the role of process integration in process synthesis€¦ · task coordination and integration ii...
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The Role of Process Integration in Process Synthesis
Jeffrey J. Siirola Purdue University / Carnegie Mellon University International Process Integration Jubilee Conference 18 March 2013
Process Innovation Sequence Need Identification Vendor Specifications Product Design Component Acquisition Basic Chemistry Construction Plan/Schedule Detailed Chemistry Plant Construction Task Identification Operating Procedures Equipment Design Commissioning/Start-up Plant Engineering Production Plan/Schedule Detailed Engineering Operation
Each step involves generating (synthesizing) alternatives Each step repeated several times at differing level of detail
Process Synthesis
♦The generation of process flowsheet alternatives
♦ Identification of... • Phenomena to exploit • Equipment to implement phenomena • Interconnections among equipment
Process Synthesis Approaches ♦ Evolutionary Modification
• Traditional Method • Alter Existing Design
♦ Superstructure Optimization
• Simplify Redundant Design • Generalized Disjunctive Programming
♦ Systematic Generation
• Build Up From Basic Components • Means-Ends Analysis • Role of Integration is Explicit
Means-Ends Analysis Systematic Generation Approach ♦ Define initial and goal states in terms of physical
properties ♦ Detect physical property differences ♦ Identify technological tasks to reduce differences ♦ Add unit operations to create flowsheet
• Retrosynthetically to goal state and specify inputs • Synthetically to present state and determine outputs • Strategically awaiting resolution of preconditions
♦ Recursively meet any technology preconditions
Hierarchical Systematic Generation Process Synthesis Paradigm ♦ Reaction Path Synthesis
• Chemistry
♦ Species Allocation • Input-output and recycle structure
♦ Task Identification • Composition, phase, temperature, pressure
♦Task Integration ♦ Utility Infrastructure ♦ Equipment Design
Onion Model, AIDES, BALTAZAR, PIP, PROSYN
Task Coordination and Integration I ♦ Integrate complementary (especially
enthalpy-changing) tasks for utility efficiency • Heat exchanger networks • Power integration • Pinch Technology
Resulting Network may Use more than the Minimum Utility Requirement
Heat was transferred across the pinch (for convenience or simplification)
Integration was not selected because utilities were desired to enable start-up
Integration was not selected because utilities were used to be able to reject disturbances
Integration was not selected because network was too complex (or insufficiently robust)
Integration was not selected because it divided streams into too many small segments
Complementary Task Integration Status
♦Wide use of heat exchanger networks ♦Power integration with expander-
compressors and some use of heat pumps
♦Techniques: Heuristic stream matching; mathematical programming; Pinch Technology
♦Overcome disturbance rejection problems with computer model-based control
♦Typical savings: 10% NPV
Task Coordination and Integration II ♦Coordinate tasks at different levels of
the process synthesis hierarchy to maximize efficiency-improving integration opportunities
• Heat-integrated distillation sequences • Multiple-effect distillation • Heat-pumped distillation
Multicomponent Distillation Sequences
A B C
D
A B
D C
A
B
C
D
D
A B
C D C B
A
Conventional Distillation Sequence
A B C
D Each sequence involves 13 enthalpy-changing tasks
1.0 Atm 1.0 Atm 1.0 Atm
Distillation Sequencing Heuristics for Constant Relative Volatility Ordering
(Seader & Westerberg, 1977; Nath & Motard, 1981; Nadgir & Liu, 1983)
1. If any product is multicomponent, favor sequences that do not split these components
2. All other things equal, use ordinary distillation
3. Avoid refrigeration (sufficient column pressure to condense overhead for reflux with water)
4. Avoid vacuum (unless reboiler temperature results in bottoms decomposition or requires expensive heating utility)
5. If on extremes of volatility ordering list (i.e., lowest boiler or highest boiler), remove unstable, reactive, or corrosive component next
6. Delay the most difficult separation (smallest relative volatility between keys) until last (i.e., in the absence of non-key components)
