Heat Requirement of Simple Distillation Units

The heat requirement of a separation unit follows from the energy balance as shown in Chapter 1.3.1. For a simple distillation unit the heat flux may be derived, as shown in Fig. 2-9. An energy balance of the distillation unit under isobaric operation gives 

The specific heat requirement, which is the required heat flux for each kmol distillate vaporized, is 

Z is the length of the evaporator tubes required to generate the distillate flux D. If the feed mixture is at a lower temperature than the boiling temperature, a preheating zone is additionally required. 

For the design of distillation facilities, it is generally sufficient to use Ah g, k and Aj averaged over the length Z in Eq. (2-17). Methods of calculating the heat transfer coefficient k are found in [2.10]. 

Applications of thin film and falling film evaporators in film distillation are reported in [2.14], together with the achieved separation effect and the economic efficiency. Possible energy savings arising from the combination of the use of the film evapora- 

---