Oxygen-blown gasification of sewage sludge and biomass for chemicals synthesis

Sewage sludge management is a current problem of extreme concern in Europe. Till now, the most frequent route for sludge management has been incineration or the reuse by shedding on agricultural land both directly or after composting. This work, carried out in the context of an industrial research program co-financed by the EU LIFE program entitled LIFE-AUGIA, has been performed in partial fulfilment of the requirements necessary for the achievement of the Doctorate. It concerns a particular line of treatment of sewage and agricultural waste transforming them into gas with a significant energy content and of important economic and industrial value. In fact, a well-known source of material destined for landfill, are forest maintenance waste and sludge from sewage treatment. If waste from forestry and agricultural maintenance can in any way be used as a marginal source of energy, conventional methods such as landfill, incineration and use in agriculture have become less and less exploitable for sewage sludge in the Countries of the European Union (EU). The new directive 99/31 / EEC introduced restrictions for landfilling of biodegradable organic waste. In some countries of the EU, the use of untreated sewage sludge in landfills is already forbidden as well as their use in agriculture. After an initial description of the treatment methods alternative to gasification, the different gasification methods and their merits and defects are described here in detail according to what can be found in the specialist literature. The following description of the LIFE- AUGIA program introduces to modern methods of gasification in presence of oxygen and carbon dioxide, identifies materials and methods of analysis of the gas and the materials used in the process. Follows a description of components and structure of the AUGIA experimental plant. A conspicuous part of the work has been then dedicated to the creation and running of two simulation models, both developed in the commercial framework Aspen Plus. The first is based on the evolution of gasification at thermodynamic equilibrium and the second instead considers the kinetics of the reactions and more accurately describes the various transformations that happen along the gasifier. Part of the work required the creation and operation, in the Lab of the University of Pisa, of a small-scale reactor with which the oxygen-based gasification has been experimentally tested, allowing the comparison between experimental results and simulations aimed at validating the latter and obtaining the necessary empirical parameters. Finally, the AUGIA industrial reactor has been completely simulated and the results are shown in the last part of this very work.