The influence of air volume on pneumatic conveying
? ? ? With the change of air volume in pneumatic conveying, the conveying capacity of pneumatic conveying will also be affected. Based on Juheng's continuous experiments, the following summary is made:
? ? ?1. The reduction effect of increasing air volume is compared with increasing air volume by 60%. There are two methods to increase air volume: switching to a large fan or increasing the speed of the original fan. If a fan with a 60% increase in air volume and a supply pressure of 60kPa is used instead, it will be changed to point B in Figure 2. Obviously, the conveying capacity has decreased to 2.7/h, resulting in a 40% reduction in production. According to Figure 3, the conveying wind speed has increased to 42.2m/s. If the fan speed is increased, it will cause a decrease in gas supply pressure. According to Figure 5, since the power of the original fan is still 7.4kw and the air volume has increased by 60%, the air mass flow rate (air volume) is 0.16kg/s, and the speed has increased to 2200r/min, the operating condition has been changed to point C, and the air supply pressure has decreased to 42kPa. Meanwhile, according to Figure 2, the conveying capacity at point C is only 1t/h, which is about a 77% reduction in production.
? ? ?2. Compare the effect of increasing production by reducing air volume by 40%. There are also two methods to reduce air volume: venting or slowing down the fan speed. If 40% of the fan's air volume is emptied, that is, the actual used air volume is reduced from 0.10kg/s to 0.06kg/s, then on the 60kPa line in Figure 2, moving from point A to point D, the conveying capacity is increased to 5.3/h, increasing production by 20%. Meanwhile, as shown in Figure 3, the inlet wind speed at this time is only 16m/s. Of course, this value should exceed the minimum conveying wind speed, otherwise blockage may occur. If the original fan speed is slowed down to reduce the air volume by 40%, the power consumption will still be 7.4kW. As shown in Figure 5, the air volume will be reduced from 0.1kg/s to 0.06kg/s and changed to point E, with a speed of about 1200m/min and an air supply pressure of 0.77kPa. According to Figure 2, the conveying capacity at point E is 7.2/h, resulting in a 64% increase in production. On Figure 3, the minimum wind speed at point E is only 14.4m/s, which exceeds the critical wind speed (see Figure 1) at a mixing ratio of 33 (see Figure 2).
