Designing the scale of a woody biomass CHP considering local forestry reformation: A case study of Tanegashima, Japan

Biomass has become a renewable resource for energy, but it needs continuous management to make it truly renewable. Planted forests in particular areas in the world are facing the challenges of reformation because of the severe maldistribution of forest age-classes caused by a stagnation in demand for wood or degradation by past deforestation. In these regions, the amount of wood processed and the overall biomass must be controlled by a schedule of forestry reformation. Particularly for energy plants, where a continuous and adequate supply of wood is required, the scale of the plants should be carefully designed to maintain a harmonized demand/supply balance in the region. In this study, we considered the scale design for a combined heating and power (CHP) system using woody biomass for district heating and cooling (DHC) in Tanegashima, a remote island in Japan, which requires immediate forestry reformation in addition to mitigating its fossil-fuel consumption. A process model representing material and energy flows associated with the life cycle of a biomass CHP system was developed, which considered the dependency of timber consumption on the scale of the CHP, together with other design parameters. The profile of the annual timber supply for the next 100 years to achieve sustainable forestry planning was calculated, which became the constraint on the feasibility of resource procurement for CHP. The ratio between the maximum and minimum timber supply in the next 20 years was determined to be about 1.8. Through simulation and life cycle assessment (LCA) using the developed model, CHP scales were specified to cover the overall heat and power demand of consumers for biomass-derived energy at 840 kWe with 1470 kW(th). We found feasible and effective scale ranges for the various stages of forest-resource status by comparing LCA results, timber consumption, and profiles for timber supply. We have been able to demonstrate that woody biomass utilization in a specific area should address forestry reformation in a sustainable way. (C) 2017 Elsevier Ltd. All rights reserved.