Re: Crushed Licorice Root Pneumatic Conveying
Dear Kevin Menar,
The application of a centrifugal fan in pneumatic vacuum conveying is always a bit tricky, due to the fan curve, whereby the airflow is high at a low vacuum and the airflow is low at a high vacuum.
At higher conveying vacuums, the airflow can reduce below the required airflow (low air velocity) to prevent sedimentation.
As you have an existing and operating system, it must be possible to measure at least the operational performance data.
-Capacity
-Vacuum at measured capacity
-Airflow by velocity measurement in fan outlet pipe at different vacuums.
From these field data, a calculation can be made.
(A preliminary calculation already indicates that the design is OK (2.5 tons/hr at approx. 0.14 bar vacuum) and that 22.5 kW is acceptable for 2.5 tons/hr)
If fan breakdowns are the problem, then the pneumatic design should be OK, because a wrong pneumatic design cannot harm the fan.
The air density at 25 degrC is 0.988 kg/m3 at an altitude of 200 m.
If you can provide more information and describe the exact problems with the fan, then a more accurate answer is possible.
Have a nice day
Teus ■
Teus
Fan Power Estimation
Originally Posted by Teus Tuinenburg
The application of a centrifugal fan in pneumatic vacuum conveying is always a bit tricky, due to the fan curve, whereby the airflow is high at a low vacuum and the airflow is low at a high vacuum.
At higher conveying vacuums, the airflow can reduce below the required airflow (low air velocity) to prevent sedimentation.
As you have an existing and operating system, it must be possible to measure at least the operational performance data.
-Capacity
-Vacuum at measured capacity
-Airflow by velocity measurement in fan outlet pipe at different vacuums.
From these field data, a calculation can be made.
(A preliminary calculation already indicates that the design is OK (2.5 tons/hr at approx. 0.14 bar vacuum) and that 22.5 kW is acceptable for 2.5 tons/hr)
If fan breakdowns are the problem, then the pneumatic design should be OK, because a wrong pneumatic design cannot harm the fan.
The air density at 25 degrC is 0.988 kg/m3 at an altitude of 200 m.
If you can provide more information and describe the exact problems with the fan, then a more accurate answer is possible.
Have a nice day
Teus
Dear Teus
Thank you so much for your comments.
Although my back ground is not engineering but because of my personal interest I have been following many of the discussions on this Forum, especially yours, and I must say that I have learned a lot from your comments since they combine some fluid mechanic fundamentals with practical experiencees that you have.
Basically my knowledge of Pneumatic Conveying is not more than three weeks old! All of which I have picked up from the forum and off course the internet on the subject of Pneumatic Conveying. I hope you bear with me if I am too inquisitive or ask silly questions!
You are absolutely right and it is best to take measurement of capacity, velocity and pressure drop along various point in the system. I intend to use Pitot tube for Static and Dynamic pressure measurements when there is gas only flowing. Can you suggests best places to do the measurements along the system? This may take time because I have to get a pitot tube first!!
With regards to Fan capacity measurement how can this be done? Do I have to take pressure measurements with Pitot tube at the fan inlet and outlet? If so, then what I have to do next? Remember I do not have any fan curve?
You mentioned the fan power of 22.5 kw seems okay for 2500 kg of material conveyed per hour with 0.14 bars of vacuum. If we assume the mass of air sucked in by the fan is 2500 kg as well ( Solid Loading Ratio of 1:1 ) then the volume of air will be 2500/0.988 around 2530 m3/h and the vacuum as you mentioned is roughly 0.14 bars or about 14000 Pa. Then the Fan Power will be [(2530 x 14000)/3600 ]/1000 = 9.38 kw. even If we assume a fan efficiency ( Radial fan) of 65% then this gives a power usage of 14.4 kw only. This is still way below 22.5 kw!!! Can you please clarify?
Thanks
Kevin Menar ■
Re: Crushed Licorice Root Pneumatic Conveying
Dear Kevin,
It is easy to make your own pitot tube from f.i. a diesel fuel injector pipe and a transparent tube.
(see attachment)
You do not have to make measurements along the system.
Capacity with corresponding conveying vacuum is sufficient.
A flow-vacuum measurement on the fan could be done in a straight pipe section at the fan outlet.
Vacuum can be generated by an orificing plate between 2 flanges in the suction piping.
Measuring the air velocity with the pitot tube at a number of places in the cross section of the pipe, the volume flow can be calculated by volume = velocity * area.
Regarding your calculation, I made a preliminary computer calculation under the assumption of a suspension velocity of the licorice roots of 8.85 m/sec (5 mm root particles at material density of 800 kg/m3)
Then I need 4140 m3/hr at approx. 1250 mmWC, resulting in a SLR=0.6.
The estimated power is then: 4140 * 12500 / 3600 / 1000 / .65 = approx. 22 kW
As we see, it is very important to know the real parameter values.
Have a nice day
Teus
Attachments
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Teus
Crushed Licorice Root Pneumatic Conveying
Improving the existing crushed licorice root vacuum pneumatic conveying set up
Can any one help please?
I am new to the field of Pneumatic Conveying and yet trying to improve the power use efficiency of an already installed pneumatic vacuum conveying system where crushed licorice root are sucked from bottom of a hammer mill crusher to a storage silo then to a separator cyclone and finally to a radial material handling centrifugal fan.
The root pieces range from very fine to a length of 1.0 cm and diameter of 0.5 cm with bulk density of 400 kg/m3. Conveying capacity required is 2500 kg /h. The pipe diameter is 20 cm. Total horizontal distance is 23m, total vertical distance is 11m with two 45 degree bends and six 90 degree bends. All is known about the fan it is 22.5 kw. No information about airflow rate capacity or pressure drop it can over come. However the system works with frequent fan break down! I believe the more realistic power requirement is much lower.
Can anyone suggest a suitable fan type with calculation on the air volume required and pressure drop to overcome? How can you estimate the pressure drop across storage silo where the velocity of the inside the pipe entering the silo comes to an almost rest.
The air density should be taken as 0.988 kg/m3 as the location is about 2000 above sea level.
Kevin Menar ■