1. LECTURE DAY 2 Timo Laukkanen

2. What was important in Lecture 1 Process Integration/Heat Exchanger Network Synthesis (HENS) is an important step in process design Energy saving is very often also economically feasible Energy saving in industry is a major contributor in CO2 savings in the next 40 years CC (Composite Curves) Course arrangements

3. What is important in Lecture 2 Problem Table Algorithm (PTA) Heat Cascade Grand Composite Curve (GCC) Pinch violations Stream grid Maximum Energy Recovery (MER) Network Targeting for minimum number of Units

4. Numerical Method(s) for Energy Targets Problem Table Algorithm, Heat Cascade, Grand Composite Curve

5. T supply (°C) T target (°C) m c p (kW/K) H14001201.0 H22501202.0 C11604001.5 C21002501.3 ∆T min = 50°C Step 1 (adjust temperatures) Hot streams: T * hot = T hot - ½∆T min Cold streams: T * cold = T cold + ½∆T min T* supply (°C) T* target (°C) m c p (kW/K) H1375951.0 H2225952.0 C11854251.5 C21252751.3

6. Step 2 (temperature intervalls) T* supply (°C) T* target (°C) m c p (kW/K) H1375951.0 H2225952.0 C11854251.5 C21252751.3 425 °C TI 1 ∆T=50°C 375 °C TI 2 ∆T=100°C 275 °C TI 3 ∆T=50°C 225 °C TI 4 ∆T=40°C 185 °C TI 5 ∆T=60°C 125 °C TI 6 ∆T=30°C 95 °C H1 H2 C1 C2

7. Step 3 (enthalpy balance) 425 °C TI 1 ∆T=50°C∆H 1 = 50 * (0.0 - 1.5) = -75 375 °C TI 2 ∆T=100°C∆H 2 = 100 * (1.0 – 1.5) = -50 275 °C TI 3 ∆T=50°C∆H 3 = 50 * (1.0 – 1.5 - 1.3) = -90 225 °C TI 4 ∆T=40°C∆H 4 = 40 * (1.0 + 2.0 – 1.5 – 1.3) = 8 185 °C TI 5 ∆T=60°C∆H 5 = 60 * (1.0 + 2.0 – 1.3) = 102 125 °C TI 6 ∆T=30°C∆H 6 = 30 * (1.0 + 2.0) = 90 95 °C H1 1.0 H2 2.0 C1 1.5 C2 1.3

8. -75 -125 -215 -207 -105 -15 Step 4 (cascade the heat flow) 425 °C TI 1 -75 375 °C TI 2 -50 275 °C TI 3 -90 225 °C TI 4 8 185 °C TI 5 102 125 °C TI 6 90 95 °C 215 140 90 0 8 110 200 Hot Utility Pinch Point Cold Utility

9. Summary Problem Table Algorithm Adjust (shift) the temperatures Find the temperature intervals Calculate the enthalpy balance for each interval – heat surplus (+) and deficit (-) Cascade the enthalpy – add large deficit at the top Make the heat cascade thermodynamically feasible

10. Grand Composite Curve 425 °C TI 1 375 °C TI 2 275 °C TI 3 225 °C TI 4 185 °C TI 5 125 °C TI 6 95 °C 215 140 90 0 8 110 200 50 100 150 200 Q (kW) T(°C)

11. Grand Composite Curve (GGC) Visualizes the surplus and deficit heat at different temperature intervals Provides an visual tool for integrating – Different utilities – Different processes – Heat pumps – Other thermodynamic cycles 50 100 150 200 Q (kW) T(°C) Other process Heat integration possibility between processes HP steam LP steam

12. 3 Pinch Rules For Maximum Energy Recovery “Pinch Violations”

13. Heat Deficit Q T pinch temperature Q S, min Heat Surplus Q W, min Heat transfer through the Pinch Q + Q Q?

14. Heat Deficit Q T pinch temperature Q S, min Heat Surplus Q W, min Cooling above and heating below the Pinch Q + Q Q

15. Summary 3 Pinch Rules Never transfer heat through the pinch – Penalty: Increased both hot and cold utility Never cool (with external cooling) above the pinch – Penalty: Increased hot utility Never heat (with external heating) below the pinch – Penalty: Increased cold utility

16. Heat Exchanger Network Design Stream Grid, MER Network

17. T supply (°C) T target (°C) m c p (kW/K) H14001201.0 H22501202.0 C11604001.5 C21002501.3 ∆T min = 50°C, T pinch = 225°C Q h = 225 kW, Q c = 200 kW Stream Grid T pinch, cold = 200°C T pinch, hot = 250°C H1 C1 H2 C2 1.0 2.0 1.5 1.3

18. Q h = 225 kW, Q c = 200 kW Stream Matches T pinch, cold = 200°C T pinch, hot = 250°C H1 C1 H2 C2 1.0 2.0 1.5 1.3 400°C120°C 400°C160°C 250°C100°C Q H1 = 1.0 * (400 – 250) = 150kW Q C1 = 1.5 * (400 – 200) = 300 kW Q = 150 kW Q C2 = 1.3 * (250 – 200) = 65 kW Q = 65 kW

19. Q h = 225 kW, Q c = 200 kW Stream splitting T pinch, cold = 200°C T pinch, hot = 250°C H1 C1 H2 C2 1.0 2.0 1.5 1.3 120°C 160°C 100°C 1.0 0.5 1.3 0.7 Q = 40 kW Q H = 130kW Q C = 40kW Q H = 91kW Q C = 20kW Q = 20 kW Q H = 169kW Q C = 130kW Q = 130 kW Q = 90 kW Q = 110 kW

20. Summary Stream Grid and MER-Network Draw the Stream Grid – draw the pinch(es) – draw the streams above and below the pinch Match streams starting at the pinch – (m c p ) out >= (m c p ) in – Split streams if necessary Calculate the heat exchanger duty – Remember hot and cold streams have different pinch temperature!