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1. Intro to Reactor Design

2. Chemical Reaction Engineering
• Chemical Reaction Engineering (CRE) is the field that study the rates,
mechanism of chemical reactions and the design of the reaction in
which they take place.

3. In majority of cases, reactor do three things, it provide
• Residence time
• Heat transfer
• Mix phase
Principle factors involved in the design of reactors
The principle factors which must be considered in the design of the reactor
are
1. Size of reactor
2. Type of reactor

4. 3. Time or duration of reaction
4. Temperature and composition of reacting material in the reactor
5. Heat transfer
6. Production rate

5. Types of reactor
• Chemical reactor may have a variety of sizes, shapes, and operating
conditions. We here to try to classify them in three different modes
1. Based on method of operation
2. Based on shape
3. Based on No. of phases involved

6. Based on Method of operation
• Batch reactor
• Continuous flow ( steady flow) Reactor
• Semi-Batch (semi-continuous)

7. Batch reactor
• A batch reactor has neither inflow nor outflow of reactants or
products while the reaction is being carried out.
• In such extent reaction and properties of the reaction vary with time
• The composition changes with time
composition change

8. Continuous Reactor or Steady State Reactor
• In this case reactants are continuously fed into the reactor and
product are continuously removed from the reactor.
• Continuous reactors are used a wide range of chemical and biological
process with in the food, chemical and pharmaceutical industries.
• The composition at any point is not changed with time.
• The continuous flow reactors are classified as
1. Continuous stirred tank reactor (CSTR)
2. Plug flow reactor (PFR)
3. Packed bed reactor (PBR)

9. • The steady state flow reactor is ideal for industrial purpose when
large quantities of material are to be processed and when the rate of
reaction is fairly high to extreme high.
• However extremely good products quality can be obtained.

10. Semi-Batch Un-steady state Reactors
• One or more reactant is in a batch modes while co-reactant is added
at once and continuously remove products as they formed .
Semi-batch reactor may be either
1. Reactors in which volume and composition changes

11. • 2. Reactor in which volume changes but the composition is
unchanged
• Reactors in which volume is constant but composition changes

12. Based on shape
• Tank Reactor
• Tubular Reactor
• Tank Reactor
An ideal reactor is one in which stirring is so efficient that the contents are
always uniform in composition and temperature throughout the tank.
This type of reactors are called Stirred tank or well – mixed reactor. The
simple tank reactor may be operated in a variety of modes, Batch, Semi
batch, or continuous flow. When it is continuous its called Continuous stirred
tank reactor (CSTR)

13. Tubular Reactor
• A tubular flow reactor (TFR) is a tube (or pipe) through which
reactants flow and are converted to products.
• The reactants are continuously consumed as they flow in the axial
direction.
• The concentration varies along the axial direction. They also called
plug flow reactor (PFR) etc.

14. Example of Tubular Reactor
Plug flow reactor
• Plug flow reactor ideal flow reactor in which no back mixing occur.
• The composition of the reactions mixture changes along the length
of the reactor.

15. Based on No. of phases involved
• Homogeneous
• Heterogeneous

16. Fundamentals Design equation
• The starting point for all design is the material balance expressed for
any reactant (or product).
• In short,
Input – Output – Loss of reaction = Accumulation

17. Factors considered in Designing
• Where the composition within the reactor is uniform , we will
consider the whole reactor of material balance.
• On the other hand, when the composition is not uniform, it must be
made over a differential element of volume and then integrated
across the whole reactor for the appropriate flow and concentration
conditions.
• For the batch reactor the first two terms are zero.
• For continuous flow reaction the fourth term disappears.

18. • Where for unsteady state condition are involved, it will be necessary
to integrate over time as over volume in order to determine the
performance of the reactor.
• Since rate of chemical reaction is normally strongly temperature
dependent. Its essential to know the temperature at each point in the
reactor in order to be able to utilize the material balance properly.
• When there temperature gradients with in the reactor it is necessary
to utilize an energy balance.

19. • The general energy balance can be written as
• However, in chemical reactor only the enthalpy term is significant.
• Although the heat effect in chemical reaction are significant, shaft
work effect are usually negligible.

20. • The energy effects associated with composition changes are a direct
reflection of enthalpy change associated with the reaction (i.e., heat
of reaction).
• For stirred tank reactor content are uniform in temperature and
composition throughout and it is possible to write the energy balance
over the entire reactor.