83 Figure 5.3: Variations of friction pressure drop with liquid-liquid mixture Reynolds number (a) for 15% (v) paraffin liquid, (b) for 15% (v) kerosene. 126 Figure 7.3: Variations of droplet size with superficial liquid and gas velocities for 5% v of (a) paraffin liquid, (b) kerosene.
Multiphase Flow
Gas-liquid Two-phase Absorption, olefin polymerization in the gas phase Gas-solid Two-phase Coal gasification, catalytic cracking, reforming. Liquid-solid Two-phase ion exchange, electrode reactions, liquid-phase olefin polymerization, enzyme reactions, peptide synthesis.
Multiphase Reactor
This has given rise to several modified designs of the bubble column which have been found to be suitable for various industrial applications. Bubble column reactors have a wide range of industrial-scale applications due to the number of advantages compared to conventional ones in terms of design and operation. a) Cascade bubble column (b) Packed bubble column (c) Multiaxial bubble column (d) Multistage bubble column.
Cocurrent Downflow Column
The co-flow column is also suitable when a small amount of dispersed phase has to be brought into contact with a large amount of liquid. A wide range of flow rates for liquid and gas can be controlled in the co-current downflow column compared to other conventional columns (Majumder, 2016).
Applications of Downflow Column
In the steel industry, the transfer of liquid metal from one vessel to another is achieved by dipping molten steel through air (Kirchner, 1974). The system created tiny bubbles with a shear force created by immersing the jet in a receiving pool of liquid.
Origin of the proposed work
The immiscible liquids then separate immediately after mixing, based on the difference in density of the two liquids. In principle, each of the phases can be distributed in the other phases, if the volumetric flow rates of the two phases are relatively close.
Scope of the research work
Very often the dispersed phase is distributed at a higher volumetric flow rate, as this results in a larger mass transfer surface area. In packed columns, if the high viscosity dispersed phase were to wet the packing, the droplets would coalesce, reducing the mass transfer surface area.
Research Formulation
- Entrainment Characteristics
- Gas Holdup Characteristics
- Pressure Drop Characteristics
- Mixing Characteristics
- Extraction Efficiency
The details of the study on the gas supply in the ejector driven downflow column are described in Chapter 4. Pressure drop is one of the important parameters to determine the energy consumption in the multiphase unit.
Outline of the thesis
This work therefore aims to investigate the droplet size and its size distribution in the bottom column. The growing importance of the three-phase gas-liquid-liquid downflow column was mentioned in the previous chapter.
Experimental setup
- Ejector Assembly
- Extended column as a contactor
- Air-liquid-liquid Separator
- Conductivity meter
The constant area and variable area throats are commonly used in the design of the ejectors. In the present experiment rotameter R1 is used to maintain the volumetric flow rate of the water.
Fluid
A solenoid valve is an electric valve, commonly used to control the flow of fluid in a fluid flow system. Four solenoid valves (S1 - S4) were used in the present experimental setup for stopping liquid in the column.
Materials and their physical properties
To estimate the surface tension of a liquid-liquid mixture; water and dispersed liquid (paraffin or kerosene) were assumed to be in equilibrium with the immiscible phase. The total mole fractions yw and yd to be assigned to water and dispersed liquid are obtained from the material balance of the system.
Experimental procedure
- Measurement of gas and liquid entrainment
- Measurement of gas holdup and dispersed liquid holdup
- Measurement of pressure drop
- Residence time distribution (RTD) technique
- Calibration of conductivity meter
- Measurement of drop size
- Extraction efficiency and mass transfer coefficient
The liquid flowing from the separator through valves V4 and V5 is adjusted to maintain a constant liquid height in the column. e) The experimental data at a certain superficial gas and liquid velocity and dispersed liquid volume in the column were recorded at steady state. When the liquid level entered the diverging diffuser, it was found that the ejector was suddenly filled with the gas-liquid mixture, i.e. the ejector became flooded.
Introduction
Phase withdrawal and its dispersion are one of the critical design parameters for characterizing the hydrodynamics of gas-liquid-liquid flow in a column. In this chapter, based on an experimental study, the characteristics of liquid entrainment and its dispersion phenomena in a gas-liquid-liquid mixing column driven by a downward jet are explained.
