Fig. 1: Distillation column with one feed, total condenser, and partial reboiler. The enthalpy balance assumes adiabatic operation except in the condenser and reboiler. Representation of the energy streams qr on the enthalpy-concentration diagram requires that they be expressed as. Ponchon-savarit Method Draft 01 - Download as Powerpoint Presentation .ppt /. pptx), PDF File .pdf), Text File .txt) or view presentation slides online. Ponchon-Savarit Graphical Equilibrium Stage Method. Download to Desktop Copying Copy to Clipboard. Source. Open in Cloud; Download.
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The Ponchon–Savarit graphical construction allows the determination of the number of equilibrium stages in the case of the separation of a binary mixture. Page 3 of 9. Figure Representation of estimation of no of stages by Ponchon-Savarit Method. Whereas in the stripping section it can be expressed as :)/. Home · Syllabus · Lectures · Downloads; FAQ binary distillation by Ponchon- Savarit Method · Stepwise procedure to determine the number of theoretical trays .
The steps to follow are given below.
Select a value of xn. The final working equations are Eqs.
Use Eq. Using a method similar to that of the enriching section to Substitute these values into Eq.
Obtain new Ln from Eq. Substitute the above values into Eq. Usually one iteration is enough.
Toluene Plot the curved operating line for the enriching section. The reflux ratio is 1. Use enthalpy Determine the number of theoretical stages needed. The feed enters at Substituting into Eq. The remained of the liquid is withdrawn as the bottoms product B. Such a reboiler is shown in fig.
Ponchon-savarit Method Draft 01
These various relationship are shown graphically in Fig. Note the similarity between a partial reboiler as represented by Fig.
Figure 5: Construction on an enthalpy-concentration diagram for a a partial reboiler and b a column with open steam where the steam V0 is slightly superheated. Open Steam: When the less volatile component in a binary mixture is water, it may be advantageous to eliminate the reboiler and add heat to the column by injecting open steam beneath the bottom stage.
The construction when open steam is used is shown in Fig.
The replacement of a partial reboiler with open steam reduces the separation obtained with a given column. Elimination of the reboiler reduces the number of equilibrium stages by one. Also, the steam acts as a diluent and a fraction of a stage is required to overcome this effect.
The net effect is that one and a fraction stages must be added to the column when the switch to open steam is made if the same separation as that obtained with the partial reboiler is desired.
Feed Stages The construction on the enthalpy-concentration diagram for a feed stage is much simpler than on an x-y diagram. The enthalpy of thermal condition of the feed stream is taken into account in the location of F on the diagram. The point F will always be located on a vertical line through xF.
Ponchon Savarit Method
If the feed is a sub-cooled feed, it will fall below the saturated-liquid curve as shown in Fig. If the feed is partially flashed, F will fall between the two saturation curves see Fig. A saturated-vapor feed will fall above the curve.
The enthalpy balance now includes the feed stream. It can be seen that as soon as the feed is introduced, the difference point which relates passing streams immediately shifts from D to B in a single feed column. Optimum Feed Location: The optimum feed-stage location is that one which, with a given set of other operating conditions, will result in the widest separation between XD and XB with the given number of stages. Or if the number of stages is not specified, the optimum location is the one which requires the fewest number of stages to accomplish a specified separation between XD and XB.
Either of these criteria will always be satisfied if the feed is introduced on that stage whose tie line crosses the over-all material-balance line which passes through F, XD, and XB. The switch from one difference point to the other at that stage will always result in the maximum separation.
This fact is illustrated by Fig. Stage 4 When numbering from the bottom is the optimum feed stage, and solid operating lines are drawn on the assumption that the feed is actually introduced on the fourth stage. Now assume that the feed was introduced on stage 3. The solid operating lines correspond to the introduction of the feed on stage 4 optimum.
The dotted operating lines assume the introduction of the feed one stage below or one stage above the optimum location. In the design of a new column, the feed-stage location is under the control of the designer and should, of course, always be located in the optimum position. In a study of an existing column, the feed-stage location is fixed and the switch from one difference point to the next one must occur at the actual feed stage which may or may not be the optimum feed stage for the separation under study.
Usually whenever a column is switched to a new service, the feed stage will not be the optimum one. Other Feed or Side-stream Stages No new principles are involved in the construction of the diagram if the column has additional feed stages or side-stream stages. The addition or withdrawal of material to heat anywhere along the column length merely requires that a new difference point be used to relate passing streams once the addition or withdrawal point has been passed on the diagram.
The relative amounts of S and D determine the location. If, instead of a side stream, a feed is introduced, Eq. The location of will lie on the other side of D from F on a straight line through the two points.That is, the liquid is first changed from temperature T0 to Tb and then evaporated at Tb , the vapor temperature is finally The diagram at a given constant pressure is based on changed back from Tb to T0.
If stage n is assumed to be adiabatic, and since no material is added or withdrawn through the column wall, no changes in the difference point will occur across stage n therefore, Vn-1 can be located by means of a straight operating line from Ln to.
Mass Transfer Operation I
The construction when open steam is used is shown in Fig. While doing constructions on the yx diagram, a "pinch" was defined as the intersection point between the equilibrium curve and the operating curve.
Feed Stages The construction on the enthalpy-concentration diagram for a feed stage is much simpler than on an x-y diagram. Figure 4b shows the construction for a partial condenser with only a vapor product withdrawn. The reflux ratios for a partial condenser are given by Eqs.
The equilibrium data is represented by the equilibrium tie lines on the Hx diagram.
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