Abstract: The two problems of electrostatic and dust explosion associated with powder boiling are discussed theoretically, thus clarifying the importance of explosion safety in boiled drying equipment and inserting this in the application of such equipment.
Keywords: boiling drying equipment, static electricity, dust explosion, explosion safety
On the boiling drying equipment, are basically based on the working principle of fluidized bed, the material drying process is based on the powder boiling. At the same time, under the action of exhaust, the fine powder in the container is filtered out by the capture bag, and the process of collecting is carried out by a large amount of ultrafine powder, whether it is boiling in the flow or in the capture operation , Boiling the whole process of drying are accompanied by ultra-fine powder movement. However, the process of powder movement often accompanied by electrostatic and dust explosion of the two issues, under certain factors will lead to the phenomenon of explosion. At present, the domestic handling of such problems, that as long as the placement of explosion-proof motor is feasible, it is considered defective. In this paper, from the powder boiling electrostatic and dust explosion problem for the theory of boiling, drying equipment for explosion-proof safety put forward their own point of view, the purpose is to manufacture and apply such equipment more complete, more reliable and more secure.
1. Analysis of the insecurity of powder in boiling drying equipment
Discussion on the Factors of Electrostatic Production in Powder Boiling by Boiling Drying Equipment
Material in the boiling drying equipment boiling process, due to dry gas and material particles on the surface of severe friction, dry solid particles will also have a strong collision between the friction and friction, while the solid particles with the cylinder wall, capture bags and tubes The surface of the wall surface of the collision and friction, making the surface of solid particles with a lot of static electricity; the other hand, with the solid particles continue to refine, resulting in a large number of new surface, the original surface charge balance of the state The surface of the nascent particles carries a large amount of charge. Due to aggregation, adhesion pipe wall and other reasons, once the machine grounded state is not good, can accumulate the electrostatic charge to form a very high voltage, under certain conditions will lead to electrostatic discharge generated by the spark. If the dry material is flammable and explosive, this static spark can easily cause the sudden burning or explosion of dry material.
Literature research that "the highest electrostatic interference in the bag", which is due to the operation of the fan to take a large number of small dust inside the container, so that a large number of accumulated dust in the collection bag dust. And the most dangerous point of spark discharge can be considered in the collection of bags, separation of small pipes.
Discussion on the Factors of Dust Explosion in Boiling Drying Equipment
Dust explosion is defined as dust particles suspended in the air and oxygen in the air in full contact with the specific conditions of the moment to complete the oxidation reaction, the reaction released a lot of heat, resulting in high temperature, high pressure phenomenon. In general, combustible solids in the air when the combustion will release the energy and produce a lot of gas, and the release of energy faster than the size of the burning speed in the solid (dust) exposed to the air area. Therefore, for the same solid material powder, the smaller the particle size, the greater the area, the faster the combustion diffusion. If the solid size is very fine, and can be suspended, once a little fire source to ignite, you can in a very short period of time to release a lot of energy, these energy too late to escape to the surrounding environment, resulting in the space The gas is heated and the absolute expansion, while the other side of the powder burning a lot of gas, the system will form a local high pressure, and even produce an explosion and spread.
The literature believes that any dust explosion to have three elements, namely ① ignition source; ② combustible dust; ③ dust floating in the air, the formation of dust in the explosion concentration range of cloud. Among them, the three elements exist at the same time will issue an explosion, so as long as the elimination of one of the elements, can effectively prevent dust explosion.
Discussion on the Factors of Non - safety of Powder in Boiling Drying Equipment
Since the boiling of the material in the boiling and drying equipment is easy to produce large amounts of dust, whether it is in the flow boiling or in the capture operation, the dust boiling can easily cause the above-mentioned electrostatic spark, which may cause the ignition source element. For the "dust cloud", the dust cloud formed is no longer explosive when the combustible powder particles are larger than 400 μm as described in the literature. "When the particle size is less than 10 μm, Large risk ", the boiling powder drying equipment between the collection bag and the discharge pipe between the fine particle size of the case, most likely the above" dust cloud. " So the general material is very likely to exist dust explosion factors, if the material contains combustible fine powder components, it means that with the dust explosion of the three elements, the possibility of dust explosion.
