stick to truly vertical and horizontal lines if you can...inclines between 20 and 80 degrees to horizontal will require more air to avoid deposition and recirculation.

also, keep number of bends as low as possible.

inclining downwards should be OK for relatively short runs.

wypych@uow.edu.au ■

previous reply is right on and correct in every respect --all I would add is that if you do decide to have a downward angle, the elbow at the bottom can see some fairly high loadings and should be braced and supported accordingly or you may have a structural failure of the elbow connection. ■

Dear friends

I tried out sloped lines, 13, 30 and 45 degress going up, we were to build a large hot pneumatic conveying facility for sponge iron at 800 degrees C. 200 tons per hr with hidrogen and Co as carrier gas.

We had of course read abouth the pittsburgh university impresive results with sloped lines , a real high tech research work.

So we were not even thinking of using sloped lines. But top management wanted to save money (they are the ones that have the money anyway) so they made us try this out, The conveyors are at 13 degrees o we could in theory use the same structure.

The sloped lines settled some of the product in the bottom and recirculated to an extent , also dunes started forming in the long run and the line started chugging.

We needed to increase the dilution , use les solid to gas ratio, less phase density.

So you can make it work, but you will pay for is with wear in the bottom of the pipeline and more gas thwt means more compressor etc.

Also you can find your line making solid flow noises long after you ended the solids feed.

If you can, get away from sloped lines .

Marco ■

Dear Mr. Graybeard,

According to our experiance it's no good to convey sloped up. It's advisable to convey vertical up and then transfering horizontal.

Please visite www.intec-kohler.ch

Greetings from switzerland Peter Kohler ■

The answer to the situation presented involves several issues.

1. Can it be done? Yes, I have seen it done many times. Typically, it

may be done over very short runs (<20') immediately following a "Y"

diverter or simply to avoid an obstruction.

2. Is it preferred? Absolutely not, it is a very inefficient way to

convey material. The direction of the conveying force is on a "diagonal"

to the surface of the material trying to fight gravity pulling directly

downward. It is recommended to go vertical or horizontal because your

forces are directly "under" or "behind" the material providing a much more

efficient lifting/conveying force on the product against gravity. The

result of inclined conveying is that material tends to want to settle out

of the airstream and ride on the bottom of the convey line. With dilute

phase it is not as critical because the required velocities are very high

in order to suspend the material (salutation velocity) anyway, however, the

required suspension velocity will be higher when conveying on a diagonal.

Inefficiencies = More air = More $$. In addition, the density of the

material is also a critical factor. If the product is very light (i.e. saw

dust) the amount of air required to suspend the material is minimal

relative to a heavier product like sand. Therefore, the amount of air

required to overcome conveying on a diagonal may not be that significant if

the product is light. Diagonal conveying is just less efficient.

3. Fittings. Custom angled fittings would be more expensive. Pipe is

very easily supported off of existing columns and equipment with off the

shelf fittings. On a diagonal the pipe would need to be

suspended/supported in space.

I hope this answers your question. ■

The pneumatic conveying course given in 1994 by the Continuous education center in New Brunswick (I believe) . Covers the issue extensively. the data was presented by professor Jorge Klinzing from Pittsburgh University .

Then Paul Solt presented Fuller`s findings in one of the Powder shows conferences in Chicago.

Mohlman`s Phd tesis from the university of Wolongong in South Africa , "Pneumatic Conveying of Large Rck Prticles" covers some aspects of slope conveying (they were conveying inside a mine , they had no choice but to follow the sloped floor).

I hope this helps .

If you need more references I can look in my library .

Consider the rolling vs lifting again.

when you roll you have the polar momentum of inertia , and the friction, the centrifugall force will act as an added gravitational force if your particle is rownd , like mine , you will hear them rolling at the bottom . They come out of supension. packing at the bottom of the pipe,

By the way there is a Russian document that covers the theoretical free body momentum exchange fron impact an bouncing in pneumatic conveying, then it goes to find adimentional numbers to scale up wall friction . Intersting though I could never do anything with that .

Mohlman`s document is easy to read and practicall to use , the results are summarized in Klinzing Marcus Risk and Lelung`s book.

a good mathematical approach to pressure drop in dilute phase conveying lines you can find in W.C. Yang`s article on pressure drop in a 4 inch pneumatic transport loop.

Yang is the father of all the other guys in dilute phase conveying .

the reading is worth your time.

regards

marco ■

Good luck with your analysis and if we can be of assistance, feel free to contact us. ■