(572c) Integrated Sustainable Design Approach for Assessing Inherent Process Safety during Early Stage of Design

In this work, a probabilistic semi-quantitative method is developed using leading safety indicators where the accident probabilistic values, available materials and design data during initial phase of plant design are used to compare different process facilities and sustainability factors. The proposed integrated safer design analysis tool (i-SDT) for the process would give the designer a useful basis for the assessment of risk and safety, which would complement other design tasks such as equipment sizing, selection of operating conditions, and process economics. During the life cycle of a process, degree of freedom for the decision of inherently safer process design continuously decreases as proceed in the life cycle [1]. Therefore, changing plant design and modifying control loops for safety management in later stage will cost more than early stage. The challenges for implicating primary inherently safer design principles during early phase of plant design are deeply related with quick quantification of risks using the limited information available and due to the lack of continuous representation of chemical and process safety parameters [2]. Current simulation modeling tools do not provide design engineers the ability to assess alternatives considering prioritization of safety parameters.

The main objectives of this works are two folds: i) to develop a tailor made semi-quantitative safety metric which will act as a design tool for implementing primary inherently safer design principles (i.e., minimization, substitution, moderation and simplification of hazards/operations) and ii) to overcome the subjective nature of the existing available safety metric for accomplishing economic and safety analysis simultaneously using available materials, design and accidents data. To accomplish those tasks a holistic bottom-up approach and an integrated safer design analysis tool (i-SDT) have been proposed. Final cluster safety parameter score (C_SP) obtaining from i-SDT will assess the risk associated with key safety parameters (flammability, toxicity, explosiveness, reactivity) considering the following: 1) chemical composition of a mixture at specified operating conditions, 2) process safety aspects of various units (i.e., pressure vessels, atmospheric vessels, STHE, fired heat exchanger, pump, compressor), 3) effects of varying operating conditions and 4) historical incident database for chemicals and process vessels.

This property based safety metrics formulation will not produce any specific and absolute cumulative score to represent the safety situation; rather it will provide a comparative score based on user input and preferences. This formulation of the process safety metrics will be flexible enough to be used as add-on equations to any techno-economic and environmental analysis. The key issue to use this safety metrics formulation is to gather previous accidents data related with the targeted process and to identify the key unit/safety parameters based on their historical incidents. Theoretical and conceptual development of the metric has been accomplished. Initial formulation shows that it can be used as continuous equation for different operation conditions which will be useful for continuous tracking of safety parameters and designing inherently safer process.

The assessment of inherent safety level using the proposed method is demonstrated through a case study. HYSYS simulation is used to design two alternative designs for ammonia production. In future, this can be integrated with any existing process design software (i.e., HYSYS) to evaluate the safety performance while designing sustainable and optimized process configuration.

1. Thiruvenkataswamy, P., et al., Safety and techno-economic analysis of ethylene technologies. Journal of Loss Prevention in the Process Industries, 2016. 39: p. 74-84.

2. Ahmad, S.I., H. Hashim, and M.H. Hassim, A graphical method for assessing inherent safety during research and development phase of process design. Journal of Loss Prevention in the Process Industries, 2016. 42: p. 59-69.