流動床、流動層

関: fluid bed

WordNet

to remain unmolested, undisturbed, or uninterrupted -- used only in infinitive form; "let her be"
work in a specific place, with a specific subject, or in a specific function; "He is a herpetologist"; "She is our resident philosopher" (同)follow
have life, be alive; "Our great leader is no more"; "My grandfather lived until the end of war" (同)live
be identical to; be someone or something; "The president of the company is John Smith"; "This is my house"
happen, occur, take place; "I lost my wallet; this was during the visit to my parents house"; "There were two hundred people at his funeral"; "There was a lot of noise in the kitchen"
have the quality of being; (copula, used with an adjective or a predicate noun); "John is rich"; "This is not a good answer"
occupy a certain position or area; be somewhere; "Where is my umbrella?" "The toolshed is in the back"; "What is behind this behavior?"
spend or use time; "I may be an hour"
put to bed; "The children were bedded at ten oclock"
a foundation of earth or rock supporting a road or railroad track; "the track bed had washed away"
a piece of furniture that provides a place to sleep; "he sat on the edge of the bed"; "the room had only a bed and chair"
a plot of ground in which plants are growing; "the gardener planted a bed of roses"
the flat surface of a printing press on which the type form is laid in the last stage of producing a newspaper or magazine or book etc.
a depression forming the ground under a body of water; "he searched for treasure on the ocean bed" (同)bottom
(geology) a stratum of rock (especially sedimentary rock); "they found a bed of sandstone"
furnish with a bed; "The inn keeper could bed all the new arrivals"
place (plants) in a prepared bed of soil
the state or fact of existing; "a point of view gradually coming into being"; "laws in existence for centuries" (同)beingness, existence

PrepTutorEJDIC

《連結語として補語を伴なって…『である』,…だ,…です / 《位置・場所を表す語句を伴って》(…に)『ある』,いる(occupy a place or situation) / 〈物事が〉『存在する』,ある(exist);〈生物が〉生存する,生きている(live) / 行われる,起こる,発生する(take place, occur) / 存続する,そのままでいる(remain as before) / 《『be to』 do》 / …する予定である,…することになっている / …すべきだ / 《受動態の不定詞を伴って》…できる / 《命令》…するのだ / 《条件節に》…する意図がある / 《『if…were to』 do》…するとしたなら / 《『be』 do『ing』》《進行形》 / 《進行中の動作》…している,しつつある / 《近い未来》…しようとしている,するつもり / 《動作の反復》(いつも)…している / 《『be』+『他動詞の過去分詞』》《受動態》…される,されている / 《『be』+『自動詞の過去分詞』》《完了形》…した[状態にある]
〈C〉〈U〉『ベット』,『寝台』 / 〈U〉睡眠,宿泊 / 〈C〉『花壇,苗床…』養殖場 / 〈C〉(海・川などの)『床』,水底 / 〈C〉地層;(一般に)土台 / …‘に'寝床を与える / 〈子供など〉'を'寝かしつける / 《古》寝る,床につく
〈U〉存在,実在(existence);生命(life) / 〈U〉本質,本性(nature) / 〈C〉生き物
存在 (existence); もの; 生存, 人生 (life); 生き物; 人間 (human being); [B#] 神; 【哲】本質, 本性

Wikipedia preview

出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2015/07/06 00:27:54」(JST)

wiki en

[Wiki en表示]

Oldest power station utilizing circular fluidized bed technology, in Lünen, Germany

A fluidized bed is formed when a quantity of a solid particulate substance (usually present in a holding vessel) is placed under appropriate conditions to cause a solid/fluid mixture to behave as a fluid. This is usually achieved by the introduction of pressurized fluid through the particulate medium. This results in the medium then having many properties and characteristics of normal fluids, such as the ability to free-flow under gravity, or to be pumped using fluid type technologies.

The resulting phenomenon is called fluidization. Fluidized beds are used for several purposes, such as fluidized bed reactors (types of chemical reactors), fluid catalytic cracking, fluidized bed combustion, heat or mass transfer or interface modification, such as applying a coating onto solid items. This technique is also becoming more common in aquaculture for the production of shellfish in integrated multi-trophic aquaculture systems.^[1]

Properties of fluidized beds

A fluidized bed consists of fluid-solid mixture that exhibits fluid-like properties. As such, the upper surface of the bed is relatively horizontal, which is analogous to hydrostatic behavior. The bed can be considered to be a heterogeneous mixture of fluid and solid that can be represented by a single bulk density.

Furthermore, an object with a higher density than the bed will sink, whereas an object with a lower density than the bed will float, thus the bed can be considered to exhibit the fluid behavior expected of Archimedes' principle. As the "density", (actually the solid volume fraction of the suspension), of the bed can be altered by changing the fluid fraction, objects with different densities comparative to the bed can, by altering either the fluid or solid fraction, be caused to sink or float.

