A New Screening Tool for Designing Energy Efficient Distillation Systems

A New Screening Tool for Designing Energy Efficient Distillation Systems

Joshua Huff, Mohit Tawarmalani, Rakesh Agrawal

School of Chemical Engineering

Purdue University, West Lafayette, IN 47907

In the traditional industrial applications of multicomponent distillation, a relatively limited number of distillation column arrangements are repeatedly applied to a wide variety of separations.  However, there are many separation process solutions differing significantly in cost and energy consumption that carry out the same overall process. Therefore a systematic method to identify and design optimal multicomponent separation sequences is needed that does not rely on the inventive activity of a few experienced engineers. Even for a commonly perceived “mature” technology such as distillation, a method to elucidate all possible multicomponent separation schemes has only been developed recently.

A matrix method has been developed to enumerate all distillation configurations which can perform a given separation. This generated “search space” includes both basic and thermally coupled configurations which complete an n-component separation in n-1 columns. The size of this search space grows increasingly large as the number of components increases – for example, a 5 component separation has 6,128 distinct ways to perform it using 4 columns. Once we have this search space, we can ranklist all configurations in terms of their vapor duty, thermodynamic efficiency or total annualized cost. However, the results of this ranklist still take the form of a series of matrix outputs, which require detailed knowledge of the method to study and implement.

For this reason, a new tool has been developed to capture and visualize system information for distillation columns designed by the matrix method. The tool is capable of drawing flowsheets for all configurations in the search space and overlaying them with information on feed conditions, flowrates and compositions, section vapor flows, and reboiler and condenser vapor duties. The list of configurations is complete (for example, for a five component configuration it will provide drawings of all 6,128 configurations) and sortable by a number of criteria including vapor duty, thermodynamic efficiency, total annualized cost, and number of thermally coupled streams. Additionally, the ability to screen configurations based on a mix of structural criteria (such as presence of particular splits or columns) and operational criteria (such as vapor duty or number of thermally coupled streams) is built into the program.

This tool provides the ability to translate the complete search space screening of the matrix method to a form which is usable by practicing engineers to study, screen, and draw designs from a very large space of possible solutions. Due to the high global energy consumption of the distillation sector, this provides the opportunity for massive energy savings through both design of new energy-efficient distillation systems and strategic retrofit of existing systems for energy savings.