Bed-size factor

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 required desiccant weight is a function of several factors the water removal requirements (mass/time), the cycle time, the equiUbrium loading of water on the desiccant at the feed conditions, the residual water loading on the desiccant after regeneration, and the size of the mass-transfer zone of the desiccant bed. These factors, in turn, depend on the flow rate, temperature, pressure, and water content of both the fluid being dried and the regeneration fluid (see Adsorption, gas separation). 

Limiting size factor Mold size Bag size Lathe bed length and swing Pull capacity Press capacity Press dimensions... 

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. 

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. 

Important criteria in the design of a fluidized-bed process are numerous and the most important are sorbent bead size and density, ligand accessibility for a given residence time, and stability of the solid phase. Upward speed is also critical and, with beads of a given density and particle size, is the result of a compromise between the maximum loading speed and the bed expansion factor. 

First, it will be shown that flow properties of the fluidized catalyst bed (FCB) are clearly different from those of other conventional fluidized beds. The different treatment required is very significant for research and development on fluidized catalytic beds. Next, factors affecting the flow properties are discussed, especially particle size distribution, and also heat and mass transfer, and mixing properties. 

Ideally it should be possible to predict simply from the fresh feed catalyst size analysis and a specific reactor and cyclone geometry how the bed analysis and reactor losses will change with time and how these will converge to an equilibrium. If attrition were not a significant factor it is obvious that the addition of fresh make-up catalyst coarser than the losses would cause the bed size distribution to become continually coarser until theoretically losses would be reduced to zero. 

The productivity is mainly determined by the permeability of sinter bed. Any factor which has an effect on the permeability will have an influence on the productivily. On one hand, coarser coke breeze and limestone produce larger porosity of the sinter bed. On the other hand, because of poor granulation characteristics of coke breeze, the position of coarser coke breeze in the granulation particle is different from that of intermediate and finer coke breeze. Fig.l shows coke breeze and limestone particle size on FFS and -5mm fraction. The result shows that FFS is faster in experiment 1 which coke breeze and limestone mean particle size are 2.33 and 2.38 mm. In addition, -5mm fraction increases and again decreases afterwards with a decrease of FFS increasing. When coke breeze and limestone are 1.71 and 1.55 mm (in experiment 5), -5mm fraction reaches minimum. 

The productivity of DR processes depeads oa chemical kinetics, as weU as mass and heat transport factors that combine to estabhsh the overall rate and extent of reduction of the charged ore. The rates of the reduction reactions are a function of the temperature and pressure ia the reductioa beds, the porosity and size distribution of the ore, the composition of the reduciag gases, and the effectiveness of gas—sohd contact ia the reductioa beds. The reductioa rate geaerahy iacreases with increasing temperature and pressure up to about 507 kPa (5 atm). 

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