2 replies to this topic

[akslzf]

Hi

I have a rotating vacuum filter drum in slurry service. Approx filter drum dia is 2m, length 2m and weight 3Tons. Drum is symmetrical & rotates on journal bearings fed with lub oil, at 1-5 rpm. Slurry SG is 1 to 1.5. Drum submergence is 10% to just below shaft OD of 200mm, which is 100%, depending on slurry availability etc. Process is continuous. At low submergence, due to low buoyancy, drum vibrates & drive torque increases.

Please share your ideas on how to calculate the min & max load on the bearings & the corresponding torque, so as to decide an optimum band of drum speed & submergence.

[JLMONTREAL]

I remember that the drum should be able to run stably at zero submergence. If not, the drum may run eccentrically. Then, I think the bearing may be too loose, or gravity center may be offset for some reason.

[akslzf]

If the filter is started with 0% level, the drum shudders violently. As buoyancy lifts the drum, the torque & vibration drop. Normal operation torque is 20% of driver max torque & normal filter level is 60-75%. At levels below 25%, the torque starts climbing steeply to as high as 50-60% of driver torque. Alarm is set at 50% torque. And along with torque, the drum vibration also shoots up as level drops, which is understandable.

Lubrication, journal surface condition are all fine. LO pressure has been jacked up to 2.5 barG from 2. LO check valves are perfect & the LO pressure is measured just before it enters the bearing. The bearings & journals axes are well aligned & clearances are within what they should be.

I need help on how to calculate buoyancy force based on drum projected area, slurry SG... and the resultant load on the bearings & the drive torque. Also want to know the effect of SG on the buoyancy & want to work out, at what speed & level the stick-slip movement (shuddering) of the drum would theoritically start. I'll then iterate the level & speed to minimise the torque & thus the vibration.

Who's going to be my saviour?