Examination of Hazardous Situations in Industrial Closed-Loop Processes Using Dynamic Simulations

Abstract

Closed-loop processes are widely used in the chemical industry, for example in separation processes to recycle waste streams. However, the recycled streams represent a source of instability, especially when the overall system suffers a (desirable or undesirable) change in the operating conditions. In this case, the time required to reach a steady state is significantly longer, because of oscillations encountered in the leaving stream characteristics. The dimensions of such oscillations can reach high and even hazardous values, even if the new steady state is reached in a safe operating condition. This is why the knowledge of the dynamic closed-loop process behavior is essential to prevent hazardous situations. In this work, a general rate-based model of a closed-loop chemical absorption process is presented and the results of dynamic simulations are compared with published experimental data on absorption of carbon dioxide with aqueous monoethanolamine solution. The periphery is considered using dynamic models of the liquid distributors, the liquid holdup in the bottom of the columns as well as of the relevant heat exchangers and pipelines. Based on the simulations, the influence of different closed-loop process elements on the dynamic behavior of the overall configuration can be evaluated, enabling a cause-effect analysis of hazardous situations.