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Dear Nitesh,

Please send complete data on your existing conveying system. I will run the calculations and guide you on how to increase the conveying rates.

I will do this work without any fee.

All the best,

A. T. Agarwal

Consulting Engineer

Pneumatic Conveying Consulting Services LLC

Email: polypcc@aol.com

Ph and Fax: 304 346 5125 ■

Dear Nitesh,

Blower is always rated at its inlet conditions. You have given these as 2010 cu m/hr at a temperature of 209 C. This temperature does not seem to be correct. Please confirm.

In the pipeline route, you show a bend after each diverter. What is the purpose of these bends and why do you have them immediately after the diverter valve? What is the angle of the diverter valve?

From now on I will discuss your project off-line. You may send answers to these questions to my Email address.

Regards,

A. T. Agarwal

Pneumatic Conveying Consulting LLC

Emailolypcc@aol.com

Ph and Fax: 304 346 5125 ■

Dear Nitesh

I suspect that all you need is a bigger blower. And "bigger" means more pressure - not more air. If you increase the energy into the system by this means you will convey more material. At the present time you are only using 300 mbar of the 650 available. Can you not utilise more of the pressure for conveying?

With your 2010 m3/h at "free air conditions" (if this is correct) you are conveying the material in dilute phase, suspension flow. At 1.65 bar absolute your conveying line inlet air velocity (pick-up velocity) is much higher than you need and you could probably convey a little more material simply by reducing the amount of air that you are using. Try reducing the speed of your blower. ■

Dear Nitesh

There is no saltation velocity for polyethylene pellets. They will convey at any velocity, provided that you have sufficient pressure and feed them at the correct flow rate. Having said that, however, for dilute phase conveying the minimum conveying air velocity necessary to convey them in suspension is around 13 to 15 m/s.

There is a very significant pressure minimum point with polyethylene pellets, however, and you will get maximum material flow rate with a conveying line inlet air velocity slightly higher than the minimum value, typically at about 20 m/s, although this does vary with pipeline routing.

I suspect that your conveying line inlet air velocity is much higher than this and so I would suggest that you try reducing the air flow rate, but I do not think that you can achieve the improvement that you are wanting by this alone. Reduce the air flow rate gradually, bit by bit, determine the value of conveying line inlet air velocity and record the corresponding change in material flow rate at each stage. ■

Dear Dr. Mills,

Nitesh has sent to me complete data on his conveying system. I have run calculations using this data and find that his system is "velocity limited", not "pressure limited". At the higher rate, velocity after the first two bends falls to near the minimum that is needed for dilute phase conveying, about 14 meters/sec. in a 6 inch dia line. My calculations show that if the blower speed is increased by about 20%, system pressure drop will increase to about 0.6 bar which is well within the blower pressure rating. At this higher flow, velocity after the bends will increase so that it is well above saltation.

Do you agree with my analysis or have any comments?

Regards,

Amrit T. Agarwal

Pneumatic Conveying Consulting LLC

Polypcc@aol.com

Ph and Fax: 304 346 5125 ■

Dear Amrit

I make 2010 m3/h of air at 20 degC and atm pres equate to a mass flow rate of about 0.673 kg/s (for the benefit of continuity). At the conveying line inlet, at a temperature of 60 degC and 0.35 bar gauge pressure the conveying air velocity in a six inch bore pipeline will be about 27 m/s. This will expand to about 36 m/s at the end of the pipeline. So I do not think that the system is velocity limited, unless the proximity of the bends to which you refer is such that they will precipitate saltation. ■

Dear Nitesh

Amrit Agarwal has already said that the minimum conveying air velocity for the conveying of polyethylene pellets in dilute phase in a six inch bore pipeline is about 14 m/s and I agree with this.

I believe that you have evaluated the conveying line inlet air velocity at 26 m/s and I have agreed with this.

So provided that you have a reasonable acceleration length after bends in the pipeline you will have scope for reducing the air flow rate that you use for conveying. As I have said before this should result in an improvement in performance but I doubt if this alone will achieve the improvement that you are looking for.

If at each stage in the process you maintain the same material flow rate when you reduce the air flow rate and you get a reduction in conveying line pressure drop you can try increasing the material flow rate to bring you back to the same presure drop.

If you are still having problems at this stage then I would suggest that you get one of the very good consultants represented here to help you. It will pay dividends in the long run. For someone closer to home you could contact my colleague Dr Vijay Agarwal at the IIT in New Delhi or Technicom Management Services in Bangalore. I would suggest that make a point of attending the 2nd Bulk Asia Exhibition and Conference to be held in Mumbai in November where there will be numerous papers and several workshops on pneumatic conveying where you will get all your questions on friction factors answered. ■

Nitesh

You are correct that velocity and pressure are related and cannot simply be looked at individually without an effect on the other.

For many materials, plastic pellets being one of them, the capacity you need can usually be obtained at a point of higher velocity and a point of lower velocity for a given pressure differential. The difference is basically the phase of flow which occurs in the pipe.

