Static electricity accidents at oil depots are very destructive and have a wide range of impacts. Among them, explosions and fire accidents have the most serious consequences. Strengthening electrostatic protection is very important for the safe operation of oil depots and oil stations. The safety protection measures taken to prevent static electricity from causing fires and explosions are also effective in preventing other electrostatic hazards.
Static electricity is generated by the friction of two different substances. There are a large amount of oil products stored in oil depots and frequent oil product receiving and dispatching operations, so the existence of static electricity is inevitable. The serious consequences of static electricity in oil depots are explosions and fires. Therefore, strengthening electrostatic protection is very important for the safe operation of oil depots.
Static electricity risk analysis
The hazards of static electricity mainly have three aspects, namely, causing explosions and fires, static electric shocks and causing electrical components to malfunction and restricting operating conditions and hindering production.
(1) Static electricity causes explosions and fires. Explosions and fire accidents caused by electrostatic discharge sparks are serious hazards of static electricity. Although the electrostatic energy is not large, it is prone to discharge and electrostatic sparks due to its high voltage. According to statistics, about 10% of fire and explosion accidents in oil depots are caused by static electricity. In November 1982, a 2000m3 metal fixed-top vertical oil tank in an oil depot was measured with a weighing instrument. The plastic tubing was installed in the oil tank’s oil measuring hole. Because the wind speed at that time reached 4m/s, the plastic pipe The static electricity of the cable will generate spark discharge with the adjacent metal pipe, which will ignite the gasoline and cause an explosion. The entire oil tank will be destroyed, causing a large-scale fire. Another example is that when an oil depot was collecting oil in 1988, due to electrostatic discharge detonating the oil and gas in the tank, 1 person was killed, 7 people were injured, and the entire tank area was destroyed.
When the operator is in activity, when the clothes, shoes, and tools that he wears rub against other objects, static electricity may be generated. When a person carrying static charges touches or walks into metal objects such as metal equipment and metal pipes, the fingers or toes of the person will release electric sparks, which often leads to static electricity disasters.
(2) Electrostatic shock. The resistivity of oil products is mostly higher than 1010 Ω·m, which is a non-conductor of static electricity, which has the characteristics of easy accumulation of static electricity. When oil is rubbed against metal, the electrostatic charge generated is often not easy to leak. When the human body approaches these charged objects, it will receive unexpected electric shocks. Similarly, when a human body with a lot of static charge is close to a grounded body, an electric shock will also occur. The degree of electric shock is related to the stored electrostatic energy. The greater the energy, the more serious the electric shock.
Electrostatic shock is not an electric shock in which current continues to pass through the human body, but an instantaneous shock shock caused by electrostatic discharge. This kind of instant shock electric shock will not directly cause death, most of which just produce pain and tremor. However, the human body may fall, fall down and other 2 accidents caused by electric shock. Repeated electric shocks may also make people nervous and fearful, thereby affecting work or reducing work efficiency.
(3) Static electricity hinders production. Static electricity may also cause malfunctions of electronic components and malfunction of electronic computer equipment. For example, a strong electrostatic field will directly interfere with the normal operation of the processor card and other cards of the control station, causing the control system to be disordered and shut down. Static control and protection
For fire and explosion accidents caused by static electricity, it is enough to eliminate any one or several of the four conditions of static discharge. That is, to prevent or reduce the generation of static electricity, try to conduct away or neutralize the generated charge so that it cannot accumulate; prevent the generation of high electric field and electrostatic discharge without sufficient energy; prevent the formation of explosive gas mixtures.
Impurities in the oil are an important factor in its electrification. However, it is difficult and uneconomical to achieve high precision in the oil. Therefore, to prevent petroleum static electricity disasters, it is not to completely eliminate the generation of static charges, but to control various indicators of static electricity from the process or equipment management, so as not to reach the dangerous level and avoid accidents.
Process control
(1) Control the flow rate. The data shows that for the same oil, the higher the flow rate and the larger the pipe diameter, the greater the amount of static electricity generated. For example, the oil loading test on the tanker shows: when the average flow velocity is 2.6m/s, the measured oil surface potential is 2.3kV; when the average flow velocity is 1.7m/s, the oil surface potential is 580V, it can be seen that controlling the flow velocity is to reduce static electricity. Effective measures for the production of loads.
In order to limit the generation of static electricity, when oil flows in the pipeline, the flow rate and pipe diameter should satisfy the following relationship:
v² D ≤0. 64 where v is the flow velocity, m/s; D is the pipe diameter, m.
(2) Control the way of refueling. When oil tanks, tank trucks, etc. splash and fill oil from the top, the oil will inevitably impact the tank wall, stir the liquid in the tank, and accelerate the evaporation, atomization and foaming of the oil, so that the amount of static electricity in the oil in the container will increase sharply. Therefore, it is required that the liquid inlet pipe of the oil storage tank should be connected from the lower part of the tank body. At 200mm.
(3) Avoid mixing substances of different properties. When oil is mixed with water, air and oils of different properties, the amount of static electricity will increase. The mixing of different oil products is also easy to cause static electricity hazards. The mixing of oil products generally occurs when mixing, switching, or when two pipelines deliver different oil products to the tank at the same time.
Compressed air and oil must be in contact with certain measures to limit electrostatic hazards. When working with oil products, it is strictly forbidden to use air to clean the bottom oil of the oil tank and the Class A and B oil pipelines. A certain company has experienced a deflagration accident caused by the residual oil that was flushed by fire-fighting water.
