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Centre for Process Integration © 2010 Improving Energy Recovery in Heat Exchanger Networks with Intensified Heat Transfer Ming Pan, Igor Bulatov, Robin.

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Presentation on theme: "Centre for Process Integration © 2010 Improving Energy Recovery in Heat Exchanger Networks with Intensified Heat Transfer Ming Pan, Igor Bulatov, Robin."— Presentation transcript:

1 Centre for Process Integration © 2010 Improving Energy Recovery in Heat Exchanger Networks with Intensified Heat Transfer Ming Pan, Igor Bulatov, Robin Smith

2 Centre for Process Integration © 2010 Outline 1.UNIMAN activities in the project 2.Introduction 3.Modelling of shell-and-tube heat exchangers 4.Modelling of intensified heat transfer 5.Optimization of retrofitting heat exchanger networks with intensified heat transfer 6.Conclusions and future work

3 Centre for Process Integration © 2010 1. UNIMAN Activities in the Project

4 Centre for Process Integration © 2010 Activity type 1 PIL 2 CALGAVIN 3 SO DR U 4 MAKATEC 5 OIKO S 6 UNIMAN 7 UNIBATH 8 UPB 9 UNIPAN 10 EMBAFFLE Total RTD/Innovation activities WP11.542.50031426033 WP21.542.500141010.524.5 WP300011000200031 WP4232.50011949.50.541.5 Total Research5117.511028242616.51130 Demonstration activities WP5222.54544850.537 Total Demo222.54544850.537 Consortium Management activities Total Management6 6 Other activities WP6021.5033405.50 19 Total other021.5034404018.5 Total131511.5158353234271.5192 UNIMAN person-months and WPs

5 Centre for Process Integration © 2010 UNIMAN in WP1 Task 1.1. Experimental fouling investigation Collaboration with UNIBATH, CALGAVIN, PIL, UPB on kinetics of fouling and incorporation of the data into the models being developed

6 Centre for Process Integration © 2010 UNIMAN in WP2 Collaboration with UNIBATH, CALGAVIN on network aspects of heat transfer intensification Task 2.1. Heat transfer enhancement for the tube-side of heat exchangers Task 2.2. Heat transfer enhancement for the shell-side of heat Collaboration with EMbaffle, UNIBATH on network aspects of heat transfer intensification

7 Centre for Process Integration © 2010 WP Numb er WP TitleType of activit y Lead beneficia ry number Perso n- month s Start month End month WP4Design, retrofit and control of intensified heat recovery networks RTD6 - UNIMAN 41.51224 UNIMAN is WP4 leader Task 4.1. Development of a streamlined and computationally efficient methodology for design of HENs – work started Collaboration with UNIPAN on incorporation of P-graph and Accelerated Branch-and-Bound algorithms for HEN retrofit

8 Centre for Process Integration © 2010 UNIMAN in WP6 PRES’11 conference presentation and Chemical Engineering Transactions publication Task 6.2. Dissemination events

9 Centre for Process Integration © 2010 2. Introduction

10 Centre for Process Integration © 2010 Heat exchanger network (HEN) Models used for units in heat- exchanger network (HEN) are very simple HEN design neglects the heat-exchanger details No account of pressure drops Specified overall UNo details of geometry, just overall area Not suitable for many retrofit applications H1 H2 H3 C1 C2 C3 C4 Assumed as 1

11 Centre for Process Integration © 2010 HEN retrofit Account for detailed performance of heat exchangers Implement intensified heat transfer techniques to suitable heat exchangers Allow new heat exchanger installation Maximize total energy saving with less network structure modifications Need an approach for retrofit

12 Centre for Process Integration © 2010 Research objectives  Develop a simple but accurate model for heat-exchanger details  Propose correlations for heat transfer enhancement  Develop a design method suitable for HEN retrofit with heat transfer enhancement

13 Centre for Process Integration © 2010 3. Modelling of shell-and-tube heat exchangers

14 Centre for Process Integration © 2010 Heat exchangers  Double pipe (DPHEX) two pairs of concentric pipes, counter flow - the simplest type  Shell and tube (STHEX) a bundle of tubes in a cylindrical shell, combining parallel and counter flows - the most widely used type in the chemical industries  Plate and frame (PFHEX) metal plates are used to separate and transfer heat between two fluids - the common typed in the food and pharmaceutical industries

