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Bubble column reactors liquid phase dispersion

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. [Pg.78]

Although the most realistic model for a bubble column reactor is that of dispersed plug-flow in both phases, this is also the most complicated model in view of the uncertainty of some of the quantities involved, such a degree of complication may not be warranted. Because the residence time of the liquid phase in the column... [Pg.219]

Commercial reactors are non isothermal and often adiabatic. In a noniso-thermal gas-liquid reactor, along with the mass dispersions in each phase, the corresponding heat dispersions are also required. Normally, the gas and liquid at any given axial position are assumed to be at the same temperature. Thus, in contrast to the case of mass, only a single heat-balance equation (and corresponding heat-dispersion coefficient) is needed. Under turbulent flow conditions (such as in the bubble-column reactor) the Peclet number for the heat dispersion is often assumed to be approximately equal to the Peclet number for the mass dispersion in a slow-moving liquid phase. [Pg.71]

Pavlica and Olson38 outlined a generalized axial dispersion model for the isothermal bubble-column reactor in which a pseudo-first-order reaction occurred in both the gas and liquid phases. The model considered axial mixing in both the gas and the liquid phases. Here, we review a model for the reactor in which a generalized (m, n)th-order reaction between a gaseous species A and a liquid species C is carried out in the liquid phase. There are many chlorination, nitration, sulfonation, alkylation, and hydrogenation reactions which can be... [Pg.135]

The other situation which may require special treatment is a boundary of multiphase dispersion through which dispersed phase particles are allowed to escape, but not the continuous phase (for example, the top surface of gas-liquid dispersion in a bubble column reactor). The standard outlet boundary conditions need to be suitably modified to represent the observed flow processes. It is possible to simulate the actual behavior by specifying appropriate sink near the top surface (see Ranade, 1998 and Chapter 11). [Pg.109]

This gas-liquid modeling approach has been used performing dynamic simulations of two-phase bubble column reactor flows operating at low gas holdups [201, 202, 19]. A major limitation revealed in these simulations is that there is some difficulties in conserving mass for the dispersed phases, so this concept is not recommended for the purpose of simulating chemically reactive flows. [Pg.469]

Finally, we studied the effect of liquid dispersion on catalyst performance by comparing the performance of the powder catalyst in a bubble column reactor with the HyperCat-FT system. As shown in Figure 6, the CO conversion is much lower for a low Peclet number (bubble colunm reactor with a back-mixed liquid phase) as opposed to a higher Peclet number for the HyperCat system. The tests were conducted under the same process conditions and Damkohler number. The change in Peclet number did not change the liquid product... [Pg.206]

When carrying out a gas-liquid reaction, the gas may be dispersed in the liquid, as in bubble-column reactors or stirred tanks, or the gas phase may be continuous, as in spray contactors or trickle-bed reactors. The fundamental kinetics are independent of the reactor type, but the reaction rate per unit volume and the selectivity may differ because of differences in surface area, mass transfer coefficient, and extent of mixing. In the following sections, gas holdup and mass transfer correlations and other performance data for gas liquid reactors are reviewed and some problems of scaleup are discussed. [Pg.288]

Mathematical models for different kinds of gas-liquid reactors are based on the mass balances of components in the gas and liquid phases. The flow pattern in a tank reactor is usually close to complete backmixing. In the case of packed and plate columns, it is often a good approximation to assume the existence of a plug flow. In bubble columns, the gas phase flows in a plug flow, whereas the axial dispersion model is the most realistic one for the liquid phase. For a bubble column, the ideal flow patterns set the limit for the reactor capacity for typical reaction kinetics. [Pg.256]

In a recent study Jakobsen et al. [71] examined the capabilities and limitations of a dynamic 2D axi-symmetric two-fluid model for simulating cylindrical bubble column reactor flows. In their in-house code all the relevant force terms consisting of the steady drag, bulk lift, added mass, turbulence dispersion and wall lift were considered. Sensitivity studies disregarding one of the secondary forces like lift, added mass and turbulent dispersion at the time in otherwise equivalent simulations were performed. Additional simulations were run with three different turbulence closures for the liquid phase, and no shear stress terms for the gas phase. A standard k — e model [95] was used to examine the effect of shear induced turbulence, case (a). In an alternative case (b), both shear- and bubble induced turbulence were accounted for by linearly superposing the turbulent viscosities obtained from the A — e model and the model of Sato and Sekoguchi [138]. A third approach, case (c), is similar to case (b) in that both shear and bubble induce turbulence contributions are considered. However, in this model formulation, case (c), the bubble induced turbulence contribution was included through an extra source term in the turbulence model equations [64, 67, 71]. The relevant theory is summarized in Sect. 8.4.4. [Pg.901]

