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CHEN 4470 – Process Design Practice Dr. Mario Richard Eden Department of Chemical Engineering Auburn University

Mass Integration. CHEN 4470 – Process Design Practice Dr. Mario Richard Eden Department of Chemical Engineering Auburn University Lecture No. 9 – Graphical Mass Integration Techniques February 9, 2012. Mass Integration 1:4. Motivating Example. Any process insights??. Mass Integration 2:4.

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CHEN 4470 – Process Design Practice Dr. Mario Richard Eden Department of Chemical Engineering Auburn University

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  1. Mass Integration CHEN 4470 – Process Design Practice Dr. Mario Richard EdenDepartment of Chemical EngineeringAuburn University Lecture No. 9 – Graphical Mass Integration Techniques February 9, 2012

  2. Mass Integration 1:4 • Motivating Example Any process insights??

  3. Mass Integration 2:4 • Mass-Energy Matrix of a Process

  4. Mass Integration 3:4 • Process from a Species Viewpoint Sources Streams laden with targeted species. Sinks Process units capable of accepting the sources.

  5. Mass Integration 4:4 • Strategies

  6. Direct Recycle 1:10 • Source-Sink Mapping Diagram

  7. Direct Recycle 2:10 • How to Identify Bounds on Sinks • From physical limitations • Flooding flowrate, weeping flowrate, channeling flowrate, saturation composition • From manufacturer’s design data • From technical constraints • To avoid scaling, corrosion, explosion, buildup, etc. • Add deviation to nominal • +/- x% from current value

  8. Direct Recycle 3:10 • How to Identify Bounds on Sinks (Continued) • From historical data

  9. Direct Recycle 4:10 • How to Identify Bounds on Sinks (Continued) • From constraints on other units

  10. Direct Recycle 5:10 • Source-Sink Mapping Diagram after Direct Recycle

  11. Direct Recycle 6:10 • Lever-arm Relationships • Component material balance

  12. Direct Recycle 7:10 • Lever-arm Relationships (Continued) Applications Minimization of fresh resources (raw materials, solvents, water). Minimize fresh material usage requires minimum fresh arm.

  13. Recycle from source b to right side of the sink box gives shortest arm for the fresh! Direct Recycle 8:10 • Example I: Recycle from Source b or c? • Example II: Which Sink Composition to use? Recycle from source b gives shortest arm for the fresh!

  14. Direct Recycle 9:10 • Targeting Rules for Recycle Alternatives • Process before recycle • Poor recycle (no change in fresh usage)

  15. Direct Recycle 10:10 • Targeting Rules for Recycle Alternatives (Cont’d) • Effective recycle from terminal • Effective recycle from terminal and intermediate

  16. Example No. 4 1:21 • Acrylonitrile (AN) Plant • Objectives • Enhance yield, debottleneck biotreatment facility by reducing wastewater production

  17. Example No. 4 2:21 • Observations • Sold-out product, need to expand • Biotreatment is a bottleneck • Intuitive solution (End of pipe approach) • Install an additional biotreatment facility ($4 million in capital investment and $360,000/year in annual operating cost) • Will solve problem, but not necessarily best solution! • Alternative solution • Use mass integration techniques to devise cost-effective strategies to debottleneck the process

  18. Example No. 4 3:21 • Synthesis Tasks • Identify target for minimum wastewater discharge • Identify recycle opportunities • Identify required separation • Identify necessary unit replacement All of that can be done systematically using mass integration techniques!

  19. Example No. 4 4:21 • Constraints • Scrubber • 5.8 ≤ flowrate of wash feed (kg/s) ≤ 6.2 • 0.0 ≤ ammonia content of wash feed (ppm NH3) ≤ 10.0 • Boiler Feed Water (BFW) • Ammonia content of BFW (ppm NH3) = 0.0 • AN content of BFW (ppm AN) = 0.0 • Decanter • 10.6 ≤ flowrate of feed (kg/s) ≤ 11.1 • Distillation Column • 5.2 ≤ flowrate of feed (kg/s) ≤ 5.7 • 0.0 ≤ ammonia content of feed (ppm NH3) ≤ 30.0 • 80.0 ≤ AN content of feed (wt% AN) ≤ 100.0

  20. Example No. 4 5:21 • Constraints (Continued) • Forbidden recycles (Quality assurance) • AN product stream (top of distillation column) • Feed to distillation column • Feed to decanter • Candidate MSA’s for Ammonia Removal • Air (S1) • Activated carbon (S2) • Adsorbing resin (S3)

  21. Water Generation GEN = OUT – IN OUT = (12.0 + 0.3) IN = (6.0 + 1.2) GEN = 12.3 – 7.2 = 5.1 Example No. 4 6:21 • MSA Data • Water Balance for AN Plant

