Pneumatic conveying can be divided into two categories: the dilute phase conveying (low voltage system) and dense phase conveying (high pressure system).
Dense-phase transport:In the process of pneumatic conveying the solid powder material, the density of particle flow in pipe is close to the critical fluidization bed density condition. Dense phase conveying needed for small gas flow, on average,the unit mass of air transportation of material quality is about 40 ~ 80 kg material/kg air. But the air pressure declination is larger, the rate of movement of the particles is low, and small wear of particles and the pipe, after completing the delivery, the particles are capture easily. Commonly seen in the oil catalytic cracking catalyst circulating tube, layers of fluidized bed of overflow pipe equipment. Generally, the transmission distance is shorter.
Low pressure dilute phase system:
Dilute phase conveying, dilute phase conveying system can be divided into three different combinations of the positive pressure conveying, negative pressure conveying and combined tconveying.
They uses the gas pressure less than 1 kg/cm. Adopting the positive pressure (pressure type) or negative pressure (suction type) or pressure combination and at high speed to push or pull material to make it through the whole conveyor line, so the transportation mode is called the low voltage high speed system, it has a very high gas - material ratio. In the beginning of the system, it has the acceleration speed of about 600 m/min, and at the end, up to 1300 m/min, so the air velocity is higher. The front pressure of the transferring line is generally less than 1 kg/m2, and the back one is basically close to the atmospheric pressure. The motivation of the dilute phase conveying general uses the air or nitrogen, generally supplied by the roots blower. The materials in the dilute phase are in the suspended state in pipeline, the conveying distance can be up to hundreds of meters.
The main characteristic of dilute phase negative pressure is that it can be more to the high point from lower or bulk material conveying. Characteristics of the positive pressure transportation are: long distance, low flow velocity, stability and its small effect on the material.The main components are the roots blower and the rotary valve. The characteristics of the combination of negative pressure conveying is that it is more suitable for multipoint transmission mode for single point material, usually for conveying powder, granules or proportional lighter materials.
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