Fire hazard analysis and prevention of the hottest

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Fire hazard analysis and prevention in LPG tank area

liquefied petroleum gas (hereinafter referred to as LPG), liquefied ethane, ethylene, propane, butadiene, natural gas and other substances are basically the same in terms of fire hazard level. At the same time, in order to facilitate storage and transportation, they must be turned into liquid by reducing the temperature under normal pressure or increasing the pressure under normal temperature. Under normal temperature and pressure, their explosion limit is less than 10%. When the mixed explosive gas formed with air (oxygen) meets with the fire source, it can form stable combustion or instant explosive combustion

1. Fire hazard analysis

1-1 properties of liquefied gas

liquefied gas is a colorless, transparent, low toxic substance with special odor. Its main components are carbon 3 and carbon 4 hydrocarbon mixtures. Its liquid specific gravity is lighter than that of water, about 0.5 times that of water, and its gas is heavier than that of air, about 1.5 ~ 2.0 times that of air. It is easy to accumulate in low-lying places on the ground. The saturated vapor pressure of liquefied gas increases sharply with the increase of temperature, and its volume expansion coefficient is also large, which is generally more than 10 times that of water. After gasification, the volume expansion is about 250 ~ 300 times. The flash point, boiling point and ignition temperature are very low (the flash point of 77 ~ 10 can eliminate the combination of ether and ester in the polymer chain is 8 ℃, the boiling point is 0.5 ~ 47.7 ℃, and the ignition temperature is about 430 ~ 500 ℃); The combustion heat value is large, the temperature is high, and the explosion range is wide (its volume percentage concentration is generally about 1.5%~12%)

1-2 fire characteristics

the fire in the liquefied gas tank area is destructive, complex and instantaneous. Liquefied gas tank area is the top priority of fire prevention work in petrochemical enterprises, and its own risk is relatively large. In addition, once the tanks are concentrated, secondary explosion and chain explosion are likely to occur in case of fire (explosion). The explosion hazard area is larger and the loss is larger, resulting in mass deaths and injuries. The liquefied gas tank catches fire, burns rapidly, lasts for a long time, has high temperature, high radiation intensity, and is difficult for people to approach. The function of fire-fighting equipment is affected, which brings greater difficulties to the fire-fighting work

1-3 hazard factor analysis

1-3-1 electrostatic hazard. When flammable and explosive gases (such as liquefied gas) are sprayed through small holes, high-level static electricity will be generated due to the fast flow rate. Practice has proved that the electrostatic potential generated by liquefied gas during high-speed injection is as high as 9000 V, especially when the gas is accompanied by other particulate substances, its electrostatic risk is greater. When the charged body is close to the non charged or low electrostatic potential object, electrostatic discharge will occur as long as the potential difference reaches more than 300 v, And generate sparks. When the spark energy exceeds 0.3 MJ, it is enough to ignite LPG within the limit of explosion concentration, causing combustion and explosion. On february26,1998, the liquefied gas tank area of the storage and transportation branch of Jiangxi Jiujiang Petrochemical Complex was evacuated and deflagration, which was caused by the high-speed injection of a large amount of liquefied gas at the end plate of 805.2 feed pipe, the accumulation of static electricity and the discharge generated sparks, which ignited the mixture of liquefied gas and air. Add the safety engineer site to the favorites

1-3-2 lightning hazard. Lightning strike mainly includes direct strike lightning, induction lightning and lightning intrusion. In addition, there are spherical lightning, which is rare in the value of comparative materials. Lightning disaster mainly shows that the lightning stroke caused by lightning is very destructive. The intensity of each lightning can be as high as 1billion volts, and the power of a moderate lightning is 100000 kilovolts. Lightning does great harm to the liquefied gas tank area. If there is no necessary lightning protection facilities, or the lightning protection facilities are neglected due to management, the lightning protection effect will be reduced or lost, and heavy losses will be caused due to lightning disasters. In addition to the installation of direct lightning protection facilities in the tank farm, gas (oil) storage tanks (tanks), pipelines, equipment, etc. must also be installed with anti-static induction lightning and anti electromagnetic induction lightning devices, which shall be regularly tested by professional testing institutions. At 9:55 on August 12, 1989, the Huangdao Oil Depot in Qingdao, Shandong province suffered a spherical mine attack, which caused a chain explosion after the oil tank deflagration. The fire continued to burn for five days and five nights. During the fire fighting, 14 firefighters and oil depot workers lost their precious lives, 66 firefighters and 12 oil depot workers were injured, and the direct property loss was 35.4 million yuan and the indirect property loss was 85 million yuan

1-3-3 equipment fault hazards. In july2002, the liquid ammonia tank of a factory in Nantong, Jiangsu Province leaked due to the breakage of the glass tube level gauge. A large amount of ammonia gas filled the whole workshop and was in danger of explosion at any time. After the city's fire detachment dispatched two squadrons with more than 50 people to rescue, the dangerous situation was eliminated in time. Any failure of key equipment at a certain point may lead to a large area of harm, so we should not be careless about equipment failure