15 Centre for Process Integration © 2010 Modelling requirements for STHEX  Tube side tube number (n t ), tube passes (n p ), tube length (L), tube inner diameter (D i ) …  Shell side tube pitch (P T ), tube pattern, tube outer diameter (D 0 ), shell inner diameter (D s ), baffle spacing (B), baffle cut (B c ), nozzle inner diameter (D n ), shell- bundle clearance (L sb ), number of baffles (n b ), number of shell (N s ) …  Stream properties flow rate (m), density (ρ), thermal conductivity (k), specific heat (C p ), viscosity (μ), inlet temperature (T inlet ) … Model Input: Model Output: Heat transfer coefficients (h), pressure drops (∆P), heat transfer area (A), stream outlet temperatures (T outlet )

16 Centre for Process Integration © 2010 Main correlations of STHEX Tube-side heat transfer coefficient (h i ): (Based on Bhatti and Shah, 1987) Bhatti, M. S., and R. K. Shah, Handbook of Single-Phase Convective Heat Transfer, Wiley, New York, Chap. 4, 1987. Serth, R. W., Process heat transfer principles and applications, Elsevier Ltd, 2007. Ayub, Z. H., Applied Thermal Engineering, 25, 2412-2420, 2005. Tube-side pressure drop (∆P i ): (Adopt existing method of Serth, 2007) Shell-side heat transfer coefficient (h 0 ): (Based on Ayub, 2005) Shell-side pressure drop (∆P 0 ): (Develop existing method of Serth, 2007)

17 Centre for Process Integration © 2010 Procedure of the new model

18 Centre for Process Integration © 2010 Examples Ten examples are considered for model validation: Heat exchanger geometry: Tube: 124 ~ 3983 Tube passes: 2 ~ 6 Tube length: 2.4 m ~ 9 m Tube diameter: 15 mm ~ 25 mm Tube pattern: 30º, 45º, 60º, 90º Shell diameter: 0.489 m ~ 1.9 m Baffle spacing: 0.0978 m ~ 0.5 m Baffle cut: 20% ~ 40% …….. Stream Properties: Specific heat (J/kg ▪ K): 642 ~ 4179 Thermal conductivity (W/m ▪ K): 0.08 ~ 0.137 Viscosity (mPa ▪ s): 0.17 ~ 18.93 Density (kg/m 3 ): 635 ~ 1000

19 Centre for Process Integration © 2010 Details of examples

20 Centre for Process Integration © 2010 Details of examples (continued)

21 Centre for Process Integration © 2010 Results – Example 1 Bell, K. J., Process Heat Transfer Course Notes, School of Chemical Engineering, Oklahoma State University, Stillwater, Oklahoma, 1991. Smith, R, Chemical Process design and integration, John Wiley & Sons Ltd, 2005. Serna, M., and Jiménez, A., An Efficient Method for the Design of Shell and Tube Heat Exchangers, Heat Transfer Engineering, 25: 2, 5-16, 2004. ● Existing models give lower heat transfer coefficients and pressure drops than HTRI ® ● Good agreement between new model and HTRI ®

22 Centre for Process Integration © 2010 Results ( New model vs. HTRI/HEXTRAN ) Tube-side: Heat transfer coefficient (hi) Pressure drop (Pi) Shell-side: Heat transfer coefficient (h0) Pressure drop (P0) 90º tube pattern

23 Centre for Process Integration © 2010 Shell-side: Heat transfer coefficient (h0) Pressure drop (P0) Results ( New model vs. HTRI/HEXTRAN ) Tube-side: Heat transfer coefficient (hi) Pressure drop (Pi) 60º tube pattern

24 Centre for Process Integration © 2010 Shell-side: Heat transfer coefficient (h0) Pressure drop (P0) Results ( New model vs. HTRI/HEXTRAN ) Tube-side: Heat transfer coefficient (hi) Pressure drop (Pi) 45º tube pattern

