Liquid-solid Circulating Fluidized Bed Research Articles

Quantum machine learning – A novel approach for hydrodynamics analysis and modeling of liquid-solid circulating fluidized bed risers

The Liquid-Solid Circulating Fluidized Bed (LSCFB) system is commonly employed in chemical and biochemical applications, serving as a reactor where solids act as catalysts or biofilm carriers. Mass and heat transfer heavily rely on the distribution of solids holdups, which are influenced by various operating conditions, including superficial liquid velocities and auxiliary liquid velocities. These operating conditions play a key role in controlling the hydrodynamics of solid distribution. Quantum machine learning (QML)-based modeling techniques are employed to investigate the solids holdup distribution in a Liquid-Solid Circulating Fluidized Bed (LSCFB) system. A novel application of quantum machine learning for the hydrodynamics analysis and modeling of the LSCFB riser. This work aims to lay the groundwork for investigating the applicability of QML for understanding and predicting the hydrodynamic behavior of CFB risers by leveraging the unique properties of quantum systems during the present Noisy Intermediate-Scale Quantum (NISQ) era. The unavailability of full-scale quantum infrastructure limits proper exploitation of different quantum computing opportunities including embedding. In this study glass beads particles with 500 µm used as the solid phase and water as liquid phase. At various axial locations (H = 1.0, 2.0, 3.0, and 3.8 m above the distributor) and with varying superficial liquid velocities, radial nonuniformity of solids holdup is observed. The derived models account for the impact of operating parameters, such as auxiliary and primary liquid velocities and superficial particulate velocity, on the radial phase distribution at various axial positions in the riser. By comparing the predicted solids holdup data with experimental data obtained from a pilot-scale LSCFB reactor, the accuracy of the models is determined. The models exhibit reasonable correlations with the experimental data and consistent phase distribution trends. The correlation coefficients between predicted outputs and experimental data for sequential and nonsequential QML models are 0.95 and 0.96, respectively.

Numerical investigation of hydrodynamics in liquid-solid circulating fluidized beds under different operating conditions

A computational fluid dynamics (CFD) model was employed to investigate the hydrodynamics of the liquid–solid circulating fluidized bed (LSCFB). The numerical simulations of the flow in the LSCFB under different operating conditions, including different superficial liquid velocities, superficial solid velocities, particle densities and shapes, are carried out using the CFD model developed in the previous work. The numerical predictions show correct trends and good agreements with the experimental data. It is demonstrated that the radial non-uniformity and axial uniformity exist in the flow structures under different operating conditions. By increasing the superficial solid velocity, the average solids holdup and radial non-uniformity increase, while the opposite trends are observed by increasing the superficial liquid velocity. Besides, the solids holdup decreases with the decrease in the particle density. It is also observed that all the flow distributions in the radial and axial directions in LSCFBs are more uniform than those in GSCFBs.

Turbulent mass transfer model for simulating protein desorption in liquid–solid circulating fluidized bed risers

An integrated model, namely the two-equation turbulent model, is introduced to simulate mass transfer in a liquid–solid circulating fluidized bed (LSCFB) riser. Protein desorption is simulated and the proposed model is validated. The protein concentration profiles simulated with this model agree well with published experimental results. This model enables direct determination of turbulent mass diffusivity, removing the need to empirically guess a constant turbulent Schmidt number for simulating mass transfer in a turbulent flow. This model is useful when the turbulent mass diffusivity is not available for simulating mass transfer in an LSCFB riser.

Turbulent mass transfer model for the simulation of liquid-solid CFB risers and its verification

Rigorous simulation of mass transfer process in liquid-solid circulating fluidized bed (LSCFB) system is challenging not only due to the fluidization but also due to the existing turbulence. In this paper, the recently developed c2¯−εc approach is introduced to characterize the turbulent mass diffusion in LSCFB riser so that the empirical turbulent mass diffusivity are abandoned. As for describing the liquid-solid turbulent flow, the kl − εl − ks − εs − Θ formulations are adopted. With the proposed model, the distributions of species concentration and phase velocity as well as solids holdup can be predicted simultaneously. In this paper the integrated model is established and simulations are conducted for a riser involving an impulse tracer test process so that the proposed model can be validated. The turbulent Schmidt number is found to be varied but not a constant throughout the riser, which reveals that the use of constant turbulent Schmidt number for the traditional model is questionable.

