Distillation continuous binary

The conlinuous binary distillation column of Fig. 3.60 follows the same general representation as that used previously in Fig. 3.58. The modelling approach again follows closely that of Luyben (1973, 1990). 

The relationships for the section of column above the feed plate, i.e., the enriching section of the column, are exactly the same as those derived previously for the case of the batch distillation column. 

The mass balance relationships for the feed plate, the plates in the stripping section, of the column and for the reboiler must, however, be modified, owing to the continuous feed to the column and the continuous withdrawal of bottom product from the reboiler. The feed is defined by its mass flow rate, F, its composition xp and the thermal quality or q-factor, q. The column bottom product is defined by its mass flow rate, W, and composition, xw and is controlled to maintain constant liquid level in the reboiler. 

The liquid and vapour molar flow rate in the enriching section, are denoted by L and V, as previously and in the stripping section as L and V. The relationship between L, V, L and V is determined by the feed rate F and the thermal quality of the feed q . 

The situation on the column feed plate, plate f, is shown in Fig. 3.61. Neglecting plate hydraulic dynamics allows all the liquid and vapour flow rates Lj and Vj with i f, in the top section of the column, to be set to L and V and with all i f, in the bottom section of the column, to be set to L and V. 

The thermal quality of the feed is defined as the heat required to raise 1 mole of feed from the feed condition to vapour at the feed plate condition divided by the molar latent heat, and the following values apply q = 0, for saturated liquid feed q = 1, for saturated vapour feed, and q 1, for cold feed. The value of q affects the relative liquid and vapour flow rates (L and V) above and (L and V) below the feed plate, as indicated in Fig. 3.54. 

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Figure 3.60. Model representation of a continuous binary distillation column. PC is the cooling water controller, LC the reflux controller.

Continuous binary distillation is illustrated by the simulation example CON-STILL. Here the dynamic simulation example is seen as a valuable adjunct to steady state design calculations, since with MADONNA the most important column design parameters (total column plate number, feed plate location and reflux ratio) come under the direct control of the simulator as facilitated by the use of sliders. Provided that sufficient simulation time is allowed for the column conditions to reach steady state, the resultant steady state profiles of composition versus plate number are easily obtained. In this way, the effects of changes in reflux ratio or choice of the optimum plate location on the resultant steady state profiles become almost immediately apparent. 

CONSTILL - Continuous Binary Distillation Column System... 

A continuous binary distillation column is represented below. The column is shown in Fig. 1 as consisting of eight theoretical plates, but the number of plates in the column may be changed, since the MADONNA program is written in array form. 

Continuous Binary Distillation Column 496 Controller Tuning Problem 427 Three-Stage Reactor Cascade with Countercurrent Cooling 287... 

The process variables for continuous binary distillation columns and four basic control strategies... 

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