Ryuji Matsuhashi

Comprehensive comparison of efficiency and CO2 emissions between biomass energy conversion technologies - position of supercritical water gasification in biomass technologies.

Abstract Efficiency and CO 2 emissions between various methods of biomass energy conversion are compared from the viewpoint of life-cycle evaluation. As for electricity generation, efficient processes are thermal gasification combined cycle, supercritical water gasification combined cycle, and direct combustion in order of efficiency for low moisture content biomass. Supercritical water gasification combined cycle is the most efficient for high moisture content biomass. Battery electric vehicle, gasoline hybrid electric vehicle, and gas full cell vehicle (FCV) show high efficiency in automobiles. Biomass FCV shows high efficiency in the vehicles utilizing biomass. Biogas combustion is the most efficient for heat utilization. Then, the position of supercritical water gasification in various technologies of energy conversion is examined by modeling an overall energy system. The tradeoff between CO 2 emissions and total cost of technologies is analyzed so that the most cost-effective technology can be determined for different CO 2 emissions constraints. Computed results show that biomass is mainly consumed for electricity and heat generation so as to utilize finite biomass resources efficiently. Transportation fuels are generally made from fossil fuels. Cost-effective processes for CO 2 reduction are thermal gasification and reforming when the present efficiency and prices are assumed. Supercritical water gasification is also one of the optimal processes when the relative cost to fuel cell decreases. Improving heat exchange efficiency also contributes toward enhancing the position of supercritical water gasification in biomass technologies.

Life cycle of CO2-emissions from electric vehicles and gasoline vehicles utilizing a process-relational model

This article aims at estimating life cycle CO2 emissions from electric vehicles (EV) and gasoline vehicles (GV), although the estimation in this study is not an LCA according to ISO14040s. For this purpose, a mathematical tool called the Process-relational model was developed. The Process-relational model is used for establishing life cycle inventories. The model has a structure which improved the principle of input-output analysis in econometrics that only one product is generated by one process. This model enabled us to overcome difficulties of LCA in retracing complicated repercussions among production systems.Then, life cycle CO2, emissions from electric vehicles (EV) and gasoline vehicles (GV) were estimated with this model. Estimated results indicated that the manufacture and driving of EV resulted in less CO2 emissions than chose of GV. However, the difference between EV and GV dramatically changed depending on traffic situations. Namely, the difference became larger as the average velocity of the vehicles became lower. We also compared CO2, emission from manufacturing EV with that from driving EV. The share of manufacture was shown to increase in total CO2, emissions as the average velocity of the EV became higher. In conclusion, we clarified the direction of research and development of EV and GV for reducing the life cycle CO2.

Environmental evaluation of introducing electric vehicles using a dynamic traffic-flow model

A dynamic traffic-flow model (DTFM) is used in this study to evaluate the effectiveness of introducing electric vehicles (EVs) into the total traffic system as one of the alternative fuel vehicles. This model simulates congested and non-congested traffic flow caused by changes in the traffic demand. An environmental evaluation is carried out on the basis that all vehicles are substituted for EVs. Calculated results indicate that by introducing EVs, the NOx emissions and the CO2 emissions can be reduced by approximately 25.7 and 14.4% respectively. If battery performance of EVs is improved further, emissions can be further reduced by 39.6% (NOx) and 27.8% (CO2). Since emissions from heavy-duty vehicles are greater than other vehicles, the following measures have to be taken for these vehicles to significantly improve their impact upon the overall environment: (1) improvement in fuel efficiency and reductions of NOx in exhaust gas, (2) traffic demand management, such as modal shift.

A study on economic measures for CO2 reduction in Japan

In this paper, we investigate the costs and effectiveness of two CO2 emission control policies: a CO2 tax and a subsidy for CO2 reduction. CRIEPIs medium-term economic forecasting system is used to analyse the CO2 tax policy. It is concluded that the national cost of CO2 reduction by taxation is prohibitively high. For the subsidy we used an integrated approach combining a bottom up model with CRIEPIs model. Although we have shown the usefulness of the integrated approach for analysing the subsidy policy, we need to gather more data to make the results more reliable.

Reliability of LCI considering the uncertainties of energy consumptions in input-output analyses

The dispersion of input-coefficients in input-output (I-O) tables and the effect on LCA results are evaluated, utilizing the data for compiling the I-O tables. CO2 emission intensity and its variance with each commodity and service categorized in the I-O tables are estimated and applied to the LCA of a specific passenger car. Calculated results show that coefficients of variation (CV) of CO2-emission intensity are about 0.8 for the intermediate commodities which are frequently assessed in LCA. CO2 emissions induced by the production of the passenger car and the CV of the emissions are estimated at 1.3 Mg-C and 0.14, respectively. The value of CV is smaller than that of the most intermediate commodities since the CV of total emissions decreases as the number of components of the passenger car increases. Although emission intensity itself given by I-O tables has large variance, I-O tables are still useful tools for LCA if the number of components of a product is large enough.

