Editing Fluidization

{{Short description|Conversion of a granular material from a solid-like to liquid-like state}}
{{more footnotes needed|date=March 2014}}

[[File:Fluidized Bed Reactor Graphic.svg|thumb|300px|Schematic drawing of a fluidized bed reactor]]

'''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 (physics)|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 intense 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 [[water pipe|pipe]]s, not requiring mechanical transport (e.g. [[conveyor belt]]).

A simplified every-day-life example of a gas-solid [[fluidized bed]] would be a hot-air [[popcorn maker|popcorn popper]].  The [[popcorn|popcorn kernel]]s, 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 [[sediment]]s and [[sedimentary rock]]s.

==Applications==
{{further|topic=applications|Fluidized bed|Fluidized bed combustion|Fluidized bed reactor}}
Most of the fluidization applications use one or more of three important characteristics of fluidized beds:
# Fluidized solids can be easily transferred between reactors.
# The intense mixing within a fluidized bed means that its temperature is uniform.
# There is excellent heat transfer between a fluidized bed and heat exchangers immersed in the bed.

In the 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,<ref>{{cite book | last1=Peters | first1=Alan W. | last2=Flank | first2=William H. | last3=Davis | first3=Burtron H. | title=Innovations in Industrial and Engineering Chemistry | chapter=The History of Petroleum Cracking in the 20th Century | publisher=American Chemical Society | publication-place=Washington, DC | date=2008-12-31 | isbn=978-0-8412-6963-7 | issn=0097-6156 | doi=10.1021/bk-2009-1000.ch005 | pages=103–187}}</ref> 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]]<ref>{{Cite web|url=http://www.acs.org/content/acs/en/education/whatischemistry/landmarks/acrylonitrile.html|title=Sohio Acrylonitrile Process - American Chemical Society|website=American Chemical Society|language=en|access-date=2018-01-13|url-status=live|archiveurl=https://web.archive.org/web/20170906181443/https://www.acs.org/content/acs/en/education/whatischemistry/landmarks/acrylonitrile.html|archivedate=2017-09-06}}</ref> and the oxychlorination process for [[vinyl chloride]].<ref>{{citation | last=Marshall | first=Kenric A. | title=Kirk-Othmer Encyclopedia of Chemical Technology | chapter=Chlorocarbons and Chlorohydrocarbons, Survey | publisher=Wiley | date=2003-04-18 | isbn=978-0-471-48494-3 | doi=10.1002/0471238961.1921182218050504.a01.pub2 | page=}}</ref>  These chemical reactions are highly exothermic and fluidization ensures a uniform temperature, minimizing unwanted side reactions, and efficient heat transfer to cooling tubes, ensuring high productivity.

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.<ref>{{cite book | last=Nowlin | first=Thomas E. | title=Business and Technology of the Global Polyethylene Industry: An In-depth Look at the History, Technology, Catalysts, and Modern Commercial Manufacture of Polyethylene and Its Products | publisher=Scrivener Publishing, John Wiley and Sons | publication-place=Salem, MA Hoboken, New Jersey | date=2014 | isbn=978-1-118-94603-9 | page=}}</ref>  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>{{cite journal | last1=Baddour | first1=Carole E | last2=Briens | first2=Cedric | title=Carbon Nanotube Synthesis: A Review | journal=International Journal of Chemical Reactor Engineering | publisher=Walter de Gruyter GmbH | volume=3 | issue=1 | date=2005-08-12 | issn=1542-6580 | doi=10.2202/1542-6580.1279 | page=| s2cid=95508695 }}</ref>  Arkema uses a fluidized bed to produce 400 tonnes/year of multiwall carbon nanotubes.<ref>{{Cite web|url=http://www.graphistrength.com/en/manufacture/|title=Graphistrength.com - Graphistrength® manufacture|last=Arkema|website=www.graphistrength.com|language=en|access-date=2018-01-13|url-status=live|archiveurl=https://web.archive.org/web/20170423155849/http://www.graphistrength.com/en/manufacture|archivedate=2017-04-23}}</ref><ref>{{cite journal | last1=Baddour | first1=Carole E. | last2=Briens | first2=Cedric L. | last3=Bordere | first3=Serge | last4=Anglerot | first4=Didier | last5=Gaillard | first5=Patrice | title=The fluidized bed jet grinding of carbon nanotubes with a nozzle/target configuration | journal=Powder Technology | publisher=Elsevier BV | volume=190 | issue=3 | year=2009 | issn=0032-5910 | doi=10.1016/j.powtec.2008.08.016 | pages=372–384}}</ref>