Conveying velocities for pellets are as low as 4 m/sec are possible.

You have had the benefit of input from two respected individuals in the industry to consider.

Should you need additional assistance, please feel free to send me an e-mail at pcchilbert@entermail.net and maybe I can help you. Our firm offers computer design programs which may interest you and we also provide services of which you may wish to take advantage. ■

Dear Nitesh,

I have followed your post for some time and though you have received replies from some eminent experts would like to contribute my views on the matter.

Your blower is designed to deliver 2010 m3/hr @ 1.65 bar abs pressure, whereas the operating pressure under the present condition is only 1.35 bar. I suspect that our blower is delivering 10 - 15 % higher free air than specified at the reduced pressure. You have to look at the blower performance curve to get the correct figure.

At the higher volume flow rate you get a differential pressure across the feed and discharge to be @ 0.3 bar (leave out 0.5 bar for clean line and cooler losses) Provided this is correct you may not have tamper with the blower speed at all and still get a higher conveying rate uto 21 tph.

Your pressure at the higher rate may go up approx. 0.2 bar and you will still have adequate air for conveying. Simply try to increase the feed from the rotary feeder till it reaches 21 tph or the pressure reaches 0.65 bar.

Thanks and Regards,

Vikas Gaikwad ■

I am always looking for data sets of industrial pneumatic conveying systems to check the usability of my software program. This thread offers in fact a set of useful specifications.

For the calculation I used a equivalent (horizontal) pipeline length of 70 m, furthermore the given bulk material throughput of 15 t/h, as well as the given bore of 150 mm. For the dilute phase minimum pressure loss the program calculated on this basis a gasflow of 2550 kg/h at a pressure loss of 286 mbar. These values correspond almost exactly to the specified set of operating data.

For the desired increase from 15 to 21 t/h the calculation resulted in a gasflow of 2920 kg/h at a pressure drop of 365 mbar. ■

Dear ManfredH,

Based on the given technical data and performance, I calculated the Solid Loss Factor.

Using the calculated SLF, I calculated the conveying pressure for an unchanged installation at a conveying rate of 21 tons/hr.

The result is:

21 tons/hr at a conveying pressure of 0.39 bar.

There is no need for increasing the airflow.

Only the rpm of the rotary lock have to be increased by a factor 1.4

It is very doubtful, whether the increase of the airflow by a factor 1.45 will increase the capacity by a factor 1.4

Increasing the airflow has the following effects at constant capacity:

-The velocity increases, increasing the pressure drop for acceleration and product resistance

-The Solid Loading Ratio decreases, thereby decreasing the pressure drop for product resistance

-The higher velocity decreases the residence time of the product in the pipeline and thereby decreasing the pressure drop for keeping the product in suspension.

The combination of these effects is very small, especially around the Zenz point (lowest point in the Zenz curve)

Your calculation suggest that the capacity is almost proportional to the airflow:

A 1.45 air flow increase generates a 1.4 times capacity increase.

Your calculation also results in an energy demand increase of :

2920/2010*365/300 = 1.77 times or 77%

Where is that energy gone?

Have a nice day

Teus ■

Dear Mr. Tuinenburg,

from published data of industrial conveying lines I developed "a sort of" universal diagram for the rough estimatimation of flow conditions using parameters of the turbulent flow through pipelines. There is no doubt, that you will get a stable conveying state for the 21 t/h by increasing the pressure only. After my calculation the border of the (stable) dilute phase state will be reached at a gas flow of 2113 kg/h and a pressure loss of 440 mbar. On the other hand these values show, that you are leaving the state of minimum pressure loss by increasing the pressure only, while my calculations are based on identical conveying states.

In case you do not know my free software, you can get it from the link given in my thread

Software Estimates Bulk Solid Behaviour

https://forum.bulk-online.com/showth...olid-Behaviour

In the program's section "Pneum. Förderung" using the "Hilfe"-button you can find the diagram and the extrapolated or interpolated parameters for three characteristic conveying states.

Kind regards

Manfred Heyde ■

Dear ManfredH,

I calculated the Zenz diagram of the installation.

The result is represented in the attachment.

The green highlighted cells represent the existing installation.

The blue highlighted cells represented the installation as modified by your proposal with a bigger blower.

-The existing installation is operating in the dense phase conveying region, close to the Zenz point.

-The existing installation operates at an energy consumption of 1.42 kWh/ton to 1.63 kWh/ton

-The existing installation has always sedimentation in the pipeline.

-The modified installation is operating in the dilute phase region.

-The modified installation operates at an energy consumption of 1.75 kWh/ton to 2.06 kWh/ton

-The pressure drop at 21 tons/hr for the modified installation I calculated at 0.4 bar.

-The modified installation is free from sedimentation in the pipeline.

Have a nice day

Teus

Attachments

zenzd (PDF)

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