Direct liquefaction of ligno-cellulosic residues for liquid fuel production

This study focuses on the valorization of biomass wastes in the Piedmont Region, in Italy, with the aim of producing synthetic liquid fuels. On the basis of a territorial survey, the selected fractions from the separate collection of municipal solid wastes (organic fraction, pruning residues and wood refuses) and, to a lesser extent, the residues of the agro-industry, were considered potentially important, due to their abundance and availability throughout the year. Dedicated arborous cultivations, evaluated on the basis of the land that is currently cultivated, also showed a great potential. The sum of the potential recoverable energy from these three categories reaches 35.99 x 10(6) GJ/year, i.e. 6.79% of the total final energy consumption of the Piedmont Region. The target of this valorization is here the conversion of these low energy density biomasses into valuable liquid fuels. The direct liquefaction technology was chosen due to its flexibility towards the feed and the possibility of working with wet substrates, these being typical constraints which are difficult to be overcome in the other thermo-chemical processes. In the direct liquefaction process, a pulp of organic material, with a water content ranging from 50% to 90%, is fed to a reactor at around 330 degrees C and 180 bar, with a residence time of 4-10 min, according to the biomass pulp composition. The resulting bio-oil can be fed to the upgrading section of a refinery, in order to reach standard fuel-grade specifications, which allows it to be blended with currently sold transportation fuels, or it could be used as a source of valuable chemicals in an alternative scenario. A 50 ktons/year plant (based on the dry biomass content) was considered, and the balance of plant was sized in order to estimate the energy requirements of the plant and the bio-oil yield. A very convenient configuration was designed, and a bio-oil net production of 37.1 wt% was reached (referring to the dry matter of the biomass), which takes into account all the fuel needs of the plant. The specific power consumption was equal to 0.258 kWh/kg(Oil), which corresponds to a ratio between the output and input energy of 35.8 (excluding the biomass lower calorific value). Finally, it should be mentioned that this target was obtained using simple and economic equipment, thus responding to the need to devise a process which could be profitable, even at a medium scale, for local applications. (C) 2011 Elsevier Ltd. All rights reserved.