CFD modeling of gas flow in porous medium and catalytic coupling reaction from carbon monoxide to diethyl oxalate in fixed-bed reactors

Computational Fluid Dynamics for Fixed Bed Reactor Design

Flow, heat, and mass transfer in fixed beds of catalyst particles are complex phenomena and, when combined with catalytic reactions, are multiscale in both time and space; therefore, advanced computational techniques are being applied to fixed bed modeling to an ever-greater extent. The fast-growing literature on the use of computational fluid dynamics (CFD) in fixed bed design reflects the rapid development of this subfield of reactor modeling. We identify recent trends and research directions in which successful methodology has been established, for example, in computer generation of packings of complex particles, and where more work is needed, for example, in the meshing of nonsphere packings and the simulation of industrial-size packed tubes. Development of fixed bed reactor models, by either using CFD directly or obtaining insight, closures, and parameters for engineering models from simulations, will increase confidence in using these methods for design along with, or instead of, expensive pilot-scale experiments.

CFD Simulation and Optimization of Gas-Solid Phase Temperature of Isothermal Acetylene Hydrogenation Reactor

Gas-solid coupled heat transfer in an industrial isothermal acetylene hydrogenation reactor was carried out using computational fluid dynamics (CFD). A two-temperature porous medium model was established by adding source terms to energy equations of the solid and gas phases. The combination of a genetic algorithm with CFD methods is applied to optimization of the kinetic and process parameters of the reaction. The model was validated by comparing the simulated results with those obtained from a one-temperature porous medium model, a two-temperature porous medium model, and industrial data. The optimal hydrogen-to-acetylene ratio and inlet temperature are 1.78 and 326K, respectively. The optimized ethylene yield increase and hydrogenation selectivity are 0.53 % and 0.18 % higher than the values before optimization, respectively. Finally, the effects of the hydrogen-to-acetylene ratio and inlet temperature on the increase in ethylene yield and hydrogenation selectivity are analyzed. Therefore, the hydrogen-to-acetylene ratio and inlet temperature should be reasonably controlled during production.

Mercury-free nitrogen-doped activated carbon catalyst: an efficient catalyst for the catalytic coupling reaction of acetylene and ethylene dichloride to synthesize the vinyl chloride monomer

The global “Minamata Convention on Mercury” came into effect in 2017 exerting huge environmental pressure on acetylene-based polyvinyl chloride (PVC) processes.

Combining catalysis and computational fluid dynamics towards improved process design for ethanol dehydration

Combining computational fluid dynamics with catalysis gives significant insights into reactor design for sustainable solid acid catalysed processes.

Study on Effective Radial Thermal Conductivity of Gas Flow through a Methanol Reactor

The heat conduction performance of the methanol synthesis reactor is significant for the development of large-scale methanol production. The present work has measured the temperature distribution in the fixed bed at air volumetric flow rate 2.4–7 m3 · h−1, inlet air temperature 160–200°C and heating tube temperature 210–270°C. The effective radial thermal conductivity and effective wall heat transfer coefficient were derived based on the steady-state measurements and the two-dimensional heat transfer model. A correlation was proposed based on the experimental data, which related well the Nusselt number and the effective radial thermal conductivity to the particle Reynolds number ranging from 59.2 to 175.8. The heat transfer model combined with the correlation was used to calculate the temperature profiles. A comparison with the predicated temperature and the measurements was illustrated and the results showed that the predication agreed very well with the experimental results. All the absolute values of the relative errors were less than 10%, and the model was verified by experiments. Comparing the correlations of both this work with previously published showed that there are considerable discrepancies among them due to different experimental conditions. The influence of the particle Reynolds number on the temperature distribution inside the bed was also discussed and it was shown that improving particle Reynolds number contributed to enhance heat transfer in the fixed bed.

Hydrodynamic instability of thermal fronts in reactive porous media: spinning patterns

The interaction of convection and reaction front propagation is known to exhibit a nonlinear phenomenons in the case of an adverse flow, i.e., when the gas velocity (V=[u,v]') and the front velocity (Vf) are of opposite directions. This was demonstrated both experimentally and analytically under isothermal conditions with Vf constant independent of V. Here we analyze thermal reaction front propagation in a porous medium in which an exothermic reaction of Arrhenius kinetics occurs. Numerical simulations of a packed-bed reactor model accounting for variable temperature, concentration, and hydrodynamic fields following the Euler-Darcy equations revealed emergence of spinning transversal patterns. Such solution cannot emerge in a two-variable (C,T) model, assuming "frozen" hydrodynamics, within a feasible domain of parameters. Two models are employed for analysis: a qualitative model based on a learning one-tube and two-tube consideration and an extended Landau-Darries instability analysis to account for the momentum losses and for a variable front propagation velocity. Both models revealed the important role of the Vf(u) dependence which can be presented as Vf=u-Vch, where the chemical component of the front velocity (Vch) depends on the main governing parameters such as the adiabatic temperature rise (ΔTa) and the inlet velocity (uin). The instability takes place if the parameter β=∂Vch/∂u<1. The effect of ΔTa, uin on the instability domain obtained in simulations can be translated to the effect of the parameter β.

A Two-Phase CFD Modeling Approach to Investigate the Flow Characteristics in Radial Flow Moving-Bed Reactors

Based on a complete CFD Eulerian–Eulerian two-fluid approach, a comprehensive three-dimensional (3D) two-phase reactor model was suggested to describe the flow behavior in radial flow moving-bed reactors (RFMBRs). A porous media model was incorporated into the reactor model in order to describe the flow resistance provided by the porous walls of the center and annular pipes. Compared with these previous reactor models, the reactor model considers the solid-phase movement instead of immobilization, which benefits for predicting the formation of cavity practically. The simulation results are agreement with the published experimental data. By employing the verified model, the flow field parameters in the reactors such as pressure drop and flow velocity were obtained. Besides, the simulations were then carried out to investigate the effect of the bed voidage on the flow behavior and to understand the phenomenon of cavity in the RFMBRs. The simulation results showed that both the centripetal and the centrifugal flow configurations have the inhomogeneous flow distribution and the phenomenon of cavity. Furthermore, the inhomogeneous distribution increases with the increase of the bed voidage, whereas the phenomenon of cavity is more obvious with the increase of gas inlet velocity. As a whole, this work provided a realistic modeling and a useful approach for the understanding of RFMBRs.

The role of carbonaceous deposits in the activity and stability of Ni-based catalysts applied in the dry reforming of methane

Highly stable Ni catalysts with varying Ni contents up to 50 mol% originating from hydrotalcite-like precursors were applied in the dry reforming of methane at 800 and 900 °C.

A nanostructured CeO2 promoted Pd/α-alumina diethyl oxalate catalyst with high activity and stability

A Pd–CeO₂/α-Al₂O₃ nanocatalyst was used as a catalyst for CO oxidative coupling to diethyl oxalate with the CO conversion significantly increased.