Dust Control Handbook for Industrial Minerals Mining and Processing

In the original design, a single nozzle is used to fill the bag with product. With the two-nozzlearrangement, the inner nozzle is used to fill the bag and the outer nozzle relieves excess pressurefrom the bag after it has been filled. Once filling is completed, depressurization of the bag isaccomplished with the aid of an eductor, which uses the venturi principle (compressed airentraining additional exhaust air) to exhaust excess air from the bag at approximately 50 cfm.This exhaust is controlled by a pinch valve, which is opened when the exhaust is on. The bag isslightly overfilled and held in place by the bag clamps, then the pinch valve is opened and theexhaust is initiated to depressurize the bag. After a few seconds, the bag clamp opens and thebag falls from the fill station. The exhaust system also continues to operate as the bag fallsaway, cleaning the bag valve area. The exhausted material can then be recycled back into thesystem.Figure 6.10. Dual-nozzle bagging system design.Another key component of this dual-nozzle bagging system is an improved bag clamp. With theoriginal bag clamp, there were only two small points of contact with the fill nozzle. Theimproved bag clamp makes direct contact with approximately 60 percent of the nozzle(concentrated at the top and sides), thus reducing the amount of product blowback during bagfilling. A controlled amount of blowback is necessary so the bag does not rupture during filling,but this should occur at the bottom of the nozzle to minimize the amount of dust contaminationto the outside of the bag.Bagging 169