Miller Magazine Issue 107 / November 2018

54 MILLER / NOVEMBER 2018 COVER STORY 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. Pneumatic systems are used; – At low pressure loss (300 mmSS) and low air velocity, aspiration and dust suppression systems, at destoning, descaling and ventilation of wheat; – At medium pressure loss and air velocity (600 – 1000 mmSS), at conveyance of passages; – At high pressure loss and air velocity (5000 mmSS), at storage and packaging departments of finished products Pneumatic conveying, used commonly in food industry, is one of many ways of transporting products. It uses pressure force to create an unbalanced environment in the pipeline. This way, the product is pushed or sucked through the pipe from the feeding stations until the very end, where it is dis- charged. To design a functional and reliable pipeline, we must go through a lot of calculations and designing before we get to a suitable and satisfactory result. If a particular product (i.e. grains, etc) has real degradation concerns, di- lute phase pnuematic conveying is not the selection of cho- ice. The generally higher velocities associated with trans- ferring in a dilute phase manner do not lend themsleves to handling products in a gentle fashion. In these instances, the product is typicaly handled with a Dense Phase Pnue- matic Conveying System or a Mechanical Conveying Sys- tem. A dense phase concept is designed with the goal of a high solids-to-air ratio. This allows the product to move in the tubing at much, much slower velocities when compa- red to a dilute phase systems. As such, these systems are quite desirable when transferring a product that has deg- radation concerns (grains and similar applications) or, that may have abrasion concerns on the handling equipment. Utilizing a lower air velocity, these systems can transfer fri- able products very effectively with little degradation. Ad- ditonally, should a process have a blended product, dense phase systems can deliver the product while minimizing product segregation. The larger the particle size difference, the more likely a dense phase concept may be required. If required, the dense phase concept systems allow for the same benefits that reside in dilute phase systems (see be- low: dust free, easy layout, robustness, etc). Dilute Phase Pnuematic Conveying references the air-to-material ratio when transferring. Generally spea- king, this is a low product-to-air ratio design that utilizes higher air velocities (and lower volumes of product) to transfer the product from one point to another within a facility. There are (2) types of Dilute Phase Pnuematic Conveying styles: • Pressure • Vacuum Generally speaking, Pressure systems provide better transfer efficiencies over longer distances. In a given appli- cation, Vacuum Systems typically will not be able to match the throughput of a Pressure System with all things being equal. However, Vacuum Systems are considered “clea- ner” as the motive air is not delivered through the blower and into the product stream like a pressure system. There are many advantages in applying dilute phase pnuematic conveying in grain/wheat applications. Below are some of the primary advantages: •Dust free handling: With the material being handled in a closed system comprised of tubing (or, piping) from one point to another, these systems are virtually dust free when designed properly. •Ease/Simplicity of layout: The layout of these systems is quite simple given the fact that the tubing is flexible in ter- ms of final layout design. Care must be taken in order to mi- nimize the distances (and turns, or elbows) of the systems. •Robustness (Maintenance & Repair): Dilute Phase Pnu- ematic Conveying Systems are typically extrememly robust and can consistantly provide years of continuous, troub- le-free operations. We have routinely witnessed system ope- rating in their 4th decade with little maintenance & repair. •Distribution: Pnuematic Conveying Systems alllow for a multitude of layout possibilities. -Materials can be transferred from one point to multip- le destinations. – Materials can be trasnferred from multiple starting points to a singal destination. – More complex systems can trasnfer from multiple starting oint to multiple destinations •Ease of Control/Automation: Either Control Relay Logic or PLC (Programmble Logic Controllers) driven Controls Systems are common. The more complex the system, the more common you will see PLC drvien sys- tems due to their robutsness and ease of operation. •Security: The materials are received and transferred in closed systems (Silos, Tubing, Filter Receivers, Scale Hop- pers, etc). Of course, as with all systems, there are disadvanta- ges when utilizing Dilute Phase Pnuematic Conveying for Wheat/Grain transport. Some of these disadvantages are: •Inefficient Material Transfer: The Horsepower requi- rements are usually higher than mechanical systems when given the same operational parameters. Simply put, the- se systems cost more to operate when comparing on a Pound of Product delivered per Horespower. • Explosion Protection/Safety Considerations: This key component is being reviewed and required per safety gu- idelines on a more continual basis than in the past. These safety systems add cost to the system.