7. Delay recovery of the component required in highest purity until last.
8. If on extremes of volatility ordering list, remove dominant component (>50% of feed) next
9 If a separation is difficult (small relative volatility <1.05), consider manipulation of activity coefficients by azeotropic or extractive distillation with introduced mass separating agent entrainers or solvents
10. If mass separation agents have been introduced, recover as soon as possible
11. Do the easiest separation (largest relative volatility between keys) next
12. Remove the most volatile species as distillate next
Pressure-Optimized Distillation Sequence
D
A B
C
0.3 Atm 2.4 Atm 1.1 Atm
Typical 10-15% Net Present Cost Savings
Pressure-Optimized Distillation Sequence Followed by Heat Integration
D
A B
C
Typical 15-20% Net Present Cost Savings
0.3 Atm 2.4 Atm 1.1 Atm
Simultaneous Distillation Sequence Pressure Optimization
Including Heat Integration
D C
A B
Typical 35-40% Net Present Cost Savings
0.3 Atm 8.7 Atm 5.6 Atm
Pressure Optimization Allowing Steam Generation as a Cooling Utility
D
A B C
Low Pressure Steam Generator
Low Pressure Steam Generator
High Pressure Steam
Medium Pressure Steam
Medium Pressure Steam
Typical 35-40% Net Present Cost Savings
11 Atm 2.7 Atm 3.3 Atm
ABC
ABC ABC
ABC
ABC
A B
C
A
B(A)
C
ABC
A B
C
C
A
B
A
B(C)
C
A
B C
Direct Sequence
Indirect Sequence Sidedraw above Feed
Sidedraw below Feed Sidestream Rectifier
Sidestream Stripper
Column and Exchanger Capital
ABC ABC ABC
A A A
C C C
B B B
Prefractionator Petyluk System Divided Wall
A(B) A(B) A(B)
C(B) C(B) C(B)
Thermally-Coupled Columns
ABC ABC
C(B)
ABC
A A A
C C C
B B
A(B) A(B)
A(B)
C(B) C(B)
B
Petyluk System Shifted Bottom Section Shifted Top Section
Lo P
Lo P
Hi P
Hi P
Overcoming Operational Issues in Thermally-Coupled Columns
Multi-effect Distillation Five basic configurations
Split feed (both columns designed for sharp splits)
First column with sloppy distillate followed by second sharp split column
Either first column or second column is high pressure column
First column with sloppy bottoms followed by second sharp split column
Either first column or second column is high pressure column
L
H
L L L L
H H H H
B
A A A AB A
B AB B B
A A A A AB
B B B B AB
Typical 40-50% Energy Savings
Heat Pump Configurations Use work to transfer heat from a condenser to
a reboiler (same column or different columns)
Heat pump cycle with separate working fluid Use of distillate as working fluid (vapor
recompression) Use of bottoms as working fluid (reboiler flashing)
Generally advantageous to pump heat across the pinch
Benefit of pumping heat on same side of pinch depends on efficiency of generating work and coefficient of performance of heat pump
Heat Pump Vapor Recompression Reboiler Flashing
W W W
Heat Pumped Distillation
Hierarchical Task Coordination Status
♦Heat-integrated distillation sequences ♦Multiple-effect distillation ♦Heat-pumped distillation
♦Techniques: Heat integration network
synthesis within column pressure optimization; exhaustive discontinuity-based search; parametric studies
♦Typical savings (optimized heat-integrated distillation sequences): 35% NPV
Task Coordination and Integration III ♦ Integrate multiple technologies for enhanced
performance or synergism • Using LLE to overcome VLE constraint
+Decanter to split heterogeneous azeotrope
• Azeotropic and extractive distillation + Mass separation agents to alter solution activity
coefficients and improve relative volatility
• Reactive separation + Simultaneous separation to enhance reaction + Reaction to eliminate the need for separation
Feed Alternate Feed
A B
Breaking Heterogeneous Minimum Boiling Azeotrope
Use of a Liquid-Liquid Decanter to Overcome Vapor-Liquid Distillation Boundary
Azeotropic Distillation Deliberate Formation of a Heterogeneous Azeotrope
For systems that form homogeneous minimum boiling azeotropes it may be possible to introduce a mass separation agent (entrainer) which increases activity coefficients to form a heterogeneous ternary azeotropic distillate whose two phases are then decanted and processed in a way analogous to the processing of heterogeneous minimum boiling azeotropes
This approach can also be used enhance the separation of a nonazeotropic but pinched systems producing a heterogeneous binary azeotropic distillate
