Pet System
Consider a Zens plot, i.e. a functional diagram for pneumatic conveying.
The vertical axis is dP/dL (change in pressure over change in conveying length) and the horizontal axis is the terminal velocity in m/s. A family of curves represents lines of constant solids loading.
In your example the terminal velocity is approx 33.2 m/s, it is constant, and is not changed by throughput rate or by distance.
What does change is the length, it dramatically increases, which in turn greatly reduces the value of dP/dL.
7.0 t/h represents a solids loading of approx 9.7 (kg of PET / kg of air). At 1.5 t/h the solids loading falls to approx 2.1. These two points are vertically in-line at a horizontal coordinate of 33.2 m/s.
So the answer to your question is conveying length.
Regards,
Dennis Hauch ■
Pet System
A proper summary to my earlier post.
Solids loading will decrease as conveying length increases. Provided the air mass flow (the denominator in the solids ratio) remains unchanged, the only way left for the solids loading ratio to decrease is for the solids mass flow (the numerator in the solids ratio) to decrease.
Stated yet another way, the solids conveying rate capability will fall off as system length increases assuming there is no change in the conveying air rate.
Dennis Hauch ■
Influence Of Conveying Distance
For a given air supply (pressure and flow rate) material flow rate (for any material to be conveyed) is approximately inversely proportional to conveying distance (allowing for vertical lift and bends) and so if you double the "equivalent length" of the pipeline you will only get half the material flow rate. This is because there is essentially no change in the energy input to the system.
Do make a point of attending the 2nd Bulk Asia Conference/
Exhibition being held in Mumbai in November. Pneumatic Conveying will feature prominently with technical papers and workshops on the subject. ■
Why Throughput Reduced
Dear Mr. Dhruv,
From the data given it appears that the system design may just be adequate for conveying of 5 tph PET Chips.
Also though the Blower is sized for a pressure of 0.5 bar pressure, the duty point remains at 0.15 bar for the longer distance. Here if the blower were not able to develop the pressure required for 5 tph conveying rate, the blower drive would most certainly trip. The fact that the blower drive does not trip suggests that the blower is not subjected to higher pressure than 0.15 bar.
You have mentioned elsewhere that the rotary feeder in isolation can deliver PET chips at the rate of 10 tph. The above facts point to the feeder not being able to feed at required rate when under differential pressure, this is most likely to happen due to improper venting of the feeder.
Should you require any support for proper venting of the Rotary feeder please contact the undersigned.
Thanks and Regards,
Vikas Gaikwad ■
Why Throughput Reduced
Dear Sirs,,,
I agree to you but no one said, how to increase the throughput.. I mean we need 5 Tons/Hr. at 40 Mtr. horizontal, 20 Meter Verticle & 5 Bends with this Root Blower.
Root blower is capable enough to produced 0.5 Bar pressure and we have checked it but with longer distance also the pressure is not required and so duty point remains at 0.15 to 0.2 bar only.
If flow is enough, pressure is enough, rotary valve is enough then why not 5 Tons/Hr.... SHOULD I DECREASE FLOW ? or INCREASE DIA. ? ■
Pet System
Go to this website -
http://www.coperion.com/pneucalc/Default-L1.aspx
Input the product, capacity, length and pipe diameter in meters.
Push the calculate button.
Immediately the pressure loss, gas flow and solids ratio will be displayed.
You will find that a 3" schedule 10 pipe is best for 5.0 t/h.
Dennis Hauch ■
Re: Why Throughput Reduced ?
Dear Dhruv,
My calculations show that you can get 5 ton/hr capacity if you use a stepped pipeline. Increase the pipe diameter from 3 inch to 4 inch and then to 5 inch. Locate the steps about 1/3rd apart. Pressure drop in the conveying line will be about 1/2 bar, approaching the pressure rating of the present blower.
I assumed that the bends were located every 10 meters apart.
Regards,
Amrit Agarwal
Pneumatic Conveying Consulting Services
polypcc@aol.com
Ph and Fax: 304 346 5125 ■
Why Is Throughput Reduced?
A conveying pipe of dia 80mm and length 60m is surely able to convey 5t/hr of PET with 700m/hr of air.
Reduction or increase of air volume only had to be considered, if a pressure limit or plugging would have been reached, but this was not the case.
Also the size of rotary feeder is big enough.
If I understood dhruv properly, then capacity decreased on longer pipe length and increased on shorter length by itself at constant speed of rotary feeder. If this is so, then there is only one reason for capacity change: The rotary feeder has a very poor quality, that is big gaps, high leakage air rate, bad leakage air venting... So fedding capacity is strongly influenced by conveying pressure.
A better rotary feeder will solve the problem ■
Why Throughput Reduced ?
We made dilute phase pneumatic conveying system for output 5 Tons/Hr. PET virgin chips.
Now when we take a trial with 2 Meters horizontal & 2 Meter verticle distance, it gives upto 7 Tons/Hr. output. When we take trial with 20 Meter verticle & 40 Meter horizontal distance with 5 bends, it gives just 1.5 Tons/Hr. output... ?
the data is as follows...
Blower : Rootblower upto 0.5 Bar pressure
Blower Capacity : Upto 700 M3/Hr...
Duty Point (with longer distance) : 0.15 Bar at 600 M3/Hr.
Pipe dia : 80 mm, Bulk density 0.7Gms/cm3..
Rotary Valve : 8 "/10" .
How this can be possible ? Is air lesser than required or more than required ? What should be best ratio ? Would there be huge leakage by Rotary Valve which may result in half of Air Flow ? ... Whose fault is this ? Blower, rotary valve or system design ? What should be ideal air velocity for dilute phase conveying system ? ■