MODULE III Introduction to Process Integration

Transcription

1 1

2 MODULE III Introduction to Process Integration 2

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

4 TIER I 4

5 1. Introduction 5

6 1. Introduction Do your best; then treat the rest Source : Pollution Prevention through Process Integration, M. M. El-Halwagi 6

7 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

8 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

9 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

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11 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

12 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 : 12

13 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 Cost reduction Efficient use of energy Other process operation issues Pollution reduction 13

14 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

15 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 : July

16 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

17 2.1 Holistic Approach of Process Integration Two designs based on the same solution Source : July

18 2.1 Holistic Approach of Process Integration Using PI tools the following solution was found, 96.9% yield and 9.93m 3 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 : July

19 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

20 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

21 2.2. Relationship of Process Integration to Process Analysis Current Situation/Opportunity (e.g. a new technology is developed etc) 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) 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 21 Source : Product and Process Design Principles : Synthesis, Analysis, and Evaluation W D. Seider J. D. Seader, D.R. Lewin

22 2.2. Relationship of Process Integration to Process Analysis Equipment Selection (Assess different options for the given process using process simulators, spreadsheets, in house software etc) Is the Gross Profit Favorable? Yes No Reject Part I a Part II Part IV 22 Source : Product and Process Design Principles : Synthesis, Analysis, and Evaluation W D. Seider J. D. Seader, D.R. Lewin

23 Create Process Flow Sheet Process Integration Separation Train Synthesis Qualitative Synthesis Create Detailed Data Base No Pilot Plant Testing Modify Flow Sheet Prepare Simulation Model Part I a Yes Second Law Analysis Heat and Power Integration Part II Flow Sheet Controllability Analysis Dynamic Simulation Part VI Go to Is the Process still Promising? Part III 23 I or I a Source : Product and Process Design Principles : Synthesis, Analysis, and Evaluation W D. Seider J. D. Seader, D.R. Lewin

24 2.2. Relationship of Process Integration to Process Analysis Is the Process still Promising? No Part I or I a Reject Yes Written Report, Presentation No Detail Design, Equipment Sizing, Capital Cost Estimation, Profitability Analysis, Optimization Yes Part III Is the Process still Feasible? Part IV Startup Assessment (Additional Equipment, Dynamic Simulation) Reliability and Safety Analysis (HAZOP, Pilot Plant Testing etc) Operation Part IV Final Design (P&ID, Bids etc) Construction Startup 24 Source : Product and Process Design Principles : Synthesis, Analysis, and Evaluation W D. Seider J. D. Seader, D.R. Lewin

25 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

26 2.2. Relationship of Process Integration to Process Analysis Process Integration Process Synthesis Process Analysis It defines what process units and how they should be interconnected Analysis of the process elements for individual study of performance Process Optimization Minimizing or maximizing a desired function, to find the best option 26

27 2.2. Relationship of Process Integration to Process Analysis As it has seen, process analysis is a step within the PI methodology. Impact 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. $ Preliminary equipment selection Committed Spent The following chart illustrate the impact of the process design steps over the budget Equipment required during design Process Conceptual Detailed Plant Detail Construction Startup & Develop Design Design Layout Mech. Commission. 27

28 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

29 2.3.1 Mass Exchangers Mass Exchangers: A mass exchanger is any directcontact 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 Lean Stream (MSA) Flow rate: L j Inlet Composition x j in Outlet Composition x j out Source : Pollution Prevention through Process Integration, M. M. El-Halwagi Mass Exchanger Outlet Composition y i out Rich (Waste) Stream, Flow rate: G i Inlet Composition y i in 29

30 2.3.1 Mass Exchangers Lean 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) Phase Rich Phase Solute Transferred to lean phase 30

31 Mass Exchangers Mass Exchange involve the following operations: Only counter current operations will be consider because of their higher efficiency Adsorption Stripping Absorption Leaching Extraction Ion Exchange 31

32 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

33 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

34 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

35 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

36 Mass Exchangers Leaching: Selective separation of some constituents within a solid by contact with a liquid solvent Mixing Solvent Solid Slurry Overflow Solution Source : University of Ottawa - Jules Thibault 36

37 Mass Exchangers Ion Exchange: Cation/anion resins are used to replace undesirable anions from a liquid phase by non hazardous ions 2+ Ca + Na R CaR + 2Na 2 + Cause of scale forming impurities Source : Université d Ottawa / University of Ottawa - Jules Thibault Water softeners 37

38 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

39 Tray Column Light Phase Out MSA Out Multiple Mixers / Settlers Heavy Phase In Shell Waste In MSA In Perforated Tray Light Phase In Heavy Phase Out Multistage Contactors Waste Out 39

40 Spray Column Light Phase Out Light Phase Out Heavy Phase In Differential / Continuous Contactors Heavy Phase In Mixer Light Phase In Heavy Phase Out Light Phase In Heavy Phase Out Mechanically Agitated Mixer 40

41 Mass Exchangers Solute in the rich phase 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 y = f ( x ) (1) i Equilibrium distribution function Maximum attainable composition in the lean phase j j * 41

42 Mass Exchangers In environmental applications the engineer will find very often, diluted systems which can be linearized over the operating range to yield: i j * j y = m x + b j (2) Special cases, Raoult s Law for absorption Partial pressure at T Mol fraction of solute in gas o P solute ( T ) * y i = x (3) j P Total Mol fraction of solute in liquid 42 Source : Pollution Prevention through Process Integration, M. M. El-Halwagi

43 Mass Exchangers Henry s Law for stripping i j * j y = H x (4) Mol Fraction of solute in stripping gas Mole fraction of solute in gas H So lub ility Total y i j = (5) o Solute P P ( T ) Liquid phase solubility of pollutant at temperature T Source : Pollution Prevention through Process Integration, M. M. El-Halwagi 43

44 Mass Exchangers For solvent extraction i j j * y = K x (6) Composition of the solvent Composition of pollutant in liquid waste Distribution Coefficient Source : Pollution Prevention through Process Integration, M. M. El-Halwagi 44

45 The following relationships are used to size multistage mass transfer exchangers: y i,1 = y i out y i,n+1 = y in i y i,2 y i,n y i,3 y i,n-1 G i X J,0 = X j in 1 2 N-1 N X J,1 L j X J,2 X J,N-2 X J,N-1 X J,N = X J out Overall Mass Balance: i in i j in j i out i j out j G y + L x = G y + L x (7) Source : Pollution Prevention through Process Integration, M. M. El-Halwagi 45

