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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
25 ppm NH30.4 kg AN/s5.5 kg H2O/s
34 ppm NH30.2 kg AN/s1.2 kg H2O/s
18 ppm NH34.6 kg AN/s6.5 kg H2O/s
10 ppm NH34.2 kg AN/s1.0 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
0 ppm NH30.1 kg AN/s0.7 kg H2O/s
1ppm NH33.9kg AN/s
0.3 kg H2O/s
• Motivating Example
Any process
insights??
Mass Integration 2:4
• 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
Mass Integration 3:4
• 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.
Mass Integration 4:4
• 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,3Terminal_Load k,4
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,1Fresh_Load k,2
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,1Terminal_Load k,2
Terminal_Load k,3Terminal_Load k,4
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,1Fresh_Load k,2
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
Terminal_Load k,1 - R k,1
Terminal_Load k,2 - R k,2
Terminal_Load k,3Terminal_Load k,4
i=1
i=2
i=3
i=4
j=1
j=2
j=3
Fresh_Load k,1 - R k,2
Fresh_Load k,2 - R k,1
Fresh_Load k,3
Effective Recycle From Terminal
1
2
3
4
5
Rk,1
Rk,2
Terminal_Load k,1 - R k,1
Terminal_Load k,2 - R k,2
Terminal_Load k,3Terminal_Load k,4
i=1
i=2
i=3
i=4
j=1
j=2
j=3
Fresh_Load k,1 - R k,2
Fresh_Load k,2 - R k,1
Fresh_Load k,3
i=5
Effective Recycle From Terminal and Intermediate
1
2
3
4
5
Rk,1
Rk,2
Terminal_Load k,1 - R k,1
Terminal_Load k,2 - R k,2
Terminal_Load k,3Terminal_Load k,4
i=1
i=2
i=3
i=4
j=1
j=2
j=3
Fresh_Load k,1 - R k,2
Fresh_Load k,2 - R k,1
Fresh_Load k,3
Effective Recycle From Terminal
1
2
3
4
5
Rk,1
Rk,2
Terminal_Load k,1 - R k,1
Terminal_Load k,2 - R k,2
Terminal_Load k,3Terminal_Load k,4
i=1
i=2
i=3
i=4
j=1
j=2
j=3
Fresh_Load k,1 - R k,2
Fresh_Load k,2 - R k,1
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
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
25 ppm NH30.4 kg AN/s5.5 kg H2O/s
34 ppm NH30.2 kg AN/s1.2 kg H2O/s
18 ppm NH34.6 kg AN/s6.5 kg H2O/s
10 ppm NH34.2 kg AN/s1.0 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
0 ppm NH30.1 kg AN/s0.7 kg H2O/s
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
Scrubber Water6.0 kg/s
B FW1.2 kg/s
Water Generation 5.1 kg/s
ACRYLONITRILE PLANT
Wastewater4.8 kg H20/s
Water Loss (with AN Product)
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
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
Scrubber Water6.0 kg/s
B FW1.2 kg/s
Water Generation 5.1 kg/s
ACRYLONITRILE PLANT
Wastewater4.8 kg H20/s
Water Loss (with AN Product)
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 $15,000/year
– Operate column under atmospheric pressure• Eliminates the need for the vacuum pump• Simulation study needed to examine effect of pressure
change
– Relax requirements to BFW purity• Recycle and interception techniques can significantly
reduce the fresh water consumption.
Example No. 4 19:21
• Optimal MEN Configuration
O2
Decanter
DistillationColumn
Reactor ScrubberNH3
C3H6
Wastewater to Biotreatment
Off-GasCondensate
Bottoms
AN toSales
14 ppm NH30.4 kg AN/s4.6 kg H2O/s
25 ppm NH30.4 kg AN/s4.8 kg H2O/s
23 ppm NH35.1 kg AN/s5.8 kg H2O/s
21 ppm NH34.7 kg AN/s1.0 kg H2O/s
5.0 kg AN/s5.1 kg H2O/s
+ Gases
25 ppm NH30.4 kg AN/s4.8 kg H2O/s
Tail Gases to Disposal
0 ppm NH30.1 kg AN/s0.7 kg H2O/s
1ppm NH34.6 kg AN/s0.3 kg H2O/s
AdsorptionColumn
Resin
VacuumPump
Tail Gases to Disposal
12 ppm NH30.4 kg AN/s4.6 kg H2O/s
To Regenerationand Recycle
10 ppm NH30.5 kg AN/s5.3 kg H2O/s
AqueousLayer
Example No.4 20:21
• Impact Diagrams (Pareto Charts)– Reduction in wastewater– Associated TAC
Strategy
Reduction in Flow
rate of Term
ianl Wastew
ater, kg/s
0.0
2.0
3.0
4.0
5.1
7.0
1.0
6.0
8.0
0.0
2.0
3.0
4.0
5.0
7.2
1.0
6.0
8.0
Segregation and
Direct Recycle
Interception Sink/Generator
Manipulation
Strategy
Total Annualized C
ost, 1000$/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
Other Business