Monday, December 17, 2007

Reactors and Reaction Vessels

16 litre Pharma Reactor


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 (gas or liquid) is passed through a granular solid material (usually a catalyst possibly shaped as tiny spheres) 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 the FBR. As a result, the fluidized bed reactor is now used in many industrial applications.

Basic diagram of a fluidized bed reactor.
1 Basic principles
2 History and current uses
3 Advantages
4 Disadvantages
5 Current research and trends
6 References
7 See also
8 External links

[edit] Basic principles
The solid substrate (the catalytic material upon which chemical species react) material in the fluidized bed reactor is typically supported by a
porous plate, known as a distributor.[1] The fluid is then forced through the distributor up through the solid material. At lower fluid velocities, the solids remain in place as the fluid passes through the voids in the material. This is known as a packed bed reactor. As the fluid velocity is increased, the reactor will reach a stage where the force of the fluid on the solids is enough to balance the weight of the solid material. This stage is known as incipient fluidization and occurs at this minimum fluidization velocity. Once this minimum velocity is surpassed, the contents of the reactor bed begin to expand and swirl around much like an agitated tank or boiling pot of water. The reactor is now a fluidized bed.Depending on the operating conditions and properties of solid phase various flow regimes can be observed in this reactor.

[edit] History and current uses
Fluidized bed reactors are a relatively new tool in the industrial engineering field. The first fluidized bed gas generator was developed by Fritz Winkler in Germany in the
1920s.[2] One of the first United States fluidized bed reactors used in the petroleum industry was the Catalytic Cracking Unit, created in Baton Rouge, LA in 1942 by the Standard Oil Company of New Jersey (now ExxonMobil).[3] This FBR and the many to follow were developed for the oil and petrochemical industries. Here catalysts were used to reduce petroleum to simpler compounds through a process known as cracking. The invention of this technology made it possible to significantly increase the production of various fuels in the United States. [4]
Today fluidized bed reactors are still used to produce gasoline and other fuels, along with many other chemicals. Many industrially produced
polymers are made using FBR technology, such as rubber, vinyl chloride, polyethylene, and styrenes. Various utilities also use FBR’s for coal gasification, nuclear power plants, and water and waste treatment settings. Used in these applications, fluidized bed reactors allow for a cleaner, more efficient process than previous standard reactor technologies.[4]

[edit] Advantages
The increase in fluidized bed reactor use in today’s industrial world is largely due to the inherent advantages of the technology.
Uniform Particle Mixing: Due to the intrinsic fluid-like behavior of the solid material, fluidized beds do not experience poor mixing as in packed beds. This complete mixing allows for a uniform product that can often be hard to achieve in other reactor designs. The elimination of radial and axial concentration
gradients also allows for better fluid-solid contact, which is essential for reaction efficiency and quality.
Uniform Temperature Gradients: Many chemical reactions produce or require the addition of heat. Local hot or cold spots within the reaction bed, often a problem in packed beds, are avoided in a fluidized situation such as a FBR. In other reactor types, these local temperature differences, especially hotspots, can result in product degradation. Thus FBRs are well suited to
exothermic reactions. Researchers have also learned that the bed-to-surface heat transfer coefficients for FBRs are high.
Ability to Operate Reactor in Continuous State: The fluidized bed nature of these reactors allows for the ability to continuously withdraw product and introduce new reactants into the reaction vessel. Operating at a
continuous process state allows manufacturers to produce their various products more efficiently due to the removal of startup conditions in batch


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