46 G Rearranging (7): i ( y in i Mass Exchangers out i y ) = L ( x x ) (8) j out j in j L j G i ( y = ( x in i out j y x out i in j Eq. (8) represents the operating line in a McCabe-Thiele diagram: ) ) (9) y i in L J / G i Operating Line y i out x J in 2 1 x J out Equilibrium Line Theoretical stages 46

47 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 in out* L j x i xj ln 1 out out* mjgi xi xj NTP= m jgi ln Lj in m jgi y i mjxj ln 1 out Lj yi mjx NTP= L j ln mjgi Li + mjgi Source : Pollution Prevention through Process Integration, M. M. El-Halwagi (11) x in in j bj b j in out* yi bj (12) j = mj 47 (10)

48 y in i out i y m x j m x j in j in j b j b j Lj = mjgi NTP 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 (13) NAP = NTP / η (14) Stage efficiency can be define on the rich or lean phase, for the rich phase we have: Source : Pollution Prevention through Process Integration, M. M. El-Halwagi o 48

49 H ln 1 NTP = in m jgi y i m jx j out Lj yi m jx j m jg ln 1+ η y Lj in i b j m jg + b L j j 1 For differential (continuous) mass exchangers, the height is calculated using: = HTU NTU (16) y y in i Based on rich phase (15) H = HTU NTU x x (17) Based on lean phase Source : Pollution Prevention through Process Integration, M. M. El-Halwagi 49

50 For mass exchangers with linear equilibrium: in out yi yi NTUy = ( y y * (18) ) i i logmean ( y i y * i ) = ( y in i m x j out j ( y ln ( y b in i out i j ) ( y m x j m x j out i out j in j m x b b j j j ) ) in j b j ) (19) Source : Pollution Prevention through Process Integration, M. M. El-Halwagi 50

51 Texas A&M University 51 For mass exchangers with linear equilibrium (cont): mean j j out j in j x x x x NTUx log * ) ( = (20) = j j out i in j j j in i out j j j out i in j j j in i out j mean j j m b y x m b y x m b y x m b y x x x ln ) ( log * (21)

52 in in m jgi y i mjxj bj m jgi ln 1 + out in Lj yi mjxj bj Lj = (22) NTP m jgi 1 Lj In order to calculate the diameter of the column (m) we have: D min = 4( VFRA) π ( MASVA) Source : Pollution Prevention through Process Integration, M. M. El-Halwagi (23) 52

53 In order to calculate the diameter of the column we need volumetric flow rate of air (VFRA), maximum allowable superficial velocity of air (MASVA): MASVA m ρ ρ water air ( / s) = (24) ρair To complete the design of a mass exchange unit, the designer has to look into the costs that the unit will have. The total annual cost (TAC) is given by: TAC = AOC+ AFC (25) Source : Pollution Prevention through Process Integration, M. M. El-Halwagi 53

54 Where AOC is the annual operating cost and AFC is the annual fixed cost of the unit. Recall equation (8) Operating Line y i in Lean End of Exchanger Driving Force y i out x J in,max ε J x J in* x J out Equilibrium Line The number of mass exchange units will be higher for a small ε, a vanishing driving force. Therefore, it is necessary to assign a minimum driving force between the two lines 54

55 We have: Mass Exchangers out.min j j in j y = m ( x + ε ) + b (26) j j By using a minimum allowable composition difference, ε J the designer can identify the minimum practically feasible outlet composition of the waste stream Source : Pollution Prevention through Process Integration, M. M. El-Halwagi 55

56 The number of mass exchange units will be higher for a small ε, a vanishing driving force. Therefore, it is necessary to assign a minimum driving force between the two lines Operating Line y i in ε J Rich End of Exchanger y i out Equilibrium Line Remainder : An outlet composition on the equilibrium line = infinite number of stages x J in x J out,max x J out* Source : Pollution Prevention through Process Integration, M. M. El-Halwagi Driving Force 56

57 Mass Exchangers We have: x out j.max = y in j m j b j ε j (27) Where, ε J is the minimum allowable composition difference and x out,max J is the maximum practically feasible outlet composition of the MSA which satisfies the ε J driving force As can be seen from (16 to 19) and (27), there is a trade off between the driving force and the cost/size of the equipment to be use for the separation. To illustrate the use of the previous equations a example is given Source : Pollution Prevention through Process Integration, M. M. El-Halwagi 57

58 Example 1 Air stripping is used to remove 95% of the rich trichloroethylene (TCE, molecular weight = 131.4) dissolved in a 200kg/s (3180gpm) waste water stream. The inlet composition of TCE in the waste water is 100ppm. Air (free of TCE) is compressed to kpa (2at) and diffused through a packed stripper. The TCE-laden air exiting the stripper is fed to the plant boiler which burns almost all the TCE. Physical Data: The stripping operation takes place isothermally at 293K and follows Henry's law. The equilibrium relation for stripping TCE from water is theoretically predicted using: Source : Pollution Prevention through Process Integration, M. M. El-Halwagi 58

59 y = (28) j x j Where y i is the mass fraction of TCE in waste water and x J is the mass fraction of TCE in air. The air-to-water ratio is recommended by the packing manufacturer to be: 24 m 3 Air / m 3 water Stripper Sizing Criteria: The maximum allowable superficial velocity of waste water in the column is taken as 0.02m/s (approximately 30 gpm/ft 2 ).The overall height of transfer unit based on the liquid phase is given by: HTU y = Superficial Velocity of waste water/k y a Source : Pollution Prevention through Process Integration, M. M. El-Halwagi 59

60 Where k y is the water-phase overall mass transfer coefficient and a is the surface area per unit volume of packing. The value of K y a is provided by the manufacturer to be 0.002s -1 Cost Information: The operation cost for air compression is basically the electricity utility needed for the isentropic compression. Electric energy needed to compress air may be calculated using: Compression Energy (CE) CE( kj γ / kg) = γ 1 M air RT η (29) in isentropic Source : Pollution Prevention through Process Integration, M. M. El-Halwagi P P out in γ 1 γ 1 60

61 The isentropic efficiency of the compressor is 60% and the electric energy cost is $0.06/kWhr. The system is operated for 8000hr/y. The fixed cost, $, of the stripper (including installation and auxiliaries, but excluding packing) is given by: Fixed cost of column = 4700HD 0.9 Where H is the height of the column (m) and D is the diameter (m). The cost of packing is $700/m 3. The fix cost of the blower, $, is 12000L J 0.6, where L J is the flow rate of air (kg/s). Assume negligible salvage value and a five year linear depreciation. (a) estimate the column size, fixed cost and annual operating cost. (b) Due to the potential error in the theoretically predicted value of Henry s coefficient, it is necessary to asses the sensitivity of your results to variation Source : Pollution Prevention through Process Integration, M. M. El-Halwagi 61

