Willow supply strategies to energy plants

The main objective of this study was to develop minimum cost supply strategies for willow to energy plants (two plant sizes: 0.5 and 30 MWe, two energy conversion technologies: combustion and gasification). Time span between harvest and energy conversion varied from 1 to 12 months. For a realistic comparison, different supply chains were based on the same initial characteristics (i.e., moisture content 50% wb at harvest) and final fuel specifications at the energy plant (moisture content 20% wb, particle size chips or chunks). Cost calculations were based on the integral cost calculation method and were presented for all process steps, The main conclusion was that the time span between harvest and energy conversion and the size and conversion technology of the energy plant largely influence the design of the supply chain and consequently the supply costs. The fuel supply costs ranged from 17.6 to 26.1 ECU/t DM (where DM stands for oven dry matter) or 0.010 to 0.023 ECU/kWh, The cost reduction which could be achieved by choosing the minimum cost chain design could be as high as 45% or 14.4 ECU/t DM. Generally, the strategy of minimum costs for supply of fuel to an energy plant running all year round on willow was as follows: for farmers who should supply their willow within 6 months after harvest: harvest as chips, forced drying at the farm and transport (if necessary); for farmers who should supply their willow beyond 6 months after harvest: harvest as chunks or stems, natural drying near the willow field, transport (if necessary) and central chipping (if applicable). (C) 1999 Elsevier Science Ltd. All rights reserved.