Matsuhei Noda

Detection of carbon content in a high-temperature and high-pressure environment using laser-induced breakdown spectroscopy

Abstract A laser-induced breakdown spectroscopy (LIBS) technique has been applied to detect the carbon content in fly ash, char and pulverized coal under high-pressure and high-temperature conditions. An automated LIBS unit has been developed and applied in this experiment to demonstrate its capability in actual power plant monitoring. Gas composition effects were examined to obtain the best operating parameters under actual plant conditions. The results were compared to those obtained using the conventional method, showing satisfactory agreement. LIBS can detect carbon content even under the high-pressure conditions typical of gasification thermal power plants. LIBS is capable of a detection time of 1 min, as compared to over 30 min of sampling and analysis time required by the conventional methods (JIS-M8814 and JIS-M8815), and offers various merits as a tool for actual power-plant monitoring.

Industrial applications of temperature and species concentration monitoring using laser diagnostics

Industrial applications of laser diagnostics have been demonstrated for the purpose of clarifying combustor chemical reaction mechanisms, as well as temperature and harmful substance monitoring in large-scale burners and commercial plant exhaust ducts, and the combustion control of commercial plants. Laser induced fluorescence (LIF), laser induced breakdown spectroscopy (LIBS), and tunable diode laser absorption spectroscopy (TDLAS) have accordingly been applied in various industrial fields. In this study, temperature and species concentration were measured inside gas turbine combustors, a diesel engine, and a large-scale industrial burner using LIF. This technique introduces a new tool with respect to practical combustors for the analysis of NO formation characteristics, turbulent flame front structure, and differences between standard and improved combustors. On-line monitoring of trace elements to the ppb level was also successfully demonstrated using LIBS. The automated LIBS unit was found to be capable of monitoring trace element concentration fluctuations at ppb levels with a 1 min detection time under actual plant conditions. In addition, real-time measurement of O2 and CO concentrations in a commercial incinerator furnace was performed using TDLAS to improve the combustion control. By using the multiple-point laser measurement results to control secondary air allocation, higher secondary combustion efficiency was achieved, and CO concentration (considered to be a substitute indicator for dioxins) was reduced from 11.9 to 8.0 ppm.

Experimental and numerical studies on voltage distribution in capacitively coupled very high-frequency plasmas

A non-uniform voltage distribution across a driven electrode results in inhomogeneous film deposition in large-area, very high-frequency (VHF) plasma reactors. Here we perform experimental and numerical studies on the voltage distribution across the electrode. Two kinds of dedicated vacuum chambers are prepared for one- and two-dimensional observations of the voltage and the plasma distributions. A comparison between the measured voltage and the plasma distribution clearly shows a good agreement between the two. In principle the plasma distribution is governed by the standing wave of the voltage on the driven electrode for an at least one-dimensional electrode. A numerical model based on transmission-line modelling is presented for calculating the voltage distribution. The influence of plasma conditions such as the electron density and the sheath length included in the model on the voltage distribution is investigated through comparison of the model predictions with the experimental results. The correlation between the plasma conditions and the propagation constant of the model suggests that the sheath length dominates the wavelength; in contrast, the electron density dominates the decay of the wave propagation. Using the parameters of the plasma conditions estimated from the experimental results, the model can predict the voltage distribution across a ladder electrode of size 45 cm × 55 cm in a large-area VHF plasma reactor.

Improvement of combustion control through real-time measurement of O2 and CO concentrations in incinerators using diode laser absorption spectroscopy

In order to reduce the emission of harmful substances from incinerator facilities, combustion within the incinerator furnace must be stabilized. This in turn requires accurate and rapid detection of changes in furnace combustion conditions, with appropriate control of factors such as combustion air volume. This report describes the real-time measurement of O 2 and CO concentrations in a 300 ton/day commercial incinerator furnace, as well as the improvement of combustion control using in-furnace multiple-point O 2 and CO concentration measurements. The use of diode laser absorption spectroscopy was confirmed to allow real-time (2 s) measurement of in-furnace O 2 and CO concentrations. An automated system was developed, and the results were utilized as input values for furnace combustion control. In-furnance laser measurements detected O 2 and CO concentration fluctuations 2–3 min faster than existing conventional monitors. Greater secondary combustion efficiency was achieved by using these multiple-point laser measurement results to control secondary air allocation, and CO concentration (a substitute indicator for dioxins) was reduced from 11.9 to 8.0 ppm. Fast detection of furnance information is essential for control of unbalanced furnance combustion, and this system will enable the improvement of commercial incinerator furnaces in terms of both control and emissions.

Uniformity of VHF plasma produced with ladder shaped electrode

The uniformity of very high frequency (VHF) plasma produced with the ladder shaped electrode was examined by changing VHF power feeding positions for different discharge frequencies. It was found that the plasma uniformity strongly depends on how to feed the VHF power. Potential distributions on the ladder shaped electrode were calculated using the moment method and compared with measured spatial profiles of the ion saturation current. It was found that when the number of feeding positions are increased, the plasma uniformity is improved.

Characteristics of VHF-excited SiH4/H2 plasmas using a ladder-shaped electrode

Abstract A VHF-excited SiH 4 /H 2 plasma was produced using a ladder-shaped electrode. By measuring the plasma parameters with a heated Langmuir probe, the effect of hydrogen dilution on SiH 4 /H 2 VHF plasma characteristics was investigated. The ion density of the SiH 4 /H 2 plasma was higher than that of the H 2 plasma. The electron temperature tended to decrease for high H 2 dilution rate and became minimum at H 2 flow rate/(SiH 4 flow rate+H 2 flow rate)=91%, corresponding to the H 2 dilution rate near the deposition condition of hydrogenated microcrystalline silicon films. Negative ions exist in the SiH 4 /H 2 plasma. The negative ion density increased with increases in the radio frequency power. At the H 2 dilution rate where the negative ions exist, the electron temperature was high approximately 1.5 eV compared with that at other dilution rates.

OH and NO Visualization Inside a Gas Turbine Combustor Using Laser-Induced Fluorescence.

This study demonstrates the applicability of 2D species visualization inside a gas turbine combustor using larer-induced fluorescence (LIF). Time-averaged and single-shot OH and NO distributions were analyzed to clarify the characteristics of the NO formation inside the combustor. The turbulent flame front was clearly seen using single-shot OH measurement to elucidate the burning pattern in the combustor. It became clear that NO was mainly produced near the pilot burner and that it tended to exist at the center of the combustor.