Regarding semi-frozen liquefied hydrocarbon storage tanks
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According to the Code for Design of Fire Dikes, for a fully refrigerated liquefied natural gas storage tank, the distance between the tank wall and the inner edge line of the fire dike should not be less than the sum of the difference between the highest liquid level of the tank and the height of the fire dike, plus the head equivalent to the pressure of the gas above the liquid surface. ..., the distance between fully pressurized and semi-refrigerated liquefied hydrocarbon storage tanks and the fire dike must be no less than 3 m. May I ask whether a vacuum-insulated cryogenic storage tank within an LNG vaporization station, operating at a pressure of 0.8 MPa and a temperature of -162°C, falls under the category of semi-frozen liquefied gas storage tanks?
After reading the owner’s description, it seems that the confusion you’re facing lies in the fact that, according to the relevant regulations, full cryogenic systems and full pressure/semi-cryogenic systems have different requirements regarding the distance from fire dikes. However, the operating conditions of the system in question (0.8 MPa, -162°C, vacuum insulation) seem to be neither entirely typical of a semi-cryogenic system nor of a full cryogenic system. In my opinion, the core of this issue lies in determining whether the type of storage tank meets the definition of a \"semi-frozen\" type. Semi-frozen storage tanks are characterized by operating pressures of around 0.5–1.0 MPa and operating temperatures ranging from -50°C to -104°C. In your case, the temperature is as low as -162°C, which falls within the temperature range of conventional fully frozen LNG storage tanks. A pressure of 0.8 MPa is indeed high at this temperature, but does the specification define a specific temperature range for the \"semi-frozen\" state? Personally, I would recommend checking the specific definition provisions regarding semi-frozen storage tanks in the \"Fire Protection Design Code for Petrochemical Enterprises\" or the \"Design Code for Spherical Storage Tanks of Liquefied Hydrocarbons\", in order to determine the exact values for temperature or pressure. If the specifications do not explicitly cover this range of parameters, it is recommended to refer to the \"Storage Tank Type Classification\" details in the design documents or the technical specifications of the tank manufacturer, as in actual projects, the classification provided by the tank manufacturer is usually taken as the standard. If it cannot be determined in the end, it is advisable to follow the strictest standard (i.e., the one with a greater distance between the fire dike), as safety comes first. It would be best to consult a design reviewer or fire safety expert for confirmation. The above is merely a personal analysis; for specific classifications and engineering design, it is recommended to follow the original text of current standards and the opinions of the design institute.