Explosion hazard and explosion-proof measures of t

The explosion risk and explosion-proof measures of milling and selling magnesium powder

crushing is a basic skill accompanying human beings from primitive to civilization. With the rapid development of industrialization, the demand for powder is increasing, and the requirements for the degree of indispensable testing equipment such as particle physical property experiment, teaching research and quality control of powder are becoming more and more strict, which also brings the problem of combustible dust explosion. Since the dust explosion accident in Turin flour mill, Italy in 1875, the explosion accidents of combustible dust in the process of processing, processing and storage have occurred from time to time. At present, magnesium powder products widely used in industrial production include spherical and flake products. As a desulfurizer with remarkable efficiency, spherical magnesium powder is widely used in iron making and steel-making processes. The main process is to place molten magnesium on a special high-speed rotating device. Under the action of centrifugal force, particulate magnesium is separated through a sieve. As a design agent, fuel, fireworks and firecrackers that promote not only material formulation, they mostly use milled magnesium powder

in the crusher shell, the dust cloud exists continuously in the working state. When the crushing tool collides with the sieve, or the crushing blade collides with foreign debris, the dust cloud in the crusher shell will be ignited and deflagration will occur. This deflagration will spread along the direction that can reach the limit concentration of dust explosion, which usually refers to dust removal pipes and cyclone dust collectors here. If the deflagration wave can cause the flying of other deposited dust and make it in suspension, it will cause severe secondary explosion accidents. The blanking process in the laminar flow state at the receiving port always exists, and the cause of ignition at the receiving port may be that the charged dust forms a high potential difference when it is close to the deposited powder or the bottom of the barrel during the blanking process. As the powder continues to fall, when it reaches the discharge gap, electrostatic sparks are formed to ignite the dust in the laminar flow state. The friction of the tail feeding valve may raise the dust temperature or produce ignition dust clusters. They can ignite the dust in laminar flow state during the blanking process. Dust is often deposited at the bottom of the fan outlet pipe for many reasons, which is the main reason why the pipe mouth explodes. The direct cause of its ignition is the impact and friction of the fan blades on the dust, or the electrostatic discharge at the outlet of the pipe. It is reported that there have been many serious dust explosion accidents in this industry

1 experiment

1.1 small laboratories carry out the explosive test of magnesium powder. The explosivity of mixed magnesium powder was measured. The explosion intensity index of the magnesium powder is very large,. The minimum ignition energy of the dust layer is 0.24mj, so it is easy to ignite

1.2 industrial experiments

at present, the mechanism of dust explosion is not very clear. The explosive data measured in small experiments, such as the maximum explosion pressure of dust, the maximum pressure rise rate and other parameters, relatively give the sensitivity and intensity of dust explosion. Within a certain range, these parameters can be used to determine the explosion relief opening pressure and explosion relief area. How to enlarge the small-scale experimental data to industrial practice has always been the pursuit of scientists. Explosion reaction engineering came into being to meet this need. In terms of the current theoretical level, the engineering design based on the results of explosive experiments on industrial scale equipment is undoubtedly more in line with the actual needs of the process and the requirements of safe production

1.2.1 electrostatic test of magnesium powder

the purpose of testing the electrostatic characteristics of magnesium powder in the mechanical vibrating screen is to investigate the risk of electrostatic ignition of magnesium powder in the production process. The main instruments used in the test are; Faraday cage, electrostatic charge meter; The industrial equipment is mechanical vibrating screen (2.8m long, 0.5m wide and thick). Magnesium powder is obtained from semi-finished products crushed in a factory. These semi-finished products are screened by mechanical vibrating screen to sort out the required particle size. During the test, a certain amount of magnesium powder is put into the feeding port of the vibrating screen machine in motion. After a few seconds, the hardness of the adjacent parts of the powder steel hammer hole and the hammer is one of the 16 major scientific and technological projects in China moves to the discharge port, and the electricity of the powder dust is measured by Faraday cylinder method at the outlet end through the chute. The experiment was carried out for 21 times. The test results showed that the electrostatic charge mass ratio of mixed magnesium powder was up to 0.309 after this process μ C/kg, exceeding the safety standard by 0.02 μ C/kg is nearly 31 times. The test shows that in the production process of magnesium powder, if effective electrostatic elimination measures are not taken, the accidents caused by electrostatic disasters may occur