Influence of liquid viscosity and bed porosity on two‐phase pressure drop in concurrent gas‐liquid upflow through packed beds

It was observed in the experimental investigations that the concurrent upflow of air‐Monoethanol amine system through the packed bed gave higher pressure drop in bubble flow regime than the air‐water system. But when the flow regime changed to spray flow, air‐water system showed higher pressure drop than the other. This phenomenon was observed for the two column packing used in this study. An attempt is made to explain this phenomenon.     

Prediction of two‐phase pressure drop and liquid holdup in co‐current gas–liquid downflow of air–Newtonian systems through packed beds

The dependency of pressure drop and liquid holdup on phase velocities, geometry of the column and packing materials as well as on the physical properties have been analyzed. Our experimental data (825 data points obtained using four liquid systems and three different particles) along with those of the available literature (776 data point from five different sources) were used for the analysis. The applicability and the limitations of the literature correlations were evaluated using the available data. Based on the analysis, new correlations for the estimation of pressure drop and liquid holdup, valid for low and high interaction regimes have been developed using the available data, with a wide range of variables. Copyright © 2005 Society of Chemical Industry     

旋转填料床气液两相流场的仿真分析

通过合理简化旋转填料床(RPB)结构,建立了三维物理模型,利用商用软件Fluent的计算平台,采用欧拉两相流模型和多孔介质模型对旋转填料床内的气液两相流场进行了仿真分析,深入分析了其压力场分布和速度场分布,并在此基础上对比了气相压降随旋转床转速变化的仿真结果与实验结果,两者变化趋势一致,表明所建立模型能近似地模拟旋转填料床的流场分布,并指导理论研究和实验研究进一步深入。     

Micromixing efficiency of rotating packed bed with premixed liquid distributor

Rotating packed bed (RPB), in which high gravity is simulated by a centrifugal force, plays an important role in process intensification of fluid mixing and mass transfer. However, uneven initial liquid distribution in RPB leads to poor micromixing efficiency in local areas of the packing. Therefore, a premixed liquid distributor is proposed in this work to improve the liquid distribution in RPB. Micromixing efficiency of RPB with the premixed liquid distributor was studied by adopting the iodide–iodate reaction as working system and show better micromixing efficiency compared to that of RPB with non-premixed liquid distributor. Also, the effects of operating conditions (e.g. rotational speed, acid concentration, volumetric flow rate) and geometries using the premixed liquid distributor on micromixing efficiency (characterized by segregation index X_S) were investigated. The results show that segregation index X_S decreases with the increase of rotational speed, and the decrease of acid concentration and volumetric flow rate.     

Experimentally‐based constitutive relations for co‐current gas‐liquid flow in randomly packed beds

Experimental Observations on average pulse velocity and frequency in concurrent gas‐liquid (down) flow through randomly packed beds are used to extract constitutive relations for the gas‐liquid interaction and mean curvature terms that appear in a recently proposed volume‐averaged two‐fluid model for bubbly flow. The proposed closures lead to a reasonably quantitative prediction of the average pressure drop and liquid saturation under bubbly flow conditions and in the near pulse regime. In addition, the proposed closures provide realistic estimates for the location of the bubble‐to‐pulse transition in microgravity and in 1g down‐flow and predict the disappearance of the bubbly flow pattern at low liquid fluxes in 1g down‐flow. © 2016 American Institute of Chemical Engineers AIChE J, 63: 812–822, 2017     

Pressure drop in two phase cocurrent upward flow in packed beds: Air/non-newtonian liquid systems

New data on the two phase pressure drop for the concurrent upflow of air-liquid (Newtonian and non-Newtonian) mixtures through packed beds of spherical and non-spherical particles are presented. The results for single phase flows and for the air-Newtonian liquid mixtures have been used both to gauge the overall accuracy of the present experimental methods and to evaluate the validity of the predictive expressions available in the literature. The two phase pressure drop has been measured as a function of the liquid and gas flow rates, column diameter and the power law model constants. Depending upon a suitable combination of the gas and liquid fluxes and the power law index, the two phase pressure drop may be less than its value for the flow of liquid alone. A simple expression is proposed which correlates the present set of experiments (nearly 500 data points) with satisfactory levels of accuracy over the following ranges of conditions: 0.54 ≤ n ≤ 1; 0.001 ≤ Re_L^* ≤ 50; 3.7 ≤ Re_G ≤ 177 and 0.9 ≤χ (Lockhart-Martinelli parameter) ≤ 104.     

