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MODULE III

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  1. MODULE III Introduction to Process Integration

  2. Outline 1. Introduction 2. Foundation Elements 3. Case Study 4. Open Ended Problem 5. Acknowledgments 6. References

  3. TIER I

  4. 1. Introduction

  5. 1. Introduction “Do your best; then treat the rest” Source : Pollution Prevention through Process Integration, M. M. El-Halwagi

  6. 1. Introduction Pollution is an ongoing concern that has been addressed in many different ways, from no pollution control, end-of the-pipe treatment (1970’s), Implementation of Reuse/Recycle (1980’s) up to Process Integration. The focus of this module is to expose PI tools for pollution reduction/elimination

  7. 1. Introduction What is Process Integration? “It is a holistic approach to process design, retrofitting and operation which emphasizes the unity of the process” Source : Pollution Prevention through Process Integration, M. M. El-Halwagi

  8. 1. Introduction The use of PI methods started as early as 1970’s with Pinch Technology (Heat Integration) in order to optimize heat exchanger networks (HEN). The moving force for mass integration was initially pollution control; El-Halwagi and Manousiouthakis (1989) proposed the use of mass exchange networks (MEN) in analogy to the previously studied HEN. PI tools can be used in a variety of industries and with approaches as wide as those involving product distribution, life cycle assessment etc (research in these an other areas is currently on their way)

  9. 2. Foundation Elements

  10. 2. Foundation Elements 2.1. Holistic approach of process integration 2.2. Relationship of process integration to process analysis 2.3. Overview of energy, mass and property integration

  11. 2. Foundation Elements 2.1 Holistic Approach of Process Integration Holistic:Emphasizing the importance of the whole and the interdependence of its parts. Concerned with wholes rather than analysis or separation into parts Heuristic:Of or constituting an educational method in which learning takes place through discoveries that result from investigations made by the student Source : http://dictionary.reference.com

  12. 2. Foundation Elements 2.1 Holistic Approach of Process Integration Process Integration can address a wide set of design issues such as: Efficient use of resources and raw materials Process debottlenecking Efficient use of energy Cost reduction Other process operation issues Pollution reduction

  13. 2. Foundation Elements 2.1 Holistic Approach of Process Integration • Traditional process design has been addressed by heuristic methods, based on experience or corporate preferences, in which unit operations equipment have been design individually. • However little attention has been placed on the relationships with other parts of the process • Process Integration as a holistic approach, looks at the Big Picture and the relationships among the different operations and equipment alternatives

  14. 2. Foundation Elements 2.1 Holistic Approach of Process Integration In order to illustrate how Process Integration (PI) can aid in the design process an illustrative example is given we have 3 options for a chemical reactor in order to produce a chemical product, the options to choose from are: Source : www.aiche.org/cep/ July 2001

  15. 2. Foundation Elements 2.1 Holistic Approach of Process Integration Using a heuristic approach the “best” option will be a mechanically agitated vessel that produces a yield of 73.9% with a volume of 12m3; however is there any other way to improve the process?

  16. 2. Foundation Elements 2.1 Holistic Approach of Process Integration Two designs based on the same solution Source : www.aiche.org/cep/ July 2001

  17. 2. Foundation Elements 2.1 Holistic Approach of Process Integration Using PI tools the following solution was found, 96.9% yield and 9.93m3 of volume. Two designs based on this solution are shown next; the benefits of using PI tools are evident. However a thorough analysis of the answer to the problem must be carried out in order to find a feasible design based on the findings obtained using a PI approach Source : www.aiche.org/cep/ July 2001

  18. 2. Foundation Elements 2.2. Relationship of Process Integration to Process Analysis • In order to find solutions that include the relationship effects among the different options for a given design task, the engineer must use PI in order to find optimum answer to the problems at hand, therefore PI tools should be included in the process design structure. Seider, Seader and Lewin illustrate it as shown in the next slides, for a complete description of the design steps, referred to the above mentioned authors • Process design is a dynamic process, always making sure that the solutions will agree with the constraints set by the stakeholders (management, governmental agencies, environmentalist groups, general public etc) and the process itself

