Types of Slurry Reactors

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... 

The approach based on the energy dissipation rate is not limited to a particular type of slurry reactor. Therefore, equations of type 46 and 52 have also been proposed for stirred-tank reactors. For e the total energy dissipation rate originating from both gas and power inputs via the stirrer must then be used. Hence,... 

INDUSTRIAL ASPECTS AND DIFFERENT TYPES OF SLURRY REACTORS... 

The two common types of slurry reactors are the bubble column (section 4.6.1.2) and the stirred gas liquid contactor (section 4.6.1.3) (Sometimes the bubble column slurry reactor is called a gasiliquid solid fluidized bed see Fan, 1989). Even when a very fine dispersion of bubbles is made, the bubble size usually exceeds the particle size of the solids by a factor of 10 to 100 or more. That means that even for relatively low volume fractions of solids the solid/liquid interfacial area is much greater than the gasAiquid interfacial area. The consequence is that in most situations the mass transfer resistance is concentrated in the film around the bubbles. An important aspect of slurry reactors is that the mass transfer around the bubbles can be influenced by the presence of the solids. The influence can be positive or negative, depending on the prevailing mechanism. Four mechanisms have been identified ... 

When deciding on the type of the reactor required for a particular chemical or physical transformation, the first question that needs to be addresses is whether the cavitation enhancement is the result of an improved mechanical process (due to enhanced mixing). If this is the case, then cavitation pretreatment of a slurry may be all that is required before the system is subjected to conventional type transformation scheme and the scale up of the pretreatment vessel would be a relatively simpler task. 

Reported residue conversion is significantly high for the five types of included reactors and largest for the slurry type of reactor. Besides, the slurry reactor together with the ebullated bed reactor can handle heaviest feedstocks and highest metal contents. Resid conversion requires higher temperatures, and pressure drop is essentially zero in these two reactors. However, product quality is better for the fixed and moving bed processes. 

The other major type of catalytic reactor is a situation where the fluid and the catalyst are stirred instead of having the catalyst fixed in a bed. If the fluid is a liquid, we call this a slurry reactor, in which catalyst pellets or powder is held in a tank through which catalyst flows. The stirring must obviously be fast enough to mix the fluid and particles. To keep the particles from settling out, catalyst particle sizes in a slurry reactor must be sufficiently small. If the catalyst phase is another Hquid that is stirred to maintain high interfacial area for reaction at the interface, we call the reactor an emulsion reactor. These are shown in Figure 74. 

In the third section an extensive writing on two types of slurry catalytic reactors is proposed Bubble Slurry Column Reactors (BSCR) and Mechanically Stirred Slurry Reactors (MSSR). All the variables relevant in the design and for the scale-up and the scale-down of slurry catalytic reactors are discussed particularly from the point of view of hydrodynamics and mass transfer. Two examples of application are included at the end of the section. 

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. 

Hydrodynamics of slurry reactors include the minimum gas velocity or power input to just suspend the particles (or to fully homogeneously suspend the particles), bubble dynamics and the holdup fractions of gas, solids and liquid phases. A complicating problem is the large variety in reactor types (sec Fig. I) and the fact that most correlations are of an empirical nature. We will therefore focus on sparged slurry columns and slurries in stirred vessels. 

As stated previously, another distinction usually made is between slurry and supported catalyst reactors. In slurry photocatalytic reactors the catalyst is present in the form of small particles suspended in the water being treated. These reactors generally tend to be more efficient than supported catalyst reactors, because the semiconductor particles provide a larger contact surface area per unit mass. In fact, the state of the photocatalyst is important both to increase contaminant adsorption and to improve the distribution of absorbed radiation. In a slurry unit the photocatalyst has a better contact with the dissolved molecules and is allowed to absorb radiation in a more homogeneous manner over the reaction volume. Using suspended catalyst has been the usual practice in PTC, CPC, and other types of tubular reactors. The drawback of this reactor design is the requirement for separation and recovery of the very small particles at the end of the water treatment process. This may eventually complicate and slow down the water throughput. 

