Chemical Engineering Reactor

8/3/2019 Chemical Engineering Reactor

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Chemical EngineeringChemical EngineeringReactorReactor

IntroductionIntroduction

By: Eko Ariyanto, ST.,MChemEngBy: Eko Ariyanto, ST.,MChemEng

Chemical Engineering DepartmentChemical Engineering DepartmentEngineering FacultyEngineering FacultyMuhammadiyah University ofMuhammadiyah University of

PalembangPalembang


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StaffStaff

Eko Ariyanto, ST. MChemEng(lecturer)

[email protected]

085669463967


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TimetableTimetable

LecturesThursday 10-12 am

Consultation Saturday 10 - 12 am (Computer

Laboratory)

consultation, group project work, revisions etc.


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ResourcesResources

Book

O.Levenspiel:Chemical Reaction

EngineeringS.Fogler: Elements of Chemical Reaction

Engineering

Internet

Lecture notes Inspired from both books


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AssessmentAssessment

Projects (15 %):

Project (group work) = 10 % Individual work / Assignment = 5 %

Mid-semester - 25%

Final Exam 50 % (exam period)

Attendance 10 %


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Reactor PerformanceReactor PerformanceInformation needed to predict the reactor behaviour:

KINETICS

how fast things happen?

input output

CONTACTING

PATTERNS

how materials flow &

contact each other?

Output = f(input, kinetics, contacting)Performance equation

very fast - equilibrium

slow - rate, mass, heat flowing patterns

contact

aggregation etc.


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The Nature of the Reactor Design ProblemThe Nature of the Reactor Design Problem

1. What is the composition of the feedstock,conditions, and purification Procedures?

2. What is the scale and capacity of the process?

3. Is Catalyst needs?

4. What is operating condition?

5. Continuous or batch process?

6. What type of the reactor best meets theprocess requirement?

7. What size and shape reactor should be used?

8. How are the energy transfer?


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How to choose the reactorHow to choose the reactor

Yield (should be large)

Cost (Should be economic)

Safety Consideration Pollution

How to Reactor Design

Firstly; You have to know reaction rate expression

Secondly; fluid velocity, temperature process,composition and characteristic of species


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Source of the essential data for reactorSource of the essential data for reactordesigndesign

1. Bench scale experiment (Laboratory Scale)The reactors is designed to operate at constant temperature,under condition (minimize heat transfer and mass transfer)

2. Pilot plant studiesThe reactors used is larger than bench scale

3. Operating data from commercial scale reactorThe data come from another company and it can be used todesign reactor. Unfortunately, data are often incomplete,inaccurate,


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Reactor TypeReactor Type

Batch Reactors (Stirred Tanks)1. The Batch reactor is the generic term for a type of

vessel (Cylinder Tank) widely used in the process

industries.2. A typical batch reactor consists of a tank with an agitatorand integral heating/cooling system. Heating/cooling usesjacketed walls, internal coil, and internal tube.

Batch reactor withsingle external

cooling jacket

Batch reactor withhalf coil jacket

Batch reactor withconstant flux

(Coflux) jacket


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AdvantagesAdvantages1. Batch reactor Can be stopped between batches, so the production

rate is flexible

2. Batch reactors are more flexible, in that one can easly use differentcompositions in different batches to produces product with differentspesification

3. If the process degrades the reactor in some way, a batch reactor canbe cleaned, relined, etc. between batches. Where continuousreactors must run a long time before that can be done.

4. If the reactant are stirred, a batche reactor can often achieve betterquality than a plug flow reactor, and better productivity than a CSTR


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Batch Reactor typesBatch Reactor types

semi-batch reactor

flexible system but more difficult to analyse

good control of reaction speed

applications:

calorimetric titrations (lab)

open hearth furnaces for steel production (ind.)


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Ideal Batch ReactorIdeal Batch Reactor-- design equationsdesign equations --

!

reactorthein

reactantof

onaccumulati

ofrate

reactorthein

reactionchemical

todueloss

reactantofrate

reactorof

outflow

reactant

ofrate

reactor

intoflow

reactant

ofrate

!

reactorthein

reactantof

onaccumulatiofrate

reactorthein

reactionchemical

toduelossreactantofrate


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fluidofvolumefluid)ofume(time)(vol

reactingAmoles

VrA )(

dt

dNA

dt

dNVr AA ! )(

!

reactorthein

reactantof

onaccumulati

ofrate

reactorthein

reactionchemical

todueloss

reactantofrate


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dt

dNVr AA ! )(

dt

dX

Ndt

XNd

dt

dN AA

AAA

0

0)]1([

!

!dt

dXNVr AAA 0)( !

!AX

A

AA

Vr

dXNt

00

)(

design

equation

= time required to

achieve conversion XA

0AN

tarea !


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Ideal Batch ReactorIdeal Batch Reactor-- design equations / special casesdesign equations / special cases --

!

AX

A

AA

Vr

dXNt

00

)(Const. density

!

!

AA X

A

AA

X

A

AA

r

dXC

r

dX

V

Nt

00

0

0

)()(

!!A

A

A C

CA

AX

A

AA

rdC

rdXCt

0 )()(00

0AC

tarea !

tarea !


