This study evaluates three bioethanol production pathways that are composed by saccarification and fermentation process (SFP), gasification and chemical synthesis process (GCP), gasification and biosynthesis process (GBP). These pathways are designed by process simulator PRO/II, and these material and energy balances are calculated. From the simulation results, the CO₂ emission reduction of each process is evaluated. It becomes clear that the CO₂ emission reduction of the process via syngas is larger than that of the process via sugars. The ethanol yield of GBP is the maximum, and GBP can support oneself a power and thermal energy in the process. In three processes, therefore, the CO₂ emission reduction of GBP is the largest. The ethanol yield of SFP and GCP is almost the same. Because the residue including lignin contains moisture, the thermal energy from which SFP can be recovered is not large. On the other hand, GCP can use the thermal energy generated by chemical synthesis for the power production. It is indicated that GCP has the possibility of increasing the CO₂ emission reduction more than SFP.

View full abstract

In order to spread economically viable distributed generation systems for apartment buildings, it is essential to develop an efficient and low-cost heat supply system. We are developing a new cogeneration system (Neighboring Co-Generation system: NCG). The key concept of this system is to install a heat storage unit with a hot water supply and a room heating function at each household and to connect heat storage units by a single-loop hot water pipe. In this study, a dynamic simulator was developed on the NCG system with solar heat utilization, and the environmental load reduction effects of solar heat utilization in the system were evaluated under the condition satisfying the whole heat demand. The simulated results for the system of 50 households showed that the annual use of the primary energy was reduced by 18 % in the case that a gas engine was used as the main generator. When a SOFC system with the higher thermal efficiency was installed, the reduction ratio increased to 29 %.

View full abstract

The information about energy efficiency of electric vehicles in comparison to petrol vehicles is useful and significant for decision making of consumers. In Japan, the travel distance per electricity (km/kWh) or petrol (km/liter) are commonly used as indexes of energy efficiency. In this study, the conversion coefficients between these 2 indexes were estimated, on the basis of tank-to-wheel, well-to-wheel, and greenhouse gas emission. For tank-to-wheel, 1km/kWh corresponded to 9.58km/liter, and 4.08 for well-to-wheel. From the catalogs of electric and hybrid vehicles, both were equivalent in well-to-wheel energy efficiency. The conversion coefficients on the basis of greenhouse gas emission were 7.14 in case of Tokyo and 7.18 for Tohoku. However, this would vary due to the change in the structure of energy source for electricity production, caused by the east-Japan earthquake. The changes in coefficients were also estimated from the forecast of energy source structure of power plants in the next summer. The revised estimation of the coefficients were 5.67 for Tokyo and 5.79 for Tohoku. Despite the damage of nuclear power plants by the earthquake and growing dependence of power plants on fossil fuel, electric vehicle had superiority from a viewpoint of greenhouse gas emission in comparison to petrol vehicles.

View full abstract

Recently, electric power storage is more important to stabilize power demand supply balance and promote use of renewable energy. Then, we have paid attention to Compressed Air Energy Storage (CAES) gas turbine system as one of more than medium-size electric power storage system. Power generation unit of CAES is necessary to have high thermal efficiency and little restriction of location.
The advanced humid air gas turbine (AHAT) system that is a regenerative cycle using humidified air is expected to achieve higher thermal efficiency than gas turbine combined cycle power plant (GTCC) even though it does not require steam turbines, high combustion temperature, or high pressure ratio. Moreover, it has the advantages that work done by compressor can be reduced by water atomization cooling and the restriction of the location is less because a large amount of cooling water is unnecessary. So, this system is thought to be suitable for CAES.
In this paper, CAES systems utilizing the AHAT system are studied about its composition and the thermal efficiency.

View full abstract