Calculation of leakage rate at ethylene oxide loading/unloading cranes
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According to clause 6.2.12 of SH/T3221-2023: “The ethylene oxide loading and unloading system shall be equipped with water spray facilities and water dilution accident tanks.” Leaks in the ethylene oxide loading and unloading system mainly occur in the area around the loading and unloading cranes, with the main weak points being the quick connectors of the loading and unloading arms, flange gaskets, valve connections, and the seals of expansion joints. The leakage rate is calculated using the orifice local leakage model at the crane position, with the most likely and controllable credible accident scenario during loading and unloading operations selected. Taking into account the engineering practices related to ethylene oxide loading and unloading equipment as well as the criteria for classification under relevant standards, this project has selected the following maximum plausible leakage scenario: – Leakage location: the sealing surface of the connection point between the piping used for loading and unloading ethylene oxide by vehicle – Leakage type: steady-state leakage from a liquid medium through an orifice – Orifice diameter: 5 mm (typical size of small orifices in such piping systems) – State of the medium: liquid ethylene oxide – System operating pressure: 0.4 MPa – Accident response level: gas detection and alarm, followed by manual confirmation for shutdown (detection system classified as level B, isolation system also classified as level B) – Effective leakage duration: 40 minutes (value determined according to relevant standards). Using the calculation formula for liquid leakage specified in HJ169-2018: Where QL represents the liquid leakage rate in kg/s ； Cd — leakage coefficient, taken as 0.65 ； A —— Leakage hole area (m²), A=πd²/4=1.96e-5 ； ρ —— liquid density (kg/m³), taken as 887 kg/m³ ； P — Absolute pressure inside the equipment (Pa), taken as 400000 Pa ； P₀ —— Ambient atmospheric pressure (Pa), taken as 101325 Pa ； h — height of the liquid column above the orifice (m), taken as 0 m. According to the calculations, QL = 0.29 kg/s; the total amount of leakage is M = QL × t = 0.29 × 2400 = 696 kg. To ensure safe handling of the leaked ethylene oxide, water in an amount at least 25 times greater than the amount of leakage can be used for dilution. V=696÷887×25=19.6 m³; the spray flow rate Q=19.6÷40×60=0.0078 m³/s=29.4 m³/h. Conclusion: A water spray system should be installed in the ethylene oxide loading and unloading system, with a spray flow rate of 29.4 m³/h; the volume of the water dilution accident tank is 25 m³
I get it now; the original poster is discussing the calculation of leakage rates at ethylene oxide loading and unloading stations based on the SH/T3221-2023 standard, right? Here are a few practical tips: The formula you’ve posted is the classic derivation for orifice leakage; when performing actual calculations, it’s necessary to distinguish between different types of leakage conditions – such as leakage due to loose connections or pipe damage – and adjust accordingly the orifice area as well as the actual parameters of the fluid ； Ethylene oxide is considered a high-risk medium. The calculation of the leakage volume is not only intended to meet standard requirements; the flow rate of the water spray systems and the capacity of the accident containment tanks also need to be determined based on this value. It is recommended to use the examples provided in the appendices of the standards, as this will better align with the regulatory requirements ； For such process safety calculations, it is best to take into account actual on-site loading and unloading pressures as well as environmental temperature. If possible, consult a professional safety engineer for review to avoid errors that may result from simply applying formulas.
The details you mentioned are indeed on the mark; during previous safety assessments related to the loading and unloading of hazardous materials, I encountered many cases where mistakes were made due to incorrect application of relevant parameters. Firstly, the saturated vapor pressure of ethylene oxide is greatly influenced by temperature compared to ordinary low-temperature hydrocarbons; it is best to use the vapor pressure values corresponding to the actual ambient temperature under loading and unloading conditions when performing calculations, rather than simply applying the standard default values ； Then, the boundaries between the two types of leakage conditions must be clearly distinguished first; for minor seal leaks, the calculation coefficients need to be adjusted taking into account the sealing structure of the transfer pipe, while for major fracture leaks, it is advisable to refer to specialized calculation manuals for hazardous material leaks in order to make the necessary adjustments for the two-phase flashing effect ； After all, ethylene oxide is a highly dangerous flammable and explosive substance; therefore, it is advisable to have the final calculation results reviewed and confirmed by a qualified safety assessment agency, which provides greater certainty.