Static electricity protection refers to the protective measures taken to prevent deflagration accidents caused by static electricity in the oil receiving container connected to the pipeline terminal.Static electricity in the petroleum industry is mostly generated by the flow of oil products in the pipeline. When oil products flow along the pipeline, the pipe wall carries a polar charge, while oil products have the opposite polaritycharge。Under the same flow conditions, oil products with conductivity in the range of 1~10pS/m, such as steam, coal, diesel, etc., will carry more charges.The electrification of oil products in the pipeline is generally not dangerous, but after the electrified oil products flow into the oil receiving container, a potential difference will be formed between the oil surface and the container shell filled with oil vapor. When the potential difference is enough to discharge, the oil vapor can be ignited to cause deflagration.[1]
Preventive measures taken to prevent personal electric shock, fire and explosion, electronic device failure and damage, and adverse impact on production caused by static accumulation.The prevention principle is mainly to restrain the generation of static electricity, accelerate the leakage of static electricity, and neutralize static electricity.When people wear non-conductive shoes, electric charges will be generated and accumulated due to walking and other activities, and the potential can reach kilovolt level.The highest potential generated by walking and undressing on blankets can reach 2450 volts.At this time, people touching other objects will produce spark discharge and receive electric shock.Human activityAntistaticThe measures mainly include:?Wear conductive shoes;Work clothes and underwear are not usedChemical fiber fabric；Wear anti-static work clothes mixed with conductive fibers or treated with anti-static agents;Conduction treatment shall be conducted on the working ground.When two different objects touch each other, they will produce charge movement on their interface, and the positive and negative charges will be arranged relatively to form a double electric layer.If the objects are separated, they will produce equal charges of different polarity on each object.
principle
The main factors causing static electricity (object characteristics, surface state, electrification history, contact area and pressureSeparation speedAnd so on) as far as possible;Make the positions of objects in contact in the electrified sequence as close as possible;The contact area and pressure between objects should be small, the temperature should be low, the contact times should be small, the separation speed should be small, and the contact state should not change sharply.Powder, liquid and gas will generate static electricity due to friction during transportation.Therefore, it is necessary to limit the flow rate and reduce pipe bending.Increase the diameter and avoid vibration.
In addition to reducing speed, pressure, friction and contact frequency, selecting appropriate materials and shapes, and increasing conductivity, the following measures can also be taken for electrostatic protection: ① grounding. ②Lap (or jumper). ③Shielding. ④For insulators that can hardly leak static electricityAntistatic agentTo increase conductivity and make static electricity easy to leak. ⑤Use spray, water spraying and other methods to improve the environmental humidity and inhibit the generation of static electricity. ⑥useElectrostatic eliminator, static neutralization.
ESD
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ESD means "electrostatic discharge" in English.As we all know, the contact, separation or friction of different substances can generate static electricity.For example, extrusion, cutting, handling, mixing and filtering in the production process, as well as walking, standing up and undressing in life, will generate static electricity.It can be seen that static electricity can be said to be ubiquitous in our daily life. We have very high static voltage on our bodies and around us, thousands of volts or even tens of thousands of volts.These static electricity may have little impact on the human body, but for some ESDS (electrostatic sensitive elements), it can directly make them lose their normal performance, or even completely lose their normal function.In this way, ESD protection is very necessary.
