This slide completely describes you about the stuff include in it and also everything about chemical engineering. Fluid Mechanics. Thermodynamics. Mass Transfer Chemical Engineering. Energy Engineering, Mass Transfer 2, Heat Transfer,

1. Intro to Reactor Design
Chap # 4
Octave LEVENSPIEL

2. Introduction
• Introduction to reactor design is given in chapter #1.
• Here we will deal with some more discussion on the reactor, their
types and basic equations needed for a reactor to be designed.
• The Reader must study chapter 1 before the start of this chapter
• For a particular type of reaction to be occurred in a controlled
manner some type of hardware is needed called “REACTOR”.
• This reactor, also called heart of Chemical process, is to be designed
to provide the conditions necessary for chemical reaction to proceed.

3. • In Majority of cases, reactor do three things, it provides
I. Residence Time
II. Transfer Heat
III. Agitates or mix phases
Principle Factors Involved in the design of Reactor:
The principle factors which must be considered in the design of the
reactor are:
 The Phase involved
 Temperature Range
 Operating Pressure
 Residence Time or Space Velocity

4.  Corrosiveness
 Heat Transfer
 Temperature Control
 Agitation for uniformity or temperature control
 Batch or Continuous operation
 Production rate

5. Types Of Reactor
• Chemical Reactor may have a variety of sizes, shapes and operating
conditions. We here try to classify them in three different modes.
a. Based on method of Operation
b. Based on shape
c. Based on No. of phases involved
a. Based on Method of Operation:
The reactor may be
• Batch Reactor
• Continuous flow (Steady Flow) Reactor
• Semi- Batch(Semi-continuous)

6. Batch Reactor
• A batch reactor has neither inflow nor outflow of reactants or
products while the reaction is being carried out.
• In such extend of reaction and properties of reaction mixture very
with time.
• Thus composition changes with time.
• For gas phases batch reactor may be constant volume or constant
pressure.

7. Continuous Reactor or Steady State Reactor
• The reactants are continuously fed and product are also continuously
removed from the reactor.
• In such reactor the extend of reaction may vary with position in
reactor not with time.
• Thus composition at any point is not changed with time(They may be
continuous-stirred tank or Tubular Reactor)

8. • 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.
Supporting equipment's need are high
However, extremely good products quality can be obtained
This reactor is widely used in the oil industry

9. Semi-Batch Un-steady State Reactors
• The Reactants are introduced partially and additional reactants are added
progressively until the desired quantity is added. Alternatively, one may
charge the reactants at once and continuously remove products as they
formed.
Semi- Batch Reactors may be either
I. Reactors in which volume and composition changes

10. ii. Reactor in which volume changes but composition is unchanged
iii. Reactors in which volume is constant but composition changes

11. • Flexible system but is more difficult to analyze than the other reactor
types.
• Good control of reaction speed b/c the reaction proceed as reactants
are added.
• Uses/application from the calorimetric titration in the laboratory to
the large open hearth furnace for steel production

12. b) Based on Shape
1. Tank Reactor
2. Tabular 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 as 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) or back mix Reactor.

13. Tubular Reactor:
• Tubular reactor is one in which there is no mixing in the direction of
flow in the reactor. The reactants are continuously consumed as they
flow in the axial (Down THE LENGTH OF REACTOR) direction. Thus the
concentration varies along the axial direction. They also called plug
flow reactor(PFR), Slug Flow Reactor, Piston Flow Reactor or un-mixed
flow reactor.

14. Example of Tubular Reactor

15. Example of Tubular Reactor

16. C) Based on No. Of Phases Involved
1. Homogeneous
2. Heterogeneous
In many cases the physical process results from
the fact that the reaction mixture is heterogeneous, e.g the reaction of
SO2 and O2 on V2O5 catalyst.
It would not exist if the reaction is a single phase homogeneous, thus
the classification is necessary.

17. Fundamental Design Equation:
• The starting point of all designs is the material balanced expressed for
any reactant/product. A material Balance on a reactant species of interest
for an element of volume say ΔV can be written as:
• In short,
INPUT – OUTPUT – LOSS OF REACTION = ACCUMULATION

19. • When the composition within the reactor is uniform (Independent of position),
we will consider the whole reactor of material balance.
• On the other hand when the composition within the reactor 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 condition (For
Tubular Flow Reactor).
For the batch reactor the first two terms are zero.
For continuous flow reactors operating at steady –state, the accumulation terms
is omitted.
Where for unsteady state condition are involved, it will be necessary to integrate
over time as well as over volume in order to determine the performance
characteristics of the reactor.

20. • Since rate of chemical reactions is normally strongly temperature dependent, it’s
essential to know the temperature at each point in the reactor in order to be able
to utilize the material balance properly.
• When there are temperature gradients with in the reactor, it is necessary to
utilize an energy balance in conjunction with the material balance in order to
determine the temperature and composition at each point in the reactor at a
particular time.
• The general Energy balance for an element of volume ΔV over a time Δt can be
written as:

21. • For completeness, the term corresponding to the entry (In) of
material to the volume element and out, therefore must contain in
addition to the ordinary enthalpy of the material, its kinetic and
potential energy.
• However in chemical reactors, only the enthalpy term is significant.
• Although the heat effects in chemical reactors are significant, shaft
work effects are usually negligible.
• The chemical reaction rates does not appear explicitly in the
equation, but its effect are implicit in all terms except third.

22. • The first, second and fourth terms reflect differences in temperature
and or in composition of the entering and leaving streams.
• The energy effects associated with composition changes are a direct
reflection of enthalpy change associated with the reaction (i.e heat of
reaction)
From the summary we can write in short:
Heat In – Heat Out – Disappearance by reaction = accumulation

23. • For the stirred tank reactor contents are uniform in temperature and
composition throughout and it is possible to write the energy balance
over the entire reactor.
• In the case of batch reactor, first and second terms are not there.
• For continuous flow systems operating at steady state, the
accumulation term disappears.
• For adiabatic operation in the absence of shaft work effects the
energy transfer/disappear term will be omitted/zero.

24. • For Tubular Flow Reactors, neither the composition nor the
temperature need to be independent of position and the energy
balance must be written on a differential element of reactor volume.
• The resultant differential equation then must be solved in conjunction
with the differential equation describing the material balance on the
differential element.
• The Purpose of the energy balance is to describe the temperature at
each point in the reactor ( or at each time for Batch Reactor) so that
the proper rate may be assigned to that point.

26. Symbols and Relationship B/W CA and XA
•

28. Special Case1: Constant Density Batch and
Flow Systems:
• This includes most liquid reactions and also those gas reactions run at
constant temperature and density. Here CA & XA are related as
follows:
Fractional change in volume of the system b/w no
conversion and complete conversion of reactant A,
Thus