Packed bed depth

TABLE 7.4 HETS, Packed Bed Depths Required for Modern Packings... 

Begley has reported temperature data taken in a bed consisting of 5 x -in. alumina pellets packed in a 2-in. pipe (actual 2.06 in. ID) through which heated air was passed. The tube was jacketed with boiling glycol to maintain the tube wall at about 197°C. For a superficial mass velocity (average) of air equal to 300 lb/(hr)(ft ) the experimental temperatures at various packed-bed depths are as follows ... 

If packed bed depth (Hi) and voidage e ) are known, then if the mass remains constant the bed depth at any voidage can be determined ... 

Table 5-8 gives some successful applications of this technique as applied to a variety of industrial odors. Such scrubber designs normally use a plastic packing, such as 1 or 2 Super Intalox packing. This type of packing presents a large surface area for malodorous material absorption and provides a high liquid residence time for oxidation of the absorbed contaminant. Typically, the tower diameter is selected to produce a superficial air velocity from 4.8 to 6.6 ft/s. The liquid circulation rate usually will be 11 to 19 gpm per 1,000 cfm of air flow. Packed-bed depth normally varies from 8 ft to 11 ft. An effective entrainment elim-... 

With the advancements in liquid distribution technology, packed bed depths are being increased in order to better utilize the available column height. Packed depths up to 40 ft, which develop over 25 theoretical stages, are becoming more common with the use of high-performance liquid distributors. 

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,...

FIG. 14-119 Aerodynamic cut diameter for a tyj)ical packed-bed entrainment separator as a function of pacldng size, bed depth, and three gas velocities curve 1-1.5 m/s, curve 2-3.0 m/s, and curve. 3-4.5 m/s. To convert meters to feet, multiply by. 3.281 to convert centimeters to inches, multiply by 0..394. [Calveti, J. Air Pollut. Control Assoc., 24, 929 (1974).]... 

For most large-scale processes, adsorbent particle size varies from 0.06 to 6 mm (0.0025 to 0.25 in), but the adsorbent packed in a fixed bed will have a fairly narrow particle size range. Pressure drop in adsorbers can be changed by changing the diameter to bed depth ratio and by changing the particle size (see Sec. 5). Adsorbent size also determines separation performance of adsorbent columns—increasing efficiency with decreasing particle size. In hquid-phase process-... 

It turns out that packed beds much less than a hundred particles thick behave as if they were weU-stirred due to the entrance effect. Although it may seem odd that a packed bed can behave as if weU-stirred, it typically takes at least a 100-particle bed depth in order for a phig-flow concentration wave to develop. 

Packed bed heights typically vary from 20 ft to 30ft. Many times the location of manholes to provide access to the redistributor will determine the packed depth. Whenever more than 15 theoretical stages are required in one packed bed, good liquid distribution is critical. ... 

Fig. 9 shows comparisons of CFD results with experimental data at a Reynolds number of 986 at three of the different bed depths at which experiments were conducted. The profiles are plotted as dimensionless temperature versus dimensionless radial position. The open symbols represent points from CFD simulation the closed symbols represent the points obtained from experiment. It can be seen that the CFD simulation reproduces the magnitude and trend of the experimental data very well. There is some under-prediction in the center of the bed however, the shapes of the profiles and the temperature drops in the vicinity of the wall are very similar to the experimental case. More extensive comparisons at different Reynolds numbers may be found in the original reference. This comparison gives confidence in interstitial CFD as a tool for studying heat transfer in packed tubes. 

The fluidized-bed depth, Ljh is calculated from the fixed-bed packed depth, Lpa, as... 

Mist Eliminators. Most modem mist eliminators use fiber beds enclosed or supported by stainless steel or alloy-20 wire mesh or the tike. Fibers are generally glass, or in some cases Teflon. Mist eliminator design, ie, fiber diameter, packing density, bed depth, etc, is determined by particle size and loading, which is in turn determined largely by the application. 

In scale-up from laboratory quantities (up to 10 kg) to production batches (300 kg and up), bed depth increases significantly. The most notable consequence is an increase in finished product bulk density, typically in the range of 15% to 20%. In some instances, this is a disadvantage (if product is packed by volume and a low density is desired). However, granule strength is usually greater as a result of the decreased interstitial void space. 

System Dia. m Packing Type Size, m Bed Depth m HETP, m HTU, m System press., kPa... 

---