  19. 2. Foundation Elements 2.2. Relationship of Process Integration to Process Analysis Process Analysis “Analysis of the process elements for individual study of performance, by using mathematical models and computer simulators” Source : Pollution Prevention through Process Integration, M. M. El-Halwagi

  20. 2. Foundation Elements 2.2. Relationship of Process Integration to Process Analysis Asses Primitive Problem (Define the objective of the design task based on the identified opportunity) Survey Literature (Identify all sources of useful information for the process design, e.g. Handbooks etc) Current Situation/Opportunity (e.g. a new technology is developed etc) Equipment Selection (Assess different options for the given process using process simulators, spreadsheets, in house software etc) Preliminary Process Synthesis, reactions, Separation, T-P Change Operations, Task Integration Preliminary Data Base Creation (Thermodynamic data, kinetics, toxicity etc) Part I Source : Product and Process Design Principles : Synthesis, Analysis, and Evaluation W D. SeiderJ. D. Seader, D.R. Lewin

  21. Is the Gross Profit Favorable? 2. Foundation Elements 2.2. Relationship of Process Integration to Process Analysis No Equipment Selection (Assess different options for the given process using process simulators, spreadsheets, in house software etc) Reject Yes Part I a Part II Part IV Source : Product and Process Design Principles : Synthesis, Analysis, and Evaluation W D. SeiderJ. D. Seader, D.R. Lewin

  22. 2. Foundation Elements Create Process Flow Sheet Separation Train Synthesis Qualitative Synthesis ProcessIntegration Second Law Analysis Create Detailed Data Base Pilot Plant Testing Modify Flow Sheet Prepare Simulation Model Flow Sheet Controllability Analysis Heat and Power Integration Part I a Dynamic Simulation Part II No Yes Part VI Is the Process still Promising? Go to I or I a Part III Source : Product and Process Design Principles : Synthesis, Analysis, and Evaluation W D. SeiderJ. D. Seader, D.R. Lewin

  23. 2. Foundation Elements 2.2. Relationship of Process Integration to Process Analysis Part I or I a Detail Design, Equipment Sizing, Capital Cost Estimation, Profitability Analysis, Optimization Part IV Yes Is the Process still Promising? Startup Assessment (Additional Equipment, Dynamic Simulation) No Part III Reject Reliability and Safety Analysis (HAZOP, Pilot Plant Testing etc) No Is the Process still Feasible? Yes Operation Written Report, Presentation Final Design (P&ID, Bids etc) Startup Construction Part IV Source : Product and Process Design Principles : Synthesis, Analysis, and Evaluation W D. SeiderJ. D. Seader, D.R. Lewin

  24. 2. Foundation Elements 2.2. Relationship of Process Integration to Process Analysis Designing a new plant, retrofitting a existing one, has several operations and for each operation different equipment options and configurations to choose from. The main problem is that the number of alternatives can be unmanageable. If only heuristics are use for the design, the engineer will risk to miss the true optimal solution to the design problem. Moreover, a design solution for a given problem cannot be use for a different one, since the initial findings are tailored for a specific problem. Using a PI approach, one can avoid this issue, due to the fact that its methodology can be applied to any problem. The PI methodology is composed of three key components

  25. 2. Foundation Elements 2.2. Relationship of Process Integration to Process Analysis It defines what process units and how they should be interconnected Process Synthesis Analysis of the process elements for individual study of performance Process Integration Process Analysis Minimizing or maximizing a desired function, to find the best option Process Optimization

  26. 2. Foundation Elements 2.2. Relationship of Process Integration to Process Analysis $ Impact As it has seen, process analysis is a step within the PI methodology. It is important to emphasize that PI will look at the generalities rather than into the details, and then the designer can analyze the performance of the solutions in order to optimize his/her findings. The following chart illustrate the impact of the process design steps over the budget Preliminary equipment selection Spent Committed Equipment required during design Process Conceptual Detailed Plant Detail Construction Startup & Develop Design Design Layout Mech. Commission.

