Sintering in Fluidized Bed

Sintering in Fluidized Bed

Length: 1306 words (3.7 double-spaced pages)

Rating: Excellent

Open Document

Essay Preview

More ↓
Sintering in Fluidized Bed

Processes for cleaner and more efficient energy generation from feed stocks such as coals, lignites, peats, and waste liquors use fluidized beds that are operated at high temperatures and pressures. These processes involve systems that are multi-phase and have complex chemical reactions. Research work has tackled a number of aspects, including mechanical engineering aspects of the reactors, reaction chemistry and products, characterization and physical properties of the ash, fouling by ash deposits and the phenomenon of defluidization by agglomeration or sintering of the ash particles. It is with this latter aspect, the phenomenon of defluidization, that this contribution is concerned. Defluidization is also a problem in a number of other elevated temperature fluidized bed production processes, including size enlargement by agglomeration, fluidized bed processes for poly-olefin production and metallurgical processes.

Defluidization occurs when the particles in the bed adhere. When two particles touch, material at the point of contact migrates forming a neck that is strong enough to withstand the disruptive forces in the fluidized bed. Two categories of adhesion can be discerned. The first type is visco-plastic sintering and it occurs with glassy materials. With these materials, migration is limited by the ability of the material to flow. With increasing temperature the viscosity of the material is reduced and hence the material flows and the size of the neck is increased. At some point, the necks are sufficiently large and strong enough to cause defluidization. The second type occurs when a large quantity of liquid is formed by melting or by chemical reaction. With an increase in temperature, a phase boundary may be crossed bring about rapid defluidization. The liquid formed has a relatively low viscosity and defluidization is caused by the amount of liquid present. This section will primarily focus on visco-plastic sintering.

Model systems, in which chemical reactions do not occur, have been used to investigate the relationship between process conditions and the tendency to defluidize due to visco-plastic sintering. Materials used have included low-density ploy-ethylene and poly-propylene, soda glasses, metals, and inorganic crystalline salts. Under sintering conditions, the fluidizing velocity has to be increased above the minimum fluidizing velocity, Umf, to a higher velocity, U; at which pronounced bubbling occurs. A fluidizing velocity, Umfs, may be defined as a velocity just sufficient to prevent sintering. This characterizes a different fluidization state from Umf, since the in the latter the bed is in an expanded but not bubbling state.

How to Cite this Page

MLA Citation:
"Sintering in Fluidized Bed." 24 Aug 2019

Need Writing Help?

Get feedback on grammar, clarity, concision and logic instantly.

Check your paper »

The Effect Of The Feed Particle On The Gas Solid Dense Phase Fluidized Bed

- Effect of the Feed Particle with Various Components on the Separation Behavior for Coal Beneficiation in the Gas–Solid Dense Phase Fluidized Bed Coal, as the primary energy resource, could be effectively cleaned with the air dense medium fluidized bed (ADMFB) and have great significance for the society development. In this study, the particle behavior of feed particles with various components was theoretically analyzed. The effect of gas velocity, bed height, and the number of middle particle (Gmiddle) on the separation efficiency was investigated....   [tags: Chemical engineering, Separation process]

Research Papers
1166 words (3.3 pages)

Essay on Fear and Tension in The Landlady and A Terribly Strange Bed

- Fear and Tension in The Landlady and A Terribly Strange Bed The two short stories 'The Landlady' and 'A Terribly Strange Bed' create fear and tension in two very separate ways. For example, A Terribly Strange Bed is a detective story where a man wins money at a gambling house, spends the night somewhere and when he lies in bed the canopy lowers trying to suffocate him. But he gets away and wants to find out why the people have made up such a machine when they could just smother him themselves and throw him in the river with no complications....   [tags: Landlady Strange Bed Essays]

Free Essays
1048 words (3 pages)

Fluidized Catalytic Cracker Essay

- Fluidized Catalytic Cracking is a technology in petroleum refining where heavier petroleum fractions are converted to more valuable lighter fractions like LPG, gasoline and diesel. Introduction: In petroleum refining, crude oil is distilled at atmospheric pressure to recover valuable petroleum products like LPG, Naphtha, Kero, ATF and Diesel. The residual heavier fraction, which has little commercial value, is further distilled under vacuum to separate Light Vacuum Gas Oil (LVGO), Heavy Vacuum Gas Oil (HVGO) and Vacuum Residue....   [tags: environment, petroleum]

Research Papers
1079 words (3.1 pages)

Essay about The Death Of A Bed

- His tiny toes, precious face were nothing but a blurry glare as they swiftly took him away. The instant relief of finally getting to see his face was not as comforting as most mothers get to experience. The room was cold empty and smelled aseptic. The exhaustion over took me and I was out. As they wheeled him in I couldn’t even bare to see him lying there in a glass box wrapped up warmly in a white blanket with machines straggling along behind him, I felt a lump in my throat. They put him right next to my bed, I was able to reach him through an opening that didn’t even make the moment seem real....   [tags: English-language films, Debut albums, Door]

