chen 4470 – process design practice dr. mario richard eden department of chemical engineering...

CHEN 4470 – Process Design Practice

Dr. Mario Richard EdenDepartment of Chemical Engineering

Auburn University

Lecture No. 9 – Graphical Mass Integration TechniquesFebruary 9, 2012

Mass Integration

Mass Integration 1:4

O2

Decanter

DistillationColumn

Aqueous Layer

Reactor ScrubberNH3

C3H6

Steam-JetEjector

Steam

Wastewater to Biotreatment

Off-GasCondensate

Condensate

Bottoms

Water

AN toSales

6.0 kg H2O/s

14 ppm NH30.4 kg AN/s4.6 kg H2O/s





5.0 kg AN/s5.1 kg H2O/s

+ Gases

20 ppm NH31.1 kg AN/s

12.0kg H2O/s

Tail Gases to Disposal

B FW1.2 kg H2O/s

Boiler


1ppm NH33.9kg AN/s

0.3 kg H2O/s

• Motivating Example

Any process

insights??


• Mass-Energy Matrix of a Process

PROCESSINGUNITS

Feedstock

Material Utilities(e.g. Fresh Water for Steam, Cooling Water, Quenching,

Coal for Power Generation, etc.)

Solvents

CatalystsMass

Products

By-Products

Effluents

Spent Materials

Mass

Heating/Cooling

PressurePower

Heating/Cooling

PressurePower

Energy

Energy

Mass-Energy Matrix of a Process


• Process from a Species ViewpointMass-Separating

Agents in

Mass-Separating Agents out

(to Regeneration and Recycle)

.

.

.

#1

#2

Nsinks

.

.

.

Sources SegregatedSources

Sinks/Generators

Sources(Back toProcess)

MEN

SourcesStreams laden with targeted

species.

SinksProcess units

capable of accepting the

sources.


• StrategiesStrategiesMass Integration Strategies

No Cost/ Low Cost Strategies

Modest Sink/GeneratorManipulation

(e.g. Moderate Changes in Operating Conditions)

Minor Structural Modifications

(Segregation, M ixing, Recycle, etc.)

Moderate-Cost Modifications

Target

Equipment Addition/Replacement

(Interception/Separation devices, etc)

Material Substitution(Solvent , Catalyst, etc.)

(New Chemistry, New Processing Technology , etc)

Technology ChangesNewTechnologies

CO

ST, I

MP

AC

T

AC

CE

PT

AB

ILIT

Y

Direct Recycle 1:10

• Source-Sink Mapping Diagram

Composition of Targeted Species

Flowrate(Or Load ofTargeted-Species) ,kg/s

sink

source

a

bc

S

Direct Recycle 2:10

• How to Identify Bounds on Sinks– From physical limitations

• Flooding flowrate, weeping flowrate, channeling flowrate, saturation composition

– From manufacturer’s design data

– From technical constraints• To avoid scaling, corrosion, explosion, buildup, etc.

– Add deviation to nominal• +/- x% from current value

Direct Recycle 3:10

• How to Identify Bounds on Sinks (Continued)– From historical data

FlowrateEntering the Sink

CompositionEntering the Sink

Upper bound

Lower bound

Upper bound

Lower bound

Time

Direct Recycle 4:10

• How to Identify Bounds on Sinks (Continued)– From constraints on other units

U n i t i U n i t j

K n o w n C o n s t r a i n t supperj

inj

lowerj yyy

U n k n o w n C o n s t r a i n t supperi

ini

loweri yyy

iniy in

jy

)( inj

ini yfy F r o m p r o c e s s m o d e l :

U s e t o m a p b o u n d s o n t o b o u n d s o n iniyin

jye . g . , in

jini yy 3 2.01.0 in

jy

6.03.0 iniy

Direct Recycle 5:10

• Source-Sink Mapping Diagram after Direct Recycle

Compositionof TargetedSpecies

Flow

rate

, kg/

s

Source (Rich Stream)

Ri

Sink

Source-Sink Mapping Diagramafter Direct Recycle

SupplyComposition

TargetComposition

yit

yis

Separation(Interception)

