Dear Glenn,

First of all, the figure is missing.

Pneumatic conveying of hulled rice is mostly damaging the rice by collisions against each other and the wall (especially in bends).

Therefore, the absolute minimum velocity must be maintained under all circumstances.

A centrifugal fan has an operating curve, whereby the air flow changes significantly with the pressure and therefore the velocity will change also significantly.

A low pressure drop design will keep the air velocity within the desired range.

(which is still not a guarantee for deterioration free conveying)

A venturi is a bad choice in this respect, as a venturi is based on giving the air a high impulse (high velocity), which is converted in rice velocity and recovered pressure for conveying.

500 kg/hr is not much.

Looking at your calculation results, the distance cannot be long.

Why not opt for a mechanical conveyor?

Have a nice day ■

Dear Glenn,

1)There should be a filter between the silo intake and silo exhaust. Otherwise the generated dust is blown into the environment.

2)A venturi/eductor as feeder could be possible, but with a higher pressure than a centrifugal fan can generate.

A venturi cools down, whereby condensation can take place, which is not a good thing when you want to dry a material. A rotary valve might be better.

How is your drying process working when the ambient RH is close to 100%.

May be the rice is then getting wetter.

Success ■

Dear Glenn,

I certainly would not use a centrifugal fan as conveying air compressor.

The air flow delivery of the centrifugal fan changes too much with the pressure.

Using a lobe blower of 0.12 m3/sec (7 m3/min), I calculate a conveying pressure of approx. 700 mmWC.

The air velocity is then between 17 m/sec to 20 m/sec, and the rice velocity is then 5.2 m/sec to 5 m/sec.

However, the first bend (horizontal to vertical) slows down the rice to a very low velocity (approx. 0.04 m/sec), close to choking in the bend.

This is caused by the assumption that in the bend, air and material is 100% separated and that the rice slides through the bend by the impulse at entering the bend.

In a bend from horizontal to vertical, the friction along the outer wall is increased by the gravity component and the rice is decelerated by the other gravity component.

Gravity is retarding the rice in 2 ways, which occurs only in a bend from horizontal to vertical.

To guarantee choking free conveying, the air flow should be approx. 0.29 m3/sec at approx. 750 mmWC.

However, the air velocity has then increased to approx. 44 m/sec and the rice velocity has then increased to approx. 9.5 m/sec. (Normal velocities in grain unloaders)

Still the problem of RH and the temperature of the conveying air (70 degr) of the conveying air and the resulting drying effect is not assessed.

Consult a drying specialist

Take care ■

Dear Glenn,

Forgot to mention:

This will cause static electricity and probably sparks when the electric charges are equalized.

The application of a rotary blow by valve requires a somewhat bigger conveying air compressor, to compensate for the rotary lock air leakage.

Have a nice day ■

Dear Glenn,

My calculation is just a rough estimate and the first bend problem might cause the design to be incorrect.

I still strongly advise to consult a manufacturer of such drying systems.

Do not take the risk yourself.

Be careful, ■

Dear Glenn,

The value of K (friction multiplier) is related to the used calculation algorithm and is derived from field measurements, which are

re-calculated by the same algorithm.

Furthermore, the friction multiplier factor K is a function of the Solid Loading Ratio and the Reynolds number.

The supplier of your software should know the K factor or you have to determine the K factor yourself by experiments with the same material that you want to design for.

As the K value is depending on the Re-number, scaling is not an option.

Be careful, ■