Product Composition Control of a New Batch Pressure Swing Rectifying System

Abstract

When operating the Double Column Batch Stripper (DCBS) configuration the liquid composition of the common vessel of the two columns must be kept between the two azeotropic compositions by affecting the flow rates of the two products. These can be varied by changing the reboil ratio and/or ratio of division of the liquid flow leaving the common vessel. The goals of this paper: - to propose and study a simple control scheme with PID parameters (providing good quality of control) for the new configuration, - investigation of the influence of the liquid division ratio, - determination of optimal value of liquid division ratio (providing the prescribed separation with minimal specific energy consumption). The calculations were made for a minimum (n-pentane – acetone) azeotropic mixture by using a professional dynamic simulator (CCDCOLUMN). By the aid of a PID controller we modified the flow rate of the bottom products (affecting the reboil ratios of the columns). We investigated the action of the control loops and the system for two different set points. In the first case the composition of the bottom products, in the second one – most common in the industry – the bottom temperatures were kept constant.