The boiling drying equipment is basically based on the working principle of the fluidized bed. The basis of the material drying process is the boiling of the powder. At the same time, under the effect of exhaust, the fine powder in the container is filtered by the trapping bag and discharged to the outside. During the process of trapping, a large amount of ultrafine powder is produced, whether it is in boiling or trapping operation. The whole process of boiling and drying is accompanied by ultrafine powder movement. However, the process of powder movement is often accompanied by two problems of static electricity and dust explosion. Under the guidance of certain factors, it may cause explosion. At present, when dealing with such problems in the country, it is considered that as long as the installation of explosion-proof motors is feasible, it is considered inappropriate. This paper discusses the theory of powder static electricity and dust explosion and puts forward their own opinions on the explosion-proof safety of boiling drying equipment. The purpose is to make the equipment more complete, reliable and safe.
1. Analysis of Unsafe Factors of Powder in Boiling Drying Equipment
1.1 Discussion on the factors of electrostatic generation in boiling of powder boiling equipment
During the boiling and drying process of the material in the boiling and drying equipment, due to the violent friction between the drying gas and the surface of the material particles, the dry solid particles will also have violent collisions and frictions. At the same time, the solid particles will also collide with the wall surface of the cylinder, trapping bags and tubes. Severe collisions and frictions occur on the wall surface of the road, which causes a large amount of static electricity on the surface of the solid particles. On the other hand, with the continuous refinement of the solid particles, a large number of new surfaces are generated, and the surface charge balance state of the original particles is destroyed. The surface of the nascent particles carries a large amount of charge. Due to aggregation, adhesion of the pipe wall and the like, once the complete machine is in a poor ground state, the accumulated electrostatic charge can form a relatively high voltage, and under certain conditions, it may result in an electric discharge generated by the electrostatic discharge. If the material being dried is flammable and explosive, the static spark can easily cause sudden burning or explosion of the dry material.
According to a literature study, "The highest point of static electricity lies in the trapping bag." This is due to the operation of the fan to remove large amounts of fine dust from the container. This causes a large amount of charged dust to accumulate in the trapping bag. The most dangerous point of spark discharge can be considered in the trapping bag and separating the small pipe.
1.2 Discussion on the Causes of Dust Explosion in Boiling Drying Equipment
Dust explosion is defined as the dust particles suspended in the air are in full contact with the oxygen in the air, and the oxidation reaction is instantaneously completed under certain conditions, and a large amount of heat is released during the reaction, thereby generating a phenomenon of high temperature and high pressure. In general, when combustible solids are burned in air, they release energy and generate large amounts of gas, while the energy released is both fast and slow. The size of the combustion velocity is related to the area of ​​the solid (dust) exposed to the air. Therefore, for the same solid material powder, the smaller the particle size, the larger the specific area, the faster the combustion and diffusion. If the particle size of the solid is so fine that it can be suspended, once it is ignited by an ignition source, a large amount of energy can be released in a very short period of time. This energy is too late to dissipate into the surrounding environment, resulting in the space The gas is heated and expands absolutely. On the other hand, when the powder is burned, a large amount of gas is generated, which will cause the system to form a local high pressure, which will cause explosion and propagation.
According to the literature, any dust explosion must have three elements, namely: 1 ignition source; 2 combustible fine dust; 3 dust floating in the air, forming a dust cloud within the explosive concentration range. Among them, the explosion of three elements will occur at the same time. Therefore, as long as one of them is eliminated, dust explosion can be effectively prevented.
1.3 Insecure Factors of Powder in Boiling Drying Equipment
Since no matter whether it is in the boiling state or in the trapping operation, the boiling of the material in the boiling and drying equipment can easily generate a large amount of dust. The boiling of dust can easily cause the aforementioned static spark, which may cause the ignition source element. For "dust clouds", as described in the literature, "the combustible powder particles are larger than 400 μm, the formed dust cloud is no longer explosive." When the powder particle size is below 10 μm, it has The “dangerous nature†means that the above-mentioned “dust cloud†is most likely to occur when the powder particle size between the trapping bag of the boiling and drying equipment and the discharge pipe is extremely fine. Therefore, there are very likely to be dust explosions for general materials. If the material contains combustible fine powder components, it means that there are three elements of a dust explosion. The possibility of dust explosion is extremely high.
