Kiyotaka Tahara

Evaluation of CO2 payback time of power plants by LCA

CO2 emissions from construction of various power plants were calculated by the LCA (Life Cycle Assessment) methodology. The LCI (Life Cycle Inventory) was calculated by “NIRE-LCA”, LCA software developed at the National Institute for Resources and Environment using a bottom-up approach. CO2 payback times of renewable energy electric power plants (hydroelectric, OTEC and PV) were calculated vs. conventional fossil fuel-fired power plants (coal, oil and LNG). The evaluated payback times were much shorter than the typical operational lifetimes of the respective renewable energy electric power plants.

Automobile life cycle assessment issues at end-of-life and recycling

Abstract Reducing and recycling automobile shredder residue (ASR) are important to improve the recycling rate of end-of-life vehicles (ELVs). In this paper, we discuss the concept of applying life cycle assessment (LCA), LCA case studies (landfill of ASR, energy recovery of ASR), and LCA issues concerning ELVs, and we introduce trends in LCA application to new technologies, aimed at achieving a recycling rate of 95%.

Consistent characterisation factors at midpoint and endpoint relevant to agricultural water scarcity arising from freshwater consumption

PurposeThe shortage of agricultural water from freshwater sources is a growing concern because of the relatively large amounts needed to sustain food production for an increasing population. In this context, an impact assessment methodology is indispensable for the identification and assessment of the potential consequences of freshwater consumption in relation to agricultural water scarcity. This paper reports on the consistent development of midpoint and endpoint characterisation factors (CFs) for assessing these impacts.MethodsMidpoint characterisation factors focus specifically on shortages in food production resulting from agricultural water scarcity. These were calculated by incorporating country-specific compensation factors for physical availability of water resources and socio-economic capacity in relation to the irrigation water demand for agriculture. At the endpoint, to reflect the more complex impact pathways from food production losses to malnutrition damage from agricultural water scarcity, international food trade relationships and economic adaptation capacity were integrated in the modelling with measures of nutritional vulnerability for each country.Results and discussionThe inter-country variances of CFs at the midpoint revealed by this study were larger than those derived using previously developed methods, which did not integrate compensation processes by food stocks. At the endpoint level, both national and trade-induced damage through international trade were quantified and visualised. Distribution of malnutrition damage was also determined by production and trade balances for commodity groups in water-consuming countries, as well as dependency on import ratios for importer countries and economic adaptation capacity in each country. By incorporating the complex relationships between these factors, estimated malnutrition damage due to freshwater consumption at the country scale showed good correlation with total reported nutritional deficiency damage.ConclusionsThe model allows the establishment of consistent CFs at the midpoint and endpoint for agricultural water scarcity resulting from freshwater consumption. The complex relationships between food production supply and nutrition damage can be described by considering the physical and socio-economic parameters used in this study. Developed CFs contribute to a better assessment of the potential impacts associated with freshwater consumption in global supply chains and to life cycle assessment and water footprint assessments.

Refinement and transportation of petroleum with hydrogen from renewable energy

Abstract A possible refinery process with higher output of gas oil and more hydrogen consumption than in conventional refinery processes was proposed. The CO 2 emissions form the proposed processes with (case B) and without (base case, A) outer source of hydrogen were evaluated. The possibility of combining the refinement and transportation of petroleum with hydrogen produced from renewable energy resources such as hydropower and solar cells (photovoltaic, PV) was discussed by life cycle assessment (LCA), where hydrogen is supplied to the refinery process installed overseas and the lighten and desulfurized products are transported to Japan (case C). The result was compared with the case when liquefied hydrogen is transported to Japan and supplied to a refinery installed in Japan (case B). CO 2 emissions from the proposed refinery processes with (case B) and without (case A) outer source of hydrogen were calculated with 159 and 141 kg-CO 2 /kl-produced oil, respectively. In any case with outer hydrogen supply (cases B and C), the total CO 2 emission was less than that for case A, when the hydrogen is produced from hydroelectricity. On the other hand, when the hydrogen is produced from PV, total CO 2 emissions for cases B and C were larger than that for case A. Finally, the characteristics of case C was identified and the conditions for the product import case (case C) can show the best one with the minimum CO 2 emission were discussed.

Ocean thermal energy conversion (OTEC) system as a countermeasure for CO2 problem - energy balance and CO2 reduction potential

Abstract We evaluated the energy balance of an ocean thermal energy conversion (OTEC) system that is one of the substitute energy sources. It was found that a 100 MW OTEC system reduces the amount of CO 2 emission by 140,000 t-C/year, as compared with a 100 MW coal fired power plant. Its energy pay back time was calculated to be 0.46 year. In addition, the synergistic CO 2 uptake effect by the compulsory circulation of the ocean was calculated to be 7,800 t-C/year for a 100 MW OTEC system on the basis of the difference between the present and pre-industrial CO 2 concentrations in the atmosphere.

