This PPT contains basics and design equations of Recycle Reactor. Also contains performance curve of it.

1. SUBJECT - CHEMICAL REACTION ENGINEERING – 1

2. What Is Recycle Reactor ??
 In certain situations it is found to be advantageous to
divide the product stream from a plug flow reactor and
return a portion of it to the entrance of the reactor.
 Let the recycle ratio R be defined as :

3. What Is Recycle Reactor ??
 This recycle ratio can be made to vary from zero to
infinity.
 Reflection suggests that as the recycle ratio is
raised the behaviour shifts from plug (R=0) to
mixed flow.
 Thus recycling provides a means for obtaining
various degrees of backmixing with a plug flow
reactor.
 Let us develop the performance equation for the
recycle reactor.

4. Recycle Reactor
 Figure of Recycle Reactor :

5. Derivation Of Performance
Equation
 Consider a recycle reactor with nomenclature as shown
in figure. Across the reactor itself equation for plug flow
gives,
 ---------(1)
 Where F’A0 would be the feed rate of A if the stream
entering the reactor (fresh feed plus recycle) were
unconverted.

6. Derivation Of Performance
Equation
 Since F’A0 and XA1 are not known directly, they
must be written in terms of known quantities before
the above equation can be used.
 The flow entering the reactor includes both fresh
feed and the recycle stream. Measuring the flow
split at point L we then have

7.  Now to evaluate XA1 from above equation we can
write ;
 ------- (2)
 Now, equation of CA1 can be written as ;
----(3)

8. Combining Eqns (2) & (3) we will get ;
----------(4)
Finally putting value of (4) in Eqn (1) we will get ;
Conversion :
Concentration :

9. These expressions are represented graphically in Fig. 6.14.

13. Advantages
 Less time required for desired
conversion than the PFR due to Back
Mixing
 We can get different percentage of
conversion by only changing Recycle
Ratio

14. Disadvantages
 Fixed cost is high because of higher
volume of reactor required
 Operating cost is also high due to
recycle
 Volume requred is higher than PFR
due to recycle
 Conversion is also less than PFR

15. Application
 The production unit in which we want
high conversion as well as production
in Lesser time then we can use this
type of reactor.
 It is generally used in petroleum
industry and when the system is
needed to recycle such as Enzyme
Rich stream back into the reactor.