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any one of various apparatus designed to wash gases with liquids in order to purify the gas or extract one or several components; the term also applies to drum machines used to wash minerals. Scrubbers are also widely used in collecting the products of coking processes and in removing dust from industrial gases (seeBY-PRODUCT COKE CHEMISTRY and GAS PURIFICATION), in humidifying and cooling gases, and in various processes in chemical engineering.
Scrubbers used to wash minerals up to 250–300 mm in size are cylindrical or conical drums. Material loaded into the scrubber is transported within the drum by internal augers or blades and is washed by water fed into the drum; any admixtures of clay are thus washed away. Flow-through scrubbers are used for materials that are relatively easy to wash. In such scrubbers the materials and the water move in the same direction, from the feed end to the unloading end, and are discharged together. Counterflow scrubbers are used for difficult-to-wash materials. In such scrubbers the water is fed from the unloading end and flows in a direction opposite to the motion of the material being washed.
Scrubbers may be designed for washing only or they may combine washing and sieving of the material. In the latter case, a drum with one end sealed is fitted with a conical, perforated fixture that extracts the water and fine material to be removed. A blade mill is a special type of scrubber, in which a rotating shaft with blades passes through the center of the drum.
Scrubbers have the following specifications: length, 3–10 m, diameter, 1.5–4 m; and water consumption, 3–6 m3/ton. The washing time depends on the degree of contamination and ranges from 2 to 12 min; the output is 25 to 200 tons.