In situ combustion measurements of CO, H2O, and temperature with a 1.58-microm diode laser and two-tone frequency modulation

An optical near-infrared process sensor for electric arc furnace pollution control and energy efficiency is proposed. A near-IR tunable diode laser has performed simultaneous in situ measurements of CO (1577.96 nm), H(2)O (1577.8 and 1578.1 nm), and temperature in the exhaust gas region above a laboratory burner fueled with methane and propane. The applicable range of conditions tested is representative of those found in a commercial electric arc furnace and includes temperatures from 1250 to 1750 K, CO concentrations from 0 to 10%, and H(2)O concentrations from 3 to 27%. Two-tone frequency modulation was used to increase the detection sensitivity. An analysis of the method's accuracy has been conducted with 209 calibration and 105 unique test burner setpoints. Based on the standard deviation of differences between optical predictions and independently measured values, the minimum accuracy of the technique has been estimated as 36 K for temperature, 0.5% for CO, and 3% for H(2)O for all 105 test data points. This accuracy is sufficient for electric arc furnace control. The sensor's ability to nonintrusively measure CO and temperature in real time will allow for improved process control in this application.     

Detection of H2O and CO2 with distributed feedback diode lasers: measurement of broadening coefficients and assessment of the accuracy levels for volcanic monitoring

We reproduced the chemical-physical conditions of fumarolic emission at Phlaegrean Fields, Pozzuoli, Italy, and we measured the CO(2) and H(2)O concentrations using an absorption spectrometer based on two distributed feedback laser diodes at wavelengths of 1.578 and 1.393 mum. We discuss the accuracy levels of the different methods used. Furthermore, we measured the broadening coefficients for H(2)O (self-broadening, 28.2 +/- 0.6 MHz/Torr; CO(2) broadening, 6.0 +/- 0.4 MHz/Torr) and CO(2) (self-broadening, 3.2 +/- 0.1 MHz/Torr; H(2)O broadening, 4.0 +/- 0.1 MHz/Torr). Using the present data, we evaluated a minimum detectable variation of 9% for H(2)O and 1% for CO(2).     

Measurements of CO, CO2, OH, and H2O in room-temperature and combustion gases by use of a broadly current-tuned multisection InGaAsP diode laser

A new laser technology that achieves nearly 100-nm quasi-continuous tuning with only injection-current control in a four-section grating-coupler sampled-reflector laser was used to detect CO and CO(2) simultaneously in room-temperature gas mixtures. The same grating-coupler sampled-reflector laser was used to perform in situ measurements of CO, H(2)O, and OH in the exhaust gases of a CH(4)-air flame. This laser is being evaluated for inclusion in a multispecies combustion-emissions exhaust-analysis sensor, and its operational characteristics as they have an impact on gas sensing are described. Preliminary results suggest that this single laser can be used to replace multilaser sensor configurations for some combustion-emissions monitoring applications.     

Ion-induced nucleation rate measurement in SO2/H2O/N2 gas mixture by soft X-ray ionization at various pressures and temperatures

This paper reports the systematic investigation of ion-induced nucleation rate measurement in a SO₂/H₂O/N₂ gas mixture, employing soft X-ray at different pressure and temperature levels. Experiments were conducted using a modified continuous flow gas-generation system employing a soft X-ray ionizer and a particle counter, with an improved integrated online temperature, pressure and a relative humidity (RH) control system. Nucleation rates were measured as a function of SO₂ concentration at different levels of RH, pressure (600–970 hPa) and temperature (5–25 °C). The results show that the nucleation rate dependence on SO₂ concentration followed a power law, and the slope varied slightly in a range from 1 to 1.26 at different RH levels (15–60%). A positive pressure effect was generally found and a power law was followed with varied scaling for different SO₂ concentrations. The trend of an increase in nucleation rate with temperature was consistent with observations in homogenous nucleation experiments, and with the behavior predicted by classical binary nucleation theory. These experimental results will be useful to explain the contribution of ion-induced nucleation in different locations and atmospheric conditions.     

