Lec 4 Isothermal Reactor Design - University of Jordaneacademic.ju.edu.jo/z.hamamre/Material/Chemical React… · · 2012-08-29Isothermal Reactor Design ... o Single CSTR o CSTR’s

Chemical Engineering Department | University of Jordan | Amman 11942, Jordan

Tel. +962 6 535 5000 | 22888

1

Dr.-Eng. Zayed Al-Hamamre

Chemical Reaction Engineering

Isothermal Reactor Design


Tel. +962 6 535 5000 | 22888

2

Content

Batch Reactor

Design of CSTR Reactors

o Single CSTR

o CSTR’s in Series

o CSTR’s in Parallel

Design of PFR Reactors

Flow Through a Packed Bed


Tel. +962 6 535 5000 | 22888

3

Isothermal reaction design

algorithm For conversion


Tel. +962 6 535 5000 | 22888

4

Algorithm Isothermal reactor


Tel. +962 6 535 5000 | 22888

5

For constant volume batch reactors

Batch Reactors


Tel. +962 6 535 5000 | 22888

6

calculate the time necessary to achieve a given conversion X for the irreversible second-order

reaction

Example

and


Tel. +962 6 535 5000 | 22888

7

Example Cont.


Tel. +962 6 535 5000 | 22888

8

Example Cont.


Tel. +962 6 535 5000 | 22888

9

Example Cont.


Tel. +962 6 535 5000 | 22888

10

Example


Tel. +962 6 535 5000 | 22888

11

Example Cont.


Tel. +962 6 535 5000 | 22888

12

Example Cont.


Tel. +962 6 535 5000 | 22888

13

Example Cont.


Tel. +962 6 535 5000 | 22888

14

CSTR’s Design

Knowing that

This equation applies to a single

CSTR or to the first reactor of

CSTRs connected in series.


Tel. +962 6 535 5000 | 22888

15

A Single CSTR

CSTR’s Design

For a first-order irreversible reaction

For liquid-phase reactions, there is no volume change during the course of the reaction,

also


Tel. +962 6 535 5000 | 22888

16

CSTR’s Design

The Damkohler number

Is the ratio of the rate of reaction of A to the rate of convective transport of A at the

entrance to the reactor

Give us a quick estimate of the degree of conversion that can be achieved in continuous

flow reactors


Tel. +962 6 535 5000 | 22888

17

CSTR’s Design

For a first-order liquid-phase reaction in a CSTR


Tel. +962 6 535 5000 | 22888

18

CSTR’s in Series

CSTR’s Design

The effluent concentration of reactant A from

the first CSTR can be found


Tel. +962 6 535 5000 | 22888

19

CSTR’s Design


Tel. +962 6 535 5000 | 22888

20

CSTR’s Design


Tel. +962 6 535 5000 | 22888

21

CSTR’s Design

Conversion as a function of the number of tanks in series for

different Damkohler numbers for a first-order reaction


Tel. +962 6 535 5000 | 22888

22

CSTR’s in Parallel

CSTR’s Design

If the reactors are of equal size, operate at the same temperature,

and have identical feed rates.

The conversion will be the same for each reactor

The rate of reaction in each reactor


Tel. +962 6 535 5000 | 22888

23

CSTR’s Design

The total molar flow rate

Since


Tel. +962 6 535 5000 | 22888

24

A Second-Order Reaction

CSTR’s Design


Tel. +962 6 535 5000 | 22888

25

CSTR’s Design


Tel. +962 6 535 5000 | 22888

26

Example


Tel. +962 6 535 5000 | 22888

27

Example Cont.

the single CSTR volume to achieve 80% conversion


Tel. +962 6 535 5000 | 22888

28

Example Cont.


Tel. +962 6 535 5000 | 22888

29

Example Cont.


Tel. +962 6 535 5000 | 22888

30

Example Cont.


Tel. +962 6 535 5000 | 22888

31

Example Cont.


Tel. +962 6 535 5000 | 22888

32

Example Cont.


