reactor design 9
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Polymer/Chemical Reactor Design
Muhammad Zafar Iqbal
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Today
• Recycle Reactors and some important considerations• Autocatalytic Reactors and their important considerations• Optimum temperature Progression • Reactor Operating Line• Basics of Non-linear flow: Fundamental Concept
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Recycle ReactorsA reactor for which product stream is split and a part of that split
stream is sent back to reactor to enhance the reactor performance is called a Recycle Reactor.
Recycle Stream is defined as:
Recycle stream is introduced to enhance the degree of mixing.Therefore it is conventionally said that for R=0, the behavior is
totally plug and for R=very large, the behavior is mixed flow reactor.
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Types of recycle reactor
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Ref:Chemical Process design andIntegration by Smith, Ch-13,14
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Performance Equation
For this plug flow reactor, the performance equation is given as:
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The actual conversion at inlet is given by:
The concentration at inlet to the reactor is given by
So finally we get the following results:
The final equation for any expansion factor value is:
Also in terms of concentration,
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Graphical representation
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Autocatalytic Reactors• In general, when conc. Of reactants is high (at start) the rate
of reaction is also high. When conc. Is lowered, the reaction proceeds slowly.
• In autocatalytic reactions, the rate of reaction at the start is slow but as the product is formed more and more, the speed of reaction increases up to a certain level then drops.
• Therefore there is always a need for optimization of reactors for autocatalytic reactions.
• A general representation of autocatalytic reaction is given as:
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Mixed flow Vs Plug flow Reactor
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Temperature and Pressure Effects in Single Reaction based Reactors
• There is a great influence of operating conditions on the reactor set up and optimization.
Normally the following three step procedure is adopted:1- T and P effects on equilibrium composition, rate of reaction and product distribution2- The Heat effects and their impact on operating Temp.3- Economic optimization of process
Single Reactions:Two factors are considerable:1- Conversion Level no product distribution2- Reactor stability
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Optimum Temperature Progression
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Reactor Operating LineThe size of a reactor for a given duty and for a given
temperature progression is found from following procedure:
• Draw XA Vs T (Reactor Operating Line)
• Find Reaction rates at different XA along this path
• Plot 1/-rA Vs XA for this path
• Find the area under the curve or area of the rectangle depending upon the type of reactor used.
Ref:Chemical Reaction Engineering by LevenspielChapter 9.
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Non-Ideal Flow: Fundamental Concepts
Three main factors which can describe the flow are:
• RTD• State of Aggregation• Earliness and Lateness of Mixing
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Residence Time Distribution
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States of Aggregation of the flowing stream
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Mixing
Ref:Chemical Reaction Engineering by LevenspielChapter 11.