I thought everyone was used metric unit now. Took me more time to convert the units, if my conversions are not wrong you are going to transfer 9 tph in a 8 – 10 “ line using 6000 m3/ hr of air. I think your blower must be using about 110 kw at these conditions. To me it looks like a dust extraction system rather a pneumatic conveying system. Any way at these conditions you have a solid loading ratio of about 1.26 which is very low. Even though stepping down is not recommended it would work. With additional pressure drop and an increase of 20m/s in velocity,

Is there any reason for using 8” line? cause a 4” line with 800m3/hr blower can do the duty. Or you can reduce the blower speed to get reasonable exit velocities in 8” line and much lower pressure drops. ■

Dear RBJ324,

I second the call of Mr Mantoo for going metric.

Specially in physics (like pneumatic conveying)

As I understand, you have a pneumatic conveying system with an 8” pipeline working satisfactorily, although at an extreme low loading ratio. (As Mr Mantoo already noticed).

When you tie in with a 10”pipeline at the beginning of the system, the air velocity in the 10”part will be dropping from approx. 36 m/sec in the 8”configuration to 23 m/sec. (providing the pressure of 0.3 bar(o) does not change too much).

Whether this velocity drop will cause a problem depends on the suspension velocity of of your product particles (380 micron, product density ??)

The velocity in the remaining 8” pipeline depends on the pressuredrop in the 10”part and the eventually switched off part of the 8” pipeline part.

A blower of 99 m3/min at .0 bar(o) (9”Hg) will use approx. 68 kW.

Your energy consumption is then 68/9 = 7.5 kWh/ton

May be you should investigate some possible savings there in energy and wear.

Let us know ■

Dear Mr Teus

I think there is a slight mistake in the exit velocity you have stated. At 6000 m3/hr velocity at atmospheric conditions will be in 36 m/s in 10” since the pipe is stepped down to 8” the velocity will increase to 53 m/s at the exit not decrease to 23 m/s as stated by you. Maximum inlet velocities in 8” line @ 0.3barg would be around 40 m/s.

I think you have assumed it was a normal step up system!

Regards ■

Dear Mr Mantoo,

Thank you for your kind (and sharp) attention.

I tried to describe the difference between a fully 8”system and a 10”to 8”system, at an intake pressure of 0.3 bar(o) # 1.3 bar(a).

As my starting figures were not exactly the same as yours (which I should have done), the resulting figures came out also a little bit different.

I will try again.

3500 cfm = 1.651667 m3/sec (atmospheric) = 1.270513 m3/sec (1.3 bar(a))

A8” = 0.031416 m2

A10”= 0.049087 m2

8” system :

v-intake at 0.3 bar(o) = 1.2705 / 0.031416 = 40.4 m/sec

v-intake at atm = 1.65167 / 0.031416 = 52.6 m/sec

v-outlet 8”at atm. = 1.65167 / 0.031416 = 52.6 m/sec

10”to 8” system :

v-intake at 0.3 bar(o) = 1.2705 / 0.049087 = 25.9 m/sec

v-intake at atm = 1.65167 / 0.049087 = 33.1 m/sec

v-outlet 8”at atm. = 1.65167 / 0.031416 = 52.6 m/sec

By changing the inlet pipe diameter from 8”to 10”, the inlet velocity at 0.3 bar(o) decreases from 40.4 m/sec to 25.9 m/sec.

The end velocity stays the same at 52.6 m/sec.

All for now ■

Dear Friend.

You might need a wear piece one that takes the back step.

I call it a reacelerator piece , but you can call it what you want.

This piece should be built from a hard wear resisting metal , ceramic or cement what suits your supply chain.

Try it out in a test jig and see what suits you better, wear in the transition can be intense and you should tconsider this in your design , a 12 to 25 inches long MB8 cast transition piece has been used in other applications and has worked well in hot pneumatic conveying . You might try NIHARD or ceramics . ■