Bed size

Shorter cycle times produce smaller bed sizes. The minimum cycle time is usually dictated by the minimum regeneration time required to heat and cool the bed. Systems of greater than two beds provide some flexibiUty in regeneration time but add to investment costs. 

In this section, representative results are reviewed to provide a prospective of reactor modeling techniques which deal with bed size. There probably is additional unpublished proprietary material in this area. Early studies of fluidized reactors recognized the influence of bed diameter on conversion due to less efficient gas-solid contacting. Experimental studies were used to predict reactor performance. Frye et al. (1958) used... 

Once a technique has been established to design a model which simulates the hydrodynamics of a hot (possibly pressurized) fluidized bed, then a series of different sized models can be used to determine the influence of bed size on the performance of commercial beds, see Fig. 20. Model A simulates the behavior of commercial bed A, model B simulates a larger commercial bed B and so forth. Then by comparing models A, B with C we can determine the expected changes in operating characteristics when commercial bed A is replaced by larger beds B and C. 

Small, properly scaled laboratory models operated at ambient conditions have been shown to accurately simulate the dynamics of large hot bubbling and circulating beds operating at atmospheric and elevated pressures. These models should shed light on the overall operating characteristics and the influence of hydrodynamics factors such as bubble distribution and trajectories. A series of different sized scale models can be used to simulate changes in bed behavior with bed size. 

Test runs using a 150 mm diameter fluid bed coater indicated that a batch of 2 kg of material could be coated using a liquid spray rate of 10 ml/min for 50 minutes and a fluidizing gas rate of 40 scfm. It is desired to scale-up this process to a batch size of 200 kg of bed material. For the scaled up process, determine the bed size the liquid and airflow rates and the new run time. 

Case B. Suppose, more realistically, that the catalyst undergoes a known, experimentally determined, rate of attrition as a function of particle size (Zenz, 1971 Zenz Kelleher, 1980). The particle loss rate from the cyclone system will now approach and finally equal the rate of production of 0 to 10 micron particles by attrition from all the larger sizes. To maintain reactor inventory, this loss rate will be replaced, at an equal rate, with fresh catalyst. Since the rate of attrition of any size particle depends on its concentration in the stream subjected to the attrition (as finer particles effectively cushion the coarser), and since the loss is replaced with fresh catalyst (containing the coarsest), the bed size distribution will reach a steady state between 10 and 150 microns in which the mean size, as well as all sizes smaller than the largest, will now be decreased from what would have prevailed under conditions of zero attrition. 

Adsorbents are available as irregular granules, extruded pellets and formed spheres. The size reflects the need to pack as much surface area as possible into a given volume of bed and at the same time minimise pressure drop for flow through the bed. Sizes of up to about 6 mm are common. 

The rest of the terms in Eq. (9.18) are readily obtained from the literature and then the resulting value of the overall mass transfer coefficient kK can then be substituted into Eq. (9.18). We now have the required added length of the mass transfer zone and the bed sizing is complete. 

The first pass at the adsorber sizing is now complete and a check on the overall pressure drop expected can be obtained from the Ergun equation. An adjustment in the bed diameter may be required and then the bed size can be fixed using one more pass through the sizing process outlined above. 

A bed size factor which is typically expressed as either the mass or volume of adsorbent required to produce 1 tonne day of O2. In either case this factor can be reduced to the relative throughput it is a measure of how long a unit must operate to produce its own volume of purified product O2. 

The capital cost of air separation machinery is linked to both the size of the beds (which dictates the cost of piping valves), of course to molecular sieve inventory and to the size of the compressor required to run the process. A low product recovery may have little impact on the bed size factor but it has an enormous effect on the amount of gas required and on the cost of compressing that gas. Thus the recovery and bed size factors have direct links to the cost of capital and operations of air separation machines. 

