Mechnical couple two motors to one pc equipment 1

[rad54]

We have an application that has been descussed electrically, but I would like some input and possible locations where similar installations are in use.
We are planning to increase the HP of a boiler ID fan from 800 to 1600 HP by adding an additional 800 on the opposite end of the fan shaft. The shaft is already extended and keyed for alternate drive. We have questioned the fan manufacture and obtained max speed and hp that the shaft and rotor can take. We have also ruled out going to one 1600 HP motor for various reasons. This will be a direct coupled application and the fans will be run on VFD.
I have concern for shaft growth from heat(425 F) and moving the second motor off of elec center as well as the proper coupling and bearings.
Anyone have experience, good or bad and recommendations as to ways this can work reliably.

 

[byrdj]

If each component has their own thrust, the coupling can allow for thermal axial growth. the coupling could either be a a hub/spline gear (amerigear)or a flex plate (koppers).

This type of coupling allowing for idividual rotor growth is common for turbine/pump. i've also seen with motor/generator through fluid coupling. A coupling with spool piece would also help with elevation thermal growth. that is a small alignment offset when cold, and then going fair when operating.

 

[byrdj]

For a 10 ft fan shaft, a 400F rise, the axial growth expect to be 3/8". Note an elevation change of 0.005" between fan and motor would cause vibration and journal bearing problems. Thus if the fan bearings are not supported on centerline, there will be an elevation change.

 

[quark]

How are you taking care that the two motors run at exactly same speed? You can have the motors to run at same frequency by VFDs, but what about the internal slip?

 

[ApC2Kp]

To rad54,
Consult the representative in your area for "SSS Clutch" by way of Google search. The homepage seems to be unavailable at this time. Their products have been used in marine drive and stationary systems. We had considered the use of the SSS clutch for a fan with turbine and motor drivers.

 

[unclesyd]

Here is the website mentioned above.

http://www.sssclutch.com/index.htm

 

[JJPellin]

We have a couple of trains that are of this configuration. The main difference is that both of ours have a motor drive on one side and a turbine drive on the other. We have SSS clutches on both sides so that the individual drivers can be shut down with the fan continuing to run on the other driver. The older train is in ID service at 650 °F. The shaft growth for that fan is about 0.250". It originally had a greased gear coupling (Koppers)on the side with the floating fan bearing. An inexperienced engineer decided to upgrade that coupling to a non-lubricated shim-pack coupling but did not compensate for shaft growth. We were lucky to find the problem before we had a catastrophic failure. When we added another similar fan train, we made sure it came with a special greased gear coupling designed for high axial displacement. That second fan has shaft growth approaching 0.500". A shim pack coupling can be installed with pre-stretch based on calculated growth if this is within the design axial deflection limit specified by the coupling manufacturer. But I would not recommend excessive pre-stretch. We get by with our old fan by pre-stretching the coupling and starting up on the other driver so the stretched coupling won't see torque until it grows into position.