62 of the value of Henry s coefficient. Plot the column height, annualized fixed cost and annual operating cost versus α the relative deviation from the nominal value, for 0.5 α 2.0. The parameter α is define by: α = Value of Henry s Coeffcient/ (c) Your company is planning to undertake extensive experimentation to obtain accurate values of Henry s coefficient that can be used in designing and evaluating the cost of this stripper. Based on your results, what would you recommend regarding the undertaking of these experiments? Source : Pollution Prevention through Process Integration, M. M. El-Halwagi 62

63 x J out =? Exhaust Gas Waste Water G i = 200kg/s y i in = 10-4 Stripper y i out = 5*10-6 Air, L J =? x J in = 0 Boiler Stripping of TCE from Wastewater Source : Pollution Prevention through Process Integration, M. M. El-Halwagi Blower 63

64 Solution: (a) 1. We will first have to calculate the flow and concentrations of the different streams as follows: ρ Mass Exchangers PM air RT 2atm kg * 29 kgmol m atm 293 K kgmolk Air = = = 3 3 kg m Air kgwater 1m L i = *25 *200 * = m 1m Water s 1000kgWater Source : Pollution Prevention through Process Integration, M. M. El-Halwagi kg m 3 kgair s 64

65 Solution: Continuation Using the overall mass balance equation we have: = 1 * 10 x 4 out J 5 * x J out = kgmol phenol / kgmol air x J out = 1575 ppm 2. We now will calculate the height and diameter of the column, superficial velocity of waste water (SVWW) HTU = SVWW / y Source : Pollution Prevention through Process Integration, M. M. El-Halwagi K y a 65

66 Solution: Continuation ( y i y i * ) Mass Exchangers logmean = m 0.02 HTU s y = = 1m s NTU (1*10 4 y = ( y i y * i ) log mean * ) (5*10 4 (1* * ) ln 6 (5* *0) Source : Pollution Prevention through Process Integration, M. M. El-Halwagi *0) 66

67 Solution: Continuation ( * 5 y i y i ) log mean = *10 = ppm NTU y = = H = 1 * = m 4(200 /1000 ) D min = = m π (0.02 ) Source : Pollution Prevention through Process Integration, M. M. El-Halwagi 67

68 Mass Exchangers Solution: Continuation 3. With the equipment dimension we can proceed to calculate the operating and fixed costs CE ( kj / kg ) = kj kg kWhr * 3600kJ * * 0.6 $0.06 * 1kWhr Source : Pollution Prevention through Process Integration, M. M. El-Halwagi 2 1 = = kJ $1.788*10 3 / / kg kg 68

69 Mass Exchangers AOC Solution: Continuation Annual Operating Cost (AOC): kj kg s 8000hr = *12.06 *3600 * = $621,234.8 / kg s 1hr year Equipment Cost (EC): Stripper = 4700(3.228*3.568 π Packing = *(3.568m) 4 Blower = 12000(12.06) $ *3.228m*700 m = $53,455.2 Source : Pollution Prevention through Process Integration, M. M. El-Halwagi ) = $47, = $22,592.8 year 69

70 Mass Exchangers Solution: Continuation Fixed Cost (FC): FC = 47, , ,455.2 = $123,714.5 Solution: (b) (c) Henry s Law coefficient will affect the FC through the change in the size of the system. By changing α one can find different values of Henry s Law coefficient and use them to calculate the size of the column and then the FC; we will use Excel for this procedure. Since we have a linear 5 year depreciation the FC will be divided by 5 Source : Pollution Prevention through Process Integration, M. M. El-Halwagi 70

71 Mass Exchangers Solution: Continuation As the plot and Table 1 show, there is a small change in the TAC and AFC with changing Alfa, meaning that we don t have appreciable savings by changing the height of the column with more accurate values of Henry s Law coefficient. Therefore the project is not required; we just saved our company a lot of money!!!! Alfa Henry H AFC TAC

72 Mass Exchangers AFC TAC Very slight change 72

73 Mass Exchange Networks Mass Exchange Networks Source : Pollution Prevention through Process Integration, M. M. El-Halwagi 73

74 Mass Exchange Networks MSA can be: Mass Separation Agents (MSA) They are Lean Streams (Ns), L J, j = 1, 2 Ns Process MSA, N SP Low cost or almost free In plant Use to remove pollutants from rich streams, N R External MSA, N SE Must be bought externally 74 Source : Pollution Prevention through Process Integration, M. M. El-Halwagi

75 Mass Exchange Networks N s = N SP + N SE (28) Flow rates, stream concentration and target concentration of rich streams are known, G i, y SS, y i t Inlet compositions of lean streams are also known, x JS flow rate of lean streams, L J, is to be determine to minimize network cost L J L J C J = 1, 2 N SP (29) L J C is the flow rate of the J th MSA available in the plant 75 Source : Pollution Prevention through Process Integration, M. M. El-Halwagi

76 Mass Exchange Networks Waste streams can be Disposed Forwarded to process Sinks (equipment) For recycle/reuse Comply with Environmental Regulations Target composition is the constraint imposed by process Sink 76 Source : Pollution Prevention through Process Integration, M. M. El-Halwagi

77 Mass Exchange Networks Target composition are assigned by designer based on the following constraints: Physical (e.g. maximum Solubility of pollutant In MSA) Technical (e.g. avoid corrosion, Viscosity) Environmental (e.g. EPA, OSHA Regulations) Safety (e.g. stay away of Flammability limits) Economic (e.g. optimize cost Of MSA regeneration) 77 Source : Pollution Prevention through Process Integration, M. M. El-Halwagi

78 Mass Exchange Networks The following questions will arise: What is the optimum configuration? How to match MSAs to the waste streams? Which MSA should be selected? Which ME operation should we use? 78

79 Mass Exchange Networks The previous questions will result in a unmanageable number of combinations A systematic approach is required Targeting Approach Source : Pollution Prevention through Process Integration, M. M. El-Halwagi 79

80 Mass Exchangers Targeting Approach It is based on the identification of performance targets ahead of design and without prior commitment to the final network configuration 80 Source : Pollution Prevention through Process Integration, M. M. El-Halwagi