Using decomposition analysis to forecast metal usage in the building stock

As large amounts of materials are used and have accumulated in buildings and civil engineering projects, it is necessary to understand material flow in terms of construction sectors for resource management. The consumption, discard and in-use stock of four metals (steel, aluminium, copper and zinc) in Japans building stock are forecast through to 2050. To clarify the factors that affect metal stocks and flows in construction, the metal consumption was decomposed into annual new floor area constructed and metal intensity (i.e. the amount of metal used per unit floor area). The decomposition was meaningful for understanding characteristic patterns of factors of different metals and for envisaging future scenarios based on past trends. It was estimated that the annual new floor area constructed will remain at current levels, whereas metal intensity will have a significant impact on stocks and flows. The methodology developed in this study can be used to evaluate the impact of technology changes that would take place in building and civil engineering projects.

Estimation of water requirement per unit carbon fixed byEucalyptus camaldulensis in semi-arid land of Western Australia

Afforestation in arid land is a promising method for carbon fixation, but the effective utilization of water is highly important and required. Thus, the evaluation of the amount of water per unit carbon fixed with the tree growth is required to minimize the amount of water supplied to the plants. In this research, a tree is regarded as a carbon fixation reactor with inflows of water and nutrients from roots, and CO2 as the carbon source from leaves with outflow of water vapor from leaves and accumulation in the tree itself. In the process of photosynthesis and respiration nutritional elements are dissolved in water flow in trees. They do not flow out by these reactions, but are accumulated in trees. Thus, we have treated the behaviour of nutrients as a marker to evaluate the water/carbon ratio.Assuming that nutrient concentration is constant in sap, and the differences in the ratios of nutrient to carbon in living trees and dead (i.e. litter fall, etc.) are neglected, the ratio of the used water to fixed carbon is given as the ratio of nutrient to carbon in the tree body divided by the ratio of nutrient to water in sap. However, some nutrients are translocated and concentrated within the tree and some may be discarded through litter fall. Thus it is important to examine which nutrient element is the most suitable as the tracer.In this paper, the results of the above method applied toEucalyptus camaldulensis in semiarid land of Western Australia are shown. The value of water requirement per unit carbon fixation determined from potassium balance is between 421 kg-H2O/kg-C for mature trees and 285 kg-H2O/kg-C for young trees, while the values from calcium balance are much larger than these. The cause of the discrepancy between these values is discussed based on the measured element concentrations in sap and trees and the plant physiology. Finally, the actual average value through the life of a tree is suggested to fall between the two values.

Comparison of the environmental impact of the conventional nickel electroplating and the new nickel electroplating

PurposeTo comply with the effluent regulation of boron, replacement of boric acid with citric acid in a nickel electroplating bath is proposed. Although the bath avoids the discharge of boron, it increases the discharge of nickel owing to the chelating effect of citric acid, which disturbs the wastewater treatment. To balance this trade-off, the environmental impacts of a traditional nickel plating process (the Watts bath) and the citrate bath must be compared by life cycle assessment.MethodsThe life cycle impact assessment method was LIME2. To estimate the trade-off between boron and nickel discharge into wastewater, the characterization and damage factors on human toxicity and ecotoxicity were calculated. The processes were then compared using data from actual processes. The functional unit was “plating per 1-kg part.” However, the plating efficiency depends on the type, shape, and surface area of the part. The data of the citrate bath were modeled. In the modeling, the amounts of nickel chloride and nickel sulfate in the citrate bath were based on the Watts bath.Results and discussionIn comparison with other chemicals, the calculated characterization and damage factors of boron and nickel were found to be reasonable. The integration results revealed that the citrate bath exerted greater environmental impact than the Watts bath. Although the Watts bath involved more environmentally damaging processes than the citrate bath, the sum of these impacts was much smaller than the impact of effluent from the citrate bath. Moreover, the environmental impact of effluent can be significantly reduced by flocculants, with almost no additional environmental impact incurred by the increased sludge.ConclusionsThe newly developed citrate plating bath exerts higher environmental impact than the traditional Watts bath because the environmental impacts of the release of nickel chelated with citric acid exceed the reduced boron emissions. Therefore, there is a trade-off between the two methods. When installing the citrate bath, the wastewater treatment must be altered to reduce the nickel emissions.

Strategy Planning Before Urban Mining: Exploring the Targets

This study is a challenge to construct the long-term strategy for recycling. To identify the adequate targets for recycling, we proposed the concept that integrates the criticality assessment and material flow analysis. Prior to the evaluation based on the concept, we developed the framework of the existing criticality assessment for Japan. Furthermore, the information on domestic metal demand and discard were reviewed to evaluate the potential of recycling. By integrating these knowledge, the result of the pilot evaluation was presented with a future perspective of the study.

Life cycle assessment of fuel production for biomass from dry land afforestation

Biomass has been focused as a fuel resource because of its huge abundance and carbon-neutral characteristics. Thus, we attempted to use tree biomass as the resource to automotive fuel. From the global warming point of view, the biomass energy production from large-scale plantation is required, however, the land use should not be changed from crop field or forest land. In the present paper, the feasibility of the use in Japan of biofuel from woody biomass produced in large arid area of Western Australia, where the present authors demonstrated that the large-scale afforestation is possible even in an arid land when introducing water management and plantation technologies, has been evaluated using LCA method, by considering the actual condition of our afforestation area. Furthermore, some sensitivity analysis is conducted on the effects of composition ratio of electric power sources.