Gas–liquid mixing in dual agitated vessels in the heterogeneous regime

Abstract

Gas-liquid multi-phase processes are widely used for reactions such as oxidation and hydrogenation. There is a trend for such processes to increase the productivity of the reactions, one method of which is to increase the gas flow rate into the vessel. This means that it is important to understand how these reactors perform as high gas flow rates occurs well into the heterogeneous regime. This paper investigates the mixing performance for the dual axial radial agitated vessel of 0.61 m in diameter. 6 blade disk turbine (Rushton turbine) below a 6 Mixed flow Up-pumping and down-pumping have been studied at very high superficial gas velocities to understand the flow regimes operating at industrial conditions. Electrical Resistance Tomography have been used to produce the 3D images using Matlab, along with analysing the mixing parameters such as Power characteristics, gas holdup and dynamic gas disengagement. Minimal difference between the two configurations have been reported in terms of gas holdup , however with the choice of upward and downward pumping impeller power characteristics show significant difference at very high gas flow rates. Also at these high superficial gas velocities, this report introduces a 3rd bubble class, as seen in dynamic gas disengagement experiments, which corresponds to very large slugs of gas. Highlights  At high gas flow rates, a maximum holdup is observed  Power for 6MFD/6MFU problematic at high gas flow rates  The gas liquid holdup results show minimal difference between the two configurations  Large slugs observed as a third bubble classes at very high gas flow rates Keywords Gas-liquid mixing; Gas HoldUp ; Gassed Power; Heterogeneous regime; Axial-radial dual system; Electrical Resistance Tomography V Volume [m 3 ] Volume of dispersion [m 3 ] Volume of liquid [m 3 ] Volume of gas [m 3 ] Superficial gas velocity [m s-1 Greek symbols Gas Holdup [%] Specific total energy input per liquid mass [W kg-1 ] Σ Conductivity (normalised) [mS cm-1 ] Density of fluid [kg m 3 ] Dimensionless numbers

Use of acoustic emission in combination with machine learning: monitoring of gas–liquid mixing in stirred tanks

“…Existing measurement techniques for identifying the different regimes are multiple, including optical (Yawalkar et al 2002), level probes (Gao et al 2001), ultrasonics (Cents et al 2005) and tomography [Electrical Resistance ERT (Forte et al 2019;Jamshed et al 2018), X-ray (Ford et al 2008), γ-ray (Veera et al 2001)], but are often limited by practical considerations (invasiveness, retrofitting, opacity, safety) and cost issues. The mentioned systems all require high investment cost in terms of devices and operations.…”

Measuring gas hold‐up in gas–liquid/gas–solid–liquid stirred tanks with an electrical resistance tomography linear probe

“…where σ c is the conductivity of the continuous phase and σ m is the conductivity of the biphasic mixture. An alternative approach was proposed by Montante and Paglianti 49 and applied extensively by Jamshed et al, 50 which used a dimensionless conductivity ε (ε = 100…”

“…where σ c is the conductivity of the continuous phase and σ m is the conductivity of the biphasic mixture. An alternative approach was proposed by Montante and Paglianti and applied extensively by Jamshed et al, which used a dimensionless conductivity ε ( ε = 100(1 − σ m / σ c )) proportional to the gas hold‐up to describe sparging performance of different impellers; however, the authors indicate this parameter as proportional to the gas hold‐up and not as an absolute value. Furthermore, in the investigated range of gas hold‐up (approximately 1–15%), the simplification used by Montante and Paglianti can be considered proportional (with a factor of approximately 0.7) to the Maxwell's equation.…”

Gas Dispersion in Non-Newtonian Fluids with Mechanically Agitated Systems: A Review

“…For gas-liquid mixing, for example, high mass transfer coefficients can be achieved when employing sparged agitated vessels [6]. Hence, many studies have investigated these mixing systems, especially with regard to gas dispersion in Newtonian fluids [7][8][9][10]. Although fewer studies refer to the aeration of non-Newtonian fluids, a broad range of industrial applicability can still be observed in food, chemical, biochemical, pulp and paper, and painting industries [11].…”