81 Minimum cost of MSA: By combining thermodynamic aspects of the problem with cost data of the MSA, the designer can identify the minimum cost of the separation, without designing the network GENERALLY INCOMPATIBLE Minimum number of mass exchange units: This objective is aim at minimizing fixed cost of the system, by doing so, one can reduce pipe work, foundations, maintenance and instrumentation Source : Pollution Prevention through Process Integration, M. M. El-Halwagi 81

82 Mass Exchangers U = N R + N i (30) U = Number of units Ni = Number of independent synthesis sub-problems in which original synthesis problem can be subdivided In most cases there will be only one independent synthesis problem. In order to avoid the incompatibility of the two targets, one have to use techniques that will identify the MOC solution and then minimize the number of exchangers that satisfy the MOC (Minimum Operating Cost) 82

83 Mass Exchangers y i in ε J Feasibility area y i out x J in x J out,max x J out* In order for the separation to be feasible one have to work in the feasibility area To relate the different concentrations in one scale, we need to use Equation (27) 83

84 Mass Exchangers In order to minimize the cost of external MSA one must maximize the use of in plant MSA The pinch diagram is a graphical representation that considers the thermodynamic constraints of the system, calculate MR with: Mass Exchanged Pinch Point MR i = i 1, = G 2,..., i ( y N i s R y t i (31) ) y x 1 84 x 2 Source : Pollution Prevention through Process Integration, M. M. El-Halwagi

85 Mass Exchangers How to construct the pinch diagram? 1. Represent each stream with an arrow MR i 2. Plot mass exchanged versus its composition 3. Tail of the arrow is the supply composition and head is target composition 4. The slope is the flow rate of the stream 5. The vertical distance between the tail and the head represent the amount of pollutant transferred ( MR i ) from the rich stream ( y i ) to the lean stream 6. Stack the arrows on top of one another starting with the one with the one having the lower composition R 2 R 1 y 1 t y 2 t y 1 s y 2 s y 85 i

86 Mass Exchangers How to construct the pinch diagram? 7. Obtain the composite diagram by using the diagonal rule MR i MR 2 8. The vertical axis is a relative scale, one can move up and down the curves while maintaining constant the vertical distance 9. Apply the same procedure for the lean streams 10. Plot both composite curves in one graph, slid the lean composite until it touches the rich (waste) composite stream MR 1 Source : Pollution Prevention through Process Integration, M. M. El-Halwagi R 2 R 1 y 1 t y 2 t y 1 s y 2 s y 86 i

87 Mass Exchangers MS i How to construct the pinch diagram? MS 2 x j = y m (32) 1 b 1 ε j MS 1 S 1 S Use the above equation to obtain the horizontal scale and Equation 33 to calculate MS y i x 1 s x 1 t Source : Pollution Prevention through Process Integration, M. M. El-Halwagi x 2 s 87 x t 2

88 Mass Exchangers Mass How to construct the pinch diagram? Exchanged MS j j = L c j = 1,2..., (33) ( x N t j SP x s j ) Excess Capacity of Process MSA s Load to be removed by external MSA s Source : Pollution Prevention through Process Integration, M. M. El-Halwagi Lean Composite Stream Rich Composite Stream x 1 y i 88 x 2

89 Mass Exchangers Mass How to construct the pinch diagram? Exchanged Integrated exchange: mass Maximum amount of pollutant that can be transfer The Pinch point is the minimum feasible concentration, it is also a bottleneck, slid up or down the composite curves until they touch, keeping the vertical distance and the concentrations Pinch Point Source : Pollution Prevention through Process Integration, M. M. El-Halwagi Lean Composite Stream Rich Composite Stream x 1 89 x 2 y i

90 Mass Exchangers In order to reduce the excess capacity of process MSA one can either reduce flow rate, or composition. Care must be given when choosing ε, since it will cause the lean composite curve to move to the right, increasing the load to be removed by external MSAs S Load of pollutant above the pinch to be removed j out j supply j = L ( x x ) (34) j In the case that 2 or more MSAs are overlapped, one have to calculate the composition that will suit the requirements of the plant and compare the costs in order to identify the MSA that will be use in the separation 90 Source : Pollution Prevention through Process Integration, M. M. El-Halwagi

91 Mass Exchangers To calculate cost of recirculation MSA (C j ) and cost of removed pollutant (c jr ) use: C = CM + CR = j $ / kg recirculating MSA (35) Cost of Make up Cost of Regeneration c r j C j = t s ( x j x j = $ / kg of removed ) Source : Pollution Prevention through Process Integration, M. M. El-Halwagi pollutant (36) 91

92 Mass Exchangers There are cases when there are no process MSAs, therefore a different approach is required in order to construct the pinch diagram MR 1. Draw the rich composite as before 2. Draw the external MSA as S j arrows with the tail as the supply composition and the head its target composition 3. Calculate the c j 4. If arrow S 2 lies completely to the left of S 1 and c 2 r < c 1 r then eliminate S 1 S 3 S 2 Rich Composite Stream S 1 92 x 1 x 2 y i Source : Pollution Prevention through Process Integration, M. M. El-Halwagi x 3

93 Mass Exchangers 5. If arrow S 3 lies completely to the left of S 2 but c 3 r is > c 2 r then retain both MSAs 6. In order to minimize the operating cost of the network one should use the cheapest MSA where it is feasible 7. In this case S 2 should be used to remove all the rich load to the left and the remaining load is removed by S 3 8. Calculate flow rates of S 2 and S 3 by diving the rich load remove by the composition difference for the MSAs 9. Construct the pinch diagram as shown MR S 3 S 2 Rich Composite Stream S 1 93 x 1 x 2 y i Source : Pollution Prevention through Process Integration, M. M. El-Halwagi x 3

94 Example 2 A process facility converts scrap tires into fuel via pyrolisis. The discarded tires are fed to a high temperature reactor where heat breaks down the hydrocarbon content of the tires into oils and gaseous fuels. The oils are further processed and separated to yield transportation fuels. The reactor off gasses are cooled to condense light oils. The condensate is decanted into two layers: organic and aqueous. The organic layer is mixed with the liquid products of the reactor The aqueous layer is a waste water stream whose organic content must be reduce prior to discharge. The primary pollutant in the waste water is a heavy hydrocarbon. The data for the waste water stream is given in the next slide. A process lean stream is a flare gas (a gaseous stream fed to the flare) which can be used as a process stripping agent. To prevent back propagation of fire from the flare, a seal pot is used. Source : Pollution Prevention through Process Integration, M. M. El-Halwagi 94

95 Mass Exchangers Stream Description Flowrate G i kg/s Supply Composition (ppmw) y i s Target Composition (ppmw) y i t R 1 Aqueous layer from decanter Table 1 95 Source : Pollution Prevention through Process Integration, M. M. El-Halwagi

