"Spring thunder" is coming, how should chemical companies deal with it?

Lightning strike is the third-largest natural disaster in the world. Most of China is in a thunderstorm-prone area. The accidents of chemical plant shutdown, damage and personal injury caused by lightning strikes continue to occur. Frequent lightning strikes have caused huge losses to enterprises. There are about a thousand casualties caused by lightning strikes every year in China, and property losses of about 50 to 10 billion yuan due to various accidents caused by lightning strikes.

Lightning is essentially a huge electrostatic discharge phenomenon in a charged cloud. The generation of lightning is mainly caused by the formation of charged clouds. There are many reasons for the formation of charged clouds. The most important reason is that the clouds rise to the air and freeze, and the bottom of the clouds is negative. Positively charged. When thunderclouds with positive and negative charges are constantly accumulating, or a thundercloud with a large amount of charge is close to the earth, it produces a discharge between the cloud and the cloud or between the cloud and the earth. With the instantaneous conversion of air energy and the intense light and sound, this is the common lightning. The huge lightning energy quickly heats the nearby air to above 20,000 °C, and the air is rapidly expanded by heat, which generates an explosion shock wave, which propagates in the air, causing strong mechanical vibration and thermal effects in the production devices and buildings within the lightning strike range, so that it is completely destroyed. .

When the lightning protection device is struck by lightning, the lightning current usually generates a very high potential. If the insulation distance between the lightning protection device and the equipment inside and outside the building is insufficient, a "counter-attack" phenomenon may occur. When a lightning current flows into the surrounding soil through a ground lightning strike or grounding body, a voltage drop is formed around it. When the lightning current is led down to the grounding device, the impedance of the down conductor itself and the grounding device will cause a high voltage drop, which can reach tens of thousands of volts or even hundreds of thousands of volts. It will be seriously damaged. All of these phenomena can generally cause disability and can cause immediate death.

According to the different shapes of lightning, it can be roughly divided into three types: sheet thunder, linear thunder and spherical thunder. From the perspective of hazard, it can be divided into direct lightning, inductive lightning (including electrostatic induction and electromagnetic induction), and spherical lightning. From the mechanism of occurrence, it can be divided into hot thunder, boundary thunder and low pressure thunder. The flaky thunder occurs between the clouds and has little effect on humans; the linear thunder is a common lightning lightning phenomenon; the spherical lightning is a special lightning phenomenon, referred to as "ball thunder", which is a kind of purple or red illuminating The sphere, from a few millimeters to a few tens of meters in diameter, is typically present for 3 to 5 seconds. A ball of mine usually rolls along the ground or floats in the air, and also enters the room through a gap and explodes.

Lightning protection is a very complicated problem. It is necessary to eliminate all kinds of factors that may cause lightning strikes against the lightning intrusion route, and adopt comprehensive prevention and control, such as lightning, equalizing, shielding, grounding, and shunting (protection). In order to reduce the damage to a minimum.

(1) A flashing device. It is the lightning rod, lightning protection belt, lightning protection line or lightning protection net that we often say. The lightning is to discharge the lightning within a certain range. The discharge channel cannot be arbitrarily selected, but only according to the provisions of the lightning protection system designed by people. The channel discharges lightning energy into the earth.

(2) Equipotential bonding. In order to completely eliminate the destructive potential difference caused by lightning, it is particularly necessary to implement equipotential bonding. Power lines, signal lines, metal pipes, etc. must be equipotentially connected through an overvoltage protector, and the interfaces of the inner protective areas are also the same. The local equipotential bonding is carried out in accordance with this and finally connected to the equipotential bonding busbar.

(3) Shielding. Shielding is to use a metal mesh, foil, shell or tube to enclose the object to be protected, so that all channels of lightning electromagnetic pulse wave intrusion are cut off. All shields, shells, etc. need to be grounded.

(4) Grounding. Grounding is to let the lightning current that has entered the lightning protection system flow smoothly into the earth, and the lightning energy can not be concentrated in a certain part of the lightning protection system to damage the protected object. Good grounding can effectively discharge the lightning energy and reduce the lead. The voltage on the lower line to avoid counterattacks.