In this chapter, we focus on our efforts to model dispersed multiphase flows in which a discrete phase (consisting of solid particles, gas bubbles, or liquid droplets) is moving through, or is moved by, a continuous Newtonian fluid phase. Such flows appear frequendy in process equipment in the chemical, metallurgical, pharmaceutical, and food industries. Examples include fluidized bed reactors, spouted bed reactors, pneumatic conveyors, bubble column reactors, slurry reactors, and spray driers. Figure 1 shows a schematic overview of typical dispersed multiphase systems. [Pg.138]

Coil and soaker reactors can be classified as gas-liquid systems wherein the dispersed phase is composed by the produced gas, the vaporized low molecular weight hydrocarbons, and superheated steam, while the continuous phase comprises the visbroken residue. Based on this, the coil reactor can be represented as a two-phase plug-flow reactor (PER) or as a series of equal-volume continuous-stirred tank reactor (CSTR), while the soaker reactor can be modeled as a bubble-column reactor or as CSTR. Visbreaking reactions proceed via free radical mechanism and take place in the liquid phase, being the feed flowrate that decides the liquid-phase residence time in both reactors. [Pg.86]

The parameter p (= 7(5 ) in gas-liquid sy.stems plays the same role as V/Aex in catalytic reactions. This parameter amounts to 10-40 for a gas and liquid in film contact, and increases to lO -lO" for gas bubbles dispersed in a liquid. If the Hatta number (see section 5.4.3) is low (below I) this indicates a slow reaction, and high values of p (e.g. bubble columns) should be chosen. For instantaneous reactions Ha > 100, enhancement factor E = 10-50) a low p should be selected with a high degree of gas-phase turbulence. The sulphonation of aromatics with gaseous SO3 is an instantaneous reaction and is controlled by gas-phase mass transfer. In commercial thin-film sulphonators, the liquid reactant flows down as a thin film (low p) in contact with a highly turbulent gas stream (high ka). A thin-film reactor was chosen instead of a liquid droplet system due to the desire to remove heat generated in the liquid phase as a result of the exothermic reaction. Similar considerations are valid for liquid-liquid systems. Sometimes, practical considerations prevail over the decisions dictated from a transport-reaction analysis. Corrosive liquids should always be in the dispersed phase to reduce contact with the reactor walls. Hazardous liquids are usually dispensed to reduce their hold-up, i.e. their inventory inside the reactor. [Pg.388]

Similar factors have been developed for bubble columns, which includes the concept of gas hold-up eG, the fraction of the reactor liquid volume occupied by the gas dispersed in the liquid phase. The number of such factors can be reduced when comparing the mass transfer of just one compound in the same liquid/gas system, e. g. for oxygen or ozone transfer in clean water/air systems the above relationship reduces to the first three terms. [Pg.92]

Bubble slurry column reactors (BSCR) and mechanically stirred slurry reactors (MSSR) are particular types of slurry catalytic reactors (Fig. 5.3-1), where the fine particles of solid catalyst are suspended in the liquid phase by a gas dispersed in the form of bubbles or by the agitator. The mixing of the slurry phase (solid and liquid) is also due to the gas flow. BSCR may be operated in batch or continuous modes. In contrast, MSSR are operated batchwise with gas recirculation. [Pg.304]

Gas-liquid reactions form an integral part of the production of many bulk and specialty chemicals, such as the dissolution of gases for oxidations, chlorin-ations, sulfonations, nitrations, and hydrogenations. When the gaseous reactant must be transferred to the liquid phase, mass transfer can become the rate-limiting step. In this case, the use of high-intensity mixers (motionless mixers or ejectors) can increase the reaction rate. Conversely, for slow reactions a coarse dispersion of gas, as produced by a bubble column, will suffice. Because a large variety of equipment is available (bubble columns, sieve trays, stirred tanks, motionless mixers, ejectors, loop reactors, etc.), a criterion for equipment selection can be established and is dictated by the required rate of mass transfer between the phases. [Pg.252]

Usually, the typology of batch reactors also includes the semi-batch gas-liquid reactors, in which a gaseous phase is fed continuously in order to provide one of the reactants. A typical example is given by the reactors used both in different oxidative industrial processes and in the active sludge processes for the treatment of wastewater. It is possible to distinguish between the bubble columns (Fig. 7.1(c)), in which the gas rises undisturbed in the liquid phase, and the bubble stirred reactor, in which a mechanical mixer is added. Finally, the slurry reactors can be considered, in which the liquid phase contains a finely dispersed solid phase as well, which can act as a reactant or as a heterogeneous catalyst these reactors assume in general the features of Fig. 7.1(d). [Pg.161]


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See also in sourсe #XX -- [ Pg.170 , Pg.171 ]




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Bubble columns

Bubble dispersed

Bubble dispersion

Bubble phase

Bubble-column reactor

Bubbling phase

Column liquid phases

Column reactor

Disperse phase

Dispersion reactor

Dispersive liquids

Dispersive phase

Liquid column

Liquid phase reactors

Liquid reactors

Phase dispersion

Reactor phase

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