25 Centre for Process Integration © 2010 L04 – 28 Modelling of Intensified Heat Transfer for the Retrofit of Heat Exchanger Networks Shell-side: Heat transfer coefficient (h0) Pressure drop (P0) Results ( New model vs. HTRI/HEXTRAN ) Tube-side: Heat transfer coefficient (hi) Pressure drop (Pi) 30º tube pattern

26 Centre for Process Integration © 2010 Modelling of heat exchanger The new model:  Fewer equations and empirical factors (compared with the existing models)  Reliable estimation for heat transfer coefficients and pressure drops (compared with HTRI ® and HEXTRAN ® ) Limits:  No phase change  Phase change will be considered in future work

27 Centre for Process Integration © 2010 4. Modelling of intensified heat transfer

28 Centre for Process Integration © 2010 Intensified heat transfer techniques  Twisted-tape inserts, which cause spiral flow along the tube length to increase turbulence  Coiled wire inserts, which consist of a helical coiled spring and function as non-integral roughness  hiTRAN ®, which consist of a wire mesh with different densities. They are usually used to improve the heat transfer coefficient for the laminar regime Tube-side:

29 Centre for Process Integration © 2010 Intensified heat transfer techniques  Helical Baffles ®, which reduce the number of dead spots created by segmented baffle design, where no heat transfer occurs between the tube-side and shell-side fluids  EM Baffles ®, which employs expanded metal baffles (tube supports) made of plate material that has been slit and expanded. The open structure allows a longitudinal flow pattern and results in lower hydraulic resistance, so that flow induced tube vibration will not occur. Shell-side:

30 Centre for Process Integration © 2010 Modelling of twisted-tape inserts Bergles A.E. and Manglik R.M. ASME Journal of Heat Transfer, 1993. Laminar region Turbulent region H: 180º twist pitch of twisted tape t : thickness of tapes μ : viscosity D i : tube inner diameter

31 Centre for Process Integration © 2010 Modelling of coil-wire inserts Uttarwar S.B. and Raja Rao M. ASME Journal of heat transfer, 1985. Garcia A., Vicente P.G. and Viedma A. Experimental study of heat transfer enhancement with wire coil inserts in laminar- transition-turbulent regimes at different Prandtl numbers. Elsevier Ltd, 2004. Laminar region Turbulent region α: insert angle Dv: hydraulic diameter, 4x(free volume/wetted surface) μ: viscosity D i : tube inner diameter e: wire diameter p: helical pitch

32 Centre for Process Integration © 2010 Modelling of hiTRAN ® MAXHTC : heat transfer coefficient for the highest density of hiTRAN; MINHTC : heat transfer coefficient for the lowest density of hiTRAN MAX∆P : pressure drop for the highest density of hiTRAN; MIN∆P : pressure drop for the lowest density of hiTRAN f 1 ( ), f 2 ( ), f 3 ( ) and f 4 ( ): relative correlations for heat transfer coefficients and pressure drops k: conductivity, D i : tube inner diameter, v: tube-side velocity, μ: viscosity, ρ: density, C p : specific heat, n p : tube passes, L: tube length

33 Centre for Process Integration © 2010 L04 – 40 Modelling of Intensified Heat Transfer for the Retrofit of Heat Exchanger Networks Compared with hiTRAN.SP ® (software programming supplied by Cal Gavin Ltd.), the new correlations can predict accurate:  Heat transfer coefficients of the highest and lowest density of hiTRAN  Pressure drops of the highest and lowest density of hiTRAN Modelling of hiTRAN ®

34 Centre for Process Integration © 2010 Modelling of helical baffles Zhang, J. F., Experimental performance comparison of shell-side heat transfer for shell and tube heat exchangers with middle-overlapped helical baffles and segmental baffles. Elsevier Ltd, 2008. k: conductivity, D o : tube outer diameter, N t : number of tube rows, L: tube length, ρ: density, Ds: shell inner diameter, β: helical angle

35 Centre for Process Integration © 2010 Example 1 (from Section 2): Helical baffles:  High heat transfer coefficients in shell side  Lower pressure drops in shell side Modelling of helical baffles