(5) Diversion. The shunt is to connect an appropriate lightning arrester in parallel between the conductor and the lightning protection grounding device or the grounding wire. When the overvoltage wave generated on the line along the direct lightning strike or lightning strike effect enters the room or equipment along these wires, the lightning arrester The resistance suddenly drops to a low value, which is close to the short-circuit state, and the lightning current flows into the ground from here.

(6) Ionization lightning protection device. The ionization lightning protection device utilizes the inductive action of the thundercloud or takes special measures to shape the lightning protection measures of the chemical production equipment and the storage tank near the ionization device.

The strong thermal and mechanical effects produced by lightning strikes can cause tremendous damage to chemical production equipment and inflammable and explosive materials stored in the tank area. It is easy to cause combustion and explosion of inflammable and explosive materials, and everything at the production site. Equipment and piping should be grounded. The exits and inlets of the metal pipes, the parallel or intersection of the pipes, the joints of the pipes, the application wires are bridged and properly grounded. The metal roof in the chemical production equipment shall be connected to the grounding wire by the down conductor along the circumference of 15 meters. For reinforced concrete roofs, the steel frame should be welded into a whole during construction and connected to the grounding wire with a down conductor every 15 meters. In order to prevent the occurrence of "thunder lightning strike", the flashover voltage of the insulating medium between the lightning protection device and the metal conductor of the building should be greater than the counterattack voltage. Pipes that transport flammable liquids in parallel, when they are less than 10 cm apart, connect the pipes with wires along the length of the pipe every 20 m. For chemical plants and their buildings, all the power supply lines used are buried by cables. Or the cable 50 to 100 meters before entering the building is changed to the cable buried to introduce power. At the connection between the cable and the overhead line, a valve type arrester is installed, and the arrester, the cable metal sheath and the insulator iron foot are commonly grounded, and the grounding resistance is generally 5 to 30 ohms.

Gas cabinets for chemical companies and storage tanks for storing flammable liquids are mostly made of metal. Some tall storage tanks are susceptible to lightning strikes during thunderstorms and should be protected by independent lightning rods. When the wall thickness of the above-ground horizontal tank equipped with the flame arrester and the thickness of the roof of the above-ground fixed top steel tank are equal to or greater than 4 mm, the lightning rod shall not be installed. Lightning rods (net) shall be installed for aluminum tanks and steel tanks with a thickness of less than 4 mm. The lightning rod (net) should protect the entire tank. Lightning rods or floating roof tanks should not be equipped with lightning rods, but the floating roof should be connected to the tank with 2 conductors.

(1) When conducting lightning activities, you should stay in the outdoors or in the wilderness as little as possible. If there are conditions, you can enter buildings with large metal structures or lightning protection facilities. They should leave the hills, hillocks or ridges as far as possible. They should leave the beach, lakeside, riverside and pool. Try to leave the barbed wire and metal. Clotheslines and flagpoles, chimneys, towers, and lonely trees should also be left as far as possible from small buildings or other facilities without lightning protection.

(2) Attention should be paid to the danger of lightning intruding waves in the household. You should leave the lighting, power lines, telephone lines, radio lines, radio power lines, radios and TV antennas, as well as the various devices connected to them to prevent secondary discharge of these lines or equipment to the human body. Attention should also be paid to closing the doors and windows to prevent the ball from entering the room and causing damage.

(3) Protection against step voltage. When the lightning current flows into the surrounding soil through the grounding body of the ground lightning strike point, it will form a high potential around it. If someone stands near the grounding body, it will be harmed by the stride voltage caused by the lightning current. In order to prevent the striding voltage from injuring people, the distance between the lightning protection grounding device and the building, the structure entrance and exit and the sidewalk should not be less than 3 meters. When it is less than 3 meters, safety measures such as deep burial of the grounding body, separation of the asphalt insulation layer, and laying of underground pressure bars shall be taken.