Ponchon method

Example 10.1. One hundred kilogram-moles per hour of saturated n-hexane-n-octane vapor containing 69 moIe% hexane is separated by distillation at atmospheric pressure into product containing 90 mole% hexane and bottoms containing 5 mole% hexane. The total condenser returns 42.5 mole% of the condensate to the column as saturated liquid. Using the graphical Ponchon method and the enthalpy-concentration data of Fig. 10.8 calculate ... 

Figure 10.11 Minimum reflux by Ponchon method, (u) Minimum reflux determined by the line through feed point, liquid feed, (b) Minimum reflux ratio determined by tie line between feed composition and overhead product.

The same procedure used to establish the pseudoequilibrium line on the McCabe-Thiele plot can be used in conjunction with the Ponchon method. If the Murphree efficiency is constant, a pseudoequilibrium curve could be drawn through y n and other points identically. This line AB, in conjunction with the difference points, could be used to step off stages. 

Using the above equilibrium data and the enthalpy data at the top of page 405, solve Problem 8.26 by the Ponchon method. 

One hundred pound-moles per hour of a mixture of 60 mole% methanol in water at 30°C and 1 atm is to be separated by distillation at the same pressure into a distillate containing 98 mole% methanol and a bottoms product containing % mole% water. The overhead condenser will produce a subcooled reflux at 40°C. Determine by the Ponchon method ... 

An equimolal mixture of carbon tetrachloride and toluene is to be fractionated so as to produce an overhead containing 4 mole% toluene and a bottoms containing 4 mole% carbon tetrachloride. Calculate by the Ponchon method the theoretical minimum reflux ratio, the theoretical minimum number of stages, and the number of theoretical stages when LID = 2.5. The thermal condition of the feed is saturated liquid, which is sent to the optimum stage. 

A refluxed stripper is to operate as shown below. The system is benzene-toluene at 1 atm. The stripping vapor is introduced directly below the bottom plate, and the liquid from this plate is taken as bottoms product. Using the Ponchon method, determine ... 

The rate of withdrawal of the side stream is 25% of the column feed rate. External reflux ratio is L/D = 2.5. Using the Ponchon method, determine the number of theoretical plates required. However, if the specifications are excessive, make revisions before obtaining a solution. 

An equimolai mixture of benzene and toluene is to be distilled in a plate column at atmospheric pressure. The feed, saturated vapor, is to be fed to the optimum plate. The distillate is to contain 98mole% benzene, while the bottoms is to contain 2 mole% benzene. Using the Ponchon method and data below [Ind. Eng. Chem., 39, 752 (1947)], calculate ... 

Ponchon Method. A weakness of the McCabe-Thiele method, as outlined heretofore, is the fact that the transfer of heat is not directly introduced. Heat must be transferred on each plate, reboiler heat must be supplied at the base of the fractionator, and cooling by reflux must be accomplished at the top. The method devised by Ponchon does not ignore these relationships, and although space is not available for an explanation of the Ponchon method, Example 16-11 will indicate its general usefulness. 

Example 16-11. Soitttioii by Graphical Ponchon Method. The same problem as that explored in Examples 16-8 to 16-10 will be solved by the Ponchon method. 

Figure 8-42A-E. Performance analysis of unequal molal overflow for binary systems using Ponchon-Savarit Method.

Unequal Molal Flow, 63 Ponchon-Savarit Method, 63 Example 8-21 Ponchon Unequal Molal Overflow, 65 Multicomponent Distillation, 68 Minimum Reflux Ratio — Infinite Plates, 68 Example 8-22 Multicomponent Distillation by Yaw s Method, 70 Algebraic Plate-to-Plate Method,... 

Himmelbau (1995) or any of the general texts on material and energy balances listed at the end of Chapter 2. The Ponchon-Savarit graphical method used in the design of distillation columns, described in Volume 2, Chapter 11, is a further example of the application of the lever rule, and the use of enthalpy-concentration diagrams. 

This method is one of the most important concepts in chemical engineering and is an invaluable tool for the solution of distillation problems. The assumption of constant molar overflow is not limiting since in very few systems do the molar heats of vaporisation differ by more than 10 per cent. The method does have limitations, however, and should not be employed when the relative volatility is less than 1.3 or greater than 5, when the reflux ratio is less than 1.1 times the minimum, or when more than twenty-five theoretical trays are required(13). In these circumstances, the Ponchon-Savarit method described in Section 11.5 should be used. 

The Ponchon-Savarit method, using an enthalpy-composition diagram, may also be used to handle sidestreams and multiple feeds, though only for binary systems. This is dealt with in Section 11.5. 

The separation analysis by established methods of McCabe -Thiele or Ponchon Savarit are compared with a flow sheeting program ASPEN+. It will be demonstrated, that a reliable scale -up is possible combining all these methods. 

Established methods like McCabe-Thiele or Ponchon-Savarit may be used to compute the number of theoretical stages for a given separation. Both methods are limited to a binary... 

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