传质与分离工程1.ppt

* * (16) Use of Murphree efficiency默弗里板效率/Determining the number of actual plates实际板 [pp.692-693] When the Murphree efficiency is known, it can readily be used in the McCabe-Thiele diagram. Fig.21.33[p.693] Fig.21.33 Triangle acd represents the ideal plate and triangle abe the actual plate. The actual plate, instead of enriching the vapor from yn+1 to y*n, accomplished a lesser enrichment yn- yn+1. To apply a known Murphree efficiency to an entire column, it is necessary only to replace the true equilibrium curve ye versus xe by an effective equilibrium curve y’e versus xe, whose ordinates are calculated from the equation (21.70). How to plot the effective equilibrium curve? Giving xn, find y*n from equilibrium curve and yn+1 from operating line, calculate yn from equation (21.70), then plot point (xn, yn) … How to determine the number of actual plates? The reboiler is not subject to a discount for plate efficiency, and the true equilibrium curve is used for the last step in the stripping section. How many actual plates are needed in the left construction? How many actual plates are needed in the left construction? No fractional actual plate, then Murphree efficiency can be different from individual plates, and this is more accurate to calculate the number of actual plates than by overall efficiency of a column全塔效率. 3. BATCH DISTILLATION（间歇精馏 ） [pp.700-703] 1)Simple Distillation简单蒸馏(自学) (1)Flow diagram (Refer to Fig.21.37) Batch Feed间歇进料 Condenser Cooling water Product receiver Still There are many cases where batch distillation间歇精馏 is preferred, particularly in the food and pharmaceutical industries. Batch distillation is used when small amounts of product are made in a pilot plant to provide samples for product sampling or testing. Features: 1)Unsteady state; 2)Without reflux; 3)One-stage partial vaporization process. The vapor leaving the still at any time is in equilibrium with the liquid in the still. [y is in equilibrium with x.] Batch Feed Condenser Coo