Precision trace gas analysis by FT-IR spectroscopy. 1. Simultaneous analysis of CO2, CH4, N2O, and CO in air

We report the development of a method of trace gas analysis based on 1-cm-1 resolution Fourier transform infrared (FT-IR) spectroscopy, deployable in both laboratory and field applications. Carbon dioxide, methane, nitrous oxide, and carbon monoxide may be analyzed simultaneously in a single air sample using this method. We have demonstrated that the method can provide analytical precision of the order of +/- 0.15 mumol mol-1 for CO2, +/- 0.9 nmol mol-1 for CH4, +/- 0.3 nmol mol-1 for N2O, and +/- 0.3 nmol mol-1 for CO, expressed as mole fractions in dry air. The analytical precision is in all cases competitive with or superior to that of the more usual methods of analysis for these trace gases, namely, nondispersive infrared spectroscopy for CO2 and gas chromatography-based techniques for CH4, N2O, and CO. The novel FT-IR method relies on calibration using synthetically calculated absorbance spectra and a chemometric multivariate calibration algorithm, classical least squares.     

Laser-induced breakdown spectroscopy of gas mixtures of air, CO2, N2, and C3H8 for simultaneous C, H, O, and N measurement

Laser-induced breakdown spectroscopy (LIBS) was applied for simultaneous measurement of the elements C, H, N, and O in CO2-air, C3H8-CO2, and C3H8-N2 gas mixtures at atmospheric pressure. A single 7-mm-diameter aperture at the sample chamber was used for 1064-nm Nd:YAG laser irradiation and plasma signal output to an echelle spectrometer. Double-pulse laser bursts of approximately 8-ns pulse width (FWHM) and 250-ns interpulse separation were applied to increase the plasma signal. Calibration curves of the LIBS signal versus the partial pressure or the atomic abundance ratios were taken by dilution series in intervals that are relevant in the combustion of heptane (C7H16) near an equivalence ratio of 1.     

Multispecies in situ monitoring of a static internal combustion engine by near-infrared diode laser sensors

A multispecies near-infrared diode laser spectrometer has been constructed for measurements of carbon monoxide, carbon dioxide, and methane directly in the exhaust of a static internal combustion engine. A wavelength modulation-division multiplexing scheme was implemented for the two distributed feedback diode lasers. Gas concentration variations were observed for changes in operating conditions such as increasing and decreasing the throttle, adjusting the air-fuel ratio, and engine start-up.     

In situ measurements of H2O from a stratospheric balloon by diode laser direct-differential absorption spectroscopy at 1.39 microm

A distributed-feedback InGaAs laser diode emitting near 1.393 mum is used in conjunction with an optical multipass cell that is open to the atmosphere to yield ambient water-vapor measurements by infrared absorption spectroscopy. To obtain the high dynamic range for the measurements that is required for continuous water-vapor monitoring in the upper troposphere and the lower stratosphere, we used a simple circuit that combined differential and direct detection. Furthermore, the laser emission wavelength was tuned to balance the steep decrease in H(2)O concentration with altitude by sweeping molecular transitions of stronger line strengths. The technique was implemented by use of the Spectromètre à Diodes Laser Accordables (SDLA), a tunable diode laser spectrometer operated from a stratospheric balloon. Absorption spectra of H(2)O in the 5-30-km altitude range obtained at 1-s intervals during recent balloon flights are reported. Water-vapor mixing ratios were retrieved from the absorption spectra by a fit to the full molecular line shape in conjunction with in situ pressure and temperature measurements, with a precision error ranging from 5% to 10%.     

Reforming natural gas for CO2 pre-combustion capture in combined cycle power plant

The aim of this study is to assess the conversion of a natural gas combined cycle power plant (NGCC) using an advanced gas turbine (GE9H) for CO₂ pre-combustion capture. The natural gas is reformed in an auto-thermal reformer (ATR) either with pure oxygen or with air. After water-shift conversion of CO into CO₂ and physical CO₂ recovery, the synthesis gas contains a high fraction of H₂. It is diluted with N₂ and steam to lower its low heating value (LHV) for NO _X emission control. Oxygen purity and reforming pressure have little impact on the performances. High-pressure reforming is preferred to reduce the process size. Air reforming results in a slightly higher efficiency but in a bigger process too. The CO₂ recovery rate has a big impact on the power plant efficiency since a lot of steam is required to lower the heating value (LHV) of the synthesis gas leaving the recovery process. Two values of LHV have been assessed. Steam consumption for natural gas reforming and synthesis gas dilution are the main consuming elements. An erratum to this article can be found at     

