What are the advantages of pneumatic conveying of dust particles
? ? ? ? With China's high emphasis on energy conservation, environmental protection, and carbon neutrality, there are higher requirements for emission pollution. However, traditional dust particle transportation has the disadvantages of low transmission efficiency and serious pollution. ThereforePneumatic conveying systemMore and more widely used, it has a very high efficiency in transporting dust particles, not only greatly improving production capacity, but also saving costs and making the production environment clean and tidy.
The main characteristics of pneumatic conveying are large conveying volume, long conveying distance, and high conveying speed; It can be loaded in one place and unloaded in multiple places.
According to the density of particles in the conveying pipeline, pneumatic conveying is divided into:
? ? ? ?①Dilute phase transportThe solid content is below 1-10 kg/m3, the operating gas velocity is relatively high (about 18-30 m/s), and the conveying distance is basically within 300 meters. For mature equipment such as material sealing pumps, the conveying operation is simple without mechanical rotating parts, the conveying pressure is low, and there is no maintenance or repair required.
? ? ? ?②Dense phase transportTransportation process with solid content of 10-30kg/m3 or solid gas ratio greater than 25. Operate at a lower air speed and use a higher air pressure for delivery. The mature equipment warehouse pump has a conveying distance of over 500m and is suitable for long-distance transportation. However, this equipment has many valves and pneumatic and electric devices. The conveying pressure is high, and all pipelines require wear-resistant materials. Intermittent inflatable tank type dense phase conveying. It is to add the particles in batches into the pressure tank, then ventilate and blow them loose. After the tank reaches a certain pressure, open the discharge valve and blow the particle material into the conveying pipe for transportation. Pulse conveying is the process of introducing a stream of compressed air into the lower tank to blow the material loose; Another pulse of compressed air with a frequency of 20-40min-1 is blown into the inlet of the conveying pipe, forming alternating small sections of material and gas columns inside the pipeline, which are pushed forward by air pressure.
? ? ? ?③Negative pressure conveyingThe pressure inside the pipeline is lower than atmospheric pressure, and the material is sucked in by itself, but it must be unloaded under negative pressure, and the distance that can be transported is relatively short; Advantages: Equipment investment and low load. Disadvantages: High operating flow rate, severe pipeline wear, and undetected leaks caused by wear.
? ? ? ?When conducting dilute phase transportation in a horizontal pipeline, the gas velocity should be high to disperse and suspend particles in the airflow. When the gas velocity decreases to a critical value, particles will begin to deposit in the lower part of the pipe wall. This critical gas velocity is called sedimentation velocity. This is the lower limit of gas velocity during dilute phase horizontal transportation. When the operating gas velocity is lower than this value, a deposition layer appears inside the tube, the cross-sectional area of the flow channel decreases, and the airflow above the deposition layer still runs at the deposition velocity.
? ? ? ?When conducting upward pneumatic conveying in a vertical pipeline, particles are dispersed and suspended in the airflow at high gas velocities. When the particle transport volume is constant, reducing the gas velocity increases the solid content in the pipeline. When the gas velocity drops to a critical value, the airflow can no longer evenly disperse the dense particles, and the particles merge into a plunger shape, resulting in a surge phenomenon and a sharp increase in pressure drop. This critical velocity is called choking velocity, which is the lower limit of the gas velocity when the dilute phase is transported vertically upwards. For uniformly sized particles, the sedimentation rate is roughly equal to the choking rate. But for materials with a certain distribution of particle size, the sedimentation rate will be 2-6 times faster than the clogging rate.
? ? ? ?The use of pneumatic conveying of powder particles is a trend in China's development. It not only provides us with efficient production, but also saves us costs and leaves us with a beautiful living environment. Pneumatic conveying of dust particles is truly a win-win situation.