Miller Magazine Issue 107 / November 2018

55 MILLER / NOVEMBER 2018 COVER STORY •Distance Limited: Dilute Phase Pnuematic Conveyin- gis more limited when required to trasnfer products over long distances. Generally speaking, systems are typically under several hundred feet in order maximize through- put. A simple rule of thumb is to remember, “Distance and Turns (i.e. Elbows) can and will drastically diminish rate for a given application” When a facility’s requirements demand high process ra- tes for flour/grain (i.e. in the tens of thousands of pounds per hour), the method of choice is typically Dilute Phase Pnuematic Conveying. In this instance, outdoor Storage Silos transferring to indoor batching points (i.e. to inter- mediate storage or scaling/weighing for process require- ments) are quite common. The bulk material is generally delivered via PD Pnuematic Truck or Railcar. Whether Truck or Railcar, the hoppers are pressurized to a certain PSI and then the material is systematically released into the transfer system by the operator. More sophisticated systems can offer unloading and transfer without requiring an operator to be constantly managing the process, but generally speaking operator controls the unload sequence. In some instances, the wheat/grain is supplied in smaller bags (50-100 lbs) or bulk bags (1,500 – 2,500 lbs). In this case the transfer is supplied via Bag Dump Station(s) (50-100 lbs bags) or Bulk Bag Unloading Sta- tion(s) (1,500 – 2,500 lbs). Just like the larger Silo appli- cations, the material is metered into the transfer tubing via a rotary airlock which allows the material to enter the conveying stream without the loss of the conveying pressure and air. In facilities with lower transfer rate requirements and shorter distances, mechanical systems can be quite com- mon. Facilities with these smaller requirements usually receive product in bags or bulk bags. In leiu of a Pnue- matic Conveying System a mechanical system can usually handle the rate and accuracy requirements using Screw Conveyors, Bucket Elevators, etc. More common are simple Flexible Screw Conveyors comprised of a typically coreless auger “floating” in a plastic flexible tube. Similar to Rigid Screw Conveyors, these bolt to the discharge of the Bag Dump Station or Bulk Bag Unloader. The screw’s discharge delivers the product to an end point a short distance away. Rigid and/or flexible augers can deliver up to 25’ away in typical designs. These smaller systems are commonly referred to as “up and in” systems due to their short distances. In the same manner, small Bucket Eleva- tors and other mechanical systems are utilized.