topic 4 - design of ideal reactors for single reaction

7/23/2019 Topic 4 - Design of Ideal Reactors for Single Reaction

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Subtopics:Ideal Batch Reactor

Steady state mixed fow reactor(MFR)

Steady state plug fow reactor

Space time and space elocity

!olding time and space time "orfow reactor

Si#e comparison o" single reactors

Re"erence: Fogler and $eenspiel







Reactors coered in %opic & are:

'Batch Reactor Steady State MFR * Mixed FlowReactor+ Steady State ,FR * ,lug Flow

Reactor






ApplicationSmall scale production/one-off production

Pharmaceutical and fermentation

Advantages

Easy to cleanHigh conversion per volume

Flexiility of operation-same reactor can

produce one product one time and a different

product the next

!isadvantages"

High operating cost

Product #uality more variale than with

continuous operation

$deal %atch &eactor






$deal %atch &eactor

Material Balance: In - .ut / ,roduct 01ccumulation

' '

Batch Reactor Design Equation

2 the reactants are initially charged into a container3 are wellmixedand are le"t to react "or certain period

4 Recall the batch reactor design e5uation

Vr dt

dNA

A = ( )X1 N NAoA −=

Vr dt

dX N

AAo −=

( )

∫ −=

tX

0A

Ao

Vr

dX Nt

diferentialorm

integralorm







$deal %atch &eactor






6raphical representation o" the per"ormancee5uations "or batch reactors3 isothermal and non*isothermal7 6eneral case

8onstant*density systems

only

$deal %atch &eactor






Steady State (ixed Flow &eactor )(F&*

1pplication

1 production o" where agitation isre5uired

8ontinuous production

1dantages

9asy to clean

6ood temperature control

$ow operating cost (labour)

isadantages:

$owest conersion per unit

olume






Steady State (ixed Flow &eactor )(F&*

4 %he contents are well stirred and uni"orm throughout

+ The exit stream from this reactor has the same

composition as the fluid within the reactor

4Recall the 8S%R esign 95uation:

( )X1FFAoA −=

A

AAo

r

FFV

−

−=

( )exit

A

Ao

r

XFV

−

=







4 esign e5uation A

A Ao

r

F F V

−

−

=

In terms o"conersion A

Ao

r

X F V

−

=

Reactor si#ing3 theolume o" MFR canbe calculated "rom

s A

Ao

r

F

−

X

A

Ao

r

F

−

X

SS-(F&






4 Reactors in series can also be designed proided there are noside streams by de;ning the oerall conersion at any point

reactor firsttofedAof moles

i pointtoupreactedAof moles=i X

Mole balance at reactor '

Mole balance at reactor

0111

=+− V r F F A A Ao

1

1

1

A

Ao

r

X F V

−

=

02221

=+− V r F F A A A

( )

2

12

2

A

Ao

r

X X F V

−

−=

SS-(F&






Steady State Plug Flow Reactor

1pplication

For large scale production

,roduction with "ast reactions<high temperature Both homogenous and heterogeneous reaction

8ontinuous production

1dantages

!igh conersion per olume

$ow operating cost

6ood heat trans"er

isadantages:

=ndesired thermal gradients may exist

,oor temperature control






4esign e5uation A

A

r dV

dF =

In terms o"conersion

A Ao r

dV

dX F −=

∫ −=

X

A

Ao

r

dX F V

0

%he olume o" ,FR can be represented as

shaded area under the cure

* 1rea under the curecan be calculated usingnumerical method such

as Simpson>s Rule

Steady State Plug Flow Reactor






Space Time and Space elocity

o

V

υ

τ =

Space time3 isobtained by diidingreactor olume by

the olumetric fowrate entering thereactor

τ

%ime ta?en "or fuid

to enter reactorbased on entrancecondition - olumeand olumetric rate






+ Space velocity, S is defined as

τ

υ 1==

V

SV o

V LHSV

liquid o |υ

=

V GHSV o STP|υ

=

Space Time and Space elocity






For %atch reactor

∫ =

A

Ao

C

C A

A

r

dC d τ

∫ −

=

Ao

A

C

C A

A

r

dC τ

A A r

dt

dC =

!olding time and Space Time or Reactor






A

A Ao

r

F F V

−

−

=

For .ST&/(F&,

A

o

A

o

Ao

o r

F F V

−

−

=

υ υ

υ

A

A Ao

r

C C

−

−

=τ







For PF&

A

A

r

dC d =τ

A

A

r dF dV =

∫ −

=

X

A

Aor

dX F V

0

∫ −=

X

A

Ao

r

dX C

0

τ







Si"e #omparison o Single Reactors






9xam @ A 1pril ''

%he li5uid phase o" reaction A -» B is an elementary

reaction in a fow reactor with 85% conersion o" 1 %he inlet concentration o" 1 is + mol<liter and theolumetric fowrate isC liter<hr1dditional in"ormation: ?1 0 D hr*'

a) etermine the space time and olume i" this

reaction is carried out in a 8S%R(& mar?s)

b) etermine the space time and olume i" thisreaction is carried out in a ,FR

(& mar?s)c) Repeat part (a) and (b) i" the reaction now obeys

nd order ?inetics(E mar?s)

d) 8hoose the best reactor "or both order o" reactionand usti"y your answer

(C mar?s)






9G .F %.,I8 &



topic 4 - design of ideal reactors for single reaction

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