Safety design of the hottest LNG gasification stat

2022-09-30
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Safety design of LNG gasification station

LNG gasification station (hereinafter referred to as LNG gasification station), as a gas supply station for small and medium-sized cities or large industrial and commercial users, or as a peak shaving gas source station for urban gas, has developed rapidly in China in recent years

lng gasification station is a small LNG receiving, storage and gasification place. LNG comes from natural gas liquefaction plant or LNG terminal receiving base and is generally transported by special truck tanker. This paper only discusses the safety design of storage tanks, vaporizers, piping systems, fire protection systems and other devices in LNG gasification stations

2 LNG storage tank

Beijing Lear will invest about 290million yuan in Haicheng area, Liaoning Province for the follow-up project of Jinhong mining and Liaoning ZTE and the process design of 2.1 LNG storage tank construction of magnesium raw material project

LNG storage tank is the most important equipment in LNG gasification station. Methane, the main component of natural gas, is a permanent gas at room temperature, that is, it cannot be liquefied by compression at room temperature, and can become liquid only at low temperature. CMT -- corrugated core compression strength (n/0.152m) the working pressure of LNG storage tank is generally 0.3 ~ 0.6MPa, the working temperature is about -140 ℃, the design pressure is 0.8MPa, and the design temperature is -196 ℃ [1]

tanks with a volume of 150m3 and below in the LNG gasification station usually adopt a double-layer plywood embedded workbench, which is coated with butter vacuum insulation structure after the experiment, and is composed of an inner tank and an outer tank. The inner tank is made of 0Cr18Ni9 stainless steel, and the outer tank is made of 16MnR pressure vessel steel. Between the inner tank and the outer tank is an insulating layer filled with insulating materials. When the outside of the outer tank is on fire, the insulation material shall not significantly deteriorate the insulation performance of the insulation layer due to melting, collapse and other reasons. At present, the thermal insulation material used by manufacturers is generally pearlescent sand, which is vacuum insulated after filling. In order to prevent the deposition and compaction of thermal insulation materials caused by periodic cooling and reheating, so that the thermal insulation performance decreases or endangers the inner tank, a layer of elastic thermal insulation materials (such as glass wool) should be wrapped outside the inner tank to compensate for the temperature deformation of the inner tank and minimize the stress concentration of the support system between the inner and outer tanks. The support system shall be designed so that the stress transmitted to the inner tank and the outer tank is within the allowable limit. The static evaporation rate of the storage tank reflects the thermal insulation performance of the storage tank when it is in use. It is defined as the ratio of the mass of low-temperature liquid lost by natural evaporation within 24 hours after the low-temperature adiabatic pressure vessel reaches thermal equilibrium when it is filled with low-temperature liquid with more than 50% effective volume to the mass of low-temperature liquid under the effective volume of the vessel. Generally, the static evaporation rate of storage tank is required to be ≤ 0.3%[1, 2]. In addition to the thermal insulation structure, the storage tank must be designed into a structure that can be filled from the top and bottom, so as to prevent the liquid stratification in the storage tank from understanding the processing principle and method of carbon fiber composites

2.2 layout of LNG storage tanks

according to GB 50028-2006 code for design of urban gas, the clear distance between storage tanks shall not be less than 1/4 of the sum of the diameters of adjacent storage tanks, and shall not be less than 1.5m. There should be no more than two rows of storage tanks in the storage tank group. The surrounding non combustible solid protective wall must be set around the storage tank group, and the storage tank foundation and protective wall must ensure that they will not be damaged in contact with liquefied natural gas. The LNG tank farm shall be designed to lead the LNG spilled in the event of an accident to a safe place through detention facilities (dikes), terrain or other means to prevent LNG from flowing into sewers, drains, canals or any other covered ditches. The effective volume V in the protective wall of the storage tank shall comply with the following provisions: ① for the leakage of other storage tanks in the protective wall that may be caused by low temperature or the leakage and fire of a storage tank in the protective wall, when preventive measures are taken for the storage tank, V shall not be less than the volume of the largest storage tank in the protective wall. ② When no preventive measures are taken for the storage tank, V shall not be less than the total volume of all storage tanks in the protective wall

2.3 anti seismic, lightning protection and anti-static design of storage tanks

gb 50223-2004 classification standard for seismic fortification of building engineering, 20 × The seismic fortification category of gas storage tanks in cities and towns with more than 104 people and major gas plants in counties and cities with seismic fortification intensity of 8 and 9 is classified as class B. Nfpa59a "liquefied natural gas (LNG) production, storage and shipping standard" (2001 Edition) stipulates that the seismic design of facilities and structures in LNG gasification station should consider the impact of two levels of earthquakes: operating basis earthquake (OBE) and safe shutdown earthquake (SSE). Operational basis earthquake (OBE) refers to the possible earthquake that the facility can withstand within its design life, that is, when an earthquake of this level occurs, the equipment will remain in operation. Safe shutdown earthquake (SSE) refers to a rare strong earthquake in the location of the gasification station. The facility design should be able to preserve LNG and prevent catastrophic failures of key equipment. It is not required that the facility maintain operation after SSE. The design of the protective wall and other storage systems in the LNG tank farm can at least bear the load of SSE level when it is empty. It is required that the LNG tank may fail after SSE, but the protective wall and other storage systems must be kept intact. All systems and components that may affect the integrity of LNG storage tanks after failure, as well as system components required to isolate the storage tanks and ensure that they are in a safe shutdown state, must be able to withstand SSE without danger. LNG storage tank shall be designed according to OBE and checked for stress limit according to SSE. The design and installation of storage tanks manufactured in the factory shall comply with the requirements of ASME Boiler and pressure vessel code (2007 Edition). The design of storage tanks and supports shall also consider the combined action of seismic force and operating load, and use the allowable stress increment specified in the storage tank or support design code standards

the storage tank area of the LNG gasification station is provided with underground lightning protection grounding, and the pillars of the LNG storage tank are connected with the lightning protection grounding. There is no need to set lightning protection devices on the LNG storage tank. The lightning protection design of the station area shall comply with the relevant provisions of "class II lightning protection buildings" in GB 50057-94 code for design of lightning protection of buildings (2000 EDITION). The anti-static design shall comply with the requirements of hg/t 20675-1990 code for design of electrostatic grounding in chemical enterprises

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