An Introduction to Heat Exchanger Network HEN Design

An Introduction to Heat Exchanger Network (HEN) Design By: Anwaruddin Hisyam Pinch technology series 1

In this lecture we will learn how to set energy recovery targets for a process. Pinch technology series 2

Pinch identification Pinch technology series 3

Base case 178 C 1620 880 160 C 180 C 130 C 60 C 2640 210 C Reactor 270 C 160 C 210 C 149 C 50 C 1220 1980 Pinch technology series 220 C 4

Data Extraction 178 C 1620 880 160 C 180 C 130 C 60 C 2640 210 C Reactor 270 C 160 C 210 C 149 C 50 C 1220 1980 Pinch technology series 220 C 5

…. . from data extraction 160 C 130 C 210 C Reactor 270 C 160 C 210 C 50 C 220 C Pinch technology series 60 C 6

Stream Data (Problem Table) T source, C T target, C 1 220 60 3520 22 Hot 2 270 160 1980 18 Hot 3 50 210 3200 20 Cold 4 160 210 2500 50 Cold No Heat duty, k. W CP Type CP = Heat duty/ABS(T source – T target) Pinch technology series 7

Composite Curve DT min Pinch technology series 8

Set DTmin = 20 C Pinch technology series 9

Shifted Stream Data Hot - ½DTmin; Cold + ½DTmin T source, C T target, C 1 210 50 3520 22 Hot 2 260 150 1980 18 Hot 3 60 220 3200 20 Cold 4 170 220 2500 50 Cold No Heat duty, k. W Pinch technology series CP Type 10

Shifted Composite Curve Temp interval (K) Shifted Composite Curve 300 250 200 150 100 50 0 0 1000 2000 3000 4000 5000 6000 7000 Heat Duty (k. W) Pinch technology series 11

Cascade Diagram 260 Stream population Cold Hot Cold. Hot 0 720 -720 SURPLUS 700 180 520 DEFICIT 2800 1600 1200 DEFICIT 400 -400 SURPLUS 1800 1980 -180 SURPLUS 0 -220 SURPLUS 220 50 210 18 170 150 60 20 22 800 220 50 Pinch technology series 12

Heat balance in the interval Hot utility 260 220 -720 520 0 Heat flow 720 200 210 1200 170 -400 150 -180 60 -220 - 1000 - 600 - 420 - 200 50 Cold utility Pinch technology series 13

The heat flow must NOT be negative Pinch technology series 14

Normalization Hot utility 260 220 -720 520 0 720 200 210 1200 170 -400 150 -180 60 -220 50 - 1000 Need additional heat - 600 - 420 - 200 Pinch technology series Cold utility 15

Original Grand Composite Curve Unfeasible region Feasible region Pinch technology series 16

…finding pinch Hot utility 260 220 -720 520 1000 1720 1200 210 1200 170 -400 150 -180 60 -220 50 0 No heat flow at this point 400 580 800 Pinch technology series Cold utility 17

Grand Composite Curve Qh min Qc min Pinch technology series 18

finally…. The PINCH POINT = 170 C which means that Hot stream PINCH = 170+½DTmin = 180 Cold stream PINCH = 170 -½DTmin = 160 Pinch technology series 19

Heat source and sink l PINCH l Heat Source Heat source this part releases heat Heat sink this part requires heat Heat Sink Pinch technology series 20

and, how can we design HEN based on the pinch? Pinch technology series 21

Base case…. the existing network 2640 60 880 C 220 1980 160 270 210 H H 50 1220 1620 H 210 Heat recovery = 1980 + 880 = 2860 k. W Cold utility = 2640 k. W Hot utility = 1220 + 1620 = 2840 k. W Pinch technology series 22

Let’s start from the pinch Pinch technology series 23

PINCH AT 170 BELOW CP ABOVE 180 2640 22 60 220 880 180 360 18 160 270 160 2200 20 50 1640 210 1000 210 2500 160 0 50 160 Pinch technology series 24

Rules…. l CP in ≤ CP out l l N stream IN ≤ N stream out l l Start finding partners for streams OUT (with streams IN, away from pinch, or utility) If Ns IN > Ns OUT, split stream(s) OUT If CP in > CP out (no match), try to split stream(s) IN Set maximum heat recovery The remaining heat duty is covered by heater or cooler Pinch technology series 25

Step 1: Below the PINCH Connect S 1(22) and S 3(20) CP in < CP out 180 60 220 1 180 160 2200 50 √ 1 2200 270 160 210 160 Pinch technology series 210 26

Step 2: Above the PINCH Connect S 2(18) and S 4(50) CP in < CP out 180 60 220 1 180 160 2200 50 √ 1 2200 1620 2 160 √ 270 1620 210 160 Pinch technology series 2 210 27

Step 3: Above the PINCH Connect S 1(22) and S 4(50) CP in < CP out 880 180 60 1 3 1620 180 160 2200 50 √ 1 2200 √ √ 2 160 880 270 1620 210 160 220 3 Pinch technology series 2 √ 210 2500 28

Step 4: Above the PINCH Install Heater at S 3(20) 880 180 60 1 1620 180 160 2200 50 √ 1 2200 √ 3 2 880 270 1620 1000 160 H 160 √ √ √ 220 3 Pinch technology series 2 210 1000 210 2500 29

Step 5: Below the PINCH Install Cooler at S 1(22) and S 2(18) 440 2640 60 C 1 √ 2200 160 50 √ 1 2200 √ 3 360 880 180 C 1620 180 √ 2 880 270 1620 1000 160 H 160 √ √ √ 220 3 2 210 1000 210 2500 All heat requirements have been met !!! Pinch technology series 30

…finally… Heat Exchanger Network (HEN) 880 60 C 220 1620 440 160 C 270 360 1000 H 50 210 2200 160 210 Maximum Energy Recovery (MER) = 2200 + 880 + 1620 = 4700 k. W Minimum cooling heat duty (Qc min) = 440 + 360 = 800 k. W Minimum heating heat duty (Qh min) = 1000 k. W Pinch technology series 31

Then draw the flowsheet… 177. 6 C 880 160 C 1620 180 C 130 C 360 210 C Reactor 270 C 160 C 210 C 160 C 180 C 1000 50 C 220 C 440 2200 60 C 80 C Pinch technology series 32

Possible modifications Pinch technology series 33

Grand Composite Curve MP steam Heat generation Cooling water Pinch technology series 34

Pinch technology series 35

Working Session Pinch technology series 36

How will the HEN be…. ? Feed 2 H= 27 MW 230 C H=-30 MW 140 C 200 C Product 2 80 C Reactor 2 Feed 1 20 C 180 C 250 C 40 C H=32 MW 40 C Reactor 1 H= -31. 5 MW 40 C Product 1 Pinch technology series 37