Continuous Phenol Removal Using a Liquid–Solid Circulating Fluidized Bed

A liquid-solid circulating fluidized bed (LSCFB) helps to overcome the shortcomings of conventional fluidized beds by using a particle separation and return system as an integral part of the overall reactor configuration. Batch adsorption experiments were carried out for the removal of phenol from a synthetically prepared solution using fresh activated-carbon-coated glass beads. The morphological features and surface chemistry of the adsorbent were analyzed via SEM and FTIR techniques. The adsorbent dosage, contact time and temperature were varied along with solution pH to assess their effects on the adsorbent performance for phenol removal. Isotherm modeling showed that the phenol removal using the activated-carbon glass beads followed the Langmuir model. Effectively, it was observed at an adsorbent loading of 2.5 g/150 mL of feed volume and a contact time of 3 h produced an 80% efficiency in the batch study. Furthermore, on scaling it up to the column, the desired 98% phenol-removal efficiency was obtained with an adsorbent dosage of 250 g and contact time of 25 min. Adsorbent regeneration using 5% (v/v) ethanol showed a 64% desorption of phenol from the sorbent within 20 min in the LSCFB.

Scale-up effect analysis and modeling of liquid–solid circulating fluidized bed risers using multigene genetic programming

Understanding scale-up effects on the hydrodynamics of a liquid‒solid circulating fluidized bed (LSCFB) unit requires both experimental and theoretical analysis. We implement multigene genetic programming (MGGP) to investigate the solid holdup and distribution in three LSCFB systems with different heights. In addition to data obtained here, we also use a portion of data sets of LSCFB systems developed by Zheng (1999) and Liang et al. (1996). Model predictions are in good agreement with the experimental data in both radial and axial directions and at different normalized superficial liquid and solid velocities. The radial profiles of the solid holdup are approximately identical at a fixed average cross-sectional solid holdup for the three LSCFB systems studied. Statistical performance indicators including the mean absolute percentage error (6.19%) and correlation coefficient (0.985) are within an acceptable range. The results suggest that a MGGP modeling approach is suitable for predicting the solid holdup and distribution of a scaled-up LSCFB system.

Review of (gas)-liquid-solid circulating fluidized beds as biochemical and environmental reactors

Circulating fluidized beds (CFBs) possess many significant advantages over conventional fluidized beds, including enhanced interfacial contact efficiency and reduced back-mixing. Building on the many successful industrial applications of gas-solid CFBs, liquid-solid circulating fluidized beds (LSCFBs) and gas-liquid-solid circulating fluidized beds (GLSCFBs) have recently also received increasing interests due to their massive potential in chemical-biochemical, environmental and pharmaceutical processes. This review summarizes the progress in the past several decades concerning LSCFBs and GLSCFBs, with more emphasis placed on the reported applications, after a general description of the unique features of the two types of CFBs. Most of the examples given in this review are still in laboratory-scale, but useful guidance can be provided to researchers or companies for further study and/or commercial exploration.

On the basic hydrodynamics of inverse liquid-solid circulating fluidized bed downer

A new type of fluidized bed called Inverse Liquid-Solid Circulating Fluidized Bed (ILSCFB) has been developed. The circulating fluidized bed consists of the downer with an inner diameter of 7.6 cm and the height of 5.4 m, upcomer with an inner diameter of 20 cm, separator, and connecting pipes between the downer to the storage column. The operation window has been demonstrated at different solids circulation rate and liquid velocity. The hydrodynamic characteristics in the downer of ILSCFB are investigated experimentally by fluidization of the styrofoam and Hollow Glassbeads whose densities are smaller than that of the fluidization media. Average solids holdup in the downer is measured where different liquid velocity and different solids circulation rate in terms of superficial solids velocity. For both types of particles, axial solids holdup distribution is quite uniform under various operating conditions, while radial solids holdup distributions are slightly non-uniform with a minor increase in solids holdup adjacent to the wall under various operating conditions, but no obvious “core-annulus” structure is observed. The comparisons of the hydrodynamics in the ILSCFB and Liquid-Solid Circulating Fluidized Bed (LSCFB) are also made based on the single particle force balance discussion, enabling the generalization of inverse and upwards circulating fluidization of particles.

