Multiple reactors

Multiple reactors

Malik Ahmad Rid Roll.No 2k13-Che-94

Multiple Reactors

CRE:Chemical Reaction Engineering (CRE) is the field that studies the rates and mechanisms of chemical reactions and the design of the reactors in which they take place.

Chemical ReactorsAn 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

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.

In addition to the basic data, includeA heat and mass transfer characteristicsPhysical, chemical and thermodynamic properties of components taking part in the reaction.CORROSION- erosion characteristics of any potential hazard associated with reaction system. Reaction Rate

Basic data:1. endothermic reactions(within- heating describes a process or reaction that absorbs energy in the form of heat.)2.exothermic reactions (Release energy in the form of heat, light, or sound.)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 Concentration The nature of reaction Temperature Pressure CatalystModeling Principle:Inputs + Sources = Output + Sink + Accumulations

Basic Reactor Element1.Material Balances2.Heat Transfer and Mass TransferMaterial 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:Input = Output + Accumulation

Mass TransferIs 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 concentrationHeat TransferIs the transition of thermal energy from a heated item to a cooler item.Transfer of Thermal Energy

Modes Of Heat Transfer jacket, internal coils, external heat exchanger, cooling by vapor phase condensationfired heater.

Reactor typesThey can be classified according to the;1. Modes of operation2. End use applications3. No. of phases4. A catalyst is use

Chemical Reactor on the basis of operation:Batch Modes Semi Continuous Modes Continuous Modes

CSTR IN SERIES:Lets have an simple derivation and example solved to illustrate you .

Example : For two CSTRS in series 40% conversion is achieved in the first reactor . What is the volume of each two reactor necessary to achieve the 80% over all conversion of entering specie first ?Table processed data:

X0.00.10.20.40.60.8faO/-ra0.891.091.332.053.548

Advantages in series/parallelThese are commonly used In industrial processing primarily in homogenous liquid phase flow reactions where constant agitation is required they may be used in series and parallel.When agitation and good mixing is required.

Disadvantages :It is not recommended for high pressure reactions because of cost consideration. For high pressure reactions it requires complex sealing arrangements for the agitator which increase the initial as well as maintenance cost.Conversion of these reactors is low due to this they are not preferred.These reactors are not suited for high heat effect since availability of both heat transfer coefficient and heat transfer per unit area is low.

Multiple reactor system PFR (in series) :Number of plug flow reactor in series are theoretically same as equivalent volume of a single plug flow reactor. Number of mixed flow reactor of equal size in series may be used when we need high conversion and cant perform in a single reactor.

PFR Design Equation

Similarly, the design equation for a PFR is FA0 dX/ dV = rA Therefore, V = FA0 X/-raParallel Reactions in parallel reactors :When a reactant gives two product (desired, and undesired)simultaneously with different rate constant then this is called a parallel reaction.To keep maximum amount of desired product we can take following steps.Ifa1>a2 or the desired reaction is of higher order then keep reactant concentration high for high product concentration.If a1