(127g) Inherent Safety Assessment Method for Hydrogen Energy Supply Chain Based on Energy Risk and Equipment Reliability

The rapid development of the chemical industry has highlighted the growing need to prioritize process safety. Inherent safer design strategies are among the most reliable and robust methods for achieving process safety, often regarded as the most cost-effective approach to preventing losses. However, accurately assessing the inherent safety level of a process is a critical prerequisite for achieving safer designs. Existing inherent safety assessment methods typically focus only on the hazards of chemicals, without incorporating the reliability of equipment or the probability of ignition and explosion. Furthermore, most assessment processes treat fire and explosion accidents as a single risk category and neglecting the toxic effects of chemicals. In reality, a fire cannot occur without an ignition source following a chemical leak, and a fire does not necessarily lead to an explosion.

This paper proposes a new inherent safety assessment method that characterizes fire, explosion, and toxicity consequences based on energy release. It integrates process energy, material impact, and storage impact factors to assess these hazards separately. Specifically, fire-related energy release is represented by a function of combustion energy, reaction energy, material impact, and storage volume factors, while explosion-related energy release is modeled using physical energy, reaction energy, material impact, and storage volume factors. The method also incorporates equipment failure probabilities and ignition probabilities. This assessment method uses Aspen Plus simulation data as the foundation for risk assessment, enabling the quantification of risks associated with individual units and processes during the design phase. A corresponding software tool is designed and developed to facilitate the comprehensive analysis of inherent process safety. This work will offer a more accurate and integrated method to assessing the inherent safety of chemical processes and provide a valuable tool for process designers to make informed decisions regarding safety improvements.

In terms of case selection, we considered the inherent safety of the supply chain of new energy sources such as hydrogen, which is considered more from the perspective of energy storage. Therefore, this study takes hydrogen compression storage as an example to validate the feasibility and the applicability of the proposed method. The hydrogen compression process is mainly composed of 3 compressors and 3 heat exchangers. Compressors are used to provide pressure to the hydrogen gas, but in the process a lot of heat is generated which causes the hydrogen gas temperature to rise. Therefore, it is necessary to set up a heat exchanger to take away the heat generated during the compression process to ensure that the high-pressure hydrogen temperature is consistent with the ambient temperature to avoid pressure changes caused by heat exchange. The results indicate that the potential accident consequences and probabilities within a compressor are higher than those in a heat exchanger, which is related to the compressor’s operating characteristics and the properties of the medium. For the example of compressor C2 and heat exchanger HX2, the potential fire consequence and explosion consequence for compressor C2 are 38.96 and 38.06, while the fire frequency and explosion frequency are 4.44E-04 and 3.11E-05. For heat exchanger HX2, the potential fire consequence and explosion consequence are 26.08 and 22.19, with fire and explosion frequencies of 1.86E-05 and 7.97E-07. The fire and explosion risks for compressor C2 are 1.81E-02 and 7.59E-04, while the fire and explosion risks for heat exchanger HX2 are 4.84E-04 and 1.77E-05. The compressor applies high pressure to hydrogen, leading to an accumulation of hydrogen mass and an increase in energy. The compression process generates significant heat, raising both the electrostatic potential and the risk of ignition. This combination of increased energy release and ignition probability results in a higher overall risk for the compressor. In the calculation of fire and explosion consequences of compressors, the values of fire and explosion consequences are similar, but the frequency of fires is relatively high, resulting in the fire risk of compressors being the highest value in the whole assessment system. In contrast, the heat exchanger, which aims for optimal heat transfer, has a shorter residence time for the medium, lower mass, and reduced temperature, significantly lowering the accident consequences and probabilities. Regarding toxicity, although hydrogen is considered a non-toxic chemical, high concentrations can lead to oxygen deficiency or asphyxiation. Prolonged inhalation of hydrogen may also affect human oxidative stress responses and cellular processes. Therefore, this study also considers the environmental emissions of hydrogen. However, the risk associated with hydrogen emissions is relatively small compared to the risks of fire and explosion accidents.

Based on the quantification of the hydrogen compression process for high-pressure hydrogen storage, this work suggests that for equipment and accident types with higher associated risks, protective measures should be incorporated during the design phase, or process optimization should be implemented to improve the intrinsic safety of the process.