Laser-Based, Optical, and Traditional Diagnostics of NO and Temperature in 400 kW Pilot-Scale Furnace

A fast sensor for simultaneous high temperature (above 800 K) diagnostics of nitrogen oxide (NO) concentration and gas temperature (T) based on the spectral fitting of low-resolution NO UV absorption near 226 nm was applied in pilot-scale LKAB’s Experimental Combustion Furnace (ECF). The experiments were performed in plasma and/or fuel preheated air at temperatures up to 1550 K, which is about 200 K higher than the maximal temperature used for the validation of the developed UV NO sensor previously. The UV absorption NO and T measurements are compared with NO probe and temperature measurements via suction pyrometry and tuneable diode laser absorption (TDL) using H2O transitions at 1398 nm, respectively. The agreement between the NO UV and NO probe measurements was better than 15%. There is also a good agreement between the temperatures obtained using laser-based, optical, and suction pyrometer measurements. Comparison of the TDL H2O measurements with the calculated H2O concentrations demonstrated an excellent agreement and confirms the accuracy of TDL H2O measurements (better than 10%). The ability of the optical and laser techniques to resolve various variations in the process parameters is demonstrated.

Research on Spectroscopy Modulation of a Distributed Feedback Laser Diode Based on the TDLAS Technique

Laser current and temperature control circuits have been developed for a distributed feedback laser diode, which is applied as the light source of a tuneable diode laser absorption spectroscopy system. The laser’s temperature fluctuation can be limited within the range of −0.02 to 0.02°C, and good operation stability was observed through 15 hours of monitoring on the emitting wavelength of the laser. Response time of temperature modulation was tested which is suitable for the tuning requirements of gas detection systems. Laser current can be injected within the range from 40 to 80 mA. In addition, a linear power supply circuit has been developed to provide stable and low-noise power supply for the system. The physical principles of laser modulation theory are discussed before experiments. Experiments show that the output wavelength of the laser can be tuned accurately through changing the working current and temperature. The wavelength can be linearly controlled by temperature at 0.115 nm/°C (I = 70 mA) and be controlled by current at 0.0140 nm/mA (T = 25°C). This is essential for the tuneable diode laser absorption spectroscopy systems. The proposed cost-effective circuits can replace commercial instruments to drive the laser to meet the requirements of methane detection experiments. It can also be applied to detect other gases by changing the light source lasers and parameters of the circuits.

A Critical Evaluation of Natural Gas-water Formula Correlations

The performance evaluation of fourteen (14) formula correlations for predicting the water content of natural gas in equilibrium with water, and the suitability of some of these correlations in predicting the water content of natural gas in equilibrium with hydrates, has been presented. Also presented was an evaluation of acid gas and gravity correction factor correlations. The evaluation was achieved by using the cubic plus association equation of state - CPA EoS, published experimental water content data from a tuneable diode laser adsorption spectrometer, and data from the gas processors supplier’s association (GPSA) chart, to validate the results of the correlations. The results of the validation showed that for the prediction of the water content of natural gas in equilibrium with water, the Bukacek correlation was best suited for low pressures of 1 and 2.5 MPa at a temperature range of 9 to 58°C. The modified ideal model (MIM) correlation was the best for pressures of 5 and 10 MPa, at temperature range of 30 to 89.6°C The Aimikhe correlation was best suited for pressures of 7.5 MPa, at a temperature range of 30 to 86°C, while the Khaled’s correlation performed better for high pressures of 25 and 50 MPa, at a temperature range of 30 to 91.5°C. The Maddox correction factor had better accuracy than other acid gas correction factors when accounting for the presence of acid gases. The Mohammadi or Chapoy gravity correction factors were the best correlations for accounting for the presence of heavy components in natural gas. For processed methane-rich natural gas in equilibrium with hydrates at a temperature range of -20 to 10°C, the Lin correlation was best suited for pressures of 2.5 and 5 MPa while the MIM correlation performed better at pressures of 7.5, 15 and 20 MPa.

SEALDH-II – a calibration-free transfer standard for airborne water vapor measurements: Pressure dependent absolute validation from 5–1200 ppmv at a metrological humidity generator

Highly accurate water vapor measurements are indispensable for understanding a variety of scientific questions as well as industrial processes. While in metrology water vapor concentrations can be defined, generated and measured with relative uncertainties in the single percentage range, field deployable airborne instruments deviate even under quasi-static laboratory conditions up to 10–20 %. The novel SEALDH-II hygrometer, a calibration-free, tuneable diode laser spectrometer, bridges this gap by implementing an entirely new concept to achieve higher accuracy levels in the field. Here we present the absolute validation of SEALDH-II at a traceable humidity generator during 23 days of permanent operation at 15 different H2O concentration levels between 5 and 1200 ppmv. At each concentration level, we studied the pressure dependence at 6 different gas pressures between 65 and 950 hPa. Further, we describe the setup for this metrological validation, the challenges to overcome when assessing water vapor measurements on a high accuracy level, as well as the comparison results. With this validation, SEALDH-II is the first metrologically validated humidity transfer standard which links several scientific airborne and laboratory measurement campaigns to the international metrological water vapor scale.

A Comparison of Ammonia Measurements Using Fourier Transform Infrared and Tuneable Diode Laser Spectroscopy

Current diesel engine after-treatment systems such as Selective Catalyst Reduction (SCR) use ammonia (NH3) to reduce Nitrogen Oxides (NOx) into Nitrogen (N2) and water. However, if the reaction between NH3 and NOx is unbalanced, it can lead either to NH3 or NOx being released into the environment. As NH3 is classified as a hazardous compound on the environment, its accurate measurement is essential. Fourier Transform Infrared (FTIR) and Tuneable Diode Laser (TDL) spectroscopy are two of the methods that can measure raw emissions from engine exhaust pipes, especially NH3. However, it is difficult to suggest which method is the right one for measuring NH3 from engine exhausts. This paper compares the effectiveness of FTIR and TDL methods for NH3 measurement from diesel engine exhausts, based on tests conducted under well-controlled laboratory conditions. The concentration of NH3 from a diesel engine was measured under both a steady-state test cycle and a transient test cycle. The NH3 readings from FTIR and TDL were analysed, for comparison of precision, response time and their accuracy. It was shown that both techniques were suitable with attention to the different sampling procedures to avoid absorption.