improving energy recovery in heat exchanger...

Improving Energy Recovery in Heat Exchanger Networks with Intensified Heat Transfer

Ming Pan, Robin Smith, Igor Bulatov

CAPE Forum 2012 – INTHEAT Training Workshop Centre for Process Integration © 2012

Ming Pan, Robin Smith, Igor Bulatov

The University of Manchester,

Process Integration Limited

Outline

1. Introduction

2. Intensified heat transfer techniques

3.Retrofit of heat exchanger networks

Centre for Process Integration © 2012CAPE Forum 2012 – INTHEAT Training Workshop

4.Optimization method

5.Case studies

6.Conclusions and future work

1. Introduction


What is INTHEAT Project?

Intensified Heat Transfer Technologiesfor Enhanced Heat Recovery - INTHEAT

FP7-SME-2010-1


Contract number: 262205

Starting date: 1 December 2010

Duration: 24 months

Partners and their Activities

• Process Integration Limited, UK – SME - Advanced process integration

• Cal Gavin Limited, UK – SME - Tube-side exchanger heat transfer intensification

• Akstionernoe Obshchestvo ‘Sodrugestvo-T’, Ukraine – SME -Plate heat exchangers

• Makatec Apparate GmbH, Germany – SME - Spiral plastic heat


• Makatec Apparate GmbH, Germany – SME - Spiral plastic heat exchangers

• Oikos, svetovanje za razvoj, d.o.o., Slovenia – SME -Environmental protection and environmental impact assessment

• The University of Manchester, UK

• University of Bath, UK

• Paderborn University, Germany

• University of Pannonia, Hungary

• EMbaffle B.V., The Netherlands – Industrial Company - Shell-side exchanger heat transfer intensification

STEAM

HOT 2

COLD 1

COLD 2

CW

Stage 1

Leve

l of

de

tails

Stage 2

Currently N/A

SPRINT and

similar software

HEN with each exchanger’s heat transfer and pressure

STEAM

HOT 2

COLD 1

COLD 2

CW

Top level overall HEN screening and optimisation

To be developed: Project outcome

Expected Project Final Output


Software tool for HEN screening, analysis, design and retrofit options which takes into account the intensified heat exchanger parameters

Stage 3 hiTRAN.SP

Complete exchanger design

heat transfer and pressure drop parameters

outcome

Heat exchanger network (HEN)

H1

H2

H3

C1

C2

C3


� Models used for units in heat- exchanger network (HEN) are very simple

� HEN design neglects the heat-exchanger details

� No account of pressure drops

� No consideration of fouling

LMT∆×A×U=Q

Specified overall U No details of geometry, just overall area

Not suitable for many retrofit applications

C4

HEN retrofit

� Geometry details of heat exchangers

Tube-side: Tube number, Tube passes, Tube length, Tube diameter

Shell-side: Tube pitch, Tube pattern, Shell diameter, Baffle spacing, Baffle cut

� Intensified heat transfer

The approach for HEN retrofit


� Intensified heat transferTube-side: Internal fins, Twisted tape, Coiled wire, hiTRAN®

Shell-side: External fins, Helical baffles, EM baffles®

� Pressure drop constraintsTotal pump duty, Parallel exchangers, Stream bypass

� FoulingFouling rates, exchanger operating period

Research objectives

� Develop accurate model of heat exchangers (including geometry) and heat transfer intensification

� Develop fouling model for intensified heat


� Develop fouling model for intensified heat exchangers

� Develop an optimization method for improving energy recovery in HEN with heat transfer intensification as an option

2. Intensified heat transfer techniques


Heat transfer intensification (tube-side)

�Internally finned tubes, which mix the tube-side flow at the tube wall to promote turbulence

�Twisted-tape inserts, which cause spiral flow along the tube length toincrease 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 thelaminar regime

For each technology heat transfer and pressure drop equations exist for both laminar and turbulent regions

�Externally Finned Tubes, which can compensate for a low heat transfer coefficient by increasing surface area

�Helical Baffles®, which reduce the number of dead spots created by segmented baffle design, where no heat

Heat transfer intensification (shell-side)


segmented baffle design, where no heat transfer occurs between tube-side and shell-side fluids

�EM Baffles®, which allow a longitudinal flow pattern and results in lower hydraulic resistance, and reduce

tube vibration

For each technology heat transfer and pressure drop equations exist for both laminar and turbulent regions

Internally finned tubes:

Laminar region

Turbulent region

Heat transfer intensification (tube-side)

Nue = 19.2 (t / p)0.5 ReDh0.26 Pr1/3 (Dh / L)1/3 (µb / µw)0.14 ϕє

ϕє = 2.25 (1+0.01GrDh1/3) / log ReDh GrDh = gρ2Dh

3β∆Tiw / µ2

f = (16.4/ReDh)(Dh/Di)


Huq, M., Aziz-ul Huq, A., & Rahman, M. Experimental Measurements of Heat Transfer in an Internally Finned Tube. Int. Comm. Heat Mass Transfer , 1998

Turbulent region

p: fin pitch

Tw : wall temperature

µ: viscosity

Dh: hydraulic diameter

Gr: Grashof number

lcsw: modified characteristic

length for swirling flows

( )

0.8

-1/2__

πDi2

Nf e t

func(geometry)lcsw

=Nue

Nust Di

4

___

πDi2

4

___

( )

1.75

-1.25__

πDi2

Nf e t

lcsw

=fe

fst Di

4

___

πDi2

4

___

3. Retrofit of heat exchanger networks


Retrofit procedure

Models of heat exchanger with intensified heat transfer

Prescreen original HEN to find potential exchangers for intensification

Steady-state optimization

Dynamic optimization

Models of heat exchanger with intensified heat transfer


Correlations of heat transfer coefficient and pressure drop

Optimization

Solutions• Max energy saving• Max retrofit profit

Fouling model of exchangers with/without intensification

Optimization

Solutions• Max energy saving• Max retrofit profit• Max operating period

Pre-screening original HEN

H1

H2

H3

C1

C2

C3

C4


C4

Potential Intensified exchanger

� Streams

flow rate, specific heat, inlet temperature, outlet temperature …

� Exchangers

area, original heat transfer coefficient, maximum heat transfer coefficient …

Given:

Potential enhanced exchangers and the augmentation level of enhancement

Identify:

HEN retrofit (steady-state)

�Tube-side intensification:

Increasing tube passes, Implementing tube inserts + changing tube passes

Constant parameters during the retrofit:

Tube inner diameter, the number of tubes

Tube-side heat transfer coefficient (h ) and pressure drop (∆P )


hi = fhi (Fri, np, Tiave, ρi)

∆Pi = f∆Pi (Fri, np, Tiave, ρi, l)

Tube-side heat transfer coefficient (hi) and pressure drop (∆Pi )

Relate to:

Tube-side flow rate (Fri), Tube passes (np),

Tube-side stream average temperature (Tiave),

Tube insert density (ρi), Exchanger length (l)

�Shell-side intensification:

Decreasing baffle spacing

Constant parameters during the retrofit:

Tube outer diameter, Tube bundle, Tube pitch,

Tube layout angle, Shell diameter, Baffle cut



h0 = fh0 (Fr0, T0ave, B)

∆P0 = f∆P0 (Fr0, T0ave, B, l)

