Patent EA-004962-B1 (EA)
Title: Method and apparatus for clarifying and/or thickening a slurry
Inventor: NYMAN BROR
IPC: B01D21/01
Filed: 2002-06-19
Abstract: 1. A method for clarifying and/or thickening a solution containing solids, whereby the slurry is fed via a feedwell into a settling space for clarification, from whence the settled solids or underflow is removed via a discharge port in the centre of the settling space and the clarified solution or overflow is removed as an overflow, and where there is a rake in the settling space rotating on its shaft for displacing the underflow from the edges of the space towards the centre, with displacement elements on said rake radially to the tank, wherein the displacement element displacement plates at the same distance from the shaft move the underflow as they rotate from a ring-shaped cross-section towards the centre, characterised in that the displacement capacity of the underflow displacement elements on concentric ring-like cross-sections is basically the same from the edges of the settling space to the central area and the displacement capacity on the innermost concentric ring-like cross-sections of the central area is smaller than on the other cross-sections. 2. A method according to claim 1, characterised in that the underflow displacement occurs using displacement plates attached to the displacement elements, forming an angle of about 30 degrees in relation to the displacement elements and tank radius. 3. A method according to claim 1, characterised in that the central area extending from the rake shaft a distance of 15-30% of the length of the settling space-length rake, has a smaller displacement capacity than the outer ring-like cross-sections. 4. An apparatus for clarifying and/or thickening a solids-containing solution, whereby the apparatus comprises a clarification and/or settling tank (1), which is equipped with a feedwell (2) for the slurry to be settled, discharge ports (9) for the settled solids or underflow in the centre of the settling space, a discharge launder (16) for the clarified solution or overflow, and a rake (10) rotating on its shaft (11), which moves the underflow from the edges of the tank to the centre, where said rake has at least two arms (12) reaching the edge of the tank in a radial direction, characterised in that, in order to keep the underflow displacement capacity constant from the edges of the clarification and/or thickening tank (1) to the centre, there are displacement plates (13) attached to the rake arms (12,17), with a height dependent on the distance of the displacement plate from the rake shaft (11) and the number of rake arms, and the height of the displacement plates (13) in the central area (8), which is ring-like in shape and reaches from the rake shaft (11) outwards for a distance of 15-30% of the length of the long rake arms (12), is kept basically the same. 5. An apparatus according to claim 4, characterised in that the height of the rake arm displacement plates (13) increases from the edge of the tank (7) towards the rake shaft as far as the central area (8). 6. An apparatus according to claim 4, characterised in that the rake is equipped with at least two auxiliary arms (17), the length of which is about half the length of the arms (12) reaching the edge of the tank. 7. An apparatus according to claim 6, characterised in that the height of the rake arm displacement plates (13) increases from the edge of the tank (7) towards the rake shaft as far as the tip of the auxiliary arm (17). 8. An apparatus according to claim 6, characterised in that the height of all the rake arm displacement plates (13) increases from the tip of the auxiliary arms as far as the central area (8). 9. An apparatus according to claim 4, characterised in that the displacement plates (13) are attached to the rake arms (12,17) at an angle of about 30 degrees in relation to the longitudinal direction of the arm and the tank radius. 10. An apparatus according to claim 4, characterised in that the displacement plates (13) are inclined forwards at an angle of 5-25 degrees in relation to the vertical axis. 11. An apparatus according to claim 4, characterised in that each of the displacement plates at the same distance from the rake shaft are the same height.