(673g) Optimal Design of Hazardous Chemical Processes with Safety and Economic Considerations

Growing demand for specialty products has shifted attention toward methods to systematically design chemical processes that are economically viable and highly efficient. Process systems engineering techniques such as optimization offer one approach to address this challenge. This is typically achieved by minimizing the costs associated with chemical processes, such as the cost of utilities, raw materials, and operation to name a few. For chemical processes with inherent variability due to changing prices and demand, this is an especially effective approach. However, from a process safety viewpoint there are some concerns. Chemical processes are inherently hazardous, where toxic and/or flammable chemicals are transformed into desired products at extreme operations conditions. As a result, a safety system implemented on an economically optimal design might be ineffective and/or costly.

To overcome this, safety can be integrated into the decision-making of chemical process design. However, this comes with several challenges. Traditional safety assessment techniques require a complete design since safety as a function of scale is difficult to quantify [1]. Multiple factors such as the properties of the chemical, operating conditions, type of unit, and site area can impact the safety assessment, creating complexity when trying to model safety. Additionally, safety in the form of risk is probabilistic in nature, making a direct comparison to the cost unsuitable.

Therefore, we propose a process safety risk framework that can be incorporated into designing optimal economic and safe chemical processes. The framework addresses the concerns in two parts. First is the Total Cost of Process Risk (TCPR) methodology that systematically identifies hazards and quantifies their risk as a function of scale. This is done by identifying the hazards through a Fire & Explosion (FEDI) and Toxic Damage Index (TDI) [2,3]. The hazards are then correlated to damage radii to assess cost of losses from damage to a process unit and/or person [4]. We demonstrate how TCPR can be modeled as a set of multiple functions dependent on both the scale of the damage area and the chemicals that contribute to the maximum overall risk. Furthermore, we show how this complex behavior can be systematically integrated into the design and optimization of chemical process as a Mixed-Integer Nonlinear Programming (MINLP) model. The second part is the Risk Transfer Premium (RTP) where the overall risk of the process can be converted into a monetary value using the idea of an insurance premium. To demonstrate the applicability of the framework, a case study examining glyphosate production in the San Joaquin Valley of California is shown [5]. The production of glyphosate is traditionally utilized in industry with three different pathways: the hydrogen cyanide (HCN), diethanolamine (DEA), and glycine routes [6]. These pathways are modeled using a superstructure-based approach. When comparing a design with safety considerations versus a design with economic considerations, the results demonstrate the difference in decision-making between the objectives. To further understand the tradeoff between cost and safety, an epsilon-constrained approach is utilized. Finally, results from a design with both safety and economic considerations using the RTP demonstrate the impact of safety directly on the cost and how an optimal design can be determined.

References:

[1] Johnes, A., Khan, F.I., Hasan M.M.F. (2024). Chapter Fourteen - Safety and risk assessment considerations in the energy supply chains. In F. I. Khan, E. N. Pistikopoulos, Z. Sajid (Eds.). Method of Process Systems in Energy Systems: Current System Part 1. pp. 457 – 506.

[2] Khan, F.I., Abbasi, S.A. (1998). Multivariate Hazard Identification and Ranking Systems. Process Safety Progress. 17(3), pp. 157 – 170.

[3] Khan, F.I., Husain, T., Abbasi, S.A. (2001). Safety Weighted Hazard Index (SWeHI): A New, User-friendly Tool for Swift yet Comprehensive Hazard Identification and Safety Evaluation in Chemical Process Industries. Process Safety and Environmental Protection. 79(2), pp. 65 – 80.

[4] Khan, F.I., Amyotte, P.R. (2005). I2SI: A comprehensive quantitative tool for inherent safety and cost evaluation. Journal of Loss Prevention in the Process Industries. 18(4 – 6), pp. 310 – 326.

[5] California Department of Pesticide Regulation. California Pesticide Information Portal (CalPIP). https://calpip.cdpr.ca.gov/main.cfm.

[6] Yushchenko D.Y., Khlebnikova, T.B., Pai, Z.P., Bukhtiyarov, V.I. (2021). Glyphosate: Methods of Synthesis. Kinetics and Catalysis. 62. pp. 331 – 341.