Co‐current descending two‐phase flows in inclined packed beds: Experiments versus simulations

The effect of inclination angle of a packed bed on its corresponding gas–liquid flow segregation and liquid saturation spatial distribution was measured in co‐current descending gas–liquid flows for varying inclinations and fluid velocities, and simulated using a two‐phase Eulerian computational fluid dynamics framework (CFD) adapted from trickle‐bed vertical configuration and based on the porous media concept. The model predictions were validated with our own experimental data obtained using electrical capacitance tomography. This preliminary attempt to forecast the hydrodynamics in inclined packed bed geometries recommends for the formulation of appropriate drag force closures which should be integrated in the CFD model for improved quantitative estimation.     

Automated measurements of gas‐liquid mass transfer in micropacked bed reactors

Gas‐liquid mass transfer in micropacked bed reactors is characterized with an automated platform integrated with in‐line Fourier transform infrared spectroscopy. This setup enables screening of a multidimensional parameter space underlying absorption with chemical reaction. Volumetric gas‐liquid mass‐transfer coefficients (k_La) are determined for the model reaction of CO₂ absorption in a methyl diethanolamine/water solution. Parametric studies are conducted varying gas and liquid superficial velocities, packed bed dimensions and packing particle sizes. The results show that k_La values are in the range of 0.12～0.39 s^?1, which is about one‐to‐two orders of magnitude larger than those of conventional trickle beds. An empirical correlation predicts k_La in micropacked bed reactors in good agreement with experimental data. © 2017 American Institute of Chemical Engineers AIChE J, 64: 564–570, 2018     

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     

Optimization of inulinase production by solid‐state fermentation in a packed‐bed bioreactor

BACKGROUND: This work is focused on inulinase production by solid‐sate fermentation (SSF) using sugarcane bagasse, corn steep liquor (CSL), pre‐treated cane molasses, and soybean bran as substrates in a 3‐kg (dry basis) packed‐bed bioreactor. SSF was carried out by the yeast Kluyveromyces marxianus NRRL Y‐7571 and response surface methodology was used to optimize the temperature, air flow rate and initial mass of cells. RESULTS: The optimum inulinase activity (436.7 ± 36.3 U g^?1 dry substrate) was obtained at 24 h at an inlet air temperature of 30 °C, air flow rate 2.2 m³ h^?1 and 22 g of cells for fermentation. Inulinase productivity at these conditions was 18.2 U gds^?1 h^?1. Kinetic evaluation at the optimized conditions showed that the maximum inulinase production was verified at 24 h of fermentation. The carbon dioxide and the metabolic heat generation are directly associated with the consumption of total reducing sugars present in the medium. CONCLUSION: The high productivity achieved in this work shows the technical viability of inulinase production by SSF in a packed‐bed bioreactor. Copyright © 2009 Society of Chemical Industry     

Modeling and simulation of non-isothermal catalytic packed bed membrane reactor for H2S decomposition

The recovery of H₂ from H₂S is an economical alternative to the Claus process in petroleum and minerals processing industries. Previous studies [React. Kinet. Catal. Lett. 62 (1997) 55; Catal. Lett. 37 (1996) 167] have demonstrated that catalytic decomposition of H₂S over bimetallic sulfide can proceed at relatively higher rates than over mono-metallic systems due to chemical synergism although conversions are still thermodynamically limited. In the present study, the performance of a catalytic membrane reactor containing a packed bed of Ru–Mo sulfide catalyst has been investigated with a view to improving H₂ yield beyond the equilibrium ceiling. A system of differential equations describing the non-isothermal reactor model has been solved to examine the effect of important hydrodynamic and transport properties on conversion. The results were obtained using a Pt-coated Nb membrane tube as the catalytic reactor enclosed in a quartz shell cylinder. Reynolds number for shell and tube side (Re^s and Re^t) as well as the modified wall Peclet number, Pe_m, dramatically affect H₂S conversions. Membrane reactor conversion rose monotonically with axial distance exceeding the equilibrium conversion by as much as eight times under some conditions.     

