Large-scale Bubble Column Research Articles

Modeling of bubble size distribution in isothermal gas–liquid flows: Numerical assessment of population balance approaches

Gas–liquid flows are commonly encountered in many industrial flow systems. In many cases, the evolution of bubble size distribution is a crucial factor governing the momentum, heat and mass transfer between phases within the system. Aiming to evaluate the capability of existing models, numerical assessment of three different population balance approaches – direct quadrature method of moments (DQMOM), average bubble number density (ABND) model and homogeneous MUlti-SIze-Group (MUSIG) models – is presented in this paper. Model predictions were validated against experimental measurements from medium and large scale bubble columns where bubble sizes within the system were found to be dominant by coalescence and break-up mechanism, respectively. In result of the bubble size change, transitions of phase distribution from wall peak to core peak profile were also found in both experiments. In general, predictions of the three models were in satisfactory agreement with experiment measurements clearly demonstrating its applicability for large scale practical systems. Encouraging results have also been obtained in capturing the evolution of bubble size distribution. Nevertheless, noticeable errors were also found in predictions of the MUSIG and DQMOM model indicating some potential deficiencies of the model. To evaluate the numerical efficiency of the three models, computational requirements of each model were also compared.

Heat Transfer Characteristics in a Large-Scale Bubble Column Operating in a Semi – Batch Mode

Heat Transfer Characteristics in a Large-Scale Bubble Column Operating in a Semi – Batch Mode

Compartmental Modeling of an Industrial Column

The industrial production of refined sodium bicarbonate is realized in large-scale bubble columns, called the BIR columns. Several complex phenomena exist in these columns, such as three-phase flow, gas-liquid mass transfer of CO2, and crystallization. This work deals with the development of an operational BIR column model using the compartmental modeling approach. It is fed by previous works and current studies. A parametric sensitivity analysis is realized to identify the more important modeling parameters and to point the future research that have to be performed. Some simulations results are presented for typical operating conditions of an industrial column.

One-Step DME Synthesis from Coal-Derived, CO-Rich Syngas in a Slurry Reactor

This study investigates one-step dimethyl ether (DME) synthesis from coal-derived, CO-rich syngas over a bifunctional catalyst comprising a methanol synthesis catalyst (Cu/ZnO/Al2O3) and a methanol dehydration catalyst (γ-Al2O3). The liquid-phase DME synthesis was carried out in a slurry reactor that provided good mixing and excellent heat removal. Higher CO conversion and DME space time yield (STY) were observed at a higher reaction temperature and a higher pressure. A lower gas hourly space velocity (GHSV) caused higher CO conversion, but a lower DME STY. Excessive content of γ-Al2O3 had an adverse effect on both CO conversion and DME STY. Among various H2:CO ratios, the maximum DME STY (13.5 mol/kg-cat/h) was observed at a H2:CO ratio of 1.0. CO2 in the feed syngas had a negative effect on DME synthesis. The results and data obtained in this study can be used as basic data for the design and operation of a large scale bubble column reactor and for further application to a three-phase fluidized bed reactor.

Gas holdup and bubble size behavior in a large-scale slurry bubble column reactor operating with an organic liquid under elevated pressures and temperatures

Abstract The holdups of small and large gas bubbles, bubble size distribution and the Sauter-mean bubble diameter were measured for N 2 and He in isoparaffinic organic liquid mixture (Isopar-M) in the absence and presence of Alumina powder under various pressures (0.67–3 MPa), temperatures (300–473 K), superficial gas velocities (0.07–0.39 m/s), and solid concentrations (0–20 vol.%) in a large-scale bubble column and slurry bubble column reactor (SBCR) (0.29 m diameter, 3 m height). The gas holdup was measured using the manometric method and the bubble size distribution, and Sauter-mean bubble diameter were obtained using the dynamic gas disengagement (DGD) technique and the photographic method. The experimental data showed that the total gas holdup increased with pressure and superficial gas velocity due to the increase of gas momentum which shifted the bubble size distribution towards smaller gas bubbles. The total gas holdup was also found to increase with temperature due to the decrease of liquid viscosity and surface tension. Increasing the solid concentration, on the other hand, resulted in a significant decrease of the total gas holdup and significantly increased the Sauter-mean bubble diameter. The online monitoring of the swarm using the high-speed camera showed a decrease of the froth stability in the reactor with increasing solid concentration and temperature which were responsible for the decrease of the total gas holdup.

