Simulation of Start-up Period

The simulation of actual start-up operation is very difficult unless there is a detailed rigorous model including plate hydraulics. However, the simulation of start-up operation from step 5 (section 3.3.1) is fairly easy and can be done without considering a detailed hydraulic model. To do this the filling of the holdup in steps 3 and 4 (section 3.3.1) can be achieved in different ways  

Step 5 (section 3.3.1) now simply requires to run the column (i.e. simulate the column operation using a model) at total reflux until the unit reaches the steady state (Holland and Liapis, 1983 Nad and Spiegel, 1987) or until the instant distillate composition reaches the product composition so that the product can be collected at constant distillate composition (Coward, 1967 Kerkhof and Vissers, 1978 Logsdon and Biegler, 1993). A variation of this total reflux operation concept can also be found in the literature and in practice. In this variation only a part of the condensed liquid is returned to the column and the rest is taken out as product (product period starts from step 3 of section 3.3.1) (Converse and Huber, 1965 Mayur and Jackson, 1971 Mujtaba, 1989 Mujtaba and Macchietto, 1992). Mujtaba and Macchietto (1988) and Mujtaba (1989) clearly explain whether and when an initial total reflux operation is required. 

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