Atmospheric CH4 and H2O monitoring with near-infrared InGaAs laser diodes by the SDLA, a balloonborne spectrometer for tropospheric and stratospheric in situ measurements

The Spectromètre à Diodes Laser Accordables (SDLA), a balloonborne spectrometer devoted to the in situ measurement of CH(4) and H(2)O in the atmosphere that uses commercial distributed-feedback InGaAs laser diodes in combination with differential absorption spectroscopy, is described. Absorption spectra of CH(4) (in the 1.653-mum region) and H(2)O (in the 1.393-mum region) are simultaneously sampled at 1-s intervals by coupling with optical fibers of two near-infrared laser diodes to a Herriott multipass cell open to the atmosphere. Spectra of methane and water vapor in an altitude range of ~1 to ~31 km recorded during the recent balloon flights of the SDLA are presented. Mixing ratios with a precision error ranging from 5% to 10% are retrieved from the atmospheric spectra by a nonlinear least-squares fit to the spectral line shape in conjunction with in situ simultaneous pressure and temperature measurements.     

Aspects of selecting the mode of mixing in CO2 + N2 + H2O gasdynamic lasers

Recommendations are made with regard to selection and organization of operating modes in gasdynamic lasers, viz., the mixing of excited nitrogen with a CO₂ + H₂O mixture.Notation T₀ stagnation temperature of the main stream - P₀ stagnation pressure of the main stream - weak-signal gain - W/G specific energy output - molar concentration - T_i vibrational temperatures of CO₂ - N_Ma,N₂ Mach number of the main stream at the mixing site - N_Ma,CO₂ Mach number of the injected stream at the mixing site - T₀,CO₂ temperature in the plenum chamber of the injected stream Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 42, No. 1, pp. 42–46, January, 1982.     

Detection and measurement of middle-distillate fuel vapors by use of tunable diode lasers

A sensor for the rapid (10-ms response time) measurement of vapors from the hydrocarbon-based fuels JP-8, DF-2, and gasoline is described. The sensor is based on a previously reported laser-mixing technique that uses two tunable diode lasers emitting in the near-infrared spectral region [Appl. Opt. 39, 5006 (2000)] to measure concentrations of gases that have unstructured absorption spectra. The fiber-mixed laser beam consists of two wavelengths: one that is absorbed by the fuel vapor and one that is not absorbed. Sinusoidally modulating the power of the two lasers at the same frequency but 180 degrees out of phase allows a sinusoidal signal to be generated at the detector (when the target gas is present in the line of sight). The signal amplitude, measured by use of standard phase-sensitive detection techniques, is proportional to the fuel-vapor concentration. Limits of detection at room temperature are reported for the vapors of the three fuels studied. Improvements to be incorporated into the next generation of the sensor are discussed.     

A life cycle assessment of biomass cofiring in a coal-fired power plant

The generation of electricity, and the consumption of energy in general, often result in adverse effects on the environment. Coal-fired power plants generate over half of the electricity used in the U.S., and therefore play a significant role in any discussion of energy and the environment. By cofiring biomass, currently operating coal plants have an opportunity to reduce the impact they have, but to what degree, and with what trade-offs? A life cycle assessment has been conducted on a coal-fired power system that cofires wood residue. The assessment was conducted in a cradle-to-grave manner to cover all processes necessary for the operation of the power plant, including raw material extraction, feed preparation, transportation, and waste disposal and recycling. Cofiring was found to significantly reduce the environmental footprint of the average coal-fired power plant. At rates of 5% and 15% by heat input, cofiring reduces greenhouse gas emissions on a CO₂-equivalent basis by 5.4% and 18.2%, respectively. Emissions of SO₂, NO _x , non-methane hydrocarbons, particulates, and carbon monoxide are also reduced with cofiring. Additionally, total system energy consumption is lowered by 3.5% and 12.4% for the 5% and 15% cofiring cases, respectively. Finally, resource consumption and solid waste generation were found to be much less for systems that cofire. Electronic Publication     

