2. Hierarchy of Decisions

3. HEAT EXCHANGER NETWORK (HEN)

4. SUCCESSFUL APPLICATIONS O ICI ---- Linnhoff, B. and Turner, J. A., Chem. Eng., Nov. 2, 1981 Energy savings Capital Cost Available Expenditure Process Facility* k$/yr or Saving, k$ Organic Bulk Chemical New 800 same Specialty Chemical New 1600 saving Crude Unit Mod 1200 saving Inorganic Bulk Chemical New 320 saving Specialty Chemical Mod 200 160 New 200 saving General Bulk Chemical New 2600 unclear Inorganic Bulk Chemical New 200 to 360 unclear Future Plant New 30 to 40 % 30 % saving Specialty Chemical New 100 150 Unspecified Mod 300 1000 New 300 saving General Chemical New 360 unclear Petrochemical Mod Phase I 1200 600 Phase II 1200 1200 *New means new plant; Mod means plant modification.

5. SUCCESSFUL APPLICATIONS Table 1. First results of applying the pinch technology in Union Carbide Project Energy Cost Installed Payback Process Type Reduction $/yr Capital Cost $ Months Petro-Chemical Mod. 1,050,000 500,000 6 Specialty Chemical Mod. 139,000 57,000 5 Specialty Chemical Mod. 82,000 6,000 1 Licensing Package New 1,300,000 Savings  Petro-Chemical Mod. 630,000 Yet Unclear ? Organic Bulk Mod. 1,000,000 600,000 7 Chemical Organic Bulk Mod. 1,243,000 1,835,000 18 Chemical Specialty Chemical Mod. 570,000 200,000 4 Organic Bulk Mod. 2,000,000 800,000 5 Chemical Linnhoff and Vredeveld, CEP, July, 1984

6. SUCESSFUL APPLICATIONS  Fluor --- IChE Symp. Ser., No. 74, 1982, P.19 --- CEP, July, 1983, P.33  FMC (Marine Colloid Division, Rockland, ME)

7. CONCLUSION HEN/MEN synthesis can be identified as a separate and distinct task in process design

8. I DENTIFY H EAT R ECOVERY AS A S EPARATE AND D ISTINCT T ASK IN P ROCESS D ESIGN. 9.60 0 1791.614 7.841 1.089 7 703 D 201 RECYCLE TO COLUMN PURGE CW 36  C 200  C 18.2 bar 200  C 180  C 153  C 141  C 40  C 115.5  C 120  C 17.6 bar 114  C 35  C 126  C 18.7 bar 17.3 bar 16 bar FEED 5  C 19.5 bar Figure 2.5 - Flowsheet for “front end” of specialty chemicals process      FLASH REACTION

9. Reactor 200  C 35  C Reactor RECYCLE  TOPS Product Purge PRODUCT 126  C 5  C FEED FOR EACH STREAM: T INITIAL, T FINAL, H = f(T). Figure 2.6-Specialty chemicals process-heat exchange duties

10. REACTOR 1 23 。 。 70 1652 654 STEAM RECYCLE PRODUCT COOLING WATER FEED  = 1722  = 654 a ) DESIGN AS USUAL C H 6 UNITS

11. REACTOR 1 2 3 。 1068 STEAM RECYCLE PRODUCT FEED  = 1068  = 0 b ) DESIGN WITH TARGETS C H 4 UNITS 。 。

12. SUGGESTED PROCEDURE FOR THE DESIGN OF NEW HEAT EXCHANGER NETWORKS 1. Determine Targets.  Energy Target -maximum recoverable energy  Capital Target -minimum number of heat transfer units. -minimum total heat transfer area 2. Generate Alternatives to Achieve Those Targets. 3. Modify the Alternatives Based on Practical Considerations. 4. Equipment Design and Costing for Each Alternative. 5. Select the Most Attractive Candidate.

