Multistage operations

When it is desired to compute, with rigorous methods, actual rather than equilibrium stages, Eqs. (13-69) and (13-94) can be modified to include the Murphree vapor-phase efficiency T ij, defined by Eq. (13-29). This is particularly desirable for multistage operations involving feeds containing components of a wide range ol volatility and/or concentration, in which only a rectification (absorption) or stripping action is provided and all components are not sharply separated. In those cases, the use of a different Murphree efficiency for each component and each tray may be necessary to compute recovery accurately. 

In fluidized-bed adsorbers, the combination of high gas rate and small adsorbent particle size results in suspension of the adsorbent, giving it many of the characteristics of a fluid. Fluidized bed adsorbers, therefore, lend themselves to truly continuous, countercurrent, multistage operation. Adsorbent inventory is minimized. 

The IGT multistage cold-gas recycle methanation process has a built-in temperature control mechanism and a low recycle ratio. Much less recycle gas is used in this multistage operation than would be required if the same amount of conversion were achieved in a single vessel with all fresh feed and recycle gas added at the inlet to one large catalytic reactor. 

Blister copper, produced from sulfide ores by matte smelting and converting, is refined to the grade known as tough pitch copper by a multistage operation known as fire refining. 

Multistage Operation with Znterstage Heat Transfer... 

Optimal Multistage Operation with Interstage Cooling... 

Multistage Operation with Cold-Shot Cooling... 

In most industrial applications, multistage countercurrent contacting is required. The hydrodynamic driving force necessary to induce countercurrent flow and subsequent phase separation may be derived from the differential effects of either gravity or centrifugal force on the two phases of different densities. Essentially there are two types of design by which effective multistage operation may be obtained ... 

As described in Section 15.2.1, eutectic systems can be purified in theory by single-stage crystallisation, whereas solid solutions always require multistage operations. Countercurrent fractional crystallisation processes in column crystallisers are described in Section 15.4.3. 

All freeze separation processes depend on the formation of pure solvent crystals from solution, as described for eutectic systems in Section 15.2.1. which allows single-stage operation. Solid-solution systems, requiring multistage-operation, are not usually economic. Several types of freeze crystallisation processes may be designated according to the kind of refrigeration system used as follows . 

The above procedure can be extended directly to multistage operations however, here the argument for equal-size units is stronger still than for the two-stage system. 

Since the main use of these and many other forms of multistage operations is with solid catalyzed gas-phase reactions we discuss these operations in Chapter 19. Design for homogeneous reactions parallels that for catalytic reactions, so the reader is referred to Chapter 19 for the development. 

Examples 9.4 through 9.7 illustrate the approach to problems dealing with noniso-thermal reactors. Chapter 19 extends this approach to multistage operations of solid catalyzed reactions. 

Orgaz, E., Dantzer, P. (1987) Thermodynamics of the hydride chemical heat pump III. Considerations for multistage operation, J. Less-Common Met., 131, 385-398. 

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