Fluidized reactors example

All these gas-liquid-particle operations are of industrial interest. For example, desulfurization of liquid petroleum fractions by catalytic hydrogenation is carried out, on the industrial scale, in trickle-flow reactors, in bubble-column slurry reactors, and in gas-liquid fluidized reactors. 

There are processes in which the total amount of catalyst is entrained by the gas. The reactors then belong to the category of transport reactors. Examples are some of the present Fischer-Tropsch reactors for the production of hydrocarbons from synthesis gas and the modern catalytic cracking units. Fig 10.11 shows the Synthol circulating solids reactor. In the dilute side of the circuit, reactant gases carry suspended catalyst upward, and the fluidized bed and stand-pipe on the other side of the circuit provide the driving force for the smooth circulation of the solid catalyst. For the removal of heat, heat exchangers are positioned in the reactor. 

Supported Ti02 photocatalysts can be implemented in fluidized beds, fixed powder layer reactors, annulai- reactors and monolith reactors. Examples of these reactors ai e described in the following section ... 

For the heterogeneous system, the problem is very simple. We just write the above equation for each phase, taking into account Q as the heat transfer between the two phases. For a nonadiabatic system, the heat added from outside, Sexternai (which is the Q in Eq. (6.44)], will be added to the phase receiving it, or distributed between the two phases if it is added to both phases (this will depend very much on the configuration and knowledge of the physical system as will be shown with the nonadiabatic bubbling fluidized-bed catalytic reactor example). 

Luss and Amundson (1968) have studied the dynamics of catalytic fluidized beds. The system is a good example of a stiff set of differential equations. Catalytic fluidized beds are utilized for a variety of reactions such as oxidation of naphthalene and ethylene and the production of alkyl chlorides. A batch fluidization reactor is usually built as a cylindrical shell with a support for the catalyst bed. The reactants enter from the bottom through a cone and cause the catalyst particles to be fluidized in the reactor. The reactants leave through a cyclone in which the entrained solids are separated and returned to the bed. 

Fluidized bed noncatalytic reactors. Fluidized heds are also suited to gas-solid noncatalytic reactions. All the advantages described earlier for gas-solid catalytic reactions apply. As an example. 

As mentioned in Section 2.2 (Fixed-Bed Reactors) and in the Micro activity test example, even fluid-bed catalysts are tested in fixed-bed reactors when working on a small scale. The reason is that the experimental conditions in laboratory fluidized-bed reactors can not even approach that in production units. Even catalyst particle size must be much smaller to get proper fluidization. The reactors of ARCO (Wachtel, et al, 1972) and that of Kraemer and deLasa (1988) are such attempts. 

The previous example was a rather unique application and not a typical case for fluidization. Although some fluidized bed reactions are executed at elevated pressure, like the naphtha reforming, most are used at atmospheric or at low pressures. The proceeding conceptual sketch. Figure 8.2.4, gives the most important features of a fluid-bed, cataljdic reactor. 

The calcium bisulfite acid used in the manufacture of sulfite cellulose is the product of reaction between gaseous sulfur dioxide, liquid water, and limestone. The reaction is normally carried out in trickle-bed reactors by the so-called Jenssen tower operation (E3). The use of gas-liquid fluidized beds has been suggested for this purpose (V7). The process is an example of a noncatalytic process involving three phases. 

Membrane reactors are defined here based on their membrane function and catalytic activity in a structured way, predominantly following Sanchez and Tsotsis [2]. The acronym used to define the type of membrane reactor applied at the reactor level can be set up as shown in Figure 10.4. The membrane reactor is abbreviated as MR and is placed at the end of the acronym. Because the word membrane suggests that it is permselective, an N is included in the acronym in case it is nonpermselective. When the membrane is inherently catalytically active, or a thin catalytic film is deposited on top of the membrane, a C (catalytic) is included. When catalytic activity is present besides the membrane, additional letters can be included to indicate the appearance of the catalyst, for example, packed bed (PB) or fluidized bed (FB). In the case of an inert and nonpermselective... 

Another important challenge is to enhance the reliability of the design and scale up of multi-phase reactors, such as fluidized bed reactors and bubble-colunms. The design uncertainty caused by the complex flow in these reactors has often led to the choice of a reactor configuration that is more reliable but less efficient. An example is Mobil use a packed-bed reactor for the methanol to gasoline process in New Zealand, even though a... 

Typical examples of XRD analysis of copper powder recovered in the inverse fluidized bed electrode reactors can be seen in Fig. 2, where the ratovered copper powder was almost pure. Effects of fluidized particles on the size distribution of copper powder recovered in the reactors can be seen in Fig. 3. Note that the addition of a small amount of fluidized particles could decrease the size of recovered copper powder, but a further increase of particle amount could increase the size of copper powder, compared with that without fluidized particles. This can be due to that the added particles(up to 1. Owt.%) can contact with the cathode plate frequently, which could be resulted in the effective cut of the copper powder growing perpendicular to the surface of the cathode plate. 

Fig. 2. Typical example of XRD analysis of copper powder recovered in inverse fluidized bed reactors(LAc=0.015m, 1=3.0 A/dm W=1.0wt.%).

The limiting-current method has been used widely for studies in packed and fluidized beds (see Table VII, Part H). Limiting current measurements in these systems overlap in part with the design and analysis of packed-bed and fluidized-bed electrochemical reactors in particular the potential distribution in, and the effectiveness of, such reactors (for example, for metal removal from waste streams) is an extensive area of research, which cannot be covered in this review. For a complete discussion of porous flow-through electrodes the reader is referred to Newman and Tiedemann (N8d). 

Different reactor networks can give rise to the same residence time distribution function. For example, a CSTR characterized by a space time Tj followed by a PFR characterized by a space time t2 has an F(t) curve that is identical to that of these two reactors operated in the reverse order. Consequently, the F(t) curve alone is not sufficient, in general, to permit one to determine the conversion in a nonideal reactor. As a result, several mathematical models of reactor performance have been developed to provide estimates of the conversion levels in nonideal reactors. These models vary in their degree of complexity and range of applicability. In this textbook we will confine the discussion to models in which a single parameter is used to characterize the nonideal flow pattern. Multiparameter models have been developed for handling more complex situations (e.g., that which prevails in a fluidized bed reactor), but these are beyond the scope of this textbook. [See Levenspiel (2) and Himmelblau and Bischoff (4).]... 

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