Toshio Nitami

Energy and carbon dioxide (CO2) balance of logging residues as alternative energy resources: system analysis based on the method of a life cycle inventory (LCI) analysis

Using the method of a life cycle inventory (LCI) analysis, the energy balance and the carbon dioxide (CO2) emission of logging residues from Japanese conventional forestry as alternative energy resources were analyzed over the entire life cycle of the residues. The fuel consumption for forestry machines was measured in field experiments for harvesting and transporting logging residues at forestry operating sites in Japan. In addition, a total audit of energy consumption was undertaken. It involved an assessment of materials, construction, and the repair and maintenance of forestry machines as well as the costs associated with an energy-conversion plant. As a result, the ratio of energy output to input was calculated to be 5.69, indicating that the system examined in this study could be feasible as an energy production system. The CO2 emission per MWhe (e: electricity) of the biomass-fired power generation plant was calculated to be 61.8 kgCO2/MWhe, while that of coal-fired power generation plants in Japan is 960 kgCO2/MWhe. Therefore, the reduction in the amount of CO2 emission that would result from replacing coal with biomass for power generation by as much as 3.0 million dry-t/year of logging residues in Japan was estimated to be 1.66 million tCO2/year, corresponding to 0.142% of the national CO2 emission. This study provides evidence that Japan could reduce its domestic CO2 emission by using logging residues as alternative energy resources.

Cost, energy and carbon dioxide (CO2) effectiveness of a harvesting and transporting system for residual forest biomass

The purpose of this study is to examine the feasibility of a system to harvest logging residues (or slashes) as a new resource for energy in Japan. A harvesting and transporting system for residual forest biomass was constructed with reference to some European countries where the utilization of bioenergy is making steady progress and examined on the basis of field experiments in Japanese forestry. The feasibility of the system is discussed from the standpoints of cost and energy, and the system is compared with those of the European countries. With respect to the system proposed in this study, it is desirable that the process of chipper comminuting is incorporated into the system as early as possible, considering the trends of harvesting cost and fuel consumption per unit weight of residual forest biomass. Such a system is not particularly feasible in Japan from the standpoint of the harvesting cost per MWh of bioenergy. However, no specific problems are found from the point of view of the energy input rate, and it is clarified that it is possible for Japan to reduce domestic carbon dioxide emissions by utilizing biomass as an energy resource. A comparison with the European countries and a preliminary sensitivity analysis of the system demonstrate that the technical development to reduce the harvesting cost,e.g., improving the forwarding and transporting efficiency, and support from the government are essential for realizing bioenergy utilization in Japan.

Motion analysis of a semi-legged vehicle with soil deformation taken into account

A semi-legged vehicle was designed for forestry use. The equation of motion for the machine coupled with the equation of motion for soil was derived. Furthermore, the motion of the machine was analyzed taking into account soil deformation. The Extended Distinct Element Method, which can analyze both continuous and non-continuous materials, was used as a soil model. The effects of foot area and spike length were simulated by using two kinds of uniform soil. The specific power of a foot area of 3,200 cm2 was smaller by 0.025 than that of a foot area of 1,600 cm2 on soft soil. This was equal to the consumption energy for moving 2.5% of the machine weight, about 140 kgf. The maximum values of the forces acting on the second hydraulic cylinder were 300 kN and 500 kN, and the weights of the hydraulic cylinder generating these forces were 121 kgf and 229 kgf with spikes that were 0 cm and 30 cm long on hard soil, respectively. In a walking motion, such as lowering the boom to the ground, raising the stabilizers, and advancing the machine, the machine with a larger foot area and shorter spikes was more suitable for lightening the total weight and improving energy efficiency.

Forest Disturbance and Efficiency of Vehicle Logging Operations through Selective Cutting Harvest in a Natural Forest

Forest disturbance and operational efficiency were discussed through a ground logging system in a selective cutting harvesting. Grapple skidder operation together with a winch skidder resulted in small disturbance when the grapple skidder mainly execute logging operations. Trees were injured often at slopes where gentler than ten degrees and at slopes steeper than twenty degrees. The former is because of easiness to run a skidder to make free direction long skidding path, and the latter is because that felled trees often roll down on the slope to hit trees when hauled. Decreasing branching of skidding paths enables shorten the paths length and is expected to suppress forest disturbance.