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Fluidization (or fluidisation) is a process similar to liquefaction whereby a granular material is converted from a static solid-like state to a dynamic fluid-like state. This process occurs when a fluid (liquid or gas) is passed up through the granular material.

When a gas flow is introduced through the bottom of a bed of solid particles, it will move upwards through the bed via the empty spaces between the particles. At low gas velocities, aerodynamic drag on each particle is also low, and thus the bed remains in a fixed state. Increasing the velocity, the aerodynamic drag forces will begin to counteract the gravitational forces, causing the bed to expand in volume as the particles move away from each other. Further increasing the velocity, it will reach a critical value at which the upward drag forces will exactly equal the downward gravitational forces, causing the particles to become suspended within the fluid. At this critical value, the bed is said to be fluidized and will exhibit fluidic behavior. By further increasing gas velocity, the bulk density of the bed will continue to decrease, and its fluidization becomes more violent, until the particles no longer form a bed and are “conveyed” upwards by the gas flow.

When fluidized, a bed of solid particles will behave as a fluid, like a liquid or gas. Like water in a bucket: the bed will conform to the volume of the chamber, its surface remaining perpendicular to gravity; objects with a lower density than the bed density will float on its surface, bobbing up and down if pushed downwards, while objects with a higher density sink to the bottom of the bed. The fluidic behavior allows the particles to be transported like a fluid, channeled through pipes, not requiring mechanical transport (e.g. conveyer belt).

A simplified every-day-life example of a gas-solid fluidized bed would be a hot-air popcorn popper. The popcorn kernels, all being fairly uniform in size and shape, are suspended in the hot-air rising from the bottom chamber. Because of the intense mixing of the particles, akin to that of a boiling liquid, this allows for a uniform temperature of the kernels throughout the chamber, minimizing the amount of burnt popcorn. After popping, the now larger popcorn particles encounter increased aerodynamic drag which pushes them out of the chamber and into a bowl.

The process is also key in the formation of a sand volcano and fluid escape structures in sediments and sedimentary rocks.

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 The process is also key in the formation of a [[sand volcano]] and fluid escape structures in [[sediment]]s and [[sedimentary rock]]s.
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-==Applications==
-In 1920s, the Winkler process was developed to gasify coal in a fluidized bed, using oxygen.  It was not commercially successful.
-The first large scale commercial implementation, in the early 1940s, was the [[Fluid catalytic cracking|fluid catalytic cracking (FCC)]] process, which converted heavier [[petroleum]] cuts into [[gasoline]].  Carbon-rich "[[Coke (fuel)|coke]]" deposits on the [[catalyst]] particles and deactivates the catalyst in less than 1 [[second]].  The fluidized catalyst particles are shuttled between the fluidized bed reactor and a fluidized bed burner where the coke deposits are burned off, generating heat for the [[endothermic]] cracking reaction.
-By the 1950s fluidized bed technology was being applied to mineral and metallurgical processes such as drying, [[Calcination|calcining]], and sulfide [[Roasting (metallurgy)|roasting]].
-In the 1960s, several fluidized bed processes dramatically reduced the cost of some important [[monomers]].  Examples are the Sohio process for [[acrylonitrile]] and the oxychlorination process for [[vinyl chloride]].
-In the late 1970s, a fluidized bed process for the synthesis of [[polyethylene]] dramatically reduced the cost of this important [[polymer]], making its use economical in many new applications.  The polymerization reaction generates heat and the intense mixing associated with fluidization prevents hot spots where the polyethylene particles would melt.  A similar process is used for the synthesis of [[polypropylene]].
-Currently, most of the processes that are being developed for the industrial production of [[carbon nanotubes]] use a fluidized bed <ref>[http://www.bepress.com/ijcre/vol3/R3/ International Journal of Chemical Reactor Engineering<!-- Bot generated title -->]</ref>.
-A new potential application of fluidization technology is [[chemical looping combustion]], which has not yet been commercialized.   One solution to reducing the potential effect of [[carbon dioxide]] generated by [[fuel combustion]] (e.g. in [[power station]]s) on [[global warming]] is carbon dioxide sequestration.  Regular [[combustion]] with [[air]] produces a gas that is mostly [[nitrogen]] (as it is air's main component at about 80% by volume), which prevents economical sequestration.  Chemical looping uses a [[metal]] [[oxide]] as a solid [[oxygen]] carrier. These metal oxide particles replace air (specifically [[oxygen]] in the air) in a combustion reaction with a solid, liquid or gaseous fuel in a fluidized bed, producing solid metal particles from the [[redox|reduction]] of the metal oxides and a mixture of carbon dioxide and [[water vapor]], the major products of any combustion reaction.  The [[water]] vapor is condensed, leaving pure carbon dioxide which can be sequestered.  The solid metal particles are circulated to another fluidized bed where they react with air (and again, specifically oxygen in the air), producing heat and [[redox|oxidizing]] the metal particles to metal oxide particles that are recirculated to the fluidized bed combustor.
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