Q&A: Understanding When Feeder Problems Arise from Inadequate Bin Design

Powder & Bulk Solids’ recently presented “Don’t Blame the Feeder: Understanding When Feeder Problems Arise from Inadequate Bin Design” as part of its DryPro webinar series. The webinar discussed problems with a feeding device that result from how the material is handled in the bin and the relationship between the device controlling discharge and the vessel from where the material is supplied.

Joe Marinelli, senior consultant at Solids Handling Technologies Inc., and Scott Miller, consultant at Solids Handling Technologies Inc., discussed the challenges and solutions of inadequate bin design and how it affects the feeder. After the presentation portion of the webinar, a live Q&A took place. Below are the questions and answers.

Did you know that often a feeder is evaluated independent of the feed bin supplying the material? When a problem arises, the feeding device is assumed to be the issue. However, in many cases, the issues can result from what is actually taking place in the bin above.

Q: Can you use a belt feeder in high pressure and high temperature environments; are you able to effectively pressure seal the feeder chamber?

A: High pressure feeders do exist say, on the coal silos, when you have to handle the back pressure from a pulverizer, so they are pretty hefty devices. The temperature we have to be careful of because a feeder is usually a rubber or canvas belt. They do have apron feeders, which are metal belts that could possibly be used for high-temp applications, but they are quite expensive.

One additional note: It would be very subjective as to how high a temp. is “high temperature.” Might want to shoot us an email to discuss it. (email: [email protected])

Q. How do you address arching diameter of the material in hopper design, especially if the rotary feeder opening is less than the calculated arching diameter?

A: The simple answer is you have to put a larger rotary valve on it. If you have a valve that’s 8 inches in diameter and your arching dimension is 12 inches in diameter then you have to put a larger rotary valve on it. One thing you can do, maybe, sometimes material gains strength after time of storage and rest. But during continuous flow with no storage hours, it flows pretty easily, so you may be able to put a 2-ft-diameter gate to take the arching diameter of the material so when you open it up it will flow into the rotary valve and will discharge. It’s difficult to do but you can do it.

One other thing you can do, though it is less practical, is in some cases you might have a very small rotary feeder, or the line is very small, and material is very cohesive, you may have to add a feeder to trickle feed the material from a chute or drop it directly into the rotary feeder. It’s not cheap but it is one thing we’ve done in the past for some applications.

Q. What would be your cautions to feed synthetic gypsum?

A. Gypsum is usually wet and difficult flowing. We had an application once where it was a rectangular box and they were feeding it onto a belt from there, and it had 11 screw feeders underneath the box and the motors were tripping out on all of those screws. We replaced the screws with 11 mass flow screws to the conical shaft section, increasing pitch section, and conveying section. It is still working quite well.

Gypsum is wet and cohesive, so you need to measure its flow property to determine if you’re going to put it into a container that you’re going to be able to get it out of that container.

Q. What is your opinion of air cannons and pop-up omnidirectional air blasters?

A. Air cannons aren’t bad depending on the application. One application that we had was with rice hulls. They were having problems getting the material out and the guys in the morning would go 15 feet up in the air in the silo, poke at it, and get it to flow. They were having storage at rest problems. Something was packing that material but if you reached in and grabbed the material it was very free flowing; it wasn’t cohesive.

In the afternoon, I noticed that a large freight train was going by the facility and the ground was shaking, the bin was shaking, everything was shaking. We realized what was causing the bridging problem is that it was getting packed in there due to the vibrations it had all day long. The problem was solved by an air cannon at the bottom of the hopper, hit it and it would fluff up the product and get it flowing.

Q. Is there a scenario where funnel flow is preferable for feeders or for processes in general?

A. One of the interesting things about bulk solids, maybe it’s frustrating, is that they are not all the same. So, depending on the material’s flow characteristics, there may be certain challenges to certain materials in mass flow. Two that can sometimes be an issue with certain materials is: we may have a material that isn’t cohesive and has good flowability but is very fragile. There can be certain funnel flow designs where we might have a fragile material and don’t want to damage the material. So, we might want to use a unique funnel flow design to minimize stresses that the particles might see and minimize damage. It’s going to be material specific.

Another example is that funnel flow might be advantageous. There are certain materials where they may be prone to, when they discharge from a silo, certain quaking or structural concerns. Certain materials (such as PET plastic pellets) where flowing in mass flow might give rise to structural problems.

Watch the entire webinar “Don’t Blame the Feeder: Understanding When Feeder Problems Arise from Inadequate Bin Design” on demand.