II Choice of Reactor

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I I

Choice of Reactor

Outline

1. I ntroduction

2. Reaction Path

3. Types of Reaction System

4. Reactor Performance

5. Rate of Reaction

6. I dealized Reactor Models

7. Reactor Configuration

(2)

Dr. Eng. Y. D. Hermawan – ChemEng - UPNVY

I I .1.

I NTRODUCTI ON

I ntroduction

 Choice of Reactor involves: 1. Type of Reactor

2. Reaction Conditions (P, T, C, phase)  Two Types of Reactor:

1. Mixed-flow: CSTR, Fluidized

2. Plug-flow: PFR, Fixed-Bed, Column  Type of Reactor depends on:

1. Type of reaction: single, parallel, series

(3)

I ntroduction



Temperature and Pressure affect to:

1. Reaction rate: Arrhenius equation, concentration

2. Reaction equilibrium: endothermic / exothermic (mole

ratio of reactant)



Reaction phase:

1. Single phase ( gas, liquid, solid)

2. Two phases or more (with or without catalyst)



Catalyst:

1. Homogen

2. Heterogen

I I .2.

(4)

I ntroduction to choice of Reactor

(Smith, R., 2005)

Reactors can be broadly classified as chemical or biochemical. Most reactors, whether chemical or biochemical, are catalyzed. The strategy will be to choose the catalyst, if one is to be used, and the ideal characteristics and operating conditions needed for the reaction system.

The issues that must be addressed for reactor design include:  Reactor type

 Catalyst  Size

 Operating conditions (temperature and pressure)  Phase

 Feed conditions (concentration and temperature).

Reactor Path

(Smith, R., 2005)

Preferred:

Reaction paths that use the cheapest raw materials and

produce the smallest quantities of byproducts are

to be

preferred.

Avoided

:

(5)

Example 2.2.1.

Given that the objective is to manufacture vinyl chloride, there are at least three reaction paths that can be readily exploited.

Molar masses and values of materials

(6)

Solution:

Decisions can be made on the basis of the economic potential of the process. At this stage, the best that can be done is to define the economic potential (EP) :

EP = (value of products) - (raw materials costs)

Path 1

EP = (62 × 0.46) - (26 × 1.0 + 36 × 0.39) = – 11.52 $· kmol-1_{vinyl chloride product}

Path 2

EP = (62 × 0.46 + 36 × 0.39) - (28 × 0.58 + 71 × 0.23) = 9.99 $· kmol-1 _{vinyl chloride product}

This assumes the sale of the byproduct HCl. I f it cannot be sold, then: EP = (62 × 0.46) - (28 × 0.58 + 71 × 0.23)

= –4.05 $· kmol-1 _{vinyl chloride product}

Path 3

EP = (62 × 0.46) - (28 × 0.58 + 36 × 0.39) = –1.76 $· kmol-1 _{vinyl chloride product}

Paths 1 and 3 are clearly not viable. Only Path 2 shows a positive economic potential when the byproduct HCl can be sold. I n practice, this might be quite difficult, since the market for HCl tends to be limited. I n general, projects should not be justified on the basis of the byproduct value.

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Example 2.2.2.

Devise a process from the three reaction paths in Example 2.2.1

that uses ethylene and chlorine as raw materials and produces no byproducts other than water. Does the process look attractive economically?

Solution:

A study of the stoichiometry of the three paths shows that this can be achieved by combining Path 2 and Path 3 to obtain a fourth path.

Path 2 and 3

These three reactions can be added to obtain the overall stoichiometry.

Now the economic potential is given by:

EP = (62 × 0.46) - (28 × 0.58 + 1/ 2 × 71 × 0.23) = 4.12 $· kmol-1 _{vinyl chloride product}

I n summary, Path 2 from Example 2.1 is the most attractive reaction path if there is a large market for hydrogen chloride. I n practice, it tends to be difficult to sell the large quantities of hydrogen chloride produced by such processes. Path 4 is the usual commercial route to vinyl chloride.

