Mixing Characteristics of External Loop Airlift Bioreactor using Electrical Resistance Tomography

In the present work, a novel packed bed external loop pneumatically agitated airlift bioreactor with an internal gas distributor (perforated plate) between two rolls of packing in the riser was designed and built. This novel approach combines advantages of packed bed and external loop airlift bioreactors. The main objective of this research work was to characterize the hydrodynamic performance of this novel reactor through a non-intrusive flow visualization technique called electrical resistance tomography (ERT). The tomography images, which were generated using a linear back projection algorithm, were employed to explore the effects of different design parameters and operating conditions. These include the effect of the two packing in the riser and the internal gas distributor (perforated plate) installed between the two packing. Other parameters investigated include the effect of sparger configuration, gas flow rate, and liquid height in the bioreactor on the different hydrodynamic parameters such as gas holdup, mixing time, and liquid circulation velocity. Results showed that the gas holdup and mixing time increased in the presence of the gas distributor, while the riser superficial liquid velocity was decreased. Furthermore, gas holdup and mixing time increased, superficial liquid velocity decreased when decreasing liquid height in the reactor, and when using packing or gas distributor between two packings in the riser. These results can be used to improve mixing characteristics in external loop airlift bioreactors for wider range of applications.

Mixing Characteristics of External Loop Airlift Bioreactor using Electrical Resistance Tomography

In the present work, a novel packed bed external loop pneumatically agitated airlift bioreactor with an internal gas distributor (perforated plate) between two rolls of packing in the riser was designed and built. This novel approach combines advantages of packed bed and external loop airlift bioreactors. The main objective of this research work was to characterize the hydrodynamic performance of this novel reactor through a non-intrusive flow visualization technique called electrical resistance tomography (ERT). The tomography images, which were generated using a linear back projection algorithm, were employed to explore the effects of different design parameters and operating conditions. These include the effect of the two packing in the riser and the internal gas distributor (perforated plate) installed between the two packing. Other parameters investigated include the effect of sparger configuration, gas flow rate, and liquid height in the bioreactor on the different hydrodynamic parameters such as gas holdup, mixing time, and liquid circulation velocity. Results showed that the gas holdup and mixing time increased in the presence of the gas distributor, while the riser superficial liquid velocity was decreased. Furthermore, gas holdup and mixing time increased, superficial liquid velocity decreased when decreasing liquid height in the reactor, and when using packing or gas distributor between two packings in the riser. These results can be used to improve mixing characteristics in external loop airlift bioreactors for wider range of applications.

Numerical simulation of the gas-liquid flow inside a horizontal static mixer

The gas-liquid flow inside a horizontal static mixer was numerically investigated by using Euler-Euler Computational Fluid Dynamics (CFD) simulations. The results confirm that the liquid superficial velocity plays a significant role on the mixing behavior of the gas and liquid. The mixing behavior in this present study at a liquid superficial velocity of 0.2 m/s was the worst both axially and radially. Increasing the liquid superficial velocity significantly improve the mixing between gas and liquid. However, the unwanted gas layer still can be found at the superficial liquid velocity less than 0.8 m/s. A good mixing behavior in this study was achieved at a relatively high velocity (i.e. larger than 0.8 m/s).

Hydrodynamics Modeling of an LSCFB Reactor Using Multigene Genetic Programming Approach: Effect of Particles Size and Shape

The multigene genetic programming (MGGP) technique based hydrodynamics models were developed to predict the solids holdups of a liquid-solid circulating fluidized bed (LSCFB) riser. Four different particles were considered to investigate the effects of particle size, shape and density on hydrodynamics behavior of the LSCFB riser. In this regard, two spherical shape glass bead particles (500 and 1200 μm), two irregular shape lava rock particles (500 and 920 μm) were employed as solid phase and water as liquid phase. The MGGP models were developed, relating the solids holdup (${\varepsilon _s}$, output parameter) with eight input parameters. The developed models were first validated by comparing the model predicted and experimental data of solids holdups. The average solids holdups decreased with the increase of net superficial liquid velocity (${U_l} - {U_t}$) and normalized superficial liquid velocity$\left( {\frac{{{U_l}}}{{{U_t}}}} \right)$. Uniform axial solids holdups observed in axial locations (H) except close to the liquid-solid distributor of the riser. The radial non-uniformity of solids holdup observed all radial positions (r/R). In the central region almost flat but increased toward the wall region. The radial profiles of the solid holdup are approximately identical at a fixed average cross-sectional solid holdup for all of the three LSCFB systems of this study. The statistical performance indicators such as the mean absolute percentage error and correlation coefficient are also found to be within acceptable range. All these findings of suggest that the MGGP modeling approach is suitable for predicting effect of particle size and shape on hydrodynamics behavior of the LSCFB system

Effects of Liquid Velocity on Pressure Gradient, Slip and Interfacial Friction Factor in Annular Flow in Horizontal Pipe

Experimental investigations on annular flow behaviour in two-phase (air/water) flow in horizontal pipe were conducted using 2-inch (0.0504m) with a total length of 28.68m closed loop system. The emphasis from the experiments were on pressure gradient, slip and interfacial friction factor in annular flow. For interfacial friction factor, the entrainment, gas quality, the droplets and slip mixture density values were obtained through the experimental results which were substituted to determine it. In all, effects of liquid velocity were felt, as increase in superficial liquid velocity, increases the interfacial friction factor and pressure gradient in annular flow in horizontal pipes. More so, increase in superficial gas velocity, reduces the interfacial friction factor. Thus, interfacial friction factor decreases with increases in superficial gas velocity, while the pressure gradient increases with increase in superficial liquid velocity. The lower the superficial liquid velocity, the higher the slip but the lower the pressure gradient. Likewise, the lower the superficial liquid velocity, the more ripple waves obtained while the higher the superficial liquid velocity, the more disturbance waves in annular flow in horizontal pipe from the experiments.