Experimental setup and procedure
The amount of gas collected depends on the energy transfer through the liquid jet. The amount of dispersed liquid based on the total volume of the gas-liquid-liquid mixture was calculated by.
Results and discussion
- Entrainment mechanism
- Effect of gas and water jet velocities on gas entrainment
- Effect of volume fractions of dispersed liquid on gas entrainment
- Depth of penetration of plunging liquid jets
- Minimum entrainment velocity
- Minimum energy required for phase entrainment
- Efficiency of gas-liquid-liquid dispersion column
- Prediction of gas entrainment rate by developing a general correlation
The different successive phases of entrainment by the liquid jet, as shown in Figure 3.2 and Figure 3.3 (a) to. The penetration depths of the plunging liquid jet at different jet velocities are typically shown in Figure 3.7.
Conclusions
If the jet penetration depth increases, the entrainment rate and phase dispersion increase. In the previous chapter, the details of gas entrainment by liquid jet and subsequent dispersion into the liquid phase in the column were discussed.
Introduction
Models have been developed for the gas hold-up in terms of several dimensionless groups consisting of operating variables, which can be used to interpret the hold-up characteristics of the phases in the gas-liquid-liquid downflow contactor. The effects of superficial gas velocity on gas accumulation have been extensively investigated in various liquid-liquid and gas-liquid-liquid systems.
Theories to analyze the gas holdup by various models
Lockhart-Martinelli correlation model
Asai and Yoshizawa (1991) presented the experimental results of gas holdup in a three-phase air-water two-phase system and an air-water-kerosene three-phase system. The calculation of the average gas nuisance in the three-phase air-water-kerosene system is based on the G-L system relationship. 2007) presented an empirical expression for the prediction of the gas phase delay in a gas stirred sieve plate extraction column.
Drift-flux model
In the present work, the gas holding characteristics in the gas-liquid-liquid jet-driven downflow column are experimentally studied, which has not yet been reported in the literature with the gas-liquid-liquid three-phase system. To analyze the gas hold data using a drift flux model, the average gas velocity is plotted against the gas-liquid mixture velocity, which is given by the following equation as:
Slip velocity model
The correlation for Km with respect to physical properties of liquid and gas and geometrical variables is given by (Mandal et al., 2004).
Experimental setup and methodology
Uncertainty analysis
Results and discussion
Effect of gas and liquid jet velocity on gas holdup
Effect of dispersed liquid volume fractions on overall gas holdup
The deviation in overall holdup of gas at different volume fractions of the paraffin liquid and kerosene at a higher flow rate of gas is shown in fig. 4.4. It is seen that the total retention of gas increases with increasing gas flow rate.
Gas holdup analysis by different correlations and models
- Correlation model
- Analysis by Lockhart-Martinelli correlation
- Analysis by drift-flux model
- Interpretation of gas holdup by slip velocity model
It is seen that the correlation equation (4.19) fits well within the range of experimental conditions. The equality graph of the experimental values against the calculated values of Co according to equation (4.22) is presented in Figure 4.7.
Conclusions
In previous chapters, the characteristics of gas entrainment and gas holdup in the ejector-induced flow column have been reported. This chapter presents a systematic study on frictional pressure drop and total gas-liquid-liquid flow.
Introduction
They noted that the pressure drop is affected by the continuous and dispersed phase flow rate and pulsation intensity. The pressure drop study is used to clarify the distribution of phases in the column.
Theoretical background
Frictional pressure drop and friction factor
By substituting equations (5.2) and (5.7) into equation (5.1), the three-phase pressure drop due to friction can be expressed as,. Similarly, the pressure drop due to gas-liquid-liquid friction can be defined based on the surface velocity of the liquid.
Different models to analyze the frictional pressure drop
- Lockhart–Martinelli model
- Kato (1958) model
- Wallis (1969) model
- Gharat and Joshi (1992) model
The friction pressure drop of the single phase ∆ PfO for the height of hm of the column is. Wallis (1969) proposed the correlation of the phase multiplier, which is dependent on the flow quality (x) of the system.
