Pneumatic Conveying Convenience and Flaws
Many industries use pneumatic conveying as part of their manufacturing process. This includes many food processing and manufacturing plants as well. It's often used for the conveying of certain "dusty" food ingredients such as grains and sugar which pose certain well documented challenges including combustible dust hazards, sanitary or flow rate control.
However, in other applications, damage to the finished food product itself can also pose a significant challenge. These may include manufacturing of cereals, snack foods and other processed food products that are somewhat fragile and susceptible to breakage. Though fragile, these products still require pneumatic conveying for the manufacturing and packing processes. How can these plants reduce product breakage in the conveying systems?
Dutifully Monitor Conveying Velocity
With both dilute and dense phase conveying, conveying velocity varies from one application to another. Numerous factors including the material being conveyed and the layout and length of the pneumatic system determine the pressure and velocity used. Target velocity, and therefore fan and air speed are calculated based on experience, gut feeling and best guess. They're then adjusted up to reduce blockages and down to reduce product loss due to damage/breaking. The bottom line is they're typically managed using indirect observation - fan speed, air/gas speed and throughput.
It's time to measure the actual velocity of the particles themselves so that velocity is optimized rather than bracketed. By using a triboelectric particle velocity monitoring system midstream operators can carefully monitor the effects of any changes to the input controls or variations in flow caused by the unloading process or problems with the material itself.
Design System to Minimize Friction
Some commonly recognized design concepts can also help to reduce damage in food processing with pneumatic transport systems. The exact design of the conveying system can also contribute to product breakage. Friction increases in sharp turns, such as 90 degree bends, and in vertical to horizontal changes. The more of these a system has, the lower the overall conveying velocity will need to be in order to prevent breakage. Therefore, endeavor to use long, straight runs as much as possible and keep turns and other transitions to a minimum.
Looking Elsewhere in the Food Manufacturing Plant
Pneumatic conveying isn't the only place in a plant where actual particle velocity is an important metric. Most food manufacturing facilities also have extensive dust collection systems, and monitoring airflow through a fabric filter dust collector provides important operational information. Similar technology is found in filter receivers in the pneumatic systems themselves as well.
Air flow in a dust collector depends on a combination of the fan output and the resistance generated by the ductwork system. Once installed, the resistance generated by ductwork, pickups and other connections stays consistent (unless a problem arises). Therefore, the only varying source of resistance under normal conditions is the dust collector filters or filter receivers. For fans that do not have a VFD or a damper to control airflow, the CFM will vary as the differential pressure rises and falls. This requires maintaining the DP within a very tight range so as to avoid large swings in CFM and thus air velocity within the system.
Maintenance technicians and operators should follow industry best practices to ensure the collector DP stays within the given range during normal operating conditions.
Where rising velocity could cause a problem, plants should consider installing a VFD (more expensive) or a fan damper (less expensive) to have some ability to regulate airflow.
Auburn Systems has successfully helped food manufactures to control conveying velocity to avoid product breakage. Click here to read the case study for a cereal manufacturer we helped to solve their conveying difficulties using our triboelectric monitoring technology. If you would like to learn more about how we can help your facility with similar challenges, please contact us today for a free consultation.