Hydrodynamics Modeling of an LSCFB Reactor Using Multigene Genetic Programming Approach: Effect of Particles Size and Shape

AbstractThe multigene genetic programming (MGGP) technique based hydrodynamics models were developed to predict the solids holdups of a liquid-solid circulating fluidized bed (LSCFB) riser. Four different particles were considered to investigate the effects of particle size, shape and density on hydrodynamics behavior of the LSCFB riser. In this regard, two spherical shape glass bead particles (500 and 1200 μm), two irregular shape lava rock particles (500 and 920 μm) were employed as solid phase and water as liquid phase. The MGGP models were developed, relating the solids holdup (${\varepsilon _s}$, output parameter) with eight input parameters. The developed models were first validated by comparing the model predicted and experimental data of solids holdups. The average solids holdups decreased with the increase of net superficial liquid velocity (${U_l} - {U_t}$) and normalized superficial liquid velocity$\left( {\frac{{{U_l}}}{{{U_t}}}} \right)$. Uniform axial solids holdups observed in axial locations (H) except close to the liquid-solid distributor of the riser. The radial non-uniformity of solids holdup observed all radial positions (r/R). In the central region almost flat but increased toward the wall region. The radial profiles of the solid holdup are approximately identical at a fixed average cross-sectional solid holdup for all of the three LSCFB systems of this study. The statistical performance indicators such as the mean absolute percentage error and correlation coefficient are also found to be within acceptable range. All these findings of suggest that the MGGP modeling approach is suitable for predicting effect of particle size and shape on hydrodynamics behavior of the LSCFB system

Development of a numerical model for the hydrodynamics simulation of liquid-solid circulating fluidized beds

Due to extensive applications of the liquid-solid circulating fluidized beds (LSCFBs) in biochemical and petroleum industries, a detailed computational fluid dynamics (CFD) study is crucial to understand the flow characteristics in LSCFBs. In this paper, the hydrodynamics in LSCFBs is numerically investigated using the Eulerian-Eulerian two-phase model combined with the kinetic theory for the granular phase (KTGP). Key factors affecting the simulation results including the drag model, near wall treatment and boundary conditions are investigated, and the CFD model is validated by comparing the numerical results with the experimental data. Among the seven different drag models examined in this study, the adjusted Syamlal O'Brien drag model and the irregular particle drag model are found to provide the best numerical solutions for spherical and irregular particles, respectively. As for the three different near wall treatments tested, the Menter-Lechner near wall treatment is found to provide the best numerical predictions in the near wall region.

Step by step methodology of designing a liquid–solid circulating fluidized bed using computational fluid dynamic approach

In this work, a systematic step-by-step methodology has been developed to identify the type of instabilities arise in achieving the continuous solids circulation achieved between riser and downcomer, and in establishing the proper pressure balance among the various units of a liquid–solid circulating fluidized bed (LSCFB) using transient three dimensional computational fluid dynamic (CFD) simulations. Different type of instabilities has been identified and systematically eliminated by choosing the appropriate measure in-terms of the geometry of a LSCFB. This resulted in studying five variant designs of LSCFB studies using CFD. The Eulerian–Eulerian approach is used to simulate the two-phase flow in LSCFB system. The hydrodynamic behavior of the system is studied in terms of the pressure drop, solids holdup at various locations as well as the axial solids hold up distribution. The steady state in the system has been characterized by the solids volume fraction and the pressure balance loop across the closed loop LSCFB. The effect of solids inventory, primary and auxiliary liquid flow, and viscosity of liquid on average solids holdup has been studied with the final LSCFB design.

A Multigene Genetic Programming approach for modeling effect of particle size in a liquid–solid circulating fluidized bed reactor

This communication presents the application of Multigene Genetic Programming, a new soft computing technique to investigate the effects of particle size on hydrodynamics behavior of a liquid–solid circulating fluidized bed (LSCFB) riser. The Multigene Genetic Programming based model is developed/trained based on experimental data collected from a pilot scale LSCFB reactor using two different size glass beads (500 & 1200μm) as solid phase and water as liquid phase. The trained Genetic Programming model successfully predicted experimental phase holdups of the LSCFB riser under different operating parameters. It is observed that the model predicted cross-sectional average of solids holdups in the axial directions and radial flow structure are well agreement with the experimental values. The statistical performance indicators including the mean absolute error (∼5.89%) and the correlation coefficient (∼0.982) also show favorable indications of the suitability of Genetic Programming modeling approach in predicting the solids holdup of the LSCFB system.