13. STEP ONE Determine the Targets

14. § E NERGY T ARGETS (T WO S TREAM H EAT E XCHANGE )  T/H D IAGRAM H HH T T TSTS Q =CP(T T -T S ) Figure 2.10 - Representation of process streams in the T/H diagram

15. H (KW) 350300400 T (  C) 100  115  135  UTILITY HEATING 140  UTILITY COOLING 70  200  TWO-STREAM HEAT EXCHANGE IN THE T/H DIAGRAM

16. H (KW) 350300400 T (  C) TT 100  120  135  UTILITY HEATING 130  UTILITY COOLING 70  200  TWO-STREAM HEAT EXCHANGE IN THE T/H DIAGRAM -100 +100 -100 =250 =400 =300

17. FACTS 1.   Total Utility Load  Increa se Increa se 2. in = in Hot Utility Cold Utility (())

18. §E NERGY T ARGETS ( MANY HOT AND COLD STREAMS )  C OMPOSITE C URVES T1T2T3T4T5T1T2T3T4T5 (T 1 -T 2 ) (B) (T 2 -T 3 ) (A+B+C) (T 3 -T 4 ) (A+C) (T 4 -T 5 ) (A) CP=A CP=B CP=C T H

19. §E NERGY T ARGETS ( MANY HOT AND COLD STREAMS )  C OMPOSITE C URVES T1T2T3T4T5T1T2T3T4T5  T H

20.  P INCH P OINT T “PINCH” minimum cold utility Minimum hot utility H Energy targets and “the Pinch” with Composite Curves

21. m hot Streams n cold Streams Q in Q out Q out - Q in =  H Heat Exchange System or

22. The “Problem Table” Algorithm - A Targeting Approach ---Linnhoff and Flower, AIChE J. (1978) Stream No. CP T S T T and Type (KW/  C) (  C) (  C) (  C) (  C) (1) Cold 2 20 25 T 6 135 140 T 3 (2) Hot 3 170 165 T 1 60 55 T 5 (3) Cold 4 80 85 T 4 140 145 T 2 (4) Hot 1.5 150 145 (T 2 ) 30 25 (T 6 )  T min = 10  C

23. T 1 * = 165  C T 2 * = 145  C T 3 * = 140  C T 4 * = 85  C T 5 * = 55  C T 6 * = 25  C Subsystem # TKTK  CP Hot -  CP cold HKHK 1 4 2 3 1 20 3.0 60 2 5 0.5 2.5 3 55 -1.5 -82.5 4 30 2.5 75 5 30 -0.5 -15

24. Heat Exchange Subsystem (3).............................. from subsys #2 To subsys #4 hot streams 145  C 135  C 90  C Cold streams 80  C

25. T 1 * = 165  C -------------------------- ( 0 )------ T 2 * = 145  C --------------------------( 60 )-----( 80 ) T 3 * = 140  C -------------------------( 62.5 )---( 82.5 ) T 4 * = 85  C -------------------------( -20.0 )-----( 0 ) T 5 * = 55  C --------------------------( 55.0 )----( 75 ) T 6 * = 25  C --------------------------( 40.0 )----  H 1 = 60  H 2 = 2.5  H 3 = -82.5  H 4 = 75  H 5 = -15 20 60 minimum hot utility minimum cold utility Pinch FROM HOT UTILITY TO COLD UTILITY

26. § “P ROBLEM T ABLE ” A LFORITHM  S UBSYSTEM T M T C =T  T min TPTP 0 (T 0 ) 1 (T 1 ) 2 (T 2 ) H h2 H c2 H h 1 H c 1

27. § “P ROBLEM T ABLE ” A LFORITHM  E NTHALPY B ALANCE OF SUBSYSTEM As  T = T 1 - T 2  0

28. 5. The Grand Composite Curve 80 60 40 20 0 -20 Q(KW) 20 40 60 80 1 00 1 20 1 40 1 60 1 80 Q c,min T 6 * T 5 * T 4 * T 3 *T 2 * T 1 * Q h,min HU CU “Pinch”

29. SIGNIFICANCE OF THE PINCH POINT 1. Do not transfer heat across the pinch 2. Do not use cold utility above 3. Do not use hot utility below

