Enhancement in gas holdup in bubble columns through use of vibrating internals

Including internals in bubble columns is known to enhance the gas holdup. In this paper, a method to achieve this objective substantially has been proposed via the use of vibrating helical spring internals. Experimental observations on effect of vibrating internals such as vibrating helical springs on gas holdup in bubble columns are presented. Effects of superficial gas velocity, H/D ratio (height of the static liquid to column diameter ratio), volume fraction of helical springs, and thickness of the helical spring wires on hydrodynamics parameters are studied. Increase in gas holdup up to 135% is observed by using vibrating helical spring internals in bubble columns compared to bubble columns without internals. This method offers a simple, cost‐effective, and easy way to enhance gas holdup even at high gas fluxes. It has been reported that this enhancement stems from the fact that the vibrating springs breakup the gas into fine bubbles, which effectively reduces their rise velocity and enhances their average residence time in the liquid column.     

Multiphase hydrodynamics and distribution characteristics in a monolith bed measured by optical fiber probe

The optical fiber probe has been for the first time applied to investigate the hydrodynamics and gas‐phase distribution at high gas/liquid ratios in a two‐phase flow monolith bed with 0.048 m diameter and 400 cpsi. Local hydrodynamic parameters including gas holdup, bubble frequency, bubble velocity, and bubble length in single channels were measured by 16 inserted single‐point optical fiber probes within the bed under a nozzle as the liquid distributor. The following findings are reported. (1) The optical fiber probe can be used as an efficient and convenient technique for measuring local hydrodynamic parameters inside the channels of a monolith bed; (2) within the range of high gas/liquid ratios under which experiments were conducted, churn flow regime occurred. In this regime, the monolith bed radial distribution of gas holdup, bubble frequency, bubble velocity, and bubble length is nonuniform in nature. © 2013 American Institute of Chemical Engineers AIChE J 60: 740–748, 2014     

Studies on Regime Transition,Operating Range and System Stability in a Liquid‐Solid Circulating Fluidized Bed

In the present work, the variations in the solids circulation rate and solids holdup were analyzed to study the behavior of a liquid‐solid circulating fluidized‐bed (LSCFB) regime. The results confirm the existence of two regions in the regime of LSCFB. A new concept of critical liquid velocity, j_lc, is proposed in the present work for demarcation between region 1 and region 2, which is found to be a constant value of about 1.3 u_t for all particles considered. The operating range of the LSCFB regime is obtained for the various particles and a correlation is developed from the data to estimate the maximum total liquid velocity. The predicted maximum liquid velocity was compared with the experimental values and found to be in good agreement within ±9 %. The effects of total liquid velocity, particle size and density on the stable operating range are discussed. Analysis of the experimental results shows that stable operation prevails both in region 1 and region 2.     

Liquid holdup in concentric annuli during cocurrent gas‐liquid upflow

In the recent paper, an in‐depth investigation of liquid holdup during air‐water upflow through concentric annuli has been reported. The liquid holdup has been determined experimentally for the bubbly, slug and churn flow regimes. The drift flux model has been adopted for the theoretical estimation of holdup in the bubbly, dispersed bubbly and slug flow regimes. The pronounced effect of flow regime on this parameter as observed from experiments has been incorporated in the model by adopting different values of U₀, n and C₀. The asymmetry of the Taylor bubbles has been incorporated in the slug flow regime. The theoretical predictions exhibit a good agreement with the experimental data of the present work and that available in literature (Caetano et al., 1989b). The Hughmark's correlation is observed to correlate the churn flow data of the present work reasonably well.     

滴流床反应器内脉冲流下动持液量实验

对气液强相互作用下滴流床反应器内的流体动力学进行了分析讨论 .实验测定了脉冲流流型下的床层平均动持液量 .考察了气液流率、液体黏度、填料材料等因素对动持液量的影响 .根据对滴流床反应器内流体流动机理的分析及实验结果 ,提出了关联脉冲流型式下动持液量的关联式 .该关联式能很好地关联实验数据 ,可用于预测温和型脉冲流下的动持液量     

Hydrodynamics of gas-liquid counter-current flow in solid foam packings

Solid foam materials combine high voidage and high surface area. These two properties are advantageous for use in chemical reactors due to the low frictional pressure drop and relatively high surface area that may be used for catalyst deposition. Hydrodynamic parameters such as liquid holdup, pressure drop, and flow regimes similar to those for packed beds, have been obtained for the gas and liquid flows through these solid foam packings. The open-celled solid foam packings used were in the range of 5-40 pores per linear inch (ppi). The regimes studied are two high liquid holdup regimes and a low liquid holdup regime (trickle flow regime). Also the flooding points for counter-current flow have been determined.     

