Heat Integration by Side Reboiling

Optimizing heat integration within a process scheme can yield significant energy savings, especially when an energy-intensive operation like distillation is involved. This article illustrates a simple graphical method for optimizing the heat integration of distillation columns using side reboilers.

A portion of the thermal duty necessary for a distillation column’s operation can be supplied using one or more side reboilers. As you move up from the bottom of the column, the temperature required to vaporize the liquid on the trays decreases. Consequently, a lower-cost hot utility can be employed in the side reboilers, compared to the hot utility used for the bottom reboiler. If a process stream that needs cooling has an adequate temperature level, it could replace the hot utility in a side reboiler, resulting in enhanced heat integration within the process scheme.

Opportunities for heat integration are best identified in earlier phases of a project, except when they are the intended objective of retrofitting an existing plant. Therefore, this article is suited for process engineers involved in conceptual design and optimization studies.

This article focuses on how to determine the thermal duty and column position for one or more side reboilers to maximize heat integration within a process scheme. A graphical method based on the principles of pinch analysis is illustrated through a case study of a demethanizer column in a natural gas liquid (NGL) recovery plant. First, the article briefly describes the gas subcooled process (GSP) for NGL recovery from natural gas and how to simulate it in Aspen HYSYS. The concept of composite curves, originating from pinch analysis, is extensively used throughout the study...