36 Centre for Process Integration © 2010 5. HEN retrofit with intensified heat transfer

37 Centre for Process Integration © 2010 Existing design methods for HEN retrofit Limits:  No account of exchanger geometry modifications  Lots of topology modifications  Too much repiping work  Large scale problems  Heuristic rules  No pressure drop restrictions

38 Centre for Process Integration © 2010 New model for HEN retrofit (MINLP) Energy balance: Heat transfer: Heat transfer coefficients: Overall heat transfer coefficient: Pressure drops: Objective: maximizing energy saving F h / F c : flow-rates of hot / cold streams, Cp h / Cp c : specific heats of hot / cold streams, T h / T c : inlet temperatures of hot / cold streams, T’ h / T’ c : outlet temperatures of hot / cold streams, A: heat transfer area of exchanger, U: overall heat transfer coefficient, ln∆T: logarithmic mean temperature, FT: ln∆T correction factor h i : tube-side heat transfer coefficient, h 0 : shell-side heat transfer coefficient, ∆P i : tube-side pressure drop, ∆P 0 : shell-side pressure drop, FR i / FR 0 : flow-rates in tube / shell side, L: exchanger length, B s : baffle spacing, ρ insert : density of tube inserts, T ave i / T ave 0 : average temperatures in tube / shell sides, ……

39 Centre for Process Integration © 2010 Optimization procedure

40 Centre for Process Integration © 2010 Case 1 Stream specific heats: (kJ/kg·K) Stream flow rate (kg/s)

41 Centre for Process Integration © 2010 Case 1 Tube-side heat transfer coefficients (kW/m 2 ·K) Without tube inserts: With tube inserts: Shell-side heat transfer coefficients (kW/m 2 ·K)

42 Centre for Process Integration © 2010 Case 1 Tube-side pressure drops (kPa) Without tube inserts: With tube inserts: Shell-side pressure drops (kPa)

43 Centre for Process Integration © 2010 Case 1 Initial HEN: Retrofitted HEN: EX Enhanced exchangers

44 Centre for Process Integration © 2010 Case 1 Initial HEN: Retrofitted HEN:

45 Centre for Process Integration © 2010 Case 1 Conclusions:  Heat transfer coefficients of exchangers increase through: tube-side enhancement: increasing tube passes, implementing tube inserts shell-side enhancement: increasing baffle spacing  Pressure drops restrictions are satisfied through: adjusting tube passes, baffle spacing, exchanger length, stream flow rates and shell passes  No topology modifications for HEN  No many geometry modifications for exchangers, heat transfer area can change with exchanger length  Based on the new approach, 27% reduction of heat duty is achieved (13 MW to 9.5 MW)

46 Centre for Process Integration © 2010 Case 2

47 Centre for Process Integration © 2010 Case 2 Stream data without utilities

48 Centre for Process Integration © 2010 Case 2 Exchanger data without utilities Objective - Maximize overall energy saving in HEN!

49 Centre for Process Integration © 2010 Case 2 Optimal solution when N exchangers can be enhanced Enhancing eight exchangers can obtain almost maximum energy saving!

50 Centre for Process Integration © 2010 Case 2 Conclusions:  Overall heat transfer coefficients of enhanced exchangers increase  Pressure drops restrictions and target temperatures are satisfied  No topology modifications for HEN  Based on the new model, up to 9.81% reduction of heat duty is achieved (65.27 MW to 58.87 MW)

51 Centre for Process Integration © 2010 6. Conclusions and future work

52 Centre for Process Integration © 2010 Conclusions New model of heat exchanger Tube-side heat transfer coefficients and pressure drops Shell-side heat transfer coefficients and pressure drops New correlations of heat transfer enhancement Heat transfer coefficients Pressure drops Retrofit of HEN with heat transfer enhancement Increase over heat transfer coefficients of enhanced exchangers Satisfy pressure drop constraints Increase energy saving

53 Centre for Process Integration © 2010 Future works  Developing correlations for heat transfer enhancement Tube-side (twisted-tape, coiled wire) Shell-side (helical baffles, EM baffles)  Improving optimal model for HEN retrofit Large scale problems Minimizing retrofitting costs  Build up optimal model for HEN design Exchanger geometry details Pressure drop constraints Maximizing total profit

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