 K). This indicates that the presence of cold gas molecules close to the windows and in the light path is negligible.

FTIR TRANSMISSION–EMISSION SPECTROMETRY OF GASES AT HIGH TEMPERATURES: DEMONSTRATION OF KIRCHHOFF’S LAW FOR A GAS IN AN ENCLOSURE

Abstract Kirchhoff’s law of heat radiation, which relates the spectral emissivity and absorptance of a material body, has been demonstrated for a hot gas (CO2) enclosed in a gas cell at a known temperature. The spectral emissivity of a hot gas in an enclosure is difficult to determine directly by experiment. The temperature-dependent effects of the radiative properties of the cell window materials and self-absorption effects of the hot CO2 gas have to be measured and accounted for before the spectral emissivity can be calculated. The experimental procedure and analytical expressions describing solely the net radiative properties of the enclosed gas are thus verified by demonstrating that Kirchhoff’s radiation law holds.

Infrared low-resolution emission spectroscopy of hot gases

Measurements of gas temperatures and concentrations in combustion and industrial processes, where hot gases are produced, can be carried out using low resolution Fourier transform IR emission spectroscopy. An experimental setup is presented for measuring transmittance as well as emittance spectra of hot gases enclosed in a heated gas cell. It is shown that the measured emissivity of a CO2 and CO mixture at 673 compare well with the absorptivity measured of the gas sample. The influence of the spectral resolution on the detection limit of CO in our experimental setup at 673 K is discussed and illustrated with experimental results and calculations. It is concluded that the most precise CO concentration measurement is obtained at low spectral resolution from a single point in the spectrum. The gas temperature and water vapor content in the hot gas of a power plant boiler can be extracted from low resolution emission spectra which is illustrated with experiments carried out on a power plant.

Oblique laser-sheet visualization

A laser-sheet visualization technique is demonstrated in which the laser and camera systems are integrated into a single unit, reducing the need for optical access to a single optical port. The technique is based on the photographing of a plane oblique to the camera optical axis and has been successfully applied to the quarl region of a power-station pulverized coal burner. The geometry of oblique photographing is presented.

Comparison of noise sources in dual- and single-beam Fourier-transform near-infrared spectrometry

We report the results of noise source investigations and stability tests in both dual- and single-beam Fourier-transform near-infrared operation. The noise sources are divided into two parts: intrinsic and extrinsic. The intrinsic noise sources, which include detector system noise, are common for both modes of operation. The extrinsic sources, which include variations in ambient conditions (room temperature, atmospheric gaseous components, and source scintillations), are shown to be smaller in dual-beam operation than in single-beam operation by a factor of 2-10. The results are based on interferograms measured in specified time intervals. The root-mean-square values are calculated at each retardation point. The values obtained near the centerburst and average values obtained for the dual-beam operation are compared with the intrinsic noise value obtained for single-beam operation. The dual-beam advantage is observed in both open-beam and liquid cell measurements, and it corresponds well with earlier results based on multivariate calibration techniques applied on aqueous solutions.

Modeling and experiments of biomass combustion in a large-scale grate boiler

Grate furnaces are currently a main workhorse in large-scale firing of biomass for heat and power production. A biomass grate fired furnace can be interpreted as a cross-flow reactor, where biomass is fed in a thick layer perpendicular to the primary air flow. The bottom of the biomass bed is exposed to preheated inlet air while the top of the bed resides within the furnace. Mathematical modeling is an efficient way to understand and improve the operation and design of combustion systems. Compared to modeling of pulverized fuel furnaces, CFD modeling of biomass-fired grate furnaces is inherently more difficult due to the complexity of the solid biomass fuel bed on the grate, the turbulent reacting flow in the combustion chamber and the intensive interaction between them. This paper presents the CFD validation efforts for a modern large-scale biomass-fired grate boiler. Modeling and experiments are both done for the grate boiler. The comparison between them shows an overall acceptable agreement in tendency. However at some measuring ports, big discrepancies between the modeling and the experiments are observed, mainly because the modeling-based boundary conditions (BCs) could differ quite much with the conditions in the real furnace. Combustion instabilities in the fuel bed impose big challenges to give reliable grate inlet BCs for the CFD modeling; the deposits formed on furnace walls and air nozzles make it difficult to define precisely the wall BCs and air jet BCs that a reliable CFD needs. The CFD results show reasonably the mixing and combustion performance in the furnace based on the design drawings; while the measurement results reflect reliably the combustion performance in the real furnace in operation.