Industrial Reactors

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Types design Examples Usage of Industrial Reactors

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Approach to Reactor Selection Reactor Systems Homogenous Reactor Heterogeneous Reactor Industrial Reactors Fluidized Bed Reactor Semi Batch Reactor Slurry Reactor Moving Bed Reactor Bio Reactors

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1. Identify number of phases present at reaction conditions – Single – Homogeneous system – Multiple – Heterogeneous systems 2 . Identify stoichiometry, number of reactions, energy requirements 3. Identify mechanism (if possible) and possible reaction pathways and active intermediates. 4. Process Requirements Maximum Productivity Maximum Conversion Stability Easy Scale up Minimum Pollution

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E xample is the fluid-solid reactor ( gas-solid or liquid-solid), where heterogeneous catalytic reactions are performed.

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Fluidized bed reactors are capable of handling large amounts of feed and catalyst. GENERAL INFORMATION Fluidized bed reactors are  heterogeneous  catalytic reactors in which the mass of catalyst is fluidized . This allows for extensive mixing in all directions. A result of the mixing is excellent temperature stability and increased mass-transfer and reaction rates.

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Before the reactor is started the catalyst pellets lie on a grate at the bottom of the reactor. Reactants are pumped into the reactor through a  distributor  continuously, causing the bed to become  fluidized . The reactants react due to the presence of the catalyst pellets, forming products that are removed continuously. Movie is

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Fluidized bed reactors are commonly used in catalytic  cracking  processes. They are also used in the Oxidation of naphthalene to P htalic anhydride Roasting of sulfide ores coking  of petroleum residues calcination of limestone. They are often used when there is a need for large amounts of heat input or output, or when closely controlled temperatures are required.

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GENERAL INFORMATION Semi-batch reactors occupy a middle ground between batch and continuous reactors. They are open systems  like CSTRs and run on an  unsteady-state  basis like batch reactors. They usually consist of a single stirred tank, similar to a batch reactor. The   half-pipe coil jacketed  reactor shown below can be used in semi-batch operations.

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Movie is: An initial amount of reactants is charged into the reactor. The reactor is then started, and additional reactants are added continuously to the tank. The reactor is then allowed to run until the desired conversion is achieved, at which point the products and remaining reactants are removed from the tank and the process can be started once more.

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Semi-batch reactors are not used as often as other reactor types. However , they can be used for many two-phase (i.e. solid/liquid) reactions. Also , semi-batch reactors are used when a reaction has many unwanted side reactions, or has a high heat of reaction. By limiting the introduction of reactants, potential problems are eliminated.

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GENERAL INFORMATION Slurry reactors are three-phase reactors, meaning they can be used to react solids, liquids, and gases simultaneously. They usually consist of a catalyst (solid) suspended in a liquid, through which a gas is bubbled. They can operate in either semi-batch or continuous mode.

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Movie is Inside the reactor are catalyst pellets suspended in a liquid. Gas reactant is bubbled into the reactor. The gas is absorbed into the liquid from the bubble surface. The absorbed gas then diffuses through the liquid to the catalyst surface, at which point it diffuses into the catalyst pellet and the reaction takes place.

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Slurry reactors are most frequently used when a liquid reactant must be contacted with a solid catalyst, and when a reaction has a high heat of reaction. They may be used in such applications as  hydrogenation , oxidation ,  hydroformation   ethynylation .

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The animation shows the operation of a moving-bed reactor. Reactants (green) and catalyst (white) enter the top of the reactor and move through the vessel. Once at the bottom the catalyst (black) is removed and regenerated; products (blue) are removed from the reaction system The catalyst is regenerated and brought to the top of the reactor.

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Solid catalyst pellets are continuously introduced at the top of the reactor, as are the fluid phase reactants . The catalyst and the fluid flow together down the reactor . The reaction takes place along the way, which establishes a  concentration gradient . Animation is

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GENERAL INFORMATION The term bioreactors typically refers to bio-CSTRs or plug flow reactors, or fixed film reactors used for cell cultures or fermentation reactions. (Pictures courtesy New Brunswick Scientific Co., Inc., Edison, NJ)

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The chemical process in a bioreactor can be aerobic, anaerobic, or a hybrid of the two. Bioreactors are usually smooth and cylindrical , are easy to clean . This is to prevent fouling, the build-up of unwanted materials on the surface of the vessel.

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Bioreactors can be used to create biodiesel from the oil of algae. Algae in the tubes grow with the assistance of a light source and carbon dioxide inputs. Once enough algae has grown, it is scraped from the tube and used for its natural oils.

Nuclear reactors:

Nuclear reactors Nuclear reactors produce power through  fission . Boiling water nuclear reactors are a type of  light water reactor . In boiling water nuclear reactors (BWRs), the heat generated by the splitting of uranium atoms is used to boil water within the reactor core. The steam produced passes through a turbine, generating power.

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In nuclear power plants electricity is produced through fission instead of by burning fuel. The fission process starts with uranium in the form of  Ceramic Pellets, such as those shown below. These solid pellets contain two isotopes of uranium. U-235 makes up less than 1 percent of natural uranium, but it fissions easily. U-238 makes up the other 99 percent of natural uranium, but fissions very little. Nuclear Energy Institute, Washington, DC

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Advantages: The direct cycle simplifies the heat exchange system. Low pressure vessel and containment requirements. In-core boiling improves the natural convection. Disadvantages: Possibility of fuel element damage due to dry out at the fuel surface Higher radiation level at the turbine due to carry-over activity from the core

REFERENCES:

REFERENCES Fogler , Scott H.  ( Elements of Chemical Reaction Engineering) . 3rd ed. Englewood Cliffs, NJ:      Prentice-Hall, 1998 . Hill , Charles G., Jr.  ( An Introduction to Chemical Engineering Kinetics and Reactor Design) . New York: John Wiley & Sons, Inc. 1977 . Perry , Robert H., and Don W. Green.  ( Perry's Chemical Engineers' Handbook) . 7th ed. New  York: McGraw-Hill Inc., 1997: 23-28 . Trambouze , Pierre, Van Landeghem , Hugo, and Wauquier , Jean-Pierre.  ( Chemical Reactors) .       Houston : Gulf Publishing Company, 1988.

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