The Best Distillation Complex for Petroleum Refining

Columns with side stripping sections were used for petroleum separation already in the first decades of twentieth century. This choice is quite grounded by the main purposes of designing increase of separability, and decrease of energy and capital expenditures on separation. 

Because petroleum is a mixture with a wide interval of bubble temperatures of components and the required purity of products is not very great, reflux and vapor numbers in the sections are not large. Therefore, the heat brought in is used up mostly not for creation of vapor reflux, but for evaporation of those products that are withdrawn above the feed cross-section. Therefore, the split (direct, indirect, intermediate) has but a weak influence over energy expenditures, but it is very important to exclude multiple evaporation and condensation like in multicolumn sequences of simple columns. Columns with side strippings exclude multiple evaporation and condensation. 

Replacement of multicolumn sequences with multisection colunms also leads to a decrease in capital expenditures because, due to the wide interval of bubble temperatures, there can be but a small number of trays in each section, and it is profitable to unite these sections into one shell. 

Among multisection distillation complexes, only columns with side strippings bring practically the whole heat into the feeding and bring hve steam into the bottom. Application of pumparounds decreases energy expenditures and recuperates withdrawn heat for heating of petroleum before separation. 

At the same time, the apphcation of pumparounds decreases vapor flow rate in the top sections of the column (i.e., to decrease the diameter and capital expenditures). 

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Therefore, column with side strippings, with live steam into the bottom, and with pumparounds is the best distillation complex for petroleum refining. An optimum way of designing such column is discussed in Section 7.5.2. 

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