If only in the boiling and drying equipment with explosion-proof motor, then, on the basis of prevention of "ignition source", which is also such equipment must be configured. The above shows that electrostatic and dust explosion is the key to explosion-proof safety of such equipment, which is often forgotten by people, and the actual production of drugs is to ensure the safety of production equipment, reliable and meet the corresponding process requirements. People can not just "in the past did not happen such accidents, do not have to be too serious" concept to produce such equipment, should be scientific and security to consider.
2. Preventive measures of powder safety in boiling and drying equipment
Boiling drying equipment in the powder caused by the safety of hidden dangers, the literature is easy to produce the two types of defects in the prevention of a certain elaboration, as a boiling drying equipment can be used as a reference.
2.1 anti-static measures of boiling drying equipment
Boiling drying equipment in the powder boiling to prevent static electricity can learn from the following measures:
1) The collection bag is made of anti-static fiber material, and the static electricity entering the powder in the bag is eliminated in time to avoid the stripping of the powder when the powder is gathered.
2) the use of conductive materials for the air duct and the connection parts of the connection, and the entire system carefully connected to the powder on the static electricity in time to guide.
3) other methods, such as increasing the diameter of the pipe, reduce the elbow, regular cleaning and discharge, the operator wear anti-static service operation, to suppress, reduce and eliminate the powder during the boiling process is also effective.
2.2 Boiling drying equipment against dust explosion measures
Burning and drying equipment in the boiling powder to prevent dust explosion can learn from the following measures:
1) Clear the ignition source, for the equipment and devices that may produce fire sources should be installed with an explosion suppression system, in the dust or dust filter equipment and piping set explosion-proof membrane or pressure relief valve.
2) often remove the pipe and the dust inside the bag, no dust accumulation.
3) electrical equipment to use explosion-proof devices, such as explosion-proof motor, installation of ground and so on.
4) plant design to meet the requirements of the prevention of dust explosion, according to anti-explosive design, and have enough explosion-proof pressure relief area.
3. Explosion-proof safety in the application of the company's boiling drying equipment
For some domestic boiling drying equipment explosion awareness is imperfect, but to take a simple explosion-proof measures, can not ensure that operators, plant safety, there are some hidden dangers in the production. Often in the "no such accident occurred in the past, do not have to be too serious," the concept of manufacturing equipment, with the safety of people to strengthen and dry material components in the future complex, such equipment explosion-proof requirements have been raised To anxious level. Changzhou Changhong Drying Equipment Co., Ltd. is based on the experience of producing boiling granulator for many years and combined with the characteristics of similar equipment abroad, especially the boiling drying equipment in the structure to take the necessary measures to prevent. Now the company developed the explosion-proof boiling drying equipment, for example, that the application of explosion-proof structure.
The new explosion-proof granulation coating machine as shown, the inlet has two to three filters, the fan with a silencer device, the entire granulation, coating process from the wind, atomization, exhaust are in a closed State, to achieve efficient energy saving effect. In addition to the use of anti-static fiber filter bag, the dust bag at both ends of the pressure difference can be automatically measured and controlled, so that the bed to maintain the best fluidization. Among them, the equipment points around the capture room, a total of two capture bags, each capture bag under the edge of the use of airbag structure and the bottom of the bag fixed, when the bag and airbag structure to the appropriate position, inflatable balloon, And the inner edge of the upper cylinder is sealed. This structure is easy to operate, the operator does not need to climb to the height of the bag.
The upper part of the host with an explosion-proof device, when the host inside the positive pressure, the explosion-proof door F in the pressure warning mechanism issued an air signal, the gas and electricity conversion to the entire system power, fast valve a, b quickly closed, Rise, forcing the explosion-proof door F automatically open, the explosion of gas from the vent channel to discharge the host to ensure the safety of personnel and equipment. Drilling test by the State Economic and Trade Commission of Tianjin Pharmaceutical Machinery Testing Center of the detection, when the host cylinder internal pressure> 0.8kg / cm2, the vent gate automatically open.
In addition, electrical equipment should be part of the explosion-proof measures, fan explosion-proof, observation lamp explosion. The installation instructions for safety grounding are also highlighted in both the instruction manual and the electrical installation, which are related to the total grounding facility of the equipment plant.
With the above structure of the explosion-proof granulation coating machine has been to the market, the equipment has granulation, coating, drying and explosion-proof performance, suitable for Chinese and Western medicine, food, chemical industry powder granulation and powder, Pill the surface coating of the coating.
4. Summary
The above two issues related to static and dust explosion of powder boiling are discussed theoretically, thus reaffirming the importance of explosion safety in boiling drying equipment.