(8)

I I .3.

TYPES OF REACTI ON SYSTEM

Reaction systems can be classified into six

broad types

(Smith, R., 2005):

1. Single Reaction

2. Multiple reactions in parallel producing byproducts.

3. Multiple reactions in series producing byproducts.

4. Mixed parallel and series reactions producing

byproducts.

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1. Single Reaction

FEED  PRODUCT

or

FEED _ PRODUCT + BYPRODUCT

or

FEED1 + FEED2 _ PRODUCT Examples:

Does not produce by product:

Produce by product:

2. Multiple Reactions in Parallel Producing Byproducts

FEED  PRODUCT

FEED _ BYPRODUCT

or

FEED _ PRODUCT + BYPRODUCT1

FEED _ BYPRODUCT2 + BYPRODUCT3

or

FEED1 + FEED2 _ PRODUCT FEED1 + FEED2 _ BYPRODUCT

(10)

Examples of a parallel reactions system occurs in the production of ethylene oxide

3. Multiple Reactions in Series Producing Byproducts

FEED  PRODUCT

PRODUCT _ BYPRODUCT

or

FEED _ PRODUCT + BYPRODUCT1

PRODUCT _ BYPRODUCT2 + BYPRODUCT3

or

FEED1 + FEED2 _ PRODUCT

(11)

Examples of series reactions system occurs in the production of formaldehyde from methanol

4. Mixed Parallel and Series Reactions Producing Byproducts

FEED _ PRODUCT

FEED  BYPRODUCT

PRODUCT _ BYPRODUCT

or

FEED _ PRODUCT

FEED _ BYPRODUCT1

PRODUCT _ BYPRODUCT2

or

FEED1 + FEED2 _ PRODUCT FEED1 + FEED2 _ BYPRODUCT1

PRODUCT _ BYPRODUCT2 + BYPRODUCT3

(12)

Examplesof mixed parallel and series reactions is the production of Ethanolamines by reaction between Ethylene Oxide and Ammonia:

5. Polimerization Reactions

•

monomer molecules are reacted together to produce a

high molar mass

polymer.

•

Depending on the mechanical

properties required of the

polymer, a mixture of monomers might be reacted

together to produce a high molar mass

copolymer.

•

Two broad types of polymerization

reactions:



those that involve a

termination step

(13)

An example of polimerization reaction that involves a termination step:

Polymerization of Vinyl Chloride from a free-radical initiator • R

I nitiation step:

Propagation step:

and so on, leading to molecules of the structure:

(14)

An example of a polymerization without a termination step is polycondensation

Here the polymer grows by successive esterification with

elimination of water and no termination step. Polymers formed

by linking monomers with carboxylic acid groups and those that

have alcohol groups are known as

polyesters.

Polymers of this

type are widely used for the manufacture of artiﬁcial ﬁbers. For

example, the esteriﬁcation of terephthalic acid with ethylene

glycol produces polyethy-lene terephthalate.

6. Biochemical Reaction



often referred to as

fermentations



can be divided into two broad types, promoted by:

1. microorganisms

2. enzymes



the advantages

1. operating under mild reaction conditions of

temperature and pressure

(15)



an example of the reaction exploits the metabolic pathways

in selected

microorganisms



I n such reactions, the microorganisms reproduce themselves.



I n addition to the feed material, it is likely that nutrients (e.g. a mixture containing phosphorus, magnesium, potassium, etc.) will need to be added for the

survival

of the

microorganisms.



Reactions involving microorganisms include:



hydrolysis



oxidation



esteriﬁcation



reduction

(16)



Enzymes are the catalyst proteins produced by

microorganisms that accelerate chemical reactions in

microorganisms.



The biochemical reactions employing enzymes are of the

general form:



An example of the reaction that promoted by

enzymes



An example in the use of enzymes is the isomerization of

glucose to fructose:

I I .4.

