Fluidized bed drying equipment is fundamentally based on the working principle of fluidized beds, with the drying process relying on the boiling of powder. Simultaneously, under exhaust ventilation, fine powder within the container is filtered through a collection bag and discharged outdoors. This collection process generates a large amount of ultrafine powder. Whether in fluidized bed operation or during collection, the entire fluidized bed drying process involves the movement of ultrafine powder. However, this powder movement is often accompanied by two problems: static electricity and dust explosions. Under certain conditions, these can lead to explosions. Currently, the domestic approach to addressing these issues is that simply installing explosion-proof motors is sufficient, which is a flawed consideration. This article theoretically explores the static electricity and dust explosion problems associated with powder boiling and proposes its own perspectives on the explosion-proof safety of fluidized bed drying equipment, aiming to make the manufacturing and application of this type of equipment more complete, reliable, and safe. 1. Analysis of Unsafe Factors of Powders in Fluidized Bed Drying Equipment 1.1 Discussion of Factors Affecting Static Electricity Generation During Fluidized Bed Drying During the fluidized bed drying process, the drying gas and the surface of the material particles experience intense friction, resulting in violent collisions and friction between the dried solid particles. Simultaneously, the solid particles also experience intense collisions and friction with the cylinder wall, the collection bag, and the pipe walls, causing the solid particle surfaces to accumulate a large amount of static electricity. Furthermore, as the solid particles become increasingly finer, a large number of new surfaces are generated, disrupting the surface charge balance of the original particles and causing the new particles to carry a large amount of charge. Due to aggregation and adhesion to the pipe walls, if the grounding of the entire machine is poor, the accumulated static charge can form a considerably high voltage, which, under certain conditions, can lead to electric sparks generated by static discharge. If the material being dried is flammable or explosive, these static sparks can easily cause sudden combustion or explosion of the dried material. Literature research suggests that "the highest point of static electricity is inside the collection bag," because the fan operation removes a large amount of fine dust from the container, thus accumulating a large amount of charged dust inside the collection bag. The most dangerous point for spark discharge can be considered to be inside the collection bag and the separation pipe. 1.2 Discussion of the factors causing dust explosions in fluidized bed dryers. A dust explosion is defined as dust particles suspended in the air coming into full contact with oxygen in the air and undergoing an instantaneous oxidation reaction under specific conditions, releasing a large amount of heat and thus generating high temperature and high pressure. Generally speaking, when combustible solids burn in the air, they release energy and produce a large amount of gas. The rate of energy release, i.e., the rate of combustion, is related to the surface area of ​​the solid (dust) exposed to the air. Therefore, for the same solid powder, the smaller the particle size and the larger the specific surface area, the faster the combustion diffusion. If the solid particles are very fine, they can be suspended. Once ignited by an ignition source, they can release a large amount of energy in a very short time. This energy does not have time to dissipate into the surrounding environment, causing the gas in that space to be heated and absolutely expanded. On the other hand, the large amount of gas produced when the powder burns will cause the system to form local high pressure, leading to an explosion and propagation. Literature suggests that any dust explosion requires three elements: ① an ignition source; ② combustible fine dust; ③ dust suspended in the air, forming a dust cloud within the explosive concentration range. An explosion requires all three elements to be present simultaneously; therefore, eliminating any one of these elements can effectively prevent dust explosions. 1.3 Discussion of Unsafe Factors of Powder in Fluidized Bed Drying Equipment Whether in fluidized bed or capture operation, the material in the fluidized bed drying equipment easily generates a large amount of dust. Dust boiling easily causes the aforementioned electrostatic sparks, which can potentially create an ignition source. Regarding the "dust cloud," as the literature states, "when the combustible powder particles are larger than 400μm, the resulting dust cloud is no longer explosive." However, "when the powder particle size is below 10μm, it poses a greater danger." Given the extremely fine particle size of the powder between the capture bag and the discharge pipe of the fluidized bed drying equipment, the aforementioned "dust cloud" is highly likely to form. Therefore, even ordinary materials are highly susceptible to dust explosions. If the material contains combustible fine powder components, it means that the three elements of a dust explosion are present, greatly increasing the likelihood of a dust explosion. If only an explosion-proof motor is installed in the fluidized bed dryer, it only fundamentally prevents the "ignition source," which is still a necessary feature for this type of equipment. As mentioned above, static electricity and dust explosion are key aspects of the explosion-proof safety of this type of equipment, often overlooked. However, the actual focus of pharmaceutical production is ensuring the safety, reliability, and compliance of production equipment with relevant process requirements. We cannot manufacture such equipment based solely on the concept that "no such accidents have occurred in the past, so we don't need to be too serious about it." Scientific and safety considerations are essential. 