Pick up velocity

Posted in: , on 19. Oct. 2007 - 20:11

Good afternoon,

My name is Jorge Velsquez and I am an electrical engineer working for a consultant firm that offers energy management studies to different types of industries.

In this particular case I am currently working in a industry that proceses corn, they have two blowers (one with an induction motor of 60 HP and the other with one of 75HP) to move the corn to five different crushing banks, and they also have two blowers to transport the final product, wich is corn starch, the first blower has a 60 HP induction motor and the second has a 75 HP).

I am trying to reduce the power consumption of the four motors by reducing the primitive diameter of the motor's pulley, by doing that it is expected to reduce the blower's speed, and by reducing the blower's speed reduce the power consumption

(by the third affinity law for pumps and fans).

I am aware that if I reduce the fan's speed it decrease the suction of product, but I am only proposing to reduce 100 rpm in each blower, and furthermore I have found some fugues in the system.

I wonder if it is plausible to make this changes to the blowers without any drastic changes in the system?

Thank for the help.

Re: Pick Up Velocity

Posted on 20. Oct. 2007 - 09:39

Dear Jorge,

Your installations for corn and corn starch are vacuum systems and therefore I assume that the vacuum pumps are positive displacement blowers.

For this type of air mover the third affinity law is not valid.

(air volume is proportional to the rpm and the power is proportional to air volume * pressure drop)

The volumetric efficiency of a positive displacement blower decreases at lower rpm.

Energy gain by decreasing blower rpm might cause extra energy loss in the pneumatic conveying system as the velocity decreases and thereby the corn has to be maintained in suspension for a longer period of time.(not the only influence)

Whether you can reduce the blower rpm depends on the actual velocities in the pipe and how close these are compared to the suspension velocities of the corn.

calculating the existing system (using field data) and recalculating the modified installation, will show you your options.

best regards



Re: Pick Up Velocity

Posted on 20. Oct. 2007 - 05:39

Dear Teus, thanks for the help, but I am pretty sure that they have centrifugal blowers for this particular application.

Re: Pick Up Velocity

Posted on 20. Oct. 2007 - 06:10

Dear Jorge,

In case the air mover is a centrifugal fan, then the third affinity law is valid.

The remarks concerning the pneumatic conveying regime are still valid.

In case of centrifugal fans, it is even more advisable to be carefull,

because the air volume - pressure curve is of great influence on the stability of the pneumatic conveying.

take care



Re: Pick Up Velocity

Posted on 20. Oct. 2007 - 08:19

Dear Teus,

Thanks again for your help, I will take that in consideration.