Shell-side heat transfer coefficient (h0) and pressure drop (∆P0)

Relate to:

Shell-side flow rate (Fr0),

Shell-side stream average temperature (T0ave),

Baffle spacing (B), Exchanger length (l)

�Exchanger area:

Increasing/reducing exchanger area

Exchanger area (A)

Relate to:

The number of tube (nt), tube outer diameter (D0), Exchanger length (l)

A= n× π × D × l



A= nt× π × D0 × l

�Shell passes (Ns):

Increasing/reducing shell passes

TA= Ns×A

TPi= Ns× ∆Pi TP0= Ns× ∆P0

Total heat transfer area of exchanger (TA):

Total pressure drop of exchanger (TPi, TP0):

� Identify suitable heat exchangers for retrofit

� Implement one or more retrofit techniques in the selected

heat exchangers

� Calculate heat transfer coefficients and pressure drops of

heat exchangers in the retrofitted HEN



� Satisfy the restrictions of heat transfer and energy

balance in each exchanger

� Satisfy the pressure drop restrictions in the retrofitted

HEN

� No topology modifications for HEN

Max Energy Saving/Retrofit Profit

�Tube-side intensification (tube inserts):

Increasing tube-side Re

The overall rate of fouling resistance growth:

dRf / dt = θ R’f

HEN retrofit with fouling effect (dynamic)

The simple threshold model (Polley et al., 2007):


Fouling resistance at t operational time:

The simple threshold model (Polley et al., 2007):

R’f = α Re-0.8 Pr-0.33 exp[-E/(R·Tw)] – γ Re0.8

Reenhanced = 1.8526 Re – 0.3945

Rf = θmax ×R’f ×t

Polley, G.T., D.I. Wilson, D. I., Pugh, S. J. and Petitjean, E., (2007), Extraction of crude oil foulingmodel parameters from plant exchanger monitoring, Heat Transfer Engineering, 28, 185-192.

� Identify suitable heat exchangers for retrofit

� Implement tube inserts in the selected heat exchangers

� Calculate heat transfer coefficients and fouling

resistances of heat exchangers in the retrofitted HEN


HEN retrofit with fouling effect (dynamic)



balance in each exchanger

� Satisfy the cleaning period restrictions in the retrofitted

HEN



4. Optimization method


Existing design methods for HEN retrofit

� Yee and Grossmann (1991), retrofit design

� Sorsak and Kravanjia (2004), different exchanger types

� Ponce-Ortega et al. (2008), phase changes

� Polley et al. (1992), potential analysis of heat recovery

� Zhu et al. (2000), network pinch approach


Yee TF, Grossmann IE. A screening and optimization approach for the retrofit of heat exchanger networks. Industry and Engineering Chemistry Research 1991; 30 (1): 146-162.

Sorsak A, Kravanja Z. MINLP retrofit of heat exchanger networks comprising different exchanger types. Computers and Chemical Engineering 2004; 28: 235-251.

Ponce-Ortega JM, Jiménez-Gutiérrez A, Grossmann IE. Optimal synthesis of heat exchanger networks involving isothermal process streams. Computers and Chemical Engineering 2008; 32: 1918-1942.

� Zhu et al. , network pinch approach

� Smith et al. (2009), structural modifications and cost- effective design

Polley GT, Reyes Athie CM, Gough M. Use of heat transfer enhancement in process integration. Heat Recovery Systems and CHP 1992; 12(3): 191-202.

Zhu X, Zanfir M, Klemes J. Heat transfer enhancement for heat exchanger network retrofit. Heat Transfer Engineering 2000; 21(2): 7-18.

Smith R, Jobson M, Chen L. Recent development in the retrofit of heat exchanger networks. Chemical Engineering Transactions 2009; 18: 27-32.

Existing design methods for HEN retrofit

Limits:

� No account of exchanger geometry modifications

� No pressure drop restrictions


� No fouling consideration

� Many potential topology modifications

� Expensive retrofit from too much repiping work

New models for HEN retrofit

� Model for pre-screening original HEN

� Model for HEN retrofit (steady-state)

� Model for HEN retrofit with fouling consideration


Objective:


Model for pre-screening original HEN (MINLP)

Energy balance:

)TT�(Cp×F=)T�T(Cp×F cccchhhh

Heat transfer:

Approximate relationships between heat transfer and pressure drop:

T∆ln×U×A=)T�T(Cp×F hhhh

Fh / Fc: flow-rates of hot / cold streams,

Cph / Cpc: specific heats of hot / cold

streams,

Th / Tc: 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,


heat transfer and pressure drop:

b+P∆×a=U i

Pressure drop restrictions:

iiP≤P ∆max∆

Stream temperature restrictions:

hh ST=T�

P≤Pi

∆max∆∑

cc ST=T�

……


ln∆T: logarithmic mean temperature,∆Pi: tube-side pressure drop,

a, b: coefficients of the correlation

between U and ∆Pi,

max∆Pi: maximum tube-side pressure

drop for each exchanger,

max∆P: maximum total tube-side pressure drop in HEN,

STh / STc: outlet temperatures of hot / cold streams in HEN,


Model for HEN retrofit-steady state (MINLP)

Energy balance:


Heat transfer:

Heat transfer coefficient:



streams,




U: overall heat transfer coefficient,hi = fhi (Fc, np, Tiave, ρi)

T∆ln×U×A=)T�T(Cp×F hhhh ×FT


Pressure drops:


ln∆T: logarithmic mean temperature,FT: ln∆T correction factorhi: tube-side heat transfer coefficient,

h0: shell-side heat transfer coefficient,∆Pi: tube-side pressure drop,∆P0: shell-side pressure drop,

FRi / FR0: flow-rates in tube / shell side, l: exchanger length,B: baffle spacing,ρi: density of tube inserts,Ti

ave / T0ave: average temperatures in

tube / shell sides,

∆Pi = f∆Pi (Fc, np, Tiave, ρi, l)

h0 = fh0 (Fh, T0ave, B)

∆P0 = f∆P0 (Fh, T0ave, B, l)

Overall heat transfer coefficient:

U-1 = hi-1 + h0

-1

……

Model for HEN retrofit-fouling (MINLP)

Energy balance:


Heat transfer:

Fouling resistance:



streams,





T∆ln×U×A=)T�T(Cp×F hhhh

Ri’f = α Rei-0.8 Pri

-0.33 exp[-Ei/(R·Tiw)] – γ Rei0.8




ln∆T: logarithmic mean temperature,hi: tube-side heat transfer coefficient,

h0: shell-side heat transfer coefficient,Ri,f: tube-side fouling resistance,R0,f: shell-side fouling resistance,

FRi / FR0: flow-rates in tube / shell side, Tiw : tube-side wall temperature, Rei : tube-side Re number without

enhancement,Rei,enhanced: tube-side Re number with

enhancement,

Overall heat transfer coefficient:

U-1 = (D0/Di)hi-1 + h0

-1 + Ri,f + R0,f

……

Rei,enhanced = 1.8526 Rei – 0.3945

Ri,f = θmax ×Ri’f ×t

Nonlinear terms in the new models

LMTD and FT:

)T �T(

)TT �(ln

)T �T()TT �(=T∆ln

ch

ch

chch -- ---

FT =(R2+1)0.5ln[(1-S)/(1-R×S)]

