Packed beds surface area

THE PACKED BED SURFACE AREA, ft 2/ft 3 BED EFFECTIVE PARTICLE DIAMETER, ft. ... 

If the flow per irrigation point is uniform, there must be the same number of irrigation points for every square foot of bed cross-sectional area. This causes the liquid flow to every square foot of the packed bed surface to be the same. To ensure conformance with these criteria, the design can be checked by any of several methods. One method involves dividing the column into quadrants plus concentric circles of equal areas. Thus, a 7-ft 6-in. ID column uses eight equal areas to be evaluated, while an 11-ft 0-in. ID column uses 12 areas, and a 15-ft 0-in. ID column uses 16 areas. The number of distribution points in each of these equal areas must be the same. 

Wetted surface area In a packed bed, the area of the packing exposed to the internal reflux. A measure of the packing s vapor-liquid contacting efficiency. 

The collector SLT combines a packing support grid with a vane collector. As a king support, it can suf iort the direct load of packings with surface areas up to 350 mVm. Fen- smaller packings, additional p plates are used. This non-welded collector SLT is often u in applications where space between packed beds is critical. This collector r iuixes a support ring inside the column. 

At high Reynolds numbers the friction factor becomes nearly constant, approaching a value of the order of unity for most packed beds. In terms of S, particle surface area per unit volume of bed,... 

From surface area to volume ratio considerations, the internal area is practically all in the small pores. One gram of the adsorbent occupies 2 cm as packed and has 0.4 cnP in small pores, which gives a surface area of 1150 m /g( or about 1 mi per 5 lb or 6.3 miVft of packing). Based on the area of the annular region filled with adsorbate, the solute occupies 22.5 percent of the internal pore volume and 13.5 percent of the total packed-bed volume. 

The three principal catalyst bed configurations are the pellet bed, the monolith, and the metallic wire meshes. An open structure with large openings is needed to fulfill the requirement of a low pressure drop even at the very high space velocities of 200,000 hr-1. On the other hand, packings with small diameters would provide more external surface area to fulfill the requirement for rapid mass transfer from the g .s stream to the solid surface. The compromise between these two ideals results in a rather narrow range of dimensions pellets are from to 1 in. in diameter, monoliths have 6 to 20 channels/in., and metallic meshes have diameters of about 0.004 to 0.03 in. 

Control of emissions of CO, VOC, and NOj, is high on the agenda. Heterogeneous catalysis plays a key role and in most cases structured reactors, in particular monoliths, outperform packed beds because of (i) low pressure drop, (ii) flexibility in design for fast reactions, that is, thin catalytic layers with large geometric surface area are optimal, and (iii) attrition resistance [17]. For power plants the large flow... 

Sintered metal fibers with filaments of uniform size (2-40 (tm), made of SS, Inconel, or Fecralloy , are fabricated in the form of panels. Gauzes based on thicker wires (100-250 tm) are made from SS, nickel, or copper. They have a low surface area of about 10 m g. Several procedures are used to increase the surface area, for example, leaching procedures, analogous to the production of Ra-Nickel, and electrophoretic deposition of particles or colloid suspensions. The porosity of structures formed from metal fibers range from 70 to 90%. The heat transfer coefficients are high, up to 2 times larger than for random packed beds [67]. 

Dixon and coworkers [25] have performed several CFD simulations of fixed beds with catalyst particles of different geometries (Figure 15.9). The vast number of surfaces and the problems with meshing the void fraction in a packed bed have made it necessary to limit the number of particles and use periodic boundary conditions to obtain a representative flow pattern. Hollow cylinders have a much higher contact area between the fluid and particles at the same pressure drop. However, with a random packing of the particles, there wiU be a large variation... 

A great savings in enzyme consumption can be achieved by immobilizing the enzyme in the reactor (Fig. 12). In addition to the smaller amount of enzyme required, immobilization often increases the stability of the enzyme. Several designs of immobiliz-ed-enzyme reactors (lERs) have been reported, with open-tubular and packed-bed being the most popular. Open-tubular reactors offer low dispersion but have a relatively small surface area for enzyme attachment. Packed-bed reactors provide extremely high surface areas and improved mass transport at the cost of more dispersion. 

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