|A thickener is a machine that de-waters slurry, separating the liquid from the solids. The solids' particle size range in thickeners is generally from 0.5 mm to a few microns. The finer the particle size, the slower settling and compaction rate. Actually, thickeners simply concentrate the solids, achieving underflow solids densities from 20% solids to 50% solids. Typical thickener feeds range from 2% solids to 10% solids (by weight).
Feed enters the thickener near the center, below the water level. Gravitational acceleration causes the solids to fall towards the bottom of the thickener. The actual surface area of a thickener will determine the capacity for solids, since the solids entering the thickener spread out over the cross sectional area of the thickener, and begin to settle. Thickeners are rated on lbs. of solids per square foot of surface area.
Solids will begin to compress as they settle and they form several zones of compression in a thickener, with the highest compression zone being on the bottom of the thickener. Chemical floculants and coagulents can greatly improve the performance of most thickeners.
The animated graphic at right shows the rotation of the rake mechanism in a thickener. The rakes slowly rotate, with scraper blades on the bottom, pushing solids in the thickener towards the cone shaped discharge located in the center of the thickener. Once the solids enter the cone discharge, they are removed by pumps, pumping the concentrated solids underflow to the next process. The clear water or liquid overflows at the top of the thickener, in a wier, which channels the clear water to the overflow discharge. The overflow is pumped from the thickener.
|Thickener Rakes In Action