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 (especially Energy Projects) • Phases are the same, but Content is different § Data Extraction has been discussed already § Targeting with focus on Optimal Value for Δ T min § 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 Heat Integration − Retrofit Design T. Gundersen Retro 1
Penalty Heat Flow Diagram T ST Hot Streams Process, Energy and System Cold Streams QP C Pinch QP P Hot Streams QP H Cold Streams CW QP = QP P + QP H + QP C Q: What Pinch ? Which Δ T min ? Heat Integration − Retrofit Design T. Gundersen Retro 2
Energy Target Plot Q H,min Process, Energy and System Q H,exist a Δ E Q H,new b c HRAT HRAT new HRAT exist HRAT = Heat Recovery Approach Temperature Heat Integration − Retrofit Design T. Gundersen Retro 3
Savings vs. Investments Savings PB=3 Process, Energy and System (US$/yr) c PB=2 d PB=1 b a Investment (US$) Inv max min HRAT subject to Inv ≤ Inv max and PB ≤ PB max Heat Integration − Retrofit Design T. Gundersen Retro 4
Examples of Cross-Pinch Heat Transfer T P,H Process, Energy and System T H,in T H,out mCp H C mCp C T C,out T C,in H H T P,C > ⎡ ⎤ ⎡ ⎤ = ⋅ − − ⋅ − Q mCp T T mCp T T = 0 ⎣ ⎦ ⎣ ⎦ < XP H H in , P H , C C out , P C , Heat Integration − Retrofit Design T. Gundersen Retro 5
”Shifting” in Retrofit Design Q C − Q XP C C Process, Energy and System Q C Q XP Q XP HP LP HP LP Q H Q H − Q XP C C Q C H H Q H Heat Integration − Retrofit Design T. Gundersen Retro 6
Example of an Existing Network Pinch mCp 180° (kW/°C) Process, Energy and System 270° 160° 214.4° H1 1 Ca 18.0 980 kW 220° 60° 120° 2 H2 Cb 22.0 1320 kW 50° 210° 160° 1 2 C1 20.0 2200 kW 1000 kW 160° 210° H C2 50.0 2500 kW 160° QP P = 22 • (220 - 180) = 880 kW QP C = 18 • (214.4 - 180) = 620 kW QP = 1500 kW = 2500 - 1000 QP H = 0 kW Heat Integration − Retrofit Design T. Gundersen Retro 7
Changing Operating Conditions (“shifting”) Pinch mCp Process, Energy and System 180° (kW/°C) 270° 160° 180° 214.4° 18.0 H1 1 Ca 620 kW 360 kW 220° 60° 22.0 180° 80° H2 2 Cb 880 kW 440 kW 50° 20.0 210° 160° 1 2 C1 1000 kW 2200 kW 50.0 160° 210° C2 H 2500 kW 160° “Releases” Heat above the Pinch by changing Operating Conditions (Temperatures) for Exchanger 2 and Cooler C a Heat Integration − Retrofit Design T. Gundersen Retro 8
Network After Modifications (Retrofit) Pinch mCp Process, Energy and System 180° (kW/°C) 270° 160° 180° 214.4° 18.0 H1 1 3 Ca 360 kW 220° 60° 180° 80° 22.0 H2 4 2 Cb 440 kW 50° 210° 160° 1 2 20.0 C1 1000 kW 2200 kW 3 160° 210° 190° 620 kW C2 H 50.0 1000 kW 4 160° 880 kW The Project requires Purchase of 2 new Units and additional Area (new shell ?) to Unit 2 (smaller Δ T ) Heat Integration − Retrofit Design T. Gundersen Retro 9
A simpler Retrofit Solution Pinch mCp 180° Process, Energy and System (kW/°C) 270° 160° 214.4° 180° H1 Ca 1 3 18.0 360 kW 220° 60° 120° H2 Cb 22.0 2 1320 kW 50° 210° 160° 1 2 C1 20.0 1000 kW 2200 kW 160° 210° 172.4° H 3 C2 50.0 1880 kW 620 kW 160° The Project requires Purchase of only 1 new Unit, while the Energy Savings is 620 kW (versus 1500) Heat Integration − Retrofit Design T. Gundersen Retro 10
WS-7: A simple Retrofit Problem mCp (kW/ºC) Given: 250°C Process, Energy and System 50°C 170°C 100 H1 I C Δ T min = 5ºC 12000 kW U = 1.0 kW/(m 2 K) C ST = 0.1 NOK/kWh 70°C 220°C 120°C 80 C CW = 0 NOK/kWh C1 I H 8000 kW 4000 kW Further: Steam available at 250ºC, Cooling Water at 20ºC (constant) 8000 Operating Hours per Year Cost of new Exchanger: C hex = 0.5 + 0.01 · A (m 2 and MNOK) Cost of moving/repiping existing Exchanger: C hex = 0.5 MNOK Maximum Payback: PB max = 3 years Heat Integration − Retrofit Design T. Gundersen Retro 11
