Centrifugation Process

Ma.nufa.cture. The batch nitration processes for nitrocellulose have included the pot process, the centrifugal process, the Thompson displacement process, and the mechanical dipper process. Semicontinuous nitration processes are also widely used for military and industrial grades. 

The UFg is then isotopicaHy enriched by gaseous diffusion or gas centrifuge processes for nuclear appHcations. 

Reversible Processes. Distillation is an example of a theoretically reversible separation process. In fractional distillation, heat is introduced at the bottom stiUpot to produce the column upflow in the form of vapor which is then condensed and turned back down as Hquid reflux or column downflow. This system is fed at some intermediate point, and product and waste are withdrawn at the ends. Except for losses through the column wall, etc, the heat energy spent at the bottom vaporizer can be recovered at the top condenser, but at a lower temperature. Ideally, the energy input of such a process is dependent only on the properties of feed, product, and waste. Among the diffusion separation methods discussed herein, the centrifuge process (pressure diffusion) constitutes a theoretically reversible separation process. 

It should be noted that the separation factor for the centrifuge process is a function of the difference in the mol wts of the components being separated rather than, as is the case in gaseous diffusion, a function of their ratio. The gas centrifuge process would therefore be expected to be relatively more suitable for the separation of heavy molecules. As an example of the equiUbrium separation factor of a gas centrifuge, consider the Zippe centrifuge, operating at 60°C with a peripheral velocity of 350 m/s. From equation 68, OC is calculated to be 1.0686 for uranium isotopes in the form of UF. ... 

For the same case of n = 1200 rpm and r = 0.5, we obtain u,/Ug = 800, whereas for the turbulent regime the ratio was only 28. This example demonstrates that the centrifugal process is more effective in the separation of small particles than of large ones. Note that after the radial velocity u, is determined, it is necessary to check whether the laminar condition. Re < 2, is fulfilled. For the transition regime, 2 < Re < 500, the sedimentation velocity in the gravity field is ... 

Figure 3-12. Single-stage, high speed (>5000 ft) centrifugal process pump. Pumps are high speed, gear driven, and especially suited for applications in light hydrocarbon liquid service. (Courtesy Sundstrand Fluid Handling, Inc.)...

The effects of impeller shape for the usual centrifugal process pump performance are given in Figure 3-34. The only part the process designer can play is in the selection... 

PVDF can be processed by all the conventional molten-state methods, such as extrusion, injection, compression, transfer, rotational and blow moulding, thermoforming and centrifugal processes. It can be also processed by powdering and dispersion applications. 

After the oil crisis in 1973, the need for large enrichment capacities for supply of fuel to the nuclear power plants became obvious and several European countries (Belgium, France, Italy and Spain) decided to build the huge Eurodif gas diffusion plant. This plant is located in France, in the Rhone valley, a few kilometers away from the Pierrelatte plant. Simultaneously, England, West Germany and the Netherlands (the Troika) chose to jointly develop the centrifugation process for uranium enrichment, which does not use membranes. 

At least three pesticide plants use priority pollutant metals separation systems in the United States [7]. One plant uses hydrogen sulfide precipitation to remove copper from its pesticide wastewater. The operating system consists of an agitated precipitator to which the H2S is added, a soak vessel to which sulfur dioxide is added, a neutralization step using ammonia, and a gravity separation and centrifuging process. Copper is removed from an influent level of 4500 mg/L to 2.2 mg/L. 

Composites (e.g., the thermite reaction, 3Fe304+8Al=4Al203+9Fe) have been used to coat the inside of steel pipes with an inner layer of Fe, and a surface layer of AI2O3, using a centrifugal process. 

The current gas centrifuge process goes back to a study by Gemot Zippe (Ref 5). According to theory, the maximum separative work which a gas centrifuge can produce per unit time is ... 

A higher yield of cheese is obtained when homogenized milk is used for cheesemaking. This is due to increased fat and moisture retention of the curd. However, the fat in the whey cannot be recovered by centrifugal processes because of the failure of homogenized fat globules to cluster. 

The ultracentrifuge can be used to separate fractions of different molecular weights in a mixture of solutes and to determine the molecular weight of a solute. Two different approaches can be taken. In the sedimentation velocity approach, the change in the concentration profile with time is determined during the centrifugation process. This nonequilibrium process requires a knowledge of diffusion rates and is not based directly on thermodynamics. We will leave a discussion of this process to other texts. 

In the commercial process, a centrifuge process is used to speed up the separation. The continuous centrifuges can operate at 2500 gs, the droplets hav-... 

There are also process-specific considerations. For example, a long-residence-time settling vessel might allow the use of a demulsifier that diffuses to the interface slowly, but which produces a very well resolved (separated) emulsion, whereas a centrifuge process (having a short residence time) may require a demulsifier that diffuses to the emulsion interface rapidly, but is slightly less effective at emulsion breaking [68],... 

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