Mass transfer with chemical reaction in liquid foam reactors

Gas holdup, effective interfacial area and volumetric mass transfer coefficient were measured in two and three phase downflow bubble columns. The mass transfer data were obtained using the chemical method of sulfite oxidation, and the gas holdup was measured using the hydrostatic technique. Glass beads and Triton 114 were used to study the effects of solids and liquid surface tension on the gas holdup and the mass transfer parameters a and kL a . The gas holdup in three phase systems was measured for non-wettable (glass bead) and wettable (coal and shale particles) solids. The mass transfer data obtained in the downflow bubble column were compared with the values published for upflow bubble columns. The results indicate that in the range of superficial gas velocities (0.002-0.025) m/s investigated, the values of the mass transfer coefficient were of the same order of magnitude as those observed in upflow systems, but the values of interfacial area were at least two fold greater. Also, the results showed that the operating variables and the physical properties had different influences on a and kL a in the downflow bubble column. Correlations for a and kL a for the downflow bubble column are proposed which predict the data with adequate accuracy in the range of operating conditions investigated.

Mass transfer studies in shallow bubble column reactors

Measurement of local specific interfacial area in bubble columns via a non-isokinetic withdrawal method coupled to electro-optical detector

Gas holdup and gas-liquid mass transfer were investigated in a vertical baffled column. Pure carbon dioxide (C02) was used as the dispersed phase and tap water was used as the continuous phase. Gas holdup and mass transfer rate of C02 were measured under semi-batch condition, while the liquid phase was measured in batch mode. Gas holdup was estimated as the volume fraction of the gas in the two-phase mixture in the column. Mass transfer was expressed in terms of the liquid-side volumetric mass transfer coefficient (kLa). The effects of oscillation frequency, oscillation amplitude and gas flow rate on gas holdup andmass transfer were also determined. The results showed that a significant increase in gas holdup and mass transfer could be achieved in an oscillatory baffled column compared to a bubble column. Gas holdup and mass transfer were correlated as a function of power density and superficial gas velocity. Keywords: gas holdup, mass transfer coefficient, power density, superficial gas velocity

Gas-solid flow behavior and heat transfer in a spiral-based reactor for calcium-based thermochemical energy storage

Multi-scale analysis of the influence of physicochemical parameters on the hydrodynamic and gas–liquid mass transfer in gas/liquid/solid reactors

The solid-solid mass transfer performance of an external-loop airlift reactor was measured by dissolution of benzoic acid coated on nylon-6 particles, and the hydrodynamics of the gas-liquid-solid multiphase system in the airlift reactor were investigated. The solid-liquid system was designed to simulate the micro-carrier culture of animal cells, and some typical suspensions of immobilized enzyme particles. The solid-liquid mass transfer coefficient remained constant below a superficial air velocity of 0.04 ms−1 for the particles examined, but increased rapidly with further increase in gas velocity. Solids loading (0.3-3.5% w/w) did not affect the mass transfer coefficient in turbulent flow. The mass transfer coefficient was correlated with energy dissipation rate in the airlift reactor. The mass transfer coefficient in stirred vessels, bubble columns, fluidized beds, and airlift reactors was compared. Over an energy dissipation Reynolds number of 4-400, the solid-liquid mass transfer coefficient...

Bubble size distribution and gas–liquid mass transfer in airlift contactors

New systems and methods for the measurement of effective interfacial area and mass transfer coefficients in gas—liquid contactors

Effect of the radical scavenger t-butanol on gas–liquid mass transfer

Gas absorption in aqueous solutions with Tween 80 and absorption processes based on hydrodynamics and mass transfer is determined. The impact of surfactant concentration on gas holdup and gas‐liquid interfacial area is analyzed, observing an increase of these parameters with surfactant concentration. The influence of liquid‐phase contamination on the absorption process is investigated on the basis of the liquid‐film mass transfer coefficient, removing the effect caused by the presence of a surfactant and the gas flow rate on the interfacial area and, thereby, on the volumetric mass transfer coefficient. The opposite effect on the mass transfer coefficient can be observed which decreases in the presence of the surfactant.

This investigation reports on the experimental and theoretical investigation carried out to evaluate the bubble diameter and effective interfacial area in a novel Hybrid Rotating and Reciprocating Perforated Plate Bubble Column. Air-water system is used in this investigation. Countercurrent mode is employed. The effects of agitation level, superficial gas velocity and superficial liquid velocity on the bubble size distribution are studied. The mean bubble diameter is predicted using photographic technique. A simple correlation is developed for the determination of mean bubble diameter. It is found that the mean bubble diameter values for hybrid column are 1.8 to 2.5 times smaller when compared with conventional reciprocating plate column. The interfacial area is calculated based on the experimental results of the gas holdup and bubble diameter. Effects of agitation level, superficial gas velocity, superficial liquid velocity and plate free area on the interfacial area have been investigated. Correlations are developed for the determination of interfacial area for both mixer-settler and emulsion regions. It could be noted that the interfacial area for the hybrid column is 3 to 6 times higher in both mixer-settler region and emulsion region than that of conventional reciprocating plate column which is quite large.

The hydrodynamic characteristics, mass transfer, and mixing performance of three different reactors, a bubble column reactor (BCR), a single-stage internal-loop airlift reactor (SSALR), and a four-stage internal-loop airlift reactor (FSALR), were investigated systematically through cold model experiments to explore the influence of draft tube configurations on the pilot-scale internal-loop airlift reactor (ILAR). The findings indicated that the BCR yielded a higher gas holdup and mass transfer coefficient due to its longer bubble residence time. Segmenting the draft tube improved the gas holdup in both the riser and downcomer, and the overall gas holdup in the downcomer increased by 9%. Compared with the SSALR, the mass transfer coefficient of the FSALR in the riser and downcomer increased by 10.2% and 9.3% on average, respectively. In addition, a higher liquid circulating velocity was obtained with the ILARs due to a higher gas holdup difference between the riser and the downcomer. Specifically, the liquid circulating velocity of the FSALR was 134.1% higher than that of the BCR and 15.8% higher than that of the SSALR. The mixing time of the ILARs was reduced due to more intense overall circulation. The mixing effect of the FSALR was the best. The mixing time was reduced by 70.2% and 51.3% compared with the BCR and SSALR for UG ranging from 4.0 cm/s to 9.1 cm/s, respectively. Empirical correlations were proposed for the gas holdup, liquid circulating velocity, mass transfer coefficient, and mixing time on the superficial gas velocity, and agreement with experimental data was satisfactory.

CFD-PBM simulations on hydrodynamics and gas-liquid mass transfer in a gas-liquid-solid circulating fluidized bed

The influences of aliphatic alcohols (CnH2n+1OH, n = 1–4) and their concentrations (0–1 vol.‐%) on gas holdup, liquid circulation velocity, mixing time, and overall volumetric gas‐liquid oxygen mass transfer coefficient were considered in a split‐cylinder airlift reactor sparged with air. The carbon chain length of the alcohols and their concentration affect the airlift reactor performance. Alcohols reduced the average bubble sizes and increased the gas holdup, the interfacial area for mass transfer, and the gas‐liquid mass transfer coefficient. Since butanol has the most carbon atoms in its chain, it had the most significant effect on gas holdup and mass transfer enhancement. It also decreased the liquid circulation velocity by surface tension reduction. Two correlations based on dimensionless groups were applied to investigate the effect of hydrodynamics and molecules on gas holdup and mass transfer. A satisfactory agreement between correlation and experimental results was observed.