1,721,176 research outputs found
Risk analysis for cement and iron&steel factories: from the definition of Best Available Techniques to the environmental compatibility assessment
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Perspectives and limits for cement kilns as a destination for RDF
No full textRDF, the high calorific value fraction of MSW obtained by conventional separation systems, can be employed in technological plants (mainly cement kilns) in order to obtain a useful energy recovery. It is interesting and important to evaluate this possibility within the general framework of waste-to-energy solutions. The solution must be assessed on the basis of different aspects, namely: technological features and clinker characteristics; local atmospheric pollution; the effects of RDF used in cement kilns on the generation of greenhouse gases; the economics of conventional solid fuels substitution and planning perspectives, from the point of view of the destination of RDF and optimal cement kiln policy. The different experiences of this issue throughout Europe are reviewed, and some applications within Italy are also been considered. The main findings of the study are that the use of RDF in cement kilns instead of coal or coke offers environmental benefits in terms of greenhouse gases, while the formation of conventional gaseous pollutants is not a critical aspect. Indeed, the generation of nitrogen oxides can probably be lower because of lower flame temperatures or lower air excess. The presence of chlorinated micro-pollutants is not influenced by the presence of RDF in fuel, whereas depending on the quality of the RDF, some problems could arise compared to the substituted fuel as far as heavy metals are concerned, chiefly the more volatile one
Simulation and performances of main processes for waste and biomass gasification
No full textIn order to define practical application conditions for thermal treatment of mixed solid wastes, the presented study has been conducted in order to describe the fundamental processes that occur during a gasification process, with the aim to construct a specific model for the gasification reactor. The model has been realized by using the tools of energy and mass balances and by considering a chemical gas phase homogeneous equilibrium; the governing equations under steady condition have been defined. In order to completely establish the set of the required equations, some assumption were made: the main concern solid residue composition formed only by inert material, no tar formation, very fast reaction kinetics, adiabatic conditions.
Subsequently, on the basis of the above mentioned model, numerical simulations have been performed, and in particular we evaluated:
• the change in the operating temperature and the performance parameters, syngas volume, Lower Heating Value (LHV), gasification yield (η), consequent to variation of the inlet air volume;
• the change of the operative parameters as a consequence of the choice of a specific gasifying agent (air, dioxide carbon, oxygen and steam);
• the change, with reference to pressure variation, of the parameters: air volume, flue gases volume, LHV and gasification yield (η).
By considering gasification fundamental processes the above mentioned numerical simulation led to a comparison between the thermal gasification treatment and the usual direct combustion (incineration) operation. The first comparison aspect has been the environmental performance (quantity and quality of the generated flue gas in the two different systems, upstream and downstream of the flue gas treatment system), and it was conducted both on local (pollutant emission) and global scale (GHG formation). Subsequently the aspect of energetic production have been considered, both for electric production or co-generation.
The obtained results can be useful to identify possibilities of use, advantages and limits for gasification technology
Solid waste and biomass gasification: fundamental processes and numerical simulation
No full textWith the aim to study the fundamental processes of MSW (Municipal Solid Waste) gasification scheme and to obtain a comparison with existing thermal utilization schemes, an useful model was realized by using the tools of energy and mass balances, and of chemical homogeneous gas equilibrium (as concerns the residual solid, it was assumed that it is constituted only of inert material). By using this model, with numerical simulation we evaluated the influence of air volume on the most important operating parameters: temperature, flue gases volume, gas heating value, gasification yield (η). On the basis of existing data and the obtained results about syngas flow rate and composition we performed a comparison between gasification and direct combustion (considered environmental performances and energetic production aspects)
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