  27. 2. Foundation Elements 2.3. Overview of Mass, Energy and Property Integration Mass Integration “Systematic methodology that provides a fundamental understanding of the global flow of mass within the process and employs this holistic understanding in identifying performance targets and optimizing the generation and routing of species throughout the process” Source : Pollution Prevention through Process Integration, M. M. El-Halwagi

  28. Mass Exchanger 2. Foundation Elements 2.3. Overview of Mass, Energy and Property Integration 2.3.1 Mass Exchangers Lean Stream (MSA) Flow rate: Lj Inlet Composition xjin Outlet Composition yiout • Mass Exchangers: A mass exchanger is any direct-contact mass transfer unit that employs a MSA (Mass Separation Agent), to remove selectively certain component (e.g. pollutant) from a rich phase (e.g. waste stream). The MSA should be partially or totally immiscible in the rich phase Rich (Waste) Stream, Flow rate: Gi Inlet Composition yiin Outlet Composition xjout Source : Pollution Prevention through Process Integration, M. M. El-Halwagi

  29. Solute Transferred to lean phase 2. Foundation Elements 2.3. Overview of Mass, Energy and Property Integration 2.3.1 Mass Exchangers Lean Phase When the two phases are in intimate contact the solutes are distributed between the two phases which leads to a depletion of solute in the rich phase and enrichment of the lean phase until equilibrium is reached. The difference in chemical potential for the solute is the moving force for mass transfer (Temperature difference for heat transfer, Pressure difference for fluid movement etc) Rich Phase

  30. 2. Foundation Elements 2.3. Overview of Mass, Energy and Property Integration 2.3.1. Mass Exchangers Mass Exchange involve the following operations: Only counter current operations will be consider because of their higher efficiency Stripping Adsorption Leaching Absorption Extraction IonExchange

  31. 2. Foundation Elements 2.3. Overview of Mass, Energy and Property Integration 2.3.1. Mass Exchangers Adsorption: Separation of a solute from a liquid or gaseous stream by contacting the carrying phase with a small porous solid particles (adsorbent), usually arranged in a packed bed. The adsorbent can be regenerated by desorption using inert gas, steam etc Source : Université d’Ottawa / University of Ottawa - Jules Thibault

  32. 2. Foundation Elements 2.3. Overview of Mass, Energy and Property Integration 2.3.1. Mass Exchangers In order to select an adsorption column the designer must select a suitable adsorbent for the given solute by looking at the appropriate isotherm data as shown in the plot for a given set of process operation Source : Université d’Ottawa / University of Ottawa - Jules Thibault

  33. 2. Foundation Elements 2.3. Overview of Mass, Energy and Property Integration 2.3.1. Mass Exchangers Absorption: A liquid solvent is place in contact with a gas containing a solute to be remove by taking advantage of the preferential solubility of the liquid. Reverse absorption is also know as stripping (separation of a solute using a gas stream from a liquid phase) Source : Université d’Ottawa / University of Ottawa - Jules Thibault

  34. 2. Foundation Elements 2.3. Overview of Mass, Energy and Property Integration 2.3.1. Mass Exchangers Liquid Extraction: It employs a liquid solvent to remove a solute from another liquid by using the preferential solubility of the solvent to the solute in the MSA Source : Université d’Ottawa / University of Ottawa - Jules Thibault

  35. Solid Solvent 2. Foundation Elements 2.3. Overview of Mass, Energy and Property Integration 2.3.1. Mass Exchangers Leaching: Selective separation of some constituents within a solid by contact with a liquid solvent Mixing Slurry Overflow Solution Source : University of Ottawa - Jules Thibault

  36. Water softeners Cause of scale forming impurities 2. Foundation Elements 2.3. Overview of Mass, Energy and Property Integration 2.3.1. Mass Exchangers Ion Exchange: Cation/anion resins are used to replace undesirable anions from a liquid phase by non hazardous ions Source : Université d’Ottawa / University of Ottawa - Jules Thibault

  37. 2. Foundation Elements 2.3. Overview of Mass, Energy and Property Integration 2.3.1. Mass Exchangers The mass exchanger is used to provide appropriate contact of the lean and rich phase; there are two principal categories of mass exchange units: • Multistage (e.g. tray columns, mixer settlers etc), they provide intimate contact follow by phase separation • Differential (e.g. packed columns, spray towers and mechanically agitated units), continuous contact between phases without intermediate separation and re-contacting