Model analyses for sustainable energy supply taking resource and environmental constraints into consideration

Abstract This paper aims at clarifying key points for realizing sustainable energy supply under restrictions on resource and environment. For this purpose, we first developed a database to estimate life cycle efficiencies and greenhouse gas emissions for various energy systems. Then on the basis of this life cycle assessment, we quantitatively define the concept of ‘Sustainability Limitations’ on resource depletion and environmental emissions. From this concept, present world is judged to be unsustainable both from resource and environmental viewpoints. At the same time, we clarify how far present world is from Sustainability Limitations. Then we describe our mathematical model simulating global energy supply and demand in ultra-long term. In this model, the concept of Sustainability Limitations is utilized so as to impose economic incentives to make energy system shift to a sustainable one in long term. Sustainability limitations of resource depletion and CO2 emissions are taken into consideration. As energy resources, this model includes coal, oil, natural gas, other unconventional fossil fuels, uranium and renewable resources. As energy technologies, it includes major technologies of mining, transport, conversion and final utilization. Computed results have shown that present energy system, which is judged to be unsustainable, shifts to a sustainable system in the ultra-long term with appropriate incentives.

Analysis on waste-heat transportation systems with different heat-energy carriers

The transport of what would otherwise be waste-heat (at temperatures between 30°C and 300°C) through pipelines using as an energy carrier either methanol or hydrogen gas has been studied. By using numerical models, the relative costs of new kinds of waste-heat transportation systems are evaluated and compared with those using vapor or hot water, which have been the major energy-carriers in pipeline transmission systems until now. Also, environmental regulations and a carbon tax are investigated as incentives for introducing these systems.

Prospective on Policies and Measures for Realizing a Secure, Economical and Low-Carbon Energy System——Taking the Effects of the Great East Japan Earthquake into Consideration

The Great East Japan Earthquake devastated the eastern regions of Japan on this March. Due to the nuclear accident caused by the earthquake, Japan’s Cabinet stated to revise energy policies. This article aims at investigating whether we could establish a secure, economical and low-carbon energy system taking account of the serious situation after the Earthquake. For this purpose, we first evaluated possible technology options along with economic options. Then we integrated these options in a computable general equilibrium model for Japan so as to evaluate the impacts to national economy. As results, we quantified the relationships between energy security, quality of life and CO2 emissions.

Recovery of fluorocarbons in Japan as a measure for abating global warming

The objective of this study is to evaluate the potential for recovering fluorocarbons as measures for the abatement of global warming. In this study, we focused on the three different kinds of fluorocarbons: CFCs, HCFCs and HFCs, and targeted refrigerant use because of the availability of relevant data. We first estimated future fluorocarbon emissions from the targeted appliances; we next compared those emissions in the units of CO2 equivalent to the level of CO2 emissions in 1990 from a quantitative point of view. As the result of this study, it was found that fluorocarbon emissions in 1999 and 2010 would be equal to approximately 7 and 3% of the level of CO2 emissions in 1990 respectively. Moreover, if we implement a 100% recovery rate in every recovery route, we can reduce a large amount of emissions which correspond to approximately 2-5% of the level of CO2 emissions in 1990, even if we take into account the energy-related CO2 emissions by the transportation and decomposition of fluorocarbons.

A study on systems for a clean development mechanism to reduce CO 2 emissions

The clean development mechanism (CDM) is expected to facilitate technology transfer from developed to developing countries, as well as to economically reduce greenhouse gas emissions. This article aims at evaluating strategies in CDM, in which developing countries can improve industrial energy efficiency with financial support from developed countries. First, we investigated characteristics of the systems utilizing game theory. Analytical results revealed that technology transfer through the system might be considerably diminished, depending on the shapes of the marginal cost functions for reducing CO2. Next we estimated actual marginal cost curves of countries involved in CDM, in order to know the cost-effectiveness of CO2 reduction options. Input-output tables were utilized in this analysis, since these are established in developing countries as well as in developed countries. We have transformed one country’s input-output table to be adjusted against another country, taking the difference in goods prices into consideration. As far as data on the economy and industry are concerned, we used those from Japan and China, since China has been rapidly increasing its economic scale and greenhouse gas emissions. However, the implications from these analyses are useful also for other countries.