96 Example 2, Continuation An aqueous stream is passed though the seal pot to form a buffer zone between the fire and the source of the flare gas. Therefore, the seal pot can be used as a stripping column in which the flare gas strips the organic pollutant off the waste water while the waste water stream constitutes a buffer solution preventing back propagation of fire. Three external MSAs are considered: a solvent extract S 2, an adsorbent S 3 and a stripping agent S 4. The equilibrium data for the jth MSA and the process MSA are given in the next slide, the equilibrium data is given by y i = m j x j Where y i and x j are the mass fractions of the organic pollutant in the waste water and the jth MSA, respectively. Use the pinch diagram to determine the minimum operating cost of the MEN Source : Pollution Prevention through Process Integration, M. M. El-Halwagi 96

97 Example 2, Continuation Stream Upper Bound on flow rate L c j kg/s Supply composition (ppmw) x s J Target Composition (ppmw) x t J m J ε J C J $/kg MSA S S S S Table 2 Source : Pollution Prevention through Process Integration, M. M. El-Halwagi 97

98 Mass Exchangers To atmosphere Example 2, Continuation Condenser Gaseous Fuel Flare Reactor Off Gases Light oil Decanter Waste water R 1 Water Seal Pot To waste water Flare Gas S 1 Shredded Tires Pyrolisis Reactor Separation Finishing Liquid Fuel 98 Source : Pollution Prevention through Process Integration, M. M. El-Halwagi

99 Mass Exchangers To atmosphere Solution Condenser Gaseous Fuel Flare S 2 S 3 S 4 Reactor Off Gases Decanter Waste water R 1 MEN To waste water Light oil Flare Gas, S 1 Shredded Tires Pyrolisis Reactor Separation Finishing Liquid Fuel 99 Source : Pollution Prevention through Process Integration, M. M. El-Halwagi

100 Mass Exchangers Solution, Continuation Calculate and plot the pinch diagram, using Equations 31,32,33 and Tables 1 and 2 R 1 MR 0 90 y Mass Exchanged Pinch Diagram S S R 1 S 1 MR y y. ppmw R 1

101 Solution, Continuation Mass Exchanged 10-6 Excess Capacity of Process MSA Integrated Mass Exchanged Pinch Diagram Pinch Point Mass to be Removed by External MSA y. ppmw New S 1 Target Composition 101

102 Solution, Continuation From the pinch diagram the load to be removed by the process MSA is 64 x 10-6 kg/s, the excess capacity is 45 x 10-6 kg/s; we have to use the whole flare gas flow rate to remove pollutant from the waste water, due to the fire hazard that it represents (we cannot by pass part of it directly to the flare, in order to reduce the excess capacity) from a mass balance or the pinch diagram we find the outlet composition of S 1 to be: 400 ppmw We now have to evaluate the different external MSAs. The load to be removed by external MSA is approximately 31 x 10-6 kg/s, we need to check the thermodynamic feasibility of each external MSA Source : Pollution Prevention through Process Integration, M. M. El-Halwagi 102

103 Solution, Continuation 103 Source : Pollution Prevention through Process Integration, M. M. El-Halwagi

104 Solution, Continuation Mass Exchanged Pinch Diagram y. ppmw S S 2 S

105 Solution, Continuation Calculating the costs of each separation agent, using Equation 36: c 2r = $/kg c 3r = $/kg c 4r = $/kg Analysis: S 2 is not a feasible MSA since its target concentration is higher that the target concentration of the rich stream therefore mass transfer is not possible. S 4 is the selected MSA, flow is 31x10-6 kg/s annual operating cost is 31x10-6 x86.2x3600x24x365 = $84,270.5/yr Source : Pollution Prevention through Process Integration, M. M. El-Halwagi 105

106 Targeting rules Process integration is conformed of mass and energy integration Energy In Mass In Process Mass Out In order to achieve a good mass integration, one has to set targeting goals; from an overall mass balance: Energy Out Mass In + Generation = Mass Out + Source : Pollution Prevention through Process Integration, M. M. El-Halwagi Depletion (37) 106

107 Targeting rules In order to reduce intake of fresh resources and reduce the discharge of waste streams one need to consider recycle, mixing, segregation and/or interception. In order to identify the recycle (direct or after segregation/interception) strategy that will have a net effect on the system the following procedure follows Fresh Load Terminal Load FL k,1 1 4 TL k,1 FL k,2 2 TL k,2 FL k,1 3 5 TL k,3 No Recycle TL k,4 107

108 Targeting rules Identify where recycle of streams will have the biggest net effect Fresh Load FL k,1 1 4 Terminal Load TL k,1 + R k,2 R k,1 FL k,2 2 TL k,2 -R k,2 FL k,1 3 5 No Net effect = Poor Recycle TL k,3 TL k,4 + R k,1 R R R + R k, 2 k,2 k,1 k,1 108 Source : Pollution Prevention through Process Integration, M. M. El-Halwagi

109 Targeting rules Fresh Load Terminal Load FL k,1 R k,2 1 4 TL k,1 R k,1 FL k,2 R k,1 2 TL k,2 R k,2 FL k,1 3 5 TL k,3 TL k,4 R R k, 2 k,1 R R k, 2 k,1 Effective Recycle from Terminal Streams Source : Pollution Prevention through Process Integration, M. M. El-Halwagi 109

110 Targeting rules Fresh Load Terminal Load FL k,1 R k,2 1 4 TL k,1 R k,1 FL k,2 R k,1 2 TL k,2 R k,2 FL k,1 3 5 TL k,3 TL k,4 R R k, 2 k,1 R R k, 2 k,1 Effective Recycle from Terminal and Intermediate Streams Source : Pollution Prevention through Process Integration, M. M. El-Halwagi 110

111 Targeting rules Recycle of streams must comply with sink constraints; such as composition and flow rate which a sink can take. In order to take advantage of direct recycle opportunities within a plant one has to identify them by using a graphical technique know and the source/sink mapping diagram Effective recycle should connect fresh intake and out streams Sink Acceptable Flow Range Acceptable Composition Range Flow Rate Load, kg/s Pollutant Composition Source 111

112 Targeting rules The interception of the two constraints is the area where any source within it can be recycled directly to the sink The maximum amount to be recycle is the minimum between the fresh inlet and outlet load. In order to recycle b and c use the mixing arm rule Direct recycling does not require new equipment Define equipment constraint from, technical data, operation conditions, physical and chemical properties etc Flow Rate Load, kg/s b S a c Sink Source Pollutant Composition Source : Pollution Prevention through Process Integration, M. M. El-Halwagi 112

