Pneumatic Conveying: Before Stepping the Line, Look Into Air Extraction

Successively larger diameters downstream can raise problems. Physical removal of air is an attractive alternative In pneumatic conveying systems that operate under high positive pressure, it is common wisdom that as the downstream end is approached, the diameters of the pipeline segments should be larger. Air (or other conveying gas) is compressible, so if a single-diameter pipeline is instead used, the gas velocity will reach very high values. If the conveyed material is abrasive, the consequence can be severe erosive wear, particularly at the pipeline bends; if the material being conveyed is instead friable, considerable particle degradation can result. This lowering of the velocity profile through the pipeline can also improve the overall system performance in other respects. The overall point is made in Figure 1, showing a high-positive-pressure system [1, 2]. The system has a free air flowrate of 2,000 ft3/min, and, because it is conveying material in dilute-phase suspension flow, its recommended minimum value of conveying-air velocity is about 3,200 ft/min, which is a typical average value for granular materials. The inlet pressure of the air is 45 psig. A 5-in.-diameter pipeline would be needed upstream for these conditions.…