(17)

Reactor Performance

(Smith, R., 2005)

Three important parameters to describe reactor performance:

The stoichiometric factor is the stoichiometric moles of reactant required per mole of product. When more than one reactant is required (or more than one desired product produced) three Equations above can be applied to each reactant (or product).

Example 2.4.1: Benzene is to be produced from toluene according to the reaction

Reactor feed and effluent streams:

Calculate the conversion, selectivity and reactor yield with respect to the: a. Toluene feed

(18)

Solution:

(19)

I I .5.

RATE OF REACTI ON

Rate of Reaction

(Smith, R., 2005)



To define the rate of a reaction, one of the components must

be selected and the rate defined in terms of that component.



The rate of reaction is the number of moles formed with

respect to time, per unit volume of reaction mixture:















dt

dN

V

r

_i

1

i

where

r

_i

= rate of reaction of Component

i

(kmol·m

-3

·s

-1

)

N

_i

= moles of Component

i

formed (kmol)

V

= reaction volume (m

3

)

t

= time (s)

(20)



I f the volume of the reactor is constant (

V

= constant):

dt

dC

dt

V

dN

dt

dN

V

r

_i i





i



i













1

where

C

_i

= molar concentration of Component

i

(kmol·m

-3

)



The rate is negative if the component is a reactant and

positive if it is a product. For example, for the general

irreversible reaction:

bB

+

cC

+ · · · →

sS

+

tT

+ ···

The rates of reaction are related by:















t

r

s

r

c

r

b

r

_B _C _S _T

… (2.5.2)

… (2.5.4) … (2.5.3)



I f the rate-controlling step in the reaction is the collision of

the reacting molecules, then the equation to quantify the

reaction rate will often follow the stoichiometry such that:



c C b B B B

k

C

r







c C b B C C

k

C

r







c C b B S S

k

C

r





c C b B T T

k

C

r



where

r_i= reaction rate for component i(kmol· m-3_{· s}-1₎

k_i= reaction rate constant for component i ([ kmol· m-3_]NC_–b_–

c-... s-1₎

NC= is the number of components in the rate expression

… (2.5.5)

… (2.5.6)

… (2.5.7)

(21)



The reaction rate constant is a function

of temperature, as

will be discussed next.





t

k

s

k

c

k

b

k

_B _C _S _T



Reactions for which the rate equations follow the

stoichiometry are known as

elementary reactions

.



I f there is no direct correspondence

between the reaction

stoichiometry and the reaction rate, these are known as

non- elementary reactions

and are often

of the form:



ε ξ δ β T S C B B

B

k

C

r







ε ξ δ β T S C B C

C

k

C

r







ε ξ δ β T S C B S

S

k

C

r





ε ξ δ β T S C B T

T

k

C

r



whereβ,δ,ε,ξ = order of reaction

… (2.5.9)

… (2.5.13) … (2.5.10)

… (2.5.11)

… (2.5.12)



I f the reaction is reversible, such that:







cC

sS

tT

bB



then the rate of reaction is the net rate of the forward and

reverse reactions. I f the forward and reverse reactions are

both elementary, then:



Tt

s S B c C b B B

B

k

C

k

C

r





'





Tt

s S C c C b B C

C

k

C

k

C

r





'





Tt

s S S c C b B S

S

k

C

k

C

r





'



Tt

s S T c C b B T

T

k

C

k

C

r





'

where

'

i

k

= reaction rate constant for Componentifor thereverse reaction

i

k

_{= reaction rate constant for Component}ifor theforward reaction … (2.5.14)

… (2.5.15)

… (2.5.16)

… (2.5.17)

(22)

I I .6.

I DEALI ZED REACTOR MODELS

I dealized Reactor Models

(Smith, R., 2005)



the reactants are

charged at the

beginning of the

operation.