Impact of gravity on the bubble‐to‐pulse transition in packed beds

A model based on two‐phase volume‐averaged equations of motion is proposed to examine the gravity dependence of the bubble‐to‐pulse transition in gas‐liquid cocurrent down‐flow through packed beds. As input, the model uses experimental correlations for the frictional pressure drop under both normal gravity conditions and in the limit of vanishing gravity, as well as correlations for the liquid‐gas interfacial area per unit volume of bed in normal gravity. In accordance with experimental observations, the model shows that, for a given liquid flow, the transition to the pulse regime occurs at lower gas‐flow rates as the gravity level or the Bond number is decreased. Predicted transition boundaries agree reasonably well with observations under both reduced and normal gravity. The model also predicts a decrease in frictional pressure drop and an increase in total liquid holdup with decreasing gravity levels. © 2013 American Institute of Chemical Engineers AIChE J 60: 778–793, 2014     

Hydrodynamics and mass transfer in a bubble column with an organic liquid

Hydrodynamic and mass transfer data in Soltrol-130 (a mixture of C₉+ iso-paraffins) were measured in a 0.305 m diameter bubble column. The gas holdup structure (i.e., the contributions to holdup from the small and large bubble fractions of the dispersion) for this hydrocarbon liquid in the churn turbulent flow regime was analyzed using the dynamic gas disengagement technique. The validity of the assumption of axially uniform gas holdup structure was checked. Literature correlations were found inadequate to explain the observed gas holdup and the volumetric mass transfer coefficients for Soltrol-130. The volumetric mass transfer coefficient per unit volume of large bubbles is shown to be independent of superficial gas velocity for the fully developed churn turbulent regime. The present hydrodynamic and mass transfer data in the churn turbulent regime should be useful in the design and scale-up of bubble columns used in organic process industries.     

The role of gas phase momentum in determining gas holdup and hydrodynamic flow regimes in bubble column operations

Experiments conducted in 0.15 m diameter bubble columns using water and non-aqueous liquids have shown that the gas velocity at which transition from the bubbly flow to the churn-turbulent flow regime occurs is a function of gas density. The transition velocity increased with increasing gas density. The direct effect of gas density on gas holdup in the bubbly flow regime is small with only a slight increase in holdup being observed at higher densities (?_G α ρ_g ^0.04). In the churnturbulent region a much greater effect of gas density on gas holdup was observed. These differences were found to be a direct function of the differences in holdup values at the transition points. Gas holdup was found to be a function of the gas phase momentum. In the bubbly flow regime holdup was directly proportional to momentum while in the churn-turbulent regime holdup was proportional to momentum to the one third power. Reasons for this behaviour are discussed, as well as the implied effects on liquid mixing in bubble column slurry reactors. The effects of gas density may offer an explanation for some apparently anomalous published results.     

Effects of viscosity and relaxation time on the hydrodynamics of gas–liquid systems

Effects of liquid properties on the hydrodynamics of gas–liquid systems were investigated in lab-scale bubble column (BC) and internal loop airlift (ILA). Alginate solutions, a glycerol solution and a Boger fluid were adopted to separately address the effects of viscosity and of surface tension for Newtonian fluids, and the effects of relaxation time for non-Newtonian fluid characterized by approximately constant viscosity (low shear thinning). Hydrodynamic regimes were characterized in terms of overall gas holdup, gas–liquid mass transfer coefficient, drift-flux and liquid circulation velocity. The superficial gas velocities at the transition between hydrodynamic regimes (homogenous regime–vortical-spiral regime–heterogeneous regime) as a function the liquid viscosity was characterized by a maximum. The same behavior was observed for the maximum stable gas holdup and gas–liquid mass transfer coefficient in BC. Viscosity enhances homogeneous regime stability for μ<4.25 mPa s, in BC, and μ<7.68 mPa s, in ILA. For non-Newtonian fluids the transition velocity increases with liquid elasticity. The stabilization mechanism related to the relaxation time of Boger fluids has been discussed.     

