"Flowability is a function of the material, flow rates, and the equipment used. Thus, we need to understand a bit about each one of these factors. Material characterization allows us to understand the material we are dealing with. We need to understand the material behavior at the micro level (that is, particles) and the macro level (that is, in bulk quantities). Material particles interact with each other (particle/particle interactions), with the equipment (particle/equipment interactions) and with the environment (particle/environment interactions). The ability to flow also depends on the throughput (Kg/hr) and velocity (Km/hr). The last factor to be considered is the handling equipment. Geometry, distances, angles, surface finish, and agitation all influence flow behavior or flowability."
Gómez went on to highlight other variables that deal more with transport of bulk materials such as can and conveying velocities (Table 1).
Only when these are fully understood can factors such as method of pneumatic conveying -- for example, pressure or vacuum, and closed-loop nitrogen systems -- together with weighing and scaling systems and vacuum sequencing be implemented successfully.
One topic that certainly commands plant attention is reducing operating and maintenance costs, notes Hapman, Kalamazoo, Mich. Its MiniVac range of pneumatic conveyors are designed for installation flexibility and do away with the need for expensive plant air or separate compressors, says the company.
MiniVac's ease of cleaning was a key plus for a pharmaceutical application requiring a cleaning system that totally eliminated any possibility of cross-contamination during product changeovers.
Hapman engineered the system with individually controlled spray-wash ports placed throughout the interior of the conveyor. This self-contained design reliably cleans and sanitizes the conveyor's stainless steel interior without the need for time-consuming external procedures. The system also boasts quick filter cartridge change-outs; a clean-in-place rotary valve that allows disassembly, cleaning and reassembly within minutes; and sealed motors and controls rated for explosive atmosphere and washdown applications.
The pneumatic conveyor not only met all of the pharmaceutical maker's requirements but led to increases in efficiency and processing rates, says Hapman.
To cut maintenance downtime, the company has launched a managed maintenance program (MMP). This involves regularly scheduled inspections to spot potential wear and tear before it becomes an issue. The MMP also offers customized training to improve equipment uptime, performance and longevity.
Meanwhile, Flexicon, Bethlehem, Pa., is taking conveying to higher levels, quite literally.
One of the company's latest successes is a project for Oplex, Mexico City, one of Mexico's largest plastics processors. Installing a bulk bag unloading system for polyvinyl chloride (PVC) resin that combines both pneumatic and flexible screw conveying has streamlined materials handling, created a safer work environment and improved worker efficiency. The two separate pneumatic conveying lines prevent cross-contamination when running different products.
Flexicon had to adjust its Pneumati-con dilute-phase pneumatic conveying system to maintain performance at Mexico City's high altitude – 7,349 ft above sea level. This primarily involved ensuring that the fans cooling the motors generated enough air flow to be effective.