30. QhQh Q h,min Q c,min QhQh Q T TcTc TpTp ThTh Q h  Q h,min Q c  Q c,min HU CU

31. Q h,min Q c,min Q T TcTc TpTp ThTh HU CU T1T1

32. QhQh Q h,min Q c,min Q T TcTc TpTp ThTh HU CU1 QcQc CU2

33. Q h,min Q c,min Q T TcTc TpTp ThTh HU CU T1T1

34. Q h,min Q c,min Q T TcTc TpTp ThTh HU1 CU T1T1 Q1Q1 Q2Q2 Tp’Tp’ HU2

35. REACTOR 1 REACTOR 2  H=27MW  H=32MW  H= -30MW  H= -3 1.5 MW FEED 2 140  FEED 1 20  180  250  230  200  80  40  PRODUCT2 PRODUCT 1 OFF GAS Figure 6.2 A simple flowsheet with two hot streams and two cold streams.

36. TABLE 6.2 Heat Exchange Stream Data for the Flowsheet in Fig. 6.2 Heat Supply Target capacity temp. temp.  H flow rate CP Stream Type TS (  C) TT (  C) (MW) (MW  C -1 ) 1. Reactor 1 feed Cold 20 180 32.0 0.2 2. Reactor 1 product Hot 250 40 -31.5 0.15 3. Reactor 2 feed Cold 140 230 27.0 0.3 4. Reactor 2 product Hot 200 80 -30.0 0.25

37.  H= -1.5  H= 6.0  H= 4.0  H= -14.0  H= 2.0  H= -14.0  H= 4.0  H= -1.0  H= 6.0  H= -1.5  H= -1.0 (a)(b) HOT UTILITY COLD UTILITY Figure 6.18 The problem table cascade. 245  C 0MW 7.5MW 235  C 1.5MW 9.0MW 195  C -4.5MW 3.0MW 185  C -3.5MW 4.0MW 145  C -7.5MW 0MW 75  C 6.5MW 14.0MW 35  C 4.5MW 12.0MW 25  C 2.5MW 10.0MW

38. Figure 6.24 The grand composite curve shows the utility requirements in both enthalpy and temperature terms.

39. pinch CW LP Steam HP Steam T*T* HH (a) BOILER Fuel Boiler Feedwater (Desuperheat) HP Stream LP Stream Process Condensate Figure 6.25. The grand composite curve allows alternative utility mixes to be evaluated.

40. pinch CW T*T* HH (b) Figure 6.25. The grand composite curve allows alternative utility mixes to be evaluated. Hot Oil Hot Oil Return Hot Oil Flow ProcessFuel FURNACE

41. 300 250 200 150 100 50 0 0 5 10 15 (a) T  C  H(MW) HP Steam LP Steam Figure 6.26 Alternative utility mixes for the process in Fig. 6.2.

42. 300 250 200 150 100 50 0 0 5 10 15 (b) T  C  H(MW) Figure 6.26 Alternative utility mixes for the process in Fig. 6.2. Hot Oil

43. T*T* HH Figure 6.27 Simple furnace model. T* TF T T* STACK Fuel Q Hmin T* O ambient temp. Stack Loss Ambient Temperature Flue Gas Theoretical Flame Temperature T* O Q Hmin Fuel Air T* TFT T* STACK

44. T*T* HH Figure 6.28 Increasing the theoretical flame temperature by reducing excess air or combusion air preheat reduces the stack loss. T*’ TFT T* TFT T* STACK Stack Loss Flue Gas T* O

45. T* T* TFT T* T* TFT T* ACID DEW T* PINCH T* C T* ACID DEW T* PINCH T* C (a)Stack temperature limited by acid dew point (b)Stack temperature limited by process away from the pinch Figure 6.29 Furnace stack temperature can be limited by other factors than pinch temperature.

46. 300 250 200 150 100 50 0 0 5 10 15  H(MW) Figure 6.30 Flue gas matched against the grand composite curve of the process in Fig. 6.2 T* 1800 1750 Flue Gas