Experimental setup and procedure
Experimental setup
Procedure
Results and discussion
- Variations of frictional pressure drop with different variables
- Effect of the gas holdup on the three-phase frictional pressure drop
- Effect of gas and liquid-liquid mixture Reynolds number on frictional pressure drop
- Effect of different dispersed liquid volume on frictional pressure drop
- Analysis of frictional pressure drop by different models
- Analysis by Lockhart Martinelli’s Model
- Analysis by Kato (1958) model
- Analysis by Wallis (1969) model
- Prediction of frictional pressure drop by developing a correlation
- Prediction of friction factor with dimensional analysis
The frictional pressure drop increases as the Reynolds number of the liquid-liquid and gas mixture increases. The variation of the frictional pressure drop with the volume of dispersed liquid (for paraffin liquid) is shown in Figure 5.5a.
Conclusion
In the previous chapters, the characteristics of a gas feed, entrainment and pressure drop in the jet driven downflow column were reported. This chapter deals with the investigations into mixing properties as well as the development of a model to analyze the intensity of mixing in the jet driven downflow column.
Introduction
Most of the previous literature for the study of mixing properties in the jet driven downflow column is shown for a two-phase and three-phase flow system. In the jet driven downflow column, the continuous liquid jet sucks the gas from the atmosphere into the column through the.
Experimental setup and procedure
Theory of estimation of the intensity of mixing
Thus Nd → 0 indicates negligible dispersion, hence plug flow while Nd → ∞ indicates large dispersion and hence mixed flow. The solution to the model based on open-open boundary condition can be expressed which is expressed as (Levenspiel, 1972).
Results and discussion
Effect of different variables on residence time distribution (RTD)
- Effect of gas and liquid flow rate
- Effect of dispersed liquid volume on RTD
Variation of tracer retention time with volume of dispersed liquid. At constant liquid and gas velocities, it is observed that the residence time of the tracer particles increases with the increase in the volume concentration of the dispersed liquid.
Effect of gas and liquid flow rate on mean residence time
With an increase in the surface velocity of the gas, the volume of the liquid-liquid mixture in the column decreases due to the increase in gas holding capacity, which reduces the average residence time. As the velocity of the superficial fluid increases, the momentum of the jet increases down the gas-liquid-liquid mixture, reducing the average residence time.
Effect of different variables on dispersion number
- Effect of gas and water flow rate on the dispersion number
- Effect of dispersed liquid volume on dispersion number
It is noted that the dispersion number increases with an increase in the volume of dispersed liquid. More droplets are formed with an increase in the volume of dispersed liquid, which increases the dispersion number.
Analysis of the degree of mixing based on flow resistance
Hydrostatic resistance and resistance due to retardation (Rh) can be calculated respectively from. From the present study, it can be seen that those coefficients depend on the volume fraction of the dispersed liquid which can be expressed as follows.
Mixing based on the velocity distribution model
Velocity distribution model
- Model equations
In the current gas-liquid-liquid down column, Equation (6.17) was used to analyze the dispersion coefficient of the dispersed liquid movement under the assumption of homogeneous flow in the column, uniform distribution of the dispersed liquid, and continuous liquid mixing. In a stable downstream system, the velocity at the center of the column is twice the average velocity (Majumder, 2016), which is expressed as.
Estimation of parameters D d and k
Based on these assumptions, the molecular dispersion in equation (6.17) is replaced by the dispersion coefficient due to the motion of the point si. 6.18) where Dd is the dispersion coefficient due to the movement of the point. The value of the characteristic factor of the velocity distribution (k) is calculated from the reciprocal of the product of the slope and the intercept.
Development of general correlation for axial dispersion coefficient
Equation (6.33) is found to predict the experimental values with a correlation coefficient of 0.97 and a standard error of 0.032.
Conclusions
The variation of the degree of dispersion is expressed based on the velocity dispersion model. The distribution coefficient is predicted from the velocity distribution model, as a function of the distribution coefficient due to the movement of droplet (Dd) and the characteristic velocity factor (k).
Introduction
The droplet size distribution and mean droplet diameter have been reported to affect mass transfer. The droplet size in the mixer is shown to depend on the residence time of the dispersed phase as well as the Weber number.
