Bubble column type reactor

FIG. 19-31 Some examples of bubble column reactor types, (a) Conventional bubble column with no internals. (6) Tray bubble column, (c) Packed bubble column with the packing being either an inert or a catalyst. [From Mills, Ramachandran, and Chaudhari, Multiphase Reaction Engineeringfor Fine Chemicals and Pharmaceuticals, Reviews in Chemical Engineering, 8(1-2), 1992, Figs. 2, 3, and 4.]... 

The major attention, both industrial and academic, during the past 15 years, has been given to the slurry bubble column reactors and the literature on this subject in general, and specifically for the FT synthesis, has exploded. Several options exist today for the slurry reactors some of these are illustrated in Figure 12.16 [61]. The simple bubble column reactor (type A) is most commonly encountered and has been applied for the... 

FT synthesis. The multishaft bubble column reactor (type D) has also been utilized for the FT synthesis or at least one of the shafts of 6 inch diameter has been utilized by Exxon. Several laboratory-scale bubble column reactors with static mixers have been evaluated for the FT synthesis at the laboratory scale. 

External and internal loop air-lifts and bubble column reactors containing a range of coalescing and non-Newtonian fluids, have been studied (52,53). It was shown that there are distinct differences in the characteristics of external and internal loop reactors (54). Overall, in this type of equipment... 

Runaway criteria developed for plug-flow tubular reactors, which are mathematically isomorphic with batch reactors with a constant coolant temperature, are also included in the tables. They can be considered conservative criteria for batch reactors, which can be operated safer due to manipulation of the coolant temperature. Balakotaiah et al. (1995) showed that in practice safe and runaway regions overlap for the three types of reactors for homogeneous reactions (1) batch reactor (BR), and, equivalently, plug-flow reactor (PFR), (2) CSTR, and (3) continuously operated bubble column reactor (BCR). 

Slurry Bubble Column Reactors (SBCR) This reactor is tubular (Figure 3.12). The liquid is agitated by means of dispersed gas bubbles. Gas bubbles provide the momentum to suspend the catalyst particles. The gas phase flows upward through the reactor at a constant rate. This reactor could be of continuous type or of semibatch type. This type is used only in catalysis. 

There are two types of slurry reactors slurry bubble column reactor (SBCR, Figure 3.25) and agitated slurry reactor (ASR, Figure 3.26). These reactors differ in that the solid... 

Bubble column reactors are quite commonly employed in the petrochemical industries for many oxidation and hydrogenation reactions (1 ). This type of reactor is ideal for reactions occurring in the slow reaction regime in which relatively low energy input is required to minimize the effect of mass transfer resistance. Nevertheless, attention has been drawn to the... 

In general, the procedure for designing a bubble column reactor (BCR) (1 ) should start with an exact definition of the requirements, i.e. the required production level, the yields and selectivities. These quantities and the special type of reaction under consideration permits a first choice of the so-called adjustable operational conditions which include phase velocities, temperature, pressure, direction of the flows, i.e. cocurrent or countercurrent operation, etc. In addition, process data are needed. They comprise physical properties of the reaction mixture and its components (densities, viscosities, heat and mass diffusivities, surface tension), phase equilibrium data (above all solubilities) as well as the chemical parameters. The latter are particularly important, as they include all the kinetic and thermodynamic (heat of reaction) information. It is understood that these first level quantities (see Fig. 3) are interrelated in various ways. 

The FT process is well known and already applied on a large scale [9,10,11,12]. Currently, the two players that operate commercial Fischer-Tropsch plants are Shell and Sasol. In the Sasol and Shell plants gasification of coal and partial oxidation of natural gas, respectively, produce the syngas for the FT synthesis with well-defined compositions. Shell operates the SMDS (Shell Middle Distillate Synthesis) process in Bintulu, Malaysia, which produces heavy waxes with a cobalt catalyst in multi-tubular fixed bed reactors. Sasol in South Afirica uses iron catalysts and operates several types of reactors, of which the slurry bubble column reactor is the most versatile (i.e. applied in the Sasol Slurry Phase Distillate SSPD),... 

Two types of polyvinylpyrrolidones (PVP-Bayer, Leverkusen, Germany) have been found beneficial to cell growth in spinner cultures, and a mixed molecular weight PVP has been found to protect hybridoma cells against shear injury in a bubble column reactor (Handa, 1986). 

With this approach, even the dispersed phase is treated as a continuum. All phases share the domain and may interpenetrate as they move within it. This approach is more suitable for modeling dispersed multiphase systems with a significant volume fraction of dispersed phase (> 10%). Such situations may occur in many types of reactor, for example, in fluidized bed reactors, bubble column reactors and multiphase stirred reactors. It is possible to represent coupling between different phases by developing suitable interphase transport models. It is, however, difficult to handle complex phenomena at particle level (such as change in size due to reactions/evaporation etc.) with the Eulerian-Eulerian approach. 

Several types of bubble column reactor are used in practice, some of which are shown in Fig. 11.1. As can be seen from this figure, several different modes of... 

Three phase fluidized bed reactor/slurry reactor FIGURE I l.l Types of bubble column reactors (from Lee and Tsui, 1999). 

The list is merely suggestive. Complexity of reactive flows may greatly expand the list of issues on which further research is required. Another area which deserves mention here is modeling of inherently unsteady flows. Most flows in engineering equipment are unsteady (gas-liquid flow in a bubble column reactor, gas-solid flow in a riser reactor and so on). However, for most engineering purposes, all the details of these unsteady flows are not required to be known. Further work is necessary to evolve adequate representation of such flows within the CFD framework without resorting to full, unsteady simulations. This development is especially necessary to simulate inherently unsteady flows in large industrial reactors where full, unsteady simulations may require unaffordable resources (and therefore, may not be cost effective). Different reactor types and different classes of multiphase flows will have different research requirements based on current and future applications under consideration. 

In its most simple form a bubble column reactor basically consists of a vertical cylinder with a gas distributor at the inlet, as sketched in Fig 8.1. Simple construction and lack of any mechanically operated parts are two characteristic aspects of the reactor. In general, the bubble column is an adaptable type of reactor which is reasonable in price and can be built in large sizes. The ratio between length and diameter may vary, but ratios between 3 and 10 are most common [28]. Units of 100 — 200 (m ) are regarded as very large in the chemical industry. 

Fig. 8.6. Special types of bubble column reactors. Figures depicted from Onken [109] (Reproduced by permission from Verein Deutscher Ingenieure (VDI)- Gesellschaft Verfahrenstechnik und Chemieingenieurwesen 2007) and Deckwer [28] (Copyright John Wiley Sons Limited. Reproduced with permission). Similar figures can also be found in Shah and Sharma [133] and Shah et al [132].

Design and operation of reactors for catalytic hydrogenation in the fine chemical industries are discussed. The requirements for a good multiproduct catalytic hydrogenation unit as well as the choice of the reactor type are considered. Packed bed bubble column reactors operated without hydrogen recycle are recommended as the best choice to obtain a flexible reactor with good selectivities. 

In fine-chemicals production with heterogeneous catalysis two main types of cylindrical reactor are in common use-stirred tank reactors with a small so-called aspect ratio (length-to-diameter ratio), and column reactors (e. g., jet-loop reactor, bubble-column reactor, trickle-bed reactor) with a relatively large aspect ratio. 

Two reactor types dominate in the synthesis of chemicals in the case of gas-liquid reactions the tank reactor and the bubble column. Both types can be operated in continuous or... 

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