Universität Stuttgart
Permanent URI for this communityhttps://elib.uni-stuttgart.de/handle/11682/1
Browse
39 results
Search Results
Item Open Access Dynamic modelling of multitubular catalytic reactors(1991) Stankiewicz, Andrzej; Eigenberger, GerhartThis paper presents a study on modelling and simulation of transient operational characteristics in multitubular fixed-bed reactors. The dynamic model of the reactor is based on a porous body approach which regards the intertubular space as a pseudo-homogeneous environment. Such an approach permits to take into account most factors in the geometrical design of the unit and thus to study the influence of various shell-side geometrical and operational parameters on the reactor behaviour. Based on the model, the dynamic responses of the two most common industrial reactor designs, i.e. the parallel flow unit with distributing plates and the crossflow reactor with disk-and-doughnut baffles have been investigated and compared. In addition, some problems of correct space discretization and use of time-dependent regridding procedures, are discussed.Item Open Access Catalyst poisoning and fixed bed reactor dynamics(1975) Weng, Hung Shan; Eigenberger, Gerhart; Butt, John B.The poisoning kinetics of thiophene on Ni-kieselguhr catalysts and the deactivation behavior of nonisothermal fixed bed reactors have been studied experimentally using benzene hydrogenation as a model exothermic reaction. The time dependent axial temperature profiles in the reactors were measured and compared with values evaluated from a dispersion model, the parameters of which have been determined in separate experimentation. Poisoning kinetics were measured in a series of differential reactor experiments at atmospheric total pressure, thiophene partial pressures of 0·037-0·19 torr, hydrogen to benzene molar ratios >8/1 and temperatures from 60-180°C. Excellent agreement was found with a power law equation for the rate of change of activity with time, first order in catalyst activity and in thiophene concentration, with an experimental activation energy of 1080 kcal/kmole. This correlation of poisoning kinetics, however, was not able to predict the propagation of the zone of activity (hot-spot) on poisoning of an integral fixed bed reactor. Initial (steady state) temperature profiles were modeled satisfactorally, but the rate of migration of the hot spot was found experimentally to be more rapid than that predicted from the correlation of poisoning kinetics. A semi-empirical two site deactivation model is shown to resolve the discrepancy.Item Open Access Acid-base flow battery, based on reverse electrodialysis with bi-polar membranes : stack experiments(2020) Xia, Jiabing; Eigenberger, Gerhart; Strathmann, Heinrich; Nieken, UlrichNeutralization of acid and base to produce electricity in the process of reverse electrodialysis with bipolar membranes (REDBP) presents an interesting but until now fairly overlooked flow battery concept. Previously, we presented single-cell experiments, which explain the principle and discuss the potential of this process. In this contribution, we discuss experiments with REDBP stacks at lab scale, consisting of 5 to 20 repeating cell units. They demonstrate that the single-cell results can be extrapolated to respective stacks, although additional losses have to be considered. As in other flow battery stacks, losses by shunt currents through the parallel electrolyte feed/exit lines increases with the number of connected cell units, whereas the relative importance of electrode losses decreases with increasing cell number. Experimental results are presented with 1 mole L^-1 acid (HCl) and base (NaOH) for open circuit as well as for charge and discharge with up to 18 mA/cm2 current density. Measures to further increase the effciency of this novel flow battery concept are discussed.Item Open Access Numerical methods for the simulation of chemical engineering processes(1994) Dieterich, Erwin; Sorescu, Gheorge; Eigenberger, GerhartFundamental aspects and the current state of the art in simulating the dynamic and steady-state behavior of chemical engineering processes are discussed. The discretization of the spatial derivatives in the equations of change leads to a system of differential algebraic equations (DAE), consisting of ordinary differential equations in the time domain, and algebraic equations. The present paper discusses the necessary steps to solve the DAE, and mentions proven standard software for these steps as well as for the solution of the differential algebraic equations as a whole.Item Open Access Problems of mathematical modelling of industrial fixed-bed reactors(1986) Eigenberger, Gerhart; Ruppel, WilhelmModelling and computer simulation for the purpose of design and operation of industrial fixed-bed reactors are discussed with the aid of examples. Emphasis is laid upon difficulties and problems arising from aiming at an adequate model formulation. The following aspects are discussed in some detail: 1) The influence of heat and mass transport in the catalyst pellet, especially with complex reactions. 