Biomass to Heat Supply Chains: Applications of Process Optimization

A systems modelling framework has been developed for the simultaneous design and operations scheduling of a biomass to heat supply chain. A state-task-network (STN) approach, originally developed for the design and scheduling of batch plants within the process industries, has been adapted to provide a generic representation of harvesting, densification, drying, storage and transportation activities. This facilitates effective system scheduling under dynamic system influences affecting harvested yield, crop moisture content, ambient drying rates and seasonal demand. Period-specific harvest tasks, biomass moisture content variations throughout the dynamic processing chain and concurrent ambient drying in storage processes have been captured analytically and integrated into the modelling framework.The model is applied to a 12-month operational cycle for a hypothetical 20 MWth peak output biomass-to-heat supply chain system. Optimized supply chain design and operational schedules are analysed; land and operational harvesting costs are observed to dominate supply chain economics. The optimized design and operational schedules are also compared with those derived through a simple heuristic strategy in order to assess potential economic benefits of applying systems optimization methods. Results suggest that improvements of 5–25% on cost minimization objectives can be achieved; equivalent to £0.6–3.0 MWhth−1 in delivered heat costs.