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    2014/04/24

    Technical Analysis of LNG storage tank safety

        Liquefied natural gas ( referred to as LNG) to transport flexible, high storage efficiency significantly , are widely used as the main source of urban air gas transmission and distribution system expansion , peaking and other aspects . LN G methane as the main component is a hydrocarbon mixture , the boiling point at atmospheric pressure of about - 160 ℃, the boiling temperature changes with the vapor pressure gradient is 1 25 × 10 -. 4 ℃ / Pa. LN G component depends on its density is usually 430 ~ 470 kg / m3, the density of a liquid is a function of temperature change per degree gradient is 1. 35 kg / m3 [1].

        According to LN G characteristics , tank only has good cold insulation properties, but also need to design, manufacture and operation management and other aspects of the LNG storage tank to make certain safety requirements .

        A layout and infrastructure

        1.1 Tank layout

        Tank LN G heat will heat is generated outside the LNG storage tank role . Therefore , arrangements LN G tanks must comply LN G fire safety requirements. Generally based on the volume of the tank is reasonable assurance that the safety distance . National Fire Protection Association standards NFPA59A minimum horizontal spacing specified in the tank wall cofferdam construction of the station area , the minimum spacing between LN G tanks , see Table 1 [ 2 ] . GB / T 20368 -2006 " liquefied natural gas (LN G) production, storage and shipping ," also shows the same data requirements.

        Location of the tank should be constructed to avoid the first downwind flammable release . Layout design should be to determine the relative position of process equipment and storage tanks according to the process of determining the flow position. Process equipment systems are generally far field station from the tank , the tank outside the cofferdam close together , the impact can be relatively small buildings, such as fire water and waste water collection tanks, etc. are arranged according to need heat hazards.

        1.2 Tank cofferdam

        Structural properties of single containment tank to be set cofferdam , whose role is to hold the liquid inside the tank leak once the outflow , preventing expansion of the scope of the leak . Cofferdam from single containment tank size of the tank from the tank to the maximum level is greater than or equal to the height of the cofferdam after subtracting the value of the liquid with a vapor pressure equivalent of the ram , and [ 2 ] . I.e., when the tank leak , there is sufficient space to accommodate the cofferdam leak fluid . Because of the special role of the cofferdam , the design should pay attention to the following points: ① strength cofferdam can withstand all impounded LN G hydrostatic head . ② cofferdam material can withstand cold temperatures generated by the sudden impact . ③ cofferdam can withstand the expected impact of the fire and the forces of nature . ④ selection of smaller thermal conductivity of the material to build the cofferdam and Tank farm level. General cofferdam constructed using reinforced concrete .

        1.3 Tank foundation

        Large vertical flat base cylindrical tank with a high shelf floor two. High frame basis for tank support on the ground extending pile cap stage, set up within the tank bottom insulation layer in order to prevent contact with cold medium to cool the tank can transfer basis , thereby avoiding the basis of an ability to accept the cold frozen expansion occurred , destroying the forces of the tank bottom , the impact of safe storage tanks . The bottom of the tank floor- based combination with perlite insulation and structural concrete structure, basic intermediate embedded heating pipes, hot air in the tube pass into electric heater or hot water in the tank or the default basis . During tank operation, keep the hot water or electrical heating devices continue to work to prevent soil heaving muster damaged tanks . The former security higher, heat the latter part of the heating system needs to be specifically designed to block the heating system to heat the tank leakage , and makes cold cryogenic medium gasification inner tank , to prevent accidents.

        Currently , a large flat -type vertical cylindrical tanks use more concrete pile foundation of a high shelf . Foundation platform supported by piling , to ensure the smooth flow of air circulation . The bottom of the tank between the outer bottom of the tank and set the insulation, the use of the thermal conductivity of glass tiles and other small perlite concrete material as a support layer , cut off the tank of cold energy that contact materials LN G is - 162 ℃, while the concrete cap can be reduced to room temperature . Small and Medium LN G tanks use more leg support columns , the support member such as a major part of the heat storage tank leak in the tank insulation measures need to be considered when designing support , generally with fiberglass or other has a smaller thermal conductivity and material has the strength to do intermediate materials , cut inside and the outside of the tank hot and cold transfer .