Numerical Simulation of Hydrodynamics in a Turbulent Contact Absorber: A Simplified Approach
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RESEARCH ARTICLE-CHEMICAL ENGINEERING
Numerical Simulation of Hydrodynamics in a Turbulent Contact Absorber: A Simplified Approach Muhammad Imran1 · Atta Ullah2 · Syed Waqas Ahmad1 · Haji Ghulam Qutab1 · Madsar Hameed1 Received: 30 January 2020 / Accepted: 28 April 2020 © King Fahd University of Petroleum & Minerals 2020
Abstract In the current work, hydrodynamics of a turbulent contact absorber (TCA) was studied in terms of bed pressure drop and expanded bed height by adopting a simplified modeling approach. The study was carried out computationally using the Eulerian multifluid model in ANSYS Fluent® where the packing was treated as a granular material. In order to simplify the complex three-phase system, it was reduced to a two-phase configuration by considering the solid packing and liquid water as a single phase with appropriate modifications. Both the laminar and turbulent viscous models were tested to study the bed characteristics at different values of liquid and gas flow rates. The covered range of liquid velocity was 0.004–0.012 m/s and that of gas velocity was 1.8–3.6 m/s. It was found that laminar model was able to produce better results as compared to turbulent one. The simulation results for pressure drop across the bed agreed well with the published experimental data. However, for a fixed gas velocity with variable liquid holdup, the bed expansion displayed a reverse trend as compared to experiments. Hence, the current model can be used to predict bed pressure drop of TCA-type systems, but not the expanded bed height. Keywords Hydrodynamics · TCA · Eulerian multifluid model · Pressure drop · Bed expansion · Computational fluid dynamics (CFD) List of Symbols 𝜀a Volume fraction 𝜌a Density, kg/m3 t Time, s va Velocity, m/s ∇P Pressure drop, Pa ∇ ⋅ 𝝉 𝐚 Stress tensor g Gravitational acceleration, m/s2 FD, Drag force, kg m/s2 KD, Momentum exchange coefficient CD Drag coefficient ds Diameter of solid ball (packing), m μ Viscosity, Pa s Re Reynolds number λ Bulk viscosity k𝜃s Kinetic energy dissipation * Muhammad Imran [email protected] 1
Department of Chemical & Polymer Engineering, University of Engineering & Technology Lahore, Faisalabad Campus, Faisalabad, Pakistan
Department of Chemical Engineering, Pakistan Institute of Engineering & Applied Sciences, Islamabad, Pakistan
2
𝜂 Dynamic viscosity, m2/s s Subscript for solid l Subscript for liquid g Subscript for gas
1 Introduction Turbulent contact absorber (TCA) is a high-efficiency mass transfer device with rigorous use in petroleum, petrochemical, biochemical and processing industries [1]. The device allows the gas and liquid phases moving counter-currently to interact in the presence of solid packing to provide enhanced contact surface area [2]. Due to the presence of three phases, the hydrodynamics gets complicated resulting in limitations of design and scale-up. Different regimes are observed which depend upon the variations in operating conditions. If the gas velocity is not enough to fluidize the bed, fixed bed
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