Gradierte poröse Strukturen zur Optimierung verfahrenstechnischer Prozesse : Anwendung in der Autothermen Dampf-Reformierung

Abstract

Many applications in chemical and process engineering are based primarily on the characteristics of porous materials. Therein, properties as pore size or porosity strongly affect mechanisms like mass transfer, heat transfer or catalytic efficiency. Against this background, this work investigates the possibility of using materials with properties distributed over space instead of using homogenous structure. The target of this investigation was to develop optimization tools for designing graded porous structures optimized for the use in process applications. As an example, this method was developed for reducing the temperature peak in the entrance of an autothermal steam-reformer by optimizing two porous elements. In the first case, an oxygen feed membrane was designed that on each position inside the reformer the right amount of oxygen is fed to the reaction such that the heat production by exothermic oxidation and the heat consumption by reforming reactions is always balanced. The result was a membrane with exponentially decreasing permeability leading to an almost constant temperature profile over the length of the reformer. This was true for simulation results as well as for experimental results in a lab scale reformer. For the other element, the structure of the catalyst support and therefore the total activity of the catalyst via the volumetric surface were on focus of the optimization. Also with this porous element, it was possible to reduce the temperature peak. The latter gives the big advantage to not only put the temperature profile on target but as well more financial values like conversion rate or selectivity.