Example of Calculating the Pressure Losses in a Pneumatic Conveying System

We study a pneumatic conveying system shown in Fig. 14.19 for the convey­ing capacity Ms = 27.3 kg/s. The material conveyed is wood chips, for which the parameters (14.133)-(14.135) are valid.

The first step in the dimensioning process is to choose the mixture ratio /la. For the compressor type, which is not considered here, we choose Fx. = 3.0,

I. e., M, = 9.1 kg/s. Next we have to decide D, the diameter of the tube, i. e., we need a criterion for the choice of velocity of air. A crucial aspect which af­fects the choice of velocity is the wearing of the tube; the higher the velocity is the greater is the wear. On the other hand, the velocity cannot be too low be­cause of the risk of plugging (the velocity difference V — c has to be positive in all parts of the piping). Here we choose VA — 50 m/s with PA =1.2 kg/m3. This gives D = 0.44 m.

The result of the calculations are shown in Table 14.2.

The compressor should give a pressure increase of Ap = 51.8 kPa and its volume flow at the suction side is V= (9.1/1.2) m3/s = 7.6 m3/s.