Human static electricity
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Electrostatic protection
When people wear non-conductive shoes (referring to objects with conductivity less than 1 × 10-6 W/m), electric charges will be generated and accumulated due to walking and other activities, and the potential can reach kilovolt level (such actions are dangerous actions).At this time, people touching other objects will produce spark discharge and receive electric shock.The E-t (potential time) curve shown in Figure 1 is obtained from the experiments conducted in China. In the figure, X, Eu, etc. represent different individuals.The highest potential generated by walking and undressing on the blanket is 2450V.Repeat these activities on the terrazzo floor, and the highest potential measured is 3500~6000 volts.It can be seen that human potential is related to the ground material.In additionRelative humidity of airThe inner and outer garments are related to the materials of shoes and socks.The experiment shows that chemical fiber materials are not allowed to be used not only in work clothes (outerwear) but also in underwear in flammable and explosive places.The anti-static measures in human activities mainly include: wear conductive shoes, anti-static work clothes mixed with conductive fibers or treated with anti-static agents, wear human grounding wrist strap, or touch the grounding copper wire with hands before some operations;If necessary, the working ground shall be conducted, such as conductive terrazzo or conductive rubber (adhesive surface) with conductivity of 10-6 W/m.
Boundary between human discharge and electric shock
Electrostatic protection
The boundary between human body discharge and electric shock is: ① discharge that generates electrostatic shock when the charge reaches (2-3) × 10-7 or more.As shown in Table 1, electrostatic shock occurs when the potential reaches about 3 kV.This is when the human electrostatic capacitance is equal to or less than the standard value of 100 pics, that is, when the value is generally 90~100 pics.When sitting on a chair or wearing thin soled shoes or old leather shoes, the capacitance is more than 100 leather methods, or even hundreds of leather methods sometimes. At this time, the limit potential of electrostatic shock is smaller than the value in Table 1. ②If the charged object is a conductor, when the charged potential is at or above the value in Table 2, there is a discharge of (2~3) × 10-7 or more discharge charges on the human body, the human body will be shocked. ③In case of more than 100 pics, when there is a static field near the human body, and when there is a charged body with large energy nearby, the human body will be continuously induced, which may be enough to make the human body with far more than 100 pics have a high different sign potential, resulting in greater danger in flammable and explosive places. Therefore, the possible upper limit value of human body capacitance should be supplemented. ④If the charged body is a non conductor, the boundary of electrostatic shock cannot be expressed as charged potential as that of conductor.However, in most cases, electrostatic shock occurs when the charged potential is more than 30 kV and discharges to the human body.Therefore, the boundary of electrostatic shock is roughly based on the charged potential of about 10 kV and the charged charge density of about 10-5 ku/m2.However, the above judgment cannot be made when the charged state is particularly uneven, there is a part with high conductivity in the non conductor, and there is a grounding body in or near the charged object.
Electrostatic protection
brief introduction
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The static electricity generated by solids and the inhibition of the contact between two different objects will generate charge movement on their interfaces, and the positive and negative charges will be arranged relatively to form a double electric layer.At this time, if the object is separated, the two objects will generate equal charges with different polarity.Generally, when two objects in contact with each other are farther away from each other in the "charged sequence", the amount of static electricity will be greater.The polarity of the charge depends on the relative position in the charged sequence.
In the process of mutual contact and separation, the excess charge of positive (+) or negative (-) stored in the volume of objects will be neutralized due to discharge and conduction, or will tend to decrease due to leakage to space and earth. This process is called charge relaxation.Generally, the static electricity will be relieved at the same time.As any object contacted and separated will produce strong or weak static electricity, for modern electronic devices, new gunpowder, flammable and explosive gases with very low flash points (such as liquid hydrogen and other special low flash point rocket fuels that can volatilize at normal temperature and pressure) that are extremely sensitive to static electricity, as long as the weak static electricity is weak, accidents, fires and explosions may occur,Therefore, it is a difficult technical problem to prevent or eliminate the harm of static electricity.As for the damage of film photosensitivity and electronic components caused by the discharge effect caused by static electricity, the fiber entanglement and uneven printing paper caused by the mechanical effect are also complex problems.
Principle of preventing static electricity
The principles to prevent static electricity are as follows: ① The main factors causing static electricity should be eliminated as far as possible.The main factors affecting the generation of static electricity are: the characteristics of objects;The surface state of the object;Charged history of objects;Contact area and its pressure;Separation speed. ②The electrification sequence shown in Table 3 shall be referred to so that the positions of the objects in contact with each other in the electrification sequence are as close as possible. ③The contact area and pressure between objects should be small, the temperature should be low, the contact times should be small, the separation speed should be small, and the contact state should not change sharply.