I deal Batch Reactor



The contents are subjected to perfect mixing for a certain

period, after which the products are discharged.

(23)

I deal Batch Model

where

t = batch time

N_i0= initial moles of Component i

N_it= final moles of Component i after time t

dt

dN

V

r

_i

1

i

converted

reactant

of

moles























Nit

i N _i i

V

r

dN

t

0 … (2.6.1)

I ntegration of (2.6.1): … (2.6.2)









V

r

dt

dX

N

dt

X

N

d

dt

dN

i i i i i

i











0 0

1

I n term of reactor conversion (X_i₎

… (2.6.3)

I deal Batch Model







Xi

i i i

V

r

dX

N

t

0

0 … (2.6.4)

I ntegration of (2.6.3):

from the definition of reactor conversion, for the special case of a constant density reaction mixture:

0 0 0 0 i it i i it i i

C

N

X









C_i = molar concentration of Component i

C_i0= initial molar concentration of Component i

C_it= final molar concentration of Component iat time t

Substitution of (2.6.5) into (2.6.3) i

r

_i

dt

dC













Cit

C i

r

dC

t

… (2.6.5) where … (2.6.6) … (2.6.7)

(24)

I dealized Reactor Models

(Smith, R., 2005)



Feed and product

takeoff are both

continuous.

Mixed- Flow or Continuous Well- Mixed or

Continuous-Stirred- Tank Reactor ( CSTR)



The reactor contents are assumed to be perfectly mixed.



This leads to uniform composition and temperature

throughout the reactor.



Because of the perfect mixing, a fluid element can leave the

instant it enters the reactor or stay for an extended period.



The residence time of individual ﬂuid elements in the reactor

varies.

Material Balance

for Component

i

per unit time









































unit time

per

product

in

reactant

of

moles

unit time

per

converted

reactant

of

moles

unit time

per

feed

in

reactant

of

moles



i



iout in

i

r

V

N

_,





_,

N_i,in= inlet moles of Component iper unit time

N_i,in= outlet moles of Component iper unit time

V

r

N

_i_,_out



_i_,_in



_i

Rearrange (2.6.9):

Substituting N_i,out=N_i,in (1-X_i) into (2.6.10): iin i

r

X

N

V



,

… (2.6.8)

… (2.6.9)

where

… (2.6.10)

(25)

Analogous to time as a measure of batch process performance, space–time (τ) can be defined for a continuous reactor:

in i out i

N

V

C

F

V

, ,



τ

where F= volumetric ﬂowrate of the feed (m3_.s-1₎

The reciprocal of space–time is space–velocity (s):



number

of

reactor vo

lume

processed

in

a

unit time



1



τ

s

… (2.6.13) … (2.6.14)

Combining Equations (2.6.12) for the mixed-ﬂow reactor with constant density and (2.6.13) gives:

i out i in i

r

C





, ,

τ

… (2.6.15)

This figure is a plot of (2.6.15), from C_i,in to C_i,out the rate of reaction decreases to a minimum at C_i,out . As the reactor is assumed to be perfectly mixed, C_i,out is the concentration throughout the reactor, that is, this gives the lowest rate throughout the reactor. The shaded area in the figure represents the space–time (V /F ).

Mixed-Flow Reactor

(26)

I dealized Reactor Models

(Smith, R., 2005)



A steady uniform movement of reactant is assumed, with

attempt to include mixing along the direction of flow



Like the ideal-batch reactor, the residence time in a PFR is

the same for all ﬂuid elements.

Plug- Flow Reactor



Plug-ﬂow operation can be approached by using a number

of mixed-ﬂow reactors in series.

