Types of Standpipe Systems

Example 8.3 In an operation of gas-solid circulating flow in a cyclone-standpipe-valve system, the particles are 100 p.m glass beads with a density of 2,500 kg/m3. The particle volume fraction in the standpipe is 0.55. The gas is air with a viscosity of 1.8 x 10-5 kg/m s and a density of 1.2 kg/m3. The particle mass flow is 70 kg/m2 s. The height of solids in the standpipe is 1.4 m. The total pressure head over the standpipe and valve is 4,500 Pa. Estimate the leakage flow of air in the standpipe. If the particle volume fraction at minimum fluidization is 0.5 and the area ratio of valve opening to pipe cross section is 0.6, what is the orifice coefficient of this valve  

Solution The interstitial velocity of particles in the standpipe is obtained by (apPpUp) 70 

the interstitial velocity of leakage flow of air is estimated from Eq. (8.95) as 

The minus sign means that the leakage flow of air is directed downward. 

Standpipes are applied to fluidized bed systems in several ways. The following describes industrial applications of standpipes. An application of nonmechanical valves which control the solids flow rates is also given. 

---