Targeting by using Pro_Pi Software Demand Curves 12000 Process, Energy and System 10000 Q (kW) 8000 6000 4000 2000 0 0 10 20 30 40 50 60 Global temperature difference (K) Result: For Δ T min ≤ 30ºC: Q H,min = 0 kW, Q C,min = 8000 kW Heat Integration − Retrofit Design T. Gundersen Retro 12
WS-7 (cont.) : Alternative Retrofit Projects mCp mCp (kW/ºC) (kW/ºC) 250°C 250°C 139.23°C 50°C 50°C 170°C H1 100 H1 100 I C I C Process, Energy and System 12000 kW 8922.9 kW 70°C 70°C 208.46°C 220°C 220°C 120°C C1 C1 I H H I 80 80 8000 kW 4000 kW 922.9 kW 11077.1 kW Existing Design: PB = n.a. Project # 1: PB = 0.20 yr = 2.4 months I = 0 MNOK, Δ E = 0 MNOK/yr I = 0.5 MNOK, Δ E = 2.46 MNOK/yr mCp mCp (kW/ºC) (kW/ºC) 250°C 250°C 130°C 170°C 50°C 50°C 170°C 130°C 100 H1 100 H1 I II H C I II C 8000 kW 8000 kW 70°C 70°C 120°C 220°C 220°C 120°C C1 I II H C1 I II 80 80 8000 kW 4000 kW 8000 kW 4000 kW Project # 2: PB = 0.38 yr = 4.6 months Project # 3: PB = 0.46 yr = 5.5 months I = 1.23 MNOK, Δ E = 3.2 MNOK/yr I = 1.47 MNOK, Δ E = 3.2 MNOK/yr Heat Integration − Retrofit Design T. Gundersen Retro 13
WS-7 (cont.) : Alternative Retrofit Projects Savings PB = 4.6 months MNOK/yr Process, Energy and System 3.0 The Optimum PB = 2.4 months 2.0 Δ PB = 11.8 months 1.0 Investment 0 MNOK 0 1.5 0.5 1.0 Heat Integration − Retrofit Design T. Gundersen Retro 14
WS-10: Stream T s T t mCp Δ H kW °C °C kW/°C Retrofit H1 250 120 40 5200 Optimization Process, Energy and System H2 200 180 80 1600 with Loops C1 130 290 50 8000 and Paths C2 140 240 20 2000 Steam 320°C (condensing) Δ T min = 10ºC Cooling Water 20°C à 30°C Q H,min = 4000 kW Q C,min = 800 kW Grand Composite Curve Grand Composite Curve T (°C) T (°C) 350 350 300 300 250 250 T Pinch = 200ºC/190ºC and 140ºC/130ºC 200 200 150 150 Q (kW) Q (kW) 100 100 0 0 500 500 1000 1000 1500 1500 2000 2000 2500 2500 3000 3000 3500 3500 4000 4000 4500 4500 Heat Integration − Retrofit Design T. Gundersen Retro 15
WS-10: Existing Network mCp (kW/ºC) 140º 200º I II 250º Process, Energy and System 200º 165º 120º H1 C [40] Q =1800 III 200º 180º H2 [80] 130º 290º 158º 190º Ha C1 [50] Q =5000 Q =1600 Q =1400 140º 240º C2 [20] Q =2000 130º 190º Cross Pinch Heat Transfer: Targeting for Δ T min = 10ºC: Q H,min = 4000 kW , Q C,min = 800 kW Q XP,I = 1000 kW , Q XP,C = 1000 kW Heat Integration − Retrofit Design T. Gundersen Retro 16
WS-10: Retrofit Network mCp (kW/ºC) IV I II 250º 120º Process, Energy and System 200º 175º 140º H1 C [40] Q =800 III [1800] 200º 180º H2 [80] 130º 290º 230º 158º 190º Ha C1 [50] Q =2000 Q =3000 Q =1600 Q =1400 [1400] UA =138.6 [5000] UA =106.1 [36.5] 140º 240º 190º Hb C2 [20] Q =1000 Q =1000 [2000] UA =9.7 UA = 50.1 [71.7] Investments: New Exchangers IV and H b Savings: 1000 kW Reduction and Additional Area for Existing Exch. II in Steam and Cooling Water Heat Integration − Retrofit Design T. Gundersen Retro 17
WS-10: Summary 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 Process, Energy and System 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 Optimization Loop A most promising, possibly combined with with 4 DOFs Path C if Existing Exchanger I becomes limiting Heat Integration − Retrofit Design T. Gundersen Retro 18
Heat Recovery and Iterative Design R Process, Energy and System S H U R S R = Reactor System H S = Separation System H = Heat Integration U U = Utility System Decomposition Interactions Process Modifications T. Gundersen Proc. Mods. 1
Process Modifications T Q H,min Process, Energy and System Q C,min Q The “ Plus / Minus “ - Principle Process Modifications T. Gundersen Proc. Mods. 2
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