  38. 2. Foundation Elements Multiple Mixers / Settlers MSA Out Light Phase Out Tray Column Heavy Phase In Shell MSA In Waste In Perforated Tray Light Phase In Multistage Contactors Waste Out Heavy Phase Out

  39. 2. Foundation Elements Spray Column Light Phase Out Light Phase Out Mixer Heavy Phase In Heavy Phase In Differential / Continuous Contactors Heavy Phase Out Light Phase In Light Phase In Heavy Phase Out Mechanically Agitated Mixer

  40. Solute in the rich phase (1) Equilibrium distribution function Maximum attainable composition in the lean phase 2. Foundation Elements 2.3. Overview of Mass, Energy and Property Integration 2.3.1. Mass Exchangers Equilibrium: When a rich phase in a solute is put in contact with a lean phase transfer of the solute to the lean phase occurs, also part of the solute In the lean phase also back transfer to the rich phase. At first the rate of solute being transfer from the rich phase is bigger than the rate of solute back transfer from the lean phase. However when the concentration of solute in the lean phase increases, the back transfer rate also increases. Eventually the mass transfer rate and the back transfer rates become equal and an equilibrium is reached Source : Pollution Prevention through Process Integration, M. M. El-Halwagi

  41. (2) Partial pressure at T (3) Mol fraction of solute in gas 2. Foundation Elements 2.3. Overview of Mass, Energy and Property Integration 2.3.1. Mass Exchangers In environmental applications the engineer will find very often, diluted systems which can be linearized over the operating range to yield: Special cases, Raoult’s Law for absorption Mol fraction of solute in liquid Source : Pollution Prevention through Process Integration, M. M. El-Halwagi

  42. (4) (5) 2. Foundation Elements 2.3. Overview of Mass, Energy and Property Integration 2.3.1. Mass Exchangers Henry’s Law for stripping Mol Fraction of solute in stripping gas Mole fraction of solute in gas Liquid phase solubility of pollutant at temperature T Source : Pollution Prevention through Process Integration, M. M. El-Halwagi

  43. (6) 2. Foundation Elements 2.3. Overview of Mass, Energy and Property Integration 2.3.1. Mass Exchangers For solvent extraction Composition of the solvent Composition of pollutant in liquid waste Distribution Coefficient Source : Pollution Prevention through Process Integration, M. M. El-Halwagi

  44. 1 2 N-1 N (7) 2. Foundation Elements The following relationships are used to size multistage mass transfer exchangers: yi,N+1= yiin Gi yi,1= yiout yi,2 yi,N-1 yi,N yi,3 XJ,0= Xjin Lj XJ,1 XJ,2 XJ,N-2 XJ,N-1 XJ,N= XJout Overall Mass Balance: Source : Pollution Prevention through Process Integration, M. M. El-Halwagi

  45. (9) (8) 2. Foundation Elements 2.3. Overview of Mass, Energy and Property Integration 2.3.1. Mass Exchangers Rearranging (7): Eq. (8) represents the operating line in a McCabe-Thiele diagram: LJ / Gi yiin 1 Theoretical stages Operating Line 2 yiout Equilibrium Line xJin xJout

  46. (10) (12) (11) 2. Foundation Elements 2.3. Overview of Mass, Energy and Property Integration 2.3.1. Mass Exchangers • The number of stages for a multistage unit can also be calculated with the following equations, with NTP being the number of theoretical plates Source : Pollution Prevention through Process Integration, M. M. El-Halwagi

  47. (13) When the contact time for each stage is not enough to reach equilibrium, the number of actual plates (NAP) can be calculated using contacting efficiency (14) Stage efficiency can be define on the rich or lean phase, for the rich phase we have: 2. Foundation Elements Source : Pollution Prevention through Process Integration, M. M. El-Halwagi

  48. (15) For differential (continuous) mass exchangers, the height is calculated using: (16) (17) 2. Foundation Elements Based on rich phase Based on lean phase Source : Pollution Prevention through Process Integration, M. M. El-Halwagi

  49. (18) (19) 2. Foundation Elements For mass exchangers with linear equilibrium: Source : Pollution Prevention through Process Integration, M. M. El-Halwagi