VFD for non-newtonian mixing 1

[mango1337]

I have a batch mix tank where the fluid undergoes a rheopectic viscosity change (thickens when mixed). The process begins as a Newtonian fluid and undergoes the change after the addition of one chemical. The chemical is metered in fairly slowly, however the viscosity change happens fairly rapidly which increases the load on the motor.

Currently, the motor is controlled by a starter and a button. I want to put a VFD on it for energy savings as well as decreasing wear on the equipment.

All the drives I have looked at have some type of torque compensation and torque control algorithms. Are there any other considerations I need to take into account? Would a certain drive have a superior ability to deal with this increased load?

I have never dealt with this type of application before, and any feedback would be appreciated.

Currently, I am looking at purchasing a WEG CFW700.

 

[itsmoked]

What size motor are you running?

Since you mention 'reduced wear and tear' are you considering something along the lines of constant torque so as the change occurs the drive lowers the speed to keep the torque constant?

Depending on the size I have two W700s I'd like to sell. I can make you a great deal on one.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[mango1337]

I am concerned about the drive slowing the motor down once the load on the system increases due to the viscosity change. From what I have read, it seems that torque control is how this would be accomplished. Does that check out?

The CFW700 has an auto tune routine and I can manually enter torque requirements; if constant torque is what I want, are there any other settings I would need to be concerned with besides basic motor info, accel, deccel etc.?

It's a 25HP motor, I think it's 36A but I would have to look.

 

[itsmoked]

So you want to keep the same speed not the same torque?



I think my WEG700s are 15HP.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[mango1337]

Sorry that wasn't very clear. I need the motor to slow down during the non-Newtonian phase, and I believe this can be accomplished with torque control. At a constant speed, torque increases with viscosity and puts more stress on the mechanical system. It would seem that torque control can alleviate this problem, especially since the CFW700 has PID torque control algorithm. If I am able to achieve a constant torque, the rotational speed would go down as viscosity increases (in theory). I just want to see if my thinking about this is correct, if a VFD will accomplish this and/or if I am overlooking something.

 

[itsmoked]

I believe your assumptions are correct. Using the torque control should do the trick. I don't think the starting issue with a low allowed torque setting will get you since your load starts out low viscosity. You may have to think about restarting under high viscosity but the non-Newtonian aspect works in your favor since as the start occurs the viscosity is at its lowest, gaining with speed.

Do note that the WEG drives are finicky about being sized correctly to the loads. Mine wouldn't do a lot of things, just flat refusing, due to a bad motor size to drive size mismatch. The sensors in the drive are apparently optimized for the rated motor size.

My drives are WEG500 not the WEG700 I thought they were though the 500 series does the same torque control. Oddly the manuals describe it differently.

Mine are:

Current looks a bit ow for you.


Keith Cress
kcress -

http://www.flaminsystems.com

 

[geesamand]

Sorry that wasn't very clear. I need the motor to slow down during the non-Newtonian phase, and I believe this can be accomplished with torque control. At a constant speed, torque increases with viscosity and puts more stress on the mechanical system. It would seem that torque control can alleviate this problem, especially since the CFW700 has PID torque control algorithm. If I am able to achieve a constant torque, the rotational speed would go down as viscosity increases (in theory). I just want to see if my thinking about this is correct, if a VFD will accomplish this and/or if I am overlooking something.

Mechanically speaking you definitely want to keep the torque limited to the full operating torque it has now.

Fortunately viscosity does not drive power draw up as rapidly as reducing RPM lowers power draw, so you will likely only need to reduce speed modestly to keep loads reasonable.

Most mixers for Newtonian / low viscosity fluids rely on recirculation within the vessel to achieve a uniform mix. Mixing shear-thickening material can go very poorly with ordinary mixer designs. The fluid movement will be limited to the area around the impellers. There are impellers designed specifically for Non-Newtonian mixing, and applied properly, can save an order of magnitude on blend time and/or energy costs. If the throughput or energy savings is important, you'll get the most bang/buck by having the entire mixer designed for the shear-thickening condition.