McCabe-Thiele analysis stripping

The Y intercept is less than zero so the operating line is below the equilibrium line. 

A volatile organic carbon (VOC) in a water stream is to be stripped out using an air stream in a countercurrent staged stripper. Inlet air is pure, and flowrate is G = 500 Ib/hr. Inlet liquid stream has a mass ratio of X = 0.10 and a flowrate of pure water of 500 Ib/hr. The desired outlet mass ratio is X = 0.005. Assume that water is non-volatile and air is insoluble. Find the number of equilibrium stages and the outlet gas mass ratio. Equilibrium data can be represented by T = 1.5 X. 

When the solute concentration in both the gas and liquid phase is very dilute, the total flowrates can be considered constant. The mole or mass ratios reduce to the corresponding 

The stripping gas enters at Stage N, and the spent gas leaves at Stage 1. 

The term LlmV = A is called the absorption factor. It is often written d L/KV where y = Kx.li would be useful to determine the ratio 

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Some extraction systems are such that the solvent and diluent phases are almost completely immiscible in each other. Hence, separation yields an extract phase essentially free of diluent and a raffinate phase that is almost pure diluent. This greatly simplifies the characterization of the system. When partial miscibility for an extraction process is very low, the system may be considered immiscible and application of McCabe-Thiele analysis is appropriate. It is important to note that McCabe-Thiele analysis for immiscible extraction applies to a countercurrent cascade. The McCabe-Thiele analysis for immiscible extraction is analogous to the analysis for absorption and stripping processes. Consider the flow scheme shown in Figure 5.23,... 

The McCabe-Thiele analysis can be used to model physical absorption and stripping processes that use equilibrium stages. 

If absorption or stripping can be assumed 1) to be isothermal and 2) to have negligible heat of absorption, then the energy balances will be satisfied. In this case the McCabe-Thiele analysis procedure can be adapted to more concentrated systems where the total flow rates L and V are not constant. We will have the desired straight operating line if we define... 

The McCabe-Thiele analysis for dilute immiscible extraction is very similar to the analysis for dilute absorption and stripping discussed in Chapter 12. It was first developed by Evans (1934) and is reviewed by Robbins (1997). In order to use a McCabe-Thiele type of analysis we must be able to plot a single equilibrium curve, have the energy balances automatically satisfied, and have one operating line for each section. 

The McCabe-Thiele procedure has been applied to flash distillation, continuous countercurrent distillation, batch distillation, absorption, stripping, and extraction. What are the common factors for the McCabe-Thiele analysis in all these cases ... 

The test separation data are analyzed using a McCabe-Thiele diagram (Fig, 7.12a), with an equilibrium curve based on experimental data (average relative volatility of about 1,7), The analysis shows that the stripping section requires 12 theoretical stages. 

The Murphree efficiency is defined using vapor concentrations as a matter of custom, but the measured efficiencies are rarely based on analysis of the vapor phase because of the difficulty in getting reliable samples. Instead, samples are taken of the liquid on the plates, and the vapor compositions are determined from a McCabe-Thiele diagram. A plate efficiency can be defined using liquid concentrations, but this is used only occasionally for desorption or stripping calculations. 

These assumptions, referred to as the McCabe-Thiele assumptions, lead to the condition of constant molar overflow. For constant molar overflow, the analysis of a distillation column is greatly simplified because it is not necessary to consider energy balances in either the rectifying or stripping sections only material balances and a VLE curve are required. 

The conventional McCabe-Thiele graphical method for analysis of binary mixtures was applied to determine the number of theoretical plates necessary for the separation, 11,3 theoretical plates are required for the rectifying section, and 9.4 for the stripping section. Thus a total of 20,7 theoretical plates are required. Since the value of chosen was 70 per... 

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