Direct Recycle 6:10

• Lever-arm Relationships

– Component material balance

Flowrate

Composition, y

ybyS

Source a

Source b

ResultingMixture

ya

Fa

Fb

+FbFa

( ) ( )a a b bs a s a b b s

a b

F y F yy F y y F y y

F F

Direct Recycle 7:10

• Lever-arm Relationships (Continued)

Arm for a Arm for a , Arm for b Total arm

a a a

b total a b

F F FF F F F

Flowrate

Composition, y

ybys

Source a

Source b

ResultingMixture

ya

Fa

Fb

+FbFaArm for a

Arm for b

ApplicationsMinimization of fresh

resources (raw materials, solvents,

water).

Minimize fresh material usage

requires minimum fresh arm.

Fresh ArmTotal Arm

fresh

total

FF

Direct Recycle 8:10

• Example I: Recycle from Source b or c?• Example II: Which Sink Composition to use?Flowrate

Composition, yybySya

Fresh source

Source b

Sink S

Fresharmwhen b is used

Arm for b

Source c

Recycle from source b gives shortest arm for

the fresh!

Flowrate

Composition, yybya

Fresh source

Source bSink

S

?? or ? or

Recycle from source b to right side of the sink box gives shortest arm for the

fresh!

Direct Recycle 9:10

• Targeting Rules for Recycle Alternatives– Process before recycle

– Poor recycle (no change in fresh usage)

1

2

3

4

5

i=1

1

2

3

4

5Rk,1

Rk,2

Terminal_Load k,1Terminal_Load k,2


Terminal_Load k,1 - R k,1 + R k,2

Terminal_Load k,2 - R k,2

Terminal_Load k,3Terminal_Load k,4+ R k,1

Fresh_Load k,1Fresh_Load k,2

Fresh_Load k,3

i=2

i=3

i=4

i=1

i=2

i=3

i=4

j=1

j=2

j=3

j=1

j=2

j=3


Fresh_Load k,3

Process Before Recycle

Poor Recycle

RECYCLE ALTERNATIVES

1

2

3

4

5

i=1

1

2

3

4

5Rk,1

Rk,2



Terminal_Load k,1 - R k,1 + R k,2


Terminal_Load k,3Terminal_Load k,4+ R k,1


Fresh_Load k,3

i=2

i=3

i=4

i=1

i=2

i=3

i=4

j=1

j=2

j=3

j=1

j=2

j=3


Fresh_Load k,3

Process Before Recycle

Poor Recycle

RECYCLE ALTERNATIVES

Direct Recycle 10:10

• Targeting Rules for Recycle Alternatives (Cont’d)

– Effective recycle from terminal

– Effective recycle from terminal and intermediate

1

2

3

4

5

Rk,1

Rk,2




i=1

i=2

i=3

i=4

j=1

j=2

j=3

Fresh_Load k,1 - R k,2


Fresh_Load k,3

Effective Recycle From Terminal

1

2

3

4

5

Rk,1

Rk,2




i=1

i=2

i=3

i=4

j=1

j=2

j=3



Fresh_Load k,3

i=5

Effective Recycle From Terminal and Intermediate

1

2

3

4

5

Rk,1

Rk,2




i=1

i=2

i=3

i=4

j=1

j=2

j=3



Fresh_Load k,3

Effective Recycle From Terminal

1

2

3

4

5

Rk,1

Rk,2




i=1

i=2

i=3

i=4

j=1

j=2

j=3



Fresh_Load k,3

i=5

Effective Recycle From Terminal and Intermediate

Example No. 4 1:21

• Acrylonitrile (AN) Plant– Objectives

• Enhance yield, debottleneck biotreatment facility by reducing wastewater production

O2

Decanter

DistillationColumn

Aqueous Layer

Reactor ScrubberNH3

C3H6

Steam-JetEjector

Steam


Off-GasCondensate

Condensate

Bottoms

Water

AN toSales

6.0 kg H2O/s







+ Gases

20 ppm NH31.1 kg AN/s

12.0kg H2O/s


B FW1.2 kg H2O/s

Boiler


1ppm NH33.9kg AN/s

0.3 kg H2O/s

Example No. 4 2:21

• Observations– Sold-out product, need to expand– Biotreatment is a bottleneck

• Intuitive solution (End of pipe approach)– Install an additional biotreatment facility ($4

million in capital investment and $360,000/year in annual operating cost)

– Will solve problem, but not necessarily best solution!

