Calculation of Columns with Side Sections

Design Calculation of Columns with Side Sections 

We propose a method of design calculation based on decomposition of the column with side strippings into a system of two-section columns, on rigorous design calculation of each two-section column and on simultaneous design of distillation columns and of system of heat exchange. 

The main task of designing columns with side strippings is the determination of necessary number of plates in each section, of optimal thermal duties on pumparounds and of the rates of steam for stripping or thermal duties on reboilers. 

Ratios of the flow rates of liquid and vapor in two-section colunms are determined by reasoning from the calculated mode of minimum reflux and specified set of values of reflux excess coefficients, taking into consideration the output of heat by pumparounds decreasing the vapor flow rate passing from one two-section column into another. The amount of heat withdrawn by pumparounds is determined through application of the pinch method (Liebmann et al., 1998). 

The same method is used to choose the method of stripping with the help of steam, reboiler, or a combination of steam and reboiler. Application of reboilers compared with steam stripping, on the one hand, requires additional investment cost and heat expenditures, but on the other hand, it leads to a decrease of vapor flow in the column (i.e., to a decrease of necessary diameter and to an increase of the temperature of stripping product used for heating the crude oil). Besides that, the application of reboilers is inadmissible for heavy products because the resulting increase of the product s temperature may lead to its chemical decomposition. In the case when apphcation of reboilers is admissible, the choice between reboilers. 

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