In fluidized beds, the contact of the solid particles with the fluidization medium (a gas or a liquid) is greatly enhanced when compared to packed beds. This behavior in fluidized combustion beds enables good thermal transport inside the system and good heat transfer between the bed and its container. Similarly to the good heat transfer, which enables thermal uniformity analogous to that of a well mixed gas, the bed can have a significant heat-capacity whilst maintaining a homogeneous temperature field.

Application

Fluidized beds are used as a technical process which has the ability to promote high levels of contact between gases and solids. In a fluidized bed a characteristic set of basic properties can be utilised, indispensable to modern process and chemical engineering, these properties include:

Extremely high surface area contact between fluid and solid per unit bed volume
High relative velocities between the fluid and the dispersed solid phase.
High levels of intermixing of the particulate phase.
Frequent particle-particle and particle-wall collisions.

Taking an example from the food processing industry: fluidized beds are used to accelerate freezing in some IQF tunnel freezers (IQF means Individually Quick Frozen, or freezing unpackaged separate pieces). These fluidized bed tunnels are typically used on small food products like peas, shrimp or sliced vegetables, and may use cryogenic or vapor-compression refrigeration. The fluid used in fluidized beds may also contain a fluid of catalytic type; that's why it is also used to catalyse the chemical reaction and also to improve the rate of reaction.

Fluidized beds are also used for efficient bulk drying of materials. Fluidized bed technology in dryers increases efficiency by allowing for the entire surface of the drying material to be suspended and therefore exposed to the air. This process can also be combined with heating or cooling, if necessary, according to the specifications of the application.

History

In 1922, Fritz Winkler made the first industrial application of fluidization in a reactor for a coal gasification process.^[2] In 1942, the first circulating fluid bed was built for catalytic cracking of mineral oils, with fluidization technology applied to metallurgical processing (roasting arsenopyrite) in the late 1940s.^[3]^[4] During this time theoretical and experimental research improved the design of the fluidized bed. In the 1960s VAW-Lippewerk in Lünen, Germany implemented the first industrial bed for the combustion of coal and later for the calcination of aluminium hydroxide.

Fluidized bed types

Bed types can be coarsely classified by their flow behavior, including:^[5]

Stationary or bubbling fluidized bed is the classical approach where the gas at low velocities is used and fluidization of the solids is relatively stationary, with some fine particles being entrained.
Circulating fluidized beds (CFB), where gases are at a higher velocity sufficient to suspend the particle bed, due to a larger kinetic energy of the fluid. As such the surface of the bed is less smooth and larger particles can be entrained from the bed than for stationary beds. Entrained particles are recirculated via an external loop back into the reactor bed. Depending on the process, the particles may be classified by a cyclone separator and separated from or returned to the bed, based upon particle cut size.
Vibratory fluidized beds are similar to stationary beds, but add a mechanical vibration to further excite the particles for increased entrainment.
Transport or flash reactor (FR). At velocities higher than CFB, particles approach the velocity of the gas. Slip velocity between gas and solid is significantly reduced at the cost of less homogeneous heat distribution.
Annular fluidized bed (AFB). A large nozzle at the center of a bubble bed introduces gas as high velocity achieving the rapid mixing zone above the surrounding bed comparable to that found in the external loop of a CFB.

Bed design

A diagram of a fluidized bed

Basic model

When the packed bed has a fluid passed over it, the pressure drop of the fluid is approximately proportional to the fluid's superficial velocity. In order to transition from a packed bed to a fluidized condition, the gas velocity is continually raised. For a free-standing bed there will exist a point, known as the minimum or incipient fluidisation point, whereby the bed's mass is suspended directly by the flow of the fluid stream. The corresponding fluid velocity, known as the "minimum fluidization velocity", .^[6]

Beyond the minimum fluidization velocity (), the bed material will be suspended by the gas-stream and further increases in the velocity will have a reduced effect on the pressure, owing to sufficient percolation of the gas flow. Thus the pressure drop for is relatively constant.

At the base of the vessel the apparent pressure drop multiplied by the cross-section area of the bed can be equated to the force of the weight of the solid particles (less the buoyancy of the solid in the fluid).

where:

is the bed pressure drop

is the bed height

is the bed voidage, i.e. the fraction of the bed volume that is occupied by the voids (the fluid spaces between the particles)

is the apparent density of bed particles

is the density of the fluidizing fluid

is the gravity acceleration

is the total mass of solids in the bed

is the cross-sectional area of the bed

Geldart Groupings

In 1973, Professor D. Geldart proposed the grouping of powders in to four so-called "Geldart Groups".^[7] The groups are defined by their locations on a diagram of solid-fluid density difference and particle size. Design methods for fluidized beds can be tailored based upon the particle's Geldart grouping:^[6]

Group A For this group the particle size is between 20 and 100 µm, and the particle density is typically less than 1.4g/cm³. Prior to the initiation of a bubbling bed phase, beds from these particles will expand by a factor of 2 to 3 at incipient fluidization, due to a decreased bulk density. Most powder-catalyzed beds utilize this group.

Group B The particle size lies between 40 and 500 µm and the particle density between 1.4-4g/cm³. Bubbling typically forms directly at incipient fluidization.

