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Chemical Reactors : Chemical Reactors An industrial chemical reactor is complex device in which heat transfer, mass transfer, diffusion and friction may occur along with chemical reaction with provisions of safety and controls. Are vessels designed to contain chemical reactions. These are the two main basic vessel types: : These are the two main basic vessel types: a tank a pipe Basic Principles: : Basic Principles: All chemical processes are centered in a chemical reactor. The design of a chemical reactor Is the most important factor in determining the overall process economics. Slide 6: At the start the design work , the following information is presumably available: . Reaction Type . Need for catalyst . Phases involve . The mode of temperature and pressure control, and . Production capacity Reaction Types : Reaction Types Direct Combination or Synthesis Reaction A + B = AB Chemical Decomposition or Analysis Reaction AB = A + B Slide 8: Single Displacement or Substitution Reaction A + BC = AC + B Metathesis or Double Displacement Reaction AB + CD = CB In addition to the basic data, include: : In addition to the basic data, include: A heat and mass transfer characteristics Physical, chemical and thermodynamic properties of components taking part in the reaction. CORROSION- erosion characteristics of any potential hazard associated with reaction system. Reaction Rate Endothermic Reactions : Endothermic Reactions “within- heating” describes a process or reaction that absorbs energy in the form of heat. Exothermic Reactions : Exothermic Reactions Release energy in the form of heat, light, or sound. ?S > 0 ?H < 0 Reaction Rate : Reaction Rate Speed at which a chemical reaction proceeds, in terms of amount of product formed or amount of reactant consumed per unit time Factors Influencing Reaction Rate : Factors Influencing Reaction Rate Concentration The nature of reaction Temperature Pressure Catalyst Modeling Principle: : Modeling Principle: Inputs + Sources = Output + Sink + Accumulations Basic Reactor Element : Basic Reactor Element Material Balances Heat Transfer and Mass Transfer Material Balances : Material Balances Also called mass balance. Is an application of conservation of mass to the analysis of physical systems. The mass that enters a system must, by conservation of mass, either leave the system or accumulate within the system . Mathematically the mass balance for a system without a chemical reaction is as follows: : Mathematically the mass balance for a system without a chemical reaction is as follows: Input = Output + Accumulation Applications of Differential Mass Balance : Applications of Differential Mass Balance Ideal (stirred) Batch reactor Ideal tank reactor, also named Continuous Stirred Tank Reactor (CSTR) Ideal Plug Flow Reactor(PFR) Mass Transfer : Mass Transfer Is the phrase commonly used in engineering for physical processes that involve molecular and convective transport of atoms and molecules within physical system. Transfer of mass from high concentration to low concentration. Heat Transfer : Heat Transfer Is the transition of thermal energy from a heated item to a cooler item. Transfer of Thermal Energy Modes Of Heat Transfer : Modes Of Heat Transfer jacket, internal coils, external heat exchanger, cooling by vapor phase condensation fired heater. Slide 23: Jacket Slide 24: Internal Coil Slide 25: External Heat Exchanger Slide 26: Cooling by Vapor Phase Condensation Slide 27: Heat Exchange in Packed Reactors Chemical Reactor can be operated in: : Chemical Reactor can be operated in: 1. Batch Modes 2. Semi Continuous Modes 3. Continuous Modes BATCH REACTOR : BATCH REACTOR One in which feed material is treated as a whole for a fixed period of time. Types of Cooling Jacket: : Types of Cooling Jacket: Single External Jacket Consists of an outer jacket which surrounds the vessel. Heat transfer fluid flows around the jacket and is injected at high velocity via nozzles. The temperature in the jacket is regulated to control heating or cooling. Slide 31: Single External Jacket Slide 32: The half coil jacket is made by welding a half pipe around the outside of the vessel to create a semi circular flow channel. A large reactor may use several coils to deliver the heat transfer fluid. Half Coil Jacket Slide 33: Half Coil Jacket Slide 34: Has a series of 20 or more small jacket elements. The temperature control valve operates by opening and closing these channels as required. Constant Flux Cooling Jacket Slide 35: Constant Flux Cooling Jacket Slide 36: SCHEMATIC DIAGRAM OF CRUDE SEWAGE Semi Batch Reactor : Semi Batch Reactor One or more reactant is in a batch modes, while co reactant is fed and withdrawn continuously. Slide 39: Schematic Diagram of Semi Batch Stirred TankReactor : Stirred TankReactor Slide 41: Consist of a tank fitted with a mechanical agitator and a cooling jacket or coils. Continuous Stirred-Tank Reactor(CSTR) : Continuous Stirred-Tank Reactor(CSTR) One or more fluid reagents are introduced