Traction-driven composite sludge raking mechanism for sedimentation tanks

Claim 1

In a continuously operating large diameter settling tank having means for supplying feed slurry to the tank, sediment discharge means at the foot of a center pier, and overflow means for supernatant liquid, the combination which comprises a center pier, a vertical cage structure surrounding said pier, and supported upon said pier by a thrust bearing at the top thereof for rotation about a vertical axis, a main drive arm of girder type construction having an upper and a lower truss and its inner end rigidly connected to said cage structure to rotate therewith, and having, its outer end supported by a track for travel along the periphery of the tank, means for propelling the outer end of said drive arm along said track, for rotation together with said cage structure, a bladed rake arm extending from the lower end of said cage structure, and by its length defining the radius and extent of an inner bottom zone of sedimentation sludge accumulation around said pier, surrounded by an outer annular bottom sedimentation zone, with the outer end portion of said drive arm extending a significant distance beyond said inner zone and radially across said outer zone, hinge means connecting the inner end of said bladed rake arm to the lower end of said cage structure, constructed and arranged so as to allow said rake arm to swing from a predetermined lowermost normal raking position rearwardly upwardly along a predetermined path, while preventing said rake arm from rotating about its own longitudinal axis, a sloping guy wire connecting said rake arm with the upper end portion of said cage structure, and normally extending in a substantially vertical plane, said guy wire being effective to support the rake arm in said lowermost position relative to the tank bottom under normal sludge raking load conditions, downwardly and rearwardly sloping draft means having its lower end connected to said rake arm, and its upper end connected to said drive arm by a drive connection whereby said drive arm and said rake arm are rotated together, said rake arm during such rotation being adapted to move the sludge in said inner zone towards said sludge discharge means, and to yield rearwardly upwardly along said predetermined path when overriding excessive sediment accumulation in said inner zone while resolving a sludge overload condition therein during continued rotation of the drive arm and rake structure, and outer complementary raking means connected to said outer end portion of the drive arm, and constructed and arranged for moving relatively light sedimentation sludge load from said outer annular zone to said inner zone of sedimentation sludge accumulation.