Anti-static facilities
(1) Grounding. Grounding is a common measure to eliminate static electricity hazards. Electrostatic grounding measures should be taken for equipment and pipelines that may generate static electricity hazards in explosion and fire hazardous locations. Automobile tank cars, railway tank cars and loading and unloading places shall be provided with special grounding wires for anti-static. The first end and the middle of the railway oil loading and unloading trestle shall be electrically connected to each other and grounded with the steel rails, oil pipelines, crane pipes, etc. The filling facilities of automobile tank trucks or oil drums for Class A, B, and C oil products shall be equipped with anti-static grounding devices that are bridged with the tank truck or oil drum. The oil product loading and unloading dock should be equipped with an anti-static grounding device that bridges the tanker. This grounding device should be used in conjunction with the anti-static grounding device of the oil loading and unloading equipment on the dock. The beginning, end, branch and straight section of the oil pipeline laid on the ground or in a trench shall be provided with anti-static grounding devices every 200-300m.
(2) Antistatic additives. Antistatic additives are compounds that increase the conductivity of oil products. Its role is not to “anti-static”, but when a small amount of this substance is added, it can increase the conductivity of oil products hundreds of times, making it impossible to get the electric charge. To accumulate without affecting the quality of the oil. There are many types of antistatic agents, such as oleate, cyclic salt, chromium salt, synthetic fatty acid salt and so on.
(3) Static eliminator. A static eliminator is a device that can generate electrons or ions. With the help of the generated electrons or ions, the static charge on the material is neutralized by the opposite charge, so as to achieve the purpose of eliminating static electricity.
Restricted operating conditions
In order to avoid the electrostatic potential of the oil surface and prevent the occurrence of electrostatic accidents, the oil must be allowed to stand for a period of time to ensure the leakage of the static charge in the container when inspecting the container just after the oil has been injected and transported. The rest time of the oil product is determined according to the conductivity of the oil product and the volume of the container.
Therefore, during the standing time of oil tanks and containers, it is strictly forbidden to perform operations such as ruler measurement, temperature measurement, and sampling. The temperature measuring box and sampler of the material must use a conductive material rope and be reliably grounded to the tank body. It is not allowed to use tools with two materials with different conductive properties for measuring scales, temperature measurement and sampling.
Try to avoid the sudden opening or stopping of the pump when entering the oil tank. Sudden opening and stopping of the pump will cause the instantaneous impact pressure and flow rate to be too high, which will cause static electricity to surge and cause accidents. It is more reasonable to use the operation sequence of using small pumps and large pumps to start, and then use large pumps and small pumps to stop, which can play a very good protective role.
Anti-static for human body
Electricity on the human body is more dangerous than electricity on machinery and equipment, because people move around. If you walk or operate in a dangerous place, it is equal to 1 flowing fire. Therefore, the anti-static of the human body cannot be ignored.
(1) Wear anti-static shoes and use conductive ground. The human body is insulated from the ground to accumulate static electricity. If the generated static electricity is dissipated from the ground, the human body cannot be charged. From the perspective of anti-static, a substance with a resistance of less than 108 Ω is a conductor. The resistance of anti-static shoes is in the range of 0.5×105Ω -10 8Ω. It is a conductor for static electricity and an insulator for power frequency alternating current. It also has anti-electric shock performance.
Wearing anti-static shoes must be on conductive ground to be effective. Soil, sand, gravel, cement and other ground, the resistance will not exceed 106Ω, all are electrostatic conductors. Conductive ground should be used wherever combustible gas and flammable liquid may leak.
In order to ensure the reliability of anti-static shoes, the following regulations should be observed when wearing anti-static shoes: ①Do not wear thick socks made of wool and chemical fiber, except for conductive fibers; ②It is forbidden to padded insoles; ③Do not pollute the soles of shoes, such as grease, paint, etc. Contaminated with insulating impurities.
(2) Wear anti-static clothing. There are conductive fibers in the anti-static clothing, which cannot accumulate static electricity. In order to ensure the reliability of anti-static clothing, the following points should be paid attention to when wearing anti-static clothing: ①It is forbidden to put on and take off in static hazardous locations; ②It is forbidden to attach or wear any metal parts on electrostatic work clothes. Metal parts must not be exposed when they must be used. The buttons must be fastened, and the front and hem must not be close to undressing; ③Must be used with anti-static shoes; ④Do not approach power distribution lines or places where electromagnetic waves are radiated; ⑤If the person wearing anti-static clothing feels electric shock , Or when you feel an electric shock when undressing, or when there is a lot of paint, resin, etc. attached to the work clothes, it is not suitable to wear; ⑥The laundry should be gentle, and strong acids and alkalis should not be used. Use the washing machine to choose “normal” instead of “strong washing”, and it should not exceed 20 minutes each time.
(3) It is forbidden to wear chemical fiber clothing. Due to the high resistivity of chemical fiber clothing, it is easy to generate static electricity, and the generated charge can hardly be moved and is difficult to dissipate. Its discharge time often lasts several hours or even several days. Therefore, it is prohibited to wear it in places with flammable gas and flammable liquid. Chemical fiber clothing.
(4) Use soft chairs with caution in static hazardous locations. Stand up from the soft chair, the battery will be larger. According to the test, standing on a soft chair with artificial leather surface, the human body is charged 1.84kV; standing on a soft chair covered with polyvinyl chloride film, the human body is charged 1.8kV. Therefore, it is not allowed to use soft chairs with insulating fabrics such as artificial leather, plastic, and chemical fiber surfaces in places where static electricity is dangerous.
in conclusion
Electrostatic accidents in oil depots are very destructive and have a wide range of impacts, especially the consequences caused by explosions and fire accidents. Preventing fire and explosion caused by static electricity is an important part of electrostatic protection in oil depots. The safety protection measures taken to prevent fire and explosion caused by static electricity are also effective in preventing other static electricity hazards.