Research Papers
1434 words (4.1 pages)

Idealism in Auden’s O who can ever gaze his fill, Out on the lawn I lie in bed (A Summer Night 193

- Idealism in Auden’s O who can ever gaze his fill, Out on the lawn I lie in bed (A Summer Night 1933), and The Shield of Achilles W.H. Auden’s poems are celebrated for their intelligence, detachedness, and musicality. Often, idealism is associated with romanticism and the excessively personal, because it is an attempt at envisioning the world as it ought to be and not as it is. However, Auden successfully blends idealism into his objective poems, and this idealism manifests itself in his “O who can ever gaze his fill,” “Out on the lawn I lie in bed” (“A Summer Night 1933”), and “The Shield of Achilles.” In “O who can ever gaze his fill,” mortals from various walks...   [tags: Shield Achilles Gaze Fill Lawn Bed]

Research Papers
1973 words (5.6 pages)

Essay Bed Bath And Beyond Inc.

- Abstract Bed Bath and Beyond is a home décor retailer established in 1971 and began selling its shares in 1992 on the NASDAQ stock market (Corporate Responsibility, n.d.). Today its common stock is trading at $41.19 (Bed Bath & Beyond Inc. Common, 2016), 49% below the “March 2014 closing peak of $80.48” (Lara, 2016). This analysis will explore Bed Bath and Beyond Inc.’s current situation as it relates to the stock market, past performance, and how it will compete for future growth, to determine if we should add this company to our portfolio and what the expected rate of return should be if our hedge fund decides to invest....   [tags: Stock market, Stock, Stock exchange, Share]

Research Papers
948 words (2.7 pages)

The Treatment Of Bed Sores Essay

- Bed sores which can also be known as decubitus ulcers, pressure ulcers, or pressure sores, are non-cancerous or contagious red patches on areas of the skin that are caused by increased exposure to pressure or weight for long periods of time. These inflamed areas are usually located where the body typically has a strong weight-bearing mass that is squeezed between a hard object, another bone or body part, chair, or bed. (World of Health, 2007) It effects most bed ridden or wheelchair bound patients in nursing homes, hospices, hospitals, or clinics....   [tags: Bedsore, Gangrene, Iatrogenesis]

Research Papers
1211 words (3.5 pages)

Signs of Bed Bugs Essay

- Page: Identification of Bed Bugs How Do I Know If I Have Bed Bugs. There are several signs of an active infestation. Most commonly an individual (designated The Host) will be experiencing bites. The tell-tale bite marks can appear on the face, neck, arms, hands, or any other body parts while sleeping. More than one individual in a household may experience bites, some may not have as strong of a reaction to the bites as others. Bites may appear as red bumps on the skin. It may be difficult to tell if you’ve been bitten by a bed bug unless you find bed bugs or signs of infestation....   [tags: bites, infestation, preventative]

Research Papers
635 words (1.8 pages)

Essay on Binge Eating Disorder (BED)

- Description: According to Nanci Hellmich in USA today, binge-eating disorder, or BED, is the consumption of large amounts of food on a frequent basis without the purging of food (2007). This occurs at least twice a week at rapid consumption, consuming a significant amount of food and calories. This is done in one sitting beyond the feeling of satiation. Obesity is almost always the result (Hellmich, 2007). Poor body image and poor health are seen more so with those who binge-eat compared to other eating disorders....   [tags: purging, food, obesity, image, health]

Research Papers
729 words (2.1 pages)

Legend of the Body in the Bed Essay

- Body in the Bed The legend of the “Body in the Bed” has been retold over and over again for years. It is a very popular story, usually taking place at a hotel or motel in the city of Las Vegas, Nevada, or in a remote location in the desert nearby (“Strange Smells from the Hotel Bed”). Various “spin-offs” and variations to the legend have arisen since its inception, believed to be in the early 1990s. Many examples supporting the legend have come to the surface over time. They provide a possible explanation to the origin of the legend....   [tags: Urban Legends]

Research Papers
1918 words (5.5 pages)

Several methods of defluidization behavior have been presented. The simplest is an empirical approach which relates the excess gas fluidizing velocity needed to maintain fluidization to the difference between the bed temperature, T, and the sintering temperature, Ts. The sintering temperature is the observed temperature at which defluidization occurs at the minimum fluidization velocity.