(27)

Plug- flow Model









































unit time

per

volume

l

incrementa

leaving

reactant

of

moles

unit time

per

converted

reactant

of

moles

unit time

per

volume

l

incrementa

entering

reactant

of

moles

… (2.6.16)



i



i i i

r

dV

N

dN

N







… (2.6.17)

(2.6.16) can be written per unit time as:

N_i= moles of Component iper unit time where

Rearrange (2.6.17):

dN

_i



r

_i

dV

… (2.6.18)

Substituting reactor conversion into (2.6.17):







N

X



r

dV

d

dN

_i



_i_,_in

1



_i



_i … (2.6.19)

N_{i ,in}= inlet moles of Component i per unit time

where

Rearrange (2.6.19):

dN

_i_,_in

dX

_i





r

_i

dV

… (2.6.20)

I ntegration of (2.6.20): _ … (2.6.21)





Xi

i i in i

r

dX

N

V

0 ,

Writing (2.6.21) in term

of the space time:







… (2.6.22)

i X i i in i

r

dX

C

0 ,

τ

For the special case of constant density systems, substitution (2.6.13) gives: … (2.6.23) 





Ciout

in i C _i i in i in i

r

dC

C

N

V

, , , , … (2.6.24) 



(28)

This Figure is a plot of (2.6.24). The rate of reaction is high at C_i,in

and decreases to C_i,outwhere it is the lowest. The area under the curve now represents the space–time.

Plug-Flow Reactor

Concentration vs Reaction Rate

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Example 2.6.1:

Benzyl acetate is used in perfumes, soaps, cosmetics and household items where it produces a fruity, jasminelike aroma, and it is used to a minor extent as a ﬂavor. I t can be manufactured by the reaction between benzyl chloride and sodium acetate in a solution of xylene in the presence of triethylamine as catalyst.

or A + B _ C + D The reaction has been investigated experimentally by Huang and Dauerman in a batch reaction carried out with initial conditions given in Table as follows:

The solution volume was 1.321 × 10-3 _m3 _{and the temperature}

maintained to be 102 ◦C. The measured mole per cent benzyl chloride versus time in hours are given as follows:

Experimental data for the production of benzyl acetate.

Derive a kinetic model for the reaction on the basis of the experimental data!

(30)

Solution:

Solution The equation for a batch reaction is given by (2.6.2):





NAt

A N _A

A

V

r

dN

t

0

I nitially, it could be postulated that the reaction could be zero order, first order or second order in the concentration of A and B. However, given that all the reaction stoichiometric coefficients are unity, and the initial reaction mixture has equimolar amounts of A and B, it seems sensible to first try to model the kinetics in terms of the concentration of A. This is because, in this case, the reaction proceeds with the same rate of change of moles for the two reactants. Thus, it could be postulated that the reaction could be zero order, first order or second order in the concentration of A. I n principle, there are many other possibilities.

Substituting the appropriate kinetic expression into (2.6.11) and integrating gives the expressions in Table as follows:

(31)

The experimental data have been substituted into the three

models and presented graphically in Figure as follows:

From Figure, all three models seem to give a reasonable representation of the data, as all three give a reasonable straight line. I t is difficult to tell from the graph which line gives the best fit. The fit can be better judged by carrying out a least squares fit to the data for the three models.

The difference between the values calculated from the model and the experimental values are summed according to:

Results of a least squares ﬁt for the three kinetic models.

the best ﬁt is given by a ﬁrst order reaction model:

(32)

Consider now which of the idealized models is preferred for the categories of reaction systems introduced in Section 2.3.

1. Single reaction:

 Clearly, the highest rate of reaction is maintained by the highest concentration of feed (C_FEED, kmol· m-3_).

 in the mixed-ﬂow reactor the incoming feed is instantly diluted by the product that has already been formed.

 The rate of reaction is thus lower in the mixed-ﬂow reactor than in the ideal-batch and plug-ﬂow reactors, since it operates at the low reaction rate corresponding with the outlet concentration of feed.

 Thus, a mixed-flow reactor requires a greater volume than an ideal-batch or plug-flow reactor. Consequently, for single reactions, an ideal-batch or plug-flow reactor is preferred.

