Dilute phase conveying refers to moving materials above their minimum suspension velocity. This allows the particles to be suspended in the air using drag force to move the particles through the system. Dilute phase conveying requires a properly balanced system in order to keep products inflow.
Operating a dilute phase pneumatic conveying system might seem like second nature to plant professionals, but maintaining the integrity of both the product being conveyed and the high-end equipment accomplishing the conveying requires steadiness and consistency.
There are pertinent benefits that dilute phase conveying can offer, but there are also some clear and cut things you shouldn't do with a convey system of this type (if you don’t want to waste significant amounts of time and money fixing and/or adjusting convey specifications). Our experienced AZO sales representative Bill Nesti came to us with a handful of mistakes manufacturers make with dilute phase pneumatic conveying systems, so here are 3 things you absolutely shouldn’t do in the context of dilute phase conveying:
1. Don’t overfeed the convey line with product
We know manufacturers want the equipment in your plant(s) to meet expectations in terms of throughput and efficiency. It can be tempting to push equipment to its limits in order to get the most out of a process. Still, when it comes to feeding a convey line, consistent and steady flow is key.
The destination point of a dilute phase vacuum system
Overfeeding a line typically occurs when an operator aims to increase the rate (some roads are paved with good intentions). The problem is, by increasing what the feeder meters into the convey line beyond what is recommended, an operator can actually bring about “surging” in the line. The operator may then be required to stop the line. If the conveying line is not set at the appropriate rate once restarted, said operator will have to try another setting and restart the line again.
If the operator is required to keep starting and stopping the line because of these problems, the overall rate is compromised due to what we call “cycling.” Essentially, the net effect would be a rate reduction rather than a rate increase. Instead of continuously conveying at a steady-state, overfeeding the convey line can cause cycling that can kill said rate. Operating in a smooth and steady-state delivers the best overall rate and performance of a convey system, hands down. These traits also relate to how product moves in a system:
2. Don’t stop the convey blower or pump when there’s product in the line
We’ve blogged at length about how extended abrasion can affect a line, but stopping a convey blower or pump while product is in the line creates unique issues as well. When you’re conveying product at high velocities (and suddenly you remove the air that is suspending such product in the air), that product will fall. Where it falls is dependent on where it is in the line.
The pick-up air-lock feed of a dilute phase pressure system
For horizontal pipe, this may not be too much of a problem as it simply lays at the bottom of the line. Still, vertical piping tells a different story. When gravity takes effect on that which is vertically lined up, all the product in a vertical line falls to the bottom elbow. Unclogging that material from the elbow will sacrifice production time.
Occasionally, restarting can accomplish unclogging the line if an operator is lucky. Still, more often than not, a clogged line will require an operator to take the time to clean it out. Cleaning out lines equates to more downtime and lost production in the end.
3. Don’t shift a convey line diverter valve during product flow
When you want the option of feeding to two or more separate destinations, a diverter valve is what will determine which destination material will be conveyed. If, in the middle of conveying, the diverter valve is flipped so that material will be transported to a separate destination, product could potentially jam the valve. The valve could also malfunction and even experience premature wear. Simply put, most convey line diverter valves are not meant to be switched while product is running through the line.
To avoid possible damage to the valves (as well as potentially costly line clogs), it is critical to finish conveying product first. The product feeder should be stopped and the pipe should be purged before (finally) the diverter valve can be shifted in sequence. After the position has shifted to the next destination point, the convey system can be restarted in a normal sequence to transport powder.
Patience often leads to success in more than one field.
It may seemingly take longer than just switching the valves on the fly, but this is a safer and more effective way to move product. As lengthy a procedure as an operator might think safely following this procedure could take, rushing it and clogging a line (or damaging the diverter valves themselves) will wind up costing a manufacturer more in downtime. Repair fees due to permanent machine damages are also a consideration to take into account.
The same can be said about overfeeding the convey line or stopping blowers/pumps while product is still being conveyed — having the patience to run a steady and consistent system will keep the ingredients and the machines that move them in a harmonious state. All in all, the way to reach conveying nirvana is by feeding the appropriate amount of product in the line and remaining patient while stopping flow before shifting the destination of the material in question.
If you do find yourself in need of spare parts (or have any other conveying queries), you can always feel free to speak to an AZO specialist. We have more than seven decades of experience in handling raw materials and shaping ingredient automation along the way. Feel free to contact our sales team for any questions on how to help your plant and processes run smoothly.