Air separation by PSA on a large scale is today dominated by machines in which the pressure swing may be from near atmospheric to substantially sub-atmospheric pressure. The industry typically calls these machines vacuum swing adsorption (VSA) separators. A second sub-class in air separation is the machines that use a pressure swing the ranges from somewhat super-atmospheric to sub-atmospheric and these may be called trans-atmospheric PSA. The distinctions made here have implications as to equipment specifications and performance limitations in both bed size factor and O2 recovery. 

Unlike PSA air separation the adsorbents used in hydrogen purification are not limited to zeolite molecular sieves. Garbons and silica gel are used in many PSA installations. Zeolites are used for obtaining certain critical specifications where the nature of the isotherms that they possess helps in recovery, achieving purity and minimizing bed size factors. 

The bed size needed for any given user may be calculated once the region s pan evaporation rate (Inches/month) and wastewater volume addition rate (gal/month) are known. The equation Is ... 

Check for slugging The bubble size (32 cm) is small compared to the bed size (200 cm), hence no slugging. 

Figure 20.12 Different bubble sizes give different bed sizes for maximum production of intermediate.

Apply 1 ml of the clear solution on top of a column containing the immobilized antigen, e.g., rabbit IgG. The bed size depends on the capacity of the support in this example it should be 4-5 ml. Wash with Soln. A until the O.D.280 of the eluate is < 0.05. 

Three compounds recovered from parfait columns were also previously tested for breakthrough from 5-mL Teflon beds (6). The capacity factors for these compounds and their recoveries from the Teflon bed of a parfait column showed a rough correlation. Phenanthrene, which was tested in the parfait column only in the presence of humate, was recovered essentially quantitatively from the 5-mL Teflon column and had a capacity factor of 368. About 15 of the caffeine applied to a parfait column in the absence of humate could be recovered from Teflon, and caffeine showed a capacity factor of 22. Only about 2 of the 2,4-dichlorophenol applied to parfait columns could be recovered on Teflon its capacity factor was 5.6. It may therefore be anticipated that compounds following the inverse correlation of solubility with capacity factor and having a capacity factor greater than about 20 should be detectably absorbed to the Teflon bed of a parfait column. Simply increasing the volume of the Teflon bed may also increase the absolute recovery of adsorbable solutes that have modest values of kFor this reason, a 150-mL bed of Teflon per 8 L of water may not be the ideal bed size a larger bed may be better. 

The size of the adsorbent beds is limited by factors such as the physical strength of the adsorbent materials, vessel transportation, efficiency of flow distribution and other practical considerations. As a result of recovery and bed size limitations, the production rate of 2.-, 3-, or 4-bed systems generally has an upper limit of 12-13 MMSCFD. 

Duration of exposure to the wind Size of the particle bed Size distribution and density of the particles Value. de Xst el 7b+... 

Avoid introducing air bubbles. Slowly pour slurry down a thin glass rod inserted into empty column. The column and bed sizes depend on the amount of His-tagged protein to be purified. Generally, the binding capacity of Ni-NTA superflow is 5-10 mg protein per mL resin Ni-NTA superflow is supplied as 50% slurry. 

The wall effect on the performance of fluidized beds can be reflected by the differences of the overall hydrodynamic behavior in beds with different diameters. Practically, in order to scale up a pilot fluidized bed to a full-size commercial unit, the size of the pilot unit should be large enough to exclude the wall effect. A critical scale-up diameter (Dcs) for the pilot fluidized bed is thus defined as the minimum bed diameter beyond which the bed behavior is almost independent of the bed size. Calculate the critical scale-up diameter for fluidized beds without internals, using the following criterion ... 

Fluidized bed Sized coal required Dry coal required for feeding... 

Figure 15. Schematic of the five grids superimposed on the outcrop face of an eolian sand (Page sandstone, Coconino county Arizona). The three largest grids contains more than one bed. Size of the largest grid is about 100 by 180 ft. and the smallest about 15 inches square. (Reproduced from Ref. 5 )...

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