into a tank reactor. Slide 44: Residence time – average amount of time a discrete quantity of reagents spend inside the tank Residence time = volumetric flow rate volume of the tank Some Important Aspects of the CSTR: : Some Important Aspects of the CSTR: Slide 46: At steady state, the flow rate in must be equal the mass flow rate out. Slide 47: All calculations performed with CSTR’s assume perfect mixing. Slide 48: The reaction proceeds at the reaction rate associated with the final (output) concentration. Economically beneficial to operate in series or in parallel Slide 49: Small CSTR operating in series would be equivalent to a PFR. Plug Flow Reactor(PFR) : Plug Flow Reactor(PFR) One or more fluid reagents are pumped through a pipe or tube Some Important Aspects of the PFR: : Some Important Aspects of the PFR: Slide 54: All calculations performed with PFR’s assume no upstream or downstream mixing. Reagents may be introduced into the reactor’s inlet Slide 55: Has a higher efficiency than a CSTR at the same value. Slide 56: Schematic Diagram of Plug Flow Reactor Tubular Flow Reactor(TFR) : Tubular Flow Reactor(TFR) are generally used for gaseous reactions but are also suitable for some liquid-phase reactions. Some Important Aspects of the TFR: : Some Important Aspects of the TFR: Slide 59: Chemical reactions take place in a stream of gas that carries reactants from the inlet to the outlet The catalysts are in tubes Slide 60: Uniform loading is ensured by using special equipment that charges the same amount of catalyst to each tube at a definite rate. CATALYSIS : CATALYSIS CATALYSIS : CATALYSIS It is the acceleration of chemical reaction by means of substance called catalyst. Slide 65: Principles of Catalysis: ·Typical mechanism: A + C ? AC (1) B + AC ? ABC (2) ABC ? CD (3) CD ? C + D (4) Slide 66: Catalysis and reaction energetic. What is Phase? : What is Phase? Slide 68: Two Types of Catalyst: ·Homogeneous ·Heterogeneous Homogeneous : Homogeneous the catalyst in the same phase as the reactants. Heterogeneous : Heterogeneous Involves the use of a catalyst in a different phase from the reactants. How the heterogeneous catalyst works? : How the heterogeneous catalyst works? Adsorption Active Sites Desorption Adsorption : Adsorption Is where something sticks to a surface. Active Sites : Active Sites Is a part of the surface which is particularly good at adsorbing things and helping them to react. Desorption : Desorption means that the product molecules break away. Kinds of Catalyst : Kinds of Catalyst Strong Acids Base Catalysis Metal oxides, Sulfides, and Hydrides Metal and Alloys Transition-metal Organometallic Catalysts Strong Acids : Strong Acids Is an acid that ionizes completely in an aqueous solution Base Catalysis : Base Catalysis Is most commonly thought of as an aqueous substance that can accept protons. Base the chemical opposite of acids. Often referred to as an alkali if OH- ions are involved. Metal Oxides : Metal Oxides Form a transition between acid/base and metal catalysts. Metal and Alloy : Metal and Alloy Metal is a chemical elements whose atoms readily lose electrons to form positive ions (cations), and form metallic bonds between other metal atoms and ionic bonds between nonmetal atoms. The principal industrial metallic catalyst, are found in periodic group VII Transition-metal Organometallic Catalysts : Transition-metal Organometallic Catalysts More effective hydrogenation than are metals such as platinum. Fluid and Solid Catalysis : Fluid and Solid Catalysis Multitubular reactors Fluidized beds Fixed Bed Spray Tower Two-Phase Flow Multitubular reactors : Multitubular reactors These reactors are shell-and-tube configuration and have catalyst in the tubes. Slide 84: Multi tubular Reactor Fluidized Bed : Fluidized Bed Device that can be used to carry out a variety of multiphase chemical reactions. A catalyst possibly shaped as tiny spheres. Slide 86: Fluidized Bed Reactor Fixed Bed : Fixed Bed Fixed bed reactor is a cylindrical tube, randomly filled with catalyst particles, which may be spheres or cylindrical pellets. Fixed Bed Reactor : Fixed Bed Reactor SPRAY TOWER : SPRAY TOWER Are a form of pollution control technology. Consist of empty cylindrical vessels made of steel or plastic and nozzles that spray liquid into the vessels Two types of Spray Towers: : Two types of Spray Towers: 1.Cocurrent Flow -are smaller than countercurrent-flow spray towers 2.Crosscurrent Flow - the gas and liquid flow in directions perpendicular to each other. Two-Phase Flow : Two-Phase Flow occurs in a system containing gas and liquid with a meniscus separating the two phases. Two-phase flow may be classified according to the phases involved as: : Two-phase flow may be classified according to the phases involved as: gas-solid mixture gas-liquid mixture liquid-solid mixture two-immiscible-liquids mixture Goodbye!!!!! : Goodbye!!!!! Eating Time!!!! Thank You!!!! You do not have the permission to view this presentation. In order to view it, please contact the author of the presentation.