This book is devoted to divided-wall distillation column theory and its application. Distillation is the most widespread separation technique and it consumes a considerable part of the world energy. The aim of the development of the distillation theory is to enhance the separation capability and to minimize energy and capital costs. The book overviews in brief are: CHAPTER 2 details the fundamentals of distillation used in this study and various arrangements of three-product separation. CHAPTER 3 details the theory of plant-wide control procedure and also the theory of selfoptimizing control, selection of controlled variables for unconstrained degrees of freedom. The methods to evaluate loss at pseudo/steady-state have also been described. In CHAPTER 4, the process has been described and plant process data for case study have been provided.CHAPTER 5 is mainly focused on the simulation procedure and the results obtained in this book. CHAPTER 6 comprises of the results and the discussion of the proposed theory. CHAPTER 7 concludes the work with suggestions on possible further study.