Engineering technology for liquefied hydrocarbon spherical tank stations

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1. Classification of spherical tanks for liquefied hydrocarbons: Spherical tanks for liquefied hydrocarbons at ambient temperature refer to fully pressurized spherical tanks whose design pressure is not lower than the saturation vapor pressure of the liquefied hydrocarbon medium at 50°C. Due to the high pressure and thick wall thickness, it is not easy to increase the volume of spherical tanks. Moreover, the larger the volume, the greater the risk becomes in the event of a leak from a medium with a large storage capacity. **Standards – In its 2018 updated version, the “Fire Protection Design Standard for Petrochemical Enterprises” GB50160-2008 added the following clause: 6.3.1A The single-tank capacity of fully pressurized or semi-frozen liquefied hydrocarbon storage tanks shall not exceed 4,000 m³. In 2024, the **Ministry of Emergency Management issued the latest capacity limits regulations – the most recent rules regarding the capacity limits for spherical tanks. Semi-frozen spherical tanks: When the pressure of the medium at room temperature is high, making it impossible to achieve a tank volume of 4000 cubic meters, it is possible to design larger spherical tanks by reducing the temperature and pressure. Such spherical tanks are known as semi-frozen spherical tanks. This design helps to reduce the initial investment in the facility, but it also increases the operational and maintenance costs of the facility. Ultra-low temperature spherical tanks generally refer to double-vacuum cryogenic spherical tanks with a design temperature below -196°C, suitable for storing large quantities of special fluids such as liquid hydrogen and liquid helium. 2. Volume data of several large spherical tanks
1) In the 1980s, China built a semi-cooled liquid ammonia spherical tank with a volume of 8,250 m³ (using imported materials; design pressure: 0.4 MPa). Subsequently, multiple liquid ammonia spherical tanks with capacities of 5,000 m³ and 6,000 m³ were constructed one after another (using domestic materials; design pressure less than 1.0 MPa). 2) The volume of natural gas spheres independently built in our country has reached 10,000 m3. 3) Currently, the largest vacuum spherical tank built in our country is 20,000 m³. 4) According to online reports, the development of larger spherical tanks in Europe and the United States started earlier, and the related technology is also more mature. For example, Germany already has the capability to produce spherical tanks with a volume of over 43,300 m³; France also has experience in manufacturing spherical tanks with a volume of 87,000 m³. In the United States, the volume of Holton-type spherical pressure storage tanks has reached 160,000 cubic meters. The liquid hydrogen spherical tanks that have been constructed and put into service have a capacity of 4,700 m³, with a design temperature of -253°C. 3. Layout of liquefied hydrocarbon spheres: During safety inspections, the following layout-related issues are most likely to arise: 1) Insufficient spacing between spheres. The spacing specified in the standards refers to the distance between the outer walls of the spheres (or the outer wall of the insulation layer, in the case of spheres with insulation). Some designers tend to arrange the design based on the inner diameter of the spherical tank, ignoring factors such as the wall thickness of the tank, the thickness of the insulation layer, construction errors in civil engineering, and construction errors of the spherical tank itself. Currently, portable laser rangefinders are generally used for inspections; if the measurements do not meet the specifications, it is easy to detect this. Relatively speaking, it is easier to make corrections when it is discovered during the drawing approval process that the spacing requirements are not met; generally, it is sufficient to reduce the inner diameter of the spherical tank accordingly. 2) The spherical tank area is not located on the outside of the site or as a separate zone, nor is an independent transportation passage provided on the side close to the road. The main purpose is to shorten the route taken by tank trucks transporting liquefied hydrocarbons within the plant premises, thereby reducing unnecessary risks. 3) There are no physical walls between the tank area and other parts of the plant. 4) The liquefied hydrocarbon spheres and the storage tanks for oils at atmospheric pressure were not arranged separately, as required by the latest version of the \"Design Code for Oil Storage Tanks\".