Design and Control of Thermally Coupled and Heat Integrated Distillation Sequences for Quaternary Separations

In this work we have extended the design and optimization methods for the separation of quaternary mixtures of hydrocarbons. Also, a controllability analysis using the singular value decomposition technique was performed in order to obtain the control properties of the distillation schemes. One conventional distillation sequence and three thermally coupled distillation sequences have been studied: one considering a side stripper and a side rectifier, one considering a side stripper and a side rectifier and heat integration between the side columns and a Petlyuk-type column. The design of a thermally coupled system starts from a conventional distillation sequence and then the recycle streams are varied until the minimum energy consumption is detected. The results show energy savings of around 30% of the thermally coupled distillation sequences in comparison to the conventional distillation sequence. Also, the system including both thermal and heat integration presented the lowest energy demand and the highest second law efficiency. When the integrated distillation sequences were subjected to a controllability analysis, the complex distillation sequence considering both thermal and heat integration presented the worst control properties in contrast to those of the complex schemes considering only thermal couplings.