chemical reaction engineering lecture reactor design 3

isothermal reactor design part 3

1. PKC2070
Unit III
Isothermal Reactor Design
Lecture 3
Reactor Design-1

2. Space time & Space velocity
•Just as the reaction time t is the natural performance
measure for a batch reactor,
•so are the space-time and space-velocity the proper
performance measures of flow reactors

3. •A space-time of 2 min means that every 2 min one reactor
volume of feed at specified conditions is being treated by
the reactor.
OR
0.5 times of reactor volumes of feed at specified conditions
are being fed into the reactor per min.


•A space-velocity of 5 hr
-1
means that five reactor volumes
of feed at specified conditions are being fed into the reactor
per hour.
OR
Every 0.2 hr one reactor volume of feed at specified conditions
is being treated by the reactor.

4. •Now we may arbitrarily select the temperature, pressure,
and state (gas, liquid, or solid) at which we choose to
measure the volume of material being fed to the reactor.

•Certainly, then, the value for space-velocity or space-time
depends on the conditions selected. If they are of the
stream entering the reactor, the relation between s and τ
and the other pertinent variables is

5. •It may be more convenient to measure the volumetric
feed rate at some standard state, especially when the
reactor is to operate at a number of temperatures
(non-isothermal).

•If, for example, the material is gaseous when fed to
the reactor at high temperature but is liquid at the
standard state, care must be taken to specify precisely
what state has been chosen.
The relation between the space-velocity and
space-time for actual feed conditions (unprimed
symbols) and at standard conditions (designated by
primes) is given by

6. Residence time
•Time spent by molecules inside the reactor

•Represent in the form of residence time
distribution E(t)

7. Reactor

Differential

Algebraic

Integral














The GMBE applied to the four major reactor types
(and the general reaction A B)
CSTR
Batch
N
A

t
PFR
F
A

V
Reactor Mole Balances
Summary

8. Reference
Chapter-5
Octave Levenspiel, Chemical Reaction Engineering, 3
rd

edition
OR
Chapter-1
H. Scott Fogler, Elements of Chemical Reaction Engineering,
4
th
edition