Improving control of Fully Heat-Integrated pressure Swing distillation through partially flooded Reboiler/Condenser

• Published in: Separation and purification technology 2023-10, Vol.322, p.124334, Article 124334
• Main Authors: Farias Neto, G.W., Brito, K.D., Brito, R.P.
• Format: Article
• Language: English
• Subjects: Acetonitrile-Water; Azeotrope; Control and Dynamic Evaluation; Separation
• ISSN: 1383-5866; 1873-3794
• DOI: 10.1016/j.seppur.2023.124334

Fig. Reflux drum level: 50% (a); full (b); at interconnection height (c); below interconnection (d). [Display omitted] •Partially flooded reboiler/condenser recover a degree of freedom in FHIPSD configurations.•This is done by manipulating the liquid level in the heat exchanger.•This strategy significantly reduced the offset values in MeCN composition and improved control of the process. The binary mixture formed by acetonitrile (MeCN) and water (H2O) presents a minimum azeotrope highly sensitive to pressure variations, which can be separated through pressure-swing distillation (PSD), which is considered a very energy efficient process due to the possibilities of heat integration, in particular integration between the condenser and the reboiler of columns, known as Fully Heat-Integrated PSD (FHIPSD); in addition to being friendly from the environmental point of view. Despite promoting energy gains, integration reduces the freedom to control the process and, consequently, allows pressure fluctuation in the high-pressure column. This study evaluates the use of a partially flooded reboiler/condenser as a way to recover a degree of freedom of the process. The ability to maintain the purity specifications of products in two FHIPSD control configurations (conventional and with partially flooded reboiler/condenser) was evaluated for disturbances in the flow rate and feed composition. The use of a partially flooded reboiler/condenser allows controlling the heat exchange area by manipulating the level of liquid in the heat exchanger. The results showed that the partially flooded reboiler/condenser configuration promoted significant reductions in the steady state error values in the MeCN composition; and for positive flow disturbances, the steady state error value was reduced from 0.109 mol% to 0.004 mol%.