Group C This group contains extremely fine and consequently the most cohesive particles. With a size of 20 to 30 µm, these particles fluidize under very difficult to achieve conditions, and may require the application of an external force, such as mechanical agitation.

Group D The particles in this region are above 600 µm and typically have high particle densities. Fluidization of this group requires very high fluid energies and is typically associated with high levels of abrasion. Drying grains and peas, roasting coffee beans, gasifying coals, and some roasting metal ores are such solids, and they are usually processed in shallow beds or in the spouting mode.

Distributor

Typically, pressurized gas or liquid enters the fluidized bed vessel through numerous holes via a plate known as a distributor plate, located at the bottom of the fluidized bed. The fluid flows upward through the bed, causing the solid particles to be suspended. If the inlet fluid is disabled, the bed may settle, pack onto the plate or trickle down through the plate. Many industrial beds use a sparger distributor instead of a distributor plate. The fluid is then distributed through a series of perforated tubes.

References

^ Wang, JK, 2003. Conceptual design of a microalgae-based recirculating oyster and shrimp system. Aquacultural Engineering 28, 37-46
^ Grace, John R.; Leckner, Bo; Zhu, Jesse; Cheng, Yi (2008), "Fluidized Beds", in Clayton T. Crow, Multiphase Flow Handbook, CRC Press, p. 5:71, doi:10.1201/9781420040470.ch5, ISBN 978-1-4200-4047-0, retrieved June 2012
^ Office of Communications (November 3, 1998), The Fluid Bed Reactor:Baton Rouge, Louisiana (PDF), American Chemical Society, retrieved June 2012
^ Grace; Leckner; Zhu; Cheng, p. 5:75 Missing or empty |title= (help)
^ Fluidization technology, Outotec, May 2007, retrieved June 2012
^ ^a ^b Holdich, Richard Graham (November 1, 2002), "Chapter 7: Fluidization", Fundamentals of Particle Technology (PDF), Midland Information Technology & Publishing, ISBN 978-0954388102, retrieved June 2012
^ Geldart, D. (1973). "Types of gas fluidization". Powder technology 7 (5): 285–292. doi:10.1016/0032-5910(73)80037-3.

External links

Video: Liquid-Solid Fluidized Bed
US DOE Fluidized Bed Technology - Overview website
US DOE NETL Fact Sheet

UpToDate Contents

全文を閲覧するには購読必要です。 To read the full text you will need to subscribe.

1. 術中の輸液マネージメント intraoperative fluid management
2. 特発性低髄液圧性頭痛の治療および予後 treatment and prognosis of spontaneous low cerebrospinal fluid pressure headache
3. 腰椎穿刺：小児における適応、禁忌、手技、および合併症 lumbar puncture indications contraindications technique and complications in children
4. 小児における血液量減少性ショック：初期評価およびマネージメント hypovolemic shock in children initial evaluation and management
5. 小児における維持輸液療法 maintenance fluid therapy in children

English Journal

Fluidized-bed denitrification of mining water tolerates high nickel concentrations.

Zou G1, Papirio S2, van Hullebusch ED3, Puhakka JA2.
Bioresource technology.Bioresour Technol.2014 Dec 19;179C:284-290. doi: 10.1016/j.biortech.2014.12.044. [Epub ahead of print]
This study revealed that fluidized-bed denitrifying cultures tolerated soluble Ni concentrations up to 500mg/L at 7-8 and 22°C. From 10 to 40mg/L of feed Ni, denitrification resulted in complete nitrate and nitrite removal. The concomitant reduction of 30mg/L of sulfate produced 10mg/L of sulfide t
PMID 25549902

Nitrogen Oxides, Sulfur Trioxide, and Mercury Emissions during Oxy-fuel Fluidized Bed Combustion of Victorian Brown Coal.

Roy B1, Chen L, Bhattacharya S.
Environmental science & technology.Environ Sci Technol.2014 Dec 16;48(24):14844-50. doi: 10.1021/es504667r. Epub 2014 Nov 26.
This study investigates, for the first time, the NOx, N2O, SO3, and Hg emissions from combustion of a Victorian brown coal in a 10 kWth fluidized bed unit under oxy-fuel combustion conditions. Compared to air combustion, lower NOx emissions and higher N2O formation were observed in the oxy-fuel atmo
PMID 25402169

Influence of various chlorine additives on the partitioning of heavy metals during low-temperature two-stage fluidized bed incineration.

Peng TH1, Lin CL2.
Journal of environmental management.J Environ Manage.2014 Dec 15;146:362-8. doi: 10.1016/j.jenvman.2014.04.039. Epub 2014 Sep 7.
In this study, a pilot-scale low-temperature two-stage fluidized bed incinerator was evaluated for the control of heavy metal emissions using various chlorine (Cl) additives. Artificial waste containing heavy metals was selected to simulate municipal solid waste (MSW). Operating parameters considere
PMID 25203439

Japanese Journal

Comparison of Pyrolysis/Steam Gasification Characteristics of Woody Biomass in a Fluidized Bed Gasifier with Triple-beds (Selected Papers from the 6th ISEM '11-Sendai/Kansai, 2011)