(93a) Computer-Aided Chemical Plant Startup Operation

A chemical plant start-up operation is a highly complex operation that usually involves discontinuous and/or parallel operating procedures, as well as a wide change of many controllers' set points. It is one of the most critical time periods with high risks of uncertainty occurrence. A large number of accidents have been reported during petrochemical plant start-ups. Thus, the start-up operational safety draws the most concerns in chemical plants.

For an EO plant start-up, the safety requirements are extremely serious because it involves critical exothermic reactions at high temperature and high pressure, whose failure may cause catastrophic personal injury, severe air pollution, and tremendous economic loss. Especially during the initial start-up phase, the catalyst experiences a so-called ?break-through phase?, during which the O2 conversion rate is very high, while the selectivity is low and the oxidation process is very difficult to control. Meanwhile, the reactant concentrations of C2H4 and O2 should be well controlled below the safety limits of 25% and 8%, respectively; otherwise, the reactants will explode directly. Besides, the main product, EO, is a flammable and colorless toxic gas. Thus, an explosion not only causes the personnel injury/death and equipment damage, but also emits large amounts of toxic EO and HRVOC. Therefore, the safe start-up of an EO plant has significant economic and environmental potentials.

In this paper, a general methodology for improving the start-up operation strategy of a chemical plant has been developed. It employs plant-wide dynamic simulations to virtually test the start-up safety by systematically examining plant dynamic behaviors and transient response of critical parameters. Based on the validated dynamic simulation model, previous plant start-up strategies have been further examined and improved to speedup the plant start-up with enhanced safety consideration. A case study of an EO plant start-up optimization has demonstrated the efficacy of the proposed methodology.