High-temperature desulfurization techniques are fundamental for the development of reliable and efficient conversion systems of low-cost fuels and biomass that answer to the nowadays environmental and energy security issues. This is particularly true for biomass gasification coupled to SOFC systems where the sulfur content has to be minimized before being fed to the SOFC. Thus, commercially available zinc oxide has been studied and characterized as a desulfurizing agent in a fixed-bed reactor at high temperatures from 400 °C to 600 °C. The sorbent material was characterized by XRD, BET, SEM, and EDS analyses before and after adsorption. The sorbent’s sorption capacity has been evaluated at different temperatures, as well as the breakthrough curves. Moreover, the kinetic parameters as the initial sorption rate constant k0, the deactivation rate constant kd, and the activation energy have been calculated using the linearized deactivation model. The best performances have been obtained at 550 °C, obtaining a sorption capacity of 5.4 g per 100 g of sorbent and a breakthrough time of 2.7 h. These results can be used to extend ZnO desulfurization techniques to a higher temperature than the ones used today (i.e., 550 °C with respect to 400 °C).
Solid Oxide Fuel Cells are a promising technology for Solid Oxide Fuel Cells (SOFC) are a promising technology For high-efficiency electrochemical conversion of a vast range of fuel gas mixtures, thigh operating temperature conditions (650–900 °C) represent a challenge both at system level and at laboratory testing level, in terms of material properties and performance dynamics. In this work a detailed procedural analysis is presented for an innovative all-ceramic compact SOFC test rig and first experimental testing results are reported in terms of polarization curves obtained under parametric variation of operating conditions (H2 content, air ratio λ and temperature) and short-term voltage stability test under load (140 h at 0.3 A/cm2). The electrochemical characterization results confirm the validity of the used all-ceramic cell holder, showing excellent cell performances in terms of polarization. H2 content has the most impact on SOFC performance, followed by temperature and finally air ratio, whose impact in the analyzed range is hardly seen. From the short-term stability test, the test bench setup reliability is demonstrated, showing no significant performance degradation after 140 continuous hours under load, which confirms the high quality and reproducibility of the results.
Hot gas conditioning is a remarkable stage for decreasing typical and harsh contaminants of syngas produced in the biomass gasification process. Downstream contaminants containing hydrogen sulphide (H2S) can significantly deteriorate fuel stream conversion reactors and fuel cell systems. Thus, an effective gas cleaning stage is required to remove critical streams that endanger the whole pathway toward the biomass conversion process. In this work, we studied H2S capture from biofuel syngas by using a kinetic deactivation model to analyze the effect of the operating conditions on the adsorption performance. Furthermore, the particle sorbent influence on other reactions, such as methane reforming and water gas shift (WGS), were also evaluated. Breakthrough curves were plotted and fitted following a first-order linearized deactivation model to perform both the H2S adsorption capacity and thermodynamic analysis. Moreover, the influence of the operating conditions was studied through a breakthrough curve simulation. By using the Arrhenius and Eyring–Polanyi expressions, it was possible to calculate the activation energy and some thermodynamic parameters from the transition state theory. Finally, a mathematical analysis was performed to obtain the diffusion coefficient (D) and the kinetic reaction constant (k¯0) of H2S gas within ZnO particles, considering a spherical geometry.
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