(R-1)ln2-S[R+1-(R2+1)0.5]

2-S[R+1+(R2+1)0.5]

Heat transfer coefficient:

hi = fhi (Fc, np, Tiave, ρi) h0 = fh0 (Fh, T0

ave, B)

Stream Cp:

Cph = fCph(Th

ave)


Pressure drops:

∆Pi = f∆Pi (Fc, np, Tiave, ρi, l) ∆P0 = f∆P0 (Fh, T0

ave, B, l)

Heat duty:

Qex = A × U × ln ∆T × FT Qh = Fh × Cph × (Th – T’h) Qc = Fc × Cpc × (Tc – T’c)

Cph = fCph(Th )

Cpc = fCpc(Tc

ave)

Fouling resistance:

Ri’f = α Rei-0.8 Pri

-0.33 exp[-Ei/(R·Tiw)] – γ Rei0.8 Rei,enhanced = 1.8526 Rei – 0.3945

Ri,f = θmax ×Ri’f ×t

Linearization of nonlinear terms

� Initialization:

The temperature-related variables (ln∆T, FT, CP) are initialized based

on the stream initial temperatures (T’h*, Th*, T’c*, Tc*, ) in the existing

HEN

)TT �(ln

)T �T()TT �(=T∆ln

ch

chch -- -- )TT�(

ln

)T�T()TT�(=T∆ln

*c*h

*c*h*c*h* -- --


)T �T(

)TT �(ln

ch

ch -- )T�T(

)TT�(ln

*c*h

*c*h --Fix temperatures

initially

FT =(R2+1)0.5ln[(1-S)/(1-R×S)]

(R-1)ln2-S[R+1-(R2+1)0.5]

2-S[R+1+(R2+1)0.5]

FT* =((R*)2+1)0.5ln[(1-S*)/(1-R*×S*)]

(R*-1)ln2-S*[R*+1-((R*)2+1)0.5]

2-S*[R*+1+((R*)2+1)0.5]

Cp = fCp (Tave) Cp* = fCp [(T*)ave]

�The first order Taylor series expansions:

The nonlinear terms in the model are described as the first order Taylor

series expansions

Y = f (X1, X2,.., Xn) = f (X*1, X*2,.., X*n) +ə [f (X1, X2,.., Xn)]

ə (X1)(X1-X*1)

ə [f (X1, X2,.., Xn)]ə (X2)

(X2-X*2)+ + ……

Linearization of nonlinear terms


ə (X2)

ə [f (X1, X2,.., Xn)]ə (Xn)

(Xn-X*n)+ + RY MIN RY

For example:

A × U = A* × U* + ə (A × U )

ə (A)(A - A*) +

=

+ RAU

ə (A × U )

ə (U)(U - U*)

A* × U* + U* × (A - A*) + A* × (U - U*) + RAU MIN RAU

A: area, U: overall heat transfer coefficient, A*: initial area in the existing HEN,

U*: initial overall heat transfer coefficient in the existing HEN, RAU: remainder term

New optimization method for HEN models

Input initial values for variables

Linearize nonlinear terms in MINLP

MILP model of HEN retrofit

Solve the MILP problem

Assume energy saving (QS’) or retrofit profit (PT’)


Replace LMTD’ex and the

initial value of variables

If the above differences are small enough

Stop

Yes

No

Obtain new values of variables

Calculate variable differences

If the MILP problem is infeasible

Yes

No

Obtain the new QS’ or PT’

Gradually increase QS’ or PT’

5. Case studies


A preheat train for a crude oil distillation column

C1

C2

C3

H1

H2

H3

30 29

21

28 27 26

26

24

24

20

20

4

18 17

17

16

16

23

13

22

12 6 5

3

1

2

31

15


CU

H4

H5

H6

H7

H8

H 9

H10

H11

HU 30

29

21

28

27

4 18

23

13

22 12

6

5

3

1

2

25

25 31

19

19 15

14

14

7

7

11

11

10

10

8

8

9

9

H Hot stream: HU Hot utility: C Cold stream: CU Cold utility:

Stream data without utilities

Stream F

(kg/s)

T

(°C)

Maximum Pressure drop

(kPa)

C1 125.91 33.5 → 95.6 600

C2 160.23 91.4 → 157.3 500

C3 153.69 151.1 → 351.9 900

H1 6.39 335.4 → 69.4 200

H2 73.11 253.2 → 116.1 300

Case 1: pre-screening original HEN


H2 73.11 253.2 → 116.1 300

H3 40.63 293.7 → 130. 300

H4 9.27 212.4 → 156.1 100

H5 9.27 212.7 → 61.7 400

H6 16.21 174.4 → 43.3 300

H7 11.64 364.3 → 65.6 400

H8 63.45 290.4 → 210.9 200

H9 9.28 284.2 → 65.6 300

H10 9.58 240.1 → 57.8 200

H11 25.05 178.7 → 69.3 300

Exchanger data without utilities

Exchanger U

(kW/m2·K)

Max enhanced U*

(kW/m2·K)

Area

(m2)

∆Tln

(°C)

Th

(°C)

Tc

(°C)

Cph

(J/kg·K)

Cpc

(J/kg·K)

Tube-side

Max ∆P (kPa)

Shell-side

Max ∆P (kPa)

1 139.75 209.63 167.6 48.3 117.2 → 61.7 33.5 → 40.8 2197.4 2450.1 100 100

3 626.92 940.38 89.9 73.1 174.4 → 76.7 33.5 → 59.9 2598.2 2474.6 100 100

4 184.78 277.17 153.1 74.4 284.2 → 203.2 160.2 →166 2831.6 2413.4 100 100

5 571.56 857.34 79.5 123.9 212.4 → 156.1 50.5 → 68.2 2598.2 2531.3 100 100

6 203.56 305.34 635.1 46.9 175.4 → 89.0 68.2 → 86.6 2813.4 2623.8 100 100

12 84.2 126.30 225.4 46.8 157.2 → 117.2 86.6 → 89.2 2397.3 2681.6 100 100

13 62.81 94.22 380.8 89.6 226.7 → 147.2 33.5 → 95.6 2316.9 2681.6 100 100

16 673.27 1009.91 113.1 110.3 262.8 → 189.6 91.4 → 139.5 2824.1 2184.8 100 100



16 673.27 1009.91 113.1 110.3 262.8 → 189.6 91.4 → 139.5 2824.1 2184.8 100 100

17 128.37 192.56 191.1 121.8 335.4 → 147.2 91.4 → 108.9 2483.8 2134.3 100 100

18 187.66 281.49 188.9 39.2 203.2 → 141.6 124.4 → 128.4 2483.8 2189.3 100 100

20 321.4 482.10 1336.3 24.3 200.1 → 140.3 128.4 → 156.6 2390.4 2310.0 100 100

21 52.71 79.07 220.2 20.1 178.7 → 175.4 156.6 → 157.3 2831.6 2344.4 100 100

22 75.18 112.77 768.5 23.1 212.7 → 157.2 151.1 → 154.8 2596.9 2343.3 100 100

23 143.03 214.55 390.9 35.7 240.1 → 166.6 154.8 → 160.2 2831.6 2368.1 100 100

24 219.1 328.65 1004.7 46 253.2 → 200.1 166 → 192.9 2601.4 2444.1 100 100

26 169.8 254.70 272.4 80.2 293.7 → 262.8 192.9 → 202.4 2965.2 2525.8 100 100

27 182.95 274.43 223.5 46.9 287.8 → 226.7 202.4 → 207.2 2577.3 2525.8 100 100

28 211.1 316.65 1003.3 44.1 290.4 → 238.4 207.2 → 230.4 2831.3 2608.7 100 100

29 126.44 189.66 227.1 87.8 364.3 → 287.8 230.4 → 236.7 2832.4 2633.6 100 100

Objective - Maximize overall energy saving in HEN!

