This was posted on the Steel Mill Facebooks group and it is a good explanation and use of a Dorr thickener. The explanation an photos by Scott Woods.
A question about the purpose of a Dorr thickener. Many industries use a circular steel tank called a thickener or a clarifier or a circular collector. Dorr is one manufacturer. Another, that I prefer, is the Walker Process, a subsidiary of Chicago Bridge and Iron where I worked for 34 years.
These tanks are used in many industries: mining, pulp and paper, sewage plants, sugar mills and steel mills. The purpose is to separate some suspended solid from some liquid (usually water). I was PM on 2 collectors in Homestead in 1981. These removed mill scale from rolling mill cooling water. I think collectors are also used to clean blast furnace/dust precipitator/baghouse cooling water.
The principle is quite simple, as shown below:
Dirty water enters the top center of the tank thru the influent pile. A circular steel stilling basin prevents the solids from heading in all directions in the tank. The solids begin to settle to the bottom. Some processes add a chemical to help the particles stick together (a flocculating agent).
There are rotating scraper arms or rakes which scrap the settled material down the sloping bottom to a sludge basin in the center of the tank. A drive motor on the bridge and a vertical drive shaft rotates the rakes. The sludge is drawn out thru the sludge line for further processing ( can be reused or disposed of). The "clean" water on top of the tank flows into weir troughs, goes out thru the effluent line, and is reused or discharged into the river.
Some processes use a skimmer arm, mounted on top of the rakes, to skim foam off the surface of the water into a scum box for disposal.
These pictures show the process along with my models. The treatment plant in my mill uses 2 Walker Process products: a circular collector and a Claricone. The Claricone serves a similar purpose but includes some patented processes.
