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Powder activated carbon transfer method

  1. Jun 22, 2012 #1

    I'm going to school for mechanical engineering and I am interning at a water filtration company. I always come here for help on hw, and I see it as a good source of using my references available, so why not come for real life problems too?

    Here is the situation:

    I need to transfer powder activated carbon from a 1,000lbs carbon bulk bag from point A to point B, a storage tank about 20 feet in the air vertically, horizontally no more than a couple of feet. We do not use the whole bag in one sitting, depending on the recipe we take anywhere from 10-300 lbs at a time accurate to about .25-.5 of a pound. Currently we put the bulk bag on a scale and zero it out, then use a water venturi vacuum to suck up the carbon and watch the scale for the desired amount (example 100 lbs, suck until scale says -100). The reason the water venturi is a good idea is because the carbon is EXTREMELY dusty, and mixing it with water eliminates the dust.

    The problem is the vacuum does not have enough power. I have looked into many options such as other industrial powered vacuums, but the filters would clog instantly because the carbon is so cakey and corrosive. I have also looked at bulk bag unloading systems designed just for this purpose... However, they are more so designed with the intension for the bag to stay on until it is empty, whereas like I said we only need X amount from the bag and then switch it with a different bag (about 8 different kinds of carbon bulk bags that we have). So it would be inefficient to put one on, install it, vacuum, and then switch it out for another. They are also very expensive and we are limited on space, so purchasing multiple systems is not an option.

    So, as of now I’m trying to stick with the water venturi system. It is simple; no moving parts so maintenance free, and eliminates our dust problem. For those who do not know how the venturi works is it sends high pressure water through a nozzle. Due to the decrease in diameter of the nozzle in order for the water to continue flowing, the velocity is increased, while the pressure is decreased. Thus the decrease in pressure creates a vacuum, which is then used to suck up the carbon. Currently the inlet pressure is about 25psi and the outlet pressure is 2.5 psi. To my understanding, the larger the change in pressure, the stronger the vacuum.

    1. Ideas that I have had and read about to strengthen this is to replace the nozzle with hopefully a more efficient on (tighten outlet diameter for increased velocity/greater decrease in pressure) and perhaps the one we have had on there for years is clogged/corroded.

    2. Also thinking of adding in a bypass in the mainline right before the nozzle. When the valve is opened it will act as a pressure differential and further decrease the pressure.

    3. Adding in a pump before the nozzle in an attempt to build more pressure for the inlet (currently 25 psi) for a greater overall decrease in pressure, thus more suction.

    I am looking either for ways to replace this system or comments on improving the current venturi system or whether you think my ideas would really be enough to make a significant difference.


  2. jcsd
  3. Jun 23, 2012 #2


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    Welcome to PF, Tucker.
    I'm sorry that it took this long for me to respond, but I frankly had not a clue about your problem until just now.
    Would it be practical (or even possible) for you to mount your source bag on a warehouse-quality forklift or scissor jack and simply lift it high enough to make your vacuum adequate?
  4. Jun 25, 2012 #3
    Its not the distance that is the problem, even if the tank was 2 feet away instead of 20 or so it is still pumping at the same rate due to the flow of the venturi system. Its just the actual suction power from the vacuum needs to be increased. I am currently looking at a by pass differential system that should help decrease pressure even further for suction... unfortunatly dealing with these damn sales representatives is a pain in the @$$... emails get repsonces take days for them.
  5. Jun 25, 2012 #4


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    I see... sort of. It's a bit beyond my abilities.

    Okay, that was a lie. It's way beyond my abilities. :redface:
  6. Jun 25, 2012 #5
    I'm not sure I understand your delivery system? So you suck it up with the Venturi, it gets mixed with the water, then what?

    Where does your venturi discharge?
  7. Jun 25, 2012 #6


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    I just had a thought that is probably useless. Would it do any good to swap your working fluid? I'm thinking of maybe using something like methanol or isopropyl alcohol instead of water. You would still have the moisturizing factor, but with less mass to resist the airflow.
    Again, that's just a beer-induced idea that might have no validity.
  8. Jun 25, 2012 #7
    Well, you don't want to saturate your PAC with either of those things before it even hits the process...
  9. Jun 25, 2012 #8


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    Unless I totally misinterpreted the original post, there is no "process". Isn't this just a carbon filtration system?
  10. Jun 26, 2012 #9
    It gets sucked up with the venturi and in the process mixed with the water and is then dumped into the mixing tank what i said earlier was 20 feet but is prob more closer to 15 feet. Then more what and other ingredients are put into the mixing tank together.

    So just to make sure we are clear the carbon is sucked up by the venturi and mixed with water. This water/carbon mix is sent directly into the mixing tank from there.
  11. Jun 26, 2012 #10
    What I mean is, do you:
    a) Suck the carbon out with the venturi and dump directly into an open tank at ground (carbon) level, where it is then pumped up to the mixing tank (like a slurry), or
    b) Suck the carbon out with the venturi, which then discharges directly into the mixing tank at 15 feet.
  12. Jun 26, 2012 #11
    option b. carbon is sucked up by the venturi which then goes up 15 feet and discharges directly into the mixing tank (carbon and water mix)
  13. Jun 26, 2012 #12
    A venturi system still has suction head. It takes energy to move mass to different heights. It is different moving something 2 feet against gravity versus 15 ft against gravity. But if I recall venturi systems have pretty decent suction pressure, so let's say you've got enough (though, if you've got a good fork truck, why not see how it fares?)

    Anyway, If you are looking for flow rate. Well, you need flow area since you are probably near your practical limit for pressure drop. Unless that bypass line works out (sorry, I don't know too much about transferring bulk material with a venturi system), I'd say you are limited by the outlet diameter. The carbon can only be sucked into the outlet so quickly (depending on the suction), and there's only a certain area that it can pass through. Velocity*Area=Capacity...

    Can you use two? Water pressure doesn't seem to be an issue for you. Parallel streams might help you.
  14. Jun 26, 2012 #13
    are you surgesting adding in a second venturi nozzle? Is that plausable? For some reason i would feel like the second one would have much less power/get clogged from all the carbon from the first one?
  15. Jun 26, 2012 #14
    Parallel nozzles. Two hoses (you may wye them into one larger diameter hose downstream).

    As I said, I don't have much experience with venturi nozzles, so I may be way off base, but if it's just flow rate you are after, why not just add another one? You can probably use one suction hose still and wye it out to the two nozzles (make sure it's wider than the original suction hose to allow for the greater capacity).
  16. Jun 27, 2012 #15
    Having two different streams from the same water supply may reduce the inlet pressure (which isnt good), but this is def an idea that i will play around with. It run it by my boss and see what she thinks

    Thanks for the consideration!
  17. Jun 27, 2012 #16
    It will reduce the inlet flow but it will not reduce the inlet pressure, assuming they are at the same height.

    The limiting factor, though, might be that the lower flow will lead to lower velocity through the nozzle, and thus a potentially lower pressure drop. I can't comment if the lower pressure differential will hinder your suction capacity, though.

    Good luck.
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