Scale-up of bubble column

It is seldom realized that many rules of thumb utilized for scale-up of different types of equipment are represented by quantities, which fulfill only a partial similarity. As examples, only the volume-related mixing power P/ V widely used for scaling-up mixing vessels and the superficial velocity V which is normally used for scale-up of bubble columns, should be mentioned here. 

Access of Hydrodynamic Parameters Required in the Design and Scale-Up of Bubble Column Reactors... 

The general difficulties in design and scale-up of bubble column reactors concern reaction specific data, such as solubilities and kinetic parameters as well as hydrodynamic properties. The paper critically reviews correlations and new results which are applicable in estimation of hydrodynamic parameters of two-phase and three-phase (slurry) bubble column reactors. 

Dekwer, W.D., Access of Hydrodynamic Parameters Required in the Design and Scale-Up of Bubble Column Reactors, in Chemical Reactors, ACS Symposium Series, American Chemical Society Washington, DC, 1981, pp. 213-241. 

Scaling up of bubble columns is generally based on the requirement of keeping kiA constant. Since A is proportional to, this imphes keeping the superflcial gas velocity constant. Some design aspects of bubble reactors will be illustrated in an example following the section on stirred vessel reactors. 

Kastanek.F., Zahradnik.J., Rylek.M. and J.Kratochvil. "Scaling-up of bubble column reactors on basis of laboratory data". Chem.Engng.Sci. 35 (1980) 456. 

Shaikh A, Al-Dahhan M. (2013b) Scale-up of bubble column reactors a review of current state-of-the-art. Ind. Eng. Chem. Res. DOI 10.1021/ie30208Qm, Publication Date (Web) 28 Mar 2013. 

Youssef A. Fluid dynamics and scale-up of bubble columns with internals [Ph.D. Thesis]. St. Louis (MO) Washington University, 2010. 

Deckwer, W.-D. Absorption and Reaction of Isobutene in Sulfuric Acid III. Considerations on the Scale up of Bubble Columns. 

The simplest form of a bubble column is a vertical tube in which a gas distributor is placed at the bottom packed or plate bubble columns are also used. The gas bubbles rise through the liquid phase, which may flow through the column either cocurrent or countercurrent to the gas. As a result of the short residence time of the gas bubbles in the liquid phase, bubble column reactors are preferred for reactions which require a short gas and a long liquid reaction time. Therefore the residence time distribution of the liquid phase is a characteristic factor for the design of the reactor. The dependence of the residence time distribution upon the column diameter has to be known for any scale-up of bubble columns. 

Mersmann A. (1978) Design an scale-up of bubble and spray column, Ger. Chem. Eng. 1 1-11. 

Failing to identify the limiting reactant can lead to failure in the scale-up of trickle-bed reactors (Dudukovic, 1999). Gas-limited reactions occur when the gaseous reactant is slightly soluble in the liquid and at moderate operating pressures. For liquid-limited reactions, concurrent upflow is preferred (packed bubble columns) as it provides for complete catalyst wetting and thus enhances the mass transfer from the liquid phase to the catalyst. On the other hand, for gas reactions, concurrent downflow operation (trickle-bed reactors), especially at partially wetted conditions, is preferred as it facilitates the mass transfer from the gas phase to the catalyst. The differences between upflow and downflow conditions disappear by the addition of fines (see Section 3.7.3, Wetting efficiency in trickle-bed reactors). 

As this trend levels off with larger columns, it is recommended that values estimated for a 60 cm column are used. If heat transfer is a problem, then heat transfer coils within the column, or even an external heat exchanger, may become necessary when operating a large, industrial bubble column-type fermentor. Scale-up of an internal loop airlift-type fermentor can be achieved in the same way as for bubble column-type fermentors for external loop airhfts see Section 7.7. 

Gas-liquid bubble columns and gas-liquid-solid slurry bubble columns are widely used in the chemical and petrochemical industries for processes such as methanol synthesis, coal liquefaction, Fischer-Tropsch synthesis and separation methods such as solvent extraction and particle/gas flotation. The hydrodynamic behavior of gas-liquid bubble columns and gas-liquid-solid slurry bubble columns are of great importance for the design and scale-up of reactors. Although the hydrodynamics of the bubble and slurry bubble columns has been a subject of intensive research through experiments and computations, the flow structure quantification of complex multi-phase flows are still not well understood, especially in the three-dimensional region. In bubble and slurry bubble columns, the presence of gas bubbles plays an important role to induce appreciable liquid/solids mixing as well as mass transfer. The flows within these systems are divided into two... 

Other work has been mainly concerned with the scale-up to pilot plant or full-scale installations. For example, Beltran et al. [225] studied the scale-up of the ozonation of industrial wastewaters from alcohol distilleries and tomato-processing plants. They used kinetic data obtained in small laboratory bubble columns to predict the COD reduction that could be reached during ozonation in a geometrically similar pilot bubble column. In the kinetic model, assumptions were made about the flow characteristics of the gas phase through the column. From the solution of mass balance equations of the main species in the process (ozone in gas and water and pollution characterized by COD) calculated results of COD and ozone concentrations were determined and compared to the corresponding experimental values. 

As far as the scale-up of a bubble column from a laboratory to an industrial scale is concerned, one will have to keep in mind that the scale-up rule is not v = idem, as is often stated in the chemical-engineering literature, but Fr = v2/(d g) = idem. This means ... 

Fig. 16. Scale-up of packed bubble column (S2). Solid symbol indicates the longer column in each pair. Lower curve, areas air-dithionite + TCP, 1-in. ceramic Intalox saddles, column heights 20 cm (e = 0.75) and 38.5 cm (e = 0.77). Middle curve, ki a COj-NajCOs + NaHCOs + TCP, 1-in. stainless steel Pall rings, heights 10 cm (e = 0.84) and 20 cm ( = 0.90) also air-CuCl + NaCl + HCI + TCP, 1-in. ceramic Raschig rings heights 20 cm (e = 0.73) and 38.5 cm ( = 0.79). Upper curve, air-CuCI + HCI, 1-in. ceramic Intalox saddles, heights 20 cm (e - 0.77) and 38.5 cm ( = 0.73).

Krishna, R., van Eaten, J.M. and Ursenau, M.I. (2000a), Three-phase Eulerian simulations of bubble column reactors operating in the churn-turbulent regime a scale-up strategy, Chem. Eng. Sci., 55, 3275-3286. 

Wilkinson, P.M. Sper, A.P. Van Dierendonck, L.L. Design parameters estimation for scale-up of high-pressure bubble columns. AIChE J. 1992, 38, 544. 

However, from the standpoint of scale up, both bubble fractionation and solvent sublation are severely limited by the low gas and liquid loading rates necessary for efficient separations. In comparison to other industrial wastewater treatment processes for hydrophobic compounds, both bubble fractionation and solvent sublation are at the present time unsatisfactory in terms of both the degrees of separation and the gas and liquid loading rates currently achievable in the bubble columns used for these processes. A lot more remains to be done before these techniques can find practical utility in large scale treatment processes. 

In the experimental design of distillative separations both bubble-cap columns with a minimum diameter of 30-40 mm and columns with random or ordered packings and a minimum diameter of 30 mm can be used. With regard to scale-up of the plate number, columns with bubble-cap plates are most favorable, since their performance depends least on loading, system pressure, and the system to be separated. Columns made of glass are preferred. 

Ellenberger, J., and Krishna, R. (1994), A unified approach to the scale-up of gas-solid fluidized bed and gas-liquid bubble column reactors, Chemical Engineering Science, 49(24B) 5391-5411. 

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