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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.
In materials science, liquefaction is a process that generates a liquid from a solid or a gas or that generates a non-liquid phase which behaves in accordance with fluid dynamics. It occurs both naturally and artificially. As an example of the latter, a "major commercial application of liquefaction is the liquefaction of air to allow separation of the constituents, such as oxygen, nitrogen, and the noble gases." Another is the conversion of solid coal into a liquid form usable as a substitute for liquid fuels.
A granular material is a conglomeration of discrete solid, macroscopic particles characterized by a loss of energy whenever the particles interact. The constituents that compose granular material are large enough such that they are not subject to thermal motion fluctuations. Thus, the lower size limit for grains in granular material is about 1 μm. On the upper size limit, the physics of granular materials may be applied to ice floes where the individual grains are icebergs and to asteroid belts of the Solar System with individual grains being asteroids.
Solid is one of the four fundamental states of matter. In solids, particles are closely packed. It is characterized by structural rigidity and resistance to changes of shape or volume. Unlike a liquid, a solid object does not flow to take on the shape of its container, nor does it expand to fill the entire volume available to it like a gas does. The atoms in a solid are tightly bound to each other, either in a regular geometric lattice or irregularly, and are typically low in energy. Solids cannot be compressed with little pressure whereas gases can be compressed with little pressure because in gases molecules are loosely packed.
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.
In fluid dynamics, drag is a force acting opposite to the relative motion of any object moving with respect to a surrounding fluid. This can exist between two fluid layers or a fluid and a solid surface. Unlike other resistive forces, such as dry friction, which are nearly independent of velocity, drag forces depend on velocity. Drag force is proportional to the velocity for a laminar flow and the squared velocity for a turbulent flow. Even though the ultimate cause of a drag is viscous friction, the turbulent drag is independent of viscosity.
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).
Water is a transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's streams, lakes, and oceans, and the fluids of most living organisms. It is vital for all known forms of life, even though it provides no calories or organic nutrients. Its chemical formula is H2O, meaning that each of its molecules contains one oxygen and two hydrogen atoms, connected by covalent bonds. Water is the name of the liquid state of H2O at standard ambient temperature and pressure. It forms precipitation in the form of rain and aerosols in the form of fog. Clouds are formed from suspended droplets of water and ice, its solid state. When finely divided, crystalline ice may precipitate in the form of snow. The gaseous state of water is steam or water vapor. Water moves continually through the water cycle of evaporation, transpiration (evapotranspiration), condensation, precipitation, and runoff, usually reaching the sea.
A bucket is typically a watertight, vertical cylinder or truncated cone or square, with an open top and a flat bottom, attached to a semicircular carrying handle called the bail.
Gravity, or gravitation, is a natural phenomenon by which all things with mass or energy—including planets, stars, galaxies, and even light—are brought toward one another. On Earth, gravity gives weight to physical objects, and the Moon's gravity causes the ocean tides. The gravitational attraction of the original gaseous matter present in the Universe caused it to begin coalescing, forming stars—and for the stars to group together into galaxies—so gravity is responsible for many of the large-scale structures in the Universe. Gravity has an infinite range, although its effects become increasingly weaker on farther objects.
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.
A fluidised bed is a physical phenomenon occurring when a quantity of a solid particulate substance 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.
A popcorn maker is a machine used to pop popcorn. Since ancient times, popcorn has been a popular snack food, produced through the explosive expansion of kernels of heated corn (maize). Commercial large scale popcorn machines were invented by Charles Cretors in the late 19th century. Many types of small scale home methods for popping corn also exist.
The process is also key in the formation of a sand volcano and fluid escape structures in sediments and sedimentary rocks.
Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sand and silt can be carried in suspension in river water and on reaching the sea bed deposited by sedimentation. If buried, they may eventually become sandstone and siltstone through lithification.
Sedimentary rocks are types of rock that are formed by the accumulation or deposition of small particles and subsequent cementation of mineral or organic particles on the floor of oceans or other bodies of water at the Earth's surface. Sedimentation is the collective name for processes that cause these particles to settle in place. The particles that form a sedimentary rock are called sediment, and may be composed of geological detritus (minerals) or biological detritus. Before being deposited, the geological detritus was formed by weathering and erosion from the source area, and then transported to the place of deposition by water, wind, ice, mass movement or glaciers, which are called agents of denudation. Biological detritus was formed by bodies and parts of dead aquatic organisms, as well as their fecal mass, suspended in water and slowly piling up on the floor of water bodies. Sedimentation may also occur as dissolved minerals precipitate from water solution.
