Heat and Power Integration CHEN 4460 – Process Synthesis, Simulation and Optimization Dr. Mario Richard Eden Department of Chemical Engineering Auburn University Lecture No. 9 – Heat and Power Integration: Network Design October 28, 2008 Contains Material Developed by Dr. Daniel R. Lewin, Technion, Israel

Lecture 9 – Objectives  Compute the pinch temperatures  Compute the Maximum Energy Recovery (MER) targets using graphical and/or algebraic methods  Design a simple Heat Exchanger Network (HEN) to meet the MER targets Given data on the hot and cold streams of a process, you should be able to: Last time!

Reviewing Simple Example Design a network of steam heaters, water coolers and exchangers for the process streams. Where possible, use exchangers in preference to utilities. Utilities: 150 o C, 25 o C

Simple Example - Targets Units:4 Steam:60 kW Cooling water:18 kW Are these numbers optimal??

Not to scale!! Reviewing Simple Example

Not to scale!! Reviewing Simple Example

Q Cmin = 6 kW Q Hmin = 48 kW T Cpinch = 60 T Hpinch = 70 Maximum Energy Recovery (MER) Targets! Reviewing Simple Example

Near Optimal Solution

Reviewing Simple Example HEN Representation (Grid Diagram)

HEN Grid Diagram The pinch divides the HEN into two parts:  the left hand side (above the pinch)  the right hand side (below the pinch) At the pinch, ALL hot streams are hotter than ALL cold streams by  T min.

MER Network Design Step 1:MER Targeting Pinch at 90° (Hot) and 80° (Cold) Energy Targets: Total Hot Utilities: 20 kW Total Cold Utilities:60 kW

MER Network Design Step 2:Divide the problem at the pinch

MER Network Design Step 3:Design hot-end starting at the pinch Pair up exchangers according to CP-constraints. Immediately above the pinch Pair up streams such that: CP HOT  CP COLD (This ensures that T H  T C   T min )  T min

MER Network Design Step 3 Cont’d: Complete hot-end design, by ticking-off streams H Add heating utilities as needed (  MER target) Q Hmin = 20 kW 20

MER Network Design Step 4:Design cold-end starting at the pinch Pair up exchangers according to CP-constraints. Immediately below the pinch Pair up streams such that: CP HOT  CP COLD (This ensures that T H  T C   T min )  T min

MER Network Design Step 4 Cont’d: Complete cold-end design, by ticking-off streams. C Add cooling utilities as needed (  MER target) Q Cmin = 60 kW o

MER Network Design Completed Design Note that this design meets the MER targets: Q Hmin = 20 kW and Q Cmin = 60 kW

Steps in MER Network Design  MER targeting: Define pinch temperatures, Q hmin and Q Cmin  Divide problem at the pinch  Design hot-end, starting at the pinch:Pair up exchangers according to CP-constraints. Immediately above the pinch, pair up streams such that: CP HOT  CP COLD. “Tick off” streams in order to minimize costs. Add heating utilities as needed (up to Q Hmin ). Do not use cold utilities above the pinch.  Design cold-end, starting at the pinch: Pair up exchangers according to CP-constraints. Immediately below the pinch, pair up streams such that: CP HOT  CP COLD. “Tick off” streams in order to minimize costs. Add heating utilities as needed (up to Q Cmin ). Do not use hot utilities below the pinch.

Simple Example Revisited Near Optimal Solution

Simple Example Revisited Utilities: 150 o C, 25 o C Q Hmin =48 Q Cmin =6 80 o C H 54 C o C H 8 40

 Compute the pinch temperatures  Compute the Maximum Energy Recovery (MER) targets using graphical and/or algebraic methods  Design a simple Heat Exchanger Network (HEN) to meet the MER targets Given data on the hot and cold streams of a process, you should be able to: Last time! Summary – Heat Integration

Other Business Homework –SSL: 10.1, 10.2 –Due Tuesday November 4 Next Lecture – November 4 –Mathematical Optimization (SSL pp )