EFFECT OF OPERATING CONDITIONS ON GAS HOLDUP IN SLURRY BUBBLE COLUMNS WITH A FOAMING LIQUID

This work presents experimental data on gas holdup in slurry bubble columns with a foaming liquid. The effects of solids concentration, solid particle size, superficial phase velocities and column dimensions on the gas holdup are analyzed. At low superficial gas velocities (less than 4cm/s), for which the liquid does not foam, the presence of solids with small particle size does not affect the gas holdup whereas solids with large particle size induce foam formation and thus their presence increases the gas holdup. In the foaming regime, an increase of solids concentration decreases the gas holdup. The operating mode has a strong effect on the gas holdup: the semi-batch operating mode (stagnant liquid-solid suspension) increases the ability of the liquid to foam with respect to the continuous mode. Regarding the effect of column dimensions, the results presented show that the height of the bubble column does not affect at an appreciable extent the gas holdup in the range 6 < LID < 12. At high gas velocities (greater than 6 cm/s) the gas holdups obtained in a 30 cm-internal diameter column are the same as those measured in a 10 cm-internal diameter column.     

A new mechanistic model to predict gas–liquid interface shape of gas–liquid flow through pipes with low liquid loading

Devising a new mechanistic method to predict gas–liquid interface shape in horizontal pipes is concerned in this article. An experiment was conducted to find the pressure gradients of air–water flow through a 1‐in. pipe diameter. Comparing results of model with some experimental data available in the literature demonstrates that the model provides quite better predictions than existed models do. This model also predicts flow regime transition from stratified to annular flow better than Apparent Rough Surface and Modified Apparent Rough Surface models for both 1‐ and 2‐in. pipe diameters. The model also leads to reliable predictions of wetted wall fraction experimental data. Although one parameter of new model was evaluated based on air–water flow pressure loss experimental data for 1 in. pipe, it was considerably successful to predict pressure drop, liquid holdup, stratified‐annular transition and wetted wall fraction for other gas–liquid systems and pipe diameters. © 2014 American Institute of Chemical Engineers AIChE J, 61: 1043–1053, 2015     

高长径比三相内环流反应器中细颗粒相含率和循环液速的分布研究

在高径比为22的三相内环流反应器中,在常温常压下以空气-水-石英砂为物系,研究了在不同粒径下上升区固含率、下降区固含率和上升区循环液速随表观气速的变化规律和不同粒径下轴向固含率的分布情况,以及在固体体积分数不同的条件下,平均气含率和上升区气含率随表观气速的变化情况。结果表明:当粒径(ds)≤0.3 mm时,上升区固含率随表观气速的增加呈平缓变化趋势,下降区固含率随表观气速的增加而增加;当0.3 mm相似文献   

Macroscopic properties of liquid-solid circulating fluidized bed with viscous liquid medium

Experiments were conducted in a liquid-solid circulating fluidized bed to study the effect of liquid viscosity and solids inventory on pressure gradient, critical transitional liquid velocity, onset average solids holdup, axial solids holdup distribution, average solids holdup and solids circulation rate in circulating fluidization regime with riser operated in fixed inventory mode. The results indicate that critical transitional liquid velocity decreases with increase in liquid viscosity. The onset average solids holdup, on the other hand, increases with increase in either auxiliary liquid velocity or solids inventory. The variation of axial solids holdup distribution, average solids holdup and solids circulation rate with liquid viscosity when solid inventory was 0.15 m was dissimilar with either 0.25 m or 0.35 m solid inventory. Correlations were proposed for estimating the average solids holdup and are satisfactorily compared with experimental values.     