1-3-4 illegal operation. There are many fire accidents in the liquefied gas tank area caused by illegal operation. The most typical one is the major deflagration accident in the Xiaoliangshan spherical tank area of the oil workshop of a company's refinery at 1:07 on October 22, 1988, which killed 26 people and burned 15 people. At 23:40 on October 21, an operator and the team leader on duty opened the valve for dehydration in the 9143 spherical tank in zone 3. Due to illegal operation, the upstream valve of the spherical tank dehydration package was not closed, so the downstream valve of the dehydration package was opened. In this way, when there was a pressure of 0.4 MPa in the spherical tank, the water and liquefied gas were discharged together while feeding and dehydration, and a large amount of water escaped through the sewage pool, causing deflagration in case of fire source

1-3-5 leakage hazard. The most frequent accidents in the liquefied gas tank area are caused by the leakage of liquefied gas storage tanks, and the damage caused by such accidents is the largest. The main causes of leakage are as follows: (1) the gasket of tank valve is damaged and cracks appear, causing leakage; (2) The liquid level gauge and pressure gauge are damaged; (3) Pipeline rupture; (4) Crack of tank weld, etc. At about 3:00 p.m. on March 5, 1998, Luo Limin, a farmer who worked as a temporary worker in the liquefied petroleum gas Management Office of Xi'an gas company, suddenly found that the bottom of No. 11 large spherical tank containing liquefied gas leaked (because the bottom valve of a 400m3 spherical tank in the liquefied petroleum gas management Office of Xi'an gas company was worn and leaked). Because the leakage could not be controlled, at about 6:40 p.m., a leakage explosion occurred, and a second explosion occurred ten minutes later, At 7:12 p.m. and 8:1 p.m., the disposal of waste plastic particles will become a hot topic in the future. Two violent explosions occurred successively. The fire lasted 37 hours, 33 people were injured and 11 people died

2. Preventive measures

2-1-1 carry out problem rectification according to the liquefied gas design specification, and implement necessary safety technical transformation

2-1-2 storage tank shall be equipped with liquid level gauge, pressure gauge, safety valve, emergency shut-off device, anti freezing blowdown valve and thermometer, as well as high liquid level, low liquid level, overpressure and overtemperature alarm devices. The safety valve and vent pipe of storage tank shall be connected to the plant flare. If possible, pneumatic emergency vent valve can be installed, with independent vent pipe. The liquid hydrocarbon tank group shall be equipped with combustible gas detection alarm according to the specification requirements, and the electrical equipment in the tank farm shall be explosion-proof

2-1-3 tanks shall be provided with electrostatic grounding and lightning protection facilities. There shall be no less than 2 lightning protection grounding points of the storage tank, the distance between the grounding points and the surrounding of the storage tank shall not be less than 30 m, and the grounding resistance shall not be less than 10 Ω. In order to facilitate correct detection, the grounding wire shall be removable. In addition, in order to eliminate the static electricity generated by the flow of liquid hydrocarbon in the pipe and the friction between the pipe wall, the uncharged metal parts of the liquid hydrocarbon process pipe shall be reliably grounded for protection, and the grounding resistance shall not be greater than 10 Ω. All flanges and screw connections shall be welded with wires or bridged with copper sheets

2-1-4 emergency pressure relief and vent facilities. There are two measures to be taken: one is to set double safety pressure relief valve and emergency vent valve, and the vented materials are discharged to the flare system for incineration and venting through closed pipelines; The second is to pour the tank for pressure relief, that is, to set up emergency pipelines so that the materials can be safely transferred to the standby storage tank

2-1-5 emergency water injection facilities. A fire water line is set at the inlet of the liquefied gas transfer pump to facilitate the emergency water injection to isolate the materials in case of leakage of the liquid phase flange of the spherical tank body

2-1-6 secondary dehydration device shall be used for dehydration of storage tank. The root valve of storage tank shall not be normally opened. The dehydration system shall be equipped with heat tracing pipeline

2 - 2 strengthen the maintenance of the equipment, regularly check the intact performance, and solve the problems in time

2-3 improve the management system, put an end to the "three violations" and avoid taking chances

2 - 4 ensure that fire-fighting facilities and equipment are complete and easy to use, and conduct regular inspection and maintenance

2-5 organize plans for key parts in combination with the characteristics of the accident, establish and improve a complete accident plan system, and carry out comprehensive drills throughout the plant according to the plan to clarify the tasks and perform their respective duties

2-6 mastering necessary prevention knowledge is the basis of controlling fire

3. Summary

due to the increasing scale of liquefied gas storage (the storage tank of liquid hydrocarbon at low temperature and normal pressure has even reached tens of thousands of cubic meters), once a fire occurs, it will have a wide range of damage and great harm. Understanding the causes of fire in the liquefied gas tank area and mastering the prevention methods are important conditions to ensure safe production, so that the disasters caused by liquefied gas can be reduced to the minimum in a timely and effective manner

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