Feed
A B
Use of Entrainer to Ease Distillation Pinch
Entrainer Feed
B
Use of Entrainer to Convert Homogeneous Binary Azeotrope to Heterogeneous Ternary
Azeotrope
Entrainer
A
Azeotropic Distillation
Extractive Distillation For systems that form minimum boiling azeotropes
or pinched distillates, it may be possible to introduce into the top of the column a mass separation agent (solvent) which decreases activity coefficient of one of the components so that the azeotrope does not form or the distillate becomes less pinched
The solvent may be chosen to interact (associate) with any of the feed species, but is usually selected to extract the species with the highest boiling point
The solvent exits with the bottoms and is usually recovered from the bottoms in a subsequent column
Feed
A B
Use Solvent to Break Homogeneous Azeotrope
Solvent
Extractive Distillation
Synergistic Technology Integration Reactive Separation
Use of Separation to enhance Reaction Remove product to shift equilibrium Remove catalyst inhibitor Improve reaction selectivity (consecutive reactions)
Use of Reaction to enhance Separation
Combine reaction equilibria and phase equilibria to alter azeotrope formation React to completion to eliminate a subsequent separation task
Multiple Technology Integration Status
♦Azeotrope-breaking schemes ♦Azeotropic and extractive distillation ♦Reactive separation ♦Hyphenated separators
♦Techniques: Reactive and non-reactive
residue curves; boundary-crossing heuristics; attainable region theory; process simulation
♦Typical results: Achieve performance not otherwise possible
Task Coordination and Integration IV
♦ Integrate consecutive tasks for process simplification
• Design equipment to accomplish multiple tasks
♦Equipment design for process intensification
• Manipulate areas, gradients, and fields for faster transport and kinetics and smaller equipment
Acetic Acid
Original Methyl Acetate Flowsheet
Azeo
Methanol Catalyst
Methyl Acetate
Solvent
Solvent/Entrainer
Water
Heavies Water
Water
Synergistic Task Integration Routing Task Coproduct Streams
Catalyst Methanol
Methyl Acetate
Acetic Acid Water
Acetic Acid
Water
Methyl Acetate Methanol
Acetic Acid Equilibrium Reaction
Task A
Distillative Separation
Task G
Solvent-Enhanced Distillative Separation
Task F
Distillative Separation
Task C
Distillative Separation
Task D
Separative Reaction
Task E
Separative Reaction
Task B
Consecutive Task Integration for Process Intensification
Single Column Methyl Acetate Process
Extractive Distillation
Task F
Distillation Task G
Reactive Distillation
Task E Reaction Task A
Reactive Distillation
Task B
Distillation Tasks
C and D
Acetic Acid
Catalyst
Methanol
Methyl Acetate
Water
Consecutive Task Integration Status
Design equipment to accomplish multiple tasks Techniques: Ad-hoc empiricism; equipment and process simulation; experimental verification Capital (and energy) reductions can be dramatic: 80% NPV
Process Intensification ♦ Fundamental process technology research
• Change driving force • Change area • Change gradient • Change coefficient • Combine multiple phenomena • Integrate functionality
Equipment Intensification Status
♦Manipulate areas, driving forces, and turbulence for faster transport and kinetics and smaller equipment
♦Techniques: Ad-hoc empiricism; equipment and process simulation; experimental verification
♦Typical savings more related to improved reaction selectivity than to down-sized equipment cost reduction
Summary Process synthesis is the generation of flowsheet alternatives Economically superior process synthesis will incorporate a number of elements of process integration
Selective integration of reaction steps Component recycle within the flowsheet Integration of complementary tasks to minimize utilities Coordination of task operating conditions to optimize the opportunity for such complementary task integration Integration of multiple phenomena to accomplish tasks Integration of multiple tasks into single equipment Adjustment of design elements, geometries, and conditions to enhance or better balance reaction and transport kinetics
All of these process intensification techniques are in routine use in industrial chemical process synthesis