Incorporating Process Safety into Heat Exchanger Network Synthesis

Abstract

Process safety of inter-connected equipment, such as heat exchanger networks (HEN), is paramount to the operation of chemical plants. While there exists considerable research on further improving HEN, little attention has been paid to incorporating the safety of HEN at the conceptual design stage. In this work, we extend the optimization-based HEN synthesis to incorporate safety using a Safety Rating (SR) based on dynamic tube rupture scenarios for all plausible heat exchanger matches. In developing the SR, we describe a model-based step-by-step methodology to predict dynamic pressure profiles during tube rupture for liquid-liquid, vapor-liquid, and flashing liquid-liquid systems. The transient effects of the relief valve are considered. The effects of choked flow are also be considered for accurate maximum pressure predictions. This SR metric allows plants to assess the risk of overpressure resulting in failure of the equipment. Specifically, imposing a minimum SR ensures compliance with overpressure standards. We obtain HEN configurations with lowest costs that can safely handle tube rupture overpressure events for the entire network. The results obtained indicate a Pareto-like curve relating the safety of an exchanger with its cost. Furthermore, we show that pressure safety valves are a low cost form of overpressure protection.