Kimishiro Tokuda

Fundamental experiment on the combustion of coal-water mixture and modeling of the process

A fundamental study of the combustion process of coal-water mixtures has been performed. The surface and center temperatures and the weight change of a single droplet under combusion were measured in detail, where the water content, properties of coal, initial diameter of droplet, and external heat flux were parameters. In the experiments, an infrared intensive laser was used as the external heat source to simulate the conditions around the droplets atomized in an actual furnace. Based on the data obtained, the reaction rates in the processes of water vaporization, devolatilization, and char combustion were formulated. For the devolatilization stage, the activation energy derived by assuming a first-order reaction was almost the same as that for the mother coal, but the apparent frequency factor was much, smaller than that for the mother coal by 1/140-1/50. For the stage of char combustion, also, the apparent frequency factor was much smaller. The specific surface area and the micropores in the coal particle were much reduced after undergoing processes of water vaporization and devolatilization. Its possible that the pore would be masked when the water trapped in the pore was escaping from it with the agglomeration of coal particles proceeding. According to the data obtained and the combustion model proposed here, computer simulation codes for the combustion of a single droplet and for the combustion process in a furnace, were written. The calculated results for the temperature variation and the concentrations of oxygen and unburned carbon in the exhaust gas agreed well with the experimental data obtained using a one-dimensional test furnace. This confirms the validity, of the combustion model and reaction data.

Detection of nitrogen oxides by high-resolution near-infrared absorption spectroscopy

Near-infrared absorption spectra of NO, NO2 and N2O were observed in the wavelength region between 1.2 and 1.9 micrometers using a high-resolution Fourier-transform spectrometer, and we have obtained precise absorption data which are useful for tunable diode laser absorption spectroscopy (TDLAS). Furthermore, the NO and N2O were detected by means of TDLAS method for the first time using InGaAs-DFB diode lasers which were designed to access absorption lines at wavelengths of 1.798 and 1.766 micrometers respectively.

Simultaneous detection of oxygen and soot particles by visible diode laser absorption spectroscopy

A technique for simultaneous detection of oxygen molecules and soot particles by means of visible tunable diode laser absorption spectroscopy was investigated. The effects of solid particles on the measurement of oxygen molecules were evaluated using a 760 nm visible diode laser. The maximum solid particle density was 5.6g/m3m, allowing measurement of the concentration of oxygen with sufficient precision. We applied this technique to analysis of real exhaust gas from a large-scale test furnace, and verified that oxygen molecules and soot particles in such gas can be directly measured from a large-scale test plant without pretreatement, such as removal of water vapor and soot.