Primary sludge thickener - how big is the risk that the rabble rake gets stuck? Mitigation?

[MartinLe]

The manufacturer of rabble rakes for static primary sludge thickeners has concerns that the rake might get stuck if it's not moving for a longer time (ay power failure). How likely is this actually? How thick does primary sludge get, when thickened statically?

The circular thickeners in question are 18m diameter, 8m depth between water level and lowest point in funnel.
The Rake is equipped with a torque warning at 35kNm and a trip at 50kNm.

input into the thickener is PS at 2-3% TS. The thickeners are also used for stacking. Target TS is 5-10%

There's also the question of what to if this happens: My only ideas are getting a mobile mixer (which is awkward to use, if they even have one on site) or try to get sludge into motion with a firehoses. Any other options?

(The other concern is of course gas generation but I believe to have this covered. Or rather not covered)

 

[bimr]

One can use a rake lifting device should the rake encounter high torque loading.

Having the rack stuck is not common.

Is this a new application or an existing installation? What type of wastewater are you processing?