Issue link: https://www.e-digitaleditions.com/i/1344205
March 2021 / 27 In an ongoing effort to amplify safety and get ahead of rising raw materials costs, a major paint manufac- turer needed to solve a dust issue occurring during the mixing process where operators manually add multiple fine powders to liquids to produce latex-, oil-, or water- based liquid paint. The paint producer was handling approximately 3,000 pounds of powder per batch through a combination of bulk bags and 50-pound bags. The dust collector was discharging the dust into 55-gallon drums, which operators would then have to manually bring back to the mix tanks. This project's purpose was to better control the dust and return the captured dust to the material handling process. In the paint industry, approximately 50 percent of costs are from raw materials. The paint producer in this example wanted to account for that material — not just to control costs but also to preserve product quality by ensuring all formulation weights made it into the process. There are several powders — mostly fine powders — that make up a paint's formulation and one of the most challenging is titanium dioxide, which has a rep- utation of sticking, bridging, plugging, clogging, and ratholing. Without an optimized vacuum conveying system incorporated into the paint-mixing process, the dust collection system that was already in place was susceptible to experiencing backups. A vacuum conveying system was installed into the paint manufacturer's process. The vacuum conveying system for this application was able to collect up to 200 pounds of dust per hour, which is on the low end for pneumatic transfer systems but was considered a higher-volume system since it was just transferring collected airborne dust. As part of the system, the dust collector outlet included a rotary airlock that discharged dust into a pickup point of the vacuum conveyor system. The discharged material was then sucked into the conveying line through a flexible hose to a compact vacuum receiver that discharged the material back into the mix tanks. The conveying system included a compact vacuum receiver with a single cartridge filter that was able to fit into the limited headroom directly above the mix tanks. The transitions from the vacuum receiver back into the tanks were customized for the process. The conveying system used a compact regenerative blower with a low-horsepower motor that was easily incorporated into the existing system. Now the paint manufacturer is able to reclaim expensive materials while eliminating potentially dangerous physical labor and a respiratory hazard that had previously required operators to wear masks. The main differentiator between mechanical and pneumatic conveying is that mechanical conveying, which includes conveyor belts, horizontal-motion conveyors, aeromechanical conveyors, flexible screw conveyors, and bucket elevators, uses a mechanical device that's in direct contact with the transferred material. A pneumatic conveying system, which includes pickup points, conveying lines, vacuum receivers, and system controls, uses gas (usually air) to transfer suspended material through tubes. Secondly, mechanical conveyors typically operate in one plane, whereas pneumatic conveyors can accom- modate changes in direction and elevation if needed. While minimizing changes in direction is desirable no matter what system you're using, a pneumatic con- veyor can be designed to convey materials in the X, Y, and Z axes without transfer points or additional motors and controls. While mechanical conveyors have lower operating costs than vacuum conveyors, mechanical conveyors have much higher maintenance costs than vacuum conveyors because mechanical conveyors have sev- eral moving parts, bearings, and drives that need regular maintenance, making them more susceptible to unscheduled downtime. Mechanical conveying is sometimes more suited for specific applications, such as coal and limestone, and routinely has lower capital costs. However, the equipment life and associated costs typically offset any difference. Pneumatic conveying's lack of moving parts makes it very popular within high-purity industries like food and pharmaceuti- cals due to the conveying system's ability to prevent material contamination. Also, the NFPA recommends vacuum conveying for moving combustible dusts because if the system were to leak, it would do so inward and not outward into the plant. Reclaiming materials Another use for vacuum conveying systems that's becoming more common is using them to reclaim materials from dust collectors for reuse. When one thinks of dust collection, the assumed idea is to capture fugitive dust and debris as a waste product. However, ancillary equipment and innovative system engineer- ing turns the task of straightforward dust collection into fully integrated systems designed to reclaim expensive ingredients and preserve quality formula- tions. Broadly used throughout the powder and bulk solids industry, especially where manual powder handling occurs, dust collection systems improve air quality, increase worker safety, protect equipment from dusts that can hinder operation, and reduce labor cost associated with housekeeping.