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Continuous Stirred Tank ReactorContinuous Stirred Tank Reactor

In a CSTR, one or more fluidreagents are introduced into a tankreactor equipped with an impeller.The impeller stirs the reagents toensure proper mixing

Impeller


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Some important aspects of the CSTRSome important aspects of the CSTR

At steady-state, the flow rate in must equal the mass flowrate out, otherwise the tank will overflow or go empty(transient state).

All calculations performed with CSTRs assume perectmixing.

The reaction proceeds at the reaction rate associated withthe final (output) concentration. Often, it is economically beneficial to operate several CSTR

in series. This allows, for example, the first CSTR to operateat a higher reagent concentration and therefore a higherreaction rate. In these cases, the sizes of the reactors maybe varied in order to minimize the total capital investmentrequired to implement the process.

It can be seen that an infinite number of infinitely smallCSTRoperating in series would be equivalent to a PFR.


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Advantages and DisadvantagesAdvantages and Disadvantages

Kinds of PhasesPresent

Usage Advantages Disadvantages

1. Liquid phase

2. Gas-liquid rxns

3. Solid-liquid rxns

1. Whenagitation isrequired

2. Seriesconfigurations

for differentconcentrationstreams

1. Continuousoperation

2. Good

temperaturecontrol

3. Easily adaptsto two phaseruns

4. Good control

5. Simplicity of

construction

6. Low operating(labor) cost

7. Easy to clean

1. Lowestconversion perunit volume

2. By-passingand

channelingpossible withpoor agitation


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CSTRReactorCSTRReactor-- design equationsdesign equations --

!

reactorthein

reactantof

onaccumulati

ofrate

reactorthein

reactionchemical

todueloss

reactantofrate

reactorof

outflow

reactant

ofrate

reactor

intoflow

reactant

ofrate

!

reactorthein

reactionchemical

todueloss

reactantofrate

reactorof

outflow

reactant

ofrate

reactor

intoflow

reactant

ofrate

VrA)(


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000)1( AAA FXF !

000 AA CvF !

flowvolumetricv !0

flowmolarFA !0

sm /3

smol/

reactorintoflow

reactantofrate smol/

reactorofoutflow

reactantofrate )1(0 AAA XFF !

VrXFFAAAA)()1(

00

!design

equation

FA 0XA ! (rA )V

smol/


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Ideal Flow ReactorIdeal Flow Reactor-- spacespace--time / spacetime / space--velocityvelocity --

X !1

s

!time required to process one reactor volume

of feed measured at specified conditions

Performance measures of flow reactors:

2 min every 2 min one reactor volume of feed at specified

conditions is treated by the reactor

s ! 1X

! number of reactor volumes of feed at specifiedconditions which can be treated in unit time

5 hr-1 5 reactor volumes of feed at specified conditions

are fed into reactor per hour

Ex.

Ex.


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Ideal Flow ReactorIdeal Flow Reactor-- spacespace--time / spacetime / space--velocityvelocity --

X !1

s!

CA0V

FA 0!

moles A entering

volume of feed

volume of reactor

moles of A enteringtime

!V

v0

!reactor volume

volumetric feed rate

Residence time


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VFA0

!X

CA 0! X

A

rA

FA0XA ! (rA )V

X !1

s!

CA0V

FA0!

V

v0

Design equation:

Residence time:

area !V

FA 0

!

X

CA0

IA { 0X !

V

v0

!CA 0V

FA0!

CA 0XA

rA


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eactoreactor-- design equations / general & specialdesign equations / general & special

casecase --

V

FA0!

XA

rA!

CA CA 0CA0(rA )

XA !1CA

CA0

Special case - constant density:

X ! Vv0

! CA 0XArA

! CA

CA 0rA

Feed entering partially converted:

V

FA0!

XAf XAi

rA f

X !VCA 0

FA0!

CA 0(XAf XAi)

rA f

IA ! 0


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Problem SolvingProblem Solving

To find problem solving, just connectthe internet and click here


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Plug Flow ReactorPlug Flow Reactor

The plug flow reactor (PFR) model isused to describe Chemical Reaction incontinuous, flowing systems. One

application of the PFRmodel is theestimation of key reactor variables, suchas the dimensions of the reactor. PFRs arealso sometimes called as Continuous

Tubular Reactors (CTRs)


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Plug Flow ReactorPlug Flow Reactor The PFR model works well for many fluids:

liquids, gases, and slurries.

Fluid Flow is sometimes turbulent flow or axialdiffusion, it is sufficient to promote mixing in the

axial direction, which undermines the requiredassumption of zero axial mixing. However if theseeffects are sufficiently small and can besubsequently ignored.

The PFR can be used to multiple reactions as wellas reactions involving changing temperatures,pressures and densities of the flow.


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Advantages and disadvantagesAdvantages and disadvantages

Plug flow reactors have a high volumetric unit conversion,run for long periods of time without labor, and can haveexcellent heat transfer due to the ability to customize thediameter to the desired value by using parallel reactors.

