Abstract: The two problems of electrostatic boiling and dust explosion accompanying powder boiling are discussed theoretically, which clarifies the importance of explosion-proof safety of boiling drying equipment, and inserts this aspect in the application of such equipment. Keywords: boiling drying equipment, static electricity, dust explosion, explosion safety, boiling boiling equipment such as boiling drying, boiling granulation, etc., basically based on the working principle of fluidized bed, the basis of the material drying process is powder Boiling. At the same time, under the action of exhaust air, the fine powder in the container is filtered through the trap bag and discharged to the outside. The process of trapping has a large amount of ultrafine powder, whether in fluid boiling or in the trapping operation. The whole process of boiling and drying is accompanied by ultra-fine powder movement. However, the process of powder movement is often accompanied by two problems of static electricity and dust explosion, which may cause an explosion phenomenon under the guidance of certain factors.

At present, when dealing with such problems in China, it is considered that it is feasible to install an explosion-proof motor. This paper discusses the electrostatic and dust explosion problems of powder boiling, and puts forward its own viewpoints on the explosion-proof safety of boiling drying equipment. The purpose is to make the manufacture and application of such equipment more complete, more reliable and safer.   

1. Analysis of unsafe factors of powder in boiling drying equipment 1.1 Factors causing static electricity in boiling of boiling equipment The material is in the boiling drying process of boiling equipment, due to the intense friction between the drying gas and the surface of the material particles, drying There are also strong collisions and frictions between the solid particles. At the same time, the solid particles also collide and rub against the wall surface of the cylinder, the trapping bag and the wall of the pipeline, causing a large amount of static electricity on the surface of the solid particles. On the other hand, As the solid particles continue to refine, a large number of new surfaces are generated, and the surface charge balance state of the original particles is destroyed, causing a large amount of electric charge on the surface of the new particles. Due to the aggregation, adhesion of the tube wall, etc., once the grounding state of the whole machine is poor, the accumulated electrostatic charge can form a relatively high voltage, which under certain conditions may cause an electric spark generated by the electrostatic discharge. If the material to be dried is a flammable or explosive material, such a static spark can easily cause sudden burning or explosion of the dry material. According to the literature research, "the highest point of static electricity lies in the trapping bag". This is because the fan operates to remove a large amount of fine dust in the container, so that a large amount of charged dust is accumulated in the collecting bag. The most dangerous point of spark discharge can be considered to be in the capture bag and separate the small pipe.

1.2 Factors arising from dust explosion in boiling drying equipment The definition of dust explosion is that 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 in the reaction, thereby generating high temperature. The phenomenon of high pressure. In general, flammable solids release energy when burned in air and produce a large amount of gas, and the rate at which energy is released is related to the rate at which the solid (dust) is exposed to the air. Therefore, for a powder of the same solid substance, the smaller the particle size, the larger the specific area, the faster the combustion spreads. If the particle size of the solid is very fine, so that it can be suspended, once an ignition source is used to ignite it, a large amount of energy can be released in a very short time, and the energy is not too dissipated into the surrounding environment, resulting in the space. The gas is heated and absolutely expanded, while on the other hand, a large amount of gas is generated when the powder is burned, which causes the system to form a local high pressure, which causes explosion and propagation. The literature believes that any dust explosion must have three elements, namely, 1 ignition source; 2 combustible fine dust; 3 dust floating in the air to form a dust cloud within the explosive concentration range. Among them, the three elements will exist at the same time to explode, so as long as one of the elements is eliminated, the dust explosion can be effectively prevented. 1.3 Discussion on the unsafe factors of powder in boiling drying equipment Because the material boiling in the boiling drying equipment is easy to generate a large amount of dust, whether it is in fluid boiling or in the trapping operation, the dust boiling is easy to cause the above static spark, that is, Causes ignition source elements. For the “dust cloud”, as described in the literature “when the combustible powder particles are larger than 400 μm, the formed dust cloud is no longer explosive.” And when “the powder particle size is below 10 μm, it has The greater the risk, the above-mentioned "dust cloud" is highly likely when the powder particle size between the collecting bag and the discharge pipe of the boiling drying device is extremely fine. Therefore, there is a high possibility that there is a dust explosion factor for general materials. If the material contains combustible fine powder components, it means that there are three elements of dust explosion, and the possibility of dust explosion is extremely high. If an explosion-proof motor is only provided in the boiling drying equipment, it is only necessary to prevent the "ignition source", which is also necessary for such equipment. As can be seen from the above, static electricity and dust explosion are the key to the explosion-proof safety of such equipment, which is often forgotten by people, and the actual production of medicines is to ensure the safety, reliability and compliance with the corresponding process requirements. People can't just rely on the concept of "no such accidents in the past, not too serious" to produce such equipment, which should be considered scientifically and safely.  

2. Preventive measures for powder safety in boiling drying equipment The safety hazard caused by powder boiling in boiling drying equipment has been described in the literature for the prevention of the second type of hidden dangers of powder, which can be used as boiling drying equipment. The following is used for reference. 2.1 Anti-static measures for boiling drying equipment The measures for boiling powder to prevent static electricity in boiling drying equipment are as follows: 1) The collecting bag is made of anti-static fiber material to eliminate static electricity entering the powder in the bag in time to avoid The peeling electrification generated when the powder aggregates fall off. 2) Use the conductor material as the connecting part of the air supply duct and each connecting part, and carefully connect the whole system to make the static electricity on the powder be guided away in time. 3) Other methods, such as increasing pipe diameter, reducing elbows, regular cleaning and discharging, and operating workers wearing anti-static clothing, are also effective in suppressing, reducing and eliminating static electricity during powder boiling. 2.2 Measures for anti-dust explosion of boiling drying equipment The measures for boiling powder to prevent dust explosion in boiling drying equipment are as follows: 1) Remove the ignition source, and install anti-explosion system for equipment and equipment that may generate fire source. An explosion-proof membrane or a pressure relief valve is provided in the dust removal or dust filter equipment and piping. 2) Frequently remove dust from pipes and trap bags, and do not accumulate dust. 3) Explosion-proof devices such as explosion-proof motors and grounding wires should be used for electrical equipment.

4) The design of the plant shall comply with the requirements for the prevention of dust explosion, according to the anti-explosion design, and there must be sufficient explosion-proof pressure relief area.

3. The summary discusses the two problems of electrostatic boiling and dust explosion caused by powder boiling, thus reaffirming the safety importance of explosion-proof equipment. At the same time, the description of the structure of the new explosion-proof granulation coating machine is also a yardstick for the manufacture of such equipment. Around these structural elements, it is possible to produce products that are energy-saving, reliable, safe and practical. The exploration of the structure of the new explosion-proof boiling granulation coating machine described in this paper is only for the purpose of throwing bricks and attracting jade. The equipment needs to be further improved, and it is waiting for China's boiling granulation coating dryer to embark on a new stage.