Intelligent catalyst carrier concept with additively manufactured structures made of shape memory alloys for the optimization of the wall heat transfer in tubular reactors

点击翻译按钮获取中文摘要

Cellular structures represent a promising alternative to classical randomly packed bed reactors owing to their very good heat transport characteristics. A key challenge of using cellular structures as catalyst carriers in tubular reactors is the contact of the structure with the tube wall, which in many cases is not sufficient and thus downgrades the overall heat transfer performance. Especially with strongly exo- or endothermic reactions, this inhibition of heat transfer leads to undesirable temperature gradients. Therefore, the main goal of this proposal is to achieve a scientific understanding for the structure-wall interactions in order to predict the design of an optimal wall coupling. Auxetic POCS (periodic open cellular structures) that are additively manufactured (selective electron beam melting, SEBM) from a shape memory alloy (NiTi, Nitinol) represent a particularly suitable and innovative model system for achieving this goal.The additive manufacturing of these POCS via SEBM offers a great degree of freedom almost without any limitations in the design process. To ensure a good wall coupling for exchangeable catalyst carriers, we propose a system that utilizes the auxetic effect. Uniaxial compression is used to decrease the diameter of the structure. The auxetic effect alone, however, would require a constant pressure to keep the structure compressed. This can be circumvented by combining the auxetic effect with the one-way memory effect of a shape memory alloy. Here, the structure is deformed once before insertion into the reactor and then re-expanded to its original shape by an in situ heat treatment inside the reactor. This method represents an elegant approach for ensuring a press fit between the cellular structure and the reactor wall.The use of Nitinol via SEBM is not sufficiently documented in literature and therefore represents a highly interesting research topic. The combination of knowledge about POCS and literature about additive manufacturing of shape memory alloys offers a promising approach to overcome the problem of wall heat transfer limitations in tubular reactors. Numerical models for mechanical and reaction engineering problems build the framework for the well-founded development of improved catalyst carriers. By performing several optimization cycles the most promising design will be identified. Finally, the feasibility and efficiency of this new concept will be demonstrated in a case study based on a reaction system of technological relevance.