Combined Two-Model CFD Simulation of Trickle Bed Reactors with Head-Sump Extension: Case Study on Hydrodynamics and Biological Methanation

Abstract

Trickle bed reactors are one of the world's most employed technologies for multiphase processing, and they have been scrutinized for decades. However, accurate prediction and scale-up of trickle bed reactors are still challenging owing to complex interactions of multiphase flow, interfacial mass transfer, and reaction kinetics. The present computational model provides an insight into process phenomena on the basis of Eulerian−Eulerian methodology. It captures all parts of a trickle bed reactorpacking, head, and sumpwhich enables simulation of co-and countercurrent flow, gas or liquid recycle, and arbitrary retention time. Applying this model, hydrodynamic simulations reveal an improved prediction of liquid holdup, liquid dispersion, and pressure drop compared to CFD models of only the trickle bed. Furthermore, the interfacial surface area is analyzed and validated on account of a literature correlation. Exemplifying the entire approach with chemical absorption and reaction, the simulation of biological methanation presents methane concentration and productivity which are of the same order of magnitude as experimental data for an operating pressure of p op = 0.1−1 MPa abs .

Biological Methanation in an Anaerobic Biofilm Reactor—Trace Element and Mineral Requirements for Stable Operation

“…They reached stable methane concentrations >96% CH 4 at a gas retention time of 2.3 h. Lee, et al [29] also performed tests in a trickling bed reactor under mesophilic conditions using bottled gas and polyurethane sponge material as biofilm carriers. They thereby achieved CO 2 conversion rates of 71% at a gas retention time of 2 h and 100% at a retention time of 3.8 h. Voelklein, et al [30] performed in-situ and ex-situ tests and reached methane concentrations of 96% at gas retention times of 9.6 h in-situ and 6.5 h ex-situ. The required reactor size is thus reduced by approximately 50% in thermophilic operation compared to the mesophilic temperature range, but more heat and insulation are required for operation.…”

“…Based on the two-film theory, due to the low solubility of hydrogen (C) (approximately 1.5 mg/L, at 1 atm and 25 • C), the mass transfer (dC/dt) is mainly dependent on the volume-related phase interface (a) (Equation ( 3)), where k L is the mass transfer coefficient of the liquid phase and C* is the equilibrium concentration. The phase interface (a) cannot be determined for the bubble milieu and is combined with (k L ) to the volume-related mass transfer coefficient k L a. Voelklein, et al [30] described the hydrogen-to-liquid transfer as the bottleneck of the BM process.…”