锥形鼓泡床内气含率特性的研究

本文分析了锥形鼓泡床内流型过渡、平均气含率及气含率轴向分布特性，考察了入口气体速度、静止液体（或淤浆）高度及淤浆浓度的影响，比较了与圆柱床的差异，结果表明对于鼓泡床内气体体积收缩的反应，用锥形床的冷态试验可以较精确地模拟其实际结果。     

POWER CONSUMPTION AND GAS HOLDUP IN A GAS-LIQUID RECIPROCATING PLATE COLUMN

The pressure fluctuation at the column base is confirmed to be proportional to the vibration intensity on a power of 2 in non-gassed conditions and up to a critical vibration intensity, corresponding to the dispersion resonance frequency, in gassed conditions. The power consumption is successfully correlated with the vibration intensity and the liquid holdup. The gas holdup in both mixer-settter and emulsion regime is well correlated with the power consumption and the superficial gas velocity. The effect of the superficial gas velocity is more important than that of the power consumption. The effects of the liquid phase properties, the wetting tendency of the plate material and the fraction free area above 41% were not observed     

Effect of liquid properties on the performance of bubble column reactors with fine pore spargers

This work is a study of the effect of liquid properties on the performance of bubble column reactors with fine pore spargers. Various liquids covering a range of surface tension and viscosity values are employed, while the gas phase is atmospheric air. A fast video technique is used for visual observations and, combined with image processing, is used for gas holdup and bubble size measurements. New data on average gas holdup values, bubble size distributions and Sauter diameters are presented and are consistent with existing physical models on coalescence/breakage. A correlation based on dimensionless groups for the prediction of gas holdup in the homogeneous regime is proposed and found to be in good agreement with available data.     

Hydrodynamics of an inverse liquid–solid circulating conventional fluidized bed

An inverse liquid–solid circulating conventional fluidized bed (I-CCFB) is realized by injecting particles from the top of a conventional liquid–solid fluidized bed (0.076 m ID and 5.4 m height) that is operated in a newly developed circulating conventional fluidization regime located between the conventional and circulating fluidization regimes. The I-CCFB can achieve a higher solids holdup compared to both conventional and circulating liquid–solid fluidized beds. A new parameter, the bed intensification factor, is defined to quantify the increased solids holdup observed with external solids circulation. The Richardson–Zaki equation is shown to be applicable to the I-CCFB regime and can be used to correlate the slip velocity and solids holdup, both of which increase with the solids circulation rate. A new flow regime map is presented, including the I-CCFB and a variety of other liquid–solid fluidized beds.     

Residence time distribution and liquid holdup in Kenics KMX static mixer with hydrogenated nitrile butadiene rubber solution and hydrogen gas system

A Kenics^® KMX static mixer that has curved-open blade internal structure was investigated to study its hydrodynamic performance related to residence time distribution and liquid holdup in a gas/liquid system. The static mixer reactor had 24 mixing elements arranged in line along the length of the reactor such that the angle between two neighboring elements is 90°. The length of the reactor was 0.98 m with an internal diameter of 3.8 cm and was operated cocurrently with vertical upflow. The fluids used were hydrogen (gas phase), monochlorobenzene (liquid phase) and hydrogenated nitrile butadiene rubber solution (liquid phase). In all the experiments, the polymer solution was maintained as a continuous phase while hydrogen gas was in the dispersed phase. All experiments were conducted in the laminar flow regime with the liquid side hydraulic Reynolds number in the range of 0.04-0.36 and the gas side hydraulic Reynolds number in the range of 3-18. Different polymer concentrations and different operating conditions with respect to gas/liquid flow rates were used to study the corresponding effects on the hydrodynamic parameters such as Peclet number (Pe) and the liquid holdup (ε_L). Empirical correlations were obtained for the axial dispersion coefficient (D_a) and liquid holdup in liquid system alone and for the gas/liquid system separately. It was observed that the Peclet number decreased with the introduction of gas in to the reactor while in the liquid system alone, an increase in viscosity decreased the Peclet number. The liquid holdup was empirically correlated as a function of the physical properties of the fluids used in addition to the operating flow rates.     

DISPERSION OF GAS AND LIQUID IN BUBBLE COLUMNS OF HOMOGENEOUS BUBBLE FLOW REGIME

Mean gas holdup, lateral distribution of gas holdup and axial mixing of gas and liquid were measured in bubble columns of 12 and 19cm i.d. The lateral distribution of gas holdup was strongly dependent on the flow regimes in the column. The axial mixing of liquid in the homogeneous bubble flow regime was much smaller than that in the heterogeneous bubble flow regime, and was not expressed by existing correlations. The axial mixing of liquid in the homogeneous bubble flow and the intermediate flow regime was simulated with a flow model based on the lateral distribution of buoyancy force and the effective viscosity. The axial mixing of gas was larger than that of liquid.