If you don't care about global warming you can just about do anything - all you need is more energy.

Wood chip is a porous media. At the first bend, or flow obstruction it will concertina into a porus plug. You will get your air to move, but the product will just sit there and laugh.

Sgt John Rozentals

CEO Bionic Research Institute

www.latviantourists.com.au ■

Global warming is just wonderful here - at the moment.

High velocity dilute phase conveying is probably your best option with wood chips. If anyone offers you a low velocity dense phase conveying system you will need some kind of proof that the system will convey your particular material, and any possible change in 'grades', reliably.

Wood can be a little abrasive and so bear this in mind when specifying pipeline, and particularly bends, for the conveying system. ■

Usually, fans conveying systems are use with large diameter lines and very high air to material ratios,

Because of the tendency for wood chips to bind very tightly together, larger diameter pipes are used and small openings and transitions must be avoided.

Regards ■

What do you mean by "large diameter"?

Does that mean like large diameter equals lower velocity?

Or large diameter equals lots more air, and higher power consumption?

Or does it mean if you try to use DN 25 pipe you must have your head examined. You need to use a pipe "large enough" to get your hand into it in case you need to scrape out all the accumulated sawdust plugging up the bend?

Duct should be sized to give an air velocity of say 20 - 25 m/s. Anything less than that will give you "dirty ducts" - which means the product will settle on the bottom of the duct until it blocks up enough of the pipe to get to transportable velocity.

Bends distort the velocity profile. They create dead spots, which allow product to settle in the "slow velocity" zones of the duct profile. There is a whole bunch of knowledge that is needed to select the right kind of bends.

Dilute phase means that if you use lots of air, and little product, you will do OK. The more product you put in, the higher your chances of a blockage. Once the system is in, you must play with it to find out just how much product it can safely carry in the as-constructed state (as opposed to the theoretical calculated state) without causing a plant shutdown due to blockages.

Regards - John Rozentals ■

In conventional pneumatic conveying, there are"rules of thumb"; for example, the pipe diameter should be a minimum of (4) times the largest particle size, etc. Those rules all go out the window with fan systems.

In fan conveying systems, we talk about diameters in the 10", 12" 14" and beyond. There are systems operating in 20" diameter ducts and even larger.

The large diameter is necessary to keep the pressure differential low enough for a fan to be used as the air mover. Air to material ratios are far beyond what one would expect for routine dilute phase systems using PD blowers ■