Static electricity generated by powder and its suppression
Electrostatic protection
In the process of air conveying, belt conveying or sieving, the powder will generate static electricity due to the friction between the powder or between the powder and the pipe wall.Therefore: ① The transportation speed in the pipeline shall not exceed a certain limit value, and the pipeline diameter shall not be less than a certain minimum value.There shall be no net, grid and other objects that hinder the transmission and generate static electricity in the pipe.The size and shape of the powder should be optimized. ②Try to reduce the bending and contraction of pipeline;Avoid sharp changes in wind speed and delivery volume. ③Proper air vibration and other measures shall be taken to clean and repair the inner surface of the pipe wall regularly to prevent the accumulation of powder. ④The transmission pipeline shall be made of conductive materials as far as possible and grounded. ⑤Should be preferredHelical bladeThe upper limit of the shape and the number of revolutions of the spiral;The conveyor belt vibration or abnormal vibration due to improper conveying capacity shall be avoided, and the powder shall not be suspended and dispersed. ⑥In bucket conveying, the wall slope of hopper and funnel should be close to vertical to reduce the friction area;The bucket wall shall not disturb the falling process of powder;Clean regularly;Try not to install metal sliding fixators on the hopper. ⑦The size and shape of the powder and the material of the hopper should be optimized to minimize static electricity. ⑧Hoppers and funnels shall be made of conductive materials as far as possible and grounded.
Static electricity generated by liquid and its suppression
Static electricity is generated due to friction between liquids or friction between liquids and pumps during pipeline transportation or flowing through hoses.Under the same other conditions, the static electricity is proportional to the 1.8~2 power of the flow rate.In order to limit static electricity, it should be noted that ① the flow rate of hydrocarbon oil should not exceed the values listed in Table 4. ②Under the condition of the same conveying capacity, the diameter of piping and hose should be increased to reduce the flow rate. ③There should be no turbulent or sharply changing transmission state. The bending and shrinking parts of the piping should be minimized, and the internal wall of the piping should be smooth.Do not install metal mesh or protruding objects in the pipe.The filter should be set at the flow source side as far as possible. ④The flow rate should not change sharply in any part or at any time. The flow rate should be controlled at a low level at the beginning and end of the transmission. The flow rate in the middle should not exceed the specified value. ⑤The liquid shall not be mixed with air, water, dust, oxides (rust, etc.) and other sundries. ⑥Large diameter relief pipe sections and tanks for reducing flow rate shall be installed at the ends of pipes and hoses. ⑦When using oil tankers, tank trucks, oil tankers, tanks and other containers to transport liquids, attention should be paid to the static electricity generated due to tank vibration and friction between the liquid and the vessel wall.During conveying, the moving speed shall not change sharply, and shall move at a uniform speed as far as possible;The tank shall be separated by a partition board, which shall not cause the liquid to wave or splash;The liquid shall not be mixed with sundries;The interior of the tank shall be cleaned regularly.
