Gas appliances require high performances such as low NOx and low noise with high intensity combustion. While significant progress has been made in the development of low NOx combustion by introducing lean premixed combustion techniques, these appliances are more likely to show a tendency to produce combustion oscillations than those with conventional burners. Conventionally, the suppression of combustion oscillation has been achieved through hardware design modifications. In general, it has been made in an attempt to prevent that the heat release fluctuation phase and the pressure fluctuation phase become the same. Rayleigh's criterion is a convenient diagnostic tool for evaluation of combustion oscillation. However, it may not always be applicable to practical combustion appliances having a complex structure. One reason is that it is difficult to model the heat release fluctuation which is strongly influenced by a type of flame, equivalence ratio and combustion intensity. In addition, combustion oscillation is sometimes generated even if the Rayleigh's criterion is positive. This paper represents an evaluation way of combustion oscillation in which amplification of the pressure fluctuation by premixed flames and the attenuation at burner are both focused on. Amplification of pressure fluctuation is measured by a burner system that the fuel-air mixture is forced to excite by a loud speaker. Obtained results are compared with the attenuation of pressure fluctuation at the burner. It is found that combustion oscillation is not observed when the attenuation excesses the amplification although Rayleigh's criterion shows a conditionally positive. It shows that present work would be a practical way to suppress combustion oscillations in the stage of designing gas appliances.
Regarding bioenergy utilization in Japan, information on generation scale distribution of biomass resources is essential for development of a policy to introduce bioenergy. In this research, investigation based on various statistic resources was carried out first in Japan for the generation scale distribution of forest residues, manufacturer waste wood, cattle manure, construction waste wood, sewage sludge, night soil, house garbage, and waste food oil. As a result, it was found that the scale of the biomass generation in Japan is relatively small, usually being several tones per day in dry weight.
In the previous study, it was presumed that the coal liquefaction plant was located in the coal production area and the natural gas was not available. Furthermore, the steam reforming of the off-gas produced from the plant, and the gasification of raw coal and residue were selected as the hydrogen production process. The capital cost and production cost were reduced by introducing the steam reforming of off-gas along with the gasification of raw coal and residue, and were minimized at the boiler turbine generator (BTG) in comparison with the integrated coal gasification combined cycle (IGCC). In this study, natural gas is available and the combined cycle generator (CCG) in the power plant is added for power generation. By using Linear Programming (LP) technique, the production costs of hydrogen and power were minimized in the combination of these production processes for the coal liquefaction plant. As a result of this LP study, the capital cost and production cost were reduced by introducing the steam reforming of natural gas and off-gas along with the gasification of raw coal and residue. They were minimized at BTG in comparison with IGCC. The production of hydrogen by the steam reforming of natural gas reduced the production cost, in which the residue is used for the power generation. On the other hand, the low consumption and the low capital cost were expected in the case of CCG, but the production costs of steam-power and hydrogen depended on the price of natural gas.