Bubble column reactor
A bubble column reactor is an apparatus used for gas-liquid reactions first applied by Helmut Gerstenberg. It consists of vertically arranged cylindrical columns. The introduction of gas takes place at the bottom of the column and causes a turbulent stream to enable an optimum gas exchange. It is built in numerous forms of construction. The mixing is done by the gas sparging and it requires less energy than mechanical stirring. The liquid can be in parallel flow or counter-current.
Bubble column reactors are characterized by a high liquid content and a moderate phase boundary surface. The bubble column is particularly useful in reactions where the gas-liquid reaction is slow in relation to the absorption rate. This is the case for gas-liquid reactions with a Hatta number Ha <0.3.
Bubble column reactors are used in various types of chemical reactions like wet oxidation, or as algae bioreactor. Since the computerized design of bubble columns is restricted to a few partial processes, experience in the choice of a particular type column still plays an important role.
Literature
Bubble column reactors belong to the general class of multiphase reactors which consist of three main categories namely, the trickle bed reactor (fixed or packed bed), fluidized bed reactor, and the bubble column reactor. Bubble columns are the devices in which gas, in the form of bubbles, come in contact with the liquid. The purpose may be simply to mix the two phases or substances are transferred from one phase to another i.e. when the gaseous reactants are dissolved in liquid or when liquid reactant products are stripped. The bubble column in which the gas is fed into the column at the bottom and rises in the liquid escaping from it at the upper surface; the gas is consumed to a greater or lesser extent depending on the intensity of mass transfer and chemical reaction.
Modeling of bubble column reactors
The wide use of bubble column reactors (e.g.: phosgenation, oxidation, hydrogenation and alkylation) has led to various modeling, design and scale up procedures for these gas-liquid contactors. Masood et al.[1] and Masood and Delgado [2][3] recently suggested various novel models to simulate bubble columns and reported good agreement with the experiments. Shimizu et al.[4] utilized Sauter mean diameter as a single bubble size and took into account the bubble break-up and coalescence in the air-water system for predicting the gas-liquid volumetric mass transfer coefficient and gas hold-up by simulation. Since the bubble size has a strong influence on hydrodynamic parameters such as bubble rise velocity, gas residence time, gas-liquid interfacial area and gas-liquid mass transfer coefficient, it can be claimed that considering bubble size distribution can assist the modeling of bubble columns more logically.[5] Ramezani et al.[5] modeled the bubble column reactor, considering the complete bubble size distribution in the governing equations of mass transfer and reported a good agreement with experimental data. Bioconversion of glucose to gluconic acid was considered in their investigation and concluded that superficial gas velocity favors volumetric mass transfer coefficient and increases the amount of oxygen transfers from gas phase to liquid. The reaction kinetics of gluconic acid production were revealed in subsequent research.[6] Recently Pourtousi et al. developed a new combination of soft computing methods (e.g., ANFIS) and Euler-Euler to predict the behavior of bubble column reactors. They found that the bubble column prediction time can rapidly decrease when the soft computing method is implemented in modeling of reactors.[7]
References
- ↑ Masood, R.M.A.; Rauh, C.; Delgado, A., CFD simulation of bubble column flows: An explicit algebraic Reynolds stress model approach. Int. J. Multiphase Flow 2014, 66, (2014), 11-25.
- ↑ Masood, R.M.A.; Delgado, A., Numerical Investigation of Three-Dimensional Bubble Column Flows: A Detached Eddy Simulation Approach. Chem. Eng. Technol. 2014, 37, (10), 1-9.
- ↑ Masood, R.M.A.; Delgado, A., Numerical investigation of the interphase forces and turbulence closure in 3D square bubble columns. Chem. Eng. Sci. 2014, 108, (2014), 154-168.
- ↑ Shimizu, K.; Takada, S.; Minekawa, K.; Kawase, Y., Phenomenological model for bubble column reactors: prediction of gas hold-ups and volumetric mass transfer coefficients. Chem. Eng. J. 2000, 78, (1), 21-28.
- 1 2 Ramezani, M.;Mostoufi, N.; Mehrnia, M.R., Improved Modeling of Bubble Column Reactors by Considering the Bubble Size Distribution. Ind. Eng. Chem. Res. 2012, 51, (16), 5705–5714.
- ↑ Ramezani, M.;Mostoufi, N.; Mehrnia, M.R., Effect of hydrodynamics on kinetics of gluconic acid enzymatic production in bubble column reactor. Chem. Ind. Chem. Eng. Quart. 2013, 19, (3), 411-442.
- ↑ M. Pourtousi, J. Sahu, P. Ganesan, S. Shamshirband, G. Redzwan, A combination of computational fluid dynamics (CFD) and adaptive neuro-fuzzy system (ANFIS) for prediction of the bubble column hydrodynamics, Powder Technology, 274 (2015) 466-481.