Eccentric discharge

The most damaging condition for most silos is the unplanned occurrence of unsymmetrical flow regimes, if the flow channel makes contact with the silo wall. This is conventionally referred to as eccentric discharge. It has caused so many silo disasters that many writers have proposed that it should never be used. But two situations arise it may be necessary to have off-centre discharge outlets for functional reasons, and conditions in the silo (blockage of feeders, uneven thermal or moisture conditions, segregation of contents etc.) may cause unintended eccentric flow. There are numerous causes of such eccentricities. 

Eccentric discharge pressures of the pattern shown in Figure 3.23 also have a very damaging effect on concrete silos, where severe bending of the wall induces substantial vertical cracks and sometimes leads to spalling. 

Figure 3.23 Flow channel geometry, typical pressure pattern and vertical waU stresses during eccentric discharge.

Rotter, J.M. (1986b) The analysis of steel bins subject to eccentric discharge. Proceedings of the Second International Conference on Bulk Materials Storage Handling and Transportation, Institution of Engineers, Wollongong, Australia, pp. 264-271. 

Rotter, J.M. (2001b) Pressures, Stresses and Buckling in Metal Silos containing Eccentrically Discharging Solids. Festschrift Richard Greiner, TU Graz, Austria, pp. 85-104. 

Poor performance can result from fan inlet eccentric or spinning dow, and discharge ductwork that does not permit development of hiU fan pressure. Sometimes inlet restrictions starve a fan and limit performance. To obtain rated performance, the air must enter the fan uniformly over the inlet area without rotation or unusual turbulence. This allows all portions of the fan wheel to do equal work. If more air is distributed to one side of the wheel, such as with an elbow on the inlet, the work performed by the lightiy loaded portions of the wheel is reduced and capacity is decreased by 5—10%. The use of an inlet box duct on a fan can reduce capacity by as much as 25% unless there are turning vanes in the duct. Use of the vanes reduces the capacity loss to around 5%. 

Reciprocating Screens These screens have rnanv applications in chemical work. An eccentric under the screen supplies oscillation, ranging from gyi atoi-v [about 0,05-m (2-in) diameter] at the feed end to reciprocating motion at the discharge end, Freqiiencv is 8 to 10... 

There is a sudden reduction in the suction between the tank and the piping. There is an eccentric 6-to-4 reducer between the suction pipe and the pump. There is a eoneentrie 3-to-4 inereascr from the pump back into the piping, and a sudden enlargement going into the discharge tank. The formula is ... 

Rotation of the pump rotor, which Is mounted eccentrically In the pump cylinder, traps entering vapor between rotor vane segments. As rotation continues, vapor is compressed then discharged into the exhaust box. Vapors then pass through four stages of Internal oil and smoke eliminators to remove 99.9% of lubricating oil from the exhaust. Oil is then returned to the recirculating oil system. 

Rotary, positive displacement machines in which axial vanes slide radially in a rotor mounted eccentrically within a cylindrical casing. Available in lubricated and non-lubricated construction the discharge air is normally free from pulsation. 

Fig. 29. A rotary-plate pump a—schematic view 6—diagram of operation f—system being evacuated I—eccentric rotor 5—stator 2—space where gas is compressed 5—movable plates d—discharge opening 7—discharge valve ...

Crusher size Approx, feed opening, in. Gyrations per min. Pinion r.p.m. Max. hp. Eccentric throw, in. Open- side setting of discharge opening, in ... 

---