The need arises regularly for transferring bulk bags of powder into silos, and in certain cases for loading out from the silos by pressure discharge road tankers.
These bags are usually around 1 to 1½ tonne capacity.
Cockburn Cement have this need at Port Headland, for transferring cement at 50 tonne per hour into silos for distribution by road tankers.
Bulk bags are lowered into a discharge hopper containing cutting knives. As the bulk bag impinges the knives, the bottom is slit fully, and the product released directly into the receiving hopper. From this hopper the product is transferred into a raised buffer hopper via a screw conveyor. The buffer hopper allows for continuous operation as it feeds the batch mode PCV (Pneumatic Conveying Vessel). While the PCV is conveying the cement powder, the buffer hopper continues to receive powder from the screw conveyor. This enables the bulk bag slitting operation to run continuously.
The PCV of 2 cubic metre capacity transfers the powder directly to the 600 tonne capacity silo nest externally via a 125 mm heavy duty conveying line with long radius channel wear backed bends.
A high efficiency Kockums KH46 pneumatic conveying air power pack is utilised for the conveying air. These units are specifically built for pneumatic conveying applications and have a long service life, based on the low rotation speed of 960 rpm.
Pressure discharge road tankers fill directly from the silos then transport and deliver the cement to a client's site silo. These road tankers usually discharge their contents at the rate of 60 tonne per hour.
Specific relocation feature
To eliminate the need for digging a pit deep enough to house the PCV, a screw conveyor is used to transfer the cement from the bulk bag discharger to the buffer hopper above the PCV. By this method the whole system may easily be relocated to another site if needed.
The bulk bag discharger is fitted with a diaphragm and two air filter/fan units to collect dust generated during the cutting operation.
The cutting operation is so efficient, that the bag is drawn clean from the hopper, thus preventing dust cloud generation during the disposal of the bag remnant.
By this process, a major difficulty of handling bulk bags related to airborne dust is overcome.
The 2 cu. Metre capacity PCV and buffer hopper together make a continuous conveying system. As the PCV discharges powder to the remote silos, the buffer hopper is being refilled from the screw conveyor. The moment conveying is complete from the PCV, the fill valve opens, and the SonoPulse system ensures a very fast fill of the PCV ready for the next discharge to occur.
The highly efficient dense phase PCV actually discharged to the silo nest at the rate of 60 tonne per hour during commissioning phase. This vessel and the line size are chosen to suit the rate the client requires, and in this case the client's design rate to feed the system is 50 tonne per hour resulting from the constraint of the crane handling time for the bulk bags.
Automation of controls
After the operator feeds the bulk bag to the cutting hopper, the whole system of the powder handling operates in fully automatic mode. Even the silos are on an automatic cycle, such that when one silo fills, the feed is automatically directed to the next silo.