Techno-economic evaluation of ethanol production from bark-containing forest residues

Bark-containing forest residues can serve as a potential feedstock for lignocellulosic ethanol production due to their abundance and low cost. Although the production of ethanol from spruce is well documented, the different physical properties and chemical composition of bark compared to the conventionally used wood chips can influence the spruce-to-ethanol bioconversion process. For instance, spruce bark was found to be more recalcitrant to hydrolyze to monomeric sugars than wood chips, and can adversely affect the whole bioconversion process. Furthermore, depending on the process design of the production plant and the feedstock the product output mix (consists of ethanol, biogas, solid lignin, electricity and district heating) can be changed to some extent. Thus, the bark content of the forest residues has a relevant impact on the plant investment cost and the ethanol production cost. We investigated different ratios of bark and wood chips to perform sensitivity analysis of the ethanol production process. Aspen Plus was used to solve mass and energy balances for the ethanol production plant and to estimate the ethanol production cost. The results show that the minimum ethanol selling price is greatly influenced not only by the overall ethanol yield, but also by the incomes from other products that can balance the yield losses.