Q&A: Feeding and Filtration in Pneumatic Conveying ApplicationsQ&A: Feeding and Filtration in Pneumatic Conveying Applications

Recently, Powder & Bulk Solids presented “Feeding and Filtration in Pneumatic Conveying Applications” as part of its DryPro webinar series.

In this presentation, Josh Marion, senior project engineer at Jenike & Johanson, discusses what to do at the “ends of the line” in pneumatic conveying systems — at both the feed end and the discharge end. Marion covered considerations and various technologies for reliably feeding your material into a pneumatic conveying line, as well as how to effectively filter the solids out of the conveying gas (e.g., in a cyclone or a baghouse) at the end of the line.

Here are the questions and answers from the webinar.

Q. How do you know or test to see if a rotary valve is leaking?

Many times, rotary valves will come with a port on the side, a body side vent port, that you can open up (I wouldn’t be running the valve when this is happening) and measure the leakage rate through the vent line. You can also stick pressure probes or airflow measurements both before and after the rotary valve, but that requires drilling into your conveying line.

Another way you can do it, is if you have a knife gate, or some other type of gate that is able to hold back the pressure above the airlock, what you can do is run your conveying line with that gate open and with it closed, and you can look to see if there is a difference in line resistance. If the line resistance when that valve above the rotary valve is open, if the line resistance is significantly lower than when that valve is closed, when there is essentially no leakage through the valve, you know you could be losing significant airflow.

Q. What is the best filtration method for sub-micron particles?

Most of the time you want to use a baghouse that is designed with a large filter area so as not to become blocked with material. Baghouses can be pretty effective at filtering out submicron particles and with the new filtration technology — cartridge filters and bag filters — coming out, they are becoming even more effective in removing submicron particulate. But oftentimes, even still with the new technology, what you want is to make sure, if you’re very sensitive to penetration of submicron particulate you can always put a HEPA filter or similar filter cartridge downstream of your baghouse to capture submicron particulate that might make it through the baghouse if it was not adequately able to capture.

Q. With horizontal cyclones becoming more popular recently, what are your recommended limitations on their usage?

I don’t have a lot of experience with horizontal cyclones. With the experience I do have, I haven’t seen them be as effective at removing particles as fine as a vertically oriented cyclone. So, what are the limitations of their use? If you are very sensitive to limiting the amount of carryover of fine particulate through a cyclone, I’m not sure I would recommend using a horizontal cyclone.

Q. What is the best strategy for cases where you need a large bin outlet to prevent obstructions to flow but you need a small feeder because your desired feed rate is low?

There can be a number of different approaches. Oftentimes what we will see, in a larger capacity storage silo, you will use a feeder, like a screw feeder or a belt feeder, to feed material out over a larger outlet and larger slotted or elongated outlet, and potentially downstream of that you will have an Acrison type loss and weight feeder, which includes intromitting agitators, or augers, to stir the material and forcibly  break up arches and they can also provide very high turndown and good accuracy at pretty low feed rates. But it really depends on the application for what approach you use.

View the Feeding and Filtration in Pneumatic Conveying Applications webinar here.