At the end of pneumatic conveying the question is how to separate bulk material and conveying medium (mostly air).

As to pressure conveying systems, separation of solids via a cyclone is a common procedure which, however, does not achieve complete separation. If no exhaust filter is installed, light particles might be blown out together with the clean air and spread in the environment. For safety reasons this problem must be avoided particularly in handling materials being harmful to health.

Due to their specific mode of operation cyclones are not suitable for solids separation in suction conveying applications which - considering dust prevention requirements in factories - increasingly gain in importance.

Suction conveying systems mainly use metal, plastic, or fabric filters designed for both positive and negative pressure.

For one of our customers handling a bulk material being difficult to convey we developed a special conveying technology combining pressure and suction conveying principles.

In that special application, the bulk material (granular plastic splits) had to be re-filled over a distance of approx. 60 m through a DN 50 pipeline sysetm from a large silo container into a FIBC

Our solution provides a conveyor screw drawing the mterial out of the silo container and dosing it into a pneumatic rotary air-lock valve. A 7.5 kW rotary piston blower presses the material from the rotary valve into the pipeline system at a volume flow rate of approx. 200 m³/ h. Pneumatic pressure conveying is maintained until just before the FIBC and ends in a separator vessel with a drum filter and in a vacuum connection aspirating the excess air out of the separator vessel. The bulk material deposits at the filter and falls into the FIBC through a filling head with pneumatic docking socket. Part of the material directly flows into the bag together with the conveying air, with the material depositing downwards into the FIBC and the excess air being exhausted upwards. To ensure constant filter performance, the filter is cleaned by three deferred pressure pulses.

Fig. 1 shows the structural design of the VSTB separator vessel which in this case has a nominal width of 250 mm at the material outlet. The round filter inside the VSTB features an effective filter surface of 0.47 m². The vacuum is generated by a 5.5 kW vacuum pump providing a suction volume of 200 m³/ h. The entire filling station is shown in Fig. 2. Apart from the VSTB separator vessel it also includes a height-adjustable FIBC suspension device with a pneumatic docking socket and a vibratory compressor for the FIBCs.

Fig. 1: System diagram of VSTB

Thanks to the electrically height-adjustable suspension device the system allows to fill FIBCs of different heights (1.25 to 2.25 m including the loops) with up to 1000 kg of bulk material. The filling level inside the bag is controlled by a level limit switch with rotating blade which is mounted in the docking socket. While standing on a pallet the bag is entered into the system by a fork-lift and is removed after filling has been finished.

Fig. 2: FIBC filling station