University of Texas at AustinMichigan Technological University 1 Module 5: Process Integration of...
-
Upload
marybeth-gray -
Category
Documents
-
view
214 -
download
1
Transcript of University of Texas at AustinMichigan Technological University 1 Module 5: Process Integration of...
University of Texas at Austin Michigan Technological University1
Module 5: Process Integration of Heat and Mass
Chapter 10
David R. Shonnard
Department of Chemical Engineering
Michigan Technological University
University of Texas at Austin Michigan Technological University2
Module 5: Outline
The environmental performance of a process depends on both theperformance of the individual unit operations, but also on the level to which the process steams have been networked and integrated
Educational goals and topics covered in the module
Potential uses of the module in chemical engineering courses
Review of heat integration concepts
Introduction to the tools of mass integration and synthesis of mass exchange networks - Chapter 10
Cast study - heat integration of the MA flowsheet
University of Texas at Austin Michigan Technological University3
Module 5: Educational goals and topics covered in the module
Students will: learn about efficient utilization of waste streams as raw
materials through application of source/sink mapping
are introduced to graphical tools of mass exchange network synthesis, composition interval diagrams and load line diagrams.
apply mass exchange network synthesis to simple flowsheets
University of Texas at Austin Michigan Technological University4
Module 5: Potential uses of the module in chemical engineering courses
Mass/energy balance course: • dilute contaminant balance calculations around process units
• source/sink matching of energy streams
Continuous/stagewise separations course:• applications to in-process recovery and recycle of contaminants
Design course:• graphical design tools for mass integration of waste streams
University of Texas at Austin Michigan Technological University5
Module 5: Analogies between process heat
and mass integration
Heat Integrationthe optimum use of heat exchangers and streams internal to the process to satisfy heating and cooling requirements.
Tools: 1. Temperature interval diagram
2. Heat load diagram (pinch diagram)
Mass Integrationthe optimum use of mass exchangers and streams internal to the process to satisfy raw material requirements, maximize production and minimize waste generation (water recycle/reuse applications).
Tools: 1. Source/sink mapping and diagrams
2. Composition interval diagram
3. Mass load diagram (pinch diagram)
University of Texas at Austin Michigan Technological University6
Module 5: Heat exchange networks -key features
Seider, Seader, and Lewin, 1999, “Process Design Principles”, John Wiley & Sons, Ch. 7
Heat exchange network • internal • external
T - Heat Load Diagram • composite curves • pinch analysis • minimum external utilities
[(mCp)1 + (mCp) 2]-1
89% reduction in external utilities
University of Texas at Austin Michigan Technological University7
Module 5: Heat exchange networks -Illustrative example - before heat
integration
1 kg/s, Cp = 1 kJ/(kg-˚C)
2 kg/s, Cp = 1 kJ/(kg-˚C)
per sec
per sec
University of Texas at Austin Michigan Technological University8
Module 5: Heat exchange networks -Temperature - load (pinch) diagram
pe
r s
ec
Placement of each load line vertically is arbitrary
10 ˚C minimum temperature difference defines the pinch
2 kg/s
1 kg/s
Cooling load for external network, 160 kJ/s
Heat transfer load by internal network, 140 kJ/s
Heating load for external network, 30 kJ/s
University of Texas at Austin Michigan Technological University9
Module 5: Heat exchange networks -Illustrative example after heat integration
46.7% reduction in heating utility
82.4% reduction in cooling utility
140 kJ/s transferred
per sec
per sec
University of Texas at Austin Michigan Technological University10
1. Segregationavoid mixing of sources
2. Recycledirect sources to sinks
3. Interceptionselectively remove pollutants from source
