Biomass is a non-intermittent energy source, which can play an important role in grid-based energy systems, since they need some non-intermittent sources in order to balance the variability of intermittent sources as wind and solar energy. Currently, this role is played mostly by fossil fuels, mainly because of the bulk size of a single source. Higher variability and lower energy concentration, among with some properties of biomass, are obstacles that prevent it from fully becoming a commodity. There are processes, such as dry torrefaction and hydrothermal carbonization (HTC) that could potentially help in terms of making biomass a tradable commodity, as is the case with fossil fuels. HTC, also known as wet torrefaction, might help solve problems that dry torrefaction is incapable of solving. These obstacles are, namely: high ash content, slagging and fouling properties of biomass (along with corrosion). Also the high moisture content of some types of biomass poses a problem, since they usually require substantial amounts of heat for drying. This paper reviews current knowledge about a process that could possibly transform problematic types of biomass into tradable commodities and compares it with other processes offering similar outcomes.
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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.
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