Reflux theoretical trays relationship

Colburn relationship found that the optimum number of trays varies from 2 to 3 times the number at total reflux. Gilliland [Ind. Eng. Chem, . 32, 1220 (1940)] from the establishment of an empirical relationship between reflux ratio and theoretical trays based on a study of existing columns indicated that... 

Figure 8-28. Relationship of reflux ratio and theoretical trays, for Example 8-12.

However, in many cases, the conditions above for using a data historian are difficult to satisfy. It could be also labor intensive and inconvenient in operation to adopt the step test method. Thus, the most common method is to use the simulation method for developing relationship correlations. To do this, a simulation model for the tower can be developed readily based on the feed conditions (rate and compositions) and tower conditions (temperature, pressure, theoretical trays) with product specifications ( 4% in the bottom and 5% in the overhead) established as set points in simulation. Operating parameters such as reflux rate and reboiling duty can be adjusted to meet product specifications. The simulation model is verified and revised against high-quality performance test data. 

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