2. Multiple reactions in parallel producing byproducts:

 The ratio of the rates:



Maximum selectivity requires a minimum ratio

r

₂

/

r

₁

 A batch or plug-ﬂow reactor maintains higher average

concentrations of feed (C_FEED ) than a mixed-ﬂow reactor, in which the incoming feed is instantly diluted by the PRODUCT and

BYPRODUCT.

(33)

3. Multiple reactions in series producing byproducts:

 For a certain reactor conversion, the FEED should have a corresponding residence time in the reactor.

 I n the mixed-flow reactor, FEED can leave the instant it enters or remains for an extended period. Similarly, PRODUCT can remain for an extended period or leave immediately. Substantial fractions of both FEED and PRODUCT leave before and after what should be the specific residence time for a given conversion. Thus, the mixed-flow model would be expected to give a poorer selectivity or yield than a batch or plug-flow reactor for a given conversion.  A batch or plug-flow reactor should be used for multiple

(34)

4. Mixed parallel and series reaction producing byproducts:

 a₁ > a₂: use a batch or plug-flow reactor

 a₁ _< a₂_{: use a mixed-flow reactor}

 Series of mixed-flow reactors  Plug-flow reactors with a recycle

 Series combination of plug-flow and mixed-flow reactors

Mixed parallel and series reactions producing byproducts

As far as the parallel byproduct reaction is concerned, for high selectivity, if:

(35)

if

a

1

<

a

2

I I .7.

(36)



there is steady movement only in one direction.



I f heat needs to be added or removed as the reaction

proceeds, the tubes may be arranged in parallel, in a

construction similar to a shell-and-tube heat exchanger.



Tubular reactors can be used for multiphase reactions.

However, it is often difﬁcult to achieve good mixing

between phases, unless static mixer tube inserts are used.



One mechanical advantage tubular devices have is when

high pressure is required. Under high-pressure conditions,

a small-diameter cylinder requires a thinner wall than a

large-diameter cylinder.

1. Tubular Reactor

(37)

2. Stirred Tank Reactor

Application include:



homogeneous liquid-phase reactions



heterogeneous gas–liquid reactions



heterogeneous liquid–liquid reactions



heterogeneous solid–liquid reactions



heterogeneous gas–solid–liquid reactions.

Can be operated:



Batch



Semi batch



Continuous

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3. Fixed- bed Catalytic Reactor

 the reactor is packed with particles of solid catalyst.  Most designs approximate to plug-ﬂow behavior.

 I f the catalyst degrades (e.g. as a result of coke formation on the surface), then a ﬁxed-bed device will have to be taken off-line to regenerate the catalyst. This can either mean shutting dow n the plant or using a standby reactor.

 I f a standby reactor is to be used, two reactors are periodically switched, keeping one online while the other is taken offline to regenerate the catalyst. Several reactors might be used in this way to maintain an overall operation that is close to steady state.

 However, if frequent regeneration is required, then ﬁxed beds are not suitable, and under these circumstances, a moving bed or a ﬂuidized bed is preferred.

 Gas–liquid mixtures are sometimes reacted in catalytic packed beds.

Heat transfer arrangements for fixed- bed catalytic reactors.

The simplest form of ﬁxed-bed catalytic reactor uses an

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Heat transfer arrangements for fixed- bed catalytic reactors

If adiabatic operation is not acceptable because of a large temperature rise for an

exothermic reaction or a large decrease for an endothermic reaction, then cold shot or hot shot can be used

Heat transfer arrangements for fixed- bed catalytic reactors

a series of adiabatic beds with intermediate cooling or heating can be used to maintain

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Heat transfer arrangements for fixed- bed catalytic reactors

Tubular reactors similar to a shell-and-tube heat exchanger can be used, in which the tubes are packed with catalyst.

The

heating or cooling medium

circulates around the outside

of the tubes.

