Modern industry also has ultra-fine requirements for flammable, explosive and oxidizable materials in many fields, but these materials are prone to explosion when air is used as the medium for airflow crushing. For example, there have been many explosion accidents when cobalt powder, sulfur and other materials were crushed with air as the medium, which brought huge losses and safety hazards to processing companies. Therefore, for the fine processing of flammable, explosive and oxidizable materials, safety and explosion prevention are the first problems that need to be solved.
The explosion of combustible powder is caused by the oxidation reaction of powder particles in contact with oxygen, which is completed instantaneously under specific conditions, causing the volume to increase suddenly, generating high temperature and releasing gas. It is well known that the explosion of combustible powder requires combustible materials, oxygen and ignition source. Therefore, the explosion characteristics of combustible powder are related to powder concentration, powder particle size, oxygen concentration and ignition source.
The inert gas protection gas flow pulverizing system uses nitrogen, argon or other inert gases as the pulverizing medium. The system protects the materials from feeding, pulverizing, grading, conveying, separation and packaging under the protection of inert gas. In the fully enclosed micro-positive pressure system, the oxygen content is controlled within the safety standard through online detection of the oxygen analyzer and the automatic oxygen replenishment device. The oxygen content in the mixture of dust and inert gas will be reduced to a value where the flame cannot spread; the reduction of oxygen content will also increase the ignition temperature, ignition energy and lower explosion limit of the dust cloud, so that the ignition temperature and ignition ability of the dust cloud will decrease. When the volume fraction of oxygen is lower than a certain limit value, no matter how high the dust concentration is, the dust cloud cannot explode. This value is called the limit oxygen content of this type of dust. In practical applications, a certain safety factor is often taken for the limit oxygen content to obtain the maximum allowable oxygen content. Inert media include nitrogen, helium, argon, carbon dioxide, etc. Among them, nitrogen is a commonly used inert medium. Generally, electrostatic sparks lose their ignition ability in nitrogen, but some metal powder particles can also burn in nitrogen. For example, magnesium powder must be protected with argon or helium.
The inert gas protected airflow mill is a dry airflow milling equipment for flammable, explosive and oxidizable materials. The system is mainly composed of a gas compressor, a gas storage tank, a silo, an airflow milling main unit, a cyclone separator, a dust collector, etc. Nitrogen or other inert gases are continuously filled into the system to drive away the air, and then the raw materials in the silo are automatically and evenly added to the crushing area of the airflow milling main unit. The compressed inert gas is sprayed to the crushing area at high speed through a special supersonic nozzle. The material is accelerated in the supersonic jet flow and repeatedly impacted, collided and rubbed at the intersection of the jet flow to achieve the crushing effect. The crushed material enters the classification area with the rising airflow under the action of the micro-positive pressure system. The fine particles that meet the particle size requirements are collected by the cyclone separator and dust collector with the airflow, and the coarse particles that do not meet the particle size requirements return to the crushing area for further crushing; and the inert gas separated from the dust collector is filtered and returned to the gas compressor with a gas port for recycling. This system is suitable for ultra-fine crushing of flammable, explosive and oxidizable materials, and can meet the requirements of safety, environmental protection, energy saving and clean production.