1. University of Texas at AustinMichigan Technological University 1 Module 5: Process Integration of Heat and Mass Chapter 10 David R. Shonnard Department of Chemical Engineering Michigan Technological University

2. University of Texas at AustinMichigan Technological University 2 Module 5: Outline The environmental performance of a process depends on both the performance of the individual unit operations, but also on the level to which the process steams have been networked and integrated l Educational goals and topics covered in the module l Potential uses of the module in chemical engineering courses l Review of heat integration concepts l Introduction to the tools of mass integration and synthesis of mass exchange networks - Chapter 10 l Cast study - heat integration of the MA flowsheet

3. University of Texas at AustinMichigan Technological University 3 Module 5: Educational goals and topics covered in the module Students will: l learn about efficient utilization of waste streams as raw materials through application of source/sink mapping l are introduced to graphical tools of mass exchange network synthesis, composition interval diagrams and load line diagrams. l apply mass exchange network synthesis to simple flowsheets

4. University of Texas at AustinMichigan Technological University 4 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

5. University of Texas at AustinMichigan Technological University 5 Module 5: Analogies between process heat and mass integration Heat Integration the 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 Integration the 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)

6. University of Texas at AustinMichigan Technological University 6 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 [(mC p ) 1 + (mC p ) 2 ] -1 89% reduction in external utilities

7. University of Texas at AustinMichigan Technological University 7 Module 5: Heat exchange networks - Illustrative example - before heat integration 1 kg/s, C p = 1 kJ/(kg- ˚C) 2 kg/s, C p = 1 kJ/(kg- ˚C) per sec

8. University of Texas at AustinMichigan Technological University 8 Module 5: Heat exchange networks - Temperature - load (pinch) diagram per sec 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

9. University of Texas at AustinMichigan Technological University 9 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

10. University of Texas at AustinMichigan Technological University 10 1. Segregation avoid mixing of sources 2. Recycle direct sources to sinks 3. Interception selectively remove pollutants from source 4. Sink/generator manipulation adjust 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

11. University of Texas at AustinMichigan Technological University 11 Module 5: Motivating example: Chloroethane process before mass integration 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

12. University of Texas at AustinMichigan Technological University 12 Module 5: Motivating example: Chloroethane process after mass integration Interception 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

13. University of Texas at AustinMichigan Technological University 13 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

14. University of Texas at AustinMichigan Technological University 14 Module 5: Source-sink mapping: acrilonitrile (AN) process before recycle 450 ˚C, 2 atm mass fraction of AN always equal to 0.068 2-phase stream always with 1 kg/s H 2 O but no H 2 O in the AN layer NH 3 equilibrium C W = 4.3 C AN 0 ppm NH 3 0 ppm AN required NH 3 partitioning C STEAM = 34 C PRODICT ≤ 10 ppm NH 3 may contain AN

15. University of Texas at AustinMichigan Technological University 15 Module 5: Source-sink map acrilonitrile (AN) process Sinks for water Sources for water

16. University of Texas at AustinMichigan Technological University 16 Module 5: Flow rates of condenser and fresh water sent to Scrubber

17. University of Texas at AustinMichigan Technological University 17 Module 5: Mass balances on AN units for remaining flow rates and compositions Scrubber to decanter ? kg/s H 2 O ? kg/s AN ? ppm NH 3 From fresh water supply 1.0 kg/s H 2 O 0 kg/s AN 0 ppm NH 3 Aqueous streams from condenser and distillation column 4.7 kg/s H 2 O 0.5 kg/s AN 12 ppm NH 3 Gas stream from condenser 0.5 kg/s H 2 O 4.6 kg/s AN 39 ppm NH 3

18. University of Texas at AustinMichigan Technological University 18 Module 5: Flow rates and compositions from Scrubber to Decanter And similarly for other units

19. University of Texas at AustinMichigan Technological University 19 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

20. University of Texas at AustinMichigan Technological University 20 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. Constraints i. 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

21. University of Texas at AustinMichigan Technological University 21 Module 5: Mass integration motivating example - Phenol-containing wastewater to waste water treatment to wastewater treatment 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

22. University of Texas at AustinMichigan Technological University 22 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

23. University of Texas at AustinMichigan Technological University 23 Module 5: Hypothetical set of rich and lean streams - stream properties Equilibrium of pollutant between rich and lean streams y = 0.67 x

24. University of Texas at AustinMichigan Technological University 24 Module 5: Composition interval diagram - a tool for MEN synthesis x scale matched to y scale using y = 0.67 x

25. University of Texas at AustinMichigan Technological University 25 Module 5: Mass transfer loads in each interval Rich Streams negative mass load denotes transfer out of the stream

26. University of Texas at AustinMichigan Technological University 26 Module 5: Composite load line for the rich stream Region 1 & 2 Region 5 Region 3 Region 4

27. University of Texas at AustinMichigan Technological University 27 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 external MSA

28. University of Texas at AustinMichigan Technological University 28 Module 5: Stream matching in MEN synthesis

29. University of Texas at AustinMichigan Technological University 29 Module 5: Heat integration of the MA flowsheet Without Heat Integration 9.70x10 7 Btu/hr -9.23x10 7 Btu/hr 2.40x10 7 Btu/hr -4.08x10 7 Btu/hr Reactor streams generate steam

30. University of Texas at AustinMichigan Technological University 30 Module 5: Heat integration of reactor feed and product streams

31. University of Texas at AustinMichigan Technological University 31 Module 5: Heat integration of absorber outlet and recycle streams

32. University of Texas at AustinMichigan Technological University 32 Module 5: Maleic anhydride flowsheet with heat integration

33. University of Texas at AustinMichigan Technological University 33 Module 5: Heat integration summary 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

34. University of Texas at AustinMichigan Technological University 34 Module 5: Recap l Educational goals and topics covered in the module l Potential uses of the module in chemical engineering courses l Review of heat integration concepts l Introduction to the tools of mass integration and synthesis of mass exchange networks - Chapter 10 l Cast study - heat integration of the MA flowsheet