4. Sink/generator manipulationadjust unit operation design or operation
Module 5: Mass integration: objectives and methods
Pollutant-rich streams
Pollutant-lean streams
objective is to prepare source streams to be acceptable to sink units within the process or to waste
treatment
Methods
El-Halwagi, M.M.1997, “Pollution Prevention Through Process Integration: Systematic Design Tools”, Academic Press
University of Texas at Austin Michigan Technological University11
Module 5: Motivating example: Chloroethane process before mass
integration
C2H5OH +HCl→ C2H5Cl +H2O
( ) Chloroethanol CE is byproduct
C2H5OCl
Mass balance in terms of CE, the minor component
Objective is to reduce the concentration of CE sent to biotreatment to < 7 ppm and a load of < 1.05x10-6 kg CE/s
El-Halwagi, M.M.1997, “Pollution Prevention Through Process Integration: Systematic Design Tools”, Academic Press
University of Texas at Austin Michigan Technological University12
Module 5: Motivating example: Chloroethane process after mass
integrationInterception
Recycle
CE load to biotreatment = 2.5x10-7 kg/s
El-Halwagi, M.M.1997, “Pollution Prevention Through Process Integration: Systematic Design Tools”, Academic Press
University of Texas at Austin Michigan Technological University13
Module 5: Mass Integration Tools:Source-sink mapping
the purpose of source-sink mapping is to determine if waste streams can be used as feedstocks within the process - direct recycle
A range of acceptable flowrates and composition for each sink , “S”
Recycle source “a” directly
or mix sources “b” and “c” to achieve the target flowrate - composition using a Lever Rule - like calculation
El-Halwagi, M.M.1997, “Pollution Prevention Through Process Integration: Systematic Design Tools”, Academic Press
University of Texas at Austin Michigan Technological University14
Module 5: Source-sink mapping: acrilonitrile (AN) process before recycle
C3H6 +NH3 +1.5 O2catalyst⏐ → ⏐ ⏐ C3H3N+ 3H2O
450 ˚C,2 atm
mass fraction of AN always equal to 0.068
2-phase stream always with 1 kg/s H2O but no H2O in the AN layer
NH3 equilibriumCW = 4.3 CAN
0 ppm NH3 0 ppm ANrequired
NH3 partitioningCSTEAM = 34 CPRODICT
≤ 10 ppm NH3
may contain AN
University of Texas at Austin Michigan Technological University15
Module 5: Source-sink map acrilonitrile (AN) process
Sinks for water Sources
for water
University of Texas at Austin Michigan Technological University16
Module 5: Flow rates of condenser and fresh water sent to Scrubber
Water Mass Balance
0.5kgs+ x+ y=6.2kg
sNH3 Balance
0.8kgs×0 ppm+ x×14 ppm+y×0 ppm
0.8kgs+x+y
=10 ppm
x = flow rate of condensate stream sent to Scrubber
= 4.4 kgs = 4.0
kg H2Os
+ 0.4 kg ANs
y = flow rate of fresh water sent to Scrubber= 1.0 kg H2Os
University of Texas at Austin Michigan Technological University17
Module 5: Mass balances on AN units for remaining flow rates and compositions
Scrubber
to decanter? kg/s H2O? kg/s AN? ppm NH3
From fresh water supply1.0 kg/s H2O0 kg/s AN0 ppm NH3
Aqueous streams from condenser and distillation column4.7 kg/s H2O0.5 kg/s AN12 ppm NH3
Gas stream from condenser0.5 kg/s H2O4.6 kg/s AN39 ppm NH3
University of Texas at Austin Michigan Technological University18
Module 5: Flow rates and compositions from Scrubber to Decanter
Water Mass Balance
0.5kgs+1.0 kg
s+ 4.0kg
s+ 0.7 kg
s=6.2 kgH2O
s AN Mass Balance
4.6kgs+ 0.4
kgs+ 0.1
kgs=5.1
kgANs
NH3 Balance
5.1kgs×39 ppm+ 0.8kg
s×0 ppm+1.0kg
s×0 ppm+ 4.4 kg
s×14 ppm
5.1kgs+ 0.8
kgs+1.0
kgs
+ 4.4kgs
=23 ppm
And similarly for other units
University of Texas at Austin Michigan Technological University19
acrilonitrile (AN) process after recycle
60% of original
freshwater feed 30% of original
rate of AN sent to biotreatment is 85% of original
AN production rate increased by 0.5 kg/s; $.6/kg AN and 350 d/yr = $9MM/yr
University of Texas at Austin Michigan Technological University20
Module 5: Mass exchange network (MEN) synthesis
1. Similar to heat exchange network (HEN) synthesis
2. Purpose is to transfer pollutants that are valuable from waste streams to process streams using mass transfer operations (extraction, membrane modules, adsorption, ..