  22. Example No. 4 7:21 • Target for Minimum Wastewate Discharge • Assuming that any water treatment required is feasible and available to us • The minimum generation of wastewater corresponds to the generated water in the plant minus what is lost with the AN product • Target for Minimum Discharge to Biotreatment • 5.1 kg/s – 0.3 kg/s = 4.8 kg/s

  23. Example No. 4 8:21 • Schematic Representation • Waste Interception Networks (WINs) is a subset of general Mass Exchange Networks (MENs)

  24. Example No. 4 9:21 • Source-Sink Mapping Diagram • To minimize fresh water usage, start with sources closest to the sink. • First distillation bottoms, then off-gas condensate Flowrate Constraint Combining the distillation bottoms and the off-gas condensate results in a flowrate of 5.0 + 0.8 = 5.8 kg/s Within bounds of scrubber!

  25. Example No. 4 10:21 • Source-Sink Mapping Diagram (Continued) • Checking the composition of the mixture • This means that not all the off-gas condensate can be recycled to the scrubber Outside sink region!!

  26. Example No. 4 11:21 • Source-Sink Mapping Diagram (Continued) • Maximum flowrate of off-gas condensate that can be recycled to the scrubber along with distillation bottoms Direct recycle reduces the fresh water feed to the scrubber by 5.1 kg/s

  27. Example No. 4 12:21 • Direct Recycle Only • Reduces fresh water consumption by 5.1 kg/s Economics The primary cost of direct recycling is pumping and piping. TAC = $48,000/yr

  28. Example No. 4 13:21 • Include Interception • Direct recycle reduced the fresh water usage by 5.1 kg/s. Target for fresh water reduction was 7.2 kg/s, i.e. still 2.1 kg/s to go. • If all fresh water is to be eliminated from scrubber, what should ammonia content of the off-gas condensate be?

  29. Example No. 4 14:21 • Include Interception (Continued) • Interception and direct recycle can eliminate fresh water usage in the scrubber Interception Task Change ammonia content of off-gas condensate ys = 14 ppm yt = 12 ppm

  30. Example No. 4 15:21 • Include Interception (Continued) • Pinch diagram for ammonia interception task MSA Selection Choose MSA with lowest removal cost, i.e. adsorbing resin (S3) Thermodynamic feasibility All MSA’s are feasible

  31. Example No. 4 16:21 • Include Interception (Continued) • Annual operating cost for removing ammonia using the resin • Annualized fixed cost is estimated at $90,000/yr. Thus the total annualized cost becomes:

  32. Example No. 4 17:21 • Include Interception (Continued) • Interception and direct recycle has eliminated the fresh water usage in the scrubber and thus reduced the overall fresh water consumption and consequently the influent to the biotreatment facility by 6.0 kg/s. • To achieve the minimum discharge target we still have 1.2 kg/s to go, which are related to the steam-jet ejector.

  33. Example No. 4 18:21 • Sink/Generator Manipulation • Replace steam-jet ejector with vacuum pump • Operating cost are comparable to steam-jet ejector • Capital investment of $75,000 is needed • 5 year linear depreciation with negligible salvage value, the annualized fixed cost of the pump is $15,000/year • Operate column under atmospheric pressure • Eliminates the need for the vacuum pump • Simulation study needed to examine effect of pressure change • Relax requirements to BFW purity • Recycle and interception techniques can significantly reduce the fresh water consumption.

  34. Example No. 4 19:21 • Optimal MEN Configuration

  35. Example No.4 20:21 • Impact Diagrams (Pareto Charts) • Reduction in wastewater • Associated TAC

  36. Example No. 4 21:21 • Merits of Identified Solution • AN production increased from 3.9 kg/s to 4.6 kg/s corresponding to an 18% increase • Fresh water usage and influent to biotreatment reduced by 7.2 kg/s corresponding to a 40% debottlenecking • Plant production can be expanded 2.5 times the current capacity before the biotreatment is bottlenecked again • FAR SUPERIOR TO THE INSTALLATION OF AN ADDITIONAL BIOTREATMENT FACILITY!!!

  37. Summary 1:2 • Observations • Target for debottlenecking the biotreatment facility was determined ahead of design • Systematic tools were used to generate optimal solutions that realize the target • Analysis study is needed to refine the results “big picture first, details later” • Unique and fundamentally different approach than using the designer’s subjective decisions to alter the process and check the consequences using detailed analysis

  38. Summary 2:2 • Observations (Continued) • It is also different from using simple end-of-pipe treatment solutions. Instead, the various species are optimally allocated throughout the process • Objectives such as yield enhancement, pollution prevention and cost savings can be simultaneously addressed

  39. Other Business • Next Lecture – February 14 • Algebraic mass integration techniques • SSLW pp. 297-308

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