Hazard characteristics analysis of cryogenic liquid - Doer equipment

1. Hazard characteristics analysis of cryogenic liquid
Low temperature liquid has the dangerous characteristics of low boiling point, large expansion, strong asphyxiation and strong oxidation.
1.1 Boiling point of cryogenic liquid at 101.3KPa: - 196 ℃ for liquid ammonia, - 183 ℃ for liquid oxygen, and - 186 ℃ for liquid xenon. When contacting with human body, it will cause severe frostbite to skin and eyes. When a small amount of cryogenic liquid leaks or the pipe valve leaks, it will absorb the heat of the surrounding environment, and the leakage point will quickly condensation and frost, and even freeze in severe cases.
1.2 Low temperature liquid receives high heat from the surrounding environment or a large amount of leakage absorbs surrounding energy, and its volume will expand due to rapid gasification. At 0 ℃ and 1013KPa, the gas volume after gasification of 1L low-temperature liquid: 674L nitrogen, 800L oxygen and 780L argon. In the closed container or pipeline, the internal pressure increases due to the gasification of low-temperature liquid, which is easy to cause overpressure explosion of the container or pipeline.
1.3 In the environment around low temperature storage tank and low temperature tank, it is easy to form a gas rich area after the leakage and gasification of low temperature liquid. If the concentration of nitrogen, argon and carbon dioxide is high, it is very easy to cause case information damage. In addition, when the oxygen concentration is high, oxygen enrichment injury will also occur.
1.4 Oxygen is a strong combustion supporting agent with strong oxidizability. The liquid oxygen is close to combustibles, which is easy to cause combustion in case of open fire; In contact with combustibles, it is easy to produce detonation due to vibration, impact, etc; Mixed with combustibles, with potential explosion hazard. Liquid oxygen can adhere to clothes and fabrics, and it is easy to cause flashover in case of ignition source, causing personal injury.
2. Gas supply mode and basic requirements of low-temperature insulated low-temperature storage tank
According to the different use occasions and user needs, the gas supply modes of cryogenic liquid storage tanks mainly include: high-pressure gas cylinder filling, low-temperature adiabatic gas cylinder subpackage, centralized gas supply through pipe network and low-temperature liquid spraying.
2.1 Filling of high-pressure gas cylinder
The cryogenic tank is used as the gas supply source for filling high-pressure gas cylinders, which is suitable for the needs of many scattered gas users, and generally must be standardized by professional production and filling units. According to the current national administrative licensing requirements, the filling unit must hold the safety production license and cylinder filling license of the approval for the designated production (storage) of hazardous chemicals, namely, "one certificate and two licenses", before filling high-pressure cylinders. At the liquid outlet of the cryogenic tank, a cryogenic liquid pump and a high-pressure vaporizer are equipped to fill the high-pressure gas into a special cylinder with a high-pressure filling system. In the process flow of cylinder filling, automatic shutdown for low temperature and overpressure of pipeline must be set
Vehicle protection system. When there is still cryogenic liquid at the outlet of the vaporizer or the pipeline pressure exceeds the high working pressure of the cylinder, the cryogenic liquid pump shall automatically stop, and the cryogenic storage tank shall stop supplying gas to prevent cryogenic liquid from directly filling into the cylinder or explosion caused by overpressure of the cylinder.
2.2 Sub packaging of cryogenic insulated gas cylinders
As the liquid outlet of the cryogenic tank of the cryogenic liquid storage tank, the cryogenic liquid is directly sub packed into special small containers such as cryogenic insulated gas cylinders with the help of the storage pressure in the tank, which can be used by relatively independent and large users. When the cryogenic insulated gas cylinder is subpackaged, if the gas cylinder is equipped with a vent valve, open the vent valve to vent. During subpackaging, the operator shall stand at the side for operation, and the liquid outlet or vent shall not stay for a long time. In the process of subpackage, if the pipe valve is frozen, it is better to defrost it with hot water at about 70 ℃ instead of electric baking or forced knocking. In the subpackage area, the air shall be kept unblocked to avoid the accumulation of low-temperature liquid or gas.
2.3 Centralized gas supply through pipe network
The liquid outlet of low-temperature storage tank is connected with low-temperature liquid low-pressure vaporizer and terminal pipeline regulating system, followed by gas pipe network, which can be used in large areas or more users. According to the gas demand of the pipe network, after the gas use pressure is determined, the terminal pipeline regulation system will adjust the set working pressure for boosting, and the gas will be output at an automatic constant pressure to meet the requirements for centralized gas use in the region. The cryogenic liquid in the cryogenic liquid storage tank shall always be kept in a certain amount, so that its contents can be kept in a dry and low temperature state, and the gas supply system can be kept in a low pressure and constant operating condition.
2.4 Low temperature liquid spraying liquid supply
The low-temperature storage tank and low-temperature tank are used to directly supply low-temperature liquid (commonly used medium is liquid nitrogen) to external objects through low-temperature pipeline for spraying, which is used for low-temperature processing processes (such as low-temperature crushing, quick food freezing, etc.).
The distance between low-temperature storage tank and low-temperature tank, which are equipped with low-temperature liquid spraying system, shall be shortened as far as possible to reduce the length of low-temperature pipeline and the loss of low-temperature cooling capacity. Low temperature liquid pipelines shall be equipped with thermal insulation protection measures and moisture-proof treatment structures. Generally, straight air thermal insulation pipelines or polyurethane foamed materials with better thermal insulation effect shall be used for connection, which shall be coated with galvanized iron pipes.