In the case of single-phase materials, sintering can potentially occur by a number of mechanisms: flow of the material, surface diffusion, volume diffusion, and vaporization/condensation. In fluidized beds, the first of these mechanisms is most important because it is the most rapid. Sintering by diffusion (surface and volume) requires the movement of atoms of the material and is relatively slow. Because of the flow of gas, vaporization/condensation of the material is probably the least significant mechanism. Glassy materials flow by viscous of plastic deformation. In the case of crystalline materials, such as metals, visco-plastic flow occurs by slip at dislocations.

The sintering of two particles has been modeled by representing the particles as smooth spheres. For two such particles in contact, the rate of neck growth is represented by an equation of the form:
(x/r)n = kt (1)
Where x is the neck radius at time t and r is the radius of the particle. The value of exponent n depends on the sintering mechanism: for visco-plastic flow n = 2. The value of k depends on the surface energy, g - the magnitude of an applied force and viscosity - m. In the Frenkel equation [3], which considers surface energy only is given by:
(x/r)2 = 3gt/2rm (2)
Rumpf [4] derived an expression which included the sintering effect of an applied load, F, and in which the proportion constant for the first term was found to be 8/5 for hydrodynamic load instead of the 3/2 found by Frenkel:
(x/r)2 = [(8g/5r)+(2F/5pr2)]t/m (3)
Assuming the stress to be evenly distributed over all particle contacts, the above equation may be rewritten using Rumpf's equation, in terms of stress, s1, applied to an assembly of spherical particles of porosity e:
(x/r)2 = [(8g/5r)+(8es1/5p(1-e))]t/m (4)
Both Equations (3) and (4) can be used in practical situations in which the applied load is significant. They also can be used to analyze data to obtain an apparent value of the viscosity and its variation with temperature. In this case the importance of the first term may be negligible compared to that of the second term.
In real systems, however, the particles are neither perfectly smooth spheres nor are they monodisperse. Taking this into consideration, Equation (4) is probably best written in the form:
(x/r)2 = k1t/m (5)
Where k1 is a factor dependant on both material properties and environmental conditions. Furthermore, in glassy systems the flow is unlikely to be Newtonian in essence. Hence, in practice, the viscosity value must be regarded as a value used to fit the data. An Arrhenius relationship of viscosity and temperature is often taken as:
m = moexp(E/RT) (6)
The magnitude of the activation energy, E, depends on the activation energy for flow and the dependence of the numbers of flowing molecules on temperature, resulting in moving through a material transition temperature. The activation energy may therefore change with temperature and different gradients may be shown in an Arrenius plot.

Gluckman [8] performed deluidization experiments using a plethora of materials, including copper shot, poly-ethylene beads, poly-propylene particles, poly-ethylene terephthalate particles, and glass spheres. It was found that for a given material a certain gas temperature existed which, when underneath, the bed could always be fluidized at the minimum fluidization velocity, Umf,. This temperature was called the minimum sintering temperature, Ts. Above this temperature, a higher fluidizing velocity, Umfs, was needed to fluidize the bed. The data that was collected correlated to a linear function between velocity and temperature:
Umfs = B + AT (7)
where A and B are constants. Also, it was concluded that there is most likely an influence of bed height.

Siegell [2] conducted defluidization tests on several types of particles and based his results in terms of the excess air velocity (Umfs - Umf) needed to keep the bed fluidized and the excess temperature, (T - Ts). It was found that there was a linear relationship between these two parameters and Siegell also reported that increasing the bed height led to the tendency to defluidize.

The conclusion in the study of sintering in fluidized beds is that the effect of temperature is the dominant factor that can result in defluidization of the system. This correlation is quite different in respect to effect of temperature on dynamic liquid bridge forces, where higher temperatures and reduced viscosity lead to weaker forces.


1. M.J. Gluckman, J. Yerushalmi, A.M. Squires, in: D.L. Keairns (Ed.), Fluidization Technology, Hemisphere, Washington, 1976, p. 395

2. J. H. Siegell, Powder Technology 38 (1984) 13

3. W.D. Kingery, H. K. Bowen, D.R. Uhlmann, in: Introduction to Ceramics, second edition, Wiley-Interscience, New York, 1976, p. 492

4. H. Rumpf, in: K.V.S Sastry (Ed.), Agglomeration, American Institute of Mining, Metallurgical, and Petroleum Engineering, 1977, p. 97



1. M.J. Gluckman, J. Yerushalmi, A.M. Squires, in: D.L. Keairns (Ed.), Fluidization Technology, Hemisphere, Washington, 1976, p. 395

2. J. H. Siegell, Powder Technology 38 (1984) 13

3. W.D. Kingery, H. K. Bowen, D.R. Uhlmann, in: Introduction to Ceramics, second edition, Wiley-Interscience, New York, 1976, p. 492

4. H. Rumpf, in: K.V.S Sastry (Ed.), Agglomeration, American Institute of Mining, Metallurgical, and Petroleum Engineering, 1977, p. 97
Return to