The purpose of this study is to evaluate biomass energy systems based on both material and energy flows. The biomass energy system consists of 4 processes such as harvesting and collection, preprocessing, energy conversion, and waste treatment. As the conventional evaluation such as energy return on investment (EROI) is based on the amount of fossil fuel consumption, it shows the efficiency of inputted fossil fuel to form biomass derived fuels without biomass material flow. In this study, the effective utilization rate of resource is defined as the ratio of the difference between produced bio-fuel energy and consumed fossil fuel energy to the biomass resource energy, and the fossil fuel substitution rate is defined as the ratio of net substituted fossil fuel energy by the bio-fuel to the biomass resource energy. As a case study, the woody biomass utilization systems considering 7 preprocessing technologies and 4 energy conversion technologies are evaluated by using EROI and suggested values. It is shown that the effective utilization ratio of resource and the fossil fuel substitution rate can be small even if EROI is enough high.

View full abstract

The objective of this paper is to show the economic and environmental effects induced by construction and operation of a system that produces fuel from green microalgae using input-output analysis. We compared two systems. The first is a simplified photobioreactor (PBR) that utilizes fallow and domestic farmland. The second system is comprised of large and open ponds in overseas with relatively long hours of sunlight. A large part of the induced economic effect in constructing a small system comes from the cost of plastic materials needed to build the PBR. When constructing a large system overseas, civil engineering and water costs are quite high. Electricity costs make up a large part of the induced economic effect from operations. We also analyzed the sensitivity of plant profitability to change in growth and oil content rates of microalgae, and to how residue remaining after oil extraction is used. It is important to improve oil productivity of microalgae and to make high quality products from residue such as fertilizer or feedstuff, in order to improve profitability. However, production of high-quality products from residue emitted more CO₂ than production of low-quality products such as solid fuels.

View full abstract

Supercharging is one way that be cited for expanding the high-load operating limit that is an issue of the homogeneous charge compression ignition (HCCI) engine. Spectroscopic measurements and chemical kinetic simulations were performed in this study to investigate in detail how varying the equivalence ratio by means of the intake air pressure influenced the low-temperature oxidation reactions and main combustion period of HCCI combustion. Experimental and simulation results showed that reducing the equivalence ratio worked to moderate the main combustion period. On the other hand, it was also observed that lowering the equivalence ratio by increasing the intake air pressure resulted in more active low-temperature oxidation reactions.

View full abstract

In coal fired power plants using low rank coal containing significant amounts of moisture, improvement of the thermal efficiency has been desired. This paper presents estimation results of thermal efficiency for an existing 316 MWe power plant with and without steam tube dryers (STDs). An original estimation methodology has built for estimation of the efficiency. Coal feed rates were predicted by coal properties and turbine heat rates, and process simulation based on heat balance was applied to estimate net thermal efficiency of the power plant with the STDs. When total moisture of low rank coal was dried from 35.0% to 11.4% by the STDs, the absolute values of boiler efficiency and net thermal efficiency were increased by up to 4.2% and 1.8%, respectively. A decrease in power consumption of mills and fans was contributed to an increase in net thermal efficiency. It found that application of the STDs for low rank coal fired power stations have the advantage of reduction of fuel cost and CO₂ mitigation.

View full abstract

Recently, non-food producing farmlands have been increasingly abandoned in Japan. In this paper, we have focused on willow cultivation. Willow can be used as woody biomass (for energy) and can be cultivated in a short rotation coppice production style to effectively utilize abandoned farmlands. A recently published Japanese willow production manual has proposed a method of harvesting in which large machines are used, as is done in Europe and the United States. Therefore, in this study we have proposed a new harvesting method, in which cutting is conducted using a bush cutter (bush cutters are commonly used by farmers and forest labors) and chipping is done using a small machine. We used three indexes, which are (a) workload (manpower/10 a), (b) energy consumption per area (MJ/10 a), (c) energy consumption per yield (MJ/dry-t), (d) input per area (MJ･manpower.10 a) and (e) input per yield (MJ･manpower/dry-t), to evaluate the method. (d) and (e) are original indexes we suggested. From the resulting estimates of workload and energy consumption, it appears that this process of willow crop farming is almost as efficient as large-scale production methods (Hokkaido Regional Development Bureau, 2010), whilst being better suited to Japanese agriculture’s socio-economic context.

View full abstract