Prediction of the Gas Holdup in Industrial-Scale Bubble Columns and Slurry Bubble Column Reactors Using Back-Propagation Neural Networks

The total gas holdup and the holdup of large gas bubbles were predicted in bubble column reactors (BCRs) and slurry bubble column rectors (SBCRs) using two Back-Propagation Neural Networks (BPNNs). Over 3880 and 1425 data points for gas holdup and Large gas bubble holdup respectively, covering wide ranges of gas-liquid-solid physical properties, operating variables, reactor geometry, and gas sparger type/size, were employed to develop, train and validate the two neural networks. The developed BPNN for gas holdup has a topology of [14,9-7,1] and was able to predict the trained and untrained data with an average absolute relative error (AARE), standard deviation, and regression coefficient (R2) of 16, 19 and 90%, respectively. The developed BPNN for large gas bubble holdup has a topology of [14,8,1] and was capable of predicting the trained and untrained data with AARE, standard deviation, and R2 of 10, 14 and 93%, respectively. The BPNNs were then used to predict the effects of pressure, superficial gas velocity, temperature and catalyst loading on the total syngas holdup for Low-Temperature Fischer-Tropsch (LTFT) synthesis carried out in a 5 m ID SBCR. The predicted total syngas holdup appeared to increase with increasing reactor pressure, superficial gas velocity and the number of orifices in the gas sparger. The predicted syngas holdup, however, was found to decrease with increasing catalyst loading and reactor temperature. Also, under similar LTFT operating conditions (P = 3 MPa, T = 513 K, CW = 30 and 50 wt%), the total syngas holdup values predicted for H2/CO ratio of 2:1 and cobalt-based catalyst are consistently lower than those obtained for H2/CO ratio of 1:1 and iron oxide catalyst in the superficial gas velocity range from 0.005 to 0.4 m/s. These predictions are in perfect agreement with reported literature trends, which underscore the reliability and validity of the developed BPNNs in predicting the total syngas holdup and the holdup of large gas bubbles in large-scale bubble columns and SBCRs operating under industrial conditions.

Multiphase fluidization in large-scale slurry jet loop bubble columns for methanol and or dimethyl ether production

A solution methodology is proposed for the process development and process engineering of a continuously operated jet loop bubble column including integrated external or internal steam generation for, e.g., a high-efficiency large-scale medium pressure methanol and or dimethyl ether production, or other gas to liquid Fischer–Tropsch applications. A jet loop bubble column is defined in the present process development to study the combined integration of a jet-eductor draft tube system with an upper bubble column. The major advantages resulting from the integrated jet-eductor draft tube system in large-scale bubble columns are the guidance and good mixing efficiency of the multiphase flow up to the upper part of the bubble column. Reducing the bubble column operating liquid level at about 2.5–3.0 times of the column diameter above the upper end of the draft tube results in a classical jet-eductor draft tube reactor suitable for small and or medium-scale industrial applications. Methanol synthesis is usually executed catalytically in multistage packed beds at higher pressure, e.g. 26 MPa, and about 350– 400 ∘ C , resulting in a higher plant installation and operating cost. The successful scale-up of a slurry jet loop bubble column can achieve a higher catalytic selectivity at a lower pressure ( ∼ 5 MPa ) and temperature ( ∼ 250 ∘ C ) , and therefore reduce the overall plant investment and production cost [ Toseland, 1999. Three phase flows under extreme conditions of pressure and temperature, Part II: industrial applications, Air products and Chemicals, Inc. Presented at the A.I.Ch.E. Annual Meeting, Dallas, TX; Fan, 1999. Three phase flows under extreme conditions of pressure and temperature, Part I: fundmental characteristics, Department of Chemical Engineering, The Ohio State University. Presented at the A.I.Ch.E. Annuxal Meeting, Dallas, TX]. In addition, the separate slurry production of dimethyl ether, or even coproduction with methanol, can be a more cost-effective process than the classical methanol dehydration process. The new Modified Slurry Process © for large-scale methanol and or dimethyl ether production is presented including internal or external heat exchanger location for steam production. A process concept is developed of a Large Scale Slurry Jet Loop Bubble Column © with external separator, auxiliary internal heat exchanger equipment and high-efficiency gas–liquid slurry jet-eductor mixing system including draft tubes and an upper bubble column. In addition, as comparison a simplified concept is discussed for a small-to-medium-scale slurry jet loop reactor including external steam production and bottom nozzle jet-eductor installation without the presence of an upper bubble column. The basic geometrical parameters of the proposed slurry jet loop bubble column and jet loop reactor are discussed. The influence of the selected geometrical parameters on the gas holdup, interfacial area and mixing is analyzed. Information about catalyst type and particle size distribution is also presented. The definition of optimal operating conditions related to the influence of the fluid dynamics and mixing on mass transfer efficiency and also information for the minimum required power input per unit volume for startup or stable reactor operation are discussed. A simplified estimation method is presented for the expected axial temperature difference across the overall length of the jet bubble column, and also the required heat transfer area of a new construction-type internal compact heat exchanger for efficient reactor cooling and operation. Scale-up is possible for large diameter jet loop bubble columns, typically up to 5 m diameter and 60 m height, including continuous three-phase slurry operation at higher power input and interfacial area, for more efficient synthesis gas absorption and reaction than in classical slurry bubble columns. Integration of suitable designed sieve trays can further guarantee an efficient operation of the lower jet loop draft tube system at higher column diameters and also achieve an efficient reactor operation in the upper bubble column section.

