Assessment of Intrinsic Hazards in an Energy-Integrated Gas Oil Hydrocracking Process

This study assesses the intrinsic hazards of an energy-integrated gas oil hydrocracking process from a sustainability-oriented process safety perspective. Hydrocracking units are essential in modern refineries for upgrading heavy gas oil fractions into higher-value fuels; however, they operate under severe conditions involving high temperatures, elevated pressures, hydrogen-rich environments, complex process structures, and large inventories of hazardous substances. In this context, improving energy efficiency through heat integration must be evaluated together with its implications for inherent safety and sustainable process design. The Inherent Safety Index (ISI) methodology was applied at the conceptual design stage to quantify the intrinsic risk level of the process and identify the main contributors to chemical and process-related hazards. The results yielded a total ISI value of 46, composed of a chemical safety index of 26 and a process safety index of 20, indicating a high intrinsic hazard level. The most significant contributors were toxic exposure (ITOX = 6), inventory magnitude (II = 5), and process structure (IST = 5), while the large ISBL inventory of 2838.3 t, together with operating conditions reaching 456.4 °C and 166.8 bar, substantially increased the inherent risk of the system. Although energy integration contributes to improved thermal performance, the results indicate that it does not significantly reduce the intrinsic hazard level. Sensitivity analysis showed that optimization of operating temperature and pressure could reduce the ISI from 46 to approximately 43. These findings demonstrate that the intrinsic risk of energy-integrated hydrocracking systems is primarily governed by operating severity, hazardous material inventories, and toxicity, highlighting the importance of incorporating inherent safety principles during the conceptual design stage to achieve safer, more resilient, and more sustainable refinery operations.