Commoditization of biomass: dry torrefaction and pelletization - a review

Abstract

Biomass is one of few renewable energy sources that is not intermittent and may be used in the same way as fossil fuels. There are some important constraints, imposed by the nature of biomass, that do not allow it to become a tradable commodity in the same way as solid fossil fuel. Torrefaction is a thermal process that is used to upgrade raw biomass into solid biofuel, more uniform with respect to its properties. Properties are changed in a way that makes torrefied fuel resemble coal more closely. That opens up some new opportunities in terms of use of biomass in furnaces designed for coal, without necessitating major changes to the installation. Biomass pre-treated this way is more suitable for co-burning with coal. Pelletization is a densification process that allows the specific energy density of biomass to be increased. The process makes biomass more uniform in size. This is beneficial with respect to transport cost, other handling operations (loading, unloading, feeding) and storage. This article gives an overview of dry torrefaction technologies, changes in fuel properties due to torrefaction and possibilities of combining torrefaction with pelletizing. Everything is analyzed in the context of a single goal - increasing the use of biomass by making it a commodity fuel.