Dear Daniel,

To determine, whether 50 m/sec is the appropriate velocity, it is essential to know the floating velocity of the particles.

The floating velocity can be calculated from the material density and the perticle size or measured.

The conveying velocity should be approx. 4-5 times the floating velocity.

In your case the floating velocity should be approx. 10 m/sec.

Judging from the (bulk or material ?) density you state, I assume the floating velocity (and thereby the required conveying velocity) will be less.

As the velocity is the key factor for the energy dissipation in collisions, the pneumatic conveying design-velocity should be as low as possible.

(see also the attachement to the thread "Dilute or Dense Phase Conveying ? "

The second parameter is of course the friabilty of the particles.

An indication can be found if you drop the particles from a certain height in free fall. If the particles who have reached their terminal velocity already break at the impact on the floor, than pneumatic conveying is not the best way of transporting this product.

best regards. ■

Dear Daniel,

Assume :

bulk density = 650 kg/m3

material density = 1000 kg/m3

average particle size = 0.003 m (3mm)

dragfactor = 0.05

air density at atmospheric conditions = 1.2 kg/m3

Then the floating velocity = SQRT(4/3 * 0.003/0.05 * 1000/1.2) = 8 m/sec

The biomass is not sticky, so that there are no bigger lumps formed.

Then :

As this product is not fluidizable and consists of large particle compared to the thickness of the boundary layer of the air flow, an average air velocity at atmospheric conditions of approx. 2.5*8 = 20 m/sec should be sufficient.

The required air velocity at the beginning of the pipeline at a conveying pressure of , f.i. 2 bar(o) should be : 8 * 1/sqrt(3) * 2.5 = 11.5 m/sec at 3 bar(abs).

This equals to 11.5 * 3 = 34.5 m/sec at atmospheric conditions at the end of the pipeline.using the same pipeline diameter.

(This is why stepped pipelines are favorable)

Compressor volume = approx. 16 m3/min.

I do not think that biomass is a very abrasive product. Wear will be minimal, even with higher velocities.

Further, I expect the capacity on a 4” pipeline of 200 m long will be rather low (In the order of 5 tons/hr or even less)

Consult people who have experience in conveying your type of biomass, to estimate a more precise capacity at a given pressure.

Success ■

Daniel,

You have not stated the abrasive nature of the solids you are conveying but if they are abrasive, you should be using dense phase instead of dilute phase.

Your present velocity of 50 meters/sec means that you are conveying in dilute phase. For your line diameter, this velocity is very high even for non-abrasive solids. You should be using a velocity of about 15 to 20 meters/sec. Lot of work has been done to determine the effect of pipe line wear as a function of conveying velocity. This work shows an exponential relationship between wear and velocity, especially at high velocities.

If you are conveying non-abrasive solids, you should reduce the conveying velocity to about 20 meters/sec.

For mildly abrasive solids, you can use dilute phase provided you use special wear-resistant bends and abrasion-resistant pipeline material such as stainless steel instead of aluminum.

Regards,

Amrit T. Agarwal

Consulting Engineer

Pneumatic Conveying Consulting

Email: polypcc@aol.com

Ph and Fax: 304 346 5125 ■