* upper bound of U by using intensification

N Enhanced exchanger: EX (U: W/m2·K)

Energy saving (kW)

Energy saving

(%) 4 EX16 ( 673.27-> 849.67), EX20 (321.4-> 457.68), EX24 (219.1-> 328.53),

EX28 (211.1-> 316.65) 4250 6.51

6 EX16 (673.27-> 1009.9), EX20 (321.4-> 468.73), EX24 (219.1-> 321.74), EX26 (169.8-> 253.15), EX28 (211.1-> 304.08), EX29 (126.44-> 189.64),

5500 8.43

Optimal solution when N exchangers can be enhanced



EX26 (169.8-> 253.15), EX28 (211.1-> 304.08), EX29 (126.44-> 189.64), 8 EX4 (184.78-> 277.00), EX6 (203.56-> 211.13), EX16 (673.27-> 1009.56),

EX20 (321.4-> 434.28), EX24 (219.1-> 328.65), EX26 (169.8-> 254.53), EX28 (211.1-> 316.65), EX29 (126.44-> 189.65)

6100 9.35

All EX4 (184.78-> 272.97), EX6 (203.56-> 219.63), EX16 (321.4-> 1009.88), EX18 (187.66-> 190.20), EX20 (321.4-> 406.29), EX22 (75.18-> 82.19), EX23 (143.03-> 207.29), EX24 (219.1-> 328.65), EX26 (169.8-> 254.68), EX27 (182.95-> 257.87), EX28 (211.1-> 316.65), EX29 (126.44-> 189.65)

6400 9.81

Enhancing eight exchangers can obtain almost maximum energy saving!

Conclusions:

� Potentially enhanced exchangers are identified

� No topology modifications required

� Based on the new model, up to 9.81% reduction



� Based on the new model, up to 9.81% reduction

of heat duty is achieved (65.27 MW to 58.87 MW)

Case 2: HEN retrofit (steady-state)

Stream data

Specific heats: Cp = A × T

ave + B (kJ/ kg· K)

Target temperature (ºC) Streams

A B

Flow rate (kg/s)

Inlet Outlet

Pressure drop (kPa)

C1 0.0042 1.8752 150 33.51 95.59 140.5 C2 0.0049 1.7898 150 91.34 157.27 90.8 C3 0.0077 0.6069 200 151.05 351.93 221.1 H1 0.0012 0.5114 20 335.40 69.44 97.3


H1 0.0012 0.5114 20 335.40 69.44 97.3 H2 0.0050 2.6809 50 253.20 116.05 133.9 H3 0.0017 0.7482 100 293.70 130.00 272.9 H4 0.0106 1.3655 30 212.44 156.05 26.1 H5 0.0013 0.5634 30 212.68 61.67 131.9 H6 0.0015 0.6541 50 174.40 43.33 160.4 H7 0.0009 0.3784 50 364.26 65.56 201.0 H8 0.0013 0.5599 200 290.38 210.90 181.1 H9 0.0008 0.3417 50 284.20 65.56 96.1

H10 0.0004 0.1851 100 240.07 57.78 82.2 H11 0.0004 0.8244 80 178.70 69.30 148.9 HU 0.00009 0.8334 100 1500.0 57.7 CW 0.0014 4.2705 2250 12.45 243.0

�Tube-side heat transfer coefficients (kW/m2·K)

Without tube inserts: hi-1 = α× FRi

-0.4 × e-0.007Ti

ave

With tube inserts: hi-1 = α× FRi

-0.6 × e-0.007Ti

ave × ρ-1.0392

�Tube-side pressure drops

Correlations for exchangers:



�Shell-side heat transfer coefficients (kW/m2·K)

h0-1 = α× FR0

-0.35 × e-0.006T0

ave × Bs

1.4444

�Tube-side pressure drops (kPa)

�Shell-side pressure drops (kPa)

Without tube inserts: ∆Pi = α× FRi1.7415

× e-0.003Tiave ×L

With tube inserts: ∆Pi = α× FRi1.85

× e-0.003Tiave × L × (2072.73-33.82ρ+ρ2)

∆P0 = α× FR01.322

× e-0.0045T0ave ×L × (0.179+0.041Bs-Bs

2)

Cost:Cost of hot utility: 100 $/(kW·year)

Cost for increasing exchanger area ($) : 4000+200·A

Cost for reducing exchanger area ($) : 1000+60·A

Cost for each bypass implementing ($) : 500

Cost for each tube-pass change ($) : 500

Cost for implementing tube inserts ($) : 500+10·A



Cost for implementing tube inserts ($) : 500+10·A

Cost for each baffle-spacing change ($) : 300

Cost for installing new exchanger ($) : 4000+200·A (without tube inserts)4000+400·A (with tube inserts)

Retrofit profit:

Profit from energy saving – Total cost of retrofit

Subject to:

No change to the network structure

Max

Energy Saving Max

Retrofit Profit

Tube-side enhancement 13 Exchangers

(60,655 $) 17 Exchangers

(61,921 $)

Shell-side enhancement 21 Exchangers


(8,400 $)

Increasing area 12 Exchangers

(920,320 $) 0

19 Exchangers 8 Exchangers

Energy cost in base case: $ 27,3 M



Reducing area 19 Exchangers


(36,687 $)

Tube-pass change 4 Exchangers

(2,000 $) 6 Exchanger

(3,000 $)

Stream bypass 28 bypasses (14,000 $)

29 bypasses (14,500 $)

New exchanger 7 Exchangers (734,745 $)

0

Cost

Total 1,937,152 $ 124,508 $

Energy saving 2,910,000 $ 2,372,000 $ Net (Energy saving – Total cost) 973,000 $ 2,247,000 $

Profit Cost reduction (Net / Energy cost in base case)

3.56% 8.22 %

EXs L

(m) np

ρinserts

(%) Bs

(m) FRi

(kg/s) h-1

i

(m2·K/kW) △Pi

(kPa) FR0

(kg/s) h-1

0

(m2·K/kW) △P0

(kPa)

U

(kW/ m2·K)

Area (m2)

LMTD Ns FT Q

(kW)