Production of sodium bicarbonate in industrial bubble columns

Industrial production of refined sodium bicarbonate proceeds in large-scale bubble columns. The main purpose of the research is to develop a mathematical model for a specific column. In order to characterize the column, several types of measurements (performed at different scales) are presented and analyzed. Consequently, a 1D model of the column is constructed including two bubble populations. Closure of the model is done using Computational Fluid Dynamics and experimental data collected on the industrial column. A model of gas–liquid mass transfer is also developed.

Bubble Behavior of a Large‐Scale Bubble Column with Elevated Pressure

AbstractGas holdups and the rising velocity of large and small bubbles are measured using the dynamic gas disengagement approach in a pressured bubble column of 0.3 m in diameter and 6.6 m in height. The effects of superficial gas velocity, liquid surface tension, liquid viscosity, and system pressure on the gas holdups and the rising velocity of small and large bubbles are investigated. The holdup of large bubbles and the rising velocity of small bubbles increase with increasing liquid viscosity and liquid surface tension. Meanwhile, the holdup of small bubbles and the rising velocity of a swarm of large bubbles decrease. Moreover, the holdup of large bubbles and the rising velocity of a swarm of small bubbles decrease with increasing system pressure. A correlation for the holdup of small bubbles is obtained from experimental data.

Hydrodynamic and Mass-Transfer Characteristics in Organic Liquid Mixtures in a Large-Scale Bubble Column Reactor for the Toluene Oxidation Process

The gas holdup (eG), Sauter mean bubble diameter (dS), and bubble size distribution, as well as the volumetric mass-transfer coefficient (kLa), gas−liquid interfacial area (a), and mass-transfer coefficient (kL), of N2 and air were measured in a large-scale (0.316-m inside diameter, 2.8-m height) bubble column reactor (BCR) in toluene and its mixtures (toluene−benzoic acid−benzaldehyde) under a wide range of pressure (0.2−0.8 MPa) and superficial gas velocities (0.06−0.14 m/s). The kLa data were determined using the transient physical gas absorption technique, whereas the bubble size distributions as well as the Sauter mean bubble diameters were obtained using the dynamic gas disengagement technique. The gas holdup values were measured employing the manometric method with two differential pressure cells located at different positions in the BCR. From the experimental gas holdup, Sauter mean bubble diameter, and kLa results, a and kL were extracted under various operating conditions. The central composite ...

Mixing effects in vertical upflow bubble columns

The phenomenon of a rising macrovortex of preferentially aerated liquid was observed in large-scale bubble columns. A theoretical explanation of this phenomenon is presented, based on the theory of the turbulent free boundary layer. The description results in a single-parameter model, based on the coefficient of Prandtl's mixing length from the phenomenological theory of turbulence after introducing acceptable simplifications. The experimental procedure of measuring the coefficients of Prandtl's mixing length from the boundaries of jets forming after introduction of a tracer fluid into a macrovortex and into single-phase flow has been devised. Finally, a mixing coefficient is defined, relating the degree of mixing in the macrovortex to the turbulence created in singlephase flow alone. Thus a dimensionless single-parameter model of non-ideal flow in a part of the total flow in a bubble column, due essentially to gas maldistribution, has been formulated.

57 Scaling-up of bubble reactors on basis of laboratory data

A simple method is suggested for the modelling of hydrodynamics of reacting gas-liquid systems in large-scale bubble column reactors. Values of liquid-side mass transfer coefficient (k L), interfacial area (a), and gas holdup ratio (e) in a large-scale apparatus can be predicted on the basis of experimental gas holdup data obtained for the reacting system and for an appropriate standard (reference) system in a laboratory-scale bubble reactor. Examples of the modelling are presented for the cases of oxidation of isobutyraldehyde to isobutyric acid and absorption of CO 2 into NaOH solution.

Behavior of bubbles in large scale bubble column.

Experimental work was conducted with a 550 cm-diameter bubble column to find the influence of column diameter on circulating liquid flow, gas holdup, bubble size and bubble velocity. The relationship between average gas holdup and superficial gas velocity in the column is almost the same as that in a small-size bubble column. When comparing the bubble velocity observed with the results of past experiments, it becomes clear that no particularly unusual phenomenon due to the large scale of the column exists in the circulating flow. Bubble sizes obtained by means of the electric resistivity probe method are larger than those measured in past experiments in small-size bubble columns. The reason for this difference is discussed briefly.