Most of the fluidization applications use one or more of three important characteristics of fluidized beds:
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 (FCC) process,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.
Fluid catalytic cracking (FCC) is one of the most important conversion processes used in petroleum refineries. It is widely used to convert the high-boiling, high-molecular weight hydrocarbon fractions of petroleum crude oils into more valuable gasoline, olefinic gases, and other products. Cracking of petroleum hydrocarbons was originally done by thermal cracking, which has been almost completely replaced by catalytic cracking because it produces more gasoline with a higher octane rating. It also produces byproduct gases that have more carbon-carbon double bonds, and hence more economic value, than those produced by thermal cracking.
Petroleum is a naturally occurring, yellowish-black liquid found in geological formations beneath the Earth's surface. It is commonly refined into various types of fuels. Components of petroleum are separated using a technique called fractional distillation, i.e. separation of a liquid mixture into fractions differing in boiling point by means of distillation, typically using a fractionating column.
Gasoline, or petrol, is a colorless petroleum-derived flammable liquid that is used primarily as a fuel in spark-ignited internal combustion engines. It consists mostly of organic compounds obtained by the fractional distillation of petroleum, enhanced with a variety of additives. On average, a 42-U.S.-gallon (160-liter) barrel of crude oil yields about 19 U.S. gallons of gasoline after processing in an oil refinery, though this varies based on the crude oil assay.
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 acrylonitrileand the oxychlorination process for vinyl chloride. 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.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.Arkema uses a fluidized bed to produce 400 tonnes/year of multiwall carbon nanotubes.
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.
Syngas, or synthesis gas, is a fuel gas mixture consisting primarily of hydrogen, carbon monoxide, and very often some carbon dioxide. The name comes from its use as intermediates in creating synthetic natural gas (SNG) and for producing ammonia or methanol. Syngas is usually a product of coal gasification and the main application is electricity generation. Syngas is combustible and can be used as a fuel of internal combustion engines. Historically, syngas has been used as a replacement for gasoline, when gasoline supply has been limited; for example, wood gas was used to power cars in Europe during WWII. Syngas, however, has less than half the energy density of natural gas.
Gasification is a process that converts organic- or fossil fuel-based carbonaceous materials into carbon monoxide, hydrogen and carbon dioxide. This is achieved by reacting the material at high temperatures (>700 °C), without combustion, with a controlled amount of oxygen and/or steam. The resulting gas mixture is called syngas or producer gas and is itself a fuel. The power derived from gasification and combustion of the resultant gas is considered to be a source of renewable energy if the gasified compounds were obtained from biomass.
Fluidized bed combustion (FBC) is a combustion technology used to burn solid fuels.
A supercritical fluid (SCF) is any substance at a temperature and pressure above its critical point, where distinct liquid and gas phases do not exist. It can effuse through solids like a gas, and dissolve materials like a liquid. In addition, close to the critical point, small changes in pressure or temperature result in large changes in density, allowing many properties of a supercritical fluid to be "fine-tuned".
A chemical reactor is an enclosed volume in which a chemical reaction takes place. In chemical engineering, it is generally understood to be a process vessel used to carry out a chemical reaction, which is one of the classic unit operations in chemical process analysis. The design of a chemical reactor deals with multiple aspects of chemical engineering. Chemical engineers design reactors to maximize net present value for the given reaction. Designers ensure that the reaction proceeds with the highest efficiency towards the desired output product, producing the highest yield of product while requiring the least amount of money to purchase and operate. Normal operating expenses include energy input, energy removal, raw material costs, labor, etc. Energy changes can come in the form of heating or cooling, pumping to increase pressure, frictional pressure loss or agitation.
The Fischer–Tropsch process is a collection of chemical reactions that converts a mixture of carbon monoxide and hydrogen into liquid hydrocarbons. These reactions occur in the presence of metal catalysts, typically at temperatures of 150–300 °C (302–572 °F) and pressures of one to several tens of atmospheres. The process was first developed by Franz Fischer and Hans Tropsch at the Kaiser-Wilhelm-Institut für Kohlenforschung in Mülheim an der Ruhr, Germany, in 1925.
