Although there have been documented instances of heat exchanger failures resulting in property damage, plant shutdowns and loss of life [1], safety has not been always the primary objective in heat exchanger network synthesis (HENS) [2-3]. In many cases, pressure-related process safety metrics, including the potential for overpressure, are neglected. If inadequately protected, they can result in devastating consequences. This work incorporates the safety of exchanger tube ruptures due to overpressure scenarios in HENS. Tube ruptures are non-steady state overpressure events whereby the low pressure side is pressurized by the high pressure side [4]. This pressurization can occur in as short as milliseconds. The severity of pressurization increases with large differences in shell and tube side pressure [5]. Using dynamic simulations that capture the over-pressurization during a tube rupture, the severity of this event in a network can be mitigated by using a combination of stream-matching and/or overpressure protection equipment (e.g. relief valve) [6]. However, the dynamic nature of tube rupture increases the complexity of designing safer heat exchange networks. To this end, we develop an optimization-based formulation that accounts for the tradeoff between the safety and cost of HENS. Unique safety profiles are generated for all plausible integration alternatives. A new piecewise approximation is used to obtain the minimal breakpoints needed to accurately capture the relationship between temperature and safety, based on the work of Rebennack and Kallrath [7]. This approximation is able to accommodate a wide range of pressures, temperatures, and fluid phase with significant accuracy. We illustrate the incorporation of process safety using several case studies. Specifically, our results demonstrate that optimization-based methods can significantly increase the safety of a heat exchanger network with minimal increase in cost.
[1] Grim, L. (2017). CSB Investigation: Williams Geismar Olefins Plant Reboiler Rupture and Fire. In ASSE Professional Development Conference and Exposition. American Society of Safety Engineers.
[2] Yee, T. F., & Grossmann, I. E. (1990). Simultaneous optimization models for heat integration—II. Heat exchanger network synthesis. Computers & Chemical Engineering, 14(10), 1165-1184.
[3] Ponce-Ortega, J. M., Jiménez-Gutiérrez, A., & Grossmann, I. E. (2008). Optimal synthesis of heat exchanger networks involving isothermal process streams. Computers & Chemical Engineering, 32(8), 1918-1942.
[4] API Standard 521. (2014). Pressureâ€Relieving and Depressuring Systems.
[5] Hellemans, M. (2009). The safety relief valve handbook: design and use of process safety valves to ASME and International codes and standards. Elsevier.
[6] Harhara, A., & Hasan, M. M. F. (2020). Dynamic modeling of heat exchanger tube rupture. BMC Chemical Engineering, 2(1), 1-20.
[7] Rebennack, S., & Kallrath, J. (2015). Continuous piecewise linear delta-approximations for univariate functions: computing minimal breakpoint systems. Journal of Optimization Theory and Applications, 167(2), 617-643.
