Process design and integration Timo Laukkanen

The main objectives of this course To learn how to use tools that can be used to design heat recovery systems To obtain a ”holistic” view for process design and especially heat recovery design Timo Laukkanen

Process Engineering, Process Systems Engineering and Process Integration Process engineering focuses on the design, operation, control, and optimization of chemical, physical, and biological processes. Process systems engineering = systematic computer- based methods to process engineering. Process Integration = a holistic approach to process design and optimization, integrated process design or process synthesis Timo Laukkanen

experiments unit operation integrationphenomena Evolution of process design Timo Laukkanen

Evolution of process design Timo Laukkanen Synthesis is the creation of a process Simulation predicts how the process would behave if built Feed streams Product streams Feed streams Product streams

Hierarchy of process design: The ”onion” diagram Timo Laukkanen Separation System Water and Effluent Treatment Heating and Cooling System Utilities Heat Recovery System Separation and Recycle System Reactor

Continuous vs. Batch process Timo Laukkanen BATCH processes –Small volumes –Flexible in changing product formulation –Flexible in production rate –Allows the use of multipurpose equipment –Best if regular cleaning necessary –Products from each batch can be identified CONTINUOUS processes –Economical for large volumes

New design (greenfield) vs. Retrofit process design Timo Laukkanen Retrofit design –Old and new equipment can be used –The wearing of old equipment needs to considered Greenfield design –Only new equipment can be used Separation System Utility System

Irreducible structure vs. Reducible stucture (super structure) approach to process design Timo Laukkanen Irreducible structure (for example the pinch approach) –Follows the onion logic –Series of local decisions –Many designs need to be made due to sequential approach –No quarantee that best possible solution is found due to fixed designs in different levels –Designer in control of the design process Superstructure approach (mathematical programming) –All design options included in a mathematical model –Huge problem that can be hard to solve –Needs simplifications in unit operations –If the best design is not one that is embeded in the superstructure, optimal solution is not found –Teoretically possible to find the global optimum Utility System

Trade-offs in process design (multi-objective optimization) Timo Laukkanen Separation System Utility System Process topology EnergyCapitalOperation Raw materials

Process Integration Methods Timo Laukkanen Separation System Utility System Systematic visual thermodynamic analysis Targets before design Pinch Analysis “Second law”-thermodynamic analysis Quantitative measure of process efficiency Suitable multicomponent plant criteria of performance Exergy Analysis Constrained single- or multiobjective optimisation Models for systematic design and analysis Mathematical Programming (Artificial intelligence) Case-based reasoning, rule-based reasoning Knowledge Based Expert Systems

Process Integration Application Timo Laukkanen Separation System Utility System Initial trade-off between operating and investment costs Heat recovery targets Number of units, total heat exchanger surface area External energy supply vs. recycling Heat exchanger networks synthesis Thermally driven Distillation, evaporation and drying Separation systems design Boilers, turbine and heat pump integration Utility system synthesis Utility systems design Flexibility, controllability, startup- and shutdown Plant operability design

Timo Laukkanen Separation System Utility System

IEA BLUE MAP Timo Laukkanen Separation System

Heat Integration with Pinch Technology Targeting before Design

Phases in Pinch based HEN-Synthesis Data Extraction Performance Targets – Energy, Area, Units, Total Annual Cost Process Modifications Design of Maximum Heat Recovery Network Improvement (tuning)

Basic Equations for a Countercurrent Heat Exchanger 0 L A = Area U = Overall Heat Transfer Coefficient T h, in T h, out T c, in T c, out T x

Data Extraction Process Streams – Flowrates – Temperatures Start (Supply) and End (Target) – Specific Heat Capacity Incl. Latent Heat – Film Heat Transfer Coefficient (for U- estimate) Utility System/Streams – Temperature(s) – Heat Content – Cost per unit Heat exchangers – Cost function(s)

Small Example Reactor with two reactant and one product stream Necessary Data m cp = 1 kW/K m cp = 2 kW/K m cp = 3 kW/K 40°C300°C 40°C300°C 315°C90°C Reactor C1 C2 H1

Alternative Networks Reactor C1 C2 H1 40°C 300°C 40°C 300°C 315°C 90°C 228°C 210°C 115°C 180 kW -75 kW

Alternative Networks Reactor C1 C2 H1 40°C 300°C 40°C 300°C 315°C 90°C 228°C 120°C 142°C 180 kW -75 kW 115°C

Alternative Networks Reactor C1 C2 H1 40°C 300°C 40°C 300°C 315°C 75°C 70 kW 35 kW 315°C 90°C

T supply (°C)T target (°C)m c p (kW/K) H H C C Minimum Q c and Q h ?

Composite Curves T supply (°C)T target (°C)m cp (kW/K)Q total (kW) C H Q c,min = 40kW Q h,min = 20kW ∆T min = 15°C

T supply (°C)T target (°C)m cp (kW/K)Q total (kW) H H

∆T min Q c,min Q h,min

T supply (°C)T target (°C)m c p (kW/K) H H C C ∆T (°C)m cp (kW/K)Q (kW) H1H2HC

∆T (°C)m cp (kW/K)Q (kW) H1H2HC Q (kW)T (°C)

T supply (°C)T target (°C)m c p (kW/K) H H C C m cp (kW/K) ∆T (°C)C1C2CCQ (kW) Q (kW)T (°C)

Q (kW)T (°C)

∆T min =50°C Q c,min = 200kW Q h,min = 220kW heat available for recovery

pinch point heat deficit heat surplus minimum driving force pinch temperature

Optimal ∆T min Trade-off between utility consumption and driving forces

T supply (°C)T target (°C)m cp (kW/K) Q total (kW) H C ∆T Qc (kW) Qh (kW) Q util (kW)T h,in T h,out T c,in T c,out ∆T lm QA

∆T min optimal min total costs Optimal ∆T min

Summary Composite Curves Visualising the system Key information about the system – minimum utility consumption, hot and cold (given ∆T min ) – pinch point decomposition (areas of heat surplus and deficit) Temperature of min. driving forces for heat exchange