Dear Dana,

The conveyed material is not mentioned, although we need this information to estimate the product collision losses.

The material data you have given sofar:

bulk density = 400 kg/m3

Conveying rate = 907 kg/hr

Conveying length < 30.5 m

3 bends

From these data, the preliminary conclusion can be:

light product

very low capacity

relatively short conveying length

The proposed pipe diameter of 7” (off standard size) seems to be too high.

Supply us with more information about the installation.

vacuum- or pressure conveying

feeding device

pipe routing, bends

compressor type

particle size

particle density

bulk density

altitude above sea level

atmospheric conditions.

Have a nice day

Teus ■

Dear Dana,

I interpreted your data as follows:

-average particle size = 400 micron

-Bulk density = 400 kg/m3

-mixture of ground plastic and sand dust. average particle density = 900 kg/m3

-altitude 250 m

-ambient temp = 35 degrC

-RH = 80%

-Centrifugal fan.

A preliminary calculation resulted in:

-4”pipeline

-720 m3/hr centrifugal fan

Calculated capacity of 1 tons/hr at a conveying pressure of approx. 750 mmWC = 7500 Pa.

I assumed that the rotary valve is injecting the material AFTER the fan.

It requires extra calculations, when the material is injected in the inlet of the fan, because then there is also a part vacuum conveying and depending on the fan design, the material is accelerated in the impeller, consuming extra energy.

The advice is to inject after the fan, unless this not possible due to other considerations.

A centrifugal fan curve is in pneumatic conveying not the best solution, as the conveying pressure influences the displaced air volume, which can lead to instable conveying or choking.

Keep in mind that these calculated results are based on assumptions and (educated) guesses.

Take care

Teus ■

Originally Posted by Carrara

I am working on a conveying system and its really to my strong suit can someone shed some light on this?

Conveying 25lb/FT^3 material under 500 microns, up to 2000 lb./Hr, less than 100 feet transportation length, with three long 90 degree bends hopefully using 7" pipe.

What is a good air to solids ratio, and how do you determine this for a dilute phase system? I have done some research and i see Air solid ratios ranging from 5 to 50.

Thank you

Dana

Dana,

What is a good air to solids ratio in dilute phase conveying? It is mostly decided by a cost analysis of capital and operating cost. This cost study is done by determining the capital investment and operating cost of the conveying system for a range of solids to air ratios. For your 2000 lbs/hr, less than 100 ft conveying system, and a 7 inch dia pipe, a fan type system will be enough at low solids to air ratios. At high solids to air ratios, pipe dia will be reduced but a more costly Roots type blower running at a higher pressure may be needed.

Regards,

Amrit Agarwal

Pneumatic Conveying Consulting

Email: polypcc@aol.com ■

Dear Dana,

From my example calculation, you can derive:

SLR (Solid Loading Ratio) = kg/sec material / kg/sec air = 1000 / (720*1.18) = 1.17

The air density is taken at 1.18 kg/m3

A SLR is depending on:

-the material

-the conveying velocities

-the conveying pressure

-conveying length

A low pressure system results in low SLR’s

Long conveying lengths result in low SLR’s

As a matter of fact, when the pipeline diameter, conveying velocity and conveying pressure are constant, the SLR is solely depending on the conveying length.

See also:

https://news.bulk-online.com/pneumat...ationship.html

Conclusion: A “normal air to solids ratios in dilute phase conveying for materials “ does not exist.

All for now

Teus ■

Originally Posted by Carrara

Teus and Amrit,

Thank you both for your information.

What are normal air to solids ratios in dilute phase conveying for materials like mine,,,25lbs/FT^3 dry dusty materials?

Best,

Dana

Dana,

I think your question is about "typical" solids to air ratios, not normal/abnormal ratios. Typical solids to air ratios in dilute phase conveying are in the range of 1 to 10. This is mainly because the required conveying velocity increases as solids to air ratio increases, resulting in higher and higher pressure drops, greater particle attrition, conveying line wear-out, etc.

Regards,

Amrit Agarwal

Pneumatic Conveying Consulting ■

Dear Amrit,

The statement:

requires some explanation.

Your statement in formula looks like: conveying velocity = function(SLR)

This formula implies that dense phase, conveying at usually high solids to air ratios, require high air velocities.

However, dense phase conveying is promoted for its low conveying velocities resulting in reduced energy consumption and the prevention of greater particle attrition, conveying line wear-out, etc.

Where am I missing something in the alleged contradiction between the formula and the accepted common view about dense phase conveying?

Have a nice day ■

[QUOTE=Teus Tuinenburg;79344]Dear Amrit,

The statement:

requires some explanation.

Your statement in formula looks like: conveying velocity = function(SLR)

This formula implies that dense phase, conveying at usually high solids to air ratios, require high air velocities.

However, dense phase conveying is promoted for its low conveying velocities resulting in reduced energy consumption and the prevention of greater particle attrition, conveying line wear-out, etc.

Where am I missing something in the alleged contradiction between the formula and the accepted common view about dense phase conveying?

++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ ++

Teus,

I think what you are missing is the QUESTION that has been asked and is being discussed in this post. This question is related to dilute phase conveying, not dense phase conveying. I think we both know very well that in dense phase the velocity vs SLR co-relation is just the opposite of that in dilute phase.

Regards,

Amrit Agarwal

Pneumatic Conveying Consulting

++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

Teus,

The question ■

Dear Amrit,

The QUESTION that has been asked and is being discussed in this post is:

The answer to that question has to be that, since the SLR is a function of:

-the conveying length (SLR=a*Length^b)

-design pressure (high pressure high SLR)

-design velocity (high velocity high velocity losses lower SLR at design pressure)

-material properties. (high solid loss factor low SLR)

A “normal air to solids ratios in dilute phase conveying for materials “ does not exist.

This applies to dense phase as well as to dilute phase.

The statement:

is in formula: conveying velocity = function(SLR)

Therefore, I calculated the Zenz diagram for a cement conveying installation, identifying the pressure drop, energy consumption and SLR as a function of the airflow (corresponds approx. with velocity).

The results are given in the attachment.

The relation between conveying velocity and SLR for a conveying installation at constant conveying rate appears to be in the calculated case:

velocity=approx. function(1/SLR)

The formula shows a continuous velocity vs SLR curve from dense phase to dilute phase conveying.

Conclusion:

In dense phase the velocity vs SLR co-relation is equal of that in dilute phase.

Best regards

Teus

Attachments

zenz diagram1 (PDF)

■

Dear TT,

Hi Tues, i see you have a nice graph plotted there with clear interpretation, can you show me the calculation of pressure drop cause by SLR ratio ? ■