• Alternative solution– Use mass integration techniques to devise cost-

effective strategies to debottleneck the process

Example No. 4 3:21

• Synthesis Tasks– Identify target for minimum wastewater

discharge– Identify recycle opportunities– Identify required separation– Identify necessary unit replacement

All of that can be done systematically using

mass integration techniques!

Example No. 4 4:21

• Constraints– Scrubber

• 5.8 ≤ flowrate of wash feed (kg/s) ≤ 6.2• 0.0 ≤ ammonia content of wash feed (ppm NH3) ≤ 10.0

– Boiler Feed Water (BFW)• Ammonia content of BFW (ppm NH3) = 0.0• AN content of BFW (ppm AN) = 0.0

– Decanter• 10.6 ≤ flowrate of feed (kg/s) ≤ 11.1

– Distillation Column• 5.2 ≤ flowrate of feed (kg/s) ≤ 5.7• 0.0 ≤ ammonia content of feed (ppm NH3) ≤ 30.0• 80.0 ≤ AN content of feed (wt% AN) ≤ 100.0

Example No. 4 5:21

• Constraints (Continued)– Forbidden recycles (Quality assurance)

• AN product stream (top of distillation column)• Feed to distillation column• Feed to decanter

• Candidate MSA’s for Ammonia Removal– Air (S1)– Activated carbon (S2)– Adsorbing resin (S3)

Example No. 4 6:21

• MSA Data

• Water Balance for AN Plant

Stream Upper

Bound

on Flowrate

L jC

Supply

Composition

(ppmw)

xjs

Target

Composition

(ppmw)

xjt

mj j

ppmw

Cj

$/kg

MSA

C jr

$/kg NH3

Removed

S1 0 6 1.4 2 0.004 667

S2 10 400 0.04 5 0.070 180

S3 3 1100 0.02 5 0.100 91

Scrubber Water6.0 kg/s

BFW1.2 kg/s

Water Generation 5.1 kg/s

ACRYLONITRILE PLANTWastewater

12.0 kg H20/s

Water Loss (with AN Product)

0.3 kg H20/s


B FW1.2 kg/s


ACRYLONITRILE PLANT

Wastewater4.8 kg H20/s


0.3 kg H20/s

NoFreshWater

(a) Overall Water Balance Before Mass Integration

(b) Overall Water Balance After Mass Integration

Water GenerationGEN = OUT – IN

OUT = (12.0 + 0.3)IN = (6.0 + 1.2)

GEN = 12.3 – 7.2 = 5.1

Example No. 4 7:21

• Target for Minimum Wastewate Discharge– Assuming that any water treatment required is

feasible and available to us– The minimum generation of wastewater

corresponds to the generated water in the plant minus what is lost with the AN product

Target for Minimum Discharge to Biotreatment5.1 kg/s – 0.3 kg/s = 4.8 kg/s


BFW1.2 kg/s


ACRYLONITRILE PLANTWastewater

12.0 kg H20/s


0.3 kg H20/s


B FW1.2 kg/s


ACRYLONITRILE PLANT

Wastewater4.8 kg H20/s


0.3 kg H20/s

NoFreshWater

(a) Overall Water Balance Before Mass Integration

(b) Overall Water Balance After Mass Integration

Example No. 4 8:21

• Schematic Representation– Waste Interception Networks (WINs) is a subset

of general Mass Exchange Networks (MENs)

Waste Interception

Network(WIN)

