Plug-flow characteristics

Plug flow was further investigated in various channel sizes of different material for both liquid-liquid flow systems, i.e. ionic liquid-deionised water (Table 4.1), and TBP/ionic liquid (30 % v/v)-nitric acid solutions (Table 3.2). Experiments were carried out at various mixmre velocities (0.0028-0.067 m s ) and volume fractions (eil = 0.4-1). In the Teflon channels plug flow was established in all cases with the aqueous phase flowing as non-continuous plugs within the TBP/ionic liquid phase (30 %, v/v) (carrier phase), whilst in the glass microchannel experiments were carried out with the aqueous phase as the carrier fluid as well. The experimental procedure and the techniques followed for these measurements are explained in Sects. 3.4 and 3.5. The setup used for the measurements is shown in Fig. 3.2. 

---

Stable expanded-bed operations promise the ability to handle whole broths efficiently, all the while maintaining plug-flow characteristics. Magnetically stabihzed fluidized beds have been shown to work effectively for bioproduct separations, but are not yet used commercially. A commerci y available process uses well-designed beads of appropriate densities and sizes to enable bed fluidization and stable operation without appreciable recirculation. 

The Kenics mixer has been shown to provide thorough radial mixing. This results in a reduction in radial gradients in velocity, composition, and temperature. Because the unit possesses nearly plug flow characteristics, both temperature and product quality controls are achieved. 

Plug flow characteristics of aging reactor Stabilization (hydrolysis)... 

Existing entrained-flow reactors with solid particle flow can be retrofitted with monoliths in which the channel structure also works as a flow straightener, providing better plug-flow characteristics in large-diameter entrained-flow reactors, which suffer from backmixing of catalyst at the reactor wall (53-55). 

Recycling increases the size of the reactor and degrades the plug flow characteristics, so there must be practical compensation by adjustment of the temperature or composition. 

Reaction kinetics and product distribution were observed in a small isothermal quartz glass reactor (diameter 8mm) with plug flow characteristics (Fig. 1). 

The plug flow reactor (PFR) presents the same concentration curve along the reactor length, which is shown for the tank reactor with reaction time. In the steady state, the concentrations of substrates and products at distinct positions of the reactor do not change with time. The reactor has plug flow characteristics,... 

Fluidized bed reactors are advantageous if small particles which would give high flow resistance in a fixed bed reactor are used to minimize external mass transfer resistances. Often it is useful to install nets at different heights of the reactor to approach plug flow characteristics. 

Slurry back-mixing in the enhanced SBCR is significantly reduced by the addition of the down-comer/dip-tube flow path consequently, the gas and liquid phases likely exhibited more plug-flow behavior. Thus, for a given space velocity, the enhanced SBCR should yield a higher conversion than that of a CSTR [4]. Differences in conversion between the enhanced SBCR and CSTR reactor types may also be caused by the dissimilarity of heat and mass transfer phenomena. In addition, the relatively large L/D ratio of the SBCR may also contribute to its plug-flow characteristics. 

Reactors systems that have plug flow characteristics (that is, iV > 5 or Bo > 7, see Sect. 3.3) differ from CSTR types in that in the former case there is a narrow residence time distribution. The whole mathematical theory of continuous cultivation discussed so far has concerned the well-mixed stirred tank reactor. 

Fast reactions are ideally suited for CFB risers. Processes in which CFB reactors are preferred include those in which high selectivities are essential, coke formation or some other poisoning mechanism is rapid, gas plug flow characteristics are desirable (i.e., where product inhibition or degradation is significant), or reactions where the solids are the primary reactant. 

---