Application of a property-based inherently safety quantification framework for integrating risk assessment into process safety life cycle

Abstract

Process plant involves different types of risks which need to be managed appropriately to avoid dangerous incidents. Some risks are associated with design decisions such as choice of unit, chemicals or design layout etc. Some are related to the management of proper operating conditions within safely operational limits. It is advantageous to consider the safety aspects and to assess the risks associated with potential hazardous sources from the early stage of process safety life cycle to avoid unfavorable conditions and complexity on the later phase. Process safety metrics provide a good balance between sophisticated quantitative evaluation and simple application. The metrics can be easily adopted, enable comparison between different alternatives and be integrated in optimization for the supply chain. There have been multiple efforts to develop process safety metrics, which are made by both industrial and academic agencies. The concept of inherent safer design is very helpful to reduce the hazardous conditions by safer design principles instead of controlling them by add-on protective systems and procedures. Degree of freedom for the decision for inherently safer process design continuously decreases as life cycle proceeds. Therefore, changing plant design in a later stage will cost more than in the early stage. But the implementing of inherent safer design principles from early stage of design remains challenging due to the lack of proper tool/methodology which can assess the safety performance continuously with the change of mixture properties, operating conditions and even for the unit types. The significant challenges of the problem related to the safety parameters are the possible means to represent the associated results for different scenarios and processes. One safety parameter which is very important to a process may not be the critical issue for others. The scope to identify the key root safety parameters from the historical accidental data base can overcome this limitation. Again, most of the time it is very hard to do the techno-economic analysis simultaneously due to the lack of continuous equations to comply with the whole system's model. In this work, an Inherently Safer Design Tool (i-SDT) is presented for early stage process synthesis to characterize and track the risk associated with different life-cycle phases of industrial processes and products. It also helps to develop characteristic equations for different safety parameters (i.e., flammability, explosiveness, toxicity, etc.) and provides cluster safety parameter score for doing inherent safer design during early stage of design using very limited amount of process information. This property-based inherent safety quantification framework is a tailor made semi-quantitative safety analysis tool which will provide safety assessment in continuous manner to overcome the subjective nature of the existing available safety metric. The proposed safety metric has the flexibility to operate by identifying the major accident-prone units of a process, as well as the major safety and operating parameters. Therefore, in the future it can be embedded to any techno-economic framework to do the cost and safety analysis simultaneously using available materials, design and accidents information. The developed i-SDT tool was used to compare different technologies and variable capacity of ammonia processes to identify the safer alternative in terms of risks associated with the accident-prone unit/section and to highlight the areas of improvement in any existing process using the inherent safer design principles.