Pyrolysis and Gasification of a Real Refuse-Derived Fuel (RDF): The Potential Use of the Products under a Circular Economy Vision.

Refuse-Derived Fuels (RDFs) are segregated forms of wastes obtained by a combined mechanical-biological processing of municipal solid wastes (MSWs). The narrower characteristics, e.g., high calorific value (18-24 MJ/kg), low moisture content (3-6%) and high volatile (77-84%) and carbon (47-56%) contents, make RDFs more suitable than MSWs for thermochemical valorization purposes. As a matter of fact, EU regulations encourage the use of RDF as a source of energy in the frameworks of sustainability and the circular economy. Pyrolysis and gasification are promising thermochemical processes for RDF treatment, since, compared to incineration, they ensure an increase in energy recovery efficiency, a reduction of pollutant emissions and the production of value-added products as chemical platforms or fuels. Despite the growing interest towards RDFs as feedstock, the literature on the thermochemical treatment of RDFs under pyrolysis and gasification conditions still appears to be limited. In this work, results on pyrolysis and gasification tests on a real RDF are reported and coupled with a detailed characterization of the gaseous, condensable and solid products. Pyrolysis tests have been performed in a tubular reactor up to three different final temperatures (550, 650 and 750 °C) while an air gasification test at 850 °C has been performed in a fluidized bed reactor using sand as the bed material. The results of the two thermochemical processes are analyzed in terms of yield, characteristics and quality of the products to highlight how the two thermochemical conversion processes can be used to accomplish waste-to-materials and waste-to-energy targets. The RDF gasification process leads to the production of a syngas with a H2/CO ratio of 0.51 and a tar concentration of 3.15 g/m3.

Combined effect of Bond and capillary numbers on hydrocarbon mobility in water saturated porous media.

The mobilization of an oil bank under the combined effect of Bond (N(B)) and capillary (N(C)) numbers, in a packed bed column of glass beads saturated with water, has been investigated. In order to reach the irreducible saturation the experiments have been run with sweeping water velocities outside the range of validity of the Darcy's law. The size of the glass beads was varied in the range between 2 mm and 5 mm. The oils used for the tests are hexadecane and hexane with viscosities different for an order of magnitude and densities smaller than that of water, and alpha-methylnaphthalene, which has a density very close to that of water, in order to single out the effect of the capillary number on the mobilization process. The plots of oil saturation as function of the trapping number (N(T)), which is the vectorial sum of N(B) and N(C), are reported and a mobilization diagram is drawn. Furthermore, a few tests in a basin, simulating an aquifer at a laboratory scale, have proved that the results obtained in the packed column are useful for determining the fate of a spill of oil above an aquifer. For these experiments also perchloroethylene (PCE), which has a density greater than that of water, has been used.

The containment of oil spills in unconsolidated granular porous media using xanthan/Cr(III) and xanthan/Al(III) gels.

The gelation in situ of aqueous solutions of the biopolymer xanthan gum may be a method for temporarily containing oil spills in soil whilst the remediation procedure is planned and accomplished. The gelling reaction has been carried out using as crosslinking agents either Cr(III) or Al(III) cations. By using Cr(III) the gelation time, which has been measured for a range of xanthan and/or Cr(III) concentrations, is of the order of the hour. On the contrary, the gelation by means of Al(III) cations takes place at quite low pH and is instantaneous. Therefore, depending on the crosslinker adopted, rather different techniques must be used for generating the gel structure in situ. The gels have proven to be suitable for the containment of water and of many hydrocarbons without loosing their strength even for a long period of time. The rheological properties of xanthan aqueous solutions evidence a shear-thinning behaviour that is most favourable for the application. Theoretical considerations have permitted the establishment of the mobility conditions of xanthan solutions in porous media before the gelation, and the estimation of a suitable injection pressure. The experiments for investigating the mobility of xanthan solutions in porous media, and for simulating the containment of an oil spill, have been done using packed beds of uniformly sized spherical glass beads, in glass columns. The glass assembly made it possible to visualize the evolution of the phenomena of interest.