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Thread: Pneumatic Conveying of Barley

  1. #1

    Lack of Understanding aka Mass Confusion

    G'day,

    I am a student in CAD/CAM Engineering Technologist and am in an Industrial project which uses a pnuematic conveyor system to transport barley from the storage bin to the upper floor of the mill ( 6 stories, I was told).

    The problem is there are two 45 degree bends then a 90 degree radius corner before it starts up the 6 floors. Near the top of the six floors it tends to choke the line. We have a max pressure of 8 psi or else the line will choke. Being new to this field and very limited resources and time I am having difficulty with this. I was wondering if anyone could give me advice on how to approach this problem, any analysis that I can do or any useful information.

    Thanks in advance for the help.

    Ken

  2. #2

    Pneumatic conveying of barley

    You have to provide more information:

    tonnes/h,
    pipe size,
    a dimensioned sketch,
    What design method are you using?

    Michael Reid.

  3. #3
    Dennis Hauch - Freeport, TX, USA Guest

    Barley Handling

    Ken,

    The conveyed barley will slow down and then reaccelerate as it passes through a bend. It is very important, therefore, that the barley be fully accelerated before it encounters that very first bend. Likewise, back-to-back bends will waste available conveying pressure at best and lead to saltation / choking at worst. Also, the riser to the sixth floor must be perfectly vertical, the slightest slope in this line will most certainly lead to choking.

    If the existing piping arrangement checks out OK there are two other possibilities to overcome the choking problem 1) reduce the conveying rate by slowing the rotary valve that meters the barley and 2) increase the conveying velocity by increasing the blower speed. Normally this action will increase the conveying pressure but when correcting a choking condition it may even reduce the conveying pressure.

    I trust this helps.

    Dennis Hauch

  4. #4
    Michael Reid

    You requested more information, here's what I know supplied from the supplier:

    The rotary valve inputs the barley @ 0.55 cu. ft/min. Then it runs in a 4" line horizontally for 56 ft then it goes into a R5" 45 degree bend. This length is 6'1" then into another R5" 45 degree bend. Thenin a horizontal 4 " line for 24'9" to a R4' 90 degree bend. Then verticalfor 64' in an 3" pipe. Then into another R4' 90 degree bend. Then a horizontal pipe for 6' then another 90 degree bend. And up another 13' in a vertical shaft.

    What do you mean "what method as we using"?

    Thank you for your time and time of everyone else.

    Ken Carpenter

  5. #5
    Dennis Hauch - Freeport, TX, USA Guest

    Barley Handling II

    Ken,

    The pipeline data that you provided is revealing, specifically, the step down in pipe size from 4 in the horizontal section at grade, to 3 in the vertical riser. If indeed this is true it is not surprising that the system is choking at 8 PSI.

    Stepped piping systems are common in high compression systems where velocity control is important, but the pipe is always stepped up in size, never down. Your system, based on the information that you provided, is not a candidate for a stepped piping system.

    Your system should be all 3 or all 4 pipe. In a straight system, at 8 PSI one should expect, arguably, 6,000 lb/hr in a 3 system or 12,000 lb/hr in a 4 system. These are conservative estimates.

    Regards,

    Dennis Hauch

  6. Dennis / Ken,
    On reading this thread I have a question and a comment.
    The effects of reducing the speed of a rotary feeder is not always obvious. In my experience, I have sometimes had to change the rotary feeder speed quite significantly before a change in actual feed rate was noticed. If the feeder then turns too slowly, the cooling fan also turns slowly, and the motor could heat up, unless external cooling is applied. Consider also controlling the feed to the feeder by using a valve arrangement.

    A question for Dennis: You have stated possible conveying rates through 3" and 4" lines. How did you get to these figures? I have always assumed that one would need both pressure and volume of conveying gas (and Mass)to perform the calcs. I am not challenging you, but am open to learning more about this art/science of pneumatic conveying.
    Regards,
    Dave.

  7. #7

    pneumatic conveyor problem

    Hi Dennis/ everyone.

    i am Vincent, new in this forum. i am an engineer doing dust collector and currently working on a pneumatic conveyor project. can anyone help me to size up the system?

    i have to conveyor 10 tonnes of coke breeze per hour, for 500', of which 300' is vertical. there is altogether 8 x 90 deg bends. coke size ranges from 1mm to 3mm. this coke is conveyoed from single source, to 4 separate silos, running exclusively. one at a time. so i decide it will be pressurised conveyor.

    using some method of calculation, i managed to work out that the airflow and pressure will be 1300SCFM and approximately 15psig. using 6'' schedule 40 pipe. this pressure seems to be to high, and i am wondering should i increase pipe diameter. besides, not sure if there is blower that can reach this pressure, other than compressor.

    at this pressure, can i use rotary feeder for material metering? furthermore coke is highly abrasive.

    from that calculation i work out the air velocity to be 17m/s to 32m/s (expanding throughout the pipe due to pressure). does this range makes sense? i am also concern about static charge built-up due to high speed conveying

    can anyone help me? should i opt for dense phase conveying? or enlarge the diameter of my pipe?

    regards;
    Vincent

  8. #8
    Dennis Hauch - Freeport, TX, USA Guest

    Coke Conveyor

    Vincent,

    Your design (pressure and pipe size) would seem to be in the ballpark, althought the pickup velocity seems a bit low. The specific density of the coke particles is important because it influences the required pickup velocity and the system pressure.

    If the system pressure calculation says 1 bar, you will want to use a compressor as opposed to a lobe-type blower. Coperion offers rotary valves capable of 1.5 bar, 3.5 bar and 6.0 bar differential pressure.

    The Coperion website also offers a calculational tool that might prove helpful.

    Regards,

    Dennis Hauch

  9. #9
    s.pandian Guest

    Re: pneumatic conveyor problem

    [QUOTE]Originally posted by Vincent Lim
    [B]Hi Dennis/ everyone.

    DEAR SIR ,


    CAN YOU PLEASE FURNISH YOUR E.MAIL ID .THEN I CAN REPLY TO DIRECTLY. I WILL DEFINTELY HELP YOU OUT

    REGARDS

    N.R.S.PANDIAN


    MY E.MAIL ID : s.pandian@rediffmail.com

    =============================================

  10. #10
    Dear Ken,

    From what you describe, your choking problem is not due to low conveying velocity but most likely due to the conveying pressure unless the line dia after the vertical section increases to 4 inches.
    If the blower has a rating of 15 psig, changing this line from 4 to 3 inch dia will increase the velocity and prevent choking. If the blower has a rating of only 8 psi, you should change the 3 inch line to 4 inch.

    Amrit Agarwal
    Pneumatic Conveying Consultants
    polypcc@aol.com
    www.powderandbulk.com/pcc

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