Selective plasmonic gas sensing: H2, NO2, and CO spectral discrimination by a single Au-CeO2 nanocomposite film

A Au-CeO(2) nanocomposite film has been investigated as a potential sensing element for high-temperature plasmonic sensing of H(2), CO, and NO(2) in an oxygen containing environment. The CeO(2) thin film was deposited by molecular beam epitaxy (MBE), and Au was implanted into the as-grown film at an elevated temperature followed by high temperature annealing to form well-defined Au nanoclusters. The Au-CeO(2) nanocomposite film was characterized by X-ray diffraction (XRD) and Rutherford backscattering spectrometry (RBS). For the gas sensing experiments, separate exposures to varying concentrations of H(2), CO, and NO(2) were performed at a temperature of 500 °C in oxygen backgrounds of 5.0, 10, and ～21% O(2). Changes in the localized surface plasmon resonance (LSPR) absorption peak were monitored during gas exposures and are believed to be the result of oxidation-reduction processes that fill or create oxygen vacancies in the CeO(2). This process affects the LSPR peak position either by charge exchange with the Au nanoparticles (AuNPs) or by changes in the dielectric constant surrounding the particles. Spectral multivariate analysis was used to gauge the inherent selectivity of the film between the separate analytes. From principal component analysis (PCA), unique and identifiable responses were seen for each of the analytes. Linear discriminant analysis (LDA) was also used and showed separation between analytes as well as trends in gas concentration. Results indicate that the Au-CeO(2) thin film is selective to O(2), H(2), CO, and NO(2) in separate exposures. This, combined with the observed stability over long exposure periods, shows the Au-CeO(2) film has good potential as an optical sensing element for harsh environmental conditions.     

O2, CH4 and CO2 gas retentions by acid smectites before and after thermal treatment

Acid smectites in natural condition and after thermal treatment up to 900 °C were studied for their O₂, CH₄ and CO₂ gas retentions at 25 °C and 1 kg/cm². Two smectites, one dioctahedral and one trioctahedral, were treated with 5.0 N sulphuric acid solution for 15 and 60 min. The gas adsorptions by the smectites increased after acid treatments. The O₂ (0.014–0.030 mmol/g) and CH₄ (0.045–0.063 mmol/g) gas retention values were small whereas the values corresponding to CO₂ (0.206–0.357 mmol/g) retentions were high for acid smectites. The acid trioctahedral smectite showed higher gas adsorption values than acid dioctahedral smectite. The CO₂ gas adsorption values by acid smectites heated up to around 600 °C, decreased around 10% and 20% for acid trioctahedral and dioctahedral smectites, respectively. After that drastically decreased and at 900 °C both acid smectites showed very small adsorption values. The chemical composition, the structure and the texture of the smectites influenced the gas retention.     

n(p)-InP-n-In2O3-P2O5-Pd diode structures as potential sensors for near-infrared radiation, moisture, and hydrogen

Diode structures based on n(p)-InP with intermediate n-In₂O₃ and P₂O₅ layers were fabricated by electrochemical deposition of Pd. It is shown that when exposed to pulses of water vapor the photo-emf of the structures varies by 60–400% and in the presence of H₂ it can vary by 1.5–2 orders of magnitude. These n(p)-InP-n-In₂O₃-P₂O₅-Pd structures are potential sensors for near-infrared radiation, moisture, and hydrogen. Pis’ma Zh. Tekh. Fiz. 25, 72–78 (December 26, 1999)     

The influence of O2, H2, H2O,N2, CO and CH4 on the structure of thin silver films investigated by ultrahigh vacuum internal stress measurements

It has been demonstrated earlier that the structure of thin metal films can be investigated continuously during deposition by measuring the internal film stress. With these experiments it has been shown that various deposition parameters (evaporation rate, ambient atmosphere etc.) considerably influence the internal stress and thus the structure of the evaporated metal films. In order to separate the various parameters determining film growth we developed an ultrahigh vacuum version of the stress measuring apparatus used previously. An application of this method to silver films deposited onto fresh MgF₂ substrate films in various gas ambients is described. The film structure deduced from the stress curves on the basis of a model for the origin of the internal stress is compared with the structure visible in the electron microscope.