113 Arm rule: Targeting rules F y s s = = F b F c + y F c c F c + + F F b b (38) y b (39) If a fresh source is mixed with a polluted one, in order to minimize the use of fresh one has to minimize fresh arm Flow Rate Load, kg/s Fs Fb Fc b Resulting Mixture Arm c Arm b yb ys yc c Sources Pollutant 113 Composition

114 Note: Targeting rules 1. The previous method can be simplified for a complex plant since no all equipment will required fresh utilities or discharge waste streams. We will identify those that do and apply the previous method 2. Identifying equipment constraints can reduce fresh and waste streams with little process modifications, by working with minimum requirements 114

115 Synthesis of MEN, Algebraic Approach The pinch diagram is a very useful tool, however it has accuracy limitations common to any graphical method, therefore an algebraic approach that will overcome these limitations is presented The Composition-Interval Diagram (CID) This diagram shows the mass exchanged between the different streams, thermodynamically feasibility and the location of the pinch point The number of scales is equal to Nsp + 1, where Nsp is the number of lean streams. Each process is represented by a vertical arrow with supply and target compositions as the tail and head respectively. The horizontal lines are the composition intervals whose number is define as: N 2( N R + N ) 1 (40) intervals Source : Pollution Prevention through Process Integration, M. M. El-Halwagi SP 115

116 116

117 Synthesis of MEN, Algebraic Approach Within each interval it is possible to transfer mass from the rich stream to the lean stream and it is possible to transfer mass from the interval to any MSA that is in an interval below it Table of Exchangeable Loads (TEL) The TEL is used to determine the load of mass exchanged within each interval; for the waste stream the load is: W i,kr = G i (y k-1 y k ) (41) And the exchangeable load for the lean streams is: W j,ks = L jc (x j,k-1 x j,k ) (42) 117

118 Synthesis of MEN, Algebraic Approach Since one or more streams will pass through one or more intervals we can express the total load of the stream that passes through that interval k; for the waste and lean streams we have W R k = Σ i passes through intervalk = W R i, k (43) W S k = Σ j passes through intervalk = W S j, k (44) 118 Source : Pollution Prevention through Process Integration, M. M. El-Halwagi

119 Synthesis of MEN, Algebraic Approach Note that mass can be transferred within each interval from a waste stream to a lean stream, as a result it is possible to transfer mass from a waste stream in a interval to a lean stream in a lower interval, the resulting mass balance is: W δ R k k S + δ k 1 Wk = δ k (45) 1, δ k are the residual mass of pollutant entering and leaving the kth interval 119 Source : Pollution Prevention through Process Integration, M. M. El-Halwagi

120 Synthesis of MEN, Algebraic Approach The graphical representation is: δ k 1 Residual Mass from Preceding Interval Waste Recovered from Waste Streams R W k K S W k Mass Transferred to MSA s Residual Mass to Next Interval δ k 120

121 Synthesis of MEN, Algebraic Approach Note: Initial residual mass for k = 0 is zero The most negative value of the residual mass load indicates the excess capacity of MSA s, in order to reduce it, one can either reduce the flow rate, or the composition of the MSA s, one this is done one needs to recalculate and apply the previous procedure. The pinch will be represented at the location when the residual mass is zero. This result will be equal to the one given by the pinch diagram After reducing flow rate or concentration, the remaining load is the load to be removed but external MSA s 121

122 Synthesis of MEN, Algebraic Approach Example 3 A lean MSA will be used to reduce the composition of a rich stream, the data is give in the table Calculate the number of intervals Calculate the compositions of each stream for the y and x scales N Intervals 2(1 + 1) 1 Prepare de CID diagram Calculate a TEL table, using 41, 42 Calculate the cascade diagram, by 43,44 N Intervals 3 122

123 Synthesis of MEN, Algebraic Approach Composition Table 123

124 Synthesis of MEN, Algebraic Approach CID Table 124

125 Synthesis of MEN, Algebraic Approach TEL Table 125

126 Cascade Diagram 126

127 Synthesis of MEN, Algebraic Approach The excess capacity of the MSA is kg/s of pollutant and the actual flow required for the separation is: L L Actual Actual Flow Flow = = L i 0.15 Excess Capacity t s x x (45)

128 Synthesis of MEN, Algebraic Approach Recalculating the TEL and cascade diagram 128 Pinch

129 Synthesis of MEN, Algebraic Approach The concentrations at which the pinch point is located are: y = x = The quantity leaving the bottom of the cascade diagram is the amount to be removed by external MSA s, kg/s 129

130 Synthesis of MEN, with Minimum Number of Exchangers U U U In order to minimize the number of mass exchangers to obtain a MOC solution, we will decompose the design problem in to two sub-problems one above and one below the pinch MOC = U MOC, abovepinch MOC, below pinch MOC, abovepinch = = N N + U R, abovepinch R, below pinch MOC, below pinch N N Source : Pollution Prevention through Process Integration, M. M. El-Halwagi + + S, abovepinch (46) S, below pinch N N i, abovepinch i, below pinch 130

131 Feasibility Criteria By starting the synthesis of mass exchangers at the pinch point one can ensure that the options will not be compromised at later steps, due to the fact that the pinch point the all streams match at the minimum driving force ε. The matching of streams will be done in two sections, above and below the pinch, two criteria must be applied to ensure feasibility Stream Population N N RAbove LBelow N L (47) Above N RBelow (48) 131 Source : Pollution Prevention through Process Integration, M. M. El-Halwagi

132 Feasibility Criteria If the previous inequalities do not hold with the rich and lean streams/branches then splitting of one or more of them is required, as before stream splitting might be required to comply with the following inequalities Thermodynamic Feasibility L m L m j j j j G Above Pinch (48) G i i Below Pinch (49) 132 Source : Pollution Prevention through Process Integration, M. M. El-Halwagi

133 Network Synthesis Example 4 The following example will illustrate the procedure for network synthesis; given a process with two waste streams and two process MSA s 133

134 Network Synthesis The composition for waste and lean streams are shown in the table Number of Intervals = 7 Calculate the CID Calculate TEL Revise TEL 134

135 CID Network Synthesis 135

136 Network Synthesis TEL 136

137 Cascade Diagram 137

138 Network Synthesis The excess load of the MSA s is kg/s; using Equation 45 and reducing the excess capacity of S 2 we have an actual flow of kg/s and a revise TEL and cascade diagram can be calculated, with its pinch point at interval 4 and compositions y, x 1, x 2 = , , 0.01, respectively 138

