Numerical and graphical descriptive technique for inherent safety assessment in petrochemical industry

Abstract

Plants should be built so that they are user-friendly and able to tolerate deviation from ideal performance as a result of operators and equipment failures without serious impacts on safety, productivity or efficiency. Before any effort for hazard reductions can be performed, it is important to first understand the hazards of a process which can be achieved through hazard assessments. Most of the current inherent safety assessment methods are index-based method which suffers from the shortcomings of subjective scaling. The aim of this research is to develop an inherent safety assessment method that eliminates the issue of subjective scaling in index scores assignment. The Numerical and Graphical Descriptive (GRAND) method is developed through the application of logistic functions. In this study, all petrochemical processes data obtained from literature was used in constructing numerical scores through the application of logistic functions. The numerical scores was then translated into graphical form. GRAND Total Score and GRAND Ranking Curve developed in this study can be used for the purpose of comparing alternative process synthesis routes to the desired product by their hazard level for inherent safety assessment during research and development (R&D) stage. Process route with a higher GRAND Total Score indicates greater hazards compared to the route with a lower GRAND Total Score. There are eight parameters involved which are divided into two groups. The first group is chemical safety parameters which consists of flammability, explosiveness, toxicity and reactivity parameters while the second group is process safety parameters which consists of temperature, pressure, heat of reaction and process inventory parameters. A gap elimination test was done on GRAND with the purpose of ensuring the elimination of subjective scaling. The gap elimination test result shows that GRAND has the ability to eliminate the problems of subjective scaling in scores assignment. The method developed was applied on two case studies which are methyl methacrylate manufacturing process and acetic acid manufacturing process. In the case study of methyl methacrylate manufacturing process, tertiary butyl alcohol based route was assessed as the safest route among the six routes evaluated while ethylene via propionaldehyde based route was assessed as the most hazardous one with the score of 311 and 509, respectively. There are ten process routes evaluated in the case study of acetic acid manufacturing process. GRAND assessment shows ethanol oxidation route as the safest route and ethane oxidation route as the most hazardous route with the score of 180 and 402 respectively. Results obtained from the gap elimination test as well as case studies performed proves that the method proposed in this research is successful in eliminating the common problem in index-based method which is subjective scaling for inherent safety assessment in petrochemical industry.