Inherent safety assessment framework for process design using numerical and graphical techniques

Abstract

Plants should be designed so that they exhibit good safety features to prevent accidents. This can be done by preventing the presence of hazards in the process during its design stages or also known as the inherent safety concept. This research proposes an inherent safety assessment framework for early process design stage. This framework consists of two inherent safety assessment techniques and one hazard prevention strategy. Both inherent safety assessment techniques can be integrated to be used together or as a standalone technique. However, the usage of one or both of these techniques must be followed by the hazard prevention strategy that will provide suggestions on hazard prevention for the hazards identified by the two inherent safety assessment techniques. The first technique is the extended graphical and numerical descriptive (GRAND) technique which is an extension of the previously developed GRAND method through the addition of the two dimensional graphical rating (2DGR) for inherent safety rating and the two dimensional inherent safety and economic graphical rating (2DISEGR) for economic evaluation. The 2DISEGR for methyl methacrylate (MMA) manufacturing process shows that tertiery butyl alcohol (TBA) route is the safest and most profitable process route with the highest net profit margin of 97% at low GRAND total score value of 371. At similar GRAND total score of 371, the 2DGR for MMA manufacturing process shows that TBA is the least hazardous route due to the low number of most hazardous parameter of 1. The second technique is the inherent safety assessment for preliminary design stage (ISAPEDS) technique. This technique consists of three inherent safety parameters which are flammability, explosiveness, and toxicity in relations to operating conditions. The evaluation is done on every equipment in the process flow diagram. ISAPEDS assessment shows that all equipment are identified as the most hazardous in the hydrodealkylation process of toluene to produce benzene. The hazard prevention strategy was developed through the utilization of thematic analysis to extract hazard prevention strategies from the accident databases producing results in the form of keywords that are called themes and generated codes. The 2DISEGR-ISAPEDS figure was developed to show the relationship between the inherent safety assessment using the parameter scores and the economic evaluation using the numerical values. The results of the 2DISEGRISAPEDS show that storage tank (V101) is ranked in the economically least preferred and most hazardous region due to high ISAPEDS total score value of about 200 and minimum economic preference factor value of 0.38. Hazard mitigation themes for strategies identified for V101 are design, operating, chemicals and control. These strategies and their generated codes can be used to maintain the balance between hazard reduction and economical benefit. High similarity that can be seen between this framework and other available inherent safety assessment techniques in the comparison made proves the effectiveness as well as the validity of this framework. In conclusion, this research has achieved its main objective to develop an inherent safety assessment framework for early stage of process design.