A new potential application of fluidization technology is [[chemical looping combustion]], which has not yet been commercialized.<ref name="Chew">{{cite journal | last1=Chew | first1=Jia Wei | last2=LaMarche | first2=W. Casey Q. | last3=Cocco | first3=Ray A. | title=100 years of scaling up fluidized bed and circulating fluidized bed reactors | journal=Powder Technology | publisher=Elsevier BV | volume=409 | year=2022 | issn=0032-5910 | doi=10.1016/j.powtec.2022.117813 | page=117813| s2cid=251426476 }}</ref>   One solution to reducing the potential effect of [[carbon dioxide]] generated by [[combustion|fuel combustion]] (e.g. in [[power station]]s) on [[global warming]] is [[Carbon sequestration|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. A similar process is used to produce [[maleic anhydride]] through the partial oxidation of n-butane, with the circulating particles acting as both catalyst and oxygen carrier; pure oxygen is also introduced directly into the bed.<ref>{{cite journal | last1=Shekari | first1=Ali | last2=Patience | first2=Gregory S. | last3=Bockrath | first3=Richard E. | title=Effect of feed nozzle configuration on n-butane to maleic anhydride yield: From lab scale to commercial | journal=Applied Catalysis A: General | publisher=Elsevier BV | volume=376 | issue=1–2 | date=2010-03-31 | issn=0926-860X | doi=10.1016/j.apcata.2009.11.033 | pages=83–90| bibcode=2010AppCA.376...83S }}</ref>

Nearly 50% of the silicon in solar cells is produced in fluidized beds.<ref name="Chew" /> For example, metallurgical-grade silicon is first reacted to [[silane]] gas. The silane gas is thermally cracked in a fluidized bed of seed silicon particles, and the silicon deposits on the seed particles. The cracking reaction is endothermic, and heat is provided through the bed wall, typically made of graphite (to avoid metal contamination of the product silicon). The bed particle size can be controlled using attrition jets. Silane is often premixed with hydrogen to reduce the explosion risk of leaked silane in the air (see [[silane]]).

Liquid-solid fluidization has a number of applications in engineering <ref>{{cite book  |chapter=Liquid-solids fluidization |last=Epstein |first=Norman | editor-last=Yang | editor-first=W.C. | title=Handbook of Fluidization and Fluid-Particle Systems | publisher=CRC Press | series=Chemical Industries | year=2003 | isbn=978-0-203-91274-4 | chapter-url=https://www.academia.edu/download/30591723/WCYang_Handbook_of_Fluidization.pdf#page=706 | pages=705–764}}</ref><ref>{{cite journal | last1=Fair | first1=Gordon M. | last2=Hatch | first2=Loranus P. | last3=Hudson | first3=Herbert E. | title=FUNDAMENTAL FACTORS GOVERNING THE STREAMLINE FLOW OF WATER THROUGH SAND [with DISCUSSION] | journal=Journal (American Water Works Association) | publisher=American Water Works Association | volume=25 | issue=11 | year=1933 | issn=1551-8833 | jstor=41225921 | pages=1551–1565 | doi=10.1002/j.1551-8833.1933.tb18342.x }}</ref> The best-known application of liquid-solid fluidization is the backwash of granular filters using water.<ref>{{cite journal | last1=Hunce | first1=Selda Yiğit | last2=Soyer | first2=Elif | last3=Akgiray | first3=Ömer | title=On the backwash expansion of graded filter media | journal=Powder Technology | publisher=Elsevier BV | volume=333 | year=2018 | issn=0032-5910 | doi=10.1016/j.powtec.2018.04.032 | pages=262–268| s2cid=104007408 }}</ref><ref>{{cite journal | last1=Yiğit Hunce | first1=Selda | last2=Soyer | first2=Elif | last3=Akgiray | first3=Ömer | title=Characterization of Granular Materials with Internal Pores for Hydraulic Calculations Involving Fixed and Fluidized Beds | journal=Industrial & Engineering Chemistry Research | publisher=American Chemical Society (ACS) | volume=55 | issue=31 | date=2016-07-27 | issn=0888-5885 | doi=10.1021/acs.iecr.6b00953 | pages=8636–8651}}</ref>

Fluidization has many applications with the use of [[ion exchange]] particles for the purification and processing of many industrial liquid streams. Industries such as food & beverage, hydrometallurgical, water softening, catalysis, bio-based chemical etc. use ion exchange as a critical step in processing.  Conventionally ion exchange has been used in a packed bed where a pre-clarified liquid passes downward through a column. Much work has been done at the University of Western Ontario in London Ontario, Canada on the use of a continuous fluidized ion exchange system, named "Liquid-solid circulating fluidized bed" (LSCFB), recently being called "Circulating fluidized ion exchange" (CFIX). This system has widespread applications extending the use of traditional ion exchange systems because it can handle feed streams with large amounts of suspended solids due to the use of fluidization.<ref>{{cite journal|last1=Prince|first1=Andrew |last2=Bassi|first2=Amarjeet S|last3 = Haas|first3 = Christine |last4 =Zhu|first4 = Jesse X|last5 = Dawe|first5 = Jennifer |journal=Biotechnology Progress|title=Soy protein recovery in a solvent-free process using continuous liquid-solid circulating fluidized bed ion exchanger|year=2012|volume=28|issue=1|pages=157–162 |doi = 10.1002/btpr.725|pmid = 22002948|s2cid=205534874 }}</ref><ref>{{cite journal|last=Mazumder|author2=Zhu, Ray|title=Optimal design of liquid-solid circulating fluidized bed for continuous protein recovery|journal=Powder Technology|date=April 2010|volume=199|issue=1|pages=32–47|doi=10.1016/j.powtec.2009.07.009}}</ref>

==References==
{{reflist}}

==External links==
*[http://frc.engineering.ubc.ca/ UBC Fluidization Research Centre]
*[http://icfar.ca/ ICFAR]

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[[Category:Fluidization| ]]
[[Category:Chemical processes]]