1 1.49 2(n) 0 0.400 81.707 3.486 18.2 30.0 3.283 30.7 0.148 87.145 66.2 1 0.992 846 2 0.86 2(n) 0 0.400 2250 1.067 16.6 100.0 1.171 27.0 0.447 49.930 129.5 1 1.000 2890 3 1.10 2(n) 0 0.150 68.293 0.817 18.2 50.0 0.192 116.2 0.991 64.338 72.1 1 0.896 4118 4 2.50 2(n) 0 0.356 200 2.730 28.7 50.0 2.286 20.4 0.199 146.058 75.7 1 0.985 2174 5 1.57 2(n) 0 0.392 150 0.879 29.8 30.0 0.850 26.1 0.578 78.650 124.8 1 0.989 5614 6 16.11 2(n) 0 0.388 150 2.467 38.1 80.0 2.365 43.7 0.207 805.600 45.7 1 0.820 6252 7 0.70 2(n) 0 0.400 2250 2.456 5.2 30.0 2.299 16.4 0.210 35.000 59.0 1 1.000 434 8 0.78 2(n) 0 0.400 2250 1.210 30.0 50.0 1.211 30.0 0.413 23.400 56.6 1 1.000 547 9 0.74 2(n) 0 0.400 2250 1.177 26.2 50.0 1.183 14.2 0.424 41.337 39.5 1 1.000 692

10 5.27 2(n) 0 0.400 2250 5.034 31.1 100.0 4.940 25.3 0.100 292.635 90.9 1 0.999 2664 11 0.89 2(n) 0 0.400 2250 1.342 26.6 80.0 1.351 30.1 0.371 49.282 64.6 1 1.000 1183

Initial HEN:



11 0.89 2(n) 0 0.400 2250 1.342 26.6 80.0 1.351 30.1 0.371 49.282 64.6 1 1.000 1183 12 3.82 2(n) 0 0.394 150 5.943 28.2 30.0 5.480 65.7 0.088 212.017 56.5 1 0.992 1042 13 7.78 2(n) 0 0.323 150 7.955 26.2 50.0 5.880 26.1 0.072 333.237 88.7 1 0.989 2115 14 1.69 2(n) 0 0.333 2250 1.841 26.7 50.0 1.413 61.6 0.307 72.391 87.0 1 1.000 1935 15 0.72 2(n) 0 0.400 2250 1.420 29.4 20.0 1.438 24.0 0.350 30.645 88.0 1 1.000 943 16 2.58 2(n) 0 0.150 74.436 0.747 28.9 100.0 0.213 82.2 1.041 110.536 81.7 1 0.898 8431 17 2.63 2(n) 0 0.316 75.564 3.881 28.9 20.0 2.805 73.2 0.150 182.006 118.4 1 0.953 3070 18 2.56 2(n) 0 0.354 150 2.663 28.1 50.0 2.222 53.9 0.205 176.952 40.7 1 0.973 1436 19 1.40 2(n) 0 0.398 2250 2.505 29.6 50.0 2.470 21.8 0.201 96.645 85.3 1 1.000 1655 20 14.69 2(n) 0 0.310 150 2.050 6.8 50.0 1.032 59.8 0.324 1016.781 32.0 1 - 10573 21 2.85 2(n) 0 0.390 150 9.482 26.9 80.0 9.138 75.2 0.054 197.582 20.2 1 0.999 214 22 5.67 2(n) 0 0.400 200 6.668 15.3 30.0 6.399 19.0 0.077 392.673 35.2 1 0.982 1039 23 3.54 2(n) 0 0.286 200 3.523 18.9 100.0 2.113 56.8 0.177 245.005 42.8 1 0.965 1796 24 10.70 2(n) 0 0.340 200 2.334 22.3 50.0 1.769 43.1 0.244 741.038 52.9 1 0.933 8909 25 1.13 2(n) 0 0.390 2250 1.419 17.9 200.0 1.418 38.1 0.352 37.563 204.6 1 1.000 2710 26 11.79 2(n) 0 0.150 200 2.988 43.5 100.0 0.772 163.6 0.266 392.861 67.7 1 0.965 6822 27 5.91 2(n) 0 0.317 200 2.600 26.4 50.0 1.894 77.2 0.223 196.847 43.4 1 0.975 1855 28 20.00 2(n) 0 0.150 200 3.095 10.7 200.0 0.595 143.0 0.271 1200.000 35.0 1 - 11369 29 3.39 2(n) 0 0.295 200 3.909 26.7 50.0 2.537 36.1 0.155 203.100 84.5 1 0.990 2635 30 2.21 2(n) 0 0.360 200 0.874 28.5 100.0 0.752 57.7 0.615 132.780 820.4 1 0.979 65583 31 0.84 2(n) 0 0.380 2250 0.627 33.1 50.0 0.507 31.0 0.882 50.580 117.3 1 1.000 5232

EXs L

(m) np

ρinserts

(%) Bs

(m) FRi

(kg/s) h-1

i (m

2·K/kW) △Pi

(kPa) FR0

(kg/s) h-1

0 (m

2·K/kW) △P0

(kPa)

U (kW/ m

2·K)

Area (m2)

LMTD Ns FT Q

(kW)

1 0.70 2(e) 51.62 0.399 76.827 0.796 25.5 28.8 3.307 13.9 0.244 40.889 67.8 1 0.995 672 2 0.70 2(n) 0 0.400 2247.575 1.072 13.5 41.5 1.778 7.5 0.351 40.831 111.3 1 1.000 1594 3 0.70 2(n) 0 0.177 72.238 0.802 12.7 43.3 0.272 60.7 0.931 40.831 57.6 2 0.956 4190 4 2.80 1(e) 34.90 0.150 198.595 1.122 22.7 50.0 0.734 60.3 0.539 163.266 35.1 1 - 3091 5 1.02 2(n) 0 0.162 150 0.881 19.2 30.0 0.237 64.8 0.894 50.750 125.1 1 0.989 5614 6 4.30 2(e) 83.93 0.400 150 0.224 87.4 80.0 2.580 9.6 0.357 214.750 39.5 2 0.958 5803 7 0.84 2(n) 0 0.398 2250 2.457 6.3 30.0 2.245 20.2 0.213 41.750 61.5 1 1.000 546 8 0.70 2(n) 0 0.365 2250 1.210 27.1 42.4 1.140 37.7 0.425 21.120 54.2 1 1.000 487 9 0.73 2(n) 0 0.398 2250 1.177 25.7 50.0 1.176 14.6 0.425 40.614 39.4 1 1.000 680

10 4.97 2(n) 0 0.400 2250 5.035 29.3 100.0 5.142 24.6 0.098 276.022 86.1 1 0.999 2339 11 0.70 2(n) 0 0.400 2250 1.342 21.0 80.0 1.368 23.9 0.369 38.892 62.8 1 1.000 901

Retrofitted HEN (max energy saving):