Scrubber

Boiler/Ejector

Air Carbon Resin

Airto AN

Condensation

Carbon ResinTo Regeneration

and Recycle

Feed toBiotreatment

Off-Gas Condensate

Aqueous Layer

Distialltion Bottoms

Ejector Condensate

Aqueous Layer

Ejector Condensate

Fresh Waterto Boiler

Fresh Waterto Scrubber

Example No. 4 9:21

• Source-Sink Mapping Diagram– To minimize fresh water usage, start with

sources closest to the sink.– First distillation bottoms, then off-gas

condensate6.0

5 10 15 20 25 30y, ppm NH3

0.0

2.0

1.0

3.0

4.0

5.0

Flowrate of a Source/Feed to a Sink, kg/s 0

5.8

35

7.0

6.26.0

0.0

2.0

1.0

3.0

4.0

5.0

7.0FreshWater

to ScrubberScrubber

DistillationBottoms

Off-GasCondensate

AqueousLayer

EjectorCondensate

1.4

0.8

Flowrate Constraint

Combining the distillation bottoms

and the off-gas condensate results

in a flowrate of

5.0 + 0.8 = 5.8 kg/s

Within bounds of scrubber!

Example No. 4 10:21

• Source-Sink Mapping Diagram (Continued)– Checking the composition of the mixture

– This means that not all the off-gas condensate can be recycled to the scrubber

0.8 kg/s 0 5.0 kg/s 14 ppm 12 ppm0.8 kg/s 5.0 kg/s

bottoms bottoms condensate condensatemix

bottoms condensate

mix

F y F yy

F F

y

Outside sink

region!!

Example No. 4 11:21

• Source-Sink Mapping Diagram (Continued)– Maximum flowrate of off-gas condensate that

can be recycled to the scrubber along with distillation bottoms

minimum feed required

0.8 kg/s 0 14 ppm10 ppm5.8 kg/s

4.1 kg/s (5.8 4.1 0.8) 0.9 kg/s

bottoms bottoms condensate condensatemix

condensate

condensate fresh water

F y F yy

F

F

F F

Direct recycle reduces the fresh water feed to the scrubber by

5.1 kg/s

Example No. 4 12:21

• Direct Recycle Only– Reduces fresh water consumption by 5.1 kg/s

6.0

5 10 15 20 25 30y, ppm NH3

0.0

2.0

3.0

4.0

5.0

Flowrate of a Source/Feed to a Sink, kg/s

0

5.8

35

7.0

6.26.0

0.0

2.0

1.0

3.0

4.0

5.0

7.0

Fresh Water

Scrubber

Distillation Bottoms

Off-GasCondensate

AqueousLayer

EjectorCondensate

0.80.9

1.7

Fraction of Off-GasCondensate to be Recycled

Fraction of Off-GasCondensate to be Discharged

4.1

14

New Feedto Scrubber Economics

The primary cost of direct recycling is

pumping and piping.

TAC = $48,000/yr

Example No. 4 13:21

• Include Interception– Direct recycle reduced the fresh water usage by

5.1 kg/s. Target for fresh water reduction was 7.2 kg/s, i.e. still 2.1 kg/s to go.

– If all fresh water is to be eliminated from scrubber, what should ammonia content of the off-gas condensate be?

intercepted 12 ppmcondensatey

intercepted0.8 kg/s 0 5.0 kg/s10 ppm

0.8 kg/s 5.0 kg/scondensatey

Example No. 4 14:21

• Include Interception (Continued)– Interception and direct recycle can eliminate

fresh water usage in the scrubber

6.0

5 10 15y, ppm NH3

0.0

2.0

3.0

4.0

5.0

Flowrate of a Source/Feed to a Sink, kg/s

0

5.8

7.0

6.26.0

0.0

2.0

1.0

3.0

4.0

5.0

7.0

Scrubber

Distillation Bottoms

Off-GasCondensate

0.8

4.1

14

New Feedto Scrubber

12

InterceptedOff-Gas

Condensate

1.0

Interception TaskChange ammonia content of off-gas

condensate ys = 14 ppm yt = 12 ppm

Example No. 4 15:21

• Include Interception (Continued)– Pinch diagram for ammonia interception task

0 3 6 9 12 15 y0.0

4.0

2.0

6.0

8.0

10.0

12.0

Mass Exchanged,10-6 kg NH3/s

x1

Off-GasCondensate

x2145 295 445 595 745x3295 595 895 1195 1495

0.1 2.3 4.4 6.6 8.7

14S1

S2

S3

Thermodynamic feasibility

All MSA’s are feasible

MSA Selection

Choose MSA with lowest

removal cost, i.e. adsorbing

resin (S3)

