Define your dense phase first !!!!!

Coz your dense phase could be someone elses lean phase..... ■

Pneumatic conveying regime is a bit like driving in Asia. The first rule is 'There are no Rules!'. As noted by Mantoo: One man's lean is another man's dense. Thankfully most of the systems work because adjustment is fairly easy at the development stage.

Where is Tuis T when we need him? ■

Dear JimLee,

To figure out, whether your system operates under dense phase or dilute phase, needs more information.

-bend radius 30 mm ? may be 300 mm?

-material (This must be Carbon black ?)

-material density

-particle size distribution

-convey air volume

-blow tank material content

-appeart density: 0.491 g/cm2 „ should be 0.491 g/cm3 „ 491 kg/m3 Is this bulk density ?

-What is the meaning of ¡§the average using volumes of one transportation 25 m3¡¨

Then, Mr Mantoo¡s remark about dense- and lean phase illustrates the wide spread confusion on this subject.

Including my confusion)

If you can clarify the above mentioned questions, then you could go for the definition given in the thread :

Dilute or Dense Phase Conveying ? of 22nd November 2005

met vriendelijke groeten

(Dutch for : with friendly greetings)

To Johngateley,

You meant me as Tuis T?

Well, I was at work, but do not worry, I stay tuned. ■

Dear Mr Teus I don’t think there is any confusion about lean or dense phase. Since there is no text book definition different people use different parameters i.e. Solid loading ratio, suspended / non suspended flow, %age solid concentration in pipes etc. That is why I asked Jimlee about it and was not to cause confusion.

Dear Mr Jim depending on your phase definition you have a constant flow air flow rate of 643 m3/hr and constant solid flow rate of about 18 tph this gives a SLR of about 24 - 25. I am sure you can redo the sums according to the number of cycles / hr and get actual tph and also decide for yourself is it lean or dense phase. ■

Yes I did mean you. Please forgive my dreadful spelling.

But if you're confused what hope for the rest of us? ■

Dear Mr Mantoo,john,

I am sure that different people understand there own definition of dense- and lean phase conveying.

And you are absolutely right, that, if the defintion is given, each time the subject is discussed, the physics should be clear.

In that sense, I must admit that "confusion" might be a too big word.

But, what is the meaning of of a physical property if we cannot decribe it uniformly.

Please read my thread :

Dilute or Dense Phase Conveying ? of 22nd November 2005

again and you will understand that I feel that the subject is not really significant for us.

By the way, you have the airflow of the system, which I could not find.

What did I miss?

Also I do enjoy straight forward and friendly discussions, so feel free to challange the forum members.

Jonh, thank you for your your nice words, but as long as we are sharing our "confusions" , we do not need hope. (I hope)

Watch the world champions soccer. ■

Dear Mr Teus, Indeed you have missed air flow rate it is given in the last line (the average using volumes of one transportation:25m^3) since it is 1.5 m^3 vessel it cant be solids . So has to be air flow rate and time is also given as 140 sec! Easy to calculate.

As far as importance of the phases is concerned I will tend to disagree with you on this one. I think it is very important to know the boundary’s between the both especially for system design purposes.

Last but not least I don’t think people challenge others on these forums its just individual opinions expressed and everyone doesn’t have to agree with them either. ■

Particle size is 457 mm ???? it is too bid for your pipe size which is 152 mm. The data is still dodgy !!! ■

25 cubic metres of air in 140 s equates to about 0.18 m3/s. In a 152 mm bore pipeline this equates to a velocity of about 10 m/s at the end of the pipeline (atmos pressure) and about 2.5 m/s at the material feed point (if this is at 3 bar gauge). This is certainly low velocity conveying, but it is not necessarily dense phase conveying.

Mantoo has correctly evaluated the solids loading ratio as about 25. Now, the equivalent length of the pipeline (taking bends and vertical lift into account, along with the horizontal) will be about 100 m and with a pressure drop of 3 bar the pressure gradient available will be about 30 mbar/m. Any average powdered material, such as cement and fly ash, would be conveyed at a solids loading ratio of about 150 through this pipeline under these conditions and so I do not think that this is dense phase conveying in the normal sense of the term.

I suspect, therefore, that the material is granular, which can not be conveyed in dense phase in such a system even with a pressure drop of 3 bar, and that the material in the blow tank is simply being conveyed as a single plug. ■

Dear JimLee,

Still some questions :

As already noticed by Mr Mantoo, the particle size.

A ball particle alone would weigh approx. 92 kg.

I need the exact particle size, to calculate the floating velocity.

Convey air volume 25 m3.

Is this the volume of air per minute, or the volume of air that is used during the unloading time of the blowtank

I assume that this is free delivered air m3 at 0 degrC and 1 bar(absolute)

Is the unloading time of one blow tank to be taken as 140 sec or 200 sec, or should I take the average ?

The bulk density should be 491 kg/m3 (0.491 kg/m3 seems far too low)

If you can clarify these questions, then I can, together with the other data you supplied, try to calculate a “Zenz diagram” as I did before in another thread.

The calculation path will then be :

Estimate the floating velocity of the particles.

Calculate the material resistance factor of the existing installation with the performance data.

Then run the calculation program for a range of airflows, maintaining the same performance.

The resulting pressure drops divided by the conveying length give the pressure drop per meter.

The lowest point in the curve “pressure drop/meter= function (airflow)” indicates the boundary between dense phase and lean phase conveying.

Left of the lowest point is dense phase and right of the lowest point is lean or dilute phase)

Loading ratios etc. are also calculated, so that other definitions of the conveying phase can be considered.

Something for me to do during a boring television program.

hear from you ■