(561a) Synthesis of Cost-Reducing Ternary Distributed Feed Distillation Columns Using Column Profile Maps

Column Profile Maps (CPMs) have recently been developed within our group as a graphical method to synthesize distillation columns. The maps generated through this technique are essentially a family of composition profiles derived from a first order differential equation for a single, generalised column section. Because the CPM method is generalised it is not specific to any one configuration, a major downfall in several other design methods. Thus, the designer is not limited by current equipment to design new structures, and the design procedure for complex columns is a relatively simple extension of simple column design.

The generalised CPM method is dependent on two main parameters: a generalised reflux ratio governing the ratio of vapour to liquid streams, and the difference point, a pseudo composition vector dictating the net flow each component in a column section. These parameters can be placed almost at will and can greatly affect the movement of composition profiles. Typically, the most interesting and potentially useful CPM behaviour occurs in column sections that are found in complex columns. Although many complex columns exist (Petlyuk, side-strippers, etc), probably the simplest means of “creating” a complex column is by adding the feed at different points along the length of the column.

In this presentation we will show how this feed addition policy can hold remarkable benefits for the cost of distillation structures. It will be shown how a significant reduction in the reflux requirement can be achieved (anywhere from 5-50%), as well as how to move around areas where the stage requirement approaches infinity.  Furthermore, this type of complex column can even enable separation beyond a distillation boundary in non-ideal systems through a creative utilization of CPM parameters to transform the CPM. We will also point out potential limitations of a distributed feed policy and show reasons why this type of column has received little to no attention in the literature.