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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2015/11/14 14:26:57」(JST)

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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 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. conveyor 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.

Applications

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 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 (FCC) process,^[1] which converted heavier petroleum cuts into gasoline. Carbon-rich "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, calcining, and sulfide roasting.

In the 1960s, several fluidized bed processes dramatically reduced the cost of some important monomers. Examples are the Sohio process for acrylonitrile^[2] and the oxychlorination process for vinyl chloride.^[3] These chemical reactions are highly exothermic and fluidization ensures a uniform temperature, minimizing unwanted side reactions, and efficient heat transfer to cooling tubes, ensuring a 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.^[4] 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.^[5]

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 stations) 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 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 oxidizing the metal particles to metal oxide particles that are recirculated to the fluidized bed combustor.

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.^[6]^[7]

External links

UBC Fluidization Research Centre
ICFAR

Notes

^ A.W. Peters, W.H. Flank, B.H. Davis, "The history of petroleum cracking in the 20th century", ACS Symposium Series, Volume 1000, 2009, Pages 103-187
^ http://www.acs.org/content/acs/en/education/whatischemistry/landmarks/acrylonitrile.html
^ Marshall, K. A. 2003. Chlorocarbons and Chlorohydrocarbons, Survey. Kirk-Othmer Encyclopedia of Chemical Technology
^ Thomas E. Nowlin, 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, 2014, ISBN 9781118946039
^ Carole Baddour, Cedric Briens, 2005, "Carbon Nanotube Synthesis: A Review", IJCRE, 3, R3.International Journal of Chemical Reactor Engineering
^ Prince; A. Bassi; C. Haas (2012). Biotechnology Progress 28 (1). Missing or empty |title= (help)
^ Mazumder; Zhu, Ray (April 2010). "Optimal design of liquid-solid circulating fluidized bed for continuous protein recovery". Powder Technology 199 (1): 32–47. doi:10.1016/j.powtec.2009.07.009.

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English Journal

High efficiency chlorine removal from polyvinyl chloride (PVC) pyrolysis with a gas-liquid fluidized bed reactor.

Yuan G, Chen D, Yin L, Wang Z, Zhao L, Wang JY.Author information Thermal & Environmental Engineering Institute, Tongji University, Shanghai 200092, China.AbstractIn this research a gas-liquid fluidized bed reactor was developed for removing chlorine (Cl) from polyvinyl chloride (PVC) to favor its pyrolysis treatment. In order to efficiently remove Cl within a limited time before extensive generation of hydrocarbon products, the gas-liquid fluidized bed reactor was running at 280-320°C, where hot N2 was used as fluidizing gas to fluidize the molten polymer, letting the molten polymer contact well with N2 to release Cl in form of HCl. Experimental results showed that dechlorination efficiency is mainly temperature dependent and 300°C is a proper reaction temperature for efficient dechlorination within a limited time duration and for prevention of extensive pyrolysis; under this temperature 99.5% of Cl removal efficiency can be obtained within reaction time around 1min after melting is completed as the flow rate of N2 gas was set around 0.47-0.85Nm3kg-1 for the molten PVC. Larger N2 flow rate and additives in PVC would enhance HCl release but did not change the final dechlorination efficiency; and excessive N2 flow rate should be avoided for prevention of polymer entrainment. HCl is emitted from PVC granules or scraps at the mean time they started to melt and the melting stage should be taken into consideration when design the gas-liquid fluidized bed reactor for dechlorination.
Waste management (New York, N.Y.).Waste Manag.2013 Sep 14. pii: S0956-053X(13)00394-2. doi: 10.1016/j.wasman.2013.08.021. [Epub ahead of print]
In this research a gas-liquid fluidized bed reactor was developed for removing chlorine (Cl) from polyvinyl chloride (PVC) to favor its pyrolysis treatment. In order to efficiently remove Cl within a limited time before extensive generation of hydrocarbon products, the gas-liquid fluidized bed react
PMID 24045169

The role of the hydrogen bond in dense nanoparticle-gas suspensions.