2) Relationships between radial heat transfer and radial flow profile and its influence upon the temperature profile in packed tubes with or without heat generation by reaction. 3) Problems of adequate modelling of catalyst activity changes during the course of operation. 4) Scale-up problem of multitubular fixed-bed reactors, i.e. the problem of achieving and maintaining the same operating conditions in and around all the tubes of the bundle.Item Open Access Fixed bed reactors(1992) Eigenberger, GerhartCatalytic fixed-bed reactors are the most important type of reactor for the synthesis of largescale basic chemicals and intermediates. In these reactors, the reaction takes place in the form of a heterogeneously catalyzed gas reaction on the surface of catalysts that are arranged as a socalled fixed bed in the reactor. In addition to the synthesis of valuable chemicals, fixed-bed reactors have been increasingly used in recent years to treat harmful and toxic substances. For example, the reaction chambers used to remove nitrogen oxides from power station flue gases constitute the largest type of fixed-bed reactors as regards reactor volume and throughput, while automobile exhaust purification represents by far the most widely employed application of fixed-bed reactors.Item Open Access Regelung eines instationär betriebenen Festbettreaktors mit Fuzzy-Kontrollregeln(1993) Nieken, Ulrich; Kolios, Gregorios; Eigenberger, GerhartKatalytiscbe Abluftreinigung in Reaktoren mit periodischer Strömungsumkehr erlaubt einen autothermen Betrieb bis zu niedrigen Schadstoffkonzentrationen. Bei höheren Schadstoffkonzentrationen ermöglicht ein Mittenabzug die vollständige Auskopplung der Verbrennungswärme. Aufgabe der Regelung ist es, den gezündeten Zustand bei geringen Rohgaskonzentrationen durch Zugabe von Stützgas aufrechtzuerhalten und bei höheren Konzentrationen Reaktionswärme in Form eines heißen Teilgassstromes zurückzugewinnen. Ein konventioneller Reglerentwurf gestaltet sich in diesem Fall als schwierig, da der Reaktor keinen definierten Arbeitspunkt besitzt, sondern nur im gezündeten Zustand gehalten werden muß, wobei er sich aufgrund der direkten Kopplung von chemischer Reaktion und Wärmetausch stark nichtlinear verhält. Aus diesem Grund werden die Methoden der Fuzzy-Regelung ausgewählt und an einem Reaktor im Labormaßstab erprobt. Im folgenden wird zunächst kurz auf das Prinzip der katalytischen Oxidation mit periodisch wechselnder Strömungsrichtung eingegangen, um die Wahl der Reglerein- und Ausgangsgrößen zu begründen. Anschließend werden der Aufbau des Fuzzy-Reglers skizziert und die erzielten Versuchsergebnisse diskutiert.Item Open Access Analyse von Stoffwechselprozessen mit der Fermentationskalorimetrie(1993) Meier-Schneiders, Martin; Grosshans, Ulrich; Busch, Claudia; Eigenberger, GerhartBiologische Aktivität ist mit der Freisetzung von Wärmeenergie verbunden. Die Wärmeproduktion ist dabei proportional zur gesamten Stoffwechselaktivität. Da Wärme kontinuierlich entsteht, eignet sie sich zur Nutzung als On-Iine-Signal. Kalorimetrische Methoden werden in den Biowissenschaften bereits seit Jahrzehnten verwendet. Fermentationskalorimetrie ist eine neu entwickelte Meßtechnik, die insbesondere für die kalorimetrische Vermessung biotechnisch relevanter Fermentationen im Labormaßstab gedacht ist.Item Open Access Kinetic instabilities in heterogeneously catalyzed reactions. Pt. 1, Rate multiplicity with Langmuir-type kinetics(1978) Eigenberger, GerhartThis paper is concerned with the occurrence of rate multiplicities (ignition-extinction phenomena). It is shown that rate multiplicity can be caused by the competing chemisorption of A and B upon the same active sites of the catalyst. Rate multiplicity can occur if at least one of the chemisorption or reaction steps is of second order. No rate multiplicity can be expected, if either A or B reacts via an Eley-Rideal type mechanism.Item Open Access Modellierung und numerische Simulation von G/L-Blasen-Strömungen(1994) Sokolichin, Alexander; Becker, Stefan; Eigenberger, GerhartIn den letzten Jahren zeigt sich ein Trend zu einer detaillierteren modellmäßigen Beschreibung der Hydrodynamik von Gas(G)/Liquid(L)-Reaktoren, wie z. B. Blasensäulen. Die genauere Erfassung der Hydrodynamik wird dabei als Voraussetzung für eine bessere Reaktorauslegung betrachtet. Wegen der Komplexität der Vorgänge scheint eine enge Kopplung von Experiment und Simulation erforderlich. Über erste Ergebnisse aus einem entsprechenden Forschungsprojekt wird nachstehend berichtet.