2. Preventive Measures for Powder Safety in Fluidized Bed Dryers Regarding the safety hazards caused by powder boiling in fluidized bed dryers, some literature has elaborated on the prevention of these two types of hazards. The following can be used as a reference for fluidized bed dryers. 2.1 Anti-static Measures for Fluidized Bed Drying Equipment The following measures can be used to prevent static electricity during powder boiling in fluidized bed drying equipment: 1) The collection bags should be made of anti-static fiber material to promptly eliminate static electricity on the powder entering the bag, preventing the powder from agglomerating and detaching, causing static charge. 2) Conductive materials should be used for the air supply ducts and connecting parts, and the entire system should be carefully connected to ensure that static electricity on the powder is conducted away promptly. 3) Other methods, such as increasing the pipe diameter, reducing bends, regular dust removal and discharge, and operators wearing anti-static clothing, are also effective in suppressing, reducing, and eliminating static electricity during powder boiling. 2.2 Dust Explosion Prevention Measures for Fluidized Bed Drying Equipment The following measures can be used to prevent dust explosions during powder boiling in fluidized bed drying equipment: 1) Eliminate ignition sources. Equipment and devices that may generate ignition sources should be equipped with explosion suppression systems. Explosion-proof membranes or pressure relief valves should be installed in dust removal or filtration equipment and pipelines. 2) Regularly remove dust from pipelines and collection bags; dust accumulation is prohibited. 3) Electrical equipment must use explosion-proof devices, such as explosion-proof motors and grounding wires. 4) The factory design must meet the requirements for preventing dust explosions, be designed for explosion resistance, and have sufficient explosion-proof pressure relief area. 3. Application of Explosion-Proof Safety in Our Company's Fluidized Bed Drying Equipment Due to the lack of awareness regarding explosion-proof safety in some domestic fluidized bed drying equipment manufacturers, only simple explosion-proof measures are adopted, which cannot ensure the safety of operators and the factory, posing certain hidden dangers in production. Equipment is often manufactured with the fixed concept that "no such accidents have occurred in the past, so there is no need to be too serious about it." However, with the increasing awareness of safety and the increasing complexity of the components of dried materials, the explosion-proof requirements for such equipment have reached an urgent level. Therefore, Changzhou Changhong Drying Equipment Co., Ltd., based on years of experience in producing fluidized bed granulators and combining the characteristics of similar foreign equipment, has taken necessary preventative measures in the structure of fluidized bed drying equipment. The application of the explosion-proof structure is illustrated below using one of our company's explosion-proof fluidized bed drying equipment as an example. The new explosion-proof granulation and coating machine, as shown in the figure, features two to three stages of air filtration at the air inlet and a silencer-equipped blower. The entire granulation and coating process, from air inlet to atomization and exhaust, is conducted in a closed system, achieving high efficiency and energy saving. In addition to the collection bags being made of anti-static fiber material, the pressure difference across the dust filter bags can be automatically measured and controlled, maintaining optimal fluidization within the bed. The equipment consists of left and right collection chambers with two collection bags. The lower edge of each bag is fixed to the bottom edge using an airbag structure. When the bag holder and airbag structure are pulled to the appropriate position, the airbag inflates, sealing the lower edge of the bag against the inner wall of the upper cylinder. This design facilitates operation, eliminating the need for operators to climb to higher positions to install or remove the bags. The main unit is equipped with an explosion-proof device. When positive pressure is generated inside the main unit, the pressure warning mechanism in the explosion-proof door F sends a gas signal, which, through gas-electric conversion, de-energizes the entire system. Quick valves a and b close rapidly. If the cylinder pressure continues to rise, the explosion-proof door F is forced to open automatically, allowing the explosive gas to escape from the main unit through the explosion venting channel, ensuring the safety of personnel and equipment. The explosion venting test, conducted by the Tianjin Pharmaceutical Machinery Testing Center of the State Economic and Trade Commission, shows that the explosion venting door opens automatically when the positive pressure inside the main unit cylinder exceeds 0.8 kg/cm². Furthermore, the electrical components of the equipment should have explosion-proof measures, including explosion-proof fans and observation lights. The instruction manual and electrical installation guidelines emphasize safety grounding requirements, which are related to the main grounding facilities of the equipment user's factory. Explosion-proof granulation and coating machines with the above structure have been launched on the market. This equipment features granulation, coating, and drying functions, as well as explosion-proof performance, and is suitable for powder granulation and surface coating of powders, granules, and pills in the Chinese and Western medicine, food, and chemical industries. 4. Summary The above discussion addresses two issues related to powder boiling: static electricity and dust explosion, thus reiterating the importance of explosion-proof safety for boiling drying equipment.