When there are concerns about product breakage while pneumatically conveying material, conveying as slowly and as gently as possible should be an operator’s goal.
Essentially, there are two factors to minimize product breakage:
- Conveying distance
- The number of elbows/impact points
Practically any place where product is sliding against the surface or interior of the pipe will cause abrasion and possibly breakage. Luckily, there are methods to minimize contact. In this blog post, we’ll outline some helpful and insightful techniques you can use in your own processes to maintain the properties of your materials to be conveyed.
Conveying at the minimum conveying velocity reduces speed
For delicate products with specific sizes and shapes, any elbow or change in the direction of product flow within a conveying line represents a potential impact point. Breakage can also occur when delicate materials enter a receiver, as there is typically an impact when material hits the hopper entry point or opposite wall. Breakage can be minimized by conveying the product at the lowest possible speed. This is known as the minimum conveying velocity -- just fast enough to move the product down the conveying line.
Utilizing proper pipe couplings is critical to ensure alignment in the convey line is smooth and there are no obstructions between sections of pipe. Beveling the edge of the pipe ends also helps to ensure that there are no ledges or rough edges after the pipes are joined together with a coupling. Bar magnets or grate magnets should be considered as obstructions. These should be avoided or at least minimized.
Utilizing a vibratory feeder can avoid product breakage
Pneumatic conveying can begin with a variety of different feeding technologies. Using a vibratory feeder (instead of a screw feeder or rotary airlock) will start the product moving with less breakage since they do not include any rotating devices.
When utilizing a rotary airlock, there’s always a chance that product will get chewed up at the inlet of the valve as blades pass the inlet of the housing. The same can be said for a screw feeder’s rotating shaft. The higher the shaft RPM, the greater the chance of product breakage.
“Stepping” the pipe size diameter to decelerate material
Another way to minimize breakage is to expand or “step” the pipe size diameter toward the end of the system. The larger diameter slows the air speed of the product entering the receiver at the end of the convey line. Just before the receiver, an oversized tangential inlet could also be incorporated to decelerate the product entering the receiver, thereby reducing breakage.
“Hybrid conveying” can reduce pneumatic conveying breakage
To avoid breakage, conveying at the lowest velocity possible is particularly ideal. Essentially, this is low-velocity vacuum conveying, which is neither dense phase nor dilute phase. At AZO, we refer to this conveying method as “hybrid conveying.” It is a hybrid of the two phases — halfway between them. In this mode, a vibratory feeder is utilized to gently introduce material into the conveying line. The system is designed so the conveying air speed is just enough to move the product (again, also known as the minimum conveying velocity).
The hybrid conveying system could also include a “stepped” conveying line at the last section of the convey run. This would help offset the normally higher velocity at the end of the convey line. Alternatively, a tangential inlet at the receiver could also help to avoid the elbow impact as the product is moved into the receiving point.
For a plethora of content related to conveying systems, check our free conveying guide. Specific benefits of conveying modes, how to avoid product smearing and more helpful topics are included in “Choosing The Right Pneumatic Conveying Method For Process Material Handling.” AZO has seven decades of experience shaping ingredient automation, so feel free to contact our sales team for any questions on how to help your plant and processes run smoothly.