Patent GB-704765-A (GB)
Title: Improvements in or relating to methods of and means for controlling the density of thickened pulps from settling tanks
IPC: B03B13/00
Filed: 1950-12-21
Abstract: 704,765. Pulp density control means. RIDLEY, F. F. March 20, 1952 [Dec. 21, 1950], No. 23151/50. Class 82 (2) [Also in Group XXXV] Density control means for thickened pulps, such as the suspension used in the sink and float separation of minerals, or in the mineral pulps fed to froth flotation apparatus, operates on the discharge of a thickener of the inverted cone or rake types of thickener. The control means comprises a weighing vessel for receiving discharged pulp into which vessel a continuous flow of pulp is maintained as long as the pulp density is above the predetermined minimum value. When the pulp falls below this value the weighirig vessel rises under the influence of its counter-weight and breaks an electric contact to actuate a switch which cuts off the mechanism controlling the continuous discharge, and connects it in series with a time-switch which allows discharge to take place at predetermined intervals to allow the pulp in the thickener to be sampled in the weighing vessel. When the pulp is again above the minimum density, the vessel falls, displacing the counter-weight and making the electric contact actuate the switch which re-makes the continuous discharge circuit and cuts out the time-switch which resets to zero. The unsatisfactory pulp can be diverted back to the thickener by mechanism also controlled by the switch. A supply of pulp may be bled from the associated separating equipment to restore the gravity of the pulp. By means of a similar weighing vessel, which controls a circuit injecting water into the thickener, the maximum density of the pulp can be regulated. As shown, the pulp is discharged from the thickener 1 by means of a ball valve 2 which is oscillated by cam 27 acting through the lever and linkage mechanism shown. The fulcrum of the lever is carried by a rod 24 displaceable electrically from the position shown, in which the discharge operates, to the dotted line position in which the oscillating motion is lost and the ball valve remains seated. This mechanism constitutes the means by which the discharge is changed from continuous to periodic and vice versa and is energized by the main switch. The discharged pulp flows into the weighing vessel 32 and the excess overflows the top and part is evacuated through the hole 37, to prevent an accumulation of solids building up in the vessel. The vessel is carried by beam 34 and the electric contact is carried at 45. The circuit controlled by the contact operates a switch (not shown) to cut in the time switch when the pulp density drops and causes the vessel to rise. A diverter 52 may be actuated by the switch to divert the flow of pulp 53 (the return to the pulp system) to 57 which latter routes the pulp through to the thickener via a vessel into which bleed from the pulp system (from line 61) may be fed to increase the gravity before the pulp returns via pump 60 to the thickener. Similar diverting means 62 controls the bleed, either directing it to the vessel 59 or to the pulp system along line 54. The diverter means are controlled by the main switch and may be cut out manually. In a modification (not shown), only part of the thickener discharge passes through the weighing vessel which is continuously supplied with a circulation of pulp irrespective of the position of the discharge valve.