fluidized bed

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A mixture of fine particles of a solid (such as a fuel) and a pressurized fluid, used especially in power plants and chemical reactors.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun An industrial unit process in which a quantity of a solid particulate substance is caused to float in a stream of a fluid (usually air or other gas) in order to create conditions in which many chemical, combustion and drying reactions take place efficiently.
• noun A reactor vessel or other piece of equipment in which a substance is maintained in the fluidized state. In this context, often used attributively.