Investigation of controllability of systems with recycle – a case-study

Abstract

In this case-study the effects of the recycles in an ethylbenzene producing system are investigated, simulated and analysed. The studied steady-state technology contains of two recycle streams, hence serves as a good model system for our study. Recirculation is often used in chemical technologies, especially in separating techniques. Being a positive feedback, it is expected that the application of recycle streams may result in controllability problems. In this study composition control is dealt with, exclusively. Based on our simulation calculations, it is shown that applying recirculation in the studied technology can effectively lead to instability if no appropriate process control system is installed. A method is shown that enables the selection of the appropriate process control structure, which ensures constant product purity. The example systems behaviour is studied with and without recirculation in both steady-state and dynamic domains. All the reasonable composition control structures are simulated and compared. Based on the steady-state results, controllability indices are calculated for the distillation columns and the best control structures are predicted. The steady-state investigations are confirmed later by dynamic simulations, and finally the best composition control scheme is selected for the entire system -based on the controllability indices.

Decomposability of the Control Structure Design Problem of Recycle Systems

“…A simple design tool is selected for more detailed study. This is the relative gain array (RGA) that shows the steady state interaction between control loops. RGA values are compared for the nonrecycle (Figure ) and recycle cases (Figure ). If the two values differ from each other, the recycle has an effect on the controllability features and, as a consequence, on the control structure design.…”

“…These incentives urge the comprehensive investigation of the effects and problems of recycling, and among them is the investigation of the controllability problems. Preliminary conceptions for our work are based on books, ,, software, and articles. ,,,,,,,− …”

Internet information for the textiles industry

“…Software packages such as that developed by British Textile Technology Group (BTTG) aim to integrate both health and safety information with chemical data [4]. In 1994 it was estimated that between one and four million host sites were connected to the Internet, an 88% increase over the previous 12 months, making the medium both attractive and plausible as a means of searching and retrieving information from remote computers [5]. Already most agencies of international repute have established net sites, amongst them the US Environmental Protection Agency, which offers daily information extracted from the Federal Register [6], and the Canadian Centre for Occupational Health and Safety, which supplies training programmes on aspects of chemical safety and other topics of relevance to the workplace [7].…”

Application of the Maillard, Strecker and modified Strecker (P–Mannich) reactions for the chemical modifications of wool

“…Based upon experiences with the Maillard reaction, further chemical reactions have been sought to enable introduction of carbohydrate molecules into the chemical structure of wool. The reaction of organic 0x0 compounds with cyanides was chosen as the first such process [5,6].…”