Gaseous diffusion stage separation factor

The ratio [y/(l —y)]l[x/(l — x)] is called the stage separation factor and is denoted by a. Analogous separation factors are used to characterize all separation processes. A value of a close to unity indicates that the separation is difficult a value far from unity, easier. For gaseous diffusion of UF, a is so close to unity that the process must be repeated many times for a useful degree of separation. To do this, the low-pressure eiuiched UF must be recompressed to the feed pressure and cooled. The depleted UF, which experiences some pressure loss, must also be recompressed (not shown). 

The development next to be given of equations for the number of stages, interstage flow rates, and fraction on each stage does depend on the process used. In subsequent numerical examples, the gaseous diffusion process with a U/ U stage separation factor of 1.00429 is assumed. 

It is proposed that B be concentrated by the gaseous diffusion process applied to BFs and "BF3. The plant is to be designed as an ideal cascade and is to separate feed containing 19 percent °B into product containing 90 percent and tails containing 8 percent. The stage-separation factor is 1.0074. 

Figure 14.7 Cross-flow gaseous diffusion stage. Stage separation factor a = > (l — )/ ( — y) stage efficiency E = (y — x)l(y — Xo) Np, Ni, N,M = molar flow rates Xp, Xf, x,y,v= mole fraction light component.

Stage separation factor. For a cross-flow gaseous diffusion stage with a cut 6 of the stage separation factor a is given by... 

Gaseous Diffusion. In the gaseous diffusion process, the UFfi flows through a porous nickel membrane called the barrier. The heavier U-238F6 flows more slowly than the U-235F6, and the theoretical separation factor for an equilibrium stage is ... 

The minimum number of stages increases as the overall separation increases and as the separation factor approaches unity. Because both these conditions hold in a typical isotope separation plant, the minimum number of stages is often very large. For example, in a gaseous diffusion plant (a = 1.00429) making product containing 90 percent and tails 0.3 percent. 

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