1 Biomass energy conversion

There are multiple methods for the conversion of biomass energy. Generally, the biomass is transformed into a more easily manageable form (solid, liquid or gaseous bio-fuel) in which it is used [1, 3, 5]. Before proceeding with the analysis of the main modalities of biomass energy conversion, it is important to note that conver­sion is only one aspect of the wider problem, which includes, on one hand, the present reality or the eventual future situation where the biomasses are produced and, on the other hand, the possible utilization of the deliverable energies. The resulting circuit is depicted as follows:

Production-Collection-Conversion-Utilization

This has to be studied in an optimal context that includes extensive co-ordinated initiatives and interventions with both public and the entrepreneurial support. The biomass energy conversion processes are divided into biochemical and thermochemical processes [3-5, 34, 35]:

• Biochemical conversion processes allow to exploit the energy obtained through chemical reactions, due to the action of enzymes, fungi and micro-organisms, that take place in the biomass under particular conditions. These processes are suitable for those biomasses in which the C/N ratio is lower than 30 and the humidity at the time of collection is higher than 30%. Water cultivations that are appropriate for biochemical conversion include the by-products of some cul­tures (leaves and beet stems, vegetable garden, potato, etc.), livestock sewage wastes and some working wastes (pot ale, vegetation water, etc.) as well as the heterogeneous stored biomasses in the controlled biomasses.

• Thermochemical processes are based on the action of heat which allows the chemical reactions that are necessary to transform the material into energy to take place. These processes are suitable for products such as cellulose and wooden residuals in which the C/N ratio has values higher than 30 and the humidity content does go beyond 30%. The most appropriate biomasses for

thermochemical conversion processes are wood and all its by-products (sawdust, shavings, etc.), the most common cultural by-products of the lignocellulosic kind (straw of cereals and orchards, vine pruning residuals, etc.) and working wastes (such as husk, chaff, hulls, hazels).

Of the several technologies available for energy conversion of biomasses, some of them can be considered to be at the development level to allow their utilization on an industrial scale, while others, on the contrary, need further experimentation to raise their efficiencies and reduce the energy conversion costs.

Usually, upstream, all the conversion processes require appropriate base material for pre-treatment, which can include water washing, drying with mechanical or thermal instruments (pressing), reduction into smaller dimensions, densification (pelletization and briquetting) and separation of the fibres (extraction with solvents). Even the final product, depending on its use, must be treated to separate them (e. g. from the substrate that does not react, catalysts, micro-organisms and solvents), purify them and concentrate them. Depending on the application, we resort to sedimentation, filtration, centrifugation, distillation, absorption and extraction with solvents [4].