Foam Breakup in CFC/GLCC© System

Foaming is a common phenomenon in the petroleum industry. Foams can be desirable for drilling applications, whereby the cutting bits are lubricated, and cuttings are carried up to the surface. However, foam can be undesirable for production operation, which hinders the gas-liquid separation process. Experimental investigation has been conducted on foam break-up in a standalone Churn Flow Coalescer (CFC), a standalone Gas Liquid Cylindrical Cyclone (GLCC©) and a combined CFC/GLCC© system. A 1-inch Foam Characterization Rig (FCR) is utilized. The FCR is equipped with a 3-inch diameter CFC, which is connected in series to a 2-inch diameter GLCC©. A total of 30 experimental runs are conducted for both Gas Mode (GM) and Liquid Mode (LM) operations. A surfactant (SI-403) with concentration of 0.025%, superficial liquid velocities of 0.1 and 0.15 m/s and superficial gas velocities of 0.5, 1, and 1.5 m/s are used in the experiments. The experimental results show that for the GM operation, the foam break-up in combined CFC/GLCC© system is more efficient than that in the standalone GLCC©, for the same flow conditions. Lowering the superficial gas velocity or increasing the superficial liquid velocity produce less stable foam, larger gas bubbles and lower half-life time. The outlet clear liquid flow rate (with no foam) under the LM operation increases with increasing superficial liquid velocity or decreasing superficial gas velocity. The recommended operational conditions for the CFC are at low superficial gas velocities, lower than the transition boundary to churn flow in the CFC.

Analysis of Two-Phase Stratified Flow and Liquid Hold Up at Dead Ends of T-Sectioned Natural Gas Pipelines

T-sectioned configurations with a deadleg at the stopple are present in natural gas pipelines, where liquid water may accumulate, increasing the potential for internal corrosion. The objectives of the present study are to explore the pipeline operating conditions under which water enters the deadleg and define an operating protocol to prevent water accumulation in deadlegs. A combined computational fluid dynamics (CFD) experimental and analytical study was conducted to understand the behavior of liquid slugs at the T-junctions with dead ends. The flow equations were solved as an unsteady multiphase (gas and water) incompressible flow problem using the Volume of Fluid (VoF) Method. The analytical calculations were based on a modified form of the macroscopic mechanical energy balance equation. In order to computationally simulate the critical velocity at which water enters the deadleg, the inlet gas flow rate was specified to be a fixed value, while the water flow rate was gradually increased. The liquid entirely bypasses the deadleg until the liquid water velocity exceeds a critical value, which was noted as the critical superficial liquid velocity. The experimental study was conducted using a flow loop to understand the behavior of liquid water at the T-junction and determine the condition when liquid enters the deadleg. The analytical and computed solutions were compared with experimental observations. The computed results follow the same pattern as the experimental and analytical data. Solutions indicate that critical superficial liquid velocity is linearly dependent on superficial inlet gas velocity.

Effects of Liquid Viscosity on the Wave Velocity and Wave Frequency in Horizontal Annular Flow

An investigation on the liquid holdup, wave velocity, and wave frequency in horizontal annular flow has been experimentally conducted through the measurement of liquid holdup using constant electric current method (CECM) sensors. To investigate the effect of viscosity, water and glycerin were used as working liquid, using superficial liquid velocity and superficial gas velocity of 0.05 to 0.2 m/s and 12 to 40 m/s, respectively. Liquids with higher viscosity give the higher liquid holdup, lower wave velocity, and lower wave frequency. Correlations for liquid holdup and mean film thickness, wave velocity, and wave frequency have been developed with mean average errors (MAE) of 13.5%, 9.2%, and 8.6%, respectively.

Abatement efficiency and controlling strategy of a cylindrical and a conical fluidized bed flocculator

The aggregation efficiency of colloidal kaolin particles by the turbulence caused by random movement of silica gel beads in a cylindrical (CFB) and an 8° conical fluidized bed (TFB) was studied in this paper, focusing on the control strategies of these novel processes. The abatement efficiencies as a function of the Camp number, velocity gradient (G) and flocculation time (T) were exploited. In general, the abatement efficiency tended to be improved with the increase of Camp number (in the study range of this work: Camp number lower than 8058 and 5639 in CFB and TFB, respectively). However, the efficiency was relatively low and sensitive to the Camp number as G was more than 186 s−1 in CFB and 178 s−1 in TFB, respectively. Whereas, increasing flocculation time clearly contributed to the improvement of the abatement efficiency, which is considered to be an effective strategy to enhance the treatment ability. Velocity gradient and flocculation time could be controlled by means of superficial liquid velocity and properties of packing particles. It should be noted that the backmixing in the TFB caused formed flocs to break and thus lower abatement efficiencies were found in the TFB than those in the CFB.