Tank used to form acidic bisulfate-active agent in digesting wood, from ingredients such as sulfur dioxide, lime, manganese, and ammonia.

A vertical, cylindrical pressure vessel in which two fluids contact each other and one fluid absorbs certain constituents from the other. An example is the contactor in a gas sweetening system, which uses amine to absorb hydrogen sulphide and carbon dioxide from raw natural gas.

A tower or column, which effects contact between a rising gas and a falling liquid, so that part of the gas may be taken up by the liquid.