Pyrometallurgy is a branch of extractive metallurgy. It consists of the thermal treatment of minerals and metallurgical ores and concentrates to bring about physical and chemical transformations in the materials to enable recovery of valuable metals. Pyrometallurgical treatment may produce products able to be sold such as pure metals, or intermediate compounds or alloys, suitable as feed for further processing. Examples of elements extracted by pyrometallurgical processes include the oxides of less reactive elements like iron, copper, zinc, chromium, tin, and manganese.
Hydrochloric acid regeneration or HCl regeneration refers to a chemical process for the reclamation of bound and unbound HCl from metal chloride solutions such as hydrochloric acid.
A fluidized bed reactor (FBR) is a type of reactor device that can be used to carry out a variety of multiphase chemical reactions. In this type of reactor, a fluid is passed through a solid granular material at high enough velocities to suspend the solid and cause it to behave as though it were a fluid. This process, known as fluidization, imparts many important advantages to an FBR. As a result, FBRs are used for many industrial applications.
A thermal oxidizer is a process unit for air pollution control in many chemical plants that decomposes hazardous gases at a high temperature and releases them into the atmosphere.
A carbon dioxide scrubber is a piece of equipment that absorbs carbon dioxide (CO2). It is used to treat exhaust gases from industrial plants or from exhaled air in life support systems such as rebreathers or in spacecraft, submersible craft or airtight chambers. Carbon dioxide scrubbers are also used in controlled atmosphere (CA) storage. They have also been researched for carbon capture in process of direct air capture as a means of combating global warming.
Chemical looping combustion (CLC) is a technological process typically employing a dual fluidized bed system. The CLC operated with an interconnected moving bed with a fluidized bed system has also been employed as a technology process. In CLC, a metal oxide is employed as a bed material providing the oxygen for combustion in the fuel reactor. The reduced metal is then transferred to the second bed and re-oxidized before being reintroduced back to the fuel reactor completing the loop. Fig 1 shows a simplified diagram of the CLC process. Fig 2 shows an example of a dual fluidized bed circulating reactor system and a moving bed-fluidized bed circulating reactor system.
The Glossary of fuel cell terms lists the definitions of many terms used within the fuel cell industry. The terms in this fuel cell glossary may be used by fuel cell industry associations, in education material and fuel cell codes and standards to name but a few.
Reactive flash volatilization (RFV) is a chemical process that rapidly converts nonvolatile solids and liquids to volatile compounds by thermal decomposition for integration with catalytic chemistries.
An electrocatalyst is a catalyst that participates in electrochemical reactions. Catalyst materials modify and increase the rate of chemical reactions without being consumed in the process. Electrocatalysts are a specific form of catalysts that function at electrode surfaces or may be the electrode surface itself. An electrocatalyst can be heterogeneous such as a platinum surface or nanoparticles, or homogeneous like a coordination complex or enzyme. The electrocatalyst assists in transferring electrons between the electrode and reactants, and/or facilitates an intermediate chemical transformation described by an overall half-reaction.
Fluidisation is a phenomenon whereby solid particulate is placed under certain conditions to cause it to behave like a fluid. A fluidized bed is a system conceived to facilitate the fluidisation. Fluidized beds have a wide range of applications including but not limited to: assisting with chemical reactions, heat transfer, mixing and drying. A recent concept devised and patented by Outotec, "An annular fluidized bed consists of a large central nozzle surrounded be a stationary fluidized".
The circulating fluidized bed (CFB) is a developing technology for coal combustion to achieve lower emission of pollutants. By using this technology, up to 95% of pollutants can be absorbed before being emitted to the atmosphere.
Aerogel is a synthetic porous ultralight material derived from a gel, in which the liquid component for the gel has been replaced with a gas. The result is a solid with extremely low density and extremely low thermal conductivity. Nicknames include frozen smoke, solid smoke, solid air, solid cloud, blue smoke owing to its translucent nature and the way light scatters in the material. It feels like fragile expanded polystyrene to the touch. Aerogels can be made from a variety of chemical compounds.
Chemical looping reforming (CLR) and gasification (CLG) are the operations that involve the use of gaseous carbonaceous feedstock and solid carbonaceous feedstock, respectively, in their conversion to syngas in the chemical looping scheme. The typical gaseous carbonaceous feedstocks used are natural gas and reducing tail gas, while the typical solid carbonaceous feedstocks used are coal and biomass. The feedstocks are partially oxidized to generate syngas using metal oxide oxygen carriers as the oxidant. The reduced metal oxide is then oxidized in the regeneration step using air. The syngas is an important intermediate for generation of such diverse products as electricity, chemicals, hydrogen, and liquid fuels.