Static electricity generated by gas and its suppression
Electrostatic protection
In the process of flowing and ejecting, the high pressure air will containCompressor oilAnd condensation water mist caused by compression, as well as pipe rust, dust and other particles flowing in the pipe, or ejected from the opening, particles collide and friction with the wall and nearby objects to generate static electricity.Therefore: ① ApplicationAir filterFilter the fog and particles before flowing and spraying. ②The ejection flow shall be small, and the ejection pressure shall be low. Pay special attention to the explosion caused by hydrogen ejection. ③Pipes and hoses shall be cleaned before use to remove rust and dust. ④Condensationcarbon dioxideWhen spraying out, dry ice shall be avoided at the opening, because it collides and rubs with liquid components, or collides, rubs and splashes with the wall surface to generate static electricity. ⑤The openings and flanges of LPG cylinders and pipes shall be cleaned and kept clean. ⑥Gas cylinders, pipelines and hoses of hydrogen, acetylene, propane, city gas and nitrogen shall be cleaned before use to remove rust and moisture.Try not to use rubber tubes, but metal tubes, and ground them. ⑦The opening of the steam pipe is easy to generate static electricity, so dry steam should be used as much as possible, the amount of spray should be small, the spray pressure should be limited to 98 N/cm2 as much as possible, and the nozzle with less static electricity should be used, and there should be enough distance between the nozzle and the object. ⑧When spraying aerosol and paint, do not spray a large amount and violently against objects in close proximity. ⑨The aircraft and spacecraft generate static electricity due to friction with the air during flight. Figure 2 shows the relationship between the rocket height (km) and the potential (kV).The static electricity can be discharged into the atmosphere by using the anti-static needle installed at an appropriate position to prevent the excessive rise of potential.China launched synchronous satellitesstrap-on rocketIt is equipped with an anti-static probe.
Protective measures
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In addition to reducing speed, pressure, friction and contact frequency, selecting appropriate materials and shapes, and increasing conductivity, the following measures can also be taken:
Electrostatic protection
① Grounding refers to the electrical connection between the metal conductor and the earth (grounding device) in order to leak the charge to the earth.This method is suitable for eliminating the static electricity on conductors and objects with resistivity below 108 Ω, but not on insulators, because the grounding of insulators is prone to spark discharge, causing ignition of flammable and explosive liquids and gases or interference to electronic facilities.The resistance between the insulator and the earth shall be 106~109 Ω.The grounding is only used to eliminate static electricity on the conductor, and the resistance value should not exceed 100~1000 Ω generally.The grounding point of non-metallic conductor shall be wrapped with reliable metal objects or usedConductive coatingThe contact area shall not be less than 10 cm2.Mobile equipment cannot be grounded frequently, and the grounding operation should be conducted in a place and time without danger.
② Lap (or jumper).Connect more than two independent metal conductors electrically, so that they are basically at the same potential with each other (Figure 3).
③ Shielding.Cover the surface of charged objects with grounded metal wires or metal nets, so as to limit the electrostatic hazard to the extent that it will not occur.Shielding measures can also prevent electronic facilities from being interfered by static electricity.
④ For insulators that can hardly leak static electricity, anti-static agents are used to increase conductivity, so that static electricity is easy to leak.
⑤ By means of spraying and watering, the relative humidity of the environment is increased to 60~70% to suppress the generation of static electricity and solve the problem of static electricity in production such as textile mills.
phenomenon
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In the sixth century BC, humans discovered thatamberAfter friction, it can attract light and small objects“Electrostatic phenomenon”。This isFree chargeThe electrical property shown after the transfer between objects.In addition, when silk or wool is rubbed, small sparks are generated, which is the effect of charge neutralization.“thunder”In nature, because the positive and negative charges accumulated in the clouds are violently neutralized, the electricity, thunder and heat are generated.
Electrostatic phenomena include many natural examples, such as the attraction between plastic bags and hands, seemingly spontaneous barn explosion, damage of electronic components during manufacturingPhotocopierThe operating principle of.When the surface of an object touches other surfaces, the charge will gather on the surface of the object and become static electricity.Although the charge exchange is caused by the contact and separation of two surfaces, only when the resistance of one surface is very high,ElectrorheologicalThe effect of charge exchange will be noticed only when it is very small.Because, the charge will be trapped on that surface and spend a long time there, enough time for this effect to be observed.
Electrostatic phenomena are caused by the interaction of point chargesElectrostatic forceGenerated.Coulomb's law specifically describes the physical properties of electrostatic force.In the hydrogen atom, the electrostatic force of the interaction between the electron and the proton is greater than the gravitational force, and the order of magnitude of the electrostatic force is about 40 times the order of magnitude of the gravitational force.