139 TEL, revised 139

140 Network Synthesis We will now define the number of mass exchangers Define feasibility criteria Match streams U MOC, above pinch = = 3 U MOC, below pinch = = 2 140

141 Cascade Diagram, revised Pinch Point 141

142 Network Synthesis The following figure will aid during checking of the feasibility criteria R 1 S 2 R 2 S 1 Pinch Point G 1 = 2.5 kg/s G 2 = 1 kg/s L 1 /m 1 = 2.5 kg/s L 2 /m 2 = 1.95 kg/s 142

143 Network Synthesis N N RAbove L Above 2 2 L Match: j G Above Pinch i R m 1 S 1 j R 2 S 2 143

144 Network Synthesis Mass Exchanged Loads R 1 = kg/s S 1 = kg/s Mass exchanged = kg/s R 2 = kg/s S 2 = kg/s Mass exchanged = kg/s 144

145 Network Synthesis Remaining load from R 1 = kg/s Excess capacity of S 2 = kg/s Note that these values are equal, due to the fact that there is no mass transferred trough the pinch. Now we proceed to match exchangers represented by circles with streams; the mass exchanged appears within the circles and composition in arrows. Load to be removed by external MSA is kg/s 145

146 Network Synthesis R kg/s 0.05 R 1 capacity not removed by S x 1 * S 2 R 2 5 kg/s S kg/s x 2 ** S 2 can remove load R 2 transfers all its load S 1 is depleted 146

147 Network Synthesis In order to calculate the intermediate compositions leaving exchanger R 2 S 2 use a material balance using Equation 37: x 2** = /3 = x 1* = /2.5 =

148 Network Synthesis After completing the network design above the pinch we will proceed to do the same below the pinch N 1 LBelow 2 N RBelow Pinch Point R 1 R 2 S 1 S 3 External MSA G 1 = 2.5 kg/s G 2 = 1 kg/s L 1 /m 1 = 2.5 kg/s 148

149 Network Synthesis Checking feasibility (Eq. 49) determines that S 1 has to be split in two since L 1 /m > G i. There are many different combinations in order to achieve it, for this case we will split them arbitrarily and match the streams Pinch Point R 1 R 2 S 1 S 3 External MSA G 1 = 2.5 kg/s G 2 = 1 kg/s L 11 /m 1 = kg/s L 12 /m 1 = kg/s L 1 = 5 kg/s 149

150 Network Synthesis Match: L j G i Below Pinch m Mass Exchanged Loads j R 1 = kg/s S 11 = kg/s Mass exchanged = kg/s R 1 S 11 R 2 S 12 R 2 = kg/s S 12 = kg/s Mass exchanged = kg/s 150

151 Network Synthesis Remaining load from R 1 = kg/s Remaining load from R 2 = kg/s In order to remove the remaining load from waste streams it is required to use external MSA s (S 3 ) 151

152 S 3 External MSA G 1 = 2.5 kg/s G 2 = 1 kg/s R 1 R 2 S 1 Pinch Point L 1 = 5 kg/s Calculate the Intermediate Compositions Can you Suggest another Configuration for S 3? 152

153 R kg/s R 2 1 kg/s 0.03 S kg/s S 1 x 2 ** x 1 * Pinch Point S L 1 = 5 kg/s Complete Network 153

154 Heat Integration Heat Exchange Networks Source : Pollution Prevention through Process Integration, M. M. El-Halwagi 154

155 Cold Streams In Every plant requires energy to be transfer from a hot stream to a cold one; hence the importance a proper heat exchange network in order to have a positive impact in the economics and operation of any process Heat Exchange Network Hot Streams Out Hot Streams In Source : Pollution Prevention through Process Integration, M. M. El-Halwagi Cold Streams Out 155

156 Heat Integration To define the HEN (Heat Exchange Network) problem first we need to define the following: A number of hot process streams that need to be cooled N H and a number of cold process streams that need to be heated N C, we need to synthesize a network that will achieve the transfer of heat at minimum cost For hot streams the heat capacity can be expressed as: Heat Capacity FCP, u = (50) Supply Temperature = T Target Temperature = T s u t u For u = 1,2, N H 156

157 Heat Integration In addition for the cold streams we have: = (51) Heat Capacity fcp, v Supply Temperature Target Temperature = = t t s v t v For v = 1,2, N C A number of cold and hot streams is available whose supply and target temperatures are known but not their flow rates. In order to design a HEN the following questions need to be answered: 157

158 Heat Integration What is the Optimal configuration How should the hot and Cold streams be matched? What is the optimal heat load to be removed/added by each utility? Which heating/cooling utilities should be used 158 Source : Pollution Prevention through Process Integration, M. M. El-Halwagi

159 Heat Integration In order to have heat transfer between two streams the following relationship will established a correspondence between the hot and cold streams temperature: T min = t + ΔT (52) 159

160 Heat Integration A special case of mass exchanged is the one that compares the heat exchanged problem corresponding T, t, ΔT min with y i,x j and ε j respectively, and having m j, b j equal to zero 160

161 Heat Integration NOTE: The order of X and Y axis used here are different from what has been commonly used in the literature. The reason is that there is a strong interactions between mass and energy making the enthalpy expression non linear function of temperature therefore it is easier to have enthalpy in function of temperature, this specially important when combining mass and heat integration T T v. H Approach ΔT min Source : Pollution Prevention through Process Integration, M. M. El-Halwagi HE H 161 T HE vs. T Approach

162 Heat Integration The procedure use to set up the pinch diagram is exactly the same as the one use for mass integration, by placing the hot and cold streams temperatures in the diagram, starting by their supply temperature as the tail of an arrow and the target temperature as the head of an arrow. The following equation can be used to calculate the vertical distance or heat loss by the hot stream HH u = F C ( T T ) (53) u P, u s u t u 162 Source : Pollution Prevention through Process Integration, M. M. El-Halwagi

163 Heat Integration And for the heat gained by the cold stream we have: HC v = f c ( t t ) (53) v P, v t v s v To construct the pinch diagram we have: 163 Source : Pollution Prevention through Process Integration, M. M. El-Halwagi

164 Heat Integration HE HH 2 H 2 HE HC 2 C 2 HH 1 HC 1 C1 H 1 T 1 t T 2 t T 1 s T 2 s T Source : Pollution Prevention through Process Integration, M. M. El-Halwagi t 1 t t 2 t t 1 s t 2 s t = T - ΔT min 164 T