In continuous or flow reactors the reactant fluid moves continually through the catalyst so at least a semblance of a steady state condition can be established inside the reactor. There are two general types of continuous reactors those in which the catalyst particles are packed into a fixed bed through which the reactant fluid is passed and those in which the reactants pass through a slurry of the catalyst particles. 

A major difference between the two types of multiphase reactors is that the amount of catalyst in the slurry reactor is only 0.01-1% of the total volume, whereas it is 50-60% of the volume of the packed bed. In this chapter the slurry reactor is considered first, because it is the more common type and because having the catalyst concentration as a variable makes it easier to evaluate the kinetic models. 

Loop Slurry Reactors Types of loop reactors... 

Various types of industrial reactors may occur in different phases as applications and desired properties of the final product, for example, the fixed bed, fluidized bed, slurry bed, and bed phase reactors. In fluidized bed reactors as in slurry bed, the solid (catalyst) is composed of very small particles and moving along the reactor. The fluid flow over these reactors is complex. In these systems, the flow of the fluid phase is not homogeneous and there are large deviations from the ideal behavior of a CSTR or plug flow reactor (PFR), characterizing them in nonideal reactors. 

The first step in the progression of a sonochemical process from laboratory to large scale is to determine whether the ultrasonic enhancement is the result of a mechanical or a truly chemical effect. If it is mechanical then ultrasonic pre-treatment of a slurry may be all that is required before the reacting system is subjected to a subsequent conventional type reaction. If the effect is truly sonochemical, however, then sonication must be provided during the reaction itself. The second decision to be made is whether the reactor should be of the batch or flow type. Whichever type is to be used there are only three basic ways in which ultrasonic energy can be introduced to the reacting medium (Table 10.9). Several different types of ultrasonic reactors are currently available (Table 10.10). 

Figure 12.16 Illustration of possible types of slurry bubble column reactors, (a) Simple bubble column, (b) cascade bubble column with sieve trays, (c) packed bubble column, (d) multishaft bubble column, and (e) bubble column with static mixers [61].

Two major types of slurry bubble column reactors are illustrated in Figure 12.17, one from Exxon [68] and the other from Sasol [69]. The reactor containing cooling coils immersed in the slurry is the one that is the most frequently encountered. The concept of one type of reactor patented by Exxon [68] has many similarities to the ARGE fixed-bed reactor except the fixed... 

In addition to the general type of slurry loop process described above, slightly different loop reactor processes also exist. A short summary of two of these processes is shown below. 

A good experimental approach to check the presence/absence of internal mass transfer resistance is to carry out experiments with various particle sizes. By gradually minimizing the particle size, the conversions, yields, and selectivities should approach a limiting value corresponding to the intrinsic kinetics. Sometimes this approach can, however, lead to a cul-de-saq the pressure drop increases, as the particle size is diminished and the kinetic conditions are not attained. Another type of test reactor should then be considered, for instance, a fluidized bed (for gas-phase reactions) or a slurry reactor (for liquid-phase reactions). 

Concerning the reactor technology, the current types of HDT reactors are FBR, MBR, EBR, and slurry-phase reactor (SPR) (Furimsky, 1998), which are also illustrated in Figure 7.3. 

Processes for HDPE with Broad MWD. Synthesis of HDPE with a relatively high molecular weight and a very broad MWD (broader than that of HDPE prepared with chromium oxide catalysts) can be achieved by two separate approaches. The first is to use mixed catalysts containing two types of active centers with widely different properties (50—55) the second is to employ two or more polymerization reactors in a series. In the second approach, polymerization conditions in each reactor are set drastically differendy in order to produce, within each polymer particle, an essential mixture of macromolecules with vasdy different molecular weights. Special plants, both slurry and gas-phase, can produce such resins (74,91—94). 

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