Packed bed irrigated

Fig. 22. Performance cut diameter predictions for typical dry packed bed particle collectors as a function of bed height or depth, packing diameter and packing porosity (void area) S. Bed irrigation increases collection efficiency or decreases cut diameter (271). SoHd lines, = 25 mm dashed lines,...

Fluidised beds have been used previously for the industrial-scale recovery of the antibiotics streptomycin and novobiocin.30 However, more recently, considerable interest has been shown in the use of fluidised beds for the direct extraction of proteins from whole fermentation broths.31 In a packed bed, the adsorbent particles are packed within the contactor. The voidage, that is, the inter-particle space, is minimal and thus feedstock clarification is mandatory to avoid clogging of the bed. In a fluidised/expanded bed, the adsorbent bed is allowed to expand by irrigation with feedstock. Bed voidage is increased, allowing the passage of particulates in the feed. The diameters of the adsorbent beads are exaggerated for illustrative clarity. 

Further work regarding the axial dispersion of gas in irrigated packed beds seems needed, and it may be noted, with particular regard to gas-liquid-particle processes, that no results have been reported for beds of cylindrically or spherically shaped packing materials. 

Fached-Bed Scrubbers Packed-bed scrubbers using gas-absorption-type tower packing may also be used for collecting soluble solids, but are not irrigated intensively enough to avoid plugging by deposits of... 

At the top of the packed bed a liquid distributor of suitable design provides for the uniform irrigation of the packing which is necessary for satisfactory operation. Four... 

When the packed bed is irrigated, the liquid holdup causes the pressure drop to increase. The experimental data are reasonably well correlated by (Billet and Schultes, 1991a)... 

A more rigorous approach to flooding is based on pressure drop models of irrigated packed beds, see Sect. 5.4.2.3. 

For packed beds used in gas and liquid contacting, the liquid can flow in the opposite direction to the gas (countercurrent operation), or it can flow in the same direction as the gas (concurrent operation), or the gas flow can be transverse to the liquid flow (crossflow operation). The theory of pressure drop in irrigated packed beds is not as well developed as that for single-phase flow. 

To reduce the CO2 content of the absorber exit gas stream, the majority of the lean solvent can be fed to the absorber to irrigate the second packed bed down from the top. A portion of the lean solvent will be cooled to about 190 F and fed to the top of the absorber as shown in Figure 3-5. The cooler solvent in contact with the exit gas stream at the top of the absorber has a lower equilibrium vapor pressure of CO2. However, this modification does add a sensible heat load to the system that somewhat increases the regenerator reboiler duty. 

A vacuum deaerator diameter typically is specified to give a liquid irrigation rate of about 40 gpm/ft of column cross-sectional area. Originally, vacuum deaerators used ceramic packings and operated at lower liquid rates however, most modern columns use 2-in. or larger-size plastic packings with a packed bed typically 7-ft to 15-ft deep. 

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