11 0.70 2(n) 0 0.400 2250 1.342 21.0 80.0 1.368 23.9 0.369 38.892 62.8 1 1.000 901 12 3.22 2(n) 0 0.388 150 6.028 24.0 30.0 5.639 64.0 0.086 178.848 51.1 1 0.995 780 13 8.67 2(e) 26.04 0.283 150 1.924 77.2 49.1 5.479 38.9 0.135 371.510 61.7 1 0.948 2931 14 1.22 2(n) 0 0.353 2247.781 1.843 19.2 50.0 1.704 40.4 0.282 52.161 73.7 1 1.000 1085 15 0.76 2(n) 0 0.400 2247.474 1.422 31.3 8.2 2.556 9.7 0.251 32.745 39.9 1 1.000 329 16 3.91 1(e) 96.87 0.368 23.819 0.125 14.2 100.0 0.873 48.9 1.003 167.497 20.8 2 - 6994 17 1.70 2(e) 44.66 0.156 43.631 1.711 14.2 20.0 1.165 91.9 0.348 117.483 54.4 2 0.828 3684 18 2.82 2(n) 0 0.153 150 2.722 31.3 50.0 0.778 159.3 0.286 195.159 17.2 1 0.928 887 19 1.20 2(n) 0 0.399 2248.155 2.509 25.4 50.0 2.604 19.0 0.196 83.076 79.2 1 1.000 1288 20 15.38 1(e) 33.06 0.201 149.252 0.971 12.4 50.0 0.605 103.0 0.635 1064.965 16.6 1 - 11265 21 9.11 2(e) 44.14 0.400 130.292 3.353 146.4 56.1 11.254 128.4 0.068 630.616 11.2 2 0.981 946 22 11.03 2(e) 22.92 0.399 200 4.007 48.9 30.0 6.649 38.9 0.094 763.676 21.6 1 0.882 1364 23 6.25 2(n) 0 0.153 200 3.490 33.2 100.0 0.890 153.5 0.228 432.341 26.9 1 0.801 2126 24 5.69 1(e) 67.00 0.177 197.426 0.672 12.2 37.9 0.837 34.2 0.663 394.057 21.5 2 - 11227 25 1.03 2(n) 0 0.400 2248.004 1.426 16.3 200.0 1.479 28.8 0.344 34.230 204.4 1 1.000 2409 26 6.66 2(e) 67.19 0.191 192.121 0.344 127.9 97.5 1.196 87.7 0.649 222.044 35.6 2 0.932 9575 27 7.24 2(n) 0 0.269 188.704 2.419 28.0 50.0 1.671 132.3 0.245 241.276 13.7 1 0.950 770 28 16.80 1(e) 38.91 0.180 179.087 0.747 20.0 200.0 0.778 114.1 0.656 1007.940 17.7 1 - 11671 29 4.28 1(e) 43.24 0.155 189.113 1.232 21.7 50.0 1.116 76.8 0.426 256.800 34.4 1 - 3755 30 1.76 2(n) 0 0.400 200 0.832 22.2 100.0 0.696 21.3 0.654 105.660 860.1 1 0.986 58604 31 0.70 2(n) 0 0.378 2242.237 0.629 27.4 12.8 0.969 5.0 0.626 42.000 85.8 1 1.000 2255

EXs L

(m) np

ρinserts

(%) Bs

(m) FRi

(kg/s) h-1

i (m

2·K/kW) △Pi

(kPa) FR0

(kg/s) h-1

0 (m

2·K/kW) △P0

(kPa)

U (kW/ m

2·K)

Area (m2)

LMTD Ns FT Q

(kW)

1 1.49 2(e) 20.00 0.283 53.043 2.629 16.3 18.7 2.473 53.4 0.196 87.145 52.4 1 0.964 863 2 0.70 2(n) 0 0.400 2250 1.071 13.6 57.7 1.528 11.3 0.385 40.831 117.6 1 1.000 1848 3 1.10 1(e) 75.83 0.214 50.375 0.220 16.3 36.8 0.396 73.2 1.622 64.338 38.2 1 - 3978 4 2.50 2(e) 50.95 0.250 199.351 0.503 103.1 48.8 1.525 40.3 0.493 146.058 45.1 1 0.894 2898 5 1.57 2(n) 0 0.323 147.945 0.886 29.1 24.3 0.723 43.4 0.622 78.650 116.6 1 0.984 5614 6 3.45 1(e) 73.60 0.160 147.196 0.392 14.9 79.8 0.686 34.7 0.927 172.350 38.1 1 - 6102 7 0.70 2(n) 0 0.177 2248.34 2.458 5.2 18.3 0.875 38.5 0.300 35.000 50.0 1 1.000 524 8 0.78 2(n) 0 0.343 2247.431 1.211 29.9 26.4 1.229 27.7 0.410 23.400 53.7 1 1.000 515 9 0.74 2(n) 0 0.213 2246.477 1.178 26.1 36.8 0.537 38.5 0.583 41.337 35.8 1 1.000 864

10 5.27 2(n) 0 0.241 1810.801 5.490 21.3 83.3 2.825 79.8 0.120 292.635 66.1 1 0.998 2322 11 0.75 2(n) 0 0.400 2246.681 1.343 22.3 46.2 1.709 12.6 0.328 41.392 57.4 1 1.000 779

Retrofitted HEN (max retrofit profit):



11 0.75 2(n) 0 0.400 2246.681 1.343 22.3 46.2 1.709 12.6 0.328 41.392 57.4 1 1.000 779 12 3.82 2(n) 0 0.384 149.941 5.978 28.3 25.5 5.574 62.8 0.087 212.017 56.7 1 0.991 1033 13 7.78 2(e) 26.99 0.235 150 1.843 69.7 39.4 4.690 32.4 0.153 333.237 50.7 1 0.928 2396 14 1.05 2(n) 0 0.156 2249.972 1.842 16.5 47.9 0.511 74.3 0.425 44.789 78.3 1 1.000 1490 15 0.72 2(e) 36.81 0.362 2243.906 0.139 120.3 12.2 1.748 25.2 0.530 30.645 47.6 1 0.999 774 16 2.58 1(e) 61.21 0.152 43.821 0.155 13.9 72.1 0.283 59.5 2.281 110.536 36.2 1 - 9122 17 2.63 1(e) 70.85 0.188 48.716 1.543 13.9 17.6 1.595 112.8 0.319 182.006 55.9 1 - 3238 18 2.56 2(e) 61.49 0.358 149.432 0.558 95.5 50.0 2.552 56.8 0.322 176.952 18.4 1 0.926 967 19 1.01 2(n) 0 0.264 2249.925 2.507 21.3 48.3 1.440 50.3 0.253 69.576 79.4 1 1.000 1400 20 14.69 1(e) 65.14 0.275 125.656 0.514 17.0 50.0 0.950 76.6 0.683 1016.781 13.8 1 - 9629 21 2.85 2(e) 84.53 0.150 150 1.568 149.7 71.5 2.456 250.9 0.249 197.582 15.9 1 0.984 768 22 5.67 2(n) 0 0.156 199.363 6.683 15.3 20.8 1.947 54.7 0.116 392.673 22.2 1 0.927 940 23 3.54 2(e) 67.22 0.266 199.897 0.694 73.2 100.0 1.982 64.1 0.374 245.005 28.2 1 0.828 2138 24 10.70 1(e) 60.63 0.178 159.547 0.830 13.2 43.4 0.792 75.9 0.616 741.038 26.4 1 - 12035 25 0.74 2(n) 0 0.390 1947.04 1.508 9.2 169.0 1.541 20.5 0.328 24.764 201.0 1 1.000 1631 26 11.79 2(e) 25.55 0.274 197.834 0.939 103.9 98.4 1.876 114.5 0.355 392.861 54.7 1 0.939 7175 27 5.91 2(n) 0 0.153 195.522 2.466 24.7 49.5 0.757 148.6 0.310 196.847 14.7 1 0.946 847 28 20.00 1(e) 55.46 0.205 137.872 0.603 21.1 199.8 0.952 129.5 0.643 1200.000 16.1 1 - 12449 29 3.39 1(e) 63.90 0.156 191.758 0.830 28.7 50.0 1.132 60.8 0.510 203.100 36.8 1 - 3807 30 0.71 2(e) 98.29 0.296 95.766 0.090 18.2 100.0 0.470 25.8 1.787 42.420 815.9 1 0.968 59895 31 0.70 2(n) 0 0.398 1936.361 0.667 21.2 25.7 0.750 8.4 0.706 42.000 101.7 1 1.000 3051

Conclusions:

� Heat transfer coefficients of exchangers increase through:

tube-side enhancement: increasing tube passes, implementing tube

inserts

shell-side enhancement: decreasing baffle spacing



shell-side enhancement: decreasing baffle spacing

� Pressure drop restrictions are satisfied through:

adjusting tube passes, baffle spacing, exchanger length, stream flow

rates and shell passes


� Not many geometry modifications for new heat exchangers

� Up to 8.2 % reduction of energy cost is achieved

Exchanger details of original HEN (operating period: 3.1 months)

Case 3: HEN retrofit (fouling)

Shell-side temperature Tube-side temperature EXs

In (ºC) Out (ºC) In (ºC) Out (ºC) LMTD

(ºC)

Wall Temperature

(ºC)

Duty (kW)

1 117.2 66.3 33.5 40.5 51.7 56.7 1130.8 2 131.2 130.0 14.2 14.2 116.4 55.4 139.8 3 174.4 76.7 33.5 57.5 74.0 76.2 3860.3 4 284.2 174.7 156.7 162.4 54.3 187.5 2682.0 5 212.4 156.1 49.0 66.5 125.5 94.1 5633.4 6 174.4 85.7 66.5 85.6 45.5 96.5 6176.5 7 66.3 61.7 13.0 13.0 50.9 31.1 102.4 8 76.7 62.2 12.5 12.6 56.6 36.1 571.6 9 62.2 43.3 12.5 12.5 39.5 29.2 745.4

10 171.1 57.8 12.6 12.9 90.2 49.0 2832.8

hi (kW/m2· ºC) h0 (kW/m2· ºC) U (kW/m2· ºC) Area (m2)

Designed Required Designed Required Designed Required Designed Required

Operating Time (month)

0.263 0.263 0.375 0.375 0.125 0.125 192.5 175.0 9.4 0.208 0.208 0.304 0.304 0.101 0.101 12.8 11.7 7.1 0.521 0.521 0.671 0.671 0.224 0.224 256.7 233.3 11.9 0.703 0.703 0.847 0.847 0.282 0.282 192.5 175.0 3.5 0.453 0.453 0.898 0.898 0.224 0.224 220.0 200.0 5.4 0.479 0.479 0.627 0.627 0.209 0.209 715.0 650.0 5.2 0.211 0.211 0.307 0.307 0.102 0.102 22.0 20.0 8.8 0.893 0.893 1.008 1.008 0.336 0.336 33.0 30.0 5.7 0.903 0.903 1.017 1.017 0.339 0.339 61.1 55.6 4.5 0.235 0.235 0.339 0.339 0.113 0.113 305.6 277.8 15.3


10 171.1 57.8 12.6 12.9 90.2 49.0 2832.8 11 85.7 69.3 12.9 13.0 64.2 39.4 1141.5 12 169.1 117.2 85.6 89.2 52.1 107.1 1150.6 13 221.1 147.2 89.2 95.6 87.5 126.7 2069.2 14 147.2 65.6 13.0 13.2 87.0 51.0 2285.9 15 109.3 69.4 13.2 13.3 74.3 41.6 566.6 16 198.4 131.2 91.3 133.7 51.3 134.3 7586.7 17 335.4 109.3 91.3 109.2 82.2 146.0 3210.1 18 174.7 139.7 121.5 123.9 31.8 135.1 858.6 19 139.7 65.6 13.3 13.5 83.9 46.1 1816.1 20 206.2 141.9 123.9 156.4 31.2 153.6 11684.2 21 178.7 174.4 156.4 157.3 19.7 164.4 296.2 22 212.7 169.1 151.1 153.1 34.7 167.4 968.6 23 240.1 171.1 153.1 156.7 42.6 175.3 1724.4 24 253.2 206.2 162.4 180.4 57.1 192.6 8525.4 25 222.7 210.9 14.0 14.2 202.7 88.4 2085.1 26 293.7 198.4 180.4 203.1 44.9 214.6 10771.6 27 249.0 221.1 203.1 204.7 29.2 215.0 780.5 28 290.4 222.7 204.7 229.9 35.1 233.5 11903.4 29 364.3 249.0 229.9 236.7 57.1 261.6 3228.0 30 1500.0 912.5 236.7 351.9 891.2 673.7 54633.2 31 141.9 116.1 13.5 14.0 114.8 55.5 4683.1

0.235 0.235 0.339 0.339 0.113 0.113 305.6 277.8 15.3 0.832 0.832 0.959 0.959 0.320 0.320 61.1 55.6 9.6 0.204 0.204 0.298 0.298 0.099 0.099 244.5 222.2 7.2 0.411 0.411 0.552 0.552 0.184 0.184 141.4 128.6 12.7 0.786 0.786 0.920 0.920 0.307 0.307 94.3 85.7 6.0 0.392 0.392 0.530 0.530 0.177 0.177 47.1 42.9 8.0 0.927 0.927 1.035 1.035 0.345 0.345 471.5 428.6 7.9 0.422 0.422 0.564 0.564 0.188 0.188 228.5 207.7 9.9 0.275 0.275 0.390 0.390 0.130 0.130 228.5 207.7 12.1 0.340 0.340 0.469 0.469 0.156 0.156 152.3 138.5 13.2 0.663 0.663 0.810 0.810 0.270 0.270 1523.1 1384.6 5.4 0.504 0.504 0.653 0.653 0.218 0.218 76.2 69.2 4.9 0.658 0.658 0.805 0.805 0.268 0.268 114.2 103.8 3.6 0.736 0.736 0.876 0.876 0.292 0.292 152.3 138.5 4.7 0.308 0.308 0.431 0.431 0.144 0.144 1142.3 1038.5 3.4 0.335 0.335 0.463 0.463 0.154 0.154 73.3 66.7 10.0 0.984 0.984 1.079 1.079 0.360 0.360 733.3 666.6 4.3 0.239 0.239 0.344 0.344 0.115 0.115 256.6 233.3 4.3 0.881 0.881 0.998 0.998 0.333 0.333 1122.0 1020.0 3.1 0.556 0.556 0.706 0.706 0.235 0.235 264.0 240.0 4.2 0.910 0.910 1.022 1.022 0.341 0.341 198.0 180.0 15.7 0.290 0.290 0.408 0.408 0.136 0.136 330.0 300.0 5.3


Shell-side temperature Tube-side temperature EXs

In (ºC) Out (ºC) In (ºC) Out (ºC) LMTD

(ºC)

Wall Temperature

(ºC)

Duty (kW)

1 115.7 66.4 33.5 40.3 51.2 56.4 1095.9 2 130.9 130.0 13.9 13.9 116.5 55.2 97.9 3 174.4 76.7 33.5 57.5 74.0 76.2 3860.5 4 284.2 179.7 157.5 162.9 58.4 188.8 2559.4 5 212.4 156.1 48.9 66.3 125.6 94.1 5633.4 6 174.7 83.3 66.3 86.1 43.3 98.8 6357.3 7 66.4 61.7 13.0 13.0 51.0 31.1 104.5 8 76.7 60.7 12.5 12.6 55.7 40.2 631.1 9 60.7 43.3 12.5 12.5 38.9 28.9 685.7

hi (kW/m2· ºC) h0 (kW/m2· ºC) U (kW/m2· ºC) Area (m2)

Designed Required Designed Required Designed Required Designed Required

Operating Time (month)

0.263 0.253 0.375 0.375 0.125 0.122 192.5 175.0 12.0 0.208 0.124 0.304 0.304 0.101 0.071 12.8 11.7 40.1 0.521 0.521 0.671 0.671 0.224 0.224 256.7 233.3 11.9 0.703 0.561 0.847 0.847 0.282 0.251 192.5 175.0 8.0 0.455 0.452 0.898 0.898 0.225 0.224 220.0 200.0 9.2 0.588 0.555 0.627 0.627 0.232 0.226 715.0 650.0 9.3 0.211 0.214 0.307 0.307 0.102 0.103 22.0 20.0 8.0 1.227 1.155 1.008 1.008 0.386 0.376 33.0 30.0 8.2 0.903 0.789 1.017 1.017 0.339 0.317 61.1 55.6 8.0

Exchanger details of HEN retrofit with fouling consideration (operating period: 8 months)

Exchanger


9 60.7 43.3 12.5 12.5 38.9 28.9 685.7 10 162.5 57.8 12.6 12.9 87.3 47.5 2619.2 11 83.3 69.3 12.9 13.0 63.1 38.9 975.8 12 162.1 115.7 86.1 89.2 48.1 105.8 1028.9 13 216.1 143.1 89.2 95.6 82.7 126.9 2044.8 14 143.1 65.6 13.0 13.2 85.5 50.1 2170.1 15 102.4 69.4 13.2 13.2 71.4 40.2 467.8 16 194.4 130.9 91.3 131.4 50.4 137.4 7179.8 17 335.4 102.4 91.3 109.8 71.1 159.5 3308.8 18 179.7 128.5 120.6 124.1 24.5 146.9 1254.2 19 128.5 65.6 13.2 13.4 79.6 44.0 1543.0 20 196.0 132.0 124.1 156.5 19.7 158.5 11611.8 21 178.7 174.7 156.5 157.3 19.8 164.4 281.1 22 212.7 162.1 151.1 153.4 28.7 179.1 1123.1 23 240.1 162.5 153.4 157.5 33.3 190.8 1938.1 24 253.2 196.0 162.9 184.8 48.6 211.5 10377.4 25 221.4 210.9 13.7 13.9 202.3 87.9 1848.4 26 293.7 194.4 184.8 208.5 34.6 233.9 11220.4 27 243.9 216.1 208.5 210.1 17.6 224.5 778.9 28 290.4 221.4 210.1 235.7 27.5 248.6 12140.1 29 364.3 243.9 235.7 242.8 42.0 288.4 3369.8 30 1500.0 944.0 242.8 351.9 906.3 682.1 51709.8 31 132.0 116.1 13.4 13.7 110.3 53.6 2903.5

0.903 0.789 1.017 1.017 0.339 0.317 61.1 55.6 8.0 0.236 0.219 0.339 0.339 0.113 0.108 305.6 277.8 25.3 0.832 0.634 0.959 0.959 0.320 0.278 61.1 55.6 26.3 0.204 0.194 0.298 0.298 0.099 0.096 244.5 222.2 10.4 0.452 0.445 0.552 0.552 0.194 0.192 141.4 128.6 21.5 0.786 0.733 0.920 0.920 0.307 0.296 94.3 85.7 8.8 0.392 0.304 0.530 0.530 0.177 0.152 47.1 42.9 24.4 1.335 0.858 1.035 1.035 0.402 0.333 471.5 428.6 33.4 0.698 0.593 0.564 0.564 0.241 0.224 228.5 207.7 15.0 1.667 1.376 0.390 0.390 0.257 0.246 228.5 207.7 9.7 0.340 0.282 0.469 0.469 0.156 0.140 152.3 138.5 34.4 3.311 2.356 0.810 0.810 0.456 0.426 1523.1 1384.6 8.0 0.504 0.454 0.653 0.653 0.218 0.205 76.2 69.2 8.0 3.289 1.509 0.805 0.805 0.453 0.377 114.2 103.8 8.0 3.676 1.901 0.876 0.876 0.484 0.420 152.3 138.5 8.0 1.541 0.636 0.431 0.431 0.269 0.205 1142.3 1038.5 8.0 0.335 0.274 0.463 0.463 0.154 0.137 73.3 66.7 24.5 4.926 2.283 1.079 1.079 0.567 0.486 733.3 666.6 8.1 1.193 0.705 0.344 0.344 0.220 0.190 256.6 233.3 8.0 4.405 1.725 0.998 0.998 0.535 0.433 1122.0 1020.0 8.0 2.762 1.263 0.706 0.706 0.408 0.334 264.0 240.0 8.0 0.910 0.785 1.022 1.022 0.341 0.317 198.0 180.0 26.7 0.290 0.149 0.408 0.408 0.136 0.088 330.0 300.0 41.5

Hot utility decreases from 54633.2 kW to 51709.8 kW

Exchanger operating times increase as their fouling rates decrease with intensification

Conclusions:

� Implementation of tube-side intensification:

increases heat transfer coefficient, reduces fouling rate, prolongs unit

operating period





� Not many geometry modifications for new heat exchangers

� Up to 5.35 % of energy saving with significantly long operating

period (3 months to 8 months)

6. Conclusions and future work


Conclusions

� Heat exchanger details including intensification have been included in heat exchanger network analysis

� Heat transfer coefficients and pressure drops

� Optimization of HEN retrofit (steady-state) � Heat transfer intensification


� Satisfy pressure drop constraints

� Maximize retrofit profit

� Optimization of HEN Retrofit with fouling consideration� Heat transfer intensification

� Reduce fouling rate

� Increase energy saving

� Maximize retrofit profit

Future Work

� Finalising the toolbox


References

Pan M., Bulatov I., Smith R., Kim J.K., Improving energy recovery in heat

exchanger network with intensified tube-side heat transfer, Chem.

Eng. Trans. 25 (2011) 375-380.

Pan M., Bulatov I., Smith R., Kim J.K., Novel optimization method for

retrofitting heat exchanger networks with intensified heat transfer,

Comput. Aided Chem. Eng. 29 (2011) 1864-1868.


www.intheat.eu

Comput. Aided Chem. Eng. 29 (2011) 1864-1868.

Pan M., Bulatov I., Smith R., Kim J.K., Novel MILP-based iterative

method for the retrofit of heat exchanger networks with intensified

heat transfer, Comput. Chem. Eng. (2012), 2012.02.002,

doi:10.1016 /j.compchemeng. In press.

Acknowledgement

The financial support is gratefully acknowledged

from the EC FP7 project “Intensified Heat Transfer

Technologies for Enhanced Heat Recovery –


Technologies for Enhanced Heat Recovery –

INTHEAT”, Grant Agreement No. 262205.

improving energy recovery in heat exchanger...

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