Tahmasebpoor M, de Martín L, Talebi M, Mostoufi N, van Ommen JR.Author information Multiphase Research Systems Lab., School of Chemical Engineering, College of Engineering, University of Tehran, Tehran, Iran.AbstractThe effect of surface characteristics on the interaction between nanoparticles and their agglomeration in dense gas suspensions is still not fully understood. It is known that when the surface is covered with hydroxyl groups, the interaction between nanoparticles becomes substantially stronger than in the absence of these groups; this strengthening is typically attributed to the formation of capillary bridges between the particles. However, this work shows that part of the increase of the interaction is due to the direct hydrogen bonds formed between the surfaces of the polar particles. Dry nitrogen was used to fluidize polar (hydrophilic) and apolar (hydrophobic) SiO2, TiO2 and Al2O3 particles, with a size ranging from 13 to 21 nm. The dry polar particles showed smaller bed expansion and larger minimum fluidization velocity compared to their apolar counterparts, indicating stronger interparticle forces. The results show the importance of including the formation of hydrogen bonds in the modeling of the interaction between dry and polar nanoparticles.
Physical chemistry chemical physics : PCCP.Phys Chem Chem Phys.2013 Apr 28;15(16):5788-93. doi: 10.1039/c3cp43687j. Epub 2013 Mar 7.
The effect of surface characteristics on the interaction between nanoparticles and their agglomeration in dense gas suspensions is still not fully understood. It is known that when the surface is covered with hydroxyl groups, the interaction between nanoparticles becomes substantially stronger than
PMID 23471179

Temperature-dependent biphasic shrinkage of lipid-coated bubbles in ultrasound.

Cox DJ, Thomas JL.Author information Department of Physics and Astronomy, University of New Mexico, Albuquerque, New Mexico 87131, USA.AbstractLipid-coated microbubbles and emulsions are of interest as possible ultrasound-mediated drug delivery vehicles and for their interesting behaviors and fundamental properties. We and others have noted that bubbles coated with the long chain saturated phospholipid distearoylphosphatidylcholine (DSPC) rapidly shrink to a quasistable size when repeatedly insonated with short ultrasound pulses; such stability may adversely affect the bubble's subsequent ability to deliver its pharmacological cargo. Bubbles coated with the unsaturated lipid dioleoylphosphatidylcholine (DOPC) did not show stability but did undergo an abrupt change from rapid initial shrinkage to a slow persistent shrinkage, leading ultimately to dissolution or dispersion. As DOPC and DSPC differ not only in chain saturation but also phase behavior, we performed additional studies using dimyristoyl PC (DMPC) as a coat lipid and controlled the solution temperature to study bubble behavior on exposure to repeated ultrasound pulses for the same coat, in both fluid and gel phases. We find, first, that essentially all bubbles show an initially rapid shrinkage, in which gas loss exceeds the limit imposed by gas diffusion into the surrounding medium; this rapid shrinkage may be evidence of nanoscopic bubble fragmentation. Second, upon reaching a fraction of their initial size, bubbles begin a slower shrinkage with a shrinkage rate that depends on the resting phase state of the coat lipid: fluid DMPC monolayers give a more rapid shrinkage than gel phase. DOPC-coated bubbles showed no temperature-dependent responses in the same temperature range. The results are especially interesting in that bubble compression during the pulse is likely to adiabatically heat the bubble and fluidize the coat, regardless of its initial phase state; thus, some structural feature of the resting coat, such as defect lines in the gel phase, may be important in the subsequent response to the ~3 μs ultrasound pulse.
Langmuir : the ACS journal of surfaces and colloids.Langmuir.2013 Apr 9;29(14):4485-91. doi: 10.1021/la400536e. Epub 2013 Mar 26.
Lipid-coated microbubbles and emulsions are of interest as possible ultrasound-mediated drug delivery vehicles and for their interesting behaviors and fundamental properties. We and others have noted that bubbles coated with the long chain saturated phospholipid distearoylphosphatidylcholine (DSPC)
PMID 23488632

Japanese Journal

Investigation of Thermal Conductivity and Heat Characteristics of Oil Sands Using Ultrasound Irradiation for Shortening the Preheating Time

Kamagata Shingo,Kawamura Youhei,Okawa Hirokazu,Mizutani Koichi
Jpn J Appl Phys 51(7), 07GE03-07GE03-6, 2012-07-25
… Hot steam is injected underground to fluidize bitumen and promote its recovery. …
NAID 150000104379

Emission characteristics of municipal solid waste resources in a fluidize bed pyrolysis

Dong Jong-In,Lee Woo-Chan,Hwang Won-Gu [他]
廃棄物学会研究発表会講演論文集 17回, 52-54, 2006-11-20
NAID 40015329489

Investigation on the Drying Kinetics in a Pulsed Fluidized Bed

LI Zhanyong,KOBAYASHI Noriyuki,DEGUCHI Seiichi,HASATANI Masanobu
Journal of chemical engineering of Japan 37(9), 1179-1182, 2004-09-01
… At the same average air flow rate, the bed is easy to fluidize in the PFB operation and there is little temperature difference along the bed height. …
NAID 10013576910