Disadvantages of plug flow reactors are that temperaturesare hard to control and can result in undesirabletemperature gradients. PFRmaintenance is expensive.

Shutdown and cleaning may be expensive.

Applications

Plug flow reactors are used for some of the following applications:

Large-scale reactionsFast reactionsHomogeneous or heterogeneous reactionsContinuous productionHigh-temperature reactions


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SteadySteady--State Plug Flow ReactorState Plug Flow Reactor-- definitiondefinition --

The composition of the fluid varies from point to point

No mixing or diffusion of the fluid along the flow path

Material balance for a differential element of volume dV (not the whole

reactor!)

Characteristics:

onaccumulatireactionby

ncedisappearaoutputinput

!

Material balance:

=0


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SteadySteady--State Plug Flow ReactorState Plug Flow Reactor-- material balancematerial balance --

Input ofA[moles/time]AF

Output ofA [moles/time] AA dFF

Disappearance ofA by rxn. dVrA)(

dV


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SteadySteady--State Plug Flow ReactorState Plug Flow Reactor-- material balancematerial balance --

dVrdFFF AAAA )(!

dV

ncedisappearaoutputinput !

? A AAAAA dXFXFddF 00 )1( !!)1(0 AAA XFF !

dVrdF AA )(!

dVrdXF AAA )(0 ! !

AfX

A

AV

A r

dX

F

dV

000

design

equation


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SteadySteady--State Plug Flow ReactorState Plug Flow Reactor-- design equationsdesign equations --

!

AfX

A

AV

A r

dX

F

dV

000

!!

AfX

A

A

AA r

dX

CF

V

000

X

!!!

AfX

A

AA

A

A

r

dXC

F

VC

v

V0

0

0

0

0

X

000AA

CvF !

flowvolumetricv !0

flowmolarFA !0

sm /3

smol/

IA { 0

If the feed enters partially converted !!Af

Ai

X

XA

A

AA rdX

CFV

00

X

!!!

Af

Ai

X

XA

AA

A

A

r

dXC

F

VC

v

V0

0

0

0

X pAf

Ai

Af X

X

X

0


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Fixed Bed ReactorFixed Bed Reactor

Solids take part in reaction unsteady state orsemi-batch mode

Over some time, solids either replaced orregenerated

1 2

CA,in

CA,out

Regeneration


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Fluidized bed reactorFluidized bed reactor A fluidized bed reactor (FBR) is a type of

reactor that can be used to carry out a variety of

multiphase chemical reactions. In this type ofreactor, a fluid (gas or liquid) is passed through agranular solid material (usually a catalystpossibly shaped as tiny spheres) at high enoughvelocity to suspend the solid.


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AdvantagesAdvantages

Uniform Particle Mixing: Due to the intrinsic fluid-like behavior

of the solid material, fluidized beds do not experience poor mixingas in packed beds. This complete mixing allows for a uniformproduct that can often be hard to achieve in other reactor designs.The elimination of radial and axial concentration also allows forbetter fluid-solid contact, which is essential for reaction efficiencyand quality.

Uniform Temperature: Many chemical reactions produce or

require the addition of heat. Local hot or cold spots within thereaction bed, often a problem in packed beds, are avoided in afluidized situation such as a FBR. In other reactor types, theselocal temperature differences, especially hotspots, can result inproduct degradation. Thus FBR are well suited to exothermicreactions. Researchers have also learned that the bed-to-surfaceheat transfer coefficients for FBR are high.

Ability to Operate Reactor in Continuous State: The fluidizedbed nature of these reactors allows for the ability to continuouslywithdraw product and introduce new reactants into the reactionvessel. Operating at a continuous process state allowsmanufacturers to produce their various products more efficientlydue to the removal of startup conditions in batch process.


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DisadvantagesDisadvantages

Increased Reactor Vessel Size: Because of the expansion of the bed materials inthe reactor, a larger vessel is often required than that for a packed bed reactor. Thislarger vessel means that more must be spent on initial startup costs.

Pumping Requirements and Pressure Drop: The requirement for the fluid tosuspend the solid material necessitates that a higher fluid velocity is attained in thereactor. In order to achieve this, more pumping power and thus higher energy costsare needed. In addition, the pressure drop associated with deep beds also requiresadditional pumping power.

Particle Entrainment: The high gas velocities present in this style of reactor oftenresult in fine particles becoming entrained in the fluid. These captured particles arethen carried out of the reactor with the fluid, where they must be separated. This canbe a very difficult and expensive problem to address depending on the design andfunction of the reactor. This may often continue to be a problem even with otherentrainment reducing technologies.

Lack of Current Understanding: Current understanding of the actual behavior ofthe materials in a fluidized bed is rather limited. It is very difficult to predict andcalculate the complex mass and heat flows within the bed. Due to this lack ofunderstanding, a pilot plant for new processes is required. Even with pilot plants, thescale-up can be very difficult and may not reflect what was experienced in the pilottrial.

Erosion of Internal Components: The fluid-like behavior of the fine solid particleswithin the bed eventually results in the wear of the reactor vessel. This can requireexpensive maintenance and upkeep for the reaction vessel and pipes.

Chemical Engineering Reactor

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