If only the explosion-proof motor is provided in the boiling and drying equipment, it is only necessary to prevent the "ignition source" on the basis that it must be configured for such equipment. The above shows that static electricity and dust explosion are the key to the explosion-proof safety of such equipment. It is often forgotten by people. The actual production of pharmaceuticals is to ensure that the production equipment is safe, reliable and in compliance with the corresponding process requirements. People can't rely solely on the notion that "in the past there have been no such incidents and they need not be too serious" to manufacture such equipment. It should be considered scientifically and safely.
1. Analysis of Unsafe Factors of Powder in Boiling Drying Equipment
1.1 Discussion on the factors of electrostatic generation in boiling of powder boiling equipment
During the boiling and drying process of the material in the boiling and drying equipment, due to the violent friction between the drying gas and the surface of the material particles, the dry solid particles will also have violent collisions and frictions. At the same time, the solid particles will also collide with the wall surface of the cylinder, trapping bags and tubes. Severe collisions and frictions occur on the wall surface of the road, which causes a large amount of static electricity on the surface of the solid particles. On the other hand, with the continuous refinement of the solid particles, a large number of new surfaces are generated, and the surface charge balance state of the original particles is destroyed. The surface of the nascent particles carries a large amount of charge. Due to aggregation, adhesion of the pipe wall and the like, once the complete machine is in a poor ground state, the accumulated electrostatic charge can form a relatively high voltage, and under certain conditions, it may result in an electric discharge generated by the electrostatic discharge. If the material being dried is flammable and explosive, the static spark can easily cause sudden burning or explosion of the dry material.
According to a literature study, "The highest point of static electricity lies in the trapping bag." This is due to the operation of the fan to remove large amounts of fine dust from the container. This causes a large amount of charged dust to accumulate in the trapping bag. The most dangerous point of spark discharge can be considered in the trapping bag and separating the small pipe.
1.2 Discussion on the Causes of Dust Explosion in Boiling Drying Equipment
Dust explosion is defined as the dust particles suspended in the air are in full contact with the oxygen in the air, and the oxidation reaction is instantaneously completed under certain conditions, and a large amount of heat is released during the reaction, thereby generating a phenomenon of high temperature and high pressure. In general, when combustible solids are burned in air, they release energy and generate large amounts of gas, while the energy released is both fast and slow. The size of the combustion velocity is related to the area of ​​the solid (dust) exposed to the air. Therefore, for the same solid material powder, the smaller the particle size, the larger the specific area, the faster the combustion and diffusion. If the particle size of the solid is so fine that it can be suspended, once it is ignited by an ignition source, a large amount of energy can be released in a very short period of time. This energy is too late to dissipate into the surrounding environment, resulting in the space The gas is heated and expands absolutely. On the other hand, when the powder is burned, a large amount of gas is generated, which will cause the system to form a local high pressure, which will cause explosion and propagation.
According to the literature, any dust explosion must have three elements, namely: 1 ignition source; 2 combustible fine dust; 3 dust floating in the air, forming a dust cloud within the explosive concentration range. Among them, the explosion of three elements will occur at the same time. Therefore, as long as one of them is eliminated, dust explosion can be effectively prevented.
1.3 Insecure Factors of Powder in Boiling Drying Equipment
Since no matter whether it is in the boiling state or in the trapping operation, the boiling of the material in the boiling and drying equipment can easily generate a large amount of dust. The boiling of dust can easily cause the aforementioned static spark, which may cause the ignition source element. For "dust clouds", as described in the literature, "the combustible powder particles are larger than 400 μm, the formed dust cloud is no longer explosive." When the powder particle size is below 10 μm, it has The “dangerous nature†means that the above-mentioned “dust cloud†is most likely to occur when the powder particle size between the trapping bag of the boiling and drying equipment and the discharge pipe is extremely fine. Therefore, there are very likely to be dust explosions for general materials. If the material contains combustible fine powder components, it means that there are three elements of a dust explosion. The possibility of dust explosion is extremely high.
If only the explosion-proof motor is provided in the boiling and drying equipment, it is only necessary to prevent the "ignition source" on the basis that it must be configured for such equipment. The above shows that static electricity and dust explosion are the key to the explosion-proof safety of such equipment. It is often forgotten by people. The actual production of pharmaceuticals is to ensure that the production equipment is safe, reliable and in compliance with the corresponding process requirements. People can't rely solely on the notion that "in the past there have been no such incidents and they need not be too serious" to manufacture such equipment. It should be considered scientifically and safely.
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