Separation stage

When a mixture contains components with a broad range of volatilities, either a partial condensation from the vapor phase or a partial vaporization from the liquid phase followed by a simple phase split often can produce an effective separation. This is in essence a single-stage distillation process. However, by its very nature, a single-stage separation does not produce pure products hence further separation of both liquid and vapor streams is often required. 

For a single stage separator i.e. only one separator vessel, there is an optimum pressure which yields the maximum amount of oil and minimises the carry over of heavy components into the gas phase (a phenomenon called stripping). By adding additional separators to the process line the yield of oil can be increased, but with each additional separator the incremental oil yield will decrease. 

Capital and operating costs will increase as more separator stages are added to the process line, so a balance has to be struck between increased oil yield and cost. It is uncommon to find that economics support more than 3 stages of separation and one or two stage separation is more typical. The increased risk of separation shut down is also a contributing factor in limiting numbers. 

Multi-stage separation may also be constrained by low wellhead pressures. The separation process involves a pressure drop, therefore the lower the wellhead pressure the less scope there is for separation. 

Each basic operation can be divided into one or more unit operations. Size reduction involves cnishing and grinding depending on the size of material handled, and these may be carried out in stages. Separations can be either soHds from soHds, based on size or mineral composition, or soHds from Hquids, ie, dewatering (qv). Size separation or classification is an integral part of any flow sheet, not only to meet product size specifications, but also to ensure a narrow size distribution for subsequent minerals separation circuits and to decrease the load and improve the efficiency of size reduction units which are energy intensive. 

Static bath mode. Feed enters at one end of the dmm and the floats exit from the other end. The sink product is removed continuously from the rotating dmm through the use of lifters attached to the dmm which empty into a launder as they move to the top. A modification of the simple dmm separator is the two-compartment dmm separator which allows a two-stage separation. In the cone-type separator (up to 6.1 m in dia and 450 t/h) feed is introduced at the top. The medium in the cone is kept in suspension by gentle agitation. The sink product is removed from the bottom of the cone either directly or by airlift in the center of the cone. The maximum particle size that can be separated is limited to 10 cm. Other separators include the Drewboy bath and the Norwaltbath (2). 

The equihbrium constant for this reaction is ca 1.022 at 100°C. The B concentrates in the Hquid phase (23). However, the vapor phase contains ca 40% undissociated complex, which lowers the effective single-stage separation factor to ca 1.014. 

To reduce catalyst losses even further, additional separation equipment external to the regenerator can be installed. Such equipment includes third-stage cyclones, electrostatic precipitators, and more recentiy the Shell multitube separator, which is Hcensed by the Shell Oil Co., UOP, and the M. W. Kellogg Co. The Shell separator removes an additional 70—80% of the catalyst fines leaving the first two cyclones. Such a third-stage separator essentially removes from the due gas stream all particles greater than 10 p.m (36). 

Table 3. Particle-Size Distribution from a Shell Third-Stage Separator ...

Equations for Large Stage Separation Factors. The preceding results have been obtaiaed with the use of equation 2 and by replacing the finite difference, by the differential, chc/ dn both of which are vaUd only when the quantity (a — 1) is very small compared with unity. However,... 

Fhe Stag C Separation Factor. The stage separation factor, in all probabiUty, is appreciably different from the ideal-point separation factor because of the existence of four efficiency terms ... 

The stage separation factor can therefore be related to the ideal-point separation factor by an equation of the form... 

The first term may be considered as the contribution of the internal circulation or convective flow to the stage length, the second term as the contribution of the axial diffusion to the stage length. The stage separation factor is given by... 

E. J. Henley and. D. Seader, Equilibrium-Stage Separation Operations in ChemicalEngineering ]ohn. Wiley Sons, Inc., New York, 1981. 

Waukat, Equilibiium-Staged Separations, Prentice Hall, 1988. 

FIG. 13-19 Liqiiid-phase activity coefficieuts for au n-fieptaue-toliieue system at 101,3 kPa (1 atm), [Henley and Sender, Eqiitlikriiim-Stage Separation Operations iu Chemical Engineering, Wiley, New York, 1981 data ofYerazunis et al., Am, Inst, Ghem, Eng, J, 10 660 (1964). ]... 

FIG. 13-20 Liqi lid-phase activity coefficients for an ethanol-n-hexane system, [Henleij and Seader, Eqiiilihriiim-Stage Separation Operations in Chemical Engineering, Wileif, New York, 1931 data of Si nor and Weher, J, Chem, Eng, Data, 5, 243-247 (I960).]... 

FIG. 13-41 Comparison of rigorous calcnlations with Gilliland correlation. [Henley and Seader, Eqnilihrinm-Stage Separation Operations in Chemical Engineering, Wiley, New York, 1981 data of Van Winkle and Todd, Chem. Eng., 78(21), 136 (Sept. 20, 1971) data of Gilliland, Elements of Fractional Distillation, 4th ed., McGraw-Hill, New York, 1950 data of Brown and Maiiin, Trans. Am. Inst. Chem. Eng., 35, 679 (1.93.9) ]... 

FIG. 22-79 Effect on permeate of dividing a one-stage separation into two equal stages having the same total membrane area. Compositions of A, D, and F are equal for both cases. Cowiesif VF R. Grace. )... 

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