Determining the Number of Stages

The number of stages between the solvent feed stage and the main feed stage, and between the main feed stage and the reboiler are estimated using the Y-X diagram of the acetone/chloroform solvent-free equilibrium curve T/ vs. X,  

With a reflux ratio R = 4, the solvent-free L/V) slope of the rectifying section operating line is 

The rectifying section operating line is drawn based on this slope and the dis- 

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To determine the number of stages, using the impeller and diffuser defined as the stage, assume 10,000 ft-lb/lb of head per stage. This value can be used if the molecular weight is in the range of 28 to 30. For other... 

Step J. Determine the number of stages, z, required using the recommended 10,000 ft-lbAb head per stage. 

The design of a distillation column is based on information derived from the VLE diagram describing the mixtures to be separated. The vapor-liquid equilibrium characteristics are indicated by the characteristic shapes of the equilibrium curves. This is what determines the number of stages, and hence the number of trays needed for a separation. Although column designs are often proprietary, the classical method of McCabe-Thiele for binary columns is instructive on the principles of design. 

The leaching is normally done using a number of stages. In this respect, the process is similar to liquid-liquid extraction, and the methods used to determine the number of stages required are similar. 

For a detailed discussion of the procedures used to determine the number of stages required for a particular process, see Volume 2, Chapter 10 or Prabhudesai (1997). 

Typically, in a design situation, the problem will be to determine the number of stages required at a specified reflux ratio and column pressure, for a given feed, and with the product compositions specified in terms of two key components and one product flow-rate. Counting up the number of variables specified it will be seen that the problem is completely defined ... 

Acetone is to be extracted from a solution in water, using 1,1,2-trichloroethane. The feed concentration is 45.0 per cent w/w acetone. Determine the number of stages required to reduce the concentration of acetone to below 10 per cent, using 32 kg of extraction-solvent per 100 kg feed. 

For a feed rate 2000 kg/h of solution, composition 30 per cent w/w MEK, determine the number of stages required to recover 95 per cent of the dissolved MEK using 700 kg/h TCE, with counter-current flow. 

Having obtained the minimum number of stages from the Fenske Equation and minimum reflux ratio from the Underwood Equations, the empirical relationship of Gilliland10 can be used to determine the number of stages. The original correlation was presented in graphical form10. Two parameters (X and Y) were used to correlate the data ... 

For multicomponent systems, Equation 10.4 can be written for the limiting component, that is, the component with the highest Kt. Having determined the number of stages, the concentrations of the other components can be determined from Equation 10.6. 

For multicomponent systems, Equations 10.13 and 10.14 can be used to determine the number of stages for the limiting component (i.e. the component with the lowest Kj). Equation 10.15 can then be applied to determine the compositions of the other components. 

An even more difficult problem is to determine the number of stages and the optimal locations for the feed(s) and side stream(s) withdrawal. Fortunately, the range of candidates for stage locations for feed and withdrawals is usually small, and from a practical viewpoint the objective function is usually not particularly sensitive to a specific location within the appropriate range. 

The vertical cylindrical column provides, in a compact form and with the minimum of ground requirements, a large number of separate stages of vaporisation and condensation. In this chapter the basic problems of design are considered and it may be seen that not only the physical and chemical properties, but also the fluid dynamics inside the unit, determine the number of stages required and the overall layout of the unit. 

Figure 13.14. Graphical method for determining the number of stages for the process shown in Figure 13.13,...

Overall cost considerations will determine the number of stages to be used, so in practice we examine 1, then 2, etc., stages until a minimum cost is obtained. 

Describe flowsheet required or used and whether one or several bodies are required (or the economic factors which are to be used in determining the number of stages or effects. These factors include steam cost, water cost, electricity cost, amortization period, etc)... 

A solvent-extraction flowsheet is broken down into sections such as extraction, scrub, and strip. For each section, one or more component in a process fluid must be moved from one phase to the other phase with a specified degree of completeness. The first design problem is to determine the number of stages for each section to accomplish the required component transfer. With the well-defined stages of the centrifugal contactor, the following extraction factor (E) can be used to estimate the number of stages required ... 

It can further be seen that helium is least efficiently enriched relative to carbon dioxide than to any other component. It is, therefore, enrichment with respect to CO2 that becomes limiting and determines the number of stages necessary to achieve the purity levels set by Table I. In this respect, selection of a 380 psi AP condition appears particularly favorable, since it yields the highest [He]/[C02] enrichment. 

McCabe-Thiele diagram to determine the number of stages. 

To determine the number of stages it best to plot the equilibrium data on a triangular diagram. Figure 11.56. Each comer of the triangle represents 100% of the feed-solvent, solute or extraction-solvent. Each side shows the composition of one of the binary pairs. The ternary compositions are shown in the interior of the triangular. Mixtures within the region bounded by the curve will separate into two phases. The tie-lines link the equilibrium... 

The procedure is similar to the McCabe-Thiele construction for determining the number of stages in distillation Section 11.5.2. The slope of the operating line is the ratio of the final raffinate to fresh solvent flow-rates. 

Create a spreadsheet to determine the number of stages (A ) required to reduce the mole fraction of hexane to its required final value [calculated in part (a)] or less for P = 760 lorr and temperatures of 30 C. 50 C. and 70 C. The spreadsheet should have the following structure (some calculated values are shown) ... 

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