Multiphase Bioreactor Design

Joaquim M.S. Cabral, Manuel Mota, Johannes Tramper

• Publisher: CRC Press
• Year: 2001
• Print ISBN: 9780415272094
• eBook ISBN: 9781134485482
• Topic: Physical Sciences
• Subtopic: Industrial & Technical Chemistry

Bioreaction engineering is fundamental to the optimization of biotechnological processes and the production of biochemicals by enzymes, microbial, plant and animal cells and higher organisms. A reference text for postgraduate students and researchers in biochemical engineering and bioreactor design, Multiphase Bioreactor Design describes the

CHAPTER ONE
NEW METHODOLOGIES FOR
MULTIPHASE BIOREACTORS 1:
HYDRODYNAMIC AND MASS
TRANSFER CHARACTERISTICS OF
MULTISTAGE SLURRY REACTORS

JINDŘICH ZAHRADNÍK^†

Institute of Chemical Process Fundamentals, Academy of Sciences of the
Czech Republic, Rozvojová 135, 165 02 Prague 6-Suchdol, Czech
Republic

ABSTRACT

The advantageous features of multistage bubble column reactors for aerated slurry systems have been illustrated by the results of an extensive experimental study aimed at examining the effect of selected construction and operating variables (number of reactor stages, distributing plate geometry, gas and liquid flow rates, solid phase concentration) on hydrodynamic and mass transfer characteristics of multistage aerated slurry reactors. Experimental results proved the favourable effect of column sectionalisation on gas holdup and k_La_L values, and on the energy effectiveness of gas-liquid contacting. The effect of increasing solid concentration on these system characteristics was negative within the whole region of experimental conditions. The relationship between k_La_L and gas holdup was independent of the solid phase concentration and gas flow rate. However, the value of k_La_L corresponding to the given gas holdup ratio increased substantially with the increasing number of column stages. Axial mixing of the liquid (slurry) phase was well described by the model of perfectly mixed tanks in series with backflow, for the number of series terms equal to the number of column stages. Evaluation of the backflow coefficient stressed the importance of plate design optimisation for particular flow conditions. Implications of the experimental findings for the performance and applicability of multistage slurry reactors has been discussed thoroughly. Recommendations for future research have been given, aimed at clarifying particular aspects of multistage reactors performance with slurry systems and ultimately at providing reliable basis for the design and scale-up of such reactors.

INTRODUCTION

According to their operation mode, the multistage bubble column reactors sectionalised by internal plates represent a class of reactors with dispersed gas phase, distinguished by the energy input with gas compression and by spatially distributed energy dissipation in the reactor (Schügerl, 1983). Although it has been commonly acknowledged that sectionalisation of bubble column reactors can significantly improve their mass transfer characteristics and, at the same time, substantially reduce the degree of backmixing in contacted phases (Schügerl et al., 1977; Shah et al., 1978; Shah et al., 1982; Deckwer, 1985), the multistage bubble column reactors have been only scarcely applied to chemical or biotechnological processes in aerated slurry systems. This type of slurry reactor has been received little coverage even in scientific literature. Accordingly, the multistage bubble column reactors were not even mentioned in the comprehensive treatment of reactors for gas-liquid-solid systems published by Shah (1979), and they were touched only marginally in the respective part of the more recent book on heterogeneous reactions authored by Doraiswamy and Sharma (1984). The Solvay towers, used in soda production (Shah et al., 1978), thus still represent the proverbial exception proving the rule, regarding the industrial application of sectionalized bubble columns for g-l-s systems. In the bioreactors area, performance of a laboratory-scale multistage tower fermentor was studied by Prokop and co-workers (1969) and the application prospects of staged bubble column fermentors were subsequently discussed e.g. by Sittig and Heine (1977) and by Schügerl (1980, 1983). On the industrial scale, various modifications of internal-loop airlift reactors with dual-flow plates in the riser have been reportedly used for SCP production by the Japanese companies Kanefuchi and Mitsubishi Co. (Schügerl, 1983) and, most notably, a similar construction principle has been employed in the 1500 m³ pressure cycle fermenter designed for the ICI PRUTEEN plant (Westlake, 1986). These applications have not, however, found many followers and the multistage tower fermenters were not even listed in the review paper of Mersmann and co-workers (1990), devoted to the selection and design of aerobic bioreactors. Apparently, it is the fear of plate holes choking and/or solid phase sedimenting on internal plates which has been primarily responsible for the reluctant approach to the application of staged bubble columns for systems with a suspended solid phase. While these phenomena may, indeed, represent a definite threat, namely in rapidly sedimenting systems, sectionalized bubble columns can be, according to our opinion, advantageously employed for pseudohomogeneous (non-sedimenting) suspensions of fine particles and/or in cases of small density differences between the solid and the liquid phases. Obviously, this latter condition is generally fulfilled in biological systems. Furthermore, the danger of plates choking can be to a large degree circumvented by the use of plates with downcomers, i.e. with the separate passage of gas and slurry phases.

