Heterogeneous Modeling Approach for Gas‐Limited Reactions in an Inclined Rotating Fixed Bed Reactor

2019 ◽  
Vol 91 (5) ◽  
pp. 637-644 ◽  
Author(s):  
Robert Timaeus ◽  
Uwe Hampel ◽  
Markus Schubert
Author(s):  
Armand Fopah Lele ◽  
Fréderic Kuznik ◽  
Holger Urs Rammelberg ◽  
Thomas Schmidt ◽  
Wolfgang K. L. Ruck

Heat storage systems using reversible chemical solid-fluid reactions to store and release thermal energy operates in charging and discharging phases. During last three decades, discussions on thermal decomposition of several salt-hydrates were done (experimentally and numerically) [1,2]. A mathematical model of heat and mass transfer in fixed bed reactor for heat storage is proposed based on a set of partial differential equations (PDEs). Beside the physical phenomena, the chemical reaction is considered via the balances or conservations of mass, extent conversion and energy in the reactor. These PDEs are numerically solved by means of the finite element method using Comsol Multiphysics 4.3a. The objective of this paper is to describe an adaptive modeling approach and establish a correct set of PDEs describing the physical system and appropriate parameters for simulating the thermal decomposition process. In this paper, kinetic behavior as stated by the ICTAC committee [3] to understand transport phenomena and reactions mechanism in gas and solid phases is taking into account using the generalized Prout-Tompkins equation with modifications based on thermal analysis experiments. The model is then applied to two thermochemical materials CaCl2 and MgCl2 with experimental activation energies and a comparison is made with TGA-DSC measurement results.


2020 ◽  
Author(s):  
Christopher Otto ◽  
Thomas Kempka

<p>In the present study, a pre-existing stoichiometric equilibrium model based on direct minimization of Gibbs free energy has been further developed and applied to estimate the equilibrium composition of synthesis gases produced by the gasification of carbon-rich feedstock (e.g., coal, municipal waste or biomass) in a fixed-bed reactor [1]. Our modeling approach is validated against thermodynamic models, laboratory gasification and demonstration-scale experiments reported in the literature. The simulated synthesis gas compositions have been found to be in good agreement under a wide range of different operating conditions. Consequently, the presented modeling approach enables an efficient quantification of synthesis gas compositions derived from feedstock gasification, considering varying feedstock and oxidizer compositions as well as pressures and temperatures. Furthermore, the developed model can be easily integrated with numerical flow and transport simulators to simulate reactive transport of a multi-componentgas phase.</p><p>[1] Otto and Kempka, Synthesis gas composition prediction for underground coal gasification using a thermochemical equilibrium modeling approach, Energies (in review)</p>


1995 ◽  
Vol 31 (9) ◽  
pp. 137-144 ◽  
Author(s):  
T. Miyahara ◽  
M. Takano ◽  
T. Noike

The relationship between the filter media and the behaviour of anaerobic bacteria was studied using anaerobic fixed-bed reactors. At an HRT of 48 hours, the number of suspended acidogenic bacteria was higher than those attached to the filter media. On the other hand, the number of attached methanogenic bacteria was more than ten times as higher than that of suspended ones. The numbers of suspended and deposited acidogenic and methanogenic bacteria in the reactor operated at an HRT of 3 hours were almost the same as those in the reactor operated at an HRT of 48 hours. Accumulation of attached bacteria was promoted by decreasing the HRT of the reactor. The number of acidogenic bacteria in the reactor packed sparsely with the filter media was higher than that in the closely packed reactor. The number of methanogenic bacteria in the sparsely packed reactor was lower than that in the closely packed reactor.


1999 ◽  
Vol 39 (4) ◽  
pp. 85-92 ◽  
Author(s):  
J. Behrendt

A mathematical model for nitrification in an aerated fixed bed reactor has been developed. This model is based on material balances in the bulk liquid, gas phase and in the biofilm area. The fixed bed is divided into a number of cells according to the reduced remixing behaviour. A fixed bed cell consists of 4 compartments: the support, the gas phase, the bulk liquid phase and the stagnant volume containing the biofilm. In the stagnant volume the biological transmutation of the ammonia is located. The transport phenomena are modelled with mass transfer formulations so that the balances could be formulated as an initial value problem. The results of the simulation and experiments are compared.


1985 ◽  
Vol 50 (10) ◽  
pp. 2122-2133 ◽  
Author(s):  
Jindřich Zahradník ◽  
Marie Fialová ◽  
Jan Škoda ◽  
Helena Škodová

An experimental study was carried out aimed at establishing a data base for an optimum design of a continuous flow fixed-bed reactor for biotransformation of ammonium fumarate to L-aspartic acid catalyzed by immobilized cells of the strain Escherichia alcalescens dispar group. The experimental program included studies of the effect of reactor geometry, catalytic particle size, and packed bed arrangement on reactor hydrodynamics and on the rate of substrate conversion. An expression for the effective reaction rate was derived including the effect of mass transfer and conditions of the safe conversion-data scale-up were defined. Suggestions for the design of a pilot plant reactor (100 t/year) were formulated and decisive design parameters of such reactor were estimated for several variants of problem formulation.


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