Tel. +962 6 535 5000 | 22888

33

PFR Reactors Gas-phase reactions are carried out primarily in tubular reactors where the flow i s generally

turbulent


Tel. +962 6 535 5000 | 22888

34

For the reaction

PFR Reactors

For the isothermal operation,


Tel. +962 6 535 5000 | 22888

35

Known that

PFR Reactors

For reaction in a Gas Phase


Tel. +962 6 535 5000 | 22888

36

PFR Reactors

For the isothermal operation,

the effect of volume change with reaction


Tel. +962 6 535 5000 | 22888

37

PFR Reactors

there i s no change in the number of mole with reaction

fluid moves through the reactor at a constant

volumetric flow rate as the conversion increases

there is a decrease in the number of moles in the gas phase

the gas molecules will spend longer in the reactor than

they would if the flow rate were constant resulting in a

higher conversion

there is an increase in the number of moles in the gas phase

then the volumetric flow rate will increase as the

conversion increase and the molecules will spend less time

in the reactor resulting in a lower conversion


Tel. +962 6 535 5000 | 22888

38

PFR Reactors


Tel. +962 6 535 5000 | 22888

39

Determine the plug-flow reactor volume necessary to produce 300 million pounds of ethylene a

year from cracking a feed stream of pure ethane. The reaction is irreversible and fallows an

elementary rate law. We want to achieve 80% conversion of ethane. operating the reactor

isothermally at 1100 K at a pressure of 6 atm.

Example


Tel. +962 6 535 5000 | 22888

40

Example Cont.


Tel. +962 6 535 5000 | 22888

41

Example Cont.


Tel. +962 6 535 5000 | 22888

42

Example Cont.


Tel. +962 6 535 5000 | 22888

43

Example Cont.

For 2-in. schedule 80

pipes in parallel that are

40 ft in length.

The number of pipes


Tel. +962 6 535 5000 | 22888

44

Pressure Drop and the Rate Law

PFR Reactors

In packed-bed reactor

Since And for


Tel. +962 6 535 5000 | 22888

45

PFR Reactors


Tel. +962 6 535 5000 | 22888

46

PFR Reactors


The pressure drop in a packed porous bed to be calculated


Tel. +962 6 535 5000 | 22888

47



Tel. +962 6 535 5000 | 22888

48

For PBR operating at steady state,


or

but

hence

Combining with Ergun Equation


Tel. +962 6 535 5000 | 22888

49



Tel. +962 6 535 5000 | 22888

50


mass of catalyst per volume of reactor bed

let


Tel. +962 6 535 5000 | 22888

51


or

and


Tel. +962 6 535 5000 | 22888

52


Two coupled first-order

differentia1 equations

In conclusion, for isothermal reactors


Tel. +962 6 535 5000 | 22888

53


then

or

or


Tel. +962 6 535 5000 | 22888

54


or


Tel. +962 6 535 5000 | 22888

55



Tel. +962 6 535 5000 | 22888

56

Example


Tel. +962 6 535 5000 | 22888

57

Example Cont.


Tel. +962 6 535 5000 | 22888

58

Example Cont.


Tel. +962 6 535 5000 | 22888

59

Example Cont.


Tel. +962 6 535 5000 | 22888

60

Example For the case where a second-order reaction


Tel. +962 6 535 5000 | 22888

61

Example


Tel. +962 6 535 5000 | 22888

62

Example Cont.


Tel. +962 6 535 5000 | 22888

63

Example Cont.


Tel. +962 6 535 5000 | 22888

64

Example Cont.


Tel. +962 6 535 5000 | 22888

65

Example Cont.


Tel. +962 6 535 5000 | 22888

66

Example Cont.


Tel. +962 6 535 5000 | 22888

67

Example Cont.


Tel. +962 6 535 5000 | 22888

68

Example Calculate the catalyst weight necessary to achieve 60% conversion when ethylene oxide is to be

made by the vapor-phase catalytic oxidation of ethylene with air


Tel. +962 6 535 5000 | 22888

69

Example Cont.


Tel. +962 6 535 5000 | 22888

70

Example Cont.


Tel. +962 6 535 5000 | 22888

71

Example Cont.


Tel. +962 6 535 5000 | 22888

72

Example Cont.


Tel. +962 6 535 5000 | 22888

73

Example Cont.


Tel. +962 6 535 5000 | 22888

74

Example Cont.


Tel. +962 6 535 5000 | 22888

75

Example Cont.


Tel. +962 6 535 5000 | 22888

76

SemiBatch Reactor


Tel. +962 6 535 5000 | 22888

77

SemiBatch Reactor


Tel. +962 6 535 5000 | 22888

78

SemiBatch Reactor

Documents

Lec 4 Isothermal Reactor Design - University of Jordaneacademic.ju.edu.jo/z.hamamre/Material/Chemical React… · · 2012-08-29Isothermal Reactor Design ... o Single CSTR o CSTR’s