Elimination method
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1. Wash your hands before going out, or put your hands on the wall to remove static electricity, and try not to wear chemical fiber clothes.
2. In order to avoid electrostatic impact, small metal devices (such as keys), cotton rags, etc. can be used to first touch the door, door handle, faucet, chair back, bed railing, etc. to eliminate static electricity, and then touch with hands.
3. Wear cotton underwear.
4. When getting ready to get off, hold the gear with your right hand, then touch the iron part below with your fingers, then open the door, put your left hand at the position where the door has iron, but don't loosen your left hand, then put your right hand away, and get off. At this time, you can hold the door with your right hand and won't be electrified~~Ha.Next, try hard to finish it~~
5. To deal with static electricity, we can take "anti" and "release" measures."Anti", we should try to choose pure cotton products as fabrics for clothing and household accessories, and try to avoid using themchemical fibre carpetAnd furniture with plastic surface material to prevent friction electrification.As far as possible away from televisionRefrigeratorTo prevent induction electrification."Discharge" means to increase humidity so that local static electricity can be easily discharged.When you turn off the TV and leave the computer, you should wash your hands and face immediately to let the static charge on the skin surface release in the water.In winter, try to choose high moisturizing cosmetics.Common humidifier.Some people like to raise ornamental fish and daffodils indoors, which is also a good way to regulate indoor humidity.
In addition, an economical and practical humidification method is recommended: place a basin of water under the heater, use an old towel (or absorbent cloth), put one end in the water and the other end on the heater, so that about three liters of water can be evaporated into the room day and night.If every heater does this, the whole room will feel moist and pleasant.You might as well try.
6. Frequent bathing and changing clothes can effectively eliminate static electricity accumulated on human body surface.
Here are two tips to helpPrevent such electric shock。
1. In the house, static electricity may be generated after the friction between the carpet and the sole of the shoe, and it may be electrified by the wind outside the house.At this time, be careful to touch the iron door when entering and exiting, and your hands may be hit by electricity.After encountering such situations repeatedly, the following measures can be taken to avoid electric shock:
When touching the iron door, do not directly touch the iron door with your hands. Instead, hold a bunch of keys in your pocket with your hands in a large area (usually this will not cause electric shock), and then use the tip of a key to touch the iron door, so that the electricity on your body will be discharged without electric shock.
Principle: The pain of discharge on the hand is caused by high-voltage discharge. Because the sudden contact between the hand and the iron door during discharge is a very small area of contact, the instantaneous high-voltage is generated.If you take out the key in your pocket, first hold the key in a large area (a string of keys cannot transfer much electric charge, so there will be no electric shock at this time), and then use the tip of a key to contact the large conductor. At this time, the contact point of the discharge is not a point on the skin of the hand, but the tip of the key, so the hand will not feel pain (maybe the key will!----If it hurts).
2. Electric shock often occurs when getting off the taxi.This is mainly due to the accumulation of static electricity caused by the friction between the body and the seat when getting off the bus. When the door is closed after getting off the bus, the hand suddenly touches the iron door and gets an electric shock.
When this happens frequently, it is best to pay attention to: when getting off the car, that is, when the body rubs against the seat, hold the metal door frame in advance, so that when static electricity is generated by friction, the static electricity on the body can be discharged at any time, instead of discharging when suddenly touching the iron door after getting off the car.