165 Heat Integration Heat How to construct the pinch diagram? Exchanged Minimum Heating Utility Integrated Heat Exchange Minimum Cooling Utility Cold Composite Stream Hot Composite Stream Thermal Pinch Point t = T - ΔT min T 165 Source : Pollution Prevention through Process Integration, M. M. El-Halwagi

166 Heat Integration The analysis of the thermal pinch diagram is as follows: The cold composite curve cannot be slid down any further otherwise there will not be thermal feasibility, if the cold composite is moved up less heat integration is possible therefore more utilities are required Above the pinch there is a surplus of cooling and below the pinch there is a surplus of heating utilities Source : Pollution Prevention through Process Integration, M. M. El-Halwagi 166

167 Heat Integration A similar analysis as the one used for mass integration can be done in order to apply an algebraic cascade diagram, the number z of intervals is: N int 2( N + N H C ) 2 (54) To construct a Table of Exchangeable Heat Load TEHL we need: HH HC u, z v, z F fc u C p, v P, u ( t ( T z 1 Source : Pollution Prevention through Process Integration, M. M. El-Halwagi = = z 1 t z ) T z ) (55) (56) 167

168 Heat Integration The collective total load for the hot and cold process streams are: HH Total z = Σ u passes z, where through interval u = 1, 2,... N H HH u, z (57) HC Total z = Σ v passes z, where through interval v = 1, 2,... N C HC v, z (58) 168 Source : Pollution Prevention through Process Integration, M. M. El-Halwagi

169 Heat Integration As it was mentioned for mass exchanged, it is feasible to transfer heat from a hot process stream to a cold one within each temperature interval, a heat balance around a temperature interval yields: Residual Heat from r z 1 Preceding Interval Total Heat Added by Process Hot Stream HH z Residual Heat to Next Interval Z rz Heat Removed by Process Cold Stream Total HC z 169

170 Synthesis of MEN, Algebraic Approach The resulting heat balance is: r z = HH Total HC Total + r z z z 1 (59) 170 Source : Pollution Prevention through Process Integration, M. M. El-Halwagi

171 Heat Integration The resulting TID is: 171

172 Property Integration Property Integration: Functionality based holistic approach to the allocation and manipulation of streams and processing units which is based on tracking, adjustment, assignment and matching of functionalities throughout the process Source : Property Integration: Componentless Design Technique and Visualization Tools 172

173 Property Integration Component mass balances are an integral part of process design. There are several design problems in which the designer is interested in a group of properties such as viscosity, corrosion, density etc. Solvent selection is a clear example in which one is interested in its volatility, viscosity, equilibrium distribution, instead of its chemical constituents. Source : Component less design of recovery and allocation systems: a functionality based approach 173

174 Property Integration Property visualization tools are limited to 3 properties, an algebraic approach is used to deal with more complex cases. The advantage of visualization tools is based on the insides that give of the process, and how the design problem can be addressed. In order to apply this method to a set of properties we need to introduced the concept of cluster Properties are not conserved, as a result they cannot be tracked among units without using mass balances, the problem is that often is not possible to identify every single chemical species e.g. Gasoline, Dowtherm 174

175 Property Integration Cluster Defines as condensed surrogate properties which can be used to characterize the complex mixture and can be tracked my mapping the raw properties of infinite compounds onto finite domains Source : Component less design of recovery and allocation systems: a functionality based approach 175

176 Property Integration The problem statement is: given a number of process streams N s which contain the chemical species of interest, can be used in a number of sinks N sinks (process units) in order to optimize a a desired objective e.g. minimize usage of fresh resources, maximize use of process resources, minimize cost of external streams etc. Each sink has a set of constraints defined as: property min < p i,sin k < property max Flow Rate min Flow rate sin k Flow Rate max 176 Source : Component less design of recovery and allocation systems: a functionality based approach

177 Property Integration Each stream can be characterized by Nc raw properties with a mixing rule that characterized a given stream ψ i ( p i ) N s = Σ s = 1 x ψ s i ( p i, s ) (60) x ψ s i = Fractional contributi on to the total flow rate ( p i, s ) = Operator of p i, s of the s th stream 177 Source : Component less design of recovery and allocation systems: a functionality based approach

178 Property Integration p i,s can be normalized as: Ω, = i s ψ ) ( p i i, s ref i ψ (61) An augmented property index (AUP) for each stream s, is define as the summation of the dimensionless raw property operators: AUP s = s N c = Σ i = 1 1,2,..., N Ω s i, s (62) 178

179 Property Integration C i,s is the cluster for property i in stream s C i, s = Ω i, s AUP s (63) For any stream s, the sum of clusters must be conserved adding up to a constant e.g. unity N c Σ i = 1 s = C s = 1 1,2,..., N s (64) C s i = s = Σ = β C N s 1 1,2,..., s N c i, s (65) 179

180 Property Integration The framework for allocation and interception for property integration is: u = 1 s =1 s =1... Property Integration Network (PIN) u = 2... Processed Sources (back to process) u = N sinks Sources Segregated Sources Sinks 180

181 Texas A&M University Property Integration Consider a cluster of stream s to unit u, with three targeted properties i, j, k we have: s j s k s j s i s k s j s i s j s j s i s k s i s j s k s j s i s i s i C C,,,,,,,,,,,,,,,,,, Ω Ω + + Ω Ω = + Ω + Ω Ω Ω = Ω Ω + Ω Ω + = + Ω + Ω Ω Ω = (66) (67)

182 Property Integration C k, s = Ω i, s Ω +Ω i, s j, s +Ω k, s = Ω Ω i, s k, s 1 Ω + Ω j, s k, s + 1 (68) In order to obtained an overestimation of the feasibility region we have: C i, s max = 1 + Ω Ω min j, s max i, s 1 + Ω Ω min k, s max i, s (69) 182

183 Property Integration C i, s min = 1 + Ω Ω min j, s min i, s 1 + Ω Ω min k, s min i, s (70) C j, s max = Ω Ω min i, s max j, s Ω Ω min k, s max j, s (72) C j, s min = Ω Ω min i, s min j, s 1 Ω Ω (71) min k, s min j, s C k, s max = Ω Ω min i, s max k, s 1 Ω + Ω min (73) k, s max k, s + 1 In order to allocate, mix or intercept streams one needs to identify a feasibility region for the sinks, by using the following relationships: 183

184 Property Integration min 1 Ω + Ω C min min min (74) k, s = Ω Ω i, s k, s j, s min k, s + 1 These points will now need to be plotted in a ternary diagram will be shown next Source : Component less design of recovery and allocation systems: a functionality based approach 184

185 Property Integration 185