Torrefaction Pretreatment for Biomass Upgrading: Fundamentals and Technologies

About this Research Topic

Background

Biomass is nowadays considered to be the renewable energy source with the highest potential for replacing fossil fuels in the short term and medium-term. In fact, it is largely available worldwide in the form of both raw materials and biogenic wastes generated by anthropic activities. Moreover, biomass is characterized by the following advantages over other renewable resources (e.g. solar and wind): i) it enables to produce not only heat and power, but also chemicals, materials and transportation liquids; ii) it is a non-intermittent source, thus it guarantees continuous power and heat; iii) it can be easily stored to accommodate changes in the market energy request, and can be also transported for meeting decentralized energy demands.
The large-scale exploitation of biomass in the energy field is economically and technically limited by a number of challenges to overcome, which are related to its chemico-physical properties. Firstly, biomass has a lower energy content compared with fossil fuels. Moreover, biomass is a bulky material prone to natural decomposition, with associated issues related to its storage and transportation from safety, logistic and economic standpoints. In addition, it is a fibrous material characterized by poor grindability (with high costs associated). This aspect is critical, in particular, when biomass is used in pulverized systems, such as entrained flow gasifier, or co-fired in existing pulverized-coal fired power plants. As a consequence, the biomass preatreatment is a necessary step to enhance its characteristics as a fuel.

Torrefaction is a relatively new pretreatment technology, which, over the past decades, has been recognized as a very promising and technically feasible method to improve the performance of biomass with regard to storage, handling, transportation and energy conversion processes.
In particular, torrefaction is a mild thermal process, which has the potential to convert any lignocellulosic material into a higher energy density, hydrophobic, brittle and biochemically stable coal-like solid, which is suitable for energy-related applications (pyrolysis, gasification and combustion). A number of demonstration plant have seen the light these years, but still very few commercial plants are currently operating. In fact, despite the global efforts to develop torrefaction technology, there are still several technical challenges that need to be taken up in order to realize biomass torrefaction in an economically feasible way at commercial scale. The major bottlenecks is nowadays the limited control of the process parameters, in particular the temperature, but the fuel flexibility (size distribution and moisture content) and scale-up of the system are often a barrier as well.

In this Research Topic, the editorial team particularly welcomes Original Research and Review manuscripts that deal with the latest advances in biomass upgrading through torrefaction, from both fundamental and practical points of view. The ultimate objective is to gain deeper insight
into such pretreatment technology to promote its technological development and commercialization. Specific themes of interest include, but are not limited to:

1. Optimization of process parameters for a specific feedstock or end-use application (e.g., pyrolysis, combustion, gasification and pelletization);
2. Environmental and economic aspects of the torrefaction processes;
3. Design and process control in torrefaction technologies;
4. Stand-alone and hybrid solutions to enhance the net thermal efficiency of the torrefaction treatment;
5. Process intensification, techno-economic analysis and life cycle impact analysis of torrefaction technologies;
6. Chemistry, reaction kinetics and modeling of biomass torrefaction;
7. Storage and milling properties of torrefied biomass;
8. Biochemical conversion of torrefied biomass.

Keywords: Torrefaction, Kinetics, Modeling, Techno-economic analysis, Life cycle analysis

Important note: All contributions to this Research Topic must be within the scope of the section and journal to which they are submitted, as defined in their mission statements. Frontiers reserves the right to guide an out-of-scope manuscript to a more suitable section or journal at any stage of peer review.

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