The most effective measure is to "connect" the human body to the earth, that is, "ground".Therefore, people should wearAnti static shoes。To keep the human body connected to the ground, it is required that the ground is also anti-static to guide the static electricity of the human body into the ground, so the ground can be used with anti-static mat, anti-static composite rubber plate, andstatic line Connect well. If the funds are sufficient, anti-static raised floor can be selected, especially in the planning and designcomputer roomIt can be considered when buildingAnti static raised floorIf the machine room and plant have been determined and the equipment has been installed, and you do not want to stop the production of these equipment due to the installation of anti-static equipment, you should choose anti-static floor mats and anti-static composite rubber plates that are both cheap and simple in construction.3。When people wear anti-static shoes and have anti-static floor mats, anti-static composite rubber plates or anti-static raised floors, they will certainly have a good anti-static effect?When people wear anti-static shoes and have anti-static floor mats, anti-static composite rubber plates or anti-static raised floors, they may not have a good anti-static effect.Usually, people have to wear socks and insoles. Young people's feet are prone to sweat. These socks and insoles can also conduct static electricity. However, in the dry season for middle-aged and elderly people, because the shoes are dry, these socks and insoles cannot conduct static electricity, and many manufacturers only require workers to wear themAnti static clothingAnd anti-static shoes, ignoring the adverse effects of socks and insoles, so that the anti-static shoes and anti-static ground can not play an anti-static role.Therefore, a "human integrated resistance detector" is placed at the entrance of the machine room or plant, which can quickly and accurately detect those who wear unqualified anti-static shoes, socks and insoles.
Electrostatic dust removal: It can eliminate coal dust in flue gas
XerographyYou can copy books, materials and documents quickly and conveniently
High voltage static electricity can also affect the production of liquor, vinegar and soy sauceAgingIt has a promoting effect.The taste of aged liquor, sour vinegar and soy sauce will be more pure.
Widely used in: production of precision electronic products;Electronic assembly line, microelectronics production, photoelectric;Pharmaceutical manufacturing assembly line, printing and packaging;Small product molding, plastic film shearing, circle and film covering, and mold product demoulding.
applied technology
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Electrostatics mainly studies electrostatic application technologies, such as electrostatic precipitation, electrostatic copying, electrostatic biological effects, etc.More importantly, electrostatic protection technology, such as electronic industry, petroleum industryOrdnance industry, textile industry, rubber industry, Xinghang and military fields, seeking to reduce the loss caused by static electricity In recent years, with the rapid development of science and technologyMicroelectronicsThe electromagnetic environment is becoming more and more complex. The electromagnetic effects of electrostatic discharge, such as electromagnetic interference (EMI) andelectromagnetic compatibility (EMC) has become an urgent problem to be solved.On the one hand, the extensive application of some high resistivity polymer materials such as plastic, rubber and other products and the high-speed modern production process have enabled the accumulation of static electricity to a high degree. On the other hand, the production and use of electrostatic sensitive materials, such as light oil products, gunpowder,Solid state electronic deviceThe harm of static electricity to industrial and mining enterprises is becoming more and more prominent, which has caused quite serious consequences and losses.It can inadvertently break down expensive electronic devices, resulting in an annual loss of tens of billions of dollars in the electronic industry.In Xinghang Industry, the electrostatic discharge caused the launch failure of rockets and satellites, which interfered with the operation of Xinghang aircraft.On July 29, 1967, an incident occurred on the US Forrestal aircraft carrierSerious accidentThe sudden ignition of a missile on an A4 aircraft caused a loss of 72 million dollars and 134 people were injured. The investigation found that the missile shielding joint was unqualified and the static electricity caused the ignition.At the end of 1969, in less than a month, the static electricity generated by the three 200000 ton super tankers from the Netherlands, Norway and the United Kingdom during tank cleaning caused explosions in succession.
In recent years, more than 30 serious fire and explosion accidents caused by static electricity have occurred in petrochemical enterprises in China.Many industrial developed countries have established electrostatic research institutions. China has carried out some electrostatic research since the late 1960s. Since the 1980s, China's electrostatic research has developed very rapidly.Established in 1981Electrostatic Committee of Chinese Physical SocietyThe first national electrostatic academic conference was held, and national and local electrostatic academic conferences were held continuously. The scope of electrostatic research and application was also growing, and the scientific research team was growing.