Our previous study (Vlaev and Zahradník, 1987) demonstrated superior energy effectiveness of sectionalised bubble columns in comparison with other types of tower reactors for aerated slurry systems, including single-stage bubble column, tower reactor with an ejector distributor, and multistage rotating-discs reactor. In the following, the advantageous features of multistage bubble column reactors for aerated slurry systems will be illustrated with the results of the experimental study (Zahradník et al., 1992) aimed at examining the effect of selected construction and operating variables (number of column stages, distributing plate geometry, gas and liquid flow rates, solid phase concentration) on hydrodynamic and mass transfer characteristics of multistage aerated slurry reactors. The particular objectives of the reported work included:

• Evaluating the effect of column sectionalisation on liquid or suspension phase backmixing in the reactor and on the values of gas holdup and volumetric coefficient of mass transfer between the gas and liquid phases (k_La_L);
• Derivating and experimentally verifying physically realistic model of liquid phase (suspension) residence time distribution in a multistage bubble column sectionalised by perforated plates with downcomer tubes without overflow weirs and investigating the effect of operating regime on the extent of liquid backflow between the adjacent column stages;
• Experimentally determining the effect of solid phase concentration on gas holdup values and on the rate of gas-liquid mass transfer, i.e. on the values of k_La_L; Evaluating the effect of column sectionalisation and solid phase concentration on the energy effectiveness of bubble bed formation and of gas-liquid interfacial mass transfer.

EXPERIMENTAL

The experiments were carried out in a bubble column reactor 0.29 m in diameter and 2 m in height. The column was built of glass cylinders mounted between metal flanges and could be alternatively divided into three or six stages (stage height 0.6 m or 0.3 m respectively) by internal perforated plates with downcomer tubes without overflows. The plates were made of brass sheets 2 mm thick, free plate area ratio was 0.25%, holes diameter 1.8 mm. The downcomer tubes were 0.1 m long and 0.04 m in diameter; some preliminary experiments in the three-stage column were performed also with the tube length 0.42 m. The scheme of the experimental set-up is given in Figure 1.1; constructing details of distributing plates (position of downcomer tubes and placing...

Table of contents

• COVER PAGE
• TITLE PAGE
• COPYRIGHT PAGE
• PREFACE
• CONTRIBUTORS
• CHAPTER ONE: NEW METHODOLOGIES FOR MULTIPHASE BIOREACTORS 1: HYDRODYNAMIC AND MASS TRANSFER CHARACTERISTICS OF MULTISTAGE SLURRY REACTORS
• CHAPTER TWO: NEW METHODOLOGIES FOR MULTIPHASE BIOREACTORS 2: IMAGE ANALYSIS AND MULTIPHASE BIOREACTORS
• CHAPTER THREE: NEW METHODOLOGIES FOR MULTIPHASE BIOREACTORS 3: DATA ACQUISITION, MODELLING AND CONTROL
• CHAPTER FOUR: DESIGN AND MODELLING OF IMMOBILISED BIOCATALYTIC REACTORS
• CHAPTER FIVE: ADVANCES IN THE SELECTION AND DESIGN OF TWO-LIQUID PHASE BIOCATALYTIC REACTORS
• CHAPTER SIX: ENZYMATIC MEMBRANE REACTORS
• CHAPTER SEVEN: REVERSED MICELLAR BIOREACTION SYSTEMS: PRINCIPLES AND OPERATION
• CHAPTER EIGHT: SOLID-TO-SOLID BIOCONVERSIONS: BATCH OR CONTINUOUS?
• CHAPTER NINE: SOLID/GAS SYSTEMS, THEORY AND APPLICATIONS
• CHAPTER TEN: BIOFILM REACTORS
• CHAPTER ELEVEN: PULSING BIOREACTORS
• CHAPTER TWELVE: DESIGN OF LIQUID-LIQUID-SOLID FLUIDISED-BED BIOREACTORS
• CHAPTER THIRTEEN: FLOCCULATION BIOREACTORS
• CHAPTER FOURTEEN: BIOREACTOR DESIGN FOR PLANT CELL SUSPENSION CULTURES
• CHAPTER FIFTEEN: LETHAL EFFECTS OF BUBBLES IN ANIMAL-CELL CULTURE
• CHAPTER SIXTEEN: A LOW-COST TECHNOLOGY FOR ENTOMOPATHOGENIC NEMATODE LARGE-SCALE PRODUCTION
• CHAPTER SEVENTEEN: MARINE SPONGES AS BIOCATALYSTS