Effect of Inventory Change in a Liquid – Solid Circulating Fluidized Bed (LSCFB)

Abstract Circulating fluidized beds (CFB) play a major role in the chemical industry especially as heterogeneous catalytic reactors. Research on hydrodynamic properties of Liquid – Solid CFBs (LSCFB) is significantly under-reported as compared to Gas – Solid CFBs (GSCFB). Steadily, prominent research is being established in fields like food industry (whey protein recovery), waste management (removal of heavy metals from radioactive wastes) and others, which use LSCFBs. In this context, it is important to have significant knowledge about the changes occurring in hydrodynamic properties like solid hold-up, rate of solid circulation etc., on changing certain critical physical properties such as inventory height. An LSCFB of height 2.95 m and riser outer diameter 0.1 m was chosen and the effect of inventory height on the properties was studied by taking the initial inventory heights as 15 cm, 25 cm and 35 cm. The hydrodynamic studies concentrated on axial solid holdup, average solid holdup, solid circulation rate and slip velocity. On increasing the inventory, uniformity of axial solid holdup was confirmed along with studying holdup patterns. Solid flux was seen to follow an inverse relationship to holdup, as expected. The change in slip velocity with varying inventory was also checked, and was found to decrease with inventory. The distribution parameter, Co of the drift flux model was used to determine the extent of non-uniformity in solid distribution. Co was calculated to be less than unity in the range of 0.983–0.994, suggesting non-uniformity in solid distribution, with higher solid concentration by the walls compared to the core.

Effect of Liquid Viscosity and Solid Inventory on Hydrodynamics in a Liquid - solid Circulating Fluidized Bed

A comprehensive hydrodynamic study of a Liquid - Solid Circulating Fluidized Bed (LSCFB) is conducted with changes in viscosity of the fluidizing medium and the inventory height of solids initially fed into the system. An LSCFB of height 2.95m and riser outer diameter 0.1m was chosen for experimentation. The three liquid media systems with varying viscosities that were chosen were water, glycerol 10% (v/v) and glycerol 20% (v/v). Effect of inventory on the hydrodynamics was also studied, by taking initial heights of inventory to be 15cm, 25cm and 35cm. The hydrodynamic studies concentrated on pressure gradients along the axial pressure tapings, axial solid holdup, average solid holdup, solid circulation rate and slip velocity. Uniformity in axial solid holdup and average solid holdup was validated for changes in viscosity and inventory. Solid flux was seen to follow an inverse relationship to holdup. The changes in slip velocity with varying viscosity and inventory were studied, and found to decrease with both variables. The distribution parameter, Co of the drift flux model was found to be in the range of 0.983-0.994, suggesting non-uniformity in radial solid distribution, with higher solid concentration by the walls compared to the core of the column.

Artificial Neural Network Modeling of Hydrodynamics of Liquid‐Solid Circulating Fluidized Beds

AbstractSolids holdup and solids circulation rate are the two important hydrodynamic variables affected by process conditions. These two variables have a significant influence on the performance of a liquid‐solid circulating fluidized bed (LSCFB). An artificial neural network (ANN) methodology was developed and simulated to predict the performance of the LSCFB for the experimental dataset collected under various process conditions. Different statistical parameters were applied to evaluate the prominent and unique characteristic features of the ANN‐predicted parameters. The ANN model successfully predicted the experimental observations and captured the actual nonlinear behavior noticed during the experiments. Model validation confirmed that this data‐driven technique can be used to model such nonlinear systems.

