Optimization of pre-treatment selection for the use of woody waste in co-combustion plants

This work is focused on the use of biomass waste to feed already existing coal combustion plants as a part of paving the way toward the reduction of the environmental impact. The biomass waste supply chain optimization is critical to conceive long-term viable projects and deal with the biomass heterogeneous nature and drawbacks to be used with coal, i.e. principally high moisture content and low bulk density. This paper studies biomass transportation, storage and change of properties (moisture content and hence dry matter, energy density and bulk density) through the use of different pre-treatments: (i) torrefaction, (ii) torrefaction combined with pelletization, (iii) pelletization, (iv) fast pyrolysis and (v) fast pyrolysis combined with char grinding, which produce a range of very different pre-treated biomass. The optimization problem is formulated as a mixed integer linear program (MILP) that evaluates the net present value and the environmental impact through a life cycle assessment (LCA). The results propose location-allocation decision together with the selection/capacity of pre-treatment technologies for each scenario. The scenarios contemplate different biomass characteristics, availability and distribution for a supply chain case study located in Spain: forest and agricultural woody residues used to replace at least 10% of the total thermal inlet power provided by coal in the existing network of thermal plants. (C) 2014 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.