4. Fixed- bed Non- catalytic Reactor

 Fixed-bed noncatalytic reactors can be used to react a gas and a solid.

 For example, hydrogen sulﬁde can be removed from fuel gases by reaction with ferric oxide:

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5. Moving- bed Catalytic Reactor

 I f a solid catalyst degradesin performance, the rate of

degradation in a ﬁxed bed might be unacceptable. I n this case, a moving-bed reactor can be used.  Here, the catalyst is kept in

motion by the feed to the reactor and the product. This makes it possible to remove the catalyst continuously for regeneration.  An example is a reﬁnery

hydrocracker reactor

6. Fluidized- bed Catalytic Reactor



I n fluidized-bed reactors,

solid material in the form of ﬁne

particles is held in suspension by the upward ﬂow of the

reacting ﬂuid.



The effect of the rapid motion of the particles is good heat

transfer and temperature uniformity. This prevents the

formation of the hot spots that can occur with ﬁxed-bed

reactors.



The

performance

of

ﬂuidized-bed

reactors

is

not

approximated by either the mixed-ﬂow or plug-ﬂow idealized

models.



The solid phase tends to be in mixed-ﬂow, but the bubbles

lead to the gas phase behaving more like plugﬂow.

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7. Fluidized- bed Non- catalytic Reactor



Fluidized beds are

also suited to gas–solid noncatalytic

reactions.



All the advantages described earlier for gas–solid catalytic

reactions apply here.



As an example, limestone (principally, calcium carbonate)

can be heated to produce calcium oxide in a ﬂuidized-bed

reactor according to the reaction

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8. Kiln

 Reactions involving free-flowing solid, paste and slurry materials can be carried out in kilns.

 I n a rotary kiln, a cylindrical shell is mounted with its axis making a small angle to the horizontal and rotated slowly.

 The solid material to be reacted is fed to the elevated end of the kiln and it tumbles down the kiln as a result of the rotation.

Rotary Kiln

 The behavior of the reactor usually approximates plug-ﬂow.

 High-temperature reactions demand refractory lined steel shells and are usually heated by direct ﬁring.

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I I .8.

DESI GN GUI DELI NE

FOR REACTOR

Design Guideline for Reactor:

I .

Single irreversible reaction (not autocatalytic)

A. I sothermal – always use a plug-flow reactor

B. Adiabatic

1. Plug-flow if the reaction rate monotonically decrease

with conversion

2. CSTR operating at the maximum reaction rate

followed by a plug-flow section

I I .

Single reversible reaction – adiabatic

A. Maximum temperature if endothermic

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Design Guideline for Reactor:

I I I . Parallel reactions – composition effects

A. for A _ B (desired) and A _ S (waste), where the ratio of the reaction rates is:

1. ifa₁>a₂, keepC_A high a. Use batch or plug-flow

b. High pressure, eliminate innerts c. Avoid recycle of products

d. Can use a small reactor

2. ifa₁<a₂, keepC_A low

a. Use a CSTR with a high conversion b. Large recycle of product

c. Low pressure, add innerts d. Need a large reactor

Design Guideline for Reactor:

B. for A + B _ R (desired) and A + B _ S (waste), where the ratio of the reaction rates is:

1. ifa₁>a₂ andb₁ >b₂, bothC_AandC_Bhigh 2. ifa₁<a₂ andb₁ >b₂, thenC_Alow andC_Bhigh 3. ifa₁>a₂ andb₁ <b₂, thenC_Ahigh andC_Blow 4. ifa₁<a₂ andb₁ <b₂, bothC_AandC_Blow 5. See fig below:

I V. Consecutive reactions – composition effects:

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Design Guideline for Reactor:

V. Parallel reactions – temperature effects:

A. if E₁ > E₂, use a high temperature

B. if E₁ < E₂, use an increasing temperature profile

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Choosing heat transfer in the reactor:

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Operating temperature for favorable product distribution