Study for the feasibility of fluidized bed membrane reactors: membrane supports reutilization and hydrodynamics at high temperature

Herrero Miguel, Cristina
Medrano Jiménez, José Antonio (dir.) ; van Sint Annaland, Martin (dir.)

Universidad de Zaragoza, EINA, 2017
Ingeniería Química y Tecnologías del Medio Ambiente department, Ingeniería Química area

Máster Universitario en Ingeniería Química

Abstract: Membrane reactors can bring various potential advantages in terms of efficiency and economics for H2 production compared to the benchmark technology based on the Fired Tubular Reforming plant. However, for further implementation at industrial scale still some different aspects should be studied and investigated more in depth, especially those with an important impact on the economics of the process. Membrane costs are still high and can represent up to 15% of the total capital costs in a large scale production plant. A main responsible of these high costs is the high price of the support material (Hastelloy-X). To enhance the success of membrane reactors for hydrogen production, the present work focuses on the study of the reutilization of metallic supported Pd-Ag membrane for high temperature applications, especially by focusing on the reutilization of the support material. In this work, a metallic supported Pd-Ag membrane has been reutilized and tested after continuous operation under high temperatures for more than 1200 h. According to N2 permeance tests done during the characterization of the support for the original membrane and the repaired one, the metallic support might have suffered some sintering during long-term test. Furthermore, part of the ceramic layer of the fresh support membrane remained after the embrittlement, and thus this layer might have become thicker. The repaired membrane has been tested for more than 700 h and lower hydrogen perm-selectivities than in the original membrane are obtained, as well as an expected decrease in permeance. The membrane has also been tested under the influence of different parameters for water gas shift reaction conditions. It has been demonstrated that there is no interaction of the Pd-Ag layer with the Ni/CaAl2O4, thus resulting in a constant permeance in the fluidized bed membrane reactor. However, a catalytic effect of the support material (Inconel) has been observed due to the high CO conversions, besides the effect of the catalyst used. Furthermore, to better understand the behaviour of membrane reactors, especially the fluidized bed membrane reactor concept, better closure equations are needed to describe the fluid-dynamic behaviour of this concept at reacting conditions. In this work, it is aimed to extend a recently fundamental research carried out by Mustafa Taşdemir [1] for fluidized beds at room temperature, who developed a correlation to predict solids movement inside fluidized beds as function of bubble properties using novel optical LED-PIV/DIA techniques. This implies to apply this findings to the recently developed technique to study the hydrodynamic characteristics of fluidized beds at high temperatures, ePIV/DIA. To do so, LED-PIV/DIA and ePIV/DIA techniques are compared at room temperature, resulting in an overestimation of the bubble diameter and an underestimation of the solids hold-up when using the endoscopic technique. It might be related to the larger interrogation area used to treat ePIV/DIA recordings, besides the fact that the endoscope reduces the intensity of the laser hampering the detection of the smallest bubbles and averaging the larger ones. Furthermore, it is located in a corner resulting in a weak illumination at the top and bottom right corners and thus, an underestimation of the solids hold-up is found. The deviations observed between both techniques result in a difficult fitting of theoretical and experimental results at high temperature, hindering the extension of the novel correlation.

Tipo de Trabajo Académico: Trabajo Fin de Master

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