Example No. 4 16:21

• Include Interception (Continued)– Annual operating cost for removing ammonia

using the resin

– Annualized fixed cost is estimated at $90,000/yr. Thus the total annualized cost becomes:

6 $kg removed0.8 kg/s (14 12) 10 91 3600 8760

$29,000 /

syrAOC

AOC yr

$119, 000 /TAC yr

Example No. 4 17:21

• Include Interception (Continued)– Interception and direct recycle has eliminated

the fresh water usage in the scrubber and thus reduced the overall fresh water consumption and consequently the influent to the biotreatment facility by 6.0 kg/s.

– To achieve the minimum discharge target we still have 1.2 kg/s to go, which are related to the steam-jet ejector.

Example No. 4 18:21

• Sink/Generator Manipulation– Replace steam-jet ejector with vacuum pump

• Operating cost are comparable to steam-jet ejector• Capital investment of $75,000 is needed• 5 year linear depreciation with negligible salvage value,

the annualized fixed cost of the pump is $15,000/year

– Operate column under atmospheric pressure• Eliminates the need for the vacuum pump• Simulation study needed to examine effect of pressure

change

– Relax requirements to BFW purity• Recycle and interception techniques can significantly

reduce the fresh water consumption.

Example No. 4 19:21

• Optimal MEN Configuration

O2

Decanter

DistillationColumn

Reactor ScrubberNH3

C3H6


Off-GasCondensate

Bottoms

AN toSales






+ Gases




1ppm NH34.6 kg AN/s0.3 kg H2O/s

AdsorptionColumn

Resin

VacuumPump



To Regenerationand Recycle


AqueousLayer

Example No.4 20:21

• Impact Diagrams (Pareto Charts)– Reduction in wastewater– Associated TAC

Strategy

Reduction in Flow

rate of Term

ianl Wastew

ater, kg/s

0.0

2.0

3.0

4.0

5.1

7.0

1.0

6.0

8.0

0.0

2.0

3.0

4.0

5.0

7.2

1.0

6.0

8.0

Segregation and

Direct Recycle

Interception Sink/Generator

Manipulation

Strategy

Total Annualized C

ost, 1000$/yr

Segregation and

Direct Recycle

Interception Sink/Generator

Manipulation

0.0

150

200

48

100

0.0

167

200

50

100

182

Example No. 4 21:21

• Merits of Identified Solution– AN production increased from 3.9 kg/s to 4.6

kg/s corresponding to an 18% increase

– Fresh water usage and influent to biotreatment reduced by 7.2 kg/s corresponding to a 40% debottlenecking

– Plant production can be expanded 2.5 times the current capacity before the biotreatment is bottlenecked again

FAR SUPERIOR TO THE INSTALLATION OF AN ADDITIONAL BIOTREATMENT FACILITY!!!

Summary 1:2

• Observations– Target for debottlenecking the biotreatment

facility was determined ahead of design

– Systematic tools were used to generate optimal solutions that realize the target

– Analysis study is needed to refine the results “big picture first, details later”

– Unique and fundamentally different approach than using the designer’s subjective decisions to alter the process and check the consequences using detailed analysis

Summary 2:2

• Observations (Continued)– It is also different from using simple end-of-pipe

treatment solutions. Instead, the various species are optimally allocated throughout the process

– Objectives such as yield enhancement, pollution prevention and cost savings can be simultaneously addressed

• Next Lecture – February 14– Algebraic mass integration techniques– SSLW pp. 297-308

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chen 4470 – process design practice dr. mario richard eden department of chemical engineering...

Documents

flowrate of feed kgs

flowrate of wash feed

content of feed wt

processmass integration

minimum fresh arm

channeling flowrate

weeping flowrate

massenergy matrix