Binary distillation packed towers

The concepts NTU and HTU are defined only for binary distillations and the transfer of a single substance in absorption or stripping. Since most processes of industrial interest involve multicomponents, the HETS of packed towers is the more useful concept, and may be evaluated readily from test data and tray calculations. 

This chapter considers the vapor-liquid equilibrium of mixtures, conditions for bubble and dew points of gaseous mixtures, isothermal equilibrium flash calculations, the design of distillation towers with valve trays, packed tower design. Smoker s equation for estimating the number of plates in a binary mixture, and finally, the computation of multi-component recovery and minimum trays in distillation columns. 

Combine material-balances information from the McCabe-Thiele graphical method with interphase mass-transfer considerations to determine the packed height of the rectifying and stripping sections of a continuous-contact binary distillation tower. 

Figure 6.22 Binary distillation in a packed tower. Integrating over the entire rectifying section yields...

Consider the packed distillation tower shown in Figure 16-1. Only binary distillation with constant molal overflow (CMO) will be considered. Let A be the more volatile conponent and B the less volatile component. In addition to making L/V constant and satisfying the energy balances, CMO automatically requires equimolal counterdiffusion, = -Ng. Thus, CMO sinplifies the mass balances, eliminates the need to solve the energy balances, and simplifies the mass transfer equations. We will also assume perfect plug flow of the liquid and vapor. This means that there is no eddy mixing to reduce the separation. 

---