For the boiling drying and boiling granulation boiling drying equipment, basically based on the working principle of the fluidized bed, the material drying process is based on 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 dry 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, there will also be violent collisions and friction between the dry solid particles. At the same time, the solid particles 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 newly generated 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 the accumulation, adhesion of the pipe wall and the like, once the complete machine is in a poor ground state, the accumulated electrostatic charge can be made to a relatively high voltage, which under certain conditions will result in an ESD resulting from 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 fact that the fan operation removes a large amount of fine dust from the container, thus accumulating a large amount of charged dust within the trapping bag. The most dangerous point for generating spark discharges can be considered in trapping bags and separating small pipes.

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. Under certain conditions, the oxidation reaction is completed instantaneously, and a large amount of heat is released during the reaction, resulting in high temperature and high pressure. In general, when combustible solids are burned in air, they release energy and generate a large amount 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 solid particle size is so fine that it can be suspended, once it is ignited by the ignition source, a large amount of energy can be released within a very short time. This energy will not be able 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.