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Abstract: Published estimates of the potential of bioenergy vary widely, mainly due to the heterogeneity of methodologies, assumptions and datasets employed. These discrepancies are confusing for policy and it is thus important to have scientific clarity on the basis of the assessment outcomes. Such clear insights can enable harmonisation of the different assessments. This review explores current state of the art approaches and methodologies used in bioenergy assessments, and identifies key elements that are critical determinants of bioenergy potentials. We apply the lessons learnt from the review exercise to compare and harmonise a selected set of country based bioenergy potential studies, and provide recommendations for conducting more comprehensive assessments. Depending on scenario assumptions, the harmonised technical biomass potential estimates up to 2030 in the selected countries range from 5.2 to 27.3EJ in China, 1.1 to 18.8EJ in India, 2.0 to 10.9EJ in Indonesia, 1.6 to 7.0EJ in Mozambique and 9.3 to 23.5EJ in the US. From the review, we observed that generally, current studies do not cover all the basic (sustainability) elements expected in an ideal bioenergy assessment and there are marked differences in the level of parametric detail and methodological transparency between studies. Land availability and suitability lack spatial detail and especially degraded and marginal lands are poorly evaluated. Competition for water resources is hardly taken into account and biomass yields are based mostly on crude ecological zoning criteria. A few studies take into account improvements in management of agricultural and forestry production systems, but the underlying assumptions are hardly discussed. Competition for biomass resources among the various applications is crudely analysed in most studies and key assumptions such as demographic dynamics, biodiversity protection criteria, etc. are not explicitly discussed. To facilitate more comprehensive bioenergy assessments, we recommend an integrated analytical framework that includes all the key factors, employs high resolution geo-referenced datasets and accounts for potential feedback effects. [Copyright &y& Elsevier]

Abstract: Torrefaction is a promising bioenergy pre-treatment technology, with potential to make a major contribution to the commodification of biomass. However, there is limited scientific knowledge on the techno-economic performance of torrefaction. This study therefore improves available knowledge on torrefaction by providing detailed insights into state of the art prospects of the commercial utilisation of torrefaction technology over time. Focussing on and based on the current status of the compact moving bed reactor, we identify process performance characteristics such as thermal efficiency and mass yield and discuss their determining factors through analysis of mass and energy balances. This study has shown that woody biomass can be torrefied with a thermal and mass efficiency of 94% and 48% respectively (on a dry ash free basis). For straw, the corresponding theoretical energetic efficiency is 96% and mass efficiency is 65%. In the long term, the technical performance of torrefaction processes is expected to improve and energy efficiencies are expected to be at least 97% as optimal torgas use and efficient heat transfer are realised. Short term production costs for woody biomass TOPs (torrefied pellets) are estimated to be between 3.3 and 4.8 US$/GJLHV, falling to 2.1–5.1 US$/GJLHV in the long term. At such cost levels, torrefied pellets would become competitive with traditional pellets. For full commercialisation, torrefaction reactors still require to be optimised. Of importance to torrefaction system performance is the achievement of consistent and homogeneous, fully hydrophobic and stable product, capable of utilising different feedstocks, at desired end-use energy densities. [Copyright &y& Elsevier]