3. Use of internal mass separating agents (MSAs) and external MSAs.
4. Constraintsi. Positive mass transfer driving force between rich and lean process
streams established by equilibrium thermodynamics
ii. Rate of mass transfer by rich streams must be equal to the rate of
mass acceptance by lean streams
iii. Given defined flow rates and compositions of rich and lean streams
University of Texas at Austin Michigan Technological University21
Module 5: Mass integration motivating example - Phenol-containing wastewater
to wastewatertreatment
to wastewatertreatment
Mass separating agents
Outlet streams for recycle or sale
- Minimize transfer to waste treatment -
El-Halwagi, M.M.1997, “Pollution Prevention Through Process Integration: Systematic Design Tools”, Academic Press
University of Texas at Austin Michigan Technological University22
Module 5: Outline of MEN synthesis
1. Construct a composition interval diagram (CID)
2. Calculate mass transfer loads in each composition interval
3. Create a composite load line for rich and lean streams
4. Combine load lines on a combined load line graph
5. Stream matching of rich and lean streams in a MEN using the CID
University of Texas at Austin Michigan Technological University23
Module 5: Hypothetical set of rich and lean streams - stream properties
Rich Stream Lean Stream
StreamFlow
Rate, kg/syin yout Stream
FlowRate, kg/s
xin xout
R1
R2
R3
5
10
5
0.10
0.07
0.08
0.03
0.03
0.01
L 15 0.0 0.14
Equilibrium of pollutant between rich and lean streams
y = 0.67 x
University of Texas at Austin Michigan Technological University24
Module 5: Composition interval diagram - a tool for MEN synthesis
x scale matched to y scale using y = 0.67 x
University of Texas at Austin Michigan Technological University25
Module 5: Mass transfer loads in each interval
Rich Streams
Region 1 and 2 = (yout −yin)× RiStreamsi∑ = (0.08- 0.1)×5 kg/ s = - 0.1 kg/ s
3 Region = (0.07- 0.08)×(5 kg/ s+ 5 kg/ ) s = - 0.1 kg/ s
4 Region = (0.03- 0.07)×(5 kg/ s+10 kg/ s+ 5 kg/ ) s = - 0.8 kg/ s
5 Region = (0.01- 0.03) ×(5 kg/ ) s = - 0.1 kg/ s
negative mass load denotes transfer out of the stream
University of Texas at Austin Michigan Technological University26
Module 5: Composite load line for the rich stream
Region 1 & 2
Region 5
Region 3
Region 4
University of Texas at Austin Michigan Technological University27
Module 5: Combined load line for rich and lean
streams
Rich Stream can be moved vertically
mass load to be added to lean stream externally
mass load to be transferred internally
mass load to be removed from rich stream by externalMSA
University of Texas at Austin Michigan Technological University28
Module 5: Stream matching in MEN synthesis
University of Texas at Austin Michigan Technological University29
Module 5: Heat integration of the MA flowsheet
Without Heat Integration
9.70x107 Btu/hr-9.23x107 Btu/hr
2.40x107 Btu/hr
-4.08x107 Btu/hr
Reactor streams generate steam
University of Texas at Austin Michigan Technological University30
Module 5: Heat integration of reactor feed and product streams
0.E+00
2.E+07
4.E+07
6.E+07
8.E+07
1.E+08
1.E+08
0 100 200 300 400 500 600 700 800 900
Temperature (F)
Q (Btu/hr)
Hot Stream Cold Stream
Internal load9.251x107 Btu/hr
External load0.468x107 Btu/hr
(795 ˚F, 9.72x10 7 Btu/hr)
(805 ˚F, 9.72x10 7 Btu/hr)
(165.3 ˚F, 0 Btu/hr)
(215 ˚F, 0.468x10 7 Btu/hr)
ΔΤmin = 10 ˚F
University of Texas at Austin Michigan Technological University31
Module 5: Heat integration of absorber outlet and recycle streams
0.E+00
1.E+07
2.E+07
3.E+07
4.E+07
5.E+07
100 200 300 400 500
Temperature (F)
Q (Btu/hr)
Hot Stream Cold Stream
Internal load2.321x107 Btu/hr
External load1.73x107 Btu/hr
(400 ˚F, 4.05x10 7 Btu/hr)
(445.6 ˚F, 4.05x10 7 Btu/hr)
(228.1 ˚F, 1.73x10 7 Btu/hr)
(100 ˚F, 0 Btu/hr)
ΔΤmin = 15 ˚F
University of Texas at Austin Michigan Technological University32
Module 5: Maleic anhydride flowsheet with heat integration
University of Texas at Austin Michigan Technological University33
Module 5: Heat integration
summary
Energy Duty Energy (Btu/hr)
No HI HI
Compressor 1.52x107 1.52x107
Reactor (Er1) -9.40x107 -9.40x107
Reactor (Er2) -9.40x107 -9.40x107
Reactor (Er3) -9.40x107 -9.40x107
Rxn. prod. cooler (E4) -9.23x107
Abs. out heater (E5) 2.40x107
Purge heater (E6) 2.36x106 2.36x106
Condenser (E7) -8.81x106 -8.80x106
Reboiler (E8) 1.28x107 1.28x107
Recycle pump (E9) 2.50x104 2.50x104
Recycle cooler (E10) -4.08x107 -1.68x107
Feed heater (E11) 9.70x107 4.69x106
Total Inputs 15.1x107 3.51x107
Total Outputs 42.4x107 30.8x107
76.8% reduction
27.4% reduction
Greater energy reductions are possible when steam generated from the reactors is used for the reboiler, purge and feed heaters
University of Texas at Austin Michigan Technological University34
Module 5: Recap
Educational goals and topics covered in the module
Potential uses of the module in chemical engineering courses
Review of heat integration concepts
Introduction to the tools of mass integration and synthesis of mass exchange networks - Chapter 10
Cast study - heat integration of the MA flowsheet