Due to the rapid increase of CO₂ emissions in the household sector, many simulations have been conducted for the yearly CO₂ emissions in a house assuming the characteristics of energy supply system. However, there is no standard for the behaviors in the household sector. We focus on the variation of personal pattern of life and estimate load curves of the houses based on the data of average and variance of the behaviors. Then, we simulate the yearly CO₂ emissions for the different regions, energy supply systems, insulation, number of persons per household, and renewable energy. Cogeneration system has more variance between households than between regions. As for the additional solar water heater, there is the effect of large offset for the gas-engine cogeneration following the heat load, and small offset for the fossil fuel of high efficiency of power generation. Utilizing the simulation results for more than 200 households, we make the regression model which explains the yearly CO₂ emissions by the temperature, ratio of total load (electricity/heat), number of person per household, and insulation. It is indicated that cogeneration system helps CO₂ emission reduction for cold region and low insulation houses.

View full abstract

In-situ observation of methane-hydrate (MH) formation and dissociation in sandy sediments, and water-permeability measurements for the sediments have been performed by the apparatus combined proton nuclear magnetic resonance (¹H NMR) and permeability measurement system, which we had originally designed. For three kinds of sand, Toyoura, No. 7 and No. 8 silica sand, the changes of pore-size distributions under MH formation and dissociation processes were discussed from the changes of transverse relaxation time, T₂, of liquid water in pore space. With forming MH, it was found that intensity and peak-top T₂ of T₂ distribution decreased. The intensity of T₂ distribution is proportional to the number of protons of water and methane in pore space. Decreasing intensity means the consumption of water and methane to form MH, and the shorter peak-top T₂ indicates smaller apparent pore size, in which MH was assumed to be solid material as well as sand grain. These changes are thought to indicate that MH growth make apparent pore size gradually smaller. On the other hand, MH dissociation is supposed to advance from water-hydrate interfaces, where apparent pore size becomes larger gradually. All the sediments used here have the same tendency of decreasing pore-size with changing water saturation due to MH formation and growth. Measured water permeability ratio, which is defined as the ratio of effective water permeability to absolute one, during MH dissociation increased rapidly in the case of higher MH saturation, S_h, condition and went up slowly at lower S_h condition, while that estimated from SDR model increased gradually for all S_h condition. But it was found that the expanded SDR model which was introduced an exponent factor to the logarithmic mean of T₂ (T_2LM) of original SDR model could express the change of measured permeability. Here, the expansion of T_2LMmeans extremely larger specific surface area (SSA) of pore space at higher S SUB>h. We interpret that higher SSA bring stronger resistance to water mobility, which leads extremely smaller water permeability at higher S SUB>h.

View full abstract

Tar generated in the biomass gasification process is currently the most difficult problem to solve. Gasification of tar and gas by catalytic steam reforming was examined in a woody biomass gasification process. The tar and gas reforming characteristics of the newly-developed Ni based catalyst that has superior resistance to coking and sulfur poisoning were investigated for the gasification of wood chips. The results of the experiment have confirmed that the newly-developed catalyst showed a high tar conversion activity at 750°C, and is stable even in a gas containing hydrogen sulfide and hydrogen chloride. A deactivation of the catalyst was not confirmed after 60 hours usage. Consequently, high cold gas efficiency (65%) and carbon conversion ratio (94%) were achieved.

View full abstract