Effects of Particle Size and Shape on Solids Holdups Distributions Modelling in a LSCFB Reactor using Abductive Network

The Abductive Network (AN), a group method data handling (GMDH) algorithm‐based self‐organizing model, was applied to study the solids holdup distribution of a liquid‐solid circulating fluidized bed (LSCFB) system. At first, the AN model was trained with experimental data sets obtained from a pilot scale LSCFB operated with spherical glass beads and irregularly shaped lava rock particles as solid phases, and water as liquid phase. In the model training the effects of various auxiliary and primary liquid velocities and superficial solids velocities on radial phase distribution at different axial positions were considered. The developed AN model was employed to predict the solids holdups at various locations of the LSCFB riser under different operating conditions. The competency of the developed AN model was confirmed by comparing the model‐predicted and experimental solids holdups of the LSCFB system. Both the experimental and model‐predicted outputs showed that under different superficial liquid velocities the solids holdup was higher for the glass beads than the lava rocks. The solids holdup decreased with increasing liquid velocity at all axial locations. The radial non‐uniformity distributions of solids holdup in the central region decreased toward the wall. The higher drag force acting on the spherical‐shaped particles was likely responsible for this variation of the solids holdups.

Development of a model for the prediction of hydrodynamics of a liquid–solid circulating fluidized beds: A full factorial design approach

Hydrodynamics of a liquid–solid circulating fluidized bed (LSCFB) system has a significant impact on the reactor design. In the present study, statistical design approach was adopted to model the hydrodynamic behavior of an LSCFB in terms of average solids holdup and solids circulation rate. Primary liquid velocity, auxiliary liquid velocity, solids inventory and liquid viscosity are the input variables, called factors, which affects the system. Average solids holdup and solids circulation rate are called responses of the system. A full factorial design approach with four factors and three levels of the factors were considered. Various models such as linear, two factor interaction, quadratic, and cubic models were tested for the adequacy. Within the range of experiments conducted, for both responses, the quadratic regression model is suggested. The model shows that some of the interaction effects between the factors are dominant. The developed model was verified by using various statistical tests. Also, the model was validated using various experimental data sets chosen at different conditions. Results based on ‘R’ value, and deviations in parity plot were falling within agreement level. This suggests that the proposed model can be adopted for various processing applications in the LSCFB unit.

Numerical simulation of counter-current flow field in the downcomer of a liquid–solid circulating fluidized bed

A comprehensive study on the hydrodynamics in the downcomer of a liquid–solid circulating fluidized bed (LSCFB) is crucial in the control and optimization of the extraction process using an ion exchange LSCFB. A computational fluid dynamics model is proposed in this study to simulate the counter-current two-phase flow in the downcomer of the LSCFB. The model is based on the Eulerian–Eulerian approach incorporating the kinetic theory of granular flow. The predicted results agree well with our earlier experimental data. Furthermore, it is shown that the bed expansion of the particles in the downcomer is directly affected by the superficial liquid velocity in downcomer and solids circulation rate. The model also predicts the residence time of solid particles in the downcomer using a pulse technique. It is demonstrated that the increase in the superficial liquid velocity decreases the solids dispersion in the downcomer of the LSCFB.

CFD modelling of continuous protein extraction process using liquid‐solid circulating fluidized beds

AbstractA computational fluid dynamics (CFD) model was developed to describe the hydrodynamics and mass transfer in the process of continuous protein extraction from broth using a liquid‐solid circulating fluidized bed (LSCFB) ion exchange system. The CFD model took into account both the adsorption and desorption processes. The quantitative predictions for the protein concentration were compared favourably with the experimental data from a lab‐scale system. The model was used to investigate the effects of hydrodynamic and kinetic parameters on the performance of the LSCFB ion exchange system. It was demonstrated that the model is a robust tool to simulate, scale up, and optimize the LSCFB ion exchange systems for protein extraction process.

A computational fluid dynamics study on the flow field in a liquid–solid circulating fluidized bed riser

A detailed study on the hydrodynamics of liquid–solid circulating fluidized bed (LSCFB) reactors is crucial in the efficient design and scale-up of these reactors. In this paper, an axisymmetric CFD model is developed to simulate the flow field in a LSCFB riser. The model is based on Eulerian–Eulerian approach incorporating the kinetic theory of granular flow. The predicted results agree well with our earlier experimental data. Furthermore, it is found that the dispersed k–ε multiphase turbulence model is more accurate and computationally efficient than other k–ε multiphase turbulence models. Also, the model predicts the residence time of both liquid and solid phases in the riser by using a Pulse technique. Finally, the proposed CFD model is used to investigate the effects of the liquid stream velocity and the solids circulation rate on the performance of the LSCFB. It is demonstrated that the proposed CFD model can be a robust tool for the scale-up and design of industrial LSCFB reactors.