Three‐dimensional simulations of gas‐liquid cocurrent downflow in vertical,inclined, and oscillating packed beds

The hydrodynamic behavior of gas‐liquid downflow in vertical, inclined, and oscillating packed beds related to offshore floating applications was analyzed by means of three‐dimensional unsteady‐state two‐fluid simulations. Angular oscillations of the column between two angled symmetrical positions and between vertical and inclined position were considered while bed non‐uniformity was described using radial porosity distributions. For vertical and slightly inclined columns, two‐phase flow was concentrated in the core area of the bed. However, the two‐phase flow was predicted to deviate significantly from axial symmetry at higher inclinations with prominent liquid accumulation in the bottommost reactor cross‐sectional area. Oscillating packed beds unveiled complex reverse secondary flows radially and circumferentially resulting in oscillatory patterns of liquid holdup and pressure drop whose amplitude and propagation frequency were affected by column inclination angle and travel time between vertical and angled positions. © 2015 American Institute of Chemical Engineers AIChE J, 62: 916–927, 2016     

CO2 capture efficiency in post‐combustion using MWNT‐PAA in a packed bed column

The adsorption capacity of polyaspartamide (PAA) and multi‐wall carbon nanotubes with polyaspartamide (MWNT‐PAA) was investigated through a packed bed column with the flowing of flue gas composed of 15 % CO₂, 5 % O₂ and the balance N₂. The adsorption performed at 25 °C, 110 kPa and inlet gas flow rate of 60 mL/min resulted in high CO₂ adsorption capacity of 5.70 and 10.20 mmol‐CO₂/g for PAA and MWNT‐PAA, respectively. The adsorption kinetics was very high, so 7 min were enough for the effluent gas to reach the breakthrough after saturation. The consistency of adsorbents in recurring regeneration was successful through a continuous TSA system of 10 cycle adsorption‐desorption with temperatures of 25–100 °C. The evaluation of heat through differential scanning calorimetry (DSC) resulted in exothermic adsorption with heat release of 45.14 kJ/mol and 124.38 kJ/mol for PAA and MWNT‐PAA, respectively. The heat release was found favourable to promote the desorption as the temperature could rise after adsorption. This is an advantage for energy efficiency, as it depicts the potential of energy recovery. Thus, both adsorbent PAA and MWNT‐PAA were demonstrated to be promising for CO₂ adsorption capture in post‐combustion.     

Production of optically pure L‐valine in fluidized and packed bed reactors with immobilized L‐aminoacylase

A process to obtain L ‐valine has been developed using fluidized and packed bed reactors with L ‐aminoacylase (from hog kidney) immobilized by covalent binding. L ‐Valine production using the immobilized derivative of L ‐aminoacylase in fluidized and packed bed reactors was studied at three different substrate concentrations and two different flow rates. Higher productions were obtained in the packed bed reactor in all cases. The different solubilities of L ‐valine and acetyl‐D ‐valine in ethanol were used to purify L ‐amino acid from the reactor effluents. The amount of added ethanol did not influence the separation yields, although the purity of L ‐valine was strongly affected by this parameter. The last step involved was racemization of the unhydrolyzed acetyl‐D ‐valine, which was then used as substrate in a new reaction cycle. © 1999 Society of Chemical Industry     

Gas holdup for high gas velocities in a gas–liquid cocurrent upward‐flow system

Gas holdup has been measured in an 83‐mm diameter, 2.2‐m high column at high gas superficial velocities — 0.22 to 2.7 m/s — and at liquid (water) superficial velocities of 0 to 0.47 m/s, by means of a differential pressure transducer. The equation of Hills (1976) based on the slip velocity gives good predictions of the gas holdup for 0.1 ≤ E_g ≤ 0.4. However, the holdups predicted by this approach are considerably higher than the experimental values at gas velocities high enough that E_g > 0.4. Other equations from the literature are also shown to be inadequate. The new data and earlier data at high gas velocities are therefore correlated with a new dimensional equation for U_l ≤ 0.23 m/s.     