Experimental procedure
Mean drop size and interfacial area
In addition to all images, good quality images were analyzed by image processing software to obtain drop size. After the drop size and liquid hold-up were estimated, the interfacial area was calculated with equation (7.3).
Theory on the drop size distribution
The mean drop diameter was treated as the Sauter mean drop diameter (d32) (also known as the volume-area mean drop diameter), which was calculated by. Under the current experimental conditions, in order to measure the number density or droplet size distribution in each run, the droplet size was divided into ten classes.
Results and Discussion
Flow regime
Effect of liquid and gas flow rate on mean drop size
Similarly, the variation of droplet size with the superficial liquid velocity of the kerosene-water system is shown in Figure 7.3b at different gas velocities. It is also observed that at a higher volume fraction (35% v) kerosene, the droplet size shows the same behavior as in lower volume fraction (5% v), but the droplet size increases as the volume fraction increases, which is shown in Figure 7.4 b, 7.5b and 7.6b.
Effect of dispersed liquid volume fraction on drop size
Drop Size Distribution
Effect of gas and liquid flow rates on the drop size distribution
The drop size distribution curve shifted from 1.62 to 1.89 mm after an increase in the superficial liquid velocity of 1.05×10-. The droplet size distribution curve shifted from to 2.29 mm after an increase in the superficial liquid velocity of 1.05×10-1 m/s.
Effect of volume fraction of dispersed liquid on the drop size distribution
The droplet size distribution curve shifted to 2.0 mm after an increase in the paraffin liquid concentration of 25. The droplet size distribution curve shifted to 1.04 mm after an increase in the kerosene concentration of 25.
Analysis of drop size distribution
It is the logistic distribution well fitted to the experimental results with a minimal error in various operating variables. It is the logistic distribution well fitted to the experimental results with a minimal error in various operating variables.
Development of general empirical correlation for drop size
The values of droplet size from the experimental results and calculated from the above correlation are compared, and a parity diagram is presented in Figure 7.18. The overall percentage error in droplet size values from the experimental and correlation is found to be +10% and -9%.
Specific interfacial area
Effect of the specific interfacial area with gas and water flow rate
Interfacial area analysis by empirical correlation
A parity diagram is presented in Figure 7.21 to show the good fit with experimental data.
Conclusions
The effect of liquid and gas surface velocities on extraction efficiency and mass transfer coefficient are expressed. The generalized correlation model for extraction efficiency and mass transfer coefficient based on system properties is developed.
Introduction
In this chapter, the mass transfer characteristics of gas-liquid-liquid extraction are explained based on the actual experiment. In the present study, a jet driven flow column is used for gas-liquid-liquid extraction studies.
Literature review
The mass transfer performance is greatly affected in the column by the periodic coalescence and breakup of the droplets. The experimental results indicated that the mass transfer performance of the column increases with an increase in continuous phase velocity and a decrease in dispersed phase velocity.
Methodologies
Theory to estimate the extraction efficiency
A correlation for measuring overall mass transfer coefficient is developed that fits the experimental data well. The overall mass transfer coefficient based on the continuous phase was calculated using the following equation:.
Experimental setup and procedure
At the beginning of the experiment, a solution of constant propionic acid concentration in water was prepared for each run. The extraction in the current experiment is performed in one stage, meaning that the dispersed liquid is collected again for each run.
Results and discussion
- Effect of superficial gas and liquid velocity on extraction efficiency
- Effect of different solvent concentrations on extraction efficiency
- Comparison of extraction efficiency with different propionic acid concentrations
- Effect of gas and liquid flow rate on height of transfer unit (HTU)
- Effect of gas and liquid flow rate on mass transfer coefficient
- Effect of solvent volume fraction on mass transfer coefficient
The changes in extraction efficiency with different concentrations of propionic acid at a constant solvent volume fraction and gas velocity are shown in Figure 8.7a, b. As the volume fraction of the dispersed liquid increases by 25%, the mass transfer coefficient increases with the surface velocity of the liquid and gas, as shown in Figure 8.14.
Empirical correlation model for mass transfer coefficient
Extraction efficiency analysis by empirical correlation
Conclusions
Overall conclusions
Recommendations for future works
