Liquid–solid Circulating Fluidized Bed System Research Articles

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.

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

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.

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.

Application of Support Vector Machine Modeling on Phase Distribution in the Riser of an LSCFB Reactor

Abstract Support vector machine (SVM) modeling approach is applied to predict the solids holdups distribution of a liquid–solid circulating fluidized bed (LSCFB) riser. The SVM model is developed/trained using experimental data collected from a pilot-scale LSCFB reactor. Two different size glass bead particles (500 μm (GB-500) and 1,290 μm (GB-1290)) are used as solid phase, and water is used as liquid phase. The trained model successfully predicted the experimental solids 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 goodness of the model prediction is verified by using different statistical performance indicators. For the both sizes of particles, the mean absolute error is found to be less than 5%. The correlation coefficients (0.998 for GB-500 and 0.994 for GB-1290) also show favorable indications of the suitability of SVM approach in predicting the solids holdup of the LSCFB system.

Study of Phase Distribution of a Liquid-Solid Circulating Fluidized Bed Reactor Using Abductive Network Modeling Approach

Abstract This communication deals with the Abductive Network modeling approach to investigate the phase holdup distributions of a liquid–solid circulating fluidized bed (LSCFB) system. The Abductive Network model is developed/trained using experimental data collected from a pilot scale LSCFB reactor involving 500-μm size glass beads and water as solid and liquid phases, respectively. The trained Abductive Network 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 (~4.67%) and the correlation coefficient (0.992) also show favorable indications of the suitability of Abductive Network modeling approach in predicting the solids holdup of the LSCFB system.

Modelling and numerical simulation of liquid–solid circulating fluidized bed system for protein purification

A novel liquid–solid circulating fluidized bed (LSCFB) was modelled for protein recovery from the feed broth. A typical LSCFB system consists of downer and riser, integrating two different operations simultaneously. A general purpose, extensible, and dynamic model was written based on the tanks-in-series framework. The model allowed adjusting the degree of backmixing in each phase for both columns. The model was validated with previously published data on extraction of bovine serum albumin (BSA) as model protein. Detailed dynamic analysis was performed on the protein recovery operation. The interaction between the riser and downer were captured. Parametric studies on protein recovery in LSCFB system were carried out using the validated model to better understand the system behaviour. Simulation results have shown that both production rate and overall recovery increased with solids circulation rate, superficial liquid velocity in the downer and riser, and feed solution concentration. The model was flexible and could use various forms of ion exchange kinetics and could simulate different hydrodynamic behaviours. It was useful to gain insight into protein recovery processes. The general nature of the model made it useful to study other protein recovery operations for plant and animal proteins. It could also be useful for further multi-objective optimization studies to optimize the LSCFB system.

Multiobjective optimization of the operation of a liquid–solid circulating fluidized bed ion‐exchange system for continuous protein recovery

Like most real-life processes, the operation of liquid-solid circulating fluidized bed (LSCFB) system for continuous protein recovery is associated with several objectives such as maximization of production rate and recovery of protein, and minimization of amount solid ion-exchange resin requirement, all of which need to be optimized simultaneously. In this article, multiobjective optimization of a LSCFB system for continuous protein recovery was carried out using an experimentally validated mathematical model to find the scope for further improvements in its operation. Elitist non-dominated sorting genetic algorithm with its jumping gene adaptation was used to solve a number of bi- and tri-objective function optimization problems. The optimization resulted in Pareto-optimal solution, which provides a broad range of non-dominated solutions due to conflicting behavior of the operating parameters on the system performance indicators. Significant improvements were achieved, for example, the production rate at optimal operation increased by 33%, using 11% less solid compared to reported experimental results for the same recovery level. The effects of operating variables on the optimal solutions are discussed in detail. The multiobjective optimization study reported here can be easily extended for the improvement of LSCFB system for other applications.

Continuous enzymatic polymerization of phenol in a liquid–solid circulating fluidized bed

A liquid–solid circulating fluidized bed (LSCFB) system consisting of 3.8 cm I.D. and 4 m high riser and 12 cm I.D. and 3.5 m high down-comer was investigated in this study for the continuous polymerization of phenol. Approximately 8.5 kg immobilized particles containing soybean seed hull peroxidase enzymes were applied in the LSCFB system. The continuous enzymatic polymerization was carried out in the riser section by introducing phenol and hydrogen peroxide at the entrance of the riser. Under optimized hydrodynamic conditions and by keeping the molar concentration ratio of phenol to H 2O 2 of 1:2, 54% conversion of phenol was achieved. The down-comer of the LSCFB was utilized for the regeneration of the coated immobilized enzyme particles. The effect of the superficial liquid velocity and an initial substrate concentration was studied. Our experimental results show that an enzymatic reaction and the regeneration of the biocatalysts can be carried out simultaneously and independently in the LSCFB system. Furthermore, this work opens the possibilities for many bioprocesses where the deactivation of the biocatalysts is a major problem and the regeneration of the biocatalysts is required.

The hydrodynamic behavior of the liquid–solid circulating fluidized bed ion exchange system for cesium removal

In this work, experimental studies on the hydrodynamics have been carried out in a cold model liquid–solid circulating fluidized bed (LSCFB) ion exchange system where the riser is operated in the circulating fluidization regime and the downcomer in the state of slow-moving packed bed, with the aim of removing cesium from high radioactive liquid waste. Two circulating fluidization zones, the initial and the fully developed, have been observed. The solids circulation rate can be controlled merely by the primary liquid flow if the auxiliary liquid flow is set to zero and the injection tap is located at the middle of the intersection of the riser and the solid-return pipe. Therefore, it is possible to minimize the number of the liquid feed assemblies (pumps, valves, flow meters, etc.), and this is crucial to the treatment of high radioactive waste. The liquid inevitably leaks through the solid-return pipe in most cases because of the “loosening effect” of the liquid feed flow, and the direction and magnitude of the leakage vary with the operating conditions. The system geometry, including the injection tap location and the riser outlet location, plays a very important role in the hydrodynamics of the LSCFB system.

Continuous protein recovery with a liquid–solid circulating fluidized‐bed ion exchanger

AbstractA liquid–solid circulating fluidized‐bed (LSCFB) ion‐exchange system was developed for continuous protein recovery. It contains a downcomer for protein adsorption and a riser for protein desorption, with ion‐exchange particles circulating continuously between the two columns. Effects of the operating conditions on the hydrodynamics and the continuous ion exchange of bovine serum albumin (BSA) in the system were investigated. Under typical operating conditions, up to 98% BSA was adsorbed in the downcomer (showing a very high efficiency of protein removal from the feed), and an overall protein recovery of up to 84% was obtained in the LSCFB system, indicating that the LSCFB system was a very promising strategy for the continuous recovery of proteins.