Paolo Deiana

MeOx/SBA-15 (Me = Zn, Fe): highly efficient nanosorbents for mid-temperature H2S removal

Zinc oxide/ and iron oxide/SBA-15 composites were synthesized using the innovative Two-Solvents procedure and tested as sorbents for the mid-temperature (300 °C) removal of hydrogen sulphide, and then compared with a commercial unsupported ZnO sorbent. The sulphur retention capacity results showed the superior performance of the iron oxide/SBA-15 composite (401 mg S g−1 Fe2O3) in comparison with the zinc oxide/SBA-15 composite (53 mg S g−1 ZnO), both these sorbents being much more efficient than the commercial sorbent (6 mg S g−1 ZnO). The different sorption behaviour was discussed in terms of the nature of the nanocomposites where: (i) the mesostructure of the support was retained with a high surface area and pore volume; (ii) the zinc oxide phase was incorporated inside the SBA-15 channels as a thin amorphous homogeneous layer while the iron oxide was dispersed in form of small maghemite crystallites; and (iii) significant interactions occurred between the silica matrix and the zinc oxide phase. Remarkable differences in the regeneration behaviour of the exhaust sorbents were revealed by temperature-programmed experiments under an oxidizing atmosphere. After regeneration, the sorption properties of the zinc oxide/SBA-15 composite appeared to be enhanced compared to the commercial sorbent. Incomplete recovery of the sorption activity was observed for the regenerated iron oxide/SBA-15 sorbent, whose performance remained far better than that of the ZnO-based one, either fresh or regenerated. In view of its higher sulphur retention capacity and appropriate regeneration temperature (T ≤ 350 °C), the iron oxide/SBA-15 composite is a promising material for the design of advanced sorbents for a thermally efficient H2S removal process from hot gas streams.

Sulcis Coal Water Jet Assisted Comminution

This study has sought to verify the effectiveness of high-speed water jets on solid minerals grinding. To this end, an innovative gyratory crusher called HERA (High Energy Reduction Apparatus) has been designed and employed. The experiment has been carried out on samples of sub-bituminous coal extracted from the Sulcis coal basin (Sardinia, Italy). The experiment has aimed to examine and evaluate the effects of high-speed water jets on the milled product. These grinding tests have returned carbon suspensions in water, which could be used to power fluidized bed combustors. The parameters used to evaluate the adequacy of the assisted water jet comminution are: jet mill pressure, nozzles size, water flow rate, jets hydraulic power and specific energy consumption. The effects of preliminary water imbibition of coal samples have also been considered. The results have shown that the synergic combination of hydraulic and mechanical energy can have positive effects on grinding.

Modelling of an Amine Based CO2 Absorption Plant: an Alternative Approach through the Identification of the Number of Stages

In the last decades, a huge number of studies on carbon dioxide removal have been presented in the literature. The non-equilibrium nature of the process involves an accurate definition of the parameters’ correlations and of the model’s assumptions. One of the most important assumptions when developing a process model is the definition of the number of discretization points. In this paper an alternative methodology has been presented for the definition of the number of stages of the absorption column in order to fit all the transport phenomena taking part in the carbon dioxide removal process. Then, it was developed a rigorous model of the absorption unit and finally implemented in Aspen Custom Modeler® environment to manage with a high level of complexity. The results obtained demonstrate that the number of stages is fundamental for the correct representation of the process and its incorrect evaluation could lead to huge errors in the prediction of the performance of the plant.