Liquid jet impaction on the single-layer stainless steel wire mesh in a rotating packed bed reactor

Liquid flow behaviors in the packing zone of a rotating packed bed reactor significantly affect the mass transfer performance. However, the interaction between the rotating packing and liquid is still not clear, due to packing's complex structure. In this work, liquid jet impaction on a rotating single-layer wire mesh was investigated to clarify the interaction and liquid flow behaviors after the impaction was observed and analyzed by visualization and simulation methods. Visual experiments showed that the interaction could be divided into the shearing action generated by vertical fibers and carrying action generated by horizontal fibers of wire mesh. A dimensionless number β was introduced as a criterion to evaluate the influence of these actions on the liquid dispersion. Simulation results agreed well with the experimental results of liquid dispersion. Dynamic liquid film behaviors on the fiber surface were further simulated and the average film thickness was 21–32 μm.     

Production of L‐methionine by immobilized pellets of Aspergillus oryzae in a packed bed reactor

Production of L ‐methionine by immobilized pellets of Aspergillus oryzae in a packed bed reactor was investigated. Based on the determination of relative enzymatic activity in the immobilized pellets, the optimum pH and temperature for the resolution reaction were 8.0 and 60 °C, respectively. The effects of substrate concentration on the resolution reaction were also investigated and the kinetic constants (K_m and V_m) of immobilized pellets were found to be 7.99 mmol dm^?3 and 1.38 mmol dm^?3 h^?1, respectively. The maximum substrate concentration for the resolution reaction without inhibition was 0.2 mol dm^?3. The L ‐methionine conversion rate reached 94% and 78% when substrate concentrations were 0.2 and 0.4 mol dm^?3, respectively, at a flow rate of 7.5 cm³ h^?1 using the small‐scale packed bed reactor developed. The half‐life of the L ‐aminoacylase in immobilized pellets was 70 days in continuous operation. All the results obtained in this paper exhibit a practical potential of using immobilized pellets of Aspergillus oryzae in the production of L ‐methionine. © 2002 Society of Chemical Industry     

不同圆球复合无序堆积床内流动传热数值分析

圆球堆积床内孔隙分布影响其内部流场及温度场分布, 且小管径-球径比堆积床由于壁面限制, 内部孔隙率变化剧烈, 其内部流动和传热不均匀现象明显。针对D/d_p为3的圆球无序堆积床构建了3种非等直径圆球复合堆积结构:径向分层复合堆积、轴向分层复合堆积以及随机复合堆积结构, 并采用DEM-CFD方法建模计算, 从径向及整体角度分析比较不同复合堆积床内流动换热特性及其流场和温度场分布的均匀性。结果表明:孔隙率及孔隙大小分布共同影响堆积床内流场和温度场分布;相对于单一等直径圆球堆积, 采用复合堆积结构能使堆积床内部孔隙率分布更均匀, 其内部流场和温度场分布也更为均匀;对于D/d_p为3的堆积通道, 径向分层堆积结构对于提高整体流动换热性能及改善内部流动换热均匀性都有显著效果。     

Multidimensional modeling of a microfibrous entrapped cobalt catalyst Fischer‐Tropsch reactor bed

Thermal management of highly exothermic Fischer‐Tropsch synthesis (FTS) has been a challenging bottleneck limiting the radial dimension of the packed‐bed (PB) reactor tube to 1.5 in. ID. A computational demonstration of a novel microfibrous entrapped cobalt catalyst (MFECC) in mitigating hot spot formation has been evaluated. Specifically, a two‐dimensional (2‐D) model was developed in COMSOL^®, validated with experimental data and subsequently employed to demonstrate scale‐up of the FTS bed from 0.59 to 4 in. ID. Significant hot spot of 102.39 K in PB was reduced to 9.4 K in MFECC bed under gas phase at 528.15 K and 2 MPa. Improvement in heat transfer within the MFECC bed facilitates higher productivities at low space velocities (≥1000 h^?1) corresponding to high CO conversion (≥90%). Additionally, the MFECC reactor provides an eightfold increase in the reactor ID at hot spots ≤ 30 K with CO% conversions ≥ 90%. This model was developed for a typical FTS cobalt‐based catalyst where CO₂ production is negligible. © 2017 American Institute of Chemical Engineers AIChE J, 64: 1723–1731, 2018