What about Retrofit Design of Heat Exchanger Networks ? Process, - - PowerPoint PPT Presentation

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What about Retrofit Design of Heat Exchanger Networks ? Process, - - PowerPoint PPT Presentation

Nov 10, 2023 185 likes •399 views

What about Retrofit Design of Heat Exchanger Networks ? Process, Energy and System Optimal Retrofit Optimal Grassroot Optimal Reuse of installed Heat Exchangers Requires accurate Modeling (Rating) Shorter Paybacks

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SLIDE 1
  • Optimal Retrofit ≠ Optimal Grassroot

§ Optimal Reuse of installed Heat Exchangers § Requires accurate Modeling (“Rating”) § Shorter Paybacks (especially Energy Projects)

  • Phases are the same, but Content is different

§ Data Extraction has been discussed already § Targeting with focus on Optimal Value for ΔTmin § Process Modifications more difficult than in Grassroot § Network Design is focused on reduced Heat Transfer

across the Pinch point (Process and Utility Pinches)

§ Optimization is used to maximize the Utilization of

Existing Heat Exchangers through Loops and Paths

What about Retrofit Design of Heat Exchanger Networks ?

  • T. Gundersen

Retro 1

Process, Energy and System Heat Integration − Retrofit Design

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SLIDE 2

Penalty Heat Flow Diagram

Pinch T Hot Streams Cold Streams ST Hot Streams Cold Streams CW

QP = QPP + QPH + QPC Q: What Pinch ? Which ΔTmin ?

  • T. Gundersen

Retro 2

Process, Energy and System Heat Integration − Retrofit Design

QP

C

QP

P

QP

H

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SLIDE 3

Energy Target Plot

HRAT QH,min QH,exist QH,new HRATnew HRATexist ΔE

a b c

HRAT = Heat Recovery Approach Temperature

  • T. Gundersen

Retro 3

Process, Energy and System Heat Integration − Retrofit Design

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SLIDE 4

Savings vs. Investments

Investment (US$) Savings (US$/yr) Invmax

a b d c

PB=1 PB=2 PB=3

min HRAT subject to Inv ≤ Invmax and PB ≤ PBmax

  • T. Gundersen

Retro 4

Process, Energy and System Heat Integration − Retrofit Design

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SLIDE 5

Examples of Cross-Pinch Heat Transfer

  • T. Gundersen

Retro 5

Process, Energy and System Heat Integration − Retrofit Design

H C H mCpH mCpC TH,in TC,out TC,in TH,out TP,H TP,C

, , , , XP H H in P H C C out P C

Q mCp T T mCp T T ⎡ ⎤ ⎡ ⎤ = ⋅ − − ⋅ − ⎣ ⎦ ⎣ ⎦

>

= 0

<

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SLIDE 6

”Shifting” in Retrofit Design

  • T. Gundersen

Retro 6

Process, Energy and System Heat Integration − Retrofit Design

LP

C

HP

QXP QC QH

LP

C

HP

QXP QC − QXP QH − QXP H C H C QH QC

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SLIDE 7

Example of an Existing Network

Pinch 180° C2 210° 160° C1 210° 50° H2 220° 60° H1 270° 160° 160° Ca

2 2 H 1 1

1000 kW 2500 kW Cb 980 kW 1320 kW 2200 kW 160° 214.4° 120°

mCp

(kW/°C) 18.0 22.0 20.0 50.0

QPP = 22 • (220 - 180) = 880 kW QPC = 18 • (214.4 - 180) = 620 kW QP = 1500 kW = 2500 - 1000 QPH = 0 kW

  • T. Gundersen

Retro 7

Process, Energy and System Heat Integration − Retrofit Design

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SLIDE 8

Changing Operating Conditions (“shifting”)

Pinch 180° C2 210° 160° C1 210° 50° H2 220° 60° H1 270° 160° 160°

Ca

2 2

H

1 1 1000 kW 2500 kW

Cb

360 kW 440 kW 2200 kW 160° 214.4° 80° mCp

(kW/°C)

18.0 22.0 20.0 50.0 180° 620 kW 880 kW 180°

“Releases” Heat above the Pinch by changing Operating Conditions (Temperatures) for Exchanger 2 and Cooler Ca

  • T. Gundersen

Retro 8

Process, Energy and System Heat Integration − Retrofit Design

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SLIDE 9

Network After Modifications (Retrofit)

Pinch 180° C2 210° 160° C1 210° 50° H2 220° 60° H1 270° 160° 160°

Ca

2 2

H

1 1 1000 kW 1000 kW

Cb

360 kW 440 kW 2200 kW 160° 214.4° 80° mCp

(kW/°C)

18.0 22.0 20.0 50.0 180° 620 kW 880 kW 180° 4 3 4 3 190°

The Project requires Purchase of 2 new Units and additional Area (new shell ?) to Unit 2 (smaller ΔT )

  • T. Gundersen

Retro 9

Process, Energy and System Heat Integration − Retrofit Design

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SLIDE 10

A simpler Retrofit Solution

The Project requires Purchase of only 1 new Unit, while the Energy Savings is 620 kW (versus 1500)

  • T. Gundersen

Pinch 180° C2 210° 160° C1 210° 50° H2 220° 60° H1 270° 160° 160° Ca

2 2 H 1 1

1000 kW 1880 kW Cb 360 kW 1320 kW 2200 kW 160° 214.4° 120°

mCp

(kW/°C) 18.0 22.0 20.0 50.0

3 3

620 kW 180° 172.4°

Retro 10

Process, Energy and System Heat Integration − Retrofit Design

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SLIDE 11

WS-7: A simple Retrofit Problem

  • T. Gundersen

Retro 11

Process, Energy and System Heat Integration − Retrofit Design

H1 C1

220°C 70°C 50°C 250°C 120°C 4000 kW H C I I 8000 kW 12000 kW 170°C mCp (kW/ºC) 100 80

Given: ΔTmin = 5ºC U = 1.0 kW/(m2K) CST = 0.1 NOK/kWh CCW = 0 NOK/kWh Further: Steam available at 250ºC, Cooling Water at 20ºC (constant) 8000 Operating Hours per Year Cost of new Exchanger: Chex = 0.5 + 0.01·A (m2 and MNOK) Cost of moving/repiping existing Exchanger: Chex = 0.5 MNOK Maximum Payback: PBmax = 3 years

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SLIDE 12

Targeting by using Pro_Pi Software

  • T. Gundersen

Retro 12

Process, Energy and System Heat Integration − Retrofit Design

Result: For ΔTmin ≤ 30ºC: QH,min = 0 kW, QC,min = 8000 kW Demand Curves

2000 4000 6000 8000 10000 12000

10 20 30 40 50 60

Global temperature difference (K) Q (kW)

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SLIDE 13

WS-7 (cont.): Alternative Retrofit Projects

  • T. Gundersen

Process, Energy and System Heat Integration − Retrofit Design

Retro 13

H1 C1

220°C 70°C 50°C 250°C 120°C 4000 kW H C I I 8000 kW 12000 kW 170°C mCp (kW/ºC) 100 80

Existing Design: PB = n.a. I = 0 MNOK, ΔE = 0 MNOK/yr

H1 C1

220°C 70°C 50°C 250°C 922.9 kW H C I I 11077.1 kW 8922.9 kW 139.23°C mCp (kW/ºC) 100 80 208.46°C

Project # 1: PB = 0.20 yr = 2.4 months I = 0.5 MNOK, ΔE = 2.46 MNOK/yr Project # 2: PB = 0.38 yr = 4.6 months I = 1.23 MNOK, ΔE = 3.2 MNOK/yr

H1 C1

220°C 70°C 50°C 250°C 120°C 4000 kW C I I 8000 kW 8000 kW 170°C mCp (kW/ºC) 100 80 II II 130°C

Project # 3: PB = 0.46 yr = 5.5 months I = 1.47 MNOK, ΔE = 3.2 MNOK/yr

H1 C1

220°C 70°C 50°C 250°C 120°C 4000 kW C I I 8000 kW 8000 kW 170°C mCp (kW/ºC) 100 80 II II 130°C H H

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SLIDE 14

WS-7 (cont.): Alternative Retrofit Projects

  • T. Gundersen

Process, Energy and System Heat Integration − Retrofit Design Savings

MNOK/yr

Investment

MNOK

1.0 2.0 3.0 0.5 1.0 1.5 PB = 2.4 months PB = 4.6 months ΔPB = 11.8 months

Retro 14

The Optimum

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SLIDE 15

WS-10:

Retrofit Optimization with Loops and Paths

  • T. Gundersen

Retro 15

Process, Energy and System Heat Integration − Retrofit Design

Stream Ts Tt mCp ΔH °C °C kW/°C kW H1 250 120 40 5200 H2 200 180 80 1600 C1 130 290 50 8000 C2 140 240 20 2000 Steam 320°C (condensing) Cooling Water 20°C à 30°C ΔTmin = 10ºC QH,min = 4000 kW QC,min = 800 kW

Grand Composite Curve

100 150 200 250 300 350 500 1000 1500 2000 2500 3000 3500 4000 4500

Q (kW) T (°C) Grand Composite Curve

100 150 200 250 300 350 500 1000 1500 2000 2500 3000 3500 4000 4500

Q (kW) T (°C)

TPinch = 200ºC/190ºC and 140ºC/130ºC

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SLIDE 16

WS-10: Existing Network

  • T. Gundersen

Retro 16

Process, Energy and System Heat Integration − Retrofit Design

mCp (kW/ºC) [40] [80] [50] [20] H1 H2 C2 C1 Ha C 200º 190º 130º 140º 130º 120º 165º 200º 200º 180º 158º 190º 290º 250º 240º 140º Q=5000 Q=2000 Q=1600 Q=1400 Q=1800

I III II

Targeting for ΔTmin = 10ºC:

QH,min = 4000 kW , QC,min = 800 kW

Cross Pinch Heat Transfer:

QXP,I = 1000 kW , QXP,C = 1000 kW

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SLIDE 17

H1 C

WS-10: Retrofit Network

  • T. Gundersen

Retro 17

Process, Energy and System Heat Integration − Retrofit Design

mCp (kW/ºC) [40] [80] [50] [20] H2 C2 C1 Ha 130º 120º 140º 175º 200º 180º 158º 190º 290º 250º 240º 140º Q=1600 Q=1400 [1400] UA=106.1 [36.5] Q=800 [1800]

I III II

200º Q=1000 [2000] UA=50.1 [71.7] Q=3000 [5000] Q=2000 UA=138.6 Hb Q=1000 UA=9.7 230º 190º

IV

Investments: New Exchangers IV and Hb

and Additional Area for Existing Exch. II

Savings: 1000 kW Reduction

in Steam and Cooling Water

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SLIDE 18

WS-10: Summary

  • T. Gundersen

Retro 18

Process, Energy and System Heat Integration − Retrofit Design

a) Unchanged Energy Consumption Loop A: Ha (+x) → IV (-x) → I (+x) → Hb (-x) b) Better Use of Existing Ha and I c) Reduces the Area for new Hb and IV a) Unchanged Energy Consumption Loop B: IV (+y) → II (-y) b) Better Use of Existing I c) Area increase in IV > Area saved in II a) Increased Energy Consumption Path C: Ha (+z) → IV (-z) → C (+z) b) Reduces Area for Exchangers IV & II c) Less (!!) Use of Existing I a) Increased Energy Consumption Path D: Ha (+w) → II (-w) → C (+w) b) Reduces Area for Exchangers II & IV (This path is dependent – Combine B and C) c) Less (!!) Use of Existing III a) Reduced (!!) Energy Consumption Path E: Hb (-v) → I (+v) → C (-v) b) Better Use of Existing I c) Increased Additional Area for II

Loop A most promising, possibly combined with Path C if Existing Exchanger I becomes limiting Optimization with 4 DOFs

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SLIDE 19
  • T. Gundersen

Heat Recovery and Iterative Design

R S H U R = Reactor System S = Separation System H = Heat Integration U = Utility System

Decomposition

R S H U

Interactions

  • Proc. Mods. 1

Process, Energy and System Process Modifications

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SLIDE 20

Process Modifications

The “ Plus / Minus “ - Principle

T Q

QC,min QH,min

  • T. Gundersen
  • Proc. Mods. 2

Process, Energy and System Process Modifications