Murphree point efficiency

Mols of distillate or overhead product, lb mols/hr or batch distillation, mols Mols component, i, in distillate Vaporization efficiency of steam distillation Overall column efficiency Overall tray efficiency Eqg = Murphree point efficiency, fraction Murphree plate/tray efficiency, = E ... 

Point efficiency (Murphree point efficiency). If the vapour and liquid compositions are taken at a point on the plate, equation 11.64 gives the local or point efficiency, Emv. 

These interaction phenomena have been discussed above in the context of ternary gas diffusion but are typical of the general multicomponent case. The practical implications of these interaction phenomena include such interesting possibilities as negative Murphree point efficiencies in multicomponent distillation as we shall see later (Chapter 13). 

Estimate the Murphree point efficiency for the system toluene (l)-methylcyclohexane (2) considered in Example 12.1.1. 

The Murphree point efficiencies conventionally defined by Eq. 13.1.3 may be expressed in terms of the elements of the matrices [g]. For a ternary mixture there are two independent compositions and two independent efficiencies. Using Eq. 12.2.3 we can show that the component efficiencies and <91/2 given by... 

Hence, compute the Murphree point efficiencies for each data set (see Example... 

Krishna, R., Martinez, H. F., Sreedhar, R., and Standart, G. L., Murphree Point Efficiencies in Multicomponent Systems, Trans. Inst. Chem. Engrs., 55, 178-183 (1977). 

The Murphree point efficiency in vapor terms is defined as (Koch-Glitsch et al., 1925 ... 

The Murphree point efficiency may be defined in liquid terms in analogy to Equation 14.31 ... 

Predict Murphree point efficiencies from tray hydraulics and mass transfer rates in the vapor and liquid. 

Murphree tray efficiency with entrainment Murphree point efficiency in liquid terms Murphree tray efficiency in liquid terms Murphree tray efficiency in vapor terms Overall tray efficiency... 

A third type of tray efficiency, the Murphree point efficiency, is used sometimes in attempts to correlate efficiency with fundamental mechanisms occurring on the iray, The point efficiency . is defined as follows ... 

THE MODIFIED MURPHREE POINT EFFICIENCY AND THE CORRESPONDING VAPORIZATION POINT EFFICIENCY... 

Since K,x( does not change with Z at a given W, this expression may be integrated and rearranged to give the definition of the modified Murphree point efficiency. 

By following the same general approach as that demonstrated for the modified Murphree point efficiency, one obtains the following expression for the Murphree point efficiency... 

ESiFi Murphree point efficiency defined by Eq. (13-63) fi fugacity of component i in a mixture evaluated at the temperature,... 

Three types of tray or plate efllciency are used overall tray efficiency Eq, Murphree tray efficiency E , and point or local tray efllciency E ff (sometimes called Murphree point efficiency). These will be considered individually. 

The Murphree Point Efficiency,, was derived by Murphree [14], who assumed a simplified expression for the instantaneous mass transfer to one bubble of vapor rising through the liquid. The derivation assumes that the vapor composition in the bubble changes continuously by mass transfer and that the bubble is rising through a liquid of constant composition. It is defined as... 

Since in general the liquid and vapor compositions vary across the vapor-liquid interface, a point efficiency is defined in terms of compositions at a given point on the tray. The Murphree point efficiency in vapor terms is defined as (Murphree, 1925)... 

The Murphree plate efficiency is the integrated effect of all the Murphree point efficiencies on the plate. 

The value of S , and E y are the most commonly used design factors for plate efficiencies. The over-all tower plate efficiency is simpler to apply than the Murphree efficiencies because only terminal conditions are required whereas in the calculation of the Murphree plate efficiency, plate-to-plate compositions are required, and for the Murphree point efficiency, complete liquid- and vapor-composition traverses are required on each plate. However, the Murphree efficiencies are probably on a more fundamental basis than the over-all efficiencies. 

Murphree point efficiency can be also expressed in terms of liquid concentration as follows ... 

The vapor-phase Murphree